Loyola University Chicago Loyola University Chicago

Loyola eCommons Loyola eCommons

Master's Theses Theses and Dissertations

1994

Modulation of Ascending Electrosensory Information by Modulation of Ascending Electrosensory Information by

Descending Pathway Stimulation in the Channel Catfish Descending Pathway Stimulation in the Channel Catfish

Lizabeth Scoma Loyola University Chicago

Follow this and additional works at: https://ecommons.luc.edu/luc_theses

Part of the Biology Commons

Recommended Citation Recommended Citation Scoma, Lizabeth, "Modulation of Ascending Electrosensory Information by Descending Pathway Stimulation in the Channel Catfish" (1994). Master's Theses. 4064. https://ecommons.luc.edu/luc_theses/4064

This Thesis is brought to you for free and open access by the Theses and Dissertations at Loyola eCommons. It has been accepted for inclusion in Master's Theses by an authorized administrator of Loyola eCommons. For more information, please contact ecommons@luc.edu.

This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License. Copyright © 1994 Lizabeth Scoma

LOYOLA UNIVERSITY CHICAGO

MODULATION OF ASCENDING ELECTROSENSORY INFORMATION

BY DESCENDING PATHWAY STIMULATION IN THE

CHANNEL CATFISH

A THESIS SUBMITTED TO

THE FACULTY OF THE GRADUATE SCHOOL

IN CANDIDACY FOR THE DEGREE OF

MASTER OF SCIENCE

DEPARTMENT OF BIOLOGY

BY

LIZABETH SCOMA

CHICAGO, ILLINOIS

MAY 1994

Copyright by Lizabeth Scoma, 1994 All rights reserved.

ii

ACKNOWLEDGEMENTS

I would like to thank my advisor Dr. John G. New for

introducing me to the world of neuroscience. His support and

guidance were invaluable. I would also like to thank my other

committee members, Ors. John Janssen and Richard Fay for their

statistical, scientific and creative assistance. Special

thanks go to Christopher Call, Susan Guggenheim and John Quinn

for technical support. Finally, my deepest gratitude goes to

my parents and two sisters, Amy and Nicole for their unending

moral support.

iii

DEDICATION

This thesis is dedicated with love to Mrs. Fred G. Noble.

TABLE OF CONTENTS

ACKNOWLEDGEMENTS

LIST OF FIGURES

LIST OF TABLES

iii

·. . vi

vii

. . viii LIST OF ABBREVIATIONS.

Chapter

I.

II.

III.

IV.

INTRODUCTION 1

Catfish Electrosensory System ...... 5 Electrosensory Processing in the Central

Nervous System . . . . . . . . 8

MATERIALS AND METHODS .. . . 12

Experimental Animals ........... 12 surgical Procedures ........... 12 Electrode Placement . . . . . . ... 13 Constant Stimulus Parameters ..... 13 Inhibition Experiments .......... 14 Voltage Curve Experiments ...... 14 Latency Experiments ........... 14 Frequency Experiments ...... 14 Marking of Recording Site ..... 15 Retrieval of Recording Marks. . ... 15 Data Analysis .............. 16 Analysis Within a Data Block . . . . . 16

RESULTS . . . . . 18

Recovery of Marked Recording Sites .... 18 The Shape of Evoked Potential Waveforms . 18 Effect of Delivering a Electric Pulse

Train to nPr Prior to Electric Field Presentation ............. 19

Results of Varied Amplitude of Electric Pulse Train Delivered to nPr ..... 20

Results of Varied Frequency of Electric Pulse Train Delivered to nPr ..... 21

Duration of nPr's Inhibitory Response .• 22

DISCUSSION • • 36

REFERENCES • . . . . . . . . . . . . . • . • . . . . . • 4 3

iv

VITA 48

V

LIST OF FIGURES

Figure

1. Circuit Diagram of the Afferent and Efferent Projections of the Electrosensory and Mechanosensory Systems of the Catfish

2. Diagram of stimulus/Recording Paradigm ..

3. An Evoked Potential Waveform Response to Electric Field Presentation Alone and Preceded by nPr Stimulation ...•.

4. A Diagram Illustrating the Amplitude of an nPr Stimulus Train Necessary to Cause Saturated

Page

. 24

. . 25

. 26

Inhibition . . . . . . . . . . ..•.. 27

5. A Diagram Illustrating the Effect of the Frequency of an nPr Stimulus Pulse Train on the Amount of Inhibition Elicited •.••.•• 28

6. A Diagram Illustrating the Duration of nPr's Inhibitory Response •.....••••... 29

vi

LIST OF TABLES

Table Page

1. Results Showing Stimulation of nPr Preceding Electric Field Presentation Inhibits Ascending Electrosensory Information ...•...•... 30

2. Results Showing an Amplitude Threshold Exists for the Activation of nPr. . . . . . . . .•.. 31

3. Results Showing Frequency is Sufficient to Cause nPr Activation . . . . . . ....••••• 32

4. Results Showing nPr's Inhibitory Response is Longer than l00ms in Duration .....•.• 33

5. Results from a Tukey's Multiple Comparison Statistical Analysis on Long Delay Data ..••. 34

6. Results Showing nPr's Inhibitory Response Lasts Between 120 and 480ms ..........• 35

vii

AENs

ALLN

cc

CON

DGR

DON

e

ELLL

EGa

EGp

LLN

m

MON

nPrd

nPrv

PLLN

SEM

TSl

TSm

LIST OF ABBREVIATIONS

afferent electrosensory neurons

anterior lateral line nerve

cerebellar crest

caudal octavolateralis nucleus

dorsal granular ridge

dorsal octavolateralis nucleus

electrosensory

electrosensory lateral line lobe

eminentia granularis anterior

eminentia granularis posterior

lateral line nerve

mechanosensory

medial octavolateralis nucleus

dorsal nucleus praeeminentialis

ventral nucleus praeeminentialis

posterior lateral line nerve

standard error of the mean

lateral torus semicircularis

medial torus semicircularis

viii

CHAPTER I

INTRODUCTION

Central mechanisms of sensory processing in the

vertebrate brain have been the focus of much research, however

relatively little is known about the strategies by which

sensory systems detect and interpret the world. The purpose of

this study is to explore neural strategies using the

electrosensory system of the catfish, Ictalurus punctatus, as

a model, specifically the influence of descending control from

midbrain centers on electrosensory information ascending from

the Medulla.

Electrosensory systems are used to detect and orient to

weak electric fields in the environment. Bioelectric fields

are generated as a result of neural and muscular activity of

both vertebrates and invertebrates, as well as from the

cellular activity of some higher plants. Electric fields can

also be generated by physicochemical sources in the

environment (Roth 1972, Peters & Meek 1973). Electroreceptive

animals use this sense in detecting and orienting toward prey,

locating predators, in some cases communicating with

conspecifics, and possibly in navigation (Kalmijn 1974, Peters

& Bretschneider 1972). One of the earliest descriptions of

electroreception was the demonstration in catfish of behaviors

associated with changes in the earth's magnetic field caused

2

by seismic events (Hatai & Abe 1932, Hatai et al 1932, Kokubo

1934).

Electroreception appears in a number of anamniotic

vertebrate taxa, as well as in two mammalian species; the

duck-billed platypus and the star-nosed mole (Bullock et al

1982, 1983, Scheich et al 1986, Gregory et al 1987, Gould et

al 1993) . There are two phylogenetic categories of

electroreception; primitive and derived. The primitive

electrosensory system is characterized by electroreceptor

organs, called the ampullary organs, that respond to low

frequency (0.2-20Hz) outward current flow (cathodal

stimulation) (Bullock et al 1982, 1983). The primitive system

is so termed because phylogenetic studies of the distribution

of electroreception indicate that such a system was present in

the common ancestor of all vertebrate taxes (Bullock et al

1982, 1983). This primitive electrosensory system is

characterized by the presence of nucleus dorsalis,

electrosensory afference transmitted via the anterior lateral

line nerve exclusively and the negative (cathodal) polarity

preference of the ampullary receptors.

The majority of non-teleost fish and some amphibians

possess the primitive electrosense. Among the agnathans the

Petromyzoniformes (lampreys) are electroreceptive, however the

Myxiniformes (hagfish) lack electroreception. Of the

gnathostomes, all of the chondricthyan fishes, the

Elasmobranchii (sharks, skates and rays) and the Holocephali

3

(chimeras) are electroreceptive. The Crossopterygii (which

includes one (extant) species, the coelacanth), the Dipneusti

(lungfish), and the Polypteriformes are all electroreceptive

groups. Additionally, some urodele and apodan amphibians are

electroreceptive during the aquatic larval stages of their

development (Bullock et al 1982, 1983). Among the primitive

Actinopterygii (ray-finned fishes), the Chondrostei

(paddlefish and sturgeon) are electroreceptive. The immediate

predecessors of the Teleosteii (bony fishes), the Holostei

(gars and bowfins) which have evolved from the Chondrostei,

and most orders of the Teleosteii lack electroreception. This

suggests that the common ancestor of the teleosts probably was

not electroreceptive. These animals lack electroreceptors or

any central nuclei associated with electrosensory processing

(Bullock et al 1982, 1983).

The derived form of electroreception has been re-evolved

independently at least twice and possibly three or four times

in teleost fishes (Greenwood et al 1966, Bullock 1974). Many

of these electroreceptive teleosts live in silty, low light

environments which are not conducive to the use of a visual

system. Electroreception may thus have re-evolved as a

strategy to compensate for this lack of visual cues and to

provide essential information about their environment. Derived

teleost electrosensory systems most likely re-evolved as a

specialization of the mechanosensory lateral line (Figure 1).

The ampullary receptors in this re-evolved system respond to

4

positive (anodal) stimulation.

The derived electrosensory system is much more limited in

its distribution than the primitive electrosense. Re-evolved

electrosenses are found in the Siluriformes (catfish), the

related Gymnotiformes (South American weakly electric fish),

and the Mormyriformes (African weakly electric fish) (Bullock

et al 1982, 1983, Heiligenberg 1986). Except for the

Siluriformes (catfish) and the Xenomystinae (a subfamily of

electric African fishes) the above fish also possess an

electric organ which generates high frequency electric fields

used in locating prey and communicating with conspecifics. The

taxa which possess electric organs also possess two types of

electroreceptors; ampullary and tuberous. The ampullary

receptors respond to external low frequency electrical stimuli

(0.2-20Hz), inward current flow (anodal stimulation) whereas

tuberous receptors respond to the high frequency electric

organ discharges (up to several thousand hertz) (Heiligenberg

1990). Thus catfish represent an intermediate step of

octavolateralis organization between most teleosts which

possess only a mechanosensory lateral line, and gymnotiforms

and mormyriforms, which possess a lateral line, ampullary and

tuberous electroreceptors.

5

Catfish Electrosensory system

The receptor cells of the ampullary organs in catfish

are innervated by fibers of the anterior, middle; and

posterior lateral line nerves. The primary afferent fibers of

the lateral line nerves terminate in a series of medullary and

cerebellar nuclei: the electrosensory lateral line lobe (ELLL) ,

the medial octavolateralis nucleus(MON), the caudal

octavolateralis nucleus (CON), and the eminentia granularis (Eg)

(Figure 1) (Finger 1986). The MON and probably the CON,

receive mechanosensory input whereas the electrosensory

lateral line lobe receives electrosensory input. Anterior and

posterior subdivisions of the eminentia granularis also

receive mechanoreceptor and electroreceptor afferent fiber

input, respectively (Figure 1) (Tong & Finger 1983, New &

Singh 1993) .

The principal target for primary electroreceptor fibers

is the electrosensory lateral line lobe(ELLL). The primary

afferent fibers of the lateral line nerves terminate within

the core of the ELLL, deep to a layer of crest cells. The

electrosensory lobe in catfish can be divided into four

layers. From superficial to deep, these are the molecular

layer (also known as the cerebellar crest), crest cell layer,

intermediate layer of fibers and cells, and a layer of round

cells (Finger 1986).

The parallel, unmyelinated fibers in the superficial

portion of the molecular layer originate from cells of the

6

posterior eminentia granular is. The deeper portion of the

molecular layer contains fibers that originate from the dorsal

portion of the nucleus praeeminentialis (nPrd). This projection

is bilateral, so that a given cell in the nPrd of one side may

project into the molecular layer of the electrosensory lobe of

both sides (Tong & Finger 1983, Finger 1986).

Directly beneath the molecular layer is a layer of large,

multipolar crest cells. The axons of the crest cells comprise

the ascending output neurons for the lemniscal pathway

emerging from the electrosensory lobe. The crest cells possess

elaborate and extensively branched apical dendrites that

extend into the molecular layer and receive synaptic contacts

from the descending parallel fibers. All of these cells have

some basilar dendrites, but some of the crest cells have a

basilar process that extends deep into the intermediate layer

(Mccreery 1977a).

The intermediate layer of the electrosensory lobe is a

complex layer containing a diversity of cell and fiber types.

Within this layer are small granule like neurons, larger

neurons that project to the lobus caudalis, basilar dendrites

of crest cells, and terminals of primary electroreceptor

afferents, as well as terminals from round cells in the

contralateral electrosensory lobe (Finger 1986).

Lastly, the deepest layer of the electrosensory lobe

contains large round bodied cells, the axons of which project

to the intermediate layer of the contralateral electrosensory

7

lobe. Round cells possess dendrites that extend upward into

the lower portion of the intermediate layer.

A lemniscal system is a series of connected nuclei within

the brain that form an ascending system devoted principally to

a single sensory modality and ultimately reach prosencephalic

levels (Nauta & Karten 1970). The ascending electrosensory

pathway within the central nervous system of catfish meets

these criteria. The electrosensory lobe gives rise to an

ascending fiber system, the lateral lemniscus, which ascends

bilaterally through the brain stem and terminates within the

lateral nucleus of the torus semicircularis(TSl). Axon

collaterals from this system also terminate in a metencephalic

nucleus, the nucleus praeeminentialis. This nucleus has

dorsal and ventral portions which receive electrosensory and

mechanosensory input, respectively (see Figure 1). Research

presented in this thesis focuses on the electrosensory dorsal

portion of nucleus praeeminentialis and its effect on

modulating ascending information. The descending parallel

fiber system of the molecular layer of ELLL and MON comprises

both feedback (LLN->ELLL->nPr->ELLL) and feedforward (LLN­

>Egl->ELLL) systems regulating the sensory information. The

electrosensory lemniscal system continues from the torus

semicircularis to a diencephalic nucleus, the nucleus

electrosensorius (see Figure 1) (Carr et al 1981, Finger 1986,

Striedter 1991).

8

Electrosensory Processing in the Central Nervous System

Afferent electrosensory fibers in the lateral line nerves

show a high resting discharge rate, approximately 50-100

impulses per second. The primary fiber increases its discharge

frequency in response to inward current (anodal stimulation)

applied to the appropriate receptors. Typical reported changes

in discharge rates are decreases of 50% and increases of 400%

(Roth 1975). The usual "working" range of the fiber may be

much smaller.

The response properties of the neurons in the

electrosensory lobe differ from those of the primary afferents

in three ways: (1) the central neurons are more sensitive than

the primary afferents by approximately one order of magnitude

(2) the central neurons do not exhibit high levels of

spontaneous activity, and (3) different central neurons are

excited by stimuli of differing polarities, whereas receptors

are excited only by anodal stimulation (Andrianov & Ilyinsky

1973, Roth 1975, Mccreery 1977a, for review see Finger 1986).

Two distinctive types of crest cells were described by

Mccreery (1977a). Type I crest cells are excited by cathodal

stimulation and Type II crest cells are excited by anodal

stimulation. Intracellular recordings in these preparations

demonstrate that the type II unit receives monosynaptic

excitatory input from the primary afferent fibers, while the

type I unit receives disynaptic input via an inhibitory

interneuron (Mccreery 1977a).

9

The receptive fields of the two types of crest cells are

distributed randomly across the body surface. The two

functional classes of the crest cells also occur at the same

depth in the electrosensory lobe. Crest cells of both types

appear to be more responsive to lower frequency stimuli than

are primary afferent fibers. The primary afferents respond

maximally to stimuli of approximately 8 Hz, whereas the crest

cells respond maximally at about 3-4 Hz (Mccreery 1977a).

Therefore, the crest cells act as a low frequency bandpass

filter.

The torus semicircularis contains one of the second-order

nuclei of the lemniscal electrosensory pathway in the CNS.

Electrosensory input reaches the lateral portion of the torus

semicircularis(TSl) via the crest cell axons (Knudsen 1977).

On the basis of a number of electrophysiological and

anatomical criteria, Knudsen suggests that the electrosensory

portion of the torus semicircularis is divisible into the two

functional zones: superficial and deep. The input to the

superficial zone is hypothesized to be predominantly from

Mccreery•s type 1 crest cells, while the input to the deep

zone is from McCreery's type 11 crest cells.

In the high frequency sensitive tuberous electrosensory

system of the gymnotiform teleost, Apteronotus leptorhynchus,

Bastian (Bastian & Bratton 1990, Bratton & Bastian 1990) has

found two projections from the nucleus praeeminentialis to the

electrosensory lateral line lobe: one direct, the other

10

indirect. The direct pathway is comprised of neurons from the

nucleus praeeminentialis projecting to the ventral portion of

the molecular layer of the electrosensory lateral line lobe.

It has been suggested that the sensitivity of restricted

populations of output cells in the electrosensory lateral line

lobe are altered by these cells and that they process

temporally and spatially restricted stimuli. They may act to

increase the intensity of the neural representation of

important stimuli (Bratton & Bastian 1990).

The indirect pathway is comprised of multipolar cells of

the nucleus praeeminentialis projecting bilaterally to the

posterior eminentia granular is. Posterior eminentia granular is

efferents project in turn to the electrosensory lateral line

lobe forming its dorsal molecular layer. Hence, these

multipolar cells influence the electrosensory lateral line

lobe through an indirect pathway. It has been hypothesized

that this indirect circuitry may act as a gain control

mechanism operative within the electrosensory lateral line

lobe (Bastian & Bratton 1990).

To summarize, in gymnotiforms the primary afferent

electrosensory neurons terminate on the crest cells of the

electrosensory lobe(ELLL) and the posterior eminentia

granularis. A bilateral projection originating from the ELLL

terminates in the lateral portion of the torus

semicircularis(TSl). Collaterals of this projection terminate

in the nucleus praeeminentialis(nPrd). A projection from the

11

nPrd may in turn descend onto the ELLL forming a feedback

loop(l). In addition, a projection originating from the

nucleus praeeminentialis terminates in the eminentia

granularis which in turn sends a projection down onto the ELLL

forming an indirect feedback loop ( 2) . Al though the direct

pathway is known to exist in catfish, the presence of an

indirect pathway, although likely, has not been experimentally

confirmed.

This study employs the ampullary electrosensory system of

the catfish as a model to examine the role of descending

projections in influencing ascending sensory information in

the vertebrate central nervous system. This system contains

only ampullary receptors and is therefore quite different from

the tuberous system used by Bastian and Bratton 1990. I have

used neurophysiological techniques to examine the influence of

neurons descending from the nucleus praeeminentialis on the

ascending electrosensory information from the electrosensory

lateral line lobe to the torus semicircularis presumably via

direct and indirect pathways.

CHAPTER II

MATERIALS AND METHODS

Experimental Animals

We used 9 Channel catfish, Ictalurus punctatus, for

inhibition experiments, 3 for voltage curves, 2 sets of 5 for

latency and 5 for frequency experiments. These fish were

maintained in aquaria (190-7501) at 22-24°C. Fish were chosen

randomly from 3 tanks. They were approximately 20cm long and

weighed between 50-75g.

Surgical Procedures

Individual specimens were anesthetized with approximately

0.03% tricaine methanesulfonate (MS 222) and placed on a flat

surface with a respiration tube delivering aerated water, inserted

through the mouth. The right medulla, cerebellum and the

contralateral optic tectum were surgically exposed. The fish

was then placed in the experimental tank (25.4 x 43.18cm) mounted

on a vibration isolated table where the animal's head was clamped

in a specially designed holder and the dorsal aspect kept just

above the water surface. The fish was artificially respirated

by a continuous flow of water over the gills. The water

temperature in the tank was approximately 17°C. The fish was

immobilized with a 0.3ml intramuscular injection of O.lM

pancuronium bromide. One hour was allowed before starting the

12

13

experiment to ensure complete recovery from the anesthetic.

Electrode Placement

A glass micropipette recording electrode ( input impedance

less than 1 Megohm) was placed in the electrosensory lateral

line lobe. Accurate placement was confirmed when a uniform

transverse electric field stimulus (150-200uV/cm, 700ms duration)

delivered across the body of the fish elicited an observable

evoked potential response in the electrosensory lateral line

lobe. A stimulating concentric bipolar electrode was placed in

the dorsal nucleus praeeminentialis. Its position was confirmed

when stimulation of the nucleus praeeminentialis elicited an

observable evoked potential in the electrosensory lateral line

lobe. A similar recording electrode was placed in the

contralateral electrosensory torus semicircularis and its position

confirmed by observing evoked potential responses to electric

field stimuli (see Figure 2 for stimulus/recording paradigm).

Constant Stimulus Parameters

Evoked potential waveforms were collected under three

different stimulus paradigms: ( 1) nucleus praeeminentialis

stimulation alone, (2) electric field stimulation alone, and

(3) nucleus praeeminentialis and electric field stimulus combined.

Electric field stimulation was kept steady during all

experimentation at an amplitude of 40volts, duration of 700ms

and field strength between 150-200uv/cm. Only the stimulus

delivered to nucleus praeeminentialis(nPrd) was varied.

14

Inhibition Experiments

The frequency and duration of the stimulus trains del_ivered

to nucleus praeeminentialis were kept constant at lOOHz and 150ms,

respectively. The amplitude of these stimulus trains was set

at 7, 10 and 12volts. Latency, the time difference between the

end of a nucleus praeeminentialis stimulus train and the beginning

of an electric field stimulus, was set at o, 60, and 120ms.

Voltage and latency parameters were tested randomly.

Voltage Curve Experiments

The frequency, latency and train duration of the nucleus

praeeminentialis stimulus trains ~ere kept constant at lOOHz,

Oms and 150ms, respectively. The amplitude of the train stimulus

was varied randomly at o, 2, 4, 5, 7, 10 and 12volts.

Latency Experiments

The amplitude and frequency of the nucleus

praeeminentialis(nPrd) stimulus train were kept constant at

lOvolts and lOOHz, respectively. Latency between the end of the

stimulus train delivered to nPrd and the beginning of the electric

field stimulus was varied randomly at short latencies of O, 20,

40, 60, 80, and lOOms and long latencies of O, 120, 480, 1000,

1500, 2000ms. Controls for each set of experiments were provided

by placing the stimulating electrode on the surface of the brain

above nPrd after the experimental data had been collected and

using Oms latency while stimulating the area.

Frequency Experiments

The amplitude and duration of the stimulus train delivered

15

to nucleus praeeminentialis were kept constant at l0volts and

150ms, respectively. The frequency of the stimulus train was

varied randomly at 10, 20, 40, 83, 166Hz. After recording the

experimental data, the stimulating electrode was place on the

surface of the brain above nPrd and this area was stimulated

at 166Hz to provide a control.

Marking of Recording Site

The recording electrodes were filled with 2M Nacl saturated

with fast green dye. After an experiment was completed the green

dye from the toral recording electrode was iontophoresed at 50u

amps de, pulse interval 15s, pulse duration 2. 9s for approximately

30 minutes. This procedure marked the recording site in the torus

semicircularis.

Retrieval of Recording Marks

After marking the recording site, the fish was decapitated

and its head stored in 4% glutaraldehyde solution for

approximately a week. The brain was then exposed, extracted from

the skull and returned to the 4% glutaraldehyde solution during

two consecutive weeks. The brain was then switched for a week

to a 20% sucrose and 4% glutaraldehyde solution to cryoprotect

the tissue. The meninges of the brain were removed. The brain

was then blocked in a 20% sucrose gelatin solution and stored

for an additional week in 20% sucrose and 4% glutaraldehyde

solution. The tissue was then sectioned into 30um sections on

a freezing microtome, mounted on Chrome-alum subbed slides,

stained in neutral red and coverslipped. The location of the

16

green mark in the torus semicircularis revealed the recording

site.

Data Analysis

Within each experiment there were different stimulus

parameters tested to determine their effect on ascending

electrosensory information. For example, in the inhibition

experiments 7v was tested with o, 60 and 120ms latencies. A data

block would be 7v tested with one latency either 0, 60 or 120ms.

For each data block, 5 averaged waveforms were collected; 2 from

electric field stimulation alone, 2 from nucleus praeeminentialis

and electric field stimulation combined and 1 from nucleus

praeeminentialis alone. These waveforms were the average of 30

sweeps. They were digitized on a Zenith 286 computer with a DAS-

16F A/D conversion board and rectified. A segment from each

waveform which contained the response to electric field onset

was extracted. The segments originated at the electric field

onset and continued in duration for 300 to 350ms. The length

of these segments encompassed entire responses and were kept

constant throughout the calculation of an experiment.

Analysis within a Data Block

A baseline segment, which indicated the horizontal non­

response position of waveforms within a data block, was subtracted

from the two segments containing the response to electric field

stimulation alone. This was done to eliminate background artifact.

The segment containing the response to nucleus praeeminenitailis

stimulation alone was subtracted from the two segments containing

17

the response to nucleus praeeminentialis and electric field

stimulus combined. This was done to remove stimulus artifact

and obtain an electric field segment modulated by nucleus

praeeminentialis stimulation (modulated electric field). The

running integrals of the subtracted segments were calculated

using Asystant Plus (Keithley Metrabyte) sofware. The integrals

of the segments containing a electric field response were averaged

and the integrals of the segments containing the modulated

response were averaged. The averaged value of the modulated

response was divided by the averaged value of the electric field

response so as to normalize the experimental to the control.

This normalized number was then multiplied by 100 to obtain what

percentage the modulated response was of the electric field

response. This was done to determine the effect of nucleus

praeeminentialis stimulation on the amplitude of the electric

field response. Each block was calculated and combined to

determine the outcome of each experiment.

CHAPTER III

RESULTS

Recovery of Marked Recording Sites

Of the twenty-seven experiments included in this study,

twenty-six recording sites were marked and out of these, thirteen

were retrieved. All thirteen were recovered from the torus

semicircularis. The recording site retrieval rate was overall

52%.

the Shape of Evoked Potential Waveforms

The evoked potential waveforms varied considerably from

specimen to specimen and between recording sites within the same

animal. The most common waveform recorded from the torus

semicircularis following a DC step electric field presentation

of 150uV/cm oriented with the anode contralateral to the recording

site had an initial positive peak (mean latency of 52.4ms, SEM

8.3) followed by a negative peak (mean latency of 129.9ms, SEM

10.8) again often followed by a positive peak (mean latency

243.lms, SEM 30.8). Another waveform type had an initial positive

peak, negative peak followed by a positive peak at different

mean latencies of 26.5ms, SEM 5.6, 47.lms, SEM 4.7 and 123.5ms,

SEM 1 7, respectively. Other waveforms recorded were a combination

of those described above.

18

19

Effect of Delivering an Electric Pulse Train to nPr Prior to

Electric field Presentation

In these nine experiments, nPr stimulus train duration and

frequency were kept constant at 150mS and l00Hz, respectively.

Nucleus praeeminentialis was stimulated with 7, 10 and 12 volts,

preceding electric field (EF) presentation by o, 60 or 120mS

delays. The electric field strength and duration were maintained

at 150-200uV/cm and 700mS, respectively. In each case there was

inhibition of the response to the electric field recorded from

the contralateral torus semicircularis. A comparison of the

integrals of the averaged waveforms recorded when combining nPr

and electric field stimulation and those recorded following

electric field stimulation alone demonstrated a reduction

reflecting an inhibition of the response to electric fields when

combined with nPr stimulation. Integrals of waveform responses

to electric fields preceded by nPr stimulation (modified electric

fields) were normalized to those of responses to electric field

stimulation alone (unmodified electric fields). Percentages of

modified to unmodified electric field responses were then

calculated (ranged from 69.60% to 87.94%, see Table 1). The

average mean reduction recorded ranged from 12.06% to 30.40%

and the standard error of each mean ranged from 3.43 to 9.76

(see Table 1). A two factor ANOVA was performed with voltage

and delay as main factors with a voltage*delay interaction.

This indicated no significant difference in effect by these

factors on the inhibitory response (volt. p=.556, 71, 2 df; lat.

20

p=.320, 71, 2 df; volt*lat p=.978, 71, 4 df all at alpha=.05).

subsequently the data from the (3x3=) 9 treatment cells were

pooled and a binomial test used to determine if the treatments

affected response (Xf. = 33.8, P < 0.001, df=l). The results showed

significant inhibition. These experiments indicate that there

was inhibition of ascending electric field information when nPr

was stimulated with the above range of parameters.

Results of Varied Amplitude of Electric Pulse Train Delivered

to nPr

Because above results showed no difference between voltages,

a wider range was tested to determine threshold. In three

experiments the frequency and delay of the nPr stimulus train

were kept constant at lOOHz and oms, respectively. The electric

field duration and strength were maintained at 700mS and

approximately 150uV/cm. The voltage of the nPr stimulus train

varied between o, 2, 4, 5, 7, 10 and 12v. The responses exhibited

a threshold at 7v, above which a saturated inhibition of the

response to electric fields occurred. Integrals of waveform

responses to electric fields modified by nPr stimulation were

normalized to those of responses to EF stimulation alone and

converted into percentages. Normalized response integrals ranged

from 106.52% to 57.77%, the average mean reduction recorded ranged

from -6. 52% to 42. 23% and the standard error of each mean ranged

from 1. 05 to 14. 44 (see table 2). A one-way analysis of variance

was calculated for voltage and the results showed a significant

difference within this parameter indicating the possibility of

21

a threshold effect (F=volt. p=.015, 6, 13). Chi-square analysis

revealed that at o, 2, 4, and 5V the amplitude of the response

to an electric field preceded by an nPr stimulus train was not

significantly different from that produced by electric field

stimulation alone (Binomial Test x2 = 1.18, p < .001, df=l).

When the nPr stimulus train amplitude was 7v, 10v or 12v the

response to electric fields preceded by nPr stimulation was

significantly inhibited (Binomial test, exact calculation p=.004).

These data indicate that the amplitude of the nPr train stimulus

had to reach a threshold of approximately 7 vol ts before

inhibiting ascending electric field information. Once threshold

has been reached the level of inhibition remained somewhat

constant (figure 4). This agrees with the previous experiment

in that the amount of inhibition under these conditions is similar

and apparently saturated.

Results of Varied Frequency of Electric Pulse Train Delivered

to nPr

In five separate experiments the amplitude, delay and

duration of the stimulus train delivered to nPr were kept constant

at l0V, oms and 150mS, respectively. The strength and duration

of the electric field stimulus was maintained at 150-200uv/cm

and 700mS, respectively. The frequency of the train stimulus

delivered to nPr was varied between 10, 20, 40, 83, and 166Hz.

The same procedure was followed to obtain the integrals of the

response waveforms for analysis. The results of the subtraction

demonstrated an overall inhibition of electric field response

22

even when presented with one . lmS pulse. The average mean

reduction recorded ranged from 15.09% to 23.645 with 2.0.2% the

only anomaly at 20Hz and the standard error of each mean ranged

from 4. 55 to 12. 85 ( see Table 3) . A one-way analysis of variance

(ANOVA) was performed on the modified electric field response

integrals and showed no significant difference between the amount

of inhibition elicited by the various frequencies (ANOVA p=.352,

19, 4 df). A binomial test was performed on modified electric

field response data and showed a significant inhibition in the

electric field responses preceded by nPr stimulation (X2 = 16. 67,

p < 0.001, df=l). Statistical results indicate that all the

frequencies were inhibitory. The overall inhibitory effect of

the frequencies used is reflected in the plateau shape of figure

5. The only anomaly was 20Hz which appears close to 100% and

therefore to the unmodulated electric field response.

Duration of nPr's Inhibitory Response

In the next set of experiments the amplitude, delay and

duration of the stimulus train delivered to nPr were kept constant

at l0V, oms and 150mS respectively. Five experiments used delays

of o, 20, 40, 60, 80 and l00mS. An additional five experiments

used delays of o, 120, 480, 1000, 1500, and 2000mS. The same

procedure was followed to obtain the integrals of the response

waveforms for analysis. The results of these ten experiments

indicate that the inhibition of an electric field response caused

by nPr stimulation lasted between 120-480mS.

The average mean reduction recorded ranged from 11.18% to

23

35.07% and the standard error of each mean ranged from 6.64 to

12. 48 for the five experiments implementing short latency

durations. The responses to an electric field preceded by nPr

stimulation with delays of O, 40, 60, 80, and lOOmS were not

significantly different from each other as indicated by one way

analysis of variance (lat.p=.536, 5,24df). When compared to a

response to an electric field alone, the electric field preceded

by nPr stimulation was significantly inhibited (Binomial test

X2 = 13.33, p < 0.001, df=l).

The average mean reduction recorded ranged from -1.32% to

46.15% and the standard error of each mean ranged from 1.30 to

8. 71 for the five experiments implementing long latency durations

(see Table 6). A one way analysis of variance was performed on

the latency parameter and the results indicated a significant

difference between them in eliciting responses (lat.p=.001,

5,24df). Using a Tukey's multiple comparison test indicated that

significant differences in latencies were between Oms and 120rns

at an alpha of 0.01 and between 120rns and 480rns at an alpha of

0.05 (see table 5). Using these two different alpha criteria

indicates that nPr's inhibitory response lasts between 120 and

480rns.

24

DESCENDING ASCENDING

I I I I TS■ I TSI I TSI TSm ID • MID BRAIN • ID

I I

nPrd nPrd

• • nPrv nPrv

ID • ---I L I I

EGa,EGp 1

cc EGp IEGa r 1, • • Ill I

' T I

I l 1 f

ELLL MON MON ELLL

• • Ill • ? I C~N

j f I I

CON I I ALLN ID t

1,111

HIND BRAIN 0- PLLN

1,111

Trunk

Figure 1.

Circuit Diagram of the afferent and efferent projections of the electrosensory and mechanosensory systems of the catfish. There are two significant features of this diagram. First, the electrosensory system is virtually parallel to the mechanosensory system in nuclei location and · axonal projections reflecting their common origin. Secondly, That higher brain centers feedback and modulate ascending information.

C\J

c., C1)

a::

Figure 2.

C

E

lJJ

z _J _J

CL

'-

C.

l

c.:, a)

0::

25

Diagram of the stimulus and recording paradigm used in the experiments. A Recording electrode is placed in the medullary electrosensory lateral line lobe (ELLL). Proper placement of the stimulating electrode is confirmed by recording evoked potentials from the ELLL in response to stimulation of nPr. The second recording electrode is placed in the torus semicircularis. Evoked potentials are recorded from the torus to determined the effect of varied stimulus train parameters delivered to nPr.

26

TORAL EVOKED POTENTIAL

A

EF

50 µV L I 00 ms

8

EF

n Pr II I 1H 111111 IHI

Figure 3.

An evoked potential waveform response to electric field presentation alone (A) top is the waveform trace, bottom is a representation of the DC step electric field (200uv/cm) presented and preceded by nPr stimulation (B) top portion of Bis the waveform trace, bottom is a representation of the train stimulus delivered to nPr prior to electric field presentation and the DC step electric field presented (200uv/cm).

120

100

~ 80 0 ~ E-t z 0 60 t)

~ 0

dP 40

20

0

Figure 4.

27

0 2 4 5 7 10 12

VOLTAGE (V)

The data in this graph is from the average of three experiments. All parameters were kept constant (nPr lOOHz, del=Oms & dur=lSOms: EF 40v, dur=700ms & 2oouv/cm). The amplitude of the stimulus train delivered to nPr was varied randomly at 2, 4, 5, 7, 10, and 12v. The evoked potential responses to electric field presentation preceded by nPr stimulation was normalized to the control ( electric field alone). Percentages were calculated and graphed in this figure.

28

120

100

..:i 80 0

~ E-c :z:

60 0 C)

r:.. 0 40

dP

20 1--- EXP -&- CONT 1

0

0 20 40 60 80 100 120 140 160 180

FREQUENCY {Hz}

Figures.

The data in this graph is from the average of five experiments. All parameters were kept constant (nPr l0v, del=0ms & dur=l50ms: EF 40v, dur=700ms & 200uv/cm). The frequency of the stimulus train delivered to nPr was varied randomly at 10, 20, 40, 83, 16GHz. The evoked potential responses to electric field presentation preceded by nPr stimulation was normalized to the control ( electric field alone). Percentages were calculated and graphed in this figure.

29

100

..:I 80 0 c:i:: -E-t z 60 SD EXP 0 CJ --rz..

40 LD EXP

0 -&-

dP SD CONT 20 ~

LD CONT

0

-200 200 600 1000 1400 1800

DELAY (MS)

Figure 6.

The data in this graph is from the average of two sets of five experiments. All parameters were kept constant except for the delay between the offset of the nPr stimulus and the onset of the electric field. In the short delay experiments (SD EXP) the delays varied at o, 20, 40, 60, so, and lOOms (see table 4). In the long delay experiments (LD EXP) the delays varied at O, 120, 480, 1000, 1500, and 2000ms (see table 6). The evoked potential responses to electric field presentation preceded by nPr stimulation was normalized to the control (electric field alone). Percentages were calculated and graphed in this figure.

30

Table 1. Results showing stimulation of nPr preceding electric field presentation inhibits ascending electrosensory information.

VOLT DEL EF+NPR/EF SEM (V} (MS} (%}

7 0 81. 37 4.91

7 60 78.13 9.40

7 120 87.94 5.95

10 0 78.24 9.52

10 60 69.60 6.64

10 120 82.51 3.43

12 0 81.08 7.98

12 60 80.35 9.76

12 120 85.07 5.16

The above table shows the results averaged over nine experiments. Column one and two show the parameters of voltage and delay used when stimulating nPr, respectively. Column three shows what percentage the modified response (electric field preceded by nPr stimulation) is of the control response (electric field alone). The last column shows the standard error of the mean for the percent averages in column three.

31

Table 2. Results showing an amplitude threshold exists for the activation of nPr

VOLTAGE EF+NPR/EF SEM (V) (%)

0 106.52 1.05

2 93.13 11.23

4 94.87 8.64

5 90.72 14.44

7 57.77 1.15

10 69.70 5.11

12 67.50 2.58

The above table shows the results averaged over 3 experiments. The first column indicates the voltages used to stimulate nPr. Column two shows what percentage the modified response (electric field preceded by nPr stimulation) is of the control response (electric field alone) (graphed in figure 4). Column three shows the standard error of the mean for the percent averages in column two.

32

Table 3. Results showing frequency is sufficient to cause nPr activation

FREQUENCY EF+NPR/EF SEM (HZ) (%)

10 76.94 7.81

20 97.98 12.85

40 84.91 5.95

83 84.91 6.29

166 76.36 4.55

166 CONT 98.92 2.72

The above table shows the results averaged over five experiments. The first column indicates the frequency used to stimulate npr. Column two shows what percentage the modified response (electric field preceded by nPr stimulation) is of the control response (electric field alone) (graphed in figure 5). Column three indicates the standard error of the mean for the percent averages in column two.

33

Table 4. Results showing nPr's inhibitory response is longer than l00ms in duration

DELAY EF+NPR/EF SEM (MS) (%)

0 64.93 7.74

20 84.65 12.48

40 74.29 7.60

60 76.63 10.75

80 88.82 9.02

100 81.58 6.64

0 CONT 106.73 7.20

The above table shows the results averaged over five experiments. The first column indicates the time delay between the offset of nPr stimulation and the onset of electric field presentation. Column two shows what percentage the modified response (electric field preceded by nPr stimulation) is of the control response (electric field alone) (graphed in figure 6). Column four shows the standard error of the mean for the percent averages in column two.

34

Table 5. Results from a Tukey' s Multiple Comparison statistical analysis on long delay data

LAT 0 120 480 1000 1500 2000 (MS)

-

RESP 53.85 76.71 97.28 93.89 99.25 101.32 (%)

a=.05 xxxxxx xxxxxx 000000 000000 000000 000000 00000

a=.01 000000 000000 000000 000000 00000

The above table shows the statistical results averaged over five experiments using the Tukey' s multiple comparison analysis. The X's indicate that latencies of o and 120ms are similar in their ability to elicit an inhibitory response. The o's also indicate a statistical similarity in evoking an inhibitory response. The results from using two different alpha values indicate that nPr' s inhibitory response lasts between 120 and 480ms.

35

Table 6. Results showing nPr's inhibitory response lasts between 120 and 480ms

DELAY EF+NPR/EF SEM (MS) (%)

0 53.85 5.90

120 76.71 8.71

480 97.28 2.21

1000 93.89 3.25

1500 99.25 1.30

2000 101.32 2.71

0 CONT 97.62 4.27

The above table shows the results averaged over five experiments. The first column indicates the time delay between the onset of nPr stimulation and electric field presentation. Column two shows what percentage the modified response (electric field preceded by nPr stimulation) is of the control response (electric field alone) (graphed in figure 6). Column four shows the standard error of the mean for the percent averages in column two.

CHAPTER IV

DISCUSSION

We have found that stimulation of nPr causes inhibition

of ascending electrosensory information as recorded from the

torus semicircularis. That this inhibition was strong is shown

by a 14. 93%-30. 40% decrease in response, long lasting ( 120-480mS)

and elicited by just one .lmS pulse. In addition, a stimulus

amplitude threshold of seven volts had be reached before this

inhibition saturated. Descending control from higher brain centers

on lower order nuclei is a recurrent theme in vertebrate neural

strategy. Previous studies in catfish have shown that stimulation

of the cerebellum inhibits the response to electric fields

recorded in the torus semicircularis (Crispino 1983). Crispino

stimulated the superficial region of the cerebellar lobus

caudalis. When he recorded from the electrosensory lateral line

lobe or from the ascending lemniscal fibers leading to the torus

semicircularis following cerebellar stimulation he recorded

no inhibition of the response to electric fields from either

recording site (Crispino 1983). He therefore concluded that he

was stimulating a direct ascending projection from the cerebellar

lobus caudalis to the torus semicircularis. Such a projection

has been anatomically proven to exist and forms a feedback loop

onto the ELLL (Crispino 1983, Tong & Finger 1983) . Why Crispino

36

37

did not see a response in ELLL upon stimulating lobus caudalis

in intact preparations is unclear as it is likely he also

stimulated the descending parallel fiber tracts originating in

Egr and nPr. Perhaps the projection from lobus caudalis to the

ELLL modifies electrosensory information in a more subtle way.

Our work does not dispute this projection but highlights another.

In our experiments, the stimulating electrode was placed deep

within the cerebellum not superficially and location in nPr was

verified by activation of the descending fiber pathway as recorded

in the ELLL. The response recorded in the electrosensory lateral

line lobe was large and resulted only after stimulating in a

localized area in the metencephalon; the nucleus praeeminentialis.

In another study, recording from single units in the ELLL

following nPr stimulation revealed a quick burst of excitatory

activity followed by a pronounced inhibition (New unpublished

data). Other studies have shown the existence of a direct

projection in catfish and gymnotiforms between nPr and ELLL

(Bratton & Bastian 1990, Tong & Finger 1983, Finger & Tong 1984).

An indirect projection between nPr-Egr-ELLL exists in gymnotiforms

and may exist in catfish but has not yet been demonstrated

(Bastian & Bratton 1990). Due to the evoked potential and single

unit responses to nPr stimulation recorded in the electrosensory

lateral line lobe and the demonstrated anatomy in both catfish

and gymnotiforms we are confident that in these experiments we

were stimulating one or more descending projections.

In elasmobranchs, the first order nucleus in the

38

electrosensory system, the dorsal octavolateralis nucleus (DON)

and the output afferent electrosensory neurons (AENs) are similar

to the catfish's electrosensory lateral line lobe (ELLL) and

the lemniscal crest cells, respectively (Bastian & Courtright

1991). The dorsal granular ridge in elasmobranchs is similar

to the eminentia granularis in electroreceptive teleosts and

is the sole source of descending parallel fibers to the DON;

there is no additional projection comparable to the nPr of

teleosts (Bass 1982, Bullock et al. 1983). Conley, working with

the skate, Raja erinacea, recorded from the projection AENs of

the DON a brief burst of excitation followed by prolonged

inhibition of approximately 200mS following DGR stimulation

(Conley 1991, Ph.D. Thesis). This is similar to the responses

observed in single unit recordings from the ELLL in the catfish

following nPr stimulation (New, unpublished data). Our work with

evoked potentials recorded from the torus semicircularis showed

a pronounced inhibition of electric field responses (120-480mS)

after nPr stimulation. Electric field presentation during this

period inhibited the electrosensory response. Crispino found

that stimulating the cerebellum inhibited electrosensory

information recorded from the torus semicircularis (Crispino

1983). In gymnotiforms, Maler et al discovered through the use

of electron microscopy that the dorsal molecular layer from the

EGr makes primarily excitatory contact with the output and

interneurons of the ELLL (Maler et al 1981, Mathieson & Maler,

1988). However, Bastian has found that physiologically, this

39

electrosensory circuit has a primarily inhibitory influence on

ELLL output neurons (Bastian, 1986a, b). When EGr was lesioned

the excitability of the output neurons of ELLL increased as if

inhibition had been removed (Bastian, 1986a, b). Having both

excitation and inhibition in a circuit is advantageous to the

shaping of ascending information.

The results of these studies suggest that descending pathways

to the medullary electrosensory nuclei form the neural substrate

of a "gain control" mechanism. Proper functioning of this

mechanism requires that the amount of ascending information be

quantified and the level modified through descending control

onto the output neurons of the ELLL to obtain the amount of

ascending information necessary for optimal functioning. The

direct and indirect feedback loops in gynotiforms and probably

in siluriforms ELLL-nPr-ELLL and ELLL-nPr-EG-ELLL has nPr

advantageously placed for the quantifying of ascending information

(Bastian & Bratton 1990, Bratton & Bastian 1990). In addition,

Bastian's work has demonstrated that nPr multipolar cells modify

their stable firing rate within about 1 sec of an EOD amplitude

change which illustrates a quickly adapting system (Bastian &

Bratton 1990). The high sensitivity of nPr encoding was

demonstrated by the average spike frequency change of 2 and 3

spikes/sec given an EOD amplitude change of 1% (Bastian & Bratton

1990). Anatomical placement, quick adaptation and high sensitivity

make nPr a strong candidate for quantifying ascending information

and modifying it's ascent through descending projections onto

40

lower order nuclei in gymnotiforms and electrosensory teleosts.

Elasmobranchs do not have a related structure to nPr. However,

electrosensory information descends from the lateral mesencephalic

nucleus to the paralemniscal nucleus to the DON and DGR indicating

descending modification of ascending electrosensory information

(Conley 1991, Ph.D. Thesis).

The purpose of the electrosensory circuits may also be

understood in the context of the searchlight hypothesis,which

suggests a mechanism providing an attentional searchlight in

the brain (Treisman 1977, Treisman & Gelade 1980, Treisman &

Schmidt 1982, Treisman 1983, Crick 1990). The searchlight provides

a neural mechanism by which to monitor activity, determine where

the excitation is, intensify it, turn it off and to finally move

on to the next area of attention. Nucleus praeeminentialis which

receives ascending axon collaterals from ELLL may monitor the

activity in this manner and intensify the excitation via

modulation of descending inhibition. Crick proposed a way in

which a nucleus using the inhibitory neurotransmitter GABA, which

is present in the nPr of catfish and in the lateral line of

goldfish, could produce excitation in a lower nucleus using

positive feedback (Crick 1990, New & Yu 1994). Assume that a

portion of nPr was excited above background via ascending

lemniscal axons. Descending GABAergic projections from nPr will

project locally onto target crest cells in the ELLL and

hyperpolarize them via GABAergic synapses (Llinas & Jahnsen 1982,

Jahnsen & Llinas 1984a; 1984b) . If there is a topographic

41

organization of ascending lemniscal axons and descending nPr

projections, selective activation of populations of crest cells

would result in localized hyperpolarization of these same cells.

Such topographic organization has been demonstrated to exist

in elasmobranchs between DGR and DON (Bodznick & Schmidt 1984,

Schmidt & Bodznick 1987) . Additionally, in thalamic slices from

the guinea pig it has been demonstrated that inhibitory inputs

causing hyperpolarization sensitized these neurons so that when

current was injected a quick excitatory burst was produced

followed by pronounced inhibition (Llinas & Jahnsen 1982, Jahnsen

& Llinas 1984a;1984b). Ascending information from the lateral

line nerves feeds onto the sensitized crest cells of the ELLL

causing a brief burst of excitatory activity followed by a

pronounced inhibition. This is an example of positive feedback

because the excitation is amplified by excitation and the surround

dampened. Once the excitation is isolated it becomes important

to defuse the positive feedback loop so that the attentional

searchlight can focus on a different area giving it mobility.

This can occur via the inhibition following the quick burst of

excitation necessary for the searchlight to attend. Working with

guinea pig, the pronounced inhibition recorded after the burst

of excitatory activity in the thalamic neurons was 80-lS0mS in

duration (Llinas & Jahnsen 1982, Jahnsen & Llinas 1984a; 1984b).

In channel catfish, New has recorded a quick burst of excitatory

activity followed by pronounced inhibition in crest cells of

the ELLL after delivering current to nPr (New unpublished data).

42

In addition, our evoked potential study recorded inhibited

electric field responses from the torus semicircularis following

nPr stimulation which lasted between 120 and 480mS. This

inhibition may allow the positive feedback loop to be defused

and the attentional searchlight to disengage and focus on new

excitatory activity.

REFERENCES

Andrianov G, Ilyinsky o (1973) Some functional properties of central neurons connected with the lateral line organs of the catfish, Ictalurus punctatus. J Comp Physiol 86:365-376

Bass AH (1982) Evolution of the vestibulolateral lobe of the cerebellum in electrorecptive and non-electroreceptive teleosts. J Morph 164:335-348

Bastian J (1986A) Gain control in the electrosensory system mediated by descending inputs to the electrosensory lateral line lobe. J Neurosci 6:553-562

Bastian J (1986B) Gain control in the electrosensory system: a role for the descending projections to the electrosensory lateral line lobe. J Comp Physiol 158:505-515

Bastian J, Bratton B (1990) Descending control of electroreception.1.properties of nucleus praeeminentialis neurons projecting indirectly to the electrosensory lateral line lobe. J Neuro 10(4):1226-1240

Bastian J, Courtright J (1991) Morphological correlates of pyramidal cell adaptation rate in electrosensory lateral line lobe of weakly electric fish. J Comp Physiol 158A:393-407

Bodznick D, Schmidt AW (1984) Somatotopy within the medullary electrosensory nucleus of the little skate, Raja erinacea. J Comp Neurol 225:581-590

Bratton B, Bastian J (1990) Descending control of electroreception.11.properties of nucleus praeeminentialis neurons projecting directly to the electrosensory lateral line lobe. J Neuro 10(4):1241-1253

Bullock TH (1974) An essay on the discovery of sensory receptors with an introduction to electroreceptors. In: Fessard A (ed) Handbook of sensoryphysiology. Berlin, Springer-Verlag, Vol III/3 pp 1-12

43

44

Bullock TH (1982) Electroreception. Ann Rev Neurosci 5:121-170

Bullock TH, Bodznick DA, Northcutt RG (1983) The phylogenetic distribution of electroreception: evidence for convergent evolution of a primitive sense modality. Brain Res Rev 6:25-46

Carr CE, Maler L, Heiligenberg W, Sas E (1981) Laminar organization of the afferent and efferent systems of the torus semicircularis of gymnotiform fish: morphological substrates for parallel processing in the electrosensory system. J Comp Neurol 203:649-670

Conley RA (1991) Electroreceptive and proprioceptive representations in the dorsal granular ridge of skates: relationship to the dorsal octavolateralis nucleus and electrosensory processing. Ph.D Dissertation, Wesleyan University

Crick F (1984) Function of the thalamic reticular complex: the searchlight hypothesis. Proc Natl Acad Sci USA 81:4586-4590

Crispino L (1983) Modification of responses from specific sensory systems in midbrain by cerebellar stimulation: experiments on a teleost fish. J Neuro 49:3-15

Finger TE, Tong SL (1984) Central organization of eighth nerve and mechanosensory lateral line systems in the brainstem of ictalurid catfish. J Comp Neurol 229:129-151

Finger TE (1986) Electroreception in catfish: behavior, anatomy, and electroreception. In: Bullock TH, Heiligenberg W (eds) Electroreception. Wiley, New York, pp. 287-313

Greenwood PH, Rosen DE, Weitzman SH, Myers GS (1966) Phyletic studies of teleostean fishes, with a provisional classification of living forms. Bull Am Mus Nat Hist 131:339-456

Gould E, Mcshea W, Grand T (1993) Function of the star in Condylura. J Mammalogy 74:108-116

Gregory JE, Iggo A, McIntyre AK, Proske U (1987) Electroreceptors in the platypus. Nature 326:386-387

Hatai s, Abe N (1932) The responses of the catfish. Parasilurus, to earthquakes. Pro Imp Acad Jpn 8:275-378

45

Hatai s, Kokubo s, Abes (1932) The earth currents in relation to the responses of catfish. Proc Imp Acad Jpn 8:478-481

Heiligenberg W (1986) Jamming avoidance responses: Model systems for neuroethology. In: Bullock TH, Heiligenberg W (eds) Electroreception. Wiley, New York, pp. 613-650

Heiligenberg W (1990) Electrosensory systems in fish. Synapse 6:196-206

Jahnsen H, Llinas R (1984) Electrophysiological properties of guinea-pig thalamic neurons-an invitro study. J Physiol 349:205-226

Jahnsen H, Llinas R (1984) Ionic basis for the electroresponsiveness and oscillatory properties of guinea-pig thalamic neurons invitro. J Physiol 349:227-247

Kalmiljn AJ (1974) The detection of electric fields from inanimate and animate sources other than electric organs. In: Fessard A (ed) Handbook of sensory physiology. Berlin, Spring-Verlag, Vol III/3 pp.147-200

Knudsen EI (1977) Distinct auditory and lateral line nuclei in the midbrain of catfishes. J Comp Neurol 173:417-432

Kokubo s (1934) on the behavior of catfish in response to galvanic stimuli. Sci Rep Tohuk Univ Biol 9:87-96

Llinas R, Jahnsen H (1982) Electrophysiology of mammalian thalamic neurons invitro. Nature(London) 297:406-408

Maler L, Sas EKB, Rogers J (1981) The cytology of the posterior lateral line lobe of high frequency weakly electric fish(gymnotidae): dendritic differentiation and synnaptic specificity in a simple cortex.

Mathieson WB, Maler L (1988) Morphological and electrophysiological properties of a novel in vitro preparation: the electrosensory lateral line lobe brain slice. J Comp Physiol 163:48-506

McCormick CA (1982) The organization of the octavolateralis area in actinoptergian fishes: a new interpretation. J Morph 171:159-181

Mccreery DB (1977A) Two types of electroreceptive lateral lemniscal neurons of the lateral line lobe of the catfish, Ictalurus nebulosus, connections from the lateral line nerve and steady-state frequency response

46

characteristics. J Comp Physiol 113:317-339

Montgomery JC (1981) Origin of the parallel fibers in the cerebellar crest overlying the intermediate nucleus of the elasmobranch hindbrain. J Comp Neural 202:185-191

Nauta WJH, Karten HJ (1970) A general profile of the vertebrate brain with sidelights on the ancestry of cerebral cortex. In: Schmitt FO (ed) The neurosciences: second study program. Rockerfeller Univ Press, New York, pp. 7-26

New JG, Fay C (1994) Distribution of gamma-aminobutyric acid immunoreactivity in the brain of the channel catfish with special reference to octavolateralis systems. Neuroscience Abstract #68.7

New JG, Singh S (1993) Central topography of anterior lateral line nerve projections in the channel catfish, Ictalurus punctatus. Brain Behav Evol 43:34-50

Peters RC, Bretschneider F (1972) Electric phenomena in the habitat of the catfish, Ictalurus nebulosus Les. J Comp Physiol 81:345-363

Peters RC, Meeks F (1973) Catfish and electric fields. Experientia(basel) 29:299-300

Roth A (1972) The function of electroreceptors in catfish. J Comp Physiol 79:113-135

Roth A (1975) Electroreception in catfish: temporal and spatial integration in receptors and central neurons. Exp Brain Res 23(5):179

Scheich H, Langner G, Tidemann c, Coles RB, Guppy A (1986) Electroreception and electrolocation in platypus. Nature 319:401-402

Schmidt AW, Bodznick D (1987) Afferent and efferent connections of the vestibulolateral cerebellum of the little skate, Raja erinacea. Brain Behav Evol 30:282-302

Striedter GF (1991) Auditory, electrosensory, and mechanosenosory lateral line pathways through the forebrain in channel catfish. J Comp Neural 312:311-331

Tong SL, Finger TE (1983) Central organization of the electrosensory lateral line systam in bullhead catfish, Ictalurus nebulosus. J Comp Neur 217:1-16

Treisman A (1977) Focused attention in perception and retrieval of multidimensionaGl stimuli. Percept Psychophys 22:1-11

47

Treisman AM, Gelade G (1980) A feature integration theory of attention. Cognit Psychol 12:97-136

Treisman A, Schmidt H (1982} Illusory conjuctions in the perception of objects. Cognit Psychol 14:107-141

Treisman A (1983} In: Physical and biological processing of images. Braddick OJ, Sleigh AC (eds) Springer, New York pp.316-325

VITA

The author, Lizabeth Scoma, was born on August 31, 1966,

in Chicago, Illinois. In the fall of 1984, she entered Loyola

University Chicago where she received a B.S. in Biology in May

of 1988. During this time, she did undergraduate research for

Dr. John Smarrelli and Dr. Jan Savitz. In August of 1991, she

entered Loyola University Chicago to pursue the degree of Master

of Science under the direction of Dr. John New. Liz was awarded

a fellowship for the years of 1991-1992 and 1992-1993. Her

research was also supported through a Sigma Xi Grant-in-Aid

awarded in 1991.

48

APPROVAL SHEET

The thesis submitted by Lizabeth Scoma has been read and approved by the following committee:

Dr. John G. New, Director Associate Professor, Biology Loyola University Chicago

Dr. John Janssen Professor, Biology Loyola University Chicago

Dr. Richard Fay Professor, Psychology Loyola University Chicago

The final copies have been examined by the director of the thesis and the signature which appears below verifies the fact that any necessary changes have been incorporated and that the thesis is now given final approval by the Committee with reference to content and form.

The thesis is therefore accepted in partial fulfillment of the requirement for the degree of Master of Science

,/7 / /

/ /.-, ~/\ ( ___ ~ ½-4~ Date i 1

Dirictor's sipnature

I