Lecture 12: olfaction: the insect antennal lobe References: H C Mulvad, thesis (mulvad/Thesis), Ch...

Lecture 12: olfaction: the insect antennal lobe

References:H C Mulvad, thesis (http://www.nordita.dk/~mulvad/Thesis), Ch 2G Laurent, Trends Neurosci 19 489-496 (1996)M Bazhenov et al, Neuron 30 553-567 and 569-581 (2001)Dayan & Abbott, Sect 7.5

http://www.nordita.dk/~mulvad/Thesis

Olfaction (smell)

Olfaction (smell)The oldest sense (even bacteria do it)


Highly conserved in evolution (mammals and insects similar)



Basic anatomy:



Basic anatomy:Insects: receptor cells -> antennal lobe -> mushroom bodies



Basic anatomy:Insects: receptor cells -> antennal lobe -> mushroom bodiesMammals: receptor cells -> olfactory bulb -> olfactory cortex




~100000 receptor cells, several hundred types (distinguished by receptor proteins)




~100000 receptor cells, several hundred types (distinguished by receptor proteins)any cell responsive to a range of odorants:




~100000 receptor cells, several hundred types (distinguished by receptor proteins)any cell responsive to a range of odorants: => an odor produces a characteristic pattern of activity

across the receptor cell population






Receptor physiology: Receptor proteins (1 kind/cell): metabotropic, G-protein coupled,

lead to opening of Na channels






Receptor physiology: Receptor proteins (1 kind/cell): metabotropic, G-protein coupled,

lead to opening of Na channels, similar to phototransductionin retina

Antennal lobe~1000-10000 neurons

in locust: 1130: 830 excitatory, 300 inhibitoryin honeybee: 800 excitatory, 4000 inhibitory



Organized into glomeruli (bunches of synapes) (~1000 in locust, 160 in bee)







Connections between ALneurons: dendrodentritic

Excitatory cells (PN)PN = projection neuron: axon takes its spikes out of the antennal

lobe, to the mushroom bodies (+ other higher areas)


lobe, to the mushroom bodies (+ other higher areas) transmitter: ACh





Dendrites have postsynaptic terminalsin 1 or more glomeruli

(10-20 in locust)

Inhibitory cells (LN)LN = local neuron: projects only within the antennal lobe


no Na spikes, only Ca “spikelets”


no Na spikes, only Ca “spikelets”transmitter: GABA





Dendrites with postsynaptic terminals in several or all glomeruli

Antennal lobe responses:temporally modulated oscillatory activity patterns


~20 hz oscillations:


(No oscillations in input from receptor cells)

~20 hz oscillations:

Oscillations and transient synchronization

membrane potentials


membrane potentials

Local field potentialIn mushroom body:Measures averageAL activity

(cell in mushroom body)


membrane potentials

Local field potentialIn mushroom body:Measures averageAL activity

PN firing transientlysynchronized toLFP

(cell in mushroom body)

Model (Bazhenov et al)

• 90 PNs, 30 LNs


•90 PNs, 30 LNs

•Single-compartment, conductance-based neurons


•90 PNs, 30 LNs


•(post)synaptic kinetics


•90 PNs, 30 LNs



•Fast excitation, fast and slow inhibition


•90 PNs, 30 LNs




•50% connectivity, random


•90 PNs, 30 LNs




•50% connectivity, random

•Stimuli: 1-s current pulse inputs to randomly-chosen 33% of neurons

Bazhenov network

Excitatory neurons

stimsynAKNaLL IIIIIVVgdtdV

C )(

Excitatory neurons


C )(

Active currents:

Excitatory neurons


C )(

)(3NaNaNa VVhmgI

Active currents:Na

Excitatory neurons


C )(

)(3NaNaNa VVhmgI )(4 KKK VVngI

Active currents:Na K

Excitatory neurons


C )(

)(3NaNaNa VVhmgI )(4 KKK VVngI )(4

KAAAA VVhmgI

Active currents:Na K A-current

Excitatory neurons


C )(


KAAAA VVhmgI

inhslowGABAnAChsyn IIIIA


Synaptic input

Excitatory neurons


C )(


KAAAA VVhmgI


)]([ ssfast VVOgI


Synaptic input

Fast (ionotropic) synaptic currents (nACh and GABAA):

( [O] is open fraction)

Excitatory neurons


C )(


KAAAA VVhmgI


)]([ ssfast VVOgI ][]])[[1(][

OTOdtOd


Synaptic input



[T] is transmitter concentration:

Excitatory neurons


C )(


KAAAA VVhmgI


)]([ ssfast VVOgI ][]])[[1(][

OTOdtOd

]/))((exp[11

][

)()(][

0

0max0

VtVT

tttttAT


Synaptic input



[T] is transmitter concentration: exc

inh

Slow inhibition

Kinetics like GABAB )(][][

4

4

Kslowinhslow VVKG

GgI

Slow inhibition


4

4

Kslowinhslow VVKG

GgI

][][][

43 GrRrdtGd G-protein concentration:

Slow inhibition


4

4

Kslowinhslow VVKG

GgI

][][][

43 GrRrdtGd

][]])[[1(][

21 RrTRrdtRd

G-protein concentration:

Activated receptor concentration

Slow inhibition


4

4

Kslowinhslow VVKG

GgI

][][][

43 GrRrdtGd

][]])[[1(][

21 RrTRrdtRd

G-protein concentration:

Activated receptor concentration

Fast and slowComponents:

Inhibitory neurons

stimsynCaKKCaLL IIIIIVVgdtdV

C )()(

Inhibitory neurons


C )()(

Active currents:

Inhibitory neurons


C )()(

)(2CaCaCaCaCa VVhmgI

Active currents:Ca

Inhibitory neurons


C )()(

)(2CaCaCaCaCa VVhmgI

Active currents:Ca

( -> Ca spikes)

Inhibitory neurons


C )()(

)(2CaCaCaCaCa VVhmgI )(4 KKK VVngI

Active currents:Ca K

( -> Ca spikes)

Inhibitory neurons


C )()(

)(2CaCaCaCaCa VVhmgI )(4 KKK VVngI )()()()( KCaKCaKCaK VVngI

Active currents:Ca K Ca-dependent K current

( -> Ca spikes)

Inhibitory neurons


C )()(



( -> spike rate adaptation)( -> Ca spikes)

Inhibitory neurons


C )()(


2][100

,2][][ )()(

CaCa

Can CaK

nCaK


Dynamics of nK(Ca):


Inhibitory neurons


C )()(


)][]([][ CaCa

IdtCad

Ca

2][100

,2][][ )()(

CaCa

Can CaK

nCaK


Dynamics of nK(Ca):

Ca dynamics:


2 neurons (1 PN, 1LN)

6 PNs + 2 LNs

6 PNs + 2 LNs(fast) inhibition between LNs



LNs take turns:

Full network (90+30)

Responses of 4 PNs to 1 stimulus

Responses of 4 PNs to 1 stimulus

Reliable (trial-to-trial reproducible) firing timing when there is largeInhibitory input

Another stimulus:Input to same set of PNs but different LNs



Same overall firing rate pattern, but different temporal fine structure

3rd stimulus:Input to 90%-different set of neurons:



Different firing pattern across neurons (but same network-average rate)

Blocking LN-LN inhibitionLNs now spike ~ regularly

Blocking LN-LN inhibitionLNs now spike ~ regularly

Less difference between responses to stimuli 1 and 2

Reducing IK(Ca) (reducing LN spike-rate adaptation)

Reducing IK(Ca) (reducing LN spike-rate adaptation)

Reducing IK(Ca)

Less precise timing, weaker temporal modulation, reduced discriminability

(reducing LN spike-rate adaptation)

Role of slow LN-PN inhibition


Slow rate modulationsabolished


Slow rate modulationsabolished

reduced discriminability

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Lecture 12: olfaction: the insect antennal lobe References: H C Mulvad, thesis (mulvad/Thesis), Ch...

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