Chapter 5 (Part A):

Male Reproductive Behavior

(Note: Chapter 6 covers Female Reproductive Behavior)

In this chapter, we examine the hormonal aspects of males that leads to their particular reproductive behaviors. Topics of focus include the examination of

Territoriality in elephant seals. The fights erupt as males guard prime locations in terms of resources.

5.2 Male sexual behavior

Proximate basis of male sexual behaviors can be subdivided as follows:

Appetitive phase – the period when the male is actively seeking sexual encounters

Consumatory phase – the period when the male is actively engaged in copulation

Charles Edouard Brown-Sequard – endocrinologist who in the late 1800s proclaimed extracts of testes injected in the body had rejuvinating effects on sexual behavior..

5.4 Testosterone treatment maintains sexual behavior after castration

Sexual behavior can be maintained in animals following castration via replacement testosterone.

Note that there is a threshold dosage of testosterone that is needed.

5.5 The Columbia University obstruction test was used to measure sexual motivation

The “motivation” of the male rat is assessed in this device by the use of an electrified grid “B”.

Some common terms to describe aspects of male reproductive behavior:

Copulatory Lock - during copulation, the penis of some male mammals (some breeds of dogs and mice are examples increases in size in a region along the shaft that it cannot be removed from the female’s vagina for a measurable amount of time. Believed to increase likelihood of paternity in species with multiple mating partners in an ovulatory period.

Thursting – during copulation, the movement of the penis within the vagina. Designed to stimulate sensory nerve endings that can culminate in ejaculation in the male (and vagino-cervical orgasm in the female).

Intromissions - a behavior where the male will engage in very brief insertions of his penis into the female vagina (in rats this behavior is roughly 0.25 seconds each occurance). The role for this behavior in species that have variable sized litters is to induce great number of ova to be released by the female.

Ejaculation - The neuroendocrine pathway that results in the release of sperm by the male. It is a result of reaching the threshold level of stimulation of the penis resulting in the initiation of a neural circuit that triggers the release of semen from the stimulation level being reached by tissues on the penis which trigger contraction of the bulbospongiosus muscle (under the control of a spinal reflex at the level of the spinal nerves).

5.7 Male copulatory patterns in mammals

*

*

*

*

5.8 Sexual behavior in the dog

5.9 Sexual behavior can be restored by testosterone therapy

A study in guinea pigs.

Start of Exam #3 Materials

5.10 Maintenance versus restoration of sexual behavior by testosterone therapy

What do you think could explain the difference in ejaculation rates?

5.13 Regions that are essential to the control of sexual performance in male rats

POA – lesions abolish male sexual behavior and regulates neuroendocrine function in the brain.

5.14 The vomeronasal organ (VNO)

The vomeronasal organ (VNO) is absent in most primates, but essential in rodent reproductive behavior…. because it is used by the male in his investigatory behavior to assess if the female is ready in the right part of her ovulatory phase.

The male’s investigation will lead to both liquid and gaesous chemicals being taken in. Typically gaseous chemicals will enter the nasal cavity and stimulate the VMO, whereas liquid chemicals that are brought into the oral cavity by the tongue will pass through the nasopalatine duct to stimulate the VMO.

5.15 The amygdala

The amygdala is the brain region that is a pair of almond-shaped groups of nuclei located deep within the medial temporal lobes of the brain. It is the site for routing of many aspects of behavior including memory & emotions in humans.

In rats, the olfactory bulbs feed into the amygdala, and hence there is a shaping of the signals by this region.

In rat studies, two amydaloid regions are identified:

Basolateral – not involved in rodent sex behavior Corticomedial – involved in rodent sex behavior

5.16 Neural pathways in the rat olfactory system

The olfactory amygdala is therefore distinct from the vomeronasal amygdala.

5.17 Castration reduces neural responsiveness in the MPOA

5.18 The distribution of sex steroid receptors

5.19 Brain regions in rodents that show fos activation after sexual stimulation

fos – one of the IEGS (intermediate early genes responsible for developing sex behavior.

5.20 Schematic depiction of neural activity in circuits underlying male sexual behavior

Difficult to learn just by talking about it, please exam in detail this figure in the text.

5.21 Extracellular dopamine in the MPOA is elevated by cues from the female

Dopamine can be supplied as a medication that acts on the sympathetic nervous system.

5.22 Copulatory sequence of rats mating in groups

5.23 LH secretion can be modified by classical conditioning

5.24 Individual differences in sex drive

5.25 Clinically low testosterone concentrations can restore mating behavior

5.29 The frequency of male sexual behavior changes with age

5.30 Plasma testosterone concentrations in human males

5.31 Individual variation in weekly frequency of sexual outlet in men

5.32 Effects of testosterone treatment on hypogonadal men (Part 1)

5.32 Effects of testosterone treatment on hypogonadal men (Part 2)

5.41 Hormones mediate pseudocopulation in parthenogenetic whiptail lizards

Box 5.1 Battles of the “Sexes”

Box 5.2(A) Anatomy of the Penis (Part 1)

Box 5.2(B) Anatomy of the Penis (Part 2)

Box 5.3(A) Erectile Dysfunction, Nitric Oxide, and Viagra (Part 1)

Box 5.3(B) Erectile Dysfunction, Nitric Oxide, and Viagra (Part 2)