Chapter 5 Flashcards
AVPV
AVPV regulates ovulation and it is the source of a sexually dimorphic projection to the arcuate nucleus
Which sex is the AVPV larger in? females
AVPV are important in the secretion of? GnRH
Male reproductive behavior
Sexual motivation is strong in males
Ultimate cause of sexual behaviors in males vs. females
Gametes…..
Eggs are relatively large and limited in supply
Sperm are relatively small and not limited (almost disposable)
Parental investment…..
Female Mammals: Pregnancy & Lactation
Invest more in their offspring than males
Reproductive fitness…..
Females: “choosy”
They must choose the best possible males with whom to combine their genes.
Males: “ardent” Mate with as many females as possible
Sexual behaviors
behaviors that evolved to bring the two gamete types together
Sexual attraction
what is necessary to bring the two sexes together, i.e. appearance, smells
In many species, sexual attraction is closely synchronized with peak fertility and the physiological readiness to reproduce
Male sexual behavior
Divided into 2 phases:
Appetitive – courtship (singing, fighting the competition, strutting, etc.)
Consummatory – copulatory behavior
Males spend much more time and energy seeking copulation than actually copulating!!
Male sexual behavior in rodents
Sexual attraction is largely olfactory
Appetitive behavior:
Consummatory behavior:
Mounting
Intromission
Ejaculation
Post-ejaculation: Ultrasonic vocalizations Self-grooming Post-ejaculatory interval Satiation if PEI is greater than 90 minutes
Coolidge Effect
The propensity of an animal that has appeared sexually satiated with a present partner to resume sexual activity when provided with a novel partner
The President and Mrs. Coolidge were being shown [separately] around an experimental government farm. When Mrs. Coolidge came to the chicken yard, she noticed that a rooster was mating very frequently. She asked the attendant how often that happened and was told, “Dozens of times each day.” Mrs. Coolidge said, “Tell that to the President when he comes by.” Upon being told, the President asked, “Same hen every time?” The reply was, “Oh, no, Mr. President, a different hen every time.” President: “Tell that to Mrs. Coolidge.”
Typical measurements
Measures of sexual motivation:
Mount latency
Obstruction tests
Measures of sexual performance:
Inter-mount interval, inter-intromission interval
Number of mounts and intromissions prior to ejaculations
Ejaculation latency
Measures of mating potential:
Number ejaculations
Number of ejaculations prior to sexual satiety
Endocrine mechanisms in rodents
Androgens play an important role in males sexual behavior
After puberty…
Sexual motivation is expressed
Sexual performance and copulatory ability increase
Castration reduces sexual behaviors and sexual motivation
Order of loss:
days, longer latency to initiate mounting and intromissions, fewer intromissions prior to ejaculation
1-2 weeks no ejaculation
After 2-3 weeks, decline in the number of mounts and intromissions
Finally Male no longer mounts
Effects of experience
Sexual experience can have a large impact on the effects of castration in many animals.
Sexually inexperienced rats will show rapid decrease in sexual behavior after castration.
Many males with prior sexual experience will continue to mate for weeks after castration.
What changes?
The effects of castration on male rodent reproductive behavior can be reversed by testosterone treatment
Order of restoration:
Mounts, intromission, ejaculation
Sequential reappearance of behavior suggests differing hormonal sensitivities
Maintenance vs Restoration in rats
Maintenance: given T immediately after castration
Restoration : T treatment began after all sexual behaviors stopped
Receptor number
Muscular atrophy
Aromatization - rodents
T exerts its activational effects on mating behavior via aromatization to estradiol:
In castrated rats, T and estradiol induce appetitive and consummatory male sexual behavior
T plus aromatase inhibitor reduces males sexual behavior
Aromatase knockout mice and alpha-beta ER knockout mice have deficits in sexual behavior
5α-DHT (product of T that can’t be converted to E) does not prevent post-castration decline in reproductive behavior
DHT is important in the periphery to maintain penile reflexes and tactile sensitivity
Individual Differences in Male Mating Behavior
Hypothesis: animals with high sex drive had higher T levels that animals with low sex drive
Individual differences in sexual behavior are NOT determined by individual differences in androgen levels
Males identified as copulators or non-copulators
All had T concentrations of 2-3 ng/ml
Copulators were castrated and implanted with testosterone capsules
What accounts for these individual differences between copulators and non-copulators?
amyloid beta precursor protien
Sometimes its an unexpected biological player: APP
Amyloid B precursor protein (APP) levels are higher in persistent copulators…
APP transgenic mice are also resistant
Behavior Affects Hormones
A rise in testosterone is seen in males during mating and prior to mating in response to sensory cues associated with females
This response can be classically conditioned
Remember
It is NOT accurate to say that androgens cause sexual behavior!
Instead, androgens affect the likelihood of mating behaviors in the presence of the appropriate stimuli in the appropriate social context.
Brain mechanisms of rodent male sexual behavior
Olfactory system
Amygdala
MPOA
Olfactory system
Olfactory bulbectomy and destruction of the vomeronasal organ (VMO) reduces male attempts to mate
VMO detects pheromone signals
Amygdala
Major input:
Lesions of basolateral: amygdala reduces appetive
Lesions of Corticomedial: amygdala disrupts consummatory
Hormone receptors
Fos (IEG) and mating
Where does the amygdala project to induce sexual behavior?
MPOA
MPOA
Critical for integrating various internal and external stimuli prior to and during copulation including environmental, sensory, physiological, and psychological info
Evidence that MPOA regulates male sexual behavior
Lesions of the MPOA
Electrical stimulation of the MPOA
Autradiographic studies have shown that the MPOA contains androgen and estrogen receptors
Using in situ hybridization, aromatase mRNA has been detected in the MPOA
Implants of T into the MPOA of castrated males facilitates sexual behavior, but not if given with an aromatase inhibitor
Fos expression
Castration reduces neural responsiveness in the MPOA
Odour of estrous females produces electrical activity in the olfactory bulbs and the MPOA
Remove and replace:
Output pathways that regulate
male sexual behavior
- Nucleus paragigantocellularis (PGN) has serotonin fibers that normally inhibit the erection response
- mPOA signals counteract the inhibition
- Sexual side effects of SSRIs and output pathways:
Dopamine and male sexual behavior
POA lesions destroy connections to dopamine neurons in PAG and VTA
Pharmacology (agonists and antagonists):
extracellular DA in MPOA increases in response to cues from an estrous female
What brain region seems to be important in male orgasm?
VTA
Chemical castration significantly reduced androgen levels but is ________ in reducing sex drive
ineffective
Gonads are _____ to increase the probability of a sexual response in the presence of appropriate stimuli
unnecessary (i.e. hypogonadal males- in hypogonadal men they don’t have their testes making the appropriate amount of androgens but they can still respond with feelings of sexual desire when looking at a photo of a naked female)
In normal men, neither blocking estrogen receptors nor treating them with an aromatase inhibitor has any effect on sexual behaviors
unlike rodents
another difference between humans and rodents
________ have a strong activational effect in men
androgens
Things to know about Brown-Sequard:
injected himself with grinded up organs of dog and pig testes and decided he felt great after
What is the role of dopamine in male sexual behavior?
Dopamine appears to facilitate male sexual behavior by removing tonic inhibition of brain regions that mediate sensorimotor abilities
How does POA lesions impact dopamine release?
- Major effect of POA lesions: destroying connections to dopaminergic neurons in PAG and VTA
- Dopamine (DA) agonists can provide some restoration
- In intact rats, DA agonists facilitate mating behavior whereas antagonists suppress mating
- Microdialysis studies show that extracellular DA in MPOA increases in response to cues from an estrous female
When the MPOA is activated, what effect does it have on the PGN
its signals counteract the inhibition from the PGN motor output- mounting & thrusting
What are the sexual side effects associated with SSRIs?
difficulty achieving erection, ejaculation and or orgasm, due to enhanced effectiveness of PGN released serotonin in the spinal cord
