(E2, L6) Male Reproductive Behavior Flashcards
Why are hormones important for reproduction?
- gamete production
- producing behaviors that bring male and female together for mating -> especially in animal models
- the endocrine and nervous system interact in mediating male sexual behavior, which has 2 components:
1. sexual motivation
2. sexual ability/performance
Describe elephant seal sexual fitness
the males fight for land to highlight their strength and drive
the best males have the most offspring
What is sexual selection?
- one sex naturally prefers characteristics in the other sex
- females improve fitness by choosing best males (have more investment)
- males improve fitness by mating with as many females as possible
Describe the skateboarding experiment and results
- First set of tricks are ones that they know they can complete
- second set is tricks they are not as comfortable with
- photographed by male photographers both times in first round
- second round they were photographed by female (abandoned less tricks and had elevated T)
What are the historical origins of male sexual behavior research?
- late 1800’s people have known that castration eliminates the source of something responsible for sexual behavior and differentiation (Berthold)
What did Charles Brown-Sequard say in terms of male sexual behavior?
- Charles Brown-Sequard claimed that injections of endocrine extracts had “rejuvenating” effects on several physical parameters, including sexual vigor
Who was Calvin Stone?
First researcher to study male rat sexual behavior and describe the behavioral events
What is “drive theory”?
(1920s) shaped the field of psychology as people wanted to determine the underlying causes of behavior
- idea of intrinsic drive, or motivation, was conceptualized
Historical origins of male sexual behavior in relation to T
- pure crystalline hormone from testicular tissue was isolated and named testosterone: could not identify until there were better techniques
- soon thereafter researchers discovered that injections of testosterone after castration could maintain male sexual behavior
What are the proximate bases of male sexual behavior?
- Male sexual behavior: all the behaviors necessary and sufficient to deliver male gametes (sperm) to female gametes (eggs)
- the hormones that regulate gamete production and development are the same ones that drive sexual motivation
What are the components of male sex behavior in rodents?
- Precopulatory behaviors (happens before)
- anogenital sniffing
- approach/chase
- copulatory behaviors
- mount
- intromission
- ejaculation
- latencies
- mount latency, intromission latencies, inter-intromission interval (III), ejaculation latency
How do we measure motivation in rodent male sexual behaviors?
- time to first mount
- crossing an electrified grid (increased shock shows increased motivation)
- obstacle test
- bar pressing
increasing hardships to get to her can measure motivation based on how quickly they get through them
What are the differences between ability and motivation in male rats?
ability is if they are physically able to ejaculate/perform sexually
motivation is if they want to do it
How do we measure ability in rodent male sex behavior?
- copulatory efficiency (hit rate)
- number of ejaculations in a given period of time
What are the hormonal correlates of male mating behaviors in rodents?
- Testosterone and androstenedione (a weakly androgenic precursor to T) can both maintain mating behavior in castrated rodents
- estradiol is also effective at maintaining sex behavior
- DHT, however, is not
- T seems to act as a prohormone for sex behavior:
- provides estrogens to the CNS to promote mating behavior -> brain and spinal cord -> make info come in, response, etc.
- DHT to the periphery to maintain tactile sensory feedback -> penile reflexes and sensitivity
What are seasonal breeders?
undergo a natural “castration” each year as they enter their nonbreeding season
- ttestes regress and gonadal hormones decline to undetectable concentrations in autumn
- decline is driven by shortened day length (energy is driven towards immunization and metabolism)
What are the brain mechanisms of male rodent mating behavior?
- Preoptic area!!! (POA) - big important: integrates environmental cues, brings it all in, processes, and initiates endocrine release
- olfacory bulb, corpus callosum, anterior commissure, optic chasim, anterior hypothalamic area, ventromedial hypothalamus, dorsomedial hypothalamus
What does the POA do?
- POA lesions reduce or eliminate male sexual PERFORMANCE but not motivation
One action of the POA is through dopamine regulation - DA is released in the mPOA as soon as male mammal or bird meets a receptive female; further elevated during copulation
- stimulation of DA receptors in the mPOA contributes to both genital reflexes and sexual motivation
- one way in which estradiol promotes copulation in males is by stimulating DA release
- DA is inhibited by serotonin after ejaculation
What is the vomeronasal organ?
the VNO is used in sensory processing
What are the keys of male rat sexual behavior?
POA, VNO and Amygdala
What does the amygdala do in rat olfactory system?
- critical for integration of sensory info for sex behavior
- basolateral amygdala is especially important for sexual motivation
What is the Coolidge Effect?
introducing a new female can shorten refractory period or even get him back online after being sated (new female = new opportunity to reproduce)
Describe the strength of the sex drive in primates
- there is not as much info bc we don’t know how much environment influences humans
- young people in all cultures examined have been found to participate in premarital sexual activities
- Still, he govt spend over $1 billion between 1997-2008 on abstinence promotion programs in the US (but did not change much in young people behavior)
- strong sex drive, T plays part
What are the hormonal correlates of primate male sex behavior?
Puberty: when it all starts (gonads turn back on)
- boys do not report sexual interest until after the onset of puberty
- GnRH is released from the hypothalamus in a pulsatile fashion, causing LH to be released form the anterior pituitary and then T to be released form the testes
- HPG axis: Hypothalamus-> pituitary-> gonadal system
How does plasma T change in human males with age?
There is a big variation, but for the most part there is a REDUCTION with age
- begins at puberty
What are the effects of testosterone treatment in hypogonadal men? What does it mean for the role of T in sexual behavior?
Colvin’s syndrome: really low testosterone productions, fewer drives and interactions, ability still present
- Administer T to help, but effects fall off after treatment stops –> TT is likely important for sexual ability and motivation, but may not be required
What are the mechanisms of primate male sex behavior?
- there are regions that are more important for sexual behavior, but lesioning the mPOA in nonhuman primates does not stop sexual activity
- Chemosensory cues are not as important
- areas with high concentrations of receptors for adrogens, estrogens, and progestins are the hypothalamus, amygdala, and hippocampus
What have brain scans found in primate male sex behaviors?
a recent study using fMRI on young men watching either fishing documentaries or pornography showed:
- differential blood flow in a number of regions
- activation in the pars opercularis
PET scans of men while they were being brought to orgasm by their female partners showed activation of the ventral tegmental area (VTA_–> dopamine/reward
What is sexual dysfunction in men?
- reduced ability to engage in sexual activity
- as many as 30 million men have reported reductions in sexual ability
- while erectile dysfunction is more common in older men, young, fit men can also be affected
