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Lecture 3

Lecture 3 - Male Sexual Behavior

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Emis Akbari

PSY395H5 – Hormones and Behavior Lecture 3 - September 27, 2013 Male Sexual Behavior Asexual vs. Sexual Reproduction  Sexual reproduction ALWAYS includes meiosis and fertilization, requiring the generation of sperm and egg. Asexual reproduction does not.  Sperm and egg production under hormonal control (along with temperature and circadian rhythm).  In animals with brains, the best way to assure reproduction when animals are most likely to produce offspring is to link sexual behavior with pleasure. “Human Style”  It is largely experientially determined and culturally sanctioned.  Hormones are often necessary but almost never sufficient... but of course, not always!  There are as many sexual preferences as there are people. Slide 9  How is the brain wired for sex?  What are the types of brain activation that occur when presented with a sexually arousing stimuli?  What happens when sexual pleasure is experienced and how does that pleasure activate neurochemical systems in the brain?  How does this feed forward to make us not only WANT sex again, but to bond with our partners, to feel intimacy with our partners?  How do we come to associate certain features of our partners with the very pleasure that we experienced?  One major result of sex research is that we have sex because it feels good, not because we want to make babies Male Sexual Behavior  Sex: Associated with a division of gamete types  Sexual Behaviour: Behaviour that has evolved to bring the two gamete types together  Male Sexual Behaviour: All behaviours necessary & sufficient to deliver male gametes (sperm) to female gamete (ovum)  Sex Drive: the motivational force that propels individuals to seek sexual union – very powerful underlining humans and animals Definitions • Sexual Arousal Increased genital blood flow; heart rate; sweating, pupil dilation • Sexual Desire Wanting or craving sexual activity; behaviors aimed at acquiring sex partners or sexual reward • Sexual Reward Pleasure; orgasm; intimacy; bonding; control; other rewards • Sexual Inhibition Satiety; primary aversion; secondary avoidance Male Sexual Behavior Male sexual behaviour can be divided: Divided into two phases 1) appetitive phase •behaviors used to gain access to females •fighting, advertising •courtship 2) consummatory phase – actual copulation •three components: PSY395H5 – Hormones and Behavior Lecture 3 - September 27, 2013 1) mounting - assuming a copulatory position – failing to insert his penis 2) intromission – penis entering vagina during a mount 3) ejaculation – expulsion of semen via urethra -can’t see; determine behaviorally Rat Male Sexual Behavior  PEI: time between ejaculation and next copulatory bout Absolute vs. Refractory Male Sexual Behavior in Rodents:  Can measure frequency or timing of these  Mount, intromission, ejaculation latency  Inter-mount interval (IMI) •Inter-intromission interval (III)  Post-ejaculatory interval (PEI) Model of Instinctive Behaviors Phase I: intrinsic motivation towards a specific stimulus in the absence of that stimulus – Restlessness Phase II: Stimulus is present – consummatory behaviours towards the stimulus occurs Phase III: Stimulus acquires aversive status - Restlessness Phase IV: Restful state - they are no longer attracted or repelled by stimulus Study of Male Sexual Behavior – History  Long known that castration eliminates mating in most species •something in testes regulates sexual behaviour o through 1800s – seminal vesicle swelling activates behaviour o Steinach (1894) – remove seminal vesicles of rats  had no effect on mating  must be something else in testes  Brown-Sequard (1899) – inject homogenized dog/pig testes o reported restorative powers - energy, libido, stamina  Stone (1922) – first real examination of sex in male rats o rats first copulate at 50 days old o still copulate for 14 days after castration Testosterone  Testosterone is necessary for the initiation of all consummatory components of male sexual behavior (Hull et al., 1997).  Castration results in abolishment of mounts, intromissions and ejaculations, while its replacement reverses these effects in both recent and long-term castrates (Beach & Holz- Tucker, 1949)  Testosterone levels increase following exposure to an unattainable receptive female and following copulation (Kamel, et al., 1975).  Manipulations that reduce circulating testosterone levels such as chronic ethanol exposure (Oliva, et al., 2006) or neonatal treatment with an anti-estrogen (Gerardin, et al., 2006), result in impairments of male sexual behavior and reproductive function.  These effects can be attributed in differences in androgen threshold (Ward, et al., 1999) Hormones and Male Sexual Behavior  Castrate males – reduced sexual motivation (investigate or work for it) - reduced performance (copulation fades) o first, longer time to mount PSY395H5 – Hormones and Behavior Lecture 3 - September 27, 2013 o then lose ejaculation, intromission, then mounts Rat Penile Erection  spontaneous reflexes disappear after castration  androgens alone do not elicit erection and other reflexes •must be a stimulation, too  skin sensitivity highest with DHT injection  •DHT? – non-aromatizable androgen Steroid Hormone Synthesis Hormones and Sexual Reinstatement Sexual Behavior in Humans PSY395H5 – Hormones and Behavior Lecture 3 - September 27, 2013 Main Point: - Testes secrete testosterone - T aromatize to estrogens and act on brain - T reduced to DHT to act on periphery Brain Areas Regulating Male Sexual Behavior Medial Preoptic Area (mPOA)  critical area for integrating environmental, physiological, and psychological information prior to and during successful copulation  lesions eliminate copulation  sexual motivation intact  does not affect non-contact erection  electrical stimulation – accelerates ejaculation *when measuring natural electrical activity o female odors increase activity o castration decreases activity in response to odors -TP replacement restores  Site of hormone action o TP implants in castrated males increases copulation •E implants also wor o TP implant + aromatase inhibitor – no copulation o TP must be converted to E  however, AR antagonist in mPOA also inhibits •must need both ER and AR activity  Note: aromatase also detected in these same sites What Do mPOA Lesions do that Disrupts Copulation?  may primarily affect dopamine neurotransmission  sensory cues from females increases DA release  in mPOA and other sites that receive DA input Olfactory Input •Critical for successful copulation in many rodent species •two types of olfactory inputs 1) volatile - olfactory bulbs (MOB) 2) non-volatile – vomeronasal organ (AOB)  olfactory bulbectomy impairs sexual motivation and performance PSY395H5 – Hormones and Behavior Lecture 3 - September 27, 2013  effects may be due to decrease in overall arousal  shock or tail pinch temporarily activates copulation  VNO lesion alone impairs or eliminates performance may be more important than main olfactory input.  bulbectomy eliminates both, but VNO alone effective  However, these effects are ONLY seen in naïve animals Once a male gains sexual experience, olfactory disruption does very little  Importance of experience on brain plasticity Amygdala •emotional regulation •Receives projections from the accessory and main olfactory bulbs •receives sensory inputs, integrates for social behaviours •basolateral lesions – reduce motivation •corticomedial lesions – increase ejaculation latency (rats) •eliminate copulation (hamsters) Barry Everitt’s Double-Dissociation  Castration abolishes copulation and reduces 2 nd-order sexual responding. nd  Lesions of the mPOA abolish copulation but not 2 order responding, whereas lesions of the medial amygdala do the opposite  Much of the neural circuitry involved in mediating male sexual behaviour Has been mapped out by tracking immediate-early genes (IEGs  In neurons, these IEGs are activated early during the signal transduction process  The presence of their protein products can be detected by Immunocytochemical (ICC)
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