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Lecture 2

Lecture 2 - Sexual Behavior (Part 1)

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University of Toronto Mississauga
Emis Akbari

PSY398H5S – Motivational Systems Lecture 2 – January 10, 2013 Sexual Behavior Introduction  How is the brain wired for sex?  What are the types of brain activation that occur when presented with 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  If a sexual behavior is observed across all pop then its biological behavior (its not learnt/ natural behaviour)  Example: masturbation, homosexuality  these are not learnt Male Rate Genital Anatomy  Seminal vesicles carries sperm out, swells when activating sexual behavior Study of Male Sexual Behavior – History  Long known that castration eliminates mating in most species o Something in testes regulates sexual behaviour
 o Through 1800s – seminal vesicle swelling activates behaviour  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 Study of Male Sexual Behavior  All 3 GRPS castrated at wk 10; when testosterone was given the intact group remained the same as before  The blue group slowing/gradually restored sexual behavior and the red group that wasn’t given any testosterone after castration did not have any sexual activity PSY398H5S – Motivational Systems Lecture 2 – January 10, 2013 Male Sexual Behavior in Rodents:  Divided into two phase o 1) Appetitive phase
  Behaviors used to gain access to females  Fighting, advertising
  Communicates how good a mate the male is o 2) Consummatory phase – actual copulation •three components:  1) Mounting - assuming a copulatory position  2) Intromission – penis entering vagina
  3) Ejaculation – expulsion of semen - can’t see; determine behaviorally  Females control the rate of copulation (intromission) o She will fight if the males gets back immediately, she goes forward or tries to run away if the intromissions are not placed accordingly to the way she wants it to be o Male grooms after intromission  Can measure frequency or timing of these o Mount, intromission, ejaculation latency o Inter-mount interval (IMI) o Inter-intromission interval (III) o Post-ejaculatory interval (PEI)  Sooner the male ejaculates the better it is and shows hs robustness  III – Time between intromission; also controlled by females  5 mins refractory period 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
 o Then lose ejaculation, intromission, then mounts  Takes longer to mount after castration  1 to lose – ejaculation which needs optimum things followed by intromission then mounts Bigger Effects if T given Immediately (maintenance) Rather than Later (Restoration)  Maintenance – administering Testosterone immediately after castration  Restoration – administering R after a long time from castration  Takes more T and longer to restore sexual behavior after a period of time because number of receptors in brain and body loses sensitivity to T PSY398H5S – Motivational Systems Lecture 2 – January 10, 2013  Nervous system loses sensitivity to T if not given immediately Testosterone Also Maintains Internal Reproductive Organs  Seminal vesicles shrinks with no T and weight increases with increase in T dosage Rat Penile Erection  Rat penis comes out only during sex; other times stays inside  Flips at 15 sec and 22 sec  Spon
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