PS271 Lecture Notes - Lecture 19: Laboratory Rat, Estrous Cycle, Ovulation

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1 Feb 2013

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Effects of Sex Hormones on Behaviour
sex hormones, secreted by testes and ovaries have effects on cells all over the body that promote reproduction
these hormones cause production of sperm, build up lining of uterus, trigger ovulation, and stimulate production of milk
also effect nerve cells in brain, affecting behaviour
sex hormones DON’T CAUSE behaviours
sex hormones affect people’s motivation to act in reproductive way
Effects of Androgens
androgens such as testosterone important for male sexual development
testosterone causes male sex organs and brain to develop
prenatal effects of sex hormones aka
organizational effects
because they alter organization of sex organs and brain
unless testosterone is present, males can’t have erection and engage in sexual intercourse
such effects aka
activational effects
because hormone activates sex organs and brain that are developed
Davidson, Camargo and Smith (1979)performed double-blind study of activational effects of testosterone on men with insufficient production of
men were given monthly injections of placebo or one of two dosages of long lasting form of testosterone
this study showed an increase in erections and intercourse in a month and larger dosage produced more of an effect than smaller one
this proves that testosterone affects male sexual performance
testosterone affects sex drive, but doesnt determine object of sexual desire
eg: homo man injected with testosterone wont suddenly be interested in women, but will have increased effects in his interest with men
Salmon and Giest (1943) found that testosterone had effect on sexual desire and sensitivity of clitoris to touch
Persky and colleges (1978) studied sexual activity of 11 married couples from ages 21- 31
Participants kept records daily of their sexual feelings and behaviour, as their testosterone blood levels were measured twice a week
couples more likely to engage in intercourse when womans testosterone level was at peak
women found intercourse to be more gratifying during these times
Effects of Progesterone and Estrogen
in most species of mammals, estradiol and progesterone hormones have strong effects on female sexual behaviour
levels of these hormones fluctuate during menstrual cycle of primates and estrous cycle of other female mammals
diff between the two cycles is that lining of primate uterus, not that of other mammals builds up during first part of the cycle and sloughs off at end
eg: female laboratory rat will receive advances of male only when levels of estradiol and progesterone in blood are high
this happens around time of ovulation when copulation is likely to make her become pregnant
during this time, female will stand while male approaches, if he attempts to mount her, she will arch her back and move her tail to the side giving him
access to her genitalia
female rat whose ovaries are removed, normally is nonreceptive- even hostile to advances of eager male
women and other female primates are potentially willing to engage in sexual behaviour at any time during their reproductive cycles
in higher primates(including ourselves) ability to mate isn’t controlled by estradiol or progesterone
changes in these hormones have little or no effect
this made monogamous relationships possible, since male can look forward to his mate receptivity at any time during menstrual cycle, making less likely
to look for another partner
Sexual Orientation
homosexual behaviour is seen in male and female animals of many species
other animals, if not exclusively heterosexual seem to be bisexual
in humans, the number of people that describe themselves as homosexual exceeds those that are bisexual
during most of 20th century, homosexuality was viewed as a disorder caused by home environment
eg: as result of having been raised by overprotective mother and indifferent father
in recent studies, this theory has been refuted, since there is no evidence that homosexuality is a disorder
it is viewed as differently by most people because majority of the population is made up of heterosexuals
Bell and Weinberg and Hammersmith (1981) studied homosexuals and came up with following conclusions:
1. Sexual orientation was determined before adolescence and any homo/hetero activity, first predictor of homosexuality was seen three years prior
to first genital homosexual activity
2. Gender nonconformality is related to homosexuality. It’s characterized by dislike in masculine behaviours in boys and dislike in feminie
behaviours in girls
Results of the study show that this may be due to biological factors
However there is no difference in testosterone levels in blood btw homo and hetero men
Research evidence shows that prenatal exposure to high androgen levels is associated with increased incidence of homosexuality in both men and
Heredity also plays a role in sexual orientation
Concordant- both twins homo, discordant- only one twin is homo
Bailey and Pillard- studied male twins and found that there’s higher rate of concordant twins than discordant twins
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