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Hormones & Sexual Behavior
Lecture 24
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Sexual Behavior of the Rat
Sex Hormones activation Testosterone male behavior Estrogens female behavior estradiol Progesterone ~
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Female behavior: rats Receptive - lordosis head down haunches up
Proceptive ear wiggling darting Hopping ~
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Male behavior: rats Mounts no testosterone no mounting
Intromits several times Ejaculates 4-5 times 5 min refractory period ~
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Organizational Effects of Hormones
SDN & SNB Critical periods Humans - prenatal Rats - perinatal easily manipulated ~
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Hormones: Sexual Behavior
Castrate XY males at birth Later... testosterone no male behavior estrogen? lordosis Brain not masculinized ~
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Hormones: Sexual Behavior
Ovariectomize female at birth give testosterone Later... estrogens no female behavior testosterone male behavior Brain masculinized ~
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Human Sexual Behavior No stereotypical M & F behaviors
Men are like rats T plays a activational role Castration decline in sexual behaviors variable rate Role of oxytocin? probably not knockout mice ~
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Hormones - Women Estrogen & Progesterone no activational effects
Ovariectomy has no effect Some fx on willingness to copulate increased during ovulation E & P are high ~
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Hormones - Women Testosterone levels
correlated with frequency of intercourse Oxytocin uterine and vaginal contractions sensations associated with orgasm ~
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Brain Mechanisms: Rats
Medial preoptic area lesion SDN no M sexual behavior NOT sexual motivation Bar press for female ~
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Brain Mechanisms: Rats
Ventromedial nucleus lesion- no female sexual behavior Masculinizes by preventing cell death Amygdala lesion increased sexual behavior Indiscriminate ~
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Homosexuality Sex hormones role? rats - yes Humans? NOT SURE
Learning experiences? or biologically determined? ~
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Biological Factors Levels of circulating sex hormones? No
Differences in brain structure? Perhaps - Where? ~
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Homosexuality Simon LeVay Brains of male AIDS victims
Anterior Hypothalamus Anterior commissure SDN (rats) Humans: 3rd interstitial nucleus ~
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3d interstitial nucleus
.15 .10 .05 Volume mm3 F H-M M Anterior commissure larger in females Similar relationship ~
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Homosexuality 2 Hypotheses
1. Androgen levels low in XY fetuses that gay high in XX fetuses lesbian 2. Genetic differences in fetal brains response to androgens Xq28 - tip of the X chromosome shared by large % of gay brothers ~
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