1. Hormones & Sexual Behavior
Lecture 24

2. Sexual Behavior of the Rat
Sex Hormones  activation
Testosterone  male behavior
Estrogens  female behavior
estradiol
Progesterone ~

3. Female behavior: rats Receptive - lordosis head down haunches up
Proceptive
ear wiggling
darting
Hopping ~

4. Male behavior: rats Mounts no testosterone  no mounting
Intromits several times
Ejaculates
4-5 times
5 min refractory period ~

5. Organizational Effects of Hormones
SDN & SNB
Critical periods
Humans - prenatal
Rats - perinatal
easily manipulated ~

6. Hormones: Sexual Behavior
Castrate XY males at birth
Later...
testosterone  no male behavior
estrogen?
lordosis
Brain not masculinized ~

7. Hormones: Sexual Behavior
Ovariectomize female at birth
give testosterone
Later...
estrogens  no female behavior
testosterone  male behavior
Brain masculinized ~

8. 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 ~

9. Hormones - Women Estrogen & Progesterone no activational effects
Ovariectomy has no effect
Some fx on willingness to copulate
increased during ovulation
E & P are high ~

10. Hormones - Women Testosterone levels
correlated with frequency of intercourse
Oxytocin
uterine and vaginal contractions
sensations associated with orgasm ~

11. Brain Mechanisms: Rats
Medial preoptic area
lesion SDN  no M sexual behavior
NOT sexual motivation
Bar press for female ~

12. Brain Mechanisms: Rats
Ventromedial nucleus
lesion- no female sexual behavior
Masculinizes by preventing cell death
Amygdala
lesion  increased sexual behavior
Indiscriminate ~

13. Homosexuality Sex hormones role? rats - yes Humans? NOT SURE
Learning experiences?
or biologically determined? ~

14. Biological Factors Levels of circulating sex hormones? No
Differences in brain structure?
Perhaps - Where? ~

15. Homosexuality Simon LeVay Brains of male AIDS victims
Anterior Hypothalamus
Anterior commissure
SDN (rats)
Humans: 3rd interstitial nucleus ~

16. 3d interstitial nucleus
.15
.10
.05
Volume
mm3
F H-M M
Anterior commissure larger in females
Similar relationship ~

17. 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 ~