sexual behaviour

Question 1

SRY gene

Answer 1

on male Y chromosome – causes gonads to develop into testes

Question 2

androgens (early, by testes)

Answer 2

• increase testes growth (positive feedback during early development)
• wolffian ducts develop into seminal vesicles & vas deferens
  =penis & scrotum development

Question 3

Mullerian ducts

Answer 3

precursor to F structures: oviducts, uterus, upper vagina

Question 4

testes, ovaries, adrenal glands produce

Answer 4

Testes: produce androgens > estrogens
Ovaries: produce estrogens (most prominent: estradiol) > androgens
Adrenal glands: both

Question 5

effects exerted by steroid hormones

Answer 5

1. Bind to membrane receptors i.e. NTs  rapid
2. Enter cells & activate certain proteins in cytoplasm
3. Bind to receptors that bind to chromosomes  activate/inactivate certain genes

Question 6

Progesterone

Answer 6

prepares uterus for implantation of a fertilized ovum & promotes maintenance of pregnancy

Question 7

Organizing effects of sex hormones

Answer 7

long lasting structural changes

Short term exposure: no apparent effect
Long term: limited changes in behaviour

–set the stage for activating effects (i.e F hypothalamus – later hormones can activate menstruation cycle)

Question 8

Sensitive period for organizing effects of sex Hormones

Answer 8

• first trimester – sex H determine M/F genitals & alter brain development
• Puberty: F—breast size; M – facila hair, penis growth; changes in voice + some brain anatomy differences increase – persist despite conc of sex H declines

Question 9

Activating effects

Answer 9

more temporary, continuing only when a H is present / shortly beyond
- i.e. H level influence degree of sex drive
- pregnancy: temporary effects on emotional arousal, aggressive behaviour
- mood changes over menstruation cycle
T / E2 levels modify behavior temporarily – behaviour influences hormonal secretions i.e oxytocin released by sexual pleasure

Question 10

differentiation of external gonads depend mainly on

Answer 10

on testosterone

• high = M (certain enzymes convert T to dihydrotestosterone – more effective at promoting penis growth  high dihydroT = tubercle grows into penis + scrotum )
• low = F (low dihydroT = clitoris+ labia)

Question 11

masculinzation of female rats (T injection)

Answer 11

T begins masculinizing the external genitals during the last several days of pregnancy & first few days after birth – rate declines after)
• F rat: partly masculinized if injected with T (larger clitoris, mounts sexually receptive Fs & make copulatory thrusting movements; T inhibited arching of back & allow being mounted)

Question 12

inject male rats with E2 before birth

Answer 12

M rat: little effect if injected with Estrogens; but if lack androgen receptors (castration, genetic etc) – F anatomy & behavior

Question 13

estradiol & some genes highly activated in F strongly affect

Answer 13

uterus development (not external genitals)  
•	Genetic F that lacks E2 during early life: normal external anatomy (E2 not important for external anatomy), abnormal sexual behaviour / internal anatomy

Question 14

sex differences in brain

Answer 14

• Parts of F hypothalamus generate a cyclic pattern of H release (menstruation) – M: hypothalamus release Hs more steadily
• Sex Hs act in different ways for different areas

Question 15

alpha-fetoprotein

Answer 15

• Early development in rats: high levels of alpha-fetoprotein in blood  bonds to circulating E2 & prevents it from entering cells
  • Female brain is not exposed to E2 at this time
  • Male : T is free to enter the hypothalamus – aromatase converts much to E2 (E2 exerts masculinizing effects at this time )
  –> sex differences in brain (mPOA, VMH, AN, anterventral PVN)

Question 16

Medial preoptic area difference

Answer 16

• Both T and E2 increase production of prostaglandin E2

- increases microglia, dendritic spines, synapses in males

Question 17

Ventromedial hypothalamus

Answer 17

contributes to aggressive & sexual behaviour & inhibits feeding (decreases insulin)
- E2 activates an enzyme (PI3 kinase) – increases release of GLUT from presynaptic neurons = increased branching in postsyn neurons in males

Question 18

Arcuate nucleus & anteroventral periventricular nucleus

Answer 18

more dendritic spines & synapses in Females (important for F sex behaviour)
– low E2 levels in early life : - E2 increases GABA production – acts on astrocytes to decrease dendritic spines

Question 19

humans: T acts on?

Answer 19

T acts on hypothalamus directly (instead of by conversion to E2

Question 20

activating effects – Sex hormones bind to receptors – effect?

Answer 20

increase responses in parts of hypothalamus (VMH, medial preoptic area (MPOA), anterior hypothalamus)

• T primes MPOA & others to release dopamine (during sexual arousal: more dopamine = more likely to copulate)
• Level of T corr positively with men’s sexual arousal & drive to seek partners
• Both M & F: higher T levels = more likely than average to seek additional sex partners

Question 21

sexual desire in women

Answer 21

• Menopause (decrease in E2 levels)/ surgical removal of ovaries : decrease in sexual desire
• Restoring E2 levels: increases sexual desire
• Administer T to levels far above normal: increases sexual desire
   but sexual desire correlates strongly with E2 not T
• Periovulatory period (middle of menstruation cycle): E2 levels peak sharply

Question 22

pregnancy hormones: oxytocin & prolactin

Answer 22

• Delivering baby: increase secretion of oxytocin & prolactin
   promotes milk production & maternal behaviour
   prolactin inhibits leptin sensitivity (eats more)
• Pattern of hormone receptors changes
  • Late pregnancy: E2 sensitivity increases in MPOA, anterior hypothalamus, nucleus accumbens (areas important for maternal behaviour)

Question 23

after pregnancy: Vasopressin

Answer 23

Vasopressin (syn by hypothalamus, secreted by posterior pituitary)
 promotes social behaviour (i.e. male prairie voles: high vaso, long term bonds with female + help rear young)

Question 24

congenital adrenal hyperplasia

Answer 24

over development of adrenal glands from birth
intermediate appearance due to atypical hormone pattern
– genetically unable to produce cortisol : pit continues to secrete more ACTH  adrenal secretes more Hs inc T
genetic F exposed to more T – partly masculinized

Question 25

individuals with XY chromosome but lack androgen receptors (androgen insensitivity / testicular feminization )

Answer 25

have testes internally – no menstruation (but has other puberty changes) if assigned as girls -- many demand reassignment as males

Question 26

5a-reductase 2: enzyme that converts testosterone to dihydrotestosterone -- effects if absent?

Answer 26

enzyme that converts testosterone to dihydrotestosterone  more effective than T for masculinizing the external genitals Case: genetic male cannot produce the enzyme - appear female at birth - brain exposed to male T levels during early development - puberty: T levels increase sharply  growth of penis & scrotum

Question 27

Sexual orientation

Answer 27

- people discover their sexual orientation | • most men discover early; many women are slower

Question 28

homosexuality in twin studies

Answer 28

- Homosexuality has a stronger concordance (agreement) for monozygotic than dizygotic twins  mono twins are more likely to have the same sexual orientation

Question 29

Possible: sex orien depends on T levels during a sensitive period of brain development -- hypotheses?

Answer 29

- Mother’s immune system may exert prenatal effects • Probability of a homo orientation is slightly higher in men with more older biological brother • Hypothesis: mother’s immune system reacts against a protein in a son & attacks subsequent sons enough to alter development - Stress during pregnancy • Animals: prenatal stress alters sexual development  daughters were normal  sons had male anatomy but arched back to another M in adulthood

Question 30

sexual orientation & hormonal levels

Answer 30

NOT correlated: | similar hormonal levels in heteroM /F and homo M/F

Question 31

stress effects on T

Answer 31

- releases endorphins: antagonize effects of T on hypothalamus - elevates levels of certain adrenal Hs (rats: corticosterone; humans: cortisol) • decrease T release

Question 32

differences in brain anatomy b/w homo & heterosexual men

Answer 32

relative to hetero, homo men tend to have: - larger anterior commissure (in F too) - larger SCN - smaller third interstitial nucleus of anterior hypothalamus (INAH 3) (has • possible role in M sex behaviour )

Question 33

oxytocin

Answer 33

- stim contractions of uterus during childbirth, milk production, maternal behaviour, social approach, pair bonding - “love (enhancing) hormone” – both M & F release it during sexual activity - in men: enhanced attraction & fidelity to partner - helps with facial recognition & emotion expression recognition - increases conformity to “in-group” opinions but not always pro-social - increases attention to possible dangers &negative reactions when perceived as being threatened

Question 34

frontotemporal dementia

Answer 34

part of frontal & temporal lobes of cortex gradually degenerate • damage often includes ventromedial prefrontal cortex& orbitofrontal cortex  evaluation of reward & others’ emotional expressions – impaired  show little empathy / concern

Question 35

monogamy in male prairie voles

Answer 35

non-monogamous males: higher expression of AVP (hormone released by post pit) receptor in lateral septum -- increase expression: shifts to monogamy direction; monogamous males: higher expression in ventral palladum

Question 36

Japanese quail study

Answer 36

in castrated male quails, a T implant would gradually (genomic effects) restore time spent at window looking at a female (a appetitive sexual behaviour measure), injecting VOR (aromatase inhibitor) will cause the time at window to gradually decrease -- E2 (converted from T by aromatase) has genomic effects E2 also has non genomic effects: single injection of VOR vs VOR+E2: VOR decreases time at window after 30 min, but that decrease is not observed in group with E2 also injected