sexual behaviour Flashcards
SRY gene
on male Y chromosome – causes gonads to develop into testes
androgens (early, by testes)
- increase testes growth (positive feedback during early development)
- wolffian ducts develop into seminal vesicles & vas deferens
=penis & scrotum development
Mullerian ducts
precursor to F structures: oviducts, uterus, upper vagina
testes, ovaries, adrenal glands produce
Testes: produce androgens > estrogens
Ovaries: produce estrogens (most prominent: estradiol) > androgens
Adrenal glands: both
effects exerted by steroid hormones
- Bind to membrane receptors i.e. NTs rapid
- Enter cells & activate certain proteins in cytoplasm
- Bind to receptors that bind to chromosomes activate/inactivate certain genes
Progesterone
prepares uterus for implantation of a fertilized ovum & promotes maintenance of pregnancy
Organizing effects of sex hormones
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)
Sensitive period for organizing effects of sex Hormones
- 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
Activating effects
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
differentiation of external gonads depend mainly on
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)
masculinzation of female rats (T injection)
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)
inject male rats with E2 before birth
M rat: little effect if injected with Estrogens; but if lack androgen receptors (castration, genetic etc) – F anatomy & behavior
estradiol & some genes highly activated in F strongly affect
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
sex differences in brain
- 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
alpha-fetoprotein
- 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)
Medial preoptic area difference
- Both T and E2 increase production of prostaglandin E2
- increases microglia, dendritic spines, synapses in males
Ventromedial hypothalamus
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
Arcuate nucleus & anteroventral periventricular nucleus
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
humans: T acts on?
T acts on hypothalamus directly (instead of by conversion to E2
activating effects – Sex hormones bind to receptors – effect?
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
sexual desire in women
- 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
pregnancy hormones: oxytocin & prolactin
- 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)
after pregnancy: Vasopressin
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)
congenital adrenal hyperplasia
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
individuals with XY chromosome but lack androgen receptors (androgen insensitivity / testicular feminization )
have testes internally – no menstruation (but has other puberty changes)
if assigned as girls – many demand reassignment as males
5a-reductase 2: enzyme that converts testosterone to dihydrotestosterone – effects if absent?
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
Sexual orientation
- people discover their sexual orientation
• most men discover early; many women are slower
homosexuality in twin studies
- Homosexuality has a stronger concordance (agreement) for monozygotic than dizygotic twins
mono twins are more likely to have the same sexual orientation
Possible: sex orien depends on T levels during a sensitive period of brain development – hypotheses?
- 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
sexual orientation & hormonal levels
NOT correlated:
similar hormonal levels in heteroM /F and homo M/F
stress effects on T
- releases endorphins: antagonize effects of T on hypothalamus
- elevates levels of certain adrenal Hs (rats: corticosterone; humans: cortisol)
• decrease T release
differences in brain anatomy b/w homo & heterosexual men
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 )
oxytocin
- 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
frontotemporal dementia
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
monogamy in male prairie voles
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
Japanese quail study
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
