Reproductive behaviour

During early stage of prenatal development…

both male and female have a set of mullerian and wolffian ducts as well as undifferentiated gonads

Wolffian ducts

• precursors to other male reproductive organs

• develop into vas deferens and seminal vesicles

Mullerian ducts

precursors to female’s oviducts, uterus, and upper vagina

Undifferentiated gonads

• release testosterone to differentiate into testes

• if no release of testosterone = ovaries (mullerian develops and wolffian degrades)

SRY gene

• gene on Y chromosome

• causes the undifferentiated gonads to develop into testes

• testes produce androgens (increases testes growth, and produces mullerian inhibiting hormone (MIH) that causes mullerian ducts to degenerate)

• females do not have this gene

Androgens

• male, steroid hormones

• testosterone most known

• females can also have them but later in life and at lower concentrations

Estrogens

• female, steroid hormone

• Estradiol most common

• also progesterone

• males also have but at low concentrations

Estradiol

• fertility cycle

• wiring the brain

• initiating sexual desire

Progesterone

• establishes proper conditions of pregnancy for it to continue

• prepares the uterus for the implantation of a fertilized ovum

• promotes thickening of uterus

• if amount is high enough = decrease sexual desire

steroid hormone

• highly lipid soluble = can cross any lipid membrane and BBB

• binds to membrane receptors like neurotransmitters

• enter cells and activate proteins/receptors in the cytoplasm and nucleus???

• bind to chromosomes where they activate or inactivate certain genes

Hormone vs. neurotransmitter

• Hormone: released by glands into the bloodstream to affect distant target

• neurotransmitter: released locally and affect target at most a synapse apart

Genes on X and Y chromosome also produce sex differences

• at least 3 genes on Y chromosome are active in specific brain areas

• at least one gene on the X chromosome is active only in the female brain

organizing effects of sex hormones

• occur at sensitive periods of development

• produce long-term changes

• determine whether the brain and body will develop male or female characteristic

activating effects of sex hormones

• occur at any time of life

• temporarily activate a particular response

• e.g. sex drive (spike of testosterone or estrogen), pregnancy, menstruation

what does sexual differentiation depend on?

mostly on level of testosterone during sensitive period of the first trimester

AIS (androgen insensitivity syndrome)

• biologically male because have X and Y

• physically and behaviourally female

• do not have a functional testosterone receptor and wolffian duct does not develop

What part of the male anatomy do estradiol and other estrogens modify?

internal structures like the prostate gland (important for reproduction)

sex diff in hypothalamus

• female hypothalamus generate a cyclic pattern of steady hormone release

• male hypothalamus release hormones more steadily

Alpha-fetoprotein

• found in the blood during early sensitive periods

• binds to estradiol, prevents it from entering developing cells (can’e be absorbed in the female fetus)

• females not exposed to estradiol at this time

• alpha-fetoprotein does not bind to testosterone and freely enters hypothalamic cells

• inside the hypothalmus, it gets converted to estradiol and exerts masculinizing effects

Medial preoptic area male and female differences

• more dendritic spines. microglia and synapses in males

• male sexual behaviour depends on this

• if lesioned, males would show female sexual behaviour

Oxytocin

• given to induce labour bc it makes you have contractions

• orgasm - released when men ejaculate

• stimulates mammary glands in releasing milk

• attachment - right after birth and first feeding session w baby

Male sexual arousal

• testosterone increases touch sensitivity in the penis (+ve feedback loop)

• sex hormones bind to receptors in the hypothalamus including ventromedial nucleus, MPOA, and anterior hypothalamus

• testosterone triggers the release of dopamine in the MPOA (axons in VTA releases the dopamine into the MPOA) - also happens when men get into fights and just grr

dopamine receptors

• Excitatory: D1 and D5

• Inhibitory: D2, D3, and D4

• stimulation of D1 and D5 is associated with sexual arousal

• facilitates erection of penis and sexually receptive posture in females

• higher concentrations of dopamine stimulate D2 receptors and lead to orgasm (even tho D2 is inhibitory it works in the same way as alcohol as an inhibitory drug but it makes u more social)

• serotonin decreases sexual activity by blocking dopamine release (reason why some ppl don’t wanna take SSRIs)

Male sexual interest

• testosterone levels and sexual interest have a positive correlation

• castration of the hormone decreases sexual interest and activity

• low testosterone is not typical reason for impotence - usually caused by impaired blood circulation

menstrual cycle

• hypothalamus and pituitary interact with ovaries to produce menstrual cycle

• in other animals: estrous cycle (not monthly; longer or shorter)

What happens after the end of a menstrual cycle?

• anterior pituitary releases follicle-stimulating hormone (FSH)

• promotes growth of follicle in the ovary (kind of like watering a plant)

• follicle nurtures the ovum and produces estrogen (estradiol)

What happens towards the middle of the menstrual cycle? (follicular phase)

• The follicle builds up receptors to FSH

• result: follicle produces increasing amounts of estradiol and grow larger and larger

What happens at the ovulation stage?

• increased estradiol causes the anterior pituitary to increase release of FSH and luteinizing hormone (LH)

• FSH and LH cause the follicle to release an ovum

• sexual desire increases as estradiol peaks

Luteal phase

• remnants of the follicle (corpus luteum) release progesterone

• corpus luteum continues to release estradiol, but the level decreases and progesterone release levels increase instead

• progesterone inhibits the release of LH so u can’t ovulate again in the same month and prepares uterus for fertilized ovum

Pregnancy

• estradiol and progesterone levels increase gradually throughout pregnancy, instead of decreasing (period)

• high levels of estradiol and progesterone produce heightened activity in the 5-HT3 receptor (only ionotropic serotonergic receptor)

• increased stimulation of 5-HT3 = nausea

• if POA is lesioned or hormone receptors in the POA are damaged = females do not take care of their pups

• ???

Birth control

• has estrogen and progesterone

• prevents anterior pituitary from releasing FSH and LH, so ovum would never be released

• thickens the mucus of the cervix (makes it harder for sperm to reach egg)

Periovulatory period

• middle of menstrual cycle = days when fertility is highest

• sexual interest peaks

• increased interest in flirting

• hair and skin become brighter

Prolactin

• necessary for milk production

• inhibits leptin so mother eats more than usual

• responsible for some maternal behaviour

• mother’s brain changes its sensitivity to hormones

Vasopressin

• hormone synthesized by the hypothalamus

• secreted by the posterior pituitary gland

• associated with social behaviour

• facilitates olfactory recognition - distinguish between certain smells

• increased during maternal behaviour

• higher vasopressin = tighter bond (monogamous)

fathers with _____ testosterone and _____ prolactin levels spent most time playing with and caring for child

low, high but very little compared to females

females are better than males at?

short-term memory tasks and verbal fluency tasks

males are better than females at?

spatial relation and mental rotation tasks

homosexuality

• feminine-type behaviours during childhood correlate strongly with homosexuality in males

• masculine-type behaviours in girls is a poor predictor of sexual orientation

• genetics is a contributor (if one identical twin is gay the other is most likely gay too) - lower chance for fraternal

MPOA cause

testosterone and estradiol increase production of prostaglandin E2 - develop prostate glands in MPOA in males

ventromedial nucleus male and female diff

• more widely branched dendrites in males = male aggression (establishing dominance), sex, feeding

• if lesioned, decreased aggression

ventromedial nucleus cause

estradiol activates PI3 kinase = increases glutamate release

arcuate nucleus and anteroventral periventricular nucleus male and female diff

• important for lordosis

• decreases dendritic spines and synapses in males, enhanced in females

arcuate nucleus and anteroventral periventricular nucleus male and female cause

estradiol increases GABA production - acts on astrocytes to decrease dendriting branching in MALES