2 ROLES OF SEX HORMONES:

1)  organizational effects - permanent, influence brain and sex organ development
2)  activational effects - occur later in life, after development of sex organs

SEX ORGAN

gonads - testes or ovaries, first to develop

internal sex organs - precursors for male and female present in embryo

• only one set develops during 3^rd month, other withers away
• Mullerian system is precursor for female internal sex organs; ovaries not necessary for development
• Wolffian system is precursor for male internal sex organs
• which sex develops depends on whether or not hormones are secreted by the testes
• Mullerian inhibiting hormone - peptide hormone, has defeminizing effect
• androgens - steroid hormones, have masculinizing effect
• testosterone secreted by the testes, converted to dihydrotestosterone
• "nature’s impulse is to create a female"
• Turner’s syndrome - XO; without Y chromosome, testes don’t develop; no ovaries, as need 2 X chromosomes; develop into females

• congenital adrenal hyperplasia - adrenal glands secrete abnormal amounts of androgens beginning prenatally
• boys develop normally
• girls are born with enlarged clitoris and labia may be partly fused
• may affect female sexual orientation; 4 times more women with andrenogenital syndrome report having had sexual contact with another woman prior to age 20
• androgen insensitivity syndrome - caused by genetic mutation that prevents formation of functioning androgen receptors
• primitive gonads of genetic male become testes, secrete Mullerian inhibiting substance and androgens
• only Mullerian-inhibiting substance is effective
• person develops female external genitalia, but lacks female internal sex organs
• Olympic athlete issue

• during puberty, cells in hypothalamus secrete gonadotropin-releasing hormone, which stimulates the production and release of two gonadotropic hormones by the anterior pituitary gland:

• follicle-stimulating hormone
• luteinizing hormone
• these stimulate gonads to produce their hormones, which lead to secondary sex characteristics:

• estradiol , type of estrogen, produced by ovaries, which also produce small amount of testosterone
• testosterone produced by testes, which also produce small amount of estradiol

• aromatization - testosterone converted to estradiol by enzyme, aromatase; thus, testosterone can have an effect on estrogen receptors in cells
• oxytocin - produced by posterior pituitary gland, released during orgasm, contributing to muscular contractions; may play a role in sexual satiety and social bonding
• prolactin - secreted by anterior pituitary gland; promotes milk production in females and has inhibitory effect on male sexual behavior
• remember, "nature’s impulse is to create a female"
• male rats castrated at birth and given estradiol and progesterone in adulthood will exhibit female sexual behavior in presence of other male rat
• female rats with ovaries removed at birth and later given testosterone will attempt to mount other female rat

Coolidge effect - restorative effect of introducing a new female sex partner to a male that has apparently become "exhausted" by sexual activity

FEMALE LABORATORY ANIMAL SEXUAL BEHAVIOR

• dependent upon gonadal hormones present during estrus: estradiol followed by progesterone
• 3 effects:
• increases receptivity - ability and willingness to copulate
• increases proceptivity - eagerness to copulate
• increases attractiveness - physiological and behavioral changes that affect the male

• Lee-Boot effect - when female mice housed together, their estrous cycles slow and stop
• Whitten effect - if the group of females is then exposed to odor of male, they start cycling again in synchrony
• Vandenbergh effect - acceleration of onset of puberty in female rat when exposed to odor of male
• Bruce effect - failure of recent pregnancy of female rat when exposed to male who is not the father
• vomeronasal organ - group of sensory receptors which project to accessory olfactory bulb
• removal of accessory olfactory bulb negates all 4 above effects
• noradrenergic axons that serve the olfactory bulbs involved in learning component of Bruce effect

• women living together tend to have menstrual cycles in synchrony-sweat study
• women exposed to men have shorter menstrual cycles than those who are not
• substance found in male sweat increased social interactions in women, but not men
• people can distinguish their own T-shirt from others and identify male vs. female shirts

• exclusive homosexuality only in humans
• differences in degree of prenatal androgenization is likely to result in subtle brain structure differences
• suprachiasmic nucleus, sexually dimorphic nucleus, anterior commissure
• bed nucleus of the stria terminalis (in forebrain) - larger in males than females; male transsexuals' same size as females' - what about male homosexuals vs. heterosexuals? What's the significance?
• concordance rate for male homosexuality in twins: 52% for monozygotic, 22% for dizygotic
• concordance rate for female homosexuality in twins: 48% for monozygotic, 18% for dizygotic
• prenatal stress found to change adult behavior in male rats, less masculine

1) spinal nucleus of the bulbocavernosus - in ventral horn of lumbar region of spinal cord of rats

• contains motor neurons that innervate muscle attached to base of penis and involved in sexual activity
• this muscle is not present in female rats
• if female rats are injected with testosterone on 2^nd day after birth, they develop this nucleus
• if male rats treated prenatally by androgen-inhibiting drugs and then castrated after birth, they don’t develop this nucleus
• direct effect - androgens prevent deterioration of this nucleus during the first 10 days after birth
• indirect effect - androgens make male rat pup urine attractive to their mothers, causing them to lick the anogenital region; if mothers fail to do so (no sense of smell), then 11% fewer neurons in the SNB

• some neurons of the MPA appear to play a role in motivation, not copulatory behaviors
• sexually dimorphic nucleus - within MPA of rat
• 3-7 times larger in males than females
• size controlled by amount of prenatal androgen exposure
• volume directly related to the animal’s level of sexual activity
• lesions decrease masculine sexual behavior

• damage to this area disrupts many effects of pheromones
• one region with many androgen receptors is 85% larger in male vs. female rats
• destruction of medial amygdala disrupts sexual behavior of male rats
• in humans, temporal lobe seizures often associated with hyposexuality
• neurotransmitters

• oxytocin - transmitter substance in brain, involved in erection and ejaculation
• vasopressin - also serves as transmitter substance in brain, positively correlated with male sexual behavior
• dopamine - medial preoptic area

• ventromedial nucleus of the hypothalamus - most critical for performance of female sexual behavior

• lesions in female rats result in no lordosis, even with hormonal treatment
• electrical stimulation facilitates female sexual behavior
• estradiol followed by progesterone activates sexual behavior of female rats
• estradiol increases production of progesterone receptors
• periaqueductal gray matter - receives info from VMH, and sends axons to reticular formation of medulla and then to spinal cord

• lesions disrupt lordosis, electrical stimulation facilitates it
• lesions disconnecting PAG from VMH disrupt female sexual behavior
• neurotransmitters

• oxytocin - after estradiol and progesterone, injections into VMH facilitate lordosis
• norepinephrine - vaginal stimulation increases activity of noradrenergic neurons (remember Bruce effect)

• hormones - progesterone during pregnancy and prolactin during lactation promote nest building

• maternal behavior can be produced by injections of hormones experienced during pregnancy
• pup exposure - odor of pup elicits maternal behavior; pup cries stimulate nest building

• virgin female rats repulsed by odor of pups; if sense of smell destroyed, will become sensitized to pups and will exhibit maternal behavior
• medial preoptic area - most important brain structure for maternal behavior

• lesions disrupt nest building and pup care
• female sexual behavior unaffected by lesions

• male monogamous voles have larger MPA than promiscuous male voles
• increased vasopression production in male parenting voles