Neuroendocrinology of Sex

Question 1

Neural circuitry of female reproductive behavior
Ventromedial hypothalamus (VMH):

Answer 1

steroid sensitive region hypothalamus crucial to lordosis sin response in female rats (steroid detector when steroid present to then send signal through midbrain medulla then spinal cord)

Projects to midbrain → medulla → spinal cord (gets signal from VMH and gets sensory info which ultimately regulates spinal circuits involved in lordosis)

When both estrogen and progesterone in circulation and activated by stimuli (mounting from male), lordosis occurs

Question 2

lesion to vmh causes

Answer 2

Lesion to VMH abolishes lordosis

Question 3

Male Reproductive Behavior

Medial preoptic area (mPOA):

Answer 3

mPOA sensitive to testosterone
Sends axons to ventral midbrain
Then to (1) basal ganglia to coordinate mounting (2) through brainstem nuclei to spinal cord to regulate copulation reflexes, control erection & ejaculation
Pheromones detected by receptors in vomeronasal organ in rodents sends signal to medial amygdala → mPOA (integrate signals then downstream signals to )

Question 4

Lesions to mPOA →

Answer 4

abolish male sex behavior (doesn’t interfere with motivation just the ability to partake in activity)

Question 5

sex differences in the poa of the hypothalamus

Answer 5

Male: Larger POA due to androgens (testosterone) during development
alter the development of POA resulting in permanently larger in males than females = organizational effect

Number of dendritic spine synapses in POA doubled in males vs. females

Size and number of neurons also greater in males

Question 6

testosterone during critical period in female mice
Organizational effects:

Activational effects:

Answer 6

external genitalia identical to males (even tho genetically female)

Activational effects:
In adulthood, give E+P (usually leads to ovulation/estrus) → no lordosis = defeminized
give T → male sexual behavior (mounting) = masculinized
only if T given during critical period!

Sex of the brain depends on whether or not testosterone present during critical period

Question 7

effects of testosterone during critical period in male mice

Answer 7

Castrating newborn male and give
No mounting and feminine morphological and behavioral characteristics in genetic males
Female phenotype is generally due to absence of testosterone
Genetic males and females are both capable of masculine and feminine physiology and behavior depending on hormone

Question 8

flow from hypothalamus to blood supply

Answer 8

Hypothalamus → Releasing hormones → anterior pituitary → tropic hormones → blood supply

Question 9

how does the hypothalamus release hormones (direct vs indirect)

Answer 9

Directly into blood via posterior pituitary

indirectly into blood via anterior pituitary

Question 10

what is function of sex hormones?

Answer 10

testosterone: inhibit fat storage, promote muscle growth, masculinizes sex organs (before birth)

estradiol: neuroprotective effect, secondary sex characteristics

Question 11

what is the sexually dimorphic behavior in rats

Answer 11

males: mounting, put it in 5-7 times, ejaculate, then refractory period

female: darting around, wiggling ears, take a receptive posture (lordosis- arched back and tail up)

Question 12

where does the female sex behavior come from?

Answer 12

ventromedial hypothalamus (VMH): steroid detector in hypothalamus that is crucial for lordosis response
- estrogen increases dendritic trees of neurons in VMH

VMH monitor for estrogen (and progesterone) → project to midbrain → then to medulla → finally to spinal cord causing motor movement

Question 13

what happens if VMH is lesioned

Answer 13

abolishes lordosis

Question 14

where does the male sex behavior come from?

Answer 14

medial preoptic area (mPOA): crucial to mounting behavior that is sensitive to testosterone

mPOA sends axons to –> ventral midbrain –> basal ganglia –> spinal cord

Question 15

what happens when there are lesions to mPOA

Answer 15

abolished male copulatory behavior (mounting not the desire to mount)

Question 16

what is the organizational activational hypothesis

Answer 16

sex hormones permanently organize the nervous system during early development reflected in typical male/female behaviors

in adulthood, the same hormones only periodically activate, inhibit, modulate those behaviors

Question 17

what is the difference between organizational vs activational effects in sexually dimorphic behaviors

Answer 17

organizational is permanent and activational is only for a period of time

Question 18

how does timing of hormone introduction affect masculinization of brain in female rats?

Answer 18

Female injected with testosterone during critical period (male perinatal period) develop large SDN-POA
During puberty, it does not lead to masculinization of brain mPOA is not getting larger

during fetal dev, testosterone administered into genetic females induces masculine behaviors (mounting) but not when induced to female adult rats

Question 19

how does timing of hormone introduction affect masculinization of brain in male rats?

Answer 19

castrating male (so they have no male hormones), it induces feminine morphological and behavioral characteristics (lordosis)

so, if no testosterone is present, female behaviors seem to be the default. nPOA and nervous system will organize itself in feminine fashion

if you castrate an adult, then treat w testosterone they’ll still mount