Hormones and Behavior EXAM 3

What are androgens?

• Male sex hormones

• Main androgen = testosterone (T)

• Help regulate sexual behavior, libido, and sperm production

How does sexual behavior relate to androgen levels in primates?

• Sexual behavior often increases with higher androgen levels

• Relationship seen across seasons

• Relationship also seen across lifespan

What happens to sexual behavior after castration in nonhuman primates?

• Sexual behavior declines

• Ejaculation affected more than mounting

• Individual responses vary a lot

What effect does testosterone replacement have after castration?

• Restores sexual behavior

• Can increase mounting and ejaculation

Which sexual behavior is most affected by castration?

• Ejaculation is most strongly affected

• Mounting behavior usually less affected

Why is sensory information from the penis important?

• Helps with intromission and ejaculation

• Nerve damage impairs sexual performance

• Sensory feedback is important during mating

What are penile spines?

• Structures over tactile receptors

• Help provide sensory feedback

• Depend on androgens

What happens in hypogonadal men (very low T levels) without testosterone replacement?

• Can still have erections from erotic stimuli

• Fewer spontaneous erections

• Reduced sexual thoughts/libido

What happens with testosterone replacement in hypogonadal men?

• Increased erections (dose dependent)

• Increased sexual fantasies

• Increased libido and sexual behavior

What are the effects of castration in male sex offenders?

• Most show rapid stop in sexual behavior

• Some show gradual decline

• Small percentage show no change

How does erectile dysfunction change with age?

• Erectile dysfunction increases with age

• Androgen levels decrease with age

• Lower androgens linked to impotence

• Negative correlation with androgen levels

What physiologically causes an erection?

• Increased blood flow into penis

• Reduced blood flow out of corpora cavernosa

What role does nitric oxide (NO) play in erection?

• increases cGMP levels

• Relaxes smooth muscle

• Increases blood flow into penis

• Produces erection

How does Viagra work?

• Blocks PDE5 enzyme

• Prevents cGMP breakdown

• Enhances erections during stimulation

What hormone stimulates nitric oxide production?

• DHT (dihydrotestosterone)

• Helps support erections

• Decreases after age 40

Are testes and high androgen levels essential for sexual performance in men?

• No, not completely essential

• Androgens still help libido and erections

• Men can still perform sexually with lower T

What are caveats about androgen effects?

• Adrenal androgens may contribute

• Effects may be indirect

• Mood and energy can influence behavior

What brain region is critical for male copulatory behavior?

• MPOA (medial preoptic area)

• Important for mating behavior

What happens after MPOA lesions in primates?

• Copulatory behavior disrupted

• Erections still possible

• Masturbation/self-ejaculation still possible

What effect does olfactory bulb removal have in primates?

• Little to no effect on sexual behavior

What effect do amygdala lesions have in primates?

• No consistent effect on sexual behavior

How does neural control differ between rodents and primates?

• Olfactory pathways more important in rodents

• Primates rely less on smell for sexual behavior

• MPOA important in both groups

What is an associated reproductive pattern?

• Mating occurs during high testosterone

• Testes active during mating

• Common in most species

What is a dissociated reproductive pattern?

• Mating and testicular function happen at different times

• Seen in some reptiles

ex : Red-sided garter snake

When does mating occur in red-sided garter snakes?

• During spring emergence

• Uses stored sperm

When do red-sided garter snakes show high testosterone and spermatogenesis?

• Later in the year

• Separate from mating season

Are androgens necessary for mating behavior in red-sided garter snakes?

• No

• Removing testes/adrenals/pituitary has little effect

What activates sexual behavior in red-sided garter snakes?

Increased ambient temperature

What systems are coordinated during the menstrual cycle?

• Ovaries

• Uterus

• Brain

• Other body systems

What hormonal axis regulates the menstrual cycle?

Hypothalamic-pituitary-ovarian axis

When does the menstrual cycle usually occur?

• Puberty to menopause

• Stops during pregnancy/lactation

What can inhibit the menstrual cycle?

• Severe stress

• Pathological conditions

What are the phases of the ovarian cycle?

• Follicular phase

• Ovulation

• Luteal phase

What are the phases of the uterine cycle?

• Menstruation

• Proliferative phase

• Secretory phase

Which ovarian phase is most variable in length?

• Follicular phase

• ~10–20 days

Which ovarian phase is most consistent?

• Luteal phase

• ~14–16 days

What is the follicular phase?

• First phase of ovarian cycle

• Dominated by developing follicles

What is a follicle?

• Egg cell (oocyte) + surrounding cells

• Protects and nourishes egg

• Produces hormones

What do thecal cells do?

• Respond to LH

• Produce androgens

• Similar to Leydig cells in males

What do granulosa cells do?

• Respond to FSH

• Convert androgens → estrogens

• Secrete inhibin

• Similar to Sertoli cells in males

Which hormone controls thecal cells?

LH

Which hormone controls granulosa cells?

FSH

How is estrogen produced in follicles?

• Thecal cells make androgens

• Granulosa cells convert androgens → estrogens

What stimulates follicular growth?

• GnRH stimulates LH and FSH

• LH/FSH promote follicle development

What hormones are secreted by developing follicles?

• Estrogen

• Inhibin

What do estrogen and inhibin do during follicular phase?

• Negative feedback on GnRH

• Decrease LH and FSH release

What is a dominant follicle?

• Single follicle that fully matures

• Suppresses other follicles

• Releases lots of estrogen/inhibin

• FSH levels drop very low

Why can the dominant follicle survive low FSH?

• More FSH receptors

• Better blood supply

• More sensitive to hormones

What happens to subordinate follicles?

• Undergo atresia

• Degenerate/die

What hormonal changes trigger menstruation?

• Low estrogen

• Low progesterone

What causes endometrial growth during proliferative phase?

Rising estrogen levels

What is ovulation?

Release of egg from follicle

What triggers ovulation?

• LH surge

• Caused by sustained high estrogen

How does estrogen switch to positive feedback?

• Sustained high estrogen stimulates hypothalamus/pituitary

• Increases hormone release instead of suppressing it

What happens during the LH surge?

• LH rises sharply

• Dominant follicle ruptures

Where does the oocyte go after ovulation?

Into the oviduct/fallopian tube

Which hormones increase before ovulation?

• GnRH

• LH

• FSH

What major hormonal event happens right before ovulation?

• Sustained high estrogen

• Positive feedback

• LH surge occurs

Lesioning of which structure(s) would block sexual behavior in adult male rats?

Olfactory bulbs (main + accessory)

Stria terminalis

Amygdala

Medial preoptic area

Lesioning of which structure(s) would block sexual behavior in adult male monkeys?

Medial preoptic area

what is true of the main olfactory system but not the accessory

olfactory system in rodents?

It mainly detects volatile chemicals

In human men, sexual behavior (including libido) appears to be…

Increased by androgens

A group of male rats is castrated in adulthood, treated with testosterone and an aromatase inhibitor, and tested with an estrous (attractive) female. Which of the following would they be most likely to exhibit?

Erections but little or no mounting

Another group of male rats is castrated in adulthood, treated with estrogen, and tested with an estrous female. Which of the following would they be most likely to exhibit?

Mounting but few or no erections

Protein products of immediate early genes are measured in the brain to

determine…

Amount of genomic activation in neurons

Which of the following is true of both thecal and granulosa cells?

They secrete steroid hormones.

The late follicular phase is characterized by…

High levels of estrogen (E) and low levels of progesterone (P)

Which of the following is the correct sequence of events in the human menstrual cycle?

E positive feedback, LH surge, ovulation