Week 9 - Reproductive Behaviour

Question 1

What is the sequence of events in which one develops into their biological sex?

Answer 1

(1) Genetic sex development (XX, XY)
(2) Gonads develop (testes/ovaries)
(3) sex organs develop (organizing effects occur, either Wolffian or Mullerian system develops)
(4) Maturation

Question 2

What are the terms for the embryonic precursors of the male and female internal sex organs?

Answer 2

The Mullerian System for female, the Wolffian system for male.

Question 3

Which gene on the Y chromosomes causes gonads to become testes?

Answer 3

The SRY (sex determining region of Y) gene.

Question 4

What determines whether the Mullerian or the Wolffian system develops?

Answer 4

One’s sex hormones, which are produced by the gonads.

Question 5

Differentiate between organizing effects and activating effects.

Answer 5

Organizing effects: when exposure to various sex hormones during prenatal development, as well as during puberty, develops the sex organs and brain of an individual. They are long lasting effects that only occur during a specific sensitive period.

Activating Effects: short term effects of an individual when exposed to sex hormones

Question 6

Androgens and estrogens are which type of hormone? Give an example of both an androgen and an estrogen.

Answer 6

Steroid hormones.

Ex. of androgen : testosterone

Ex. of estrogen : estradiol

Question 7

What hormones produced by the testes get produced to cause male sex organs to develop and what do they do? What about the hormones produced by ovaries to cause female sex organs?

Answer 7

(1) AMH (Anti-Mullerian Hormone)
(2) MIH (Mullerian Inhibiting Hormone)
(3) androgens (Testosterone and Metabolite Dihydrotestosterone)

AMH and MIH do not allow the Mullerian system to develop, while androgens ensure that the Wolffian system develops.

If one has ovaries, they will produce estrogen. The default is for the Mullerian system to develop because the ovaries are not producing AMH, MIH, or androgens.

Question 8

This syndrome is characterized by having the SRY gene translocated on the X chromosome during meiosis, leading to the individual’s genetic sex being “female”, despite having all male characteristics.

Answer 8

XX Male Syndrome.

Question 9

Having the genetic sex male (XY), this syndrome is characterized by having an extra X chromosome, being taller than average, more abdominal fat, low muscle tone, infertile, and hypogonadal.

Answer 9

XXY, Klinefelter Syndrome.

Question 10

Having the genetic sex male (XY), this syndrome is characterized by the dysfunction of androgen receptors during male sex development, while the AMH and MIH hormones are intact. What would this result in?

Answer 10

This syndrome is Androgen Sensitivity Syndrome (AIS). If the androgen receptors are not intact, then the male sex organs will not fully or properly develop, but the Mullerian system will be inhibited/prevented from developing due to the intact AMH and MIH receptors.

Question 11

Having the genetic sex male (XY), this syndrome is characterized by having an autosomal recessive gene causing the failure to produce AMH or no receptors for this hormone, resulting in them developing both testes and ovaries (both female and male sex organs).

Answer 11

Persistent Mullerian Duct Syndrome.

Question 12

Having the genetic sex female (XX), this syndrome is characterized by the dysfunction of a female’s gonads (non-working ovaries), as no estrogen is being produced by the ovaries. The female has symptoms of poor breast development, short stature, broad chest, and webbed neck, and is the result of a defective sperm.

Answer 12

Turner’s Syndrome.

Question 13

Having the genetic sex female (XX), this syndrome is characterized by high production of androgens during development, causing one to develop their appropriate Mullerian system from their ovaries, but have external organs that are “intersex” or “ambiguous” due to the high androgen exposure. They also demonstrate more masculine behaviour.

Answer 13

Congenital Adrenal Hyperplasia (CAH)

Question 14

Describe behavioral masculinization and behavioral defeminization.

Answer 14

Behavioral Masculinization: promotion of male behaviour through activating male neural circuits.

Behavioral Defeminization: prevention of (or failure to produce) female behavior through suppressing female neural circuits.

Question 15

Describe what happens what ovariectomized rats (rats that are not producing estrogen) that are exposed to the following 5 conditions:

1. testosterone right after birth and also later on in life
2. testosterone only later on in life
3. testosterone right after birth, and then progesterone and estradiol later on in life
4. estradiol and progesterone only later on in life

What does this tell us about testosterone on activating effects?

Answer 15

1. Masculinizing effects occur (behavioral masculinization)
2. no activating effects
3. Defeminizing effects (neither male nor female sexual behavior develops)
4. female sexual behavior occurs, feminizing effects

This tells us that there is a sensitive period for which testosterone can have masculinizing and defeminizing effects, which is injecting it right after birth.

Question 16

Which two areas of the brain are important for sexual behavior for both male and female rats? What are some characteristics of these brain areas that cause sexual behavior?

Answer 16

Males –> medial preoptic area of the anterior hypothalamus (mPOA of AH)

• releases DA
• more testosterone receptors

Females –> ventromedial nucleus of the hypothalamus
- abundance of estradiol and progesterone receptors in this area

Question 17

Describe the neural pathway for the lordosis response in females and the neural pathway for the mounting behavior in males.

Answer 17

Males mounting behavior:
nPGi –> inhibits sexual behavior
PAG –> activates nPGi
mPOA –> inhibitory effect on both PAG and nPGi

Therefore, to cause sexual behavior in males, the mPOA would have to inhibit 2 areas: the PAG so that it doesn’t activate the nPGi, and the nPGi directly so it doesn’t inhibit sexual behavior.

Females lordosis response:
VMH –> excitatory effect on PAG
PAG –> excitatory effect on nPGi
nPGi –> excitatory effect on sexual behavior

Therefore, to cause sexual behavior in females, the VMH has to be activates to activate the PAG, to then activate the nPGi.

Question 18

What are the hormones involved in the menstrual cycle and what are all of their roles?

Answer 18

GrNH : new menstrual cycle begins when hypothalamus releases this hormone into blood vessels that surround that pituitary gland to let the pituitary gland know to secrete another hormone called FSH

FSH : travels through the bloodstream until it reaches the ovaries, where it will stimulate the growth and development of an ovarian follicle in the ovaries

LH: During maturation of follicle, hypothalamus increases production of GnRH and FSH, leading the pituitary gland to secrete LH. Around the middle of the cycle, LH eventually reaches a peak inside the ovaries, triggering the egg to be released (ovulation) and guided through fallopian tube which takes 5-6 days until it reaches uterus

Question 19

What is the ovarian follicle made up? What happens when the follicle ruptures during the menstrual cycle to release an egg?

Answer 19

Ovarian follicle consists of an egg inside it, fluid, and surrounding cells that secrete estrogen hormones.

When the follicle ruptures, it turns into the corpus luteum, and the surrounding cells that secreted estrogen hormones inside it release progesterone to ensure the endometrium is suitable for a fertilized egg in case of pregnancy. The secretion of progesterone is maintained for several days, but if a fertilized egg does not reach the uterus in that time, the corpus luteum withers (known as the luteal phase) leading to falling levels of progesterone and estrogen. These falling levels trigger shedding of the uterine lining.

Question 20

What would happen if GnRH were to be inhibited in males? Explain why this would occur.

Answer 20

Sexual behaviour would be inhibited. This is because when GnRH is produced by the hypothalamus, which activates the pituitary gland to secrete hormones that activate the gonads (testes) to produce testosterone. So by inhibiting GnRH, we are inhibiting testosterone, thereby inhibiting sexual behavior.

Question 21

During what period are women more likely to engage in sexual activity?

Answer 21

Their periovulatory phase.

Question 22

Which brain area is both involved in maternal behavior in female rats and sexual behavior in male humans?

Answer 22

The mPOA of the AH.

Question 23

What is the role of vasopressin and oxytocin for bonding and parental behavior?

Answer 23

Oxytocin is important for female bonding/attachment, vasopressin is important for male bonding/attachment.

Question 24

What is one important takeaway from the David Reimer clip about Janet’s twins?

Answer 24

You cannot change one’s gender on nurture alone, biological factors matter.

Question 25

What is the term for the pathway that orchestrates the release of sex hormones (testosterone/estradiol) from the testes/ovaries for humans?

Describe the pathway and what differs in this process between males and females.

Answer 25

The Hypothalamic-Pituitary-Gonadal (HPG) Axis.

Pathway begins with hypothalamus releasing GnRH, which triggers the pituitary to release FSH and LH, which triggers the testes or ovaries to produce testosterone or estradiol.

For males, activation of the HPG axis is relatively continuous/steady, while it is cyclical for females.