NEUR 3207 L5 - Sex and the Brain

Why is sex a motivated behaviour?

• Essential for species survival.

What is the SRY?

• Sex determining region of Y chromosome.

• Contains TDF (for testes)

• SRY is enough to masculinize on its own.

What is Turner Syndrom?

• Only getting one X chromosome.

• Most lead to miscarriage.

What is Klinefelter Syndrome?

• XXY

• Phenotypically male

• Basically feminized man

What is Jacobs Syndrome?

• XYY

• Individuals are male

• Tall, low libido, delayed speech onset.

How is sex determined in womb?

• Two key hormonal influences are Mullerian duct and Wolffian duct.

• Organism that contains SRY will produce testosterone.

• Genotypic males experience early test surge that masculinizes them.

• Test causes wolffian duct to develop into internal male reproductive system.

• Test also promotes production of Mullerian inhibiting factor.

• Intersex occurs when no clear path is chosen.

What are Sex Hormones?

• Males: Androgens (testosterone)

• Females: estrogens (Estradiol and Progesterone)

• extremely lipid soluble steroid hormones

How are Sex Hormones controlled?

• Pituitary controls release of gonadotropins.

  • Luteinizing Hormone

  • Follicle-Stimulating Hormone

• GnRH is released by Hypothalamus to stim pituitary

LH and FSH In Males

• LH = testes produce test

• FSH = mature sperm

• Testosterone also with sperm production

• Both needed for male fertility

LH and FSH in Females

• Both cause secretion of estrogen

• Ovaries not active without gonadotropins

• Menstrual cycle determined by changes in LH and FSH

How is sexual behaviour controlled?

• Through mechanoreceptors in genitalia (dorsal roots to dorsal horn)

• Through efferent pathways for cerebral stimuli. (Parasympathetic)

• Sympathetic division needed for an orgasm. Sympathetic neurons that are stimulated by sensory axons in genital tissues cause muscle contractions.

Other Sex hormones effects

Estradiol can enhance learning and memory, as well as LTP at parallel fibre/purkinje synapse.

What is the neurochemistry of mating strategies?

• Vasopressin and OXT are protein hormones and bind to extracellular receptors.

• expression patterns are plastic.

• Sharp increase in both during mating, causes them to bond.

• Antagonists of these prevent bonding.

• Monogamous species tend to have OXT receptors in brain regions associated with reward.