NB12-5 - Sex and the Brain

Question 1

List and describe the sex difference classifications we need to know.

Answer 1

Sexual Dimorphism: binary differences; the characteristic is one way in males and another in females

Sex Differences: characteristic is present in both males and females but is more prevalent in one sex

Sex Convergence: characteristic is the same in both sexes but the neural unerpinnings are different.

Question 2

List the CNS disorders that are male and female biased. What is the trend in these disorders?

Answer 2

Male Biased: ADHD, Autisum, Dyslexia, and Tourettes

Female Biased: Anorexia, Autoimmune Disorders, Depression/Anxiety Disorders

Male biased disorders tend to be developmental while female biased disorders are adult onset.

Question 3

List the major sources of sex differences?

Answer 3

Genetic - XX vs XY

Hormonal - females experience cyclical changes in hormone concentrations while males experience very limited variations. This causes many of the differences between men and women

Question 4

In which area of the brain are most sexual dimophisms seen? List those areas

Answer 4

Hypothalamus:

1. Sexually dimorphic nucleus (SDN, INAH1)
2. Interstitial nuclei of the anterior hypothalamus (INAH 2, 3, 4)
3. Suprachiasmatic nucleus (SCN)
4. Supraoptic nucleus (SON)
5. Paraventricular nucleus
6. Ventromedial nucleus

Question 5

What areas of the brain appear to be correlated with sexual orientation and gender identity? Explain that correlation.

Answer 5

• The INAH-3 and bed nucleus stria terminalis (BNST) are larger in males than in females normally. It is generally female sized in homosexual men and transgender (m to f) persons.

Question 6

When are the critical periods for sexual differentiatin and describe the general molecular mechanism behind this differentiation.

Answer 6

Critical periods are 12-20 weeks gestation and puberty

If the SRY gene (Y chromosome) is expressed then testes develop by week 8 and testosterone is produced. If not, ovaries develop. During weeks 12-20, many cells in the brain (particularly the hypothalamus) begin to produce aromatase which will convert testosterone to estradiol which will enter the nucleus and drastically change gene expression of those cells, causing them to permanently adhere to the male dimorphic form.

Question 7

Answer 7

A

Aromatase can also convert estrogen to estradiol, so estrogen also has masculinization effects in the brain

Question 8

What is and what causes androgen insensitivity syndrome (AIS)?

Answer 8

AIS is caused by a loss of function mutation to the gene that produces angrogen receptors. This means that cells during the critical period will be insensitive to testosterone and the child will phenotypically develop into a female even they are XY.

Question 9

What are DES daughters and what is important to learn about their existence?

Answer 9

In the past, to prevent miscarriages, expectant mothers were given a synthetic form of estrogen, diethylstilbestrol (DES). This lead to some masculization of the brain. There is a much higher incidence of lesbianism amongst the DES daughter population which is more evidence that homosexuality isn’t necessarily a choice.