1. Neuroscience: Exploring the Brain, 3e
Chapter 17: Sex and the Brain

2. Introduction Neural machinery underlying reproduction
Reproduction and eating
Regulated by subcortical structures
Conscious control by cerebral cortex
Influence of brain on sex hormones
Sexual and reproductive behaviors
Male and female brains

3. Sex and Gender Concept of Gender
Biological characteristics and qualities
Gender-specific behaviors
Self-assessment
Societal expectations
Genetics (XX: female, XY: male)
Hormones
Gender-identity
Perception of gender

4. Sex and Gender The Genetics of Sex (Cont’d) Discovery of SRY
Location of SRY on Y chromosome
Encodes testis-determining factor
Causes development of testes and testicular hormones
Makes fetus develop as male
Default pathway, female
Exposure to testosterone masculinizes the brain

5. Sex and Gender
Differentiation of fetus and development of gonads

6. The Hormonal Control of Sex
Hormones regulate physiological processes
Sex hormones: Steroids
Endocrine glands: Release sex hormones
Pituitary gland: Regulates endocrine glands
Structure affects function of hormone
Male hormone: testosterone
Female hormone: estradiol

7. The Hormonal Control of Sex
The Principle Male and Female Hormones
Men: High concentration of androgens
Women: High concentration of estrogens
Testosterone (androgen) + aromatase  estradiol (estrogen)
Protein hormones- do not pass through cell membranes, bind surface receptors
Steroid hormones- pass through cell membrane, bind cytoplasmic receptors
Receptor concentrations vary in different brain regions

8. The Hormonal Control of Sex
Concentration of estradiol receptors in sagittal section of rat brain

9. The Hormonal Control of Sex
The Principle Male and Female Hormones (Cont’d)
Males: Testes- release androgen
Testosterone – increase at puberty leads to development of secondary sex characteristics
Females: Ovaries- secrete estradiol (estrogen) and progesterone (progestin)
Blood concentrations of sex hormones vary
Males- levels fluctuate daily
Females- levels fluctuate, 28-day cycle

10. The Hormonal Control of Sex
Pituitary and Hypothalamus Control of Sex Hormones
Gonadotropins: LH and FSH
Males- LH produces testosterone; FSH aids sperm maturation
Females- LH, FSH cause estrogen secretion
Menstrual cycle- Follicular phase, Luteal phase
Estrous cycle in nonprimates

11. The Neural Basis of Sexual Behaviors
Reproductive Organs and Their Control
Cerebral cortex
Neural control of sexual response
Spinal cord
Mediates sexual response of genitals

12. The Neural Basis of Sexual Behaviors
Neural control of human sex organs

13. The Neural Basis of Sexual Behaviors
Mating Strategies: Ecology
Polygyny
Male mates with many females
Polyandry
Female mates with many males
Monogamy
One mate

14. The Neural Basis of Sexual Behaviors
The Neurochemistry of Reproductive Behavior
Prairie voles: Solid ‘family values’; monogamous
Meadow voles: Asocial and promiscuous
Affected by oxytocin and vasopressin

15. The Neural Basis of Sexual Behaviors
Role of oxytocin and vasopressin receptors in reproductive behavior
Prairie voles more oxytocin (female) and vasopressin male receptors
Meadow voles, fewer receptors
Experiments: Vasopressin antagonists prevent pair- bond formation; increasing vasopressin receptors in meadow voles promotes pair-bond formation.

16. Why and How Male and Female Brains Differ
Sexual Dimorphisms of the CNS
Onuf’s nucleus
Controls motor neuron pool
Sexually dimorphic nucleus (SDN)- in rats, much larger in males
INAH in humans analogous to rat SDN

17. Why and How Male and Female Brains Differ
Sexual Dimorphisms of Cognition
Evolutionary explanations for cognitive dimorphisms
Role of distinctive hormonal environment triggers differences in performance
Low estrogen levels
Better performance by women in spatial reasoning
Relation between cognition and hormones

18. Why and How Male and Female Brains Differ
Sex Hormones, The Brain, and Behavior: Steroids
Alter membrane excitability, sensitivity to neurotransmitters, neurotransmitter release
Modulate functions of various enzymes, channels and transmitter receptors
Diffuse across outer cell membrane
Bind to specific steroid receptors in cytoplasm and nucleus

19. Why and How Male and Female Brains Differ
Sex Hormones, The Brain, and Behavior (Cont’d)
Prostaglandins - downstream from sex hormones
Synthesized from arachadonic acid via COX enzyme
Involved in tissue damage, pain/fever
Fetal and neonatal rats exposed to COX inhibitors
Reduced copulatory behavior in male rats
Male-like copulatory behavior in female rats

20. Why and How Male and Female Brains Differ
Sex Hormones, the Brain, and Behavior (Cont'd)
Organizational effect of hormones
Tend to be irreversible
Activational effect of hormones
Tend to be temporary

21. Why and How Male and Female Brains Differ
Sex Hormones, The Brain, and Behavior (Cont’d)
Mismatches Between Genetic Sex and Hormone Action: Treatment with testosterone in mammals, reduced features of female reproductive behavior
Androgen-insensitive genetic males: Defective androgen gene, X chromosome
Congenital adrenal hyperplasia genetic females: Abnormally large adrenals overproduce androgens

22. Why and How Male and Female Brains Differ
Sex Hormones, The Brain, and Behavior (Cont’d)
Direct Genetic Effects on Sexual Differentiation of the Brain
Gynandromorphic zebra finch (naturally occurring)
Brain: Female left side, male right
Differential gene expression

23. Why and How Male and Female Brains Differ
The Activational Effects of Sex Hormones
Temporary modifications in brain organization, structural changes in neurites
Men: Rise in testosterone, anticipation of sex, fall in testosterone, decreased sexual interest
Women: Rise in estrogen, increased sexual interest

24. Why and How Male and Female Brains Differ
The Activational Effects of Sex Hormones
Brain Plasticity and Maternal Behavior

25. Why and How Male and Female Brains Differ
The Activational Effects of Sex Hormones (Cont’d)
Estrogens, Neurite Growth, and Disease
Toran-Allerand – estradiol treatment of hypothalamic tissue promotes neurite outgrowth
Songbirds: Testosterone mediates seasonal fluctuation in size of sexually dimorphic vocal-motor regions.

26. Why and How Male and Female Brains Differ
The Activational Effects of Sex Hormones
Gould, Woolley, and McEwen – estradiol treatment has dramatic effects on hippocampal neuronal dendrites

27. Why and How Male and Female Brains Differ
The Activational Effects of Sex Hormones
Estrogens, Neurite growth, and Disease (Cont’d)
Increase in hippocampal spine numbers coincides with female rat’s peak fertility
May play a role in changing reproductive needs
Estradiol
Protective effect on neurons (in culture)
Hypoxia, oxidative stress, toxins, etc.

28. Concluding Remarks Most human behaviors
Not distinctly masculine or feminine
Reproduction demands
Sex-specific behaviors
Sex hormones
Crucial role in sexual development and behavior

29. Sex and Gender The Genetics of Sex Genotype- Male: XY, Female: XX
X chromosome larger than Y
X contains 1500 and Y contains 50 genes
X-linked diseases
Occur more often in men than women
SRY: Gene on Y chromosome, encodes TDF (testis determing factor)

30. Why and How Male and Female Brains Differ
Sexual Orientation
INAH-3
Twice as large in men: Sexually dimorphic
INAH-3 in gay men: Similar to that in women
Significance: Results difficult to interpret

31. End of Presentation

32. The Neural Basis of Sexual Behaviors
Reproductive Organs and Their Control (Cont’d)
Neurotransmitters: Relax smooth muscle
Acetylcholine, vasoactive intestinal polypeptide (VIP), and nitric oxide (NO)
Male orgasm: Muscular contractions
Ejaculation
Female orgasm: Muscular contractions