topic 18 sex and the brain lange biology 463 - neurobiology
TRANSCRIPT
Topic 18
Sex and the Brain
Lange
Biology 463 - Neurobiology
Introduction
Influence of brain on sex hormones…. and the influence of the sex hormones back on the brain.
• Sexual and reproductive behaviors
• Male and female brains
Sex and Gender
• Concepts of Gender are very much inter-realated, but will involve specifics of:
– Biological characteristics of gender associated with architecture:• Morphology• Organization of the brain
– Gender features associated with psychology and perception:
• Self-assessment• Societal expectations• Gender-identity• Perception of gender
– Gender features associated with biochemistry:• Genetics• Hormones
Some chromosomal systems of sex determination
44 +XY
44 +XX
22 +X
22 +Y
22 +XY
44 +XX
44 +XY
22 +X
22 +XX
Parents
OvaSperm
Zygotes(offspring)
(a) The X-Y system
(b) The X-0 system
(c) The Z-W system
76 +ZW
76 +ZZ
32(Diploid)
16(Haploid)
(d) The haplo-diploid system
Female = default sex
Male = default sex
Male = default sex
Male = default sex
Sex and Gender
The Genetics of Sexual Determination
– Y Chromosome encodes testis-determining factor (Tdf)
– Tdf is produced from the SRY gene on Y chromosome
– Guides development of testes and production of testicular hormones
– Promotes fetal development as male
Sex and GenderDifferentiation of fetus and development of gonads
The Hormonal Control of SexHormones regulate physiological processes
– Sex hormones: Steroidal hormones
– Endocrine glands: Gonads release sex hormones
– Pituitary gland: Regulates endocrine glands (LH & FSH)
– Small structural differences affects function of hormone
– Primary “male” hormones: androgens (testosterones)
– Primary “female” hormones: estradiols and progestins
The Hormonal Control of SexThe Hormonal Control of Sex
The Principle Male and Female Hormones in adulthood
– Men: High concentration of androgens
– Women: High concentration of estrogens & progestins
Aromatization Process for Steroid Hormones:
Testosterone (androgen) + aromatase estradiol (estrogen)
The Hormonal Control of SexConcentration of estradiol receptors in sagittal section of rat brain
The Hormonal Control of Sex
– Males: Testes- release androgens
• Androgens (testosterones) – increase at puberty leads to development of secondary sex characteristics
– Females: Ovaries- secrete estradiol (estrogens) and progesterone (progestins)
For both sexes, blood concentrations of sex hormones vary:
• Males- levels fluctuate mildly during a 24 hour cycle
• Females- levels fluctuate more extensively but on a 28-day cycle
The Hormonal Control of SexThe Hormonal Control of SexPituitary and Hypothalamus Control of
Sex Hormones
– Gonadotropins: LH and FSH
– Males- LH stimulates testosterone; FSH aids sperm maturation
– Females- LH, FSH cause estrogen secretion
The Neural Basis of Sexual Behaviors
Mammalian Mating Strategies:
– Polygyny• Male mates with many females
– Polyandry • Female mates with many males
– Monogamy • One mate
The Neural Basis of Sexual Behaviors
The Neural Basis of Sexual Behaviors
• The Neurochemistry of Reproductive Behavior
– Prairie voles: Solidly monogamous
– Meadow voles: Asocial and promiscuous
– Affected by oxytocin and vasopressin… Prairie voles exhibit higher levels of vasopressin and oxytocin…. Suggesting a role in the brain
The Neural Basis of Sexual Behaviors
Role of oxytocin and vasopressin receptors in reproductive behavior
• Prairie voles display more oxytocin receptors in females and more vasopressin receptors in males
• Meadow voles, fewer receptors in both sexes
Why and How Male and Female Brains Differ
Sexual Dimorphisms of the CNS
– Sexually dimorphic nucleus (SDN)
– INAH in humans analogous to rat SDN
Why and How Male and Female Brains Differ
Why and How Male and Female Brains Differ
– Organizational effect of hormones• Tend to be irreversible
– Activational effect of hormones• Tend to be temporary
Why and How Male and Female Brains DifferWhy and How Male and Female Brains Differ
An example of the activational effects of hormones… in the somatosensory cortex, the plasticity of the ventral surface for the nipples increases by ~100% to encourage lacation .
This increase in sensation is associated also with increases in prolactin, oxytocin, and a variety of birthing, parental care, and reproductive behaviors.
Why and How Male and Female Brains Differ
Sexual Orientation
– INAH-3 - twice as large in heterosexual males compared to heterosexual females: Sexually dimorphic
– INAH-3 in homosexual males: Similar in size to that in heterosexual females
– INAH – 3 in homosexual females does not appear to differ from heterosexual females
– See Levay, 1991.
END.