Lecture 12: Sex steroids and the nervous system Flashcards
What are sex chromosomes?
the location of genes responsible for sex determination i.e. gonad development
What is the testis-determining factor and which gene does it come from?
a transcription factor the determines development of male gonadal tissues
the SRY gene
Which sex hormones do the male and female gonads synthesise?
male: testosterone is produced by the testes
female: estrogens and progesterone is produced by the ovaries
What do sex chromosomes determine?
the primary types of circulating sex hormones
What is the common precursor of sex steroids?
cholesterol
What is the solubility of steroid hormones?
lipid-soluble so pass through all membranes
What is aromatase expression critical for?
determining whether androgen or estrogen is the primary active factor
How are sex steroids synthesised?
cholesterol -> progesterone -> testosterone
testosterone is converted to 5ɑ-dihydrotestosterone by 5ɑ-reductase and it is converted to 17-β-estradiol by aromatase
What causes masculinization of genitalia? How do levels of testosterone change in males during puberty?
early (pre-birth; second trimester) transient synthesis of testosterone
testosterone levels increase at puberty to (relatively) constant adult levels
How do levels of estrogen and progesterone change in females throughout their life?
circulating estrogens and progesterone from ovaries are low until puberty
cyclical patterns of estrogen and progesterone synthesis during adulthood and decreased synthesis in menopause
What is sex steroid synthesis regulated by?
pituitary hormones (FSH, LH) that are released into the bloodstream
What are levels and patterns of FSH/LH secretion determined by?
the hypothalamus
What is hypothalamus activity determined by?
circulating hormone levels (feedback circuits) and other brain inputs
What are gynandromorphs?
comprise a mixture of genetically male and female tissues but both sides of the brain will be exposed to the same circulating hormones, so any differences between sides must be due to genes
How many genes are expressed at different levels in male vs. female brains BEFORE gonad formation (in mammals)?
> 50 genes
What is sexual dimorphism?
permanent anatomical, physiological and behavioral differences between sexes
What are examples of behaviours that differ between male and female?
courtship and mating, parenting, aggressive/defensive behaviours, release of pheromones
What are contributors to sexual dimorphic behaviours?
sex-specific neurons
sex-specific expression of hormone receptors in neurons common to both sexes
What do anatomical and physiological differences define? What are permanent anatomical and physiological differences initiated by?
sexually dimorphic behaviours
initiated by exposure to (or deprivation of) steroids during developmental critical periods
Where do steroid receptors have discrete patterns of localisation?
in the developing and adult nervous system, so only a minority of regions become sexually dimorphic
What is the mechanism of steroid action?
steroid (androgen or estrogen) binds to its specific cytoplasmic receptor (AR or ER, respectively)
steroid-receptor complex translocates to nucleus to activate specific response elements -> specific RNA and protein
What is the duration of steroid action?
slow onset and offset (hours-days)
When is estrogen a critical masculinizing factor?
in neurons that express aromatase AND estrogen receptors
What happens if a neuron expresses aromatase?
within the neuron testosterone is converted to estradiol: actions can occur via estrogen receptors or via androgen receptors or via both receptor types
