Flashcards in lecture 24 Deck (13)
What do you need to know?
- genetic determinants of sex
- parts of brain involved in sexual behaviour
- developmental issues relating to sexual dimorphism
- roles of oestrogen and testosterone in development and normal adult behaviour
-- organisational, activational
- monogamy vs polygamy
What is the basic determination of gender?
- XX: female
- XY: male
- Y chromosome contains SRY gene which determines development of mail reproductive organs
-- absent get female phenotype
-- leads to development of testosterone secreting cells in early development
- female is the default
- the literature on sexual dimorphism is heavily tainted by the huge problems that there are socially in identifying differences between males and females
- people often use to difference to indicate superiority or inferiority
- so the dominant paradigm automatically puts females in the negative position
- so different becomes
- makes it very difficult to do certain sorts of research
What are the principal sex hormones?
- testosterone (androgen) - male sex hormone
- estradiol (oestrogen) - one of two main female sex hormones
- progesterone - other main female sex hormone
- aromatase converts testosterone to oestradiol
- cholesterol --> progesterone --> (many intermediate steps) --> testosterone --> oestrogen or dihydrotestosterone
When do sex steroids appear?
in males, circulating testosterone seen early in foetal development
- falls to very low levels are birth
- rises again at puberty
in females, circulating oestrogen and progesterone appear at or around puberty
- fall to very low levels at menopause
- testosterone synthesised in adrenal cortex-present throughout life
Where do sex steroids act in the brain?
- sites of action of oestrogen in rat brain:
-- at synapses, membrane action
-- altering the action of gamma receptors in the neuronal membrane
-- in cell bodies, DNA transcription, oestrogen receptors (ER)
- most regions with ER involved in sexual behaviour or regulation of steroid production
- androgen and progesterone receptors found in overlapping, but distinct regions
-- similar subcellular sites of action
How are sex steroid levels set?
- feedback circuit through hypothalamus
- hypothalamus acts to cause release of hormones (FSH, LH) from the pituitary that regulate production of oestrogen or testosterone
- hormone secretion depends on environment and levels of the relevant sex steroid
- because steroids go through BBB
What are established differences between males and females?
- mating (maybe not terribly different?) (in animals - different positions need to be adopted by male and female to achieve mating, e.g. lordosis in female)
- bonding (penguins bringing rocks to females, females flirt to get more rocks even if they are pair-bonded to someone else)
- stress-mediated analgesia
- males and females have slightly different versions, involve different transmitter receptors in the brain
Cognitive function (most controversial)
- males score better than females on spatial rotation tasks
- males score higher, and lower, than females on tests of higher mathematical skills
- argued that females have better language skills
- females perform bettern in learning during period after puberty
What are some examples of difference in sexual behaviour?
A: sexually dimorphic nucleus of preoptic area (SDN=POA) female coverted to male structure by testosterone treatment around birth
-- depends on conversion of testosterone to oestrogen by local aromatse
-- so will still become male if you inject oestrogen
B: firing of SDN-POA neuron in female rat at different stages of act of mating. *insertion of penis, ejaculation arrows
C: firing of neuron in medial POA of male monkey when exposed to receptive female
- minimum of four different subtypes of this nucleus in humans
- distinctly different in size and shape between male rats and female rats
- controversial: homosexuals have a feminised part of their brain associated with this ??
- this particular region is really important for sexual function
What is stress mediated analgesia?
- stress reduces sensitivity to painful stimuli
- males and females both exhibit this, but pharmacological differences that depend on circumstances
- swim in warm water analgesia depends on endogenous opiods
-- males more sensitive to antagonists than females
- swim in cold water analgesia depends on NMDA receptors in males, by not in females
-- difference disappears if oestrogen is removed
What are organisational effects that contribute to sexuality?
- occur during development and determine structure
- absence of testosterone during development get female phenotype
-- androgen-insensitivity syndrome leads to genotypic males being pheonytpic females : more feminine than women in several ways
- many effecs in brain due to conversion of testosterone to oestrdiol via aromatase within neurons
What are activational effects?
- responses to levels of circulating hormones once development is complete
- examples include
- estradiol increases number of dendritic spines in hippocampus (more potential synapses in hippocampus, women are more vulnerable to dementia than man (excluding risk factor of age))
- premesntrual syndrom
- stress mediate analgesia
- aggression due to use of anabolic steroids (androgens)
- regulation of steroid hormone production
What do voles tell us about sexuality?
- prairie voles and montane voles
- love and lust
- prairie voles pair bond, although not strictly monogamous
- montane voles are polygamous
-- no pair bonds
- in prairie voles, first mating leads to strong changes in behaviour
- montane voles - love them and leave them