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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?

sexual behaviour
- 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)
- courtship
- bonding (penguins bringing rocks to females, females flirt to get more rocks even if they are pair-bonded to someone else)
- rhythms

- 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

Maternal behaviour


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


How do you get polygamy vs monogamy?

- difference is in expression of oxytocin receptors in females and in form of vasopressin synthesised in males
-- markedly different between two types of vole
-- oxytocin receptors more dense in reward system of females
-- vasopressin molecule longer in males
- mating releases vasopressin males and oxytocin in females
- blocking vasopressin prevents pairing in prairie vole males
- giving long vasopressin to an unmated male induces pairing with novel female even when mating does not take place
- blocking oxytocin prevents pairing in females