lecture 24

Question 1

What do you need to know?

Answer 1

• 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

Question 2

What is the basic determination of gender?

Answer 2

• 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

Question 3

What are the principal sex hormones?

Answer 3

• 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

Question 4

When do sex steroids appear?

Answer 4

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

Question 5

Where do sex steroids act in the brain?

Answer 5

• 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

Question 6

How are sex steroid levels set?

Answer 6

• 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

Question 7

What are established differences between males and females?

Answer 7

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

Pain

• 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

Question 8

What are some examples of difference in sexual behaviour?

Answer 8

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

Question 9

What is stress mediated analgesia?

Answer 9

• 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

Question 10

What are organisational effects that contribute to sexuality?

Answer 10

• 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

Question 11

What are activational effects?

Answer 11

• 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

Question 12

What do voles tell us about sexuality?

Answer 12

• 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

Question 13

How do you get polygamy vs monogamy?

Answer 13

• 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