Oxytocin and Vasopressin

• Overview of oxytocin and vasopressin?

  These are both 9 amino acid peptide hormones released into the blood from the posterior pituitary

  Oxytocin binds to the OTR receptor in the hypothalamus, vasopressin to the V1 and V2 receptors in the CNS and kidney respectively

  Oxytocin controls maternal behaviour in females (released during birth), lactation, and contraction of the uterus in labour

  Vasopressin controls courtship, aggression, paternal care of young, and pair bonding in males, as well as water balance an blood pressure in the periphery

  Not complete split of female/male though
• Difference in behaviours of male meadow and prairie voles?

  Meadow = promiscuous, don't care for young, indifferent to territory and mate

  Prairie = monogamous, care for young, aggressive defence of territory and mate
• Fahrback 1985 - effect of oxytocin on maternal behaviour

  Injected female virgin mice with different levels of oestrogen, showed higher concentration increased signs of maternal behaviour (crouching over young, grooming, hours of pup contact), then also injected oxytocin antagonist (atosiban) with oestrogen, found that it significantly decreased the maternal behaviour - same effect also seen when anti-oxytocin injected (antibody for oxytocin)

  Used corn oil and anti-vasopressin as controls, very good experiment
• How could oxytocin influence difference in behaviour of meadow and prairie voles?

  Immunocytochemistry shows oxytocin receptors much denser in monogamous prairie vole brains

  Oxytocin receptor KO mice lack maternal behaviour (measured percentage of scattered pups and latency of crouching over all pups)

  Oxytocin KO in mice, if no oxytocin injected then all commit infanticide, but if inject oxytocin then far fewer do

  If apply oxytocin antagonist then inhibition maternal behaviour
• How does mating affect prairie vole behaviour?

  Mating increases oxytocin and vasopressin release, leads to pair bonding, parental care, and aggression of males to males (measured before mating, and 24hrs after either mating or no mating - Winslow 1993) - sig increase in attacks etc after mating only

  Vasopressin antagonist blocks mating induced aggression (increased conc reduces behaviour)

  Vasopressin injection increases aggression prairie but not meadow voles no matter conc, suggests aggression due to presence/not of vasopressin receptor
• Effect of vasopressin on partner preference

  Vasopressin induces pair bonding in male prairie voles - partner preference test (3 chambers, free vole in middle chooses partner or stranger)

  Vasopressin antagonist stops pair bonding, not if oxytocin antagonist

  Vasopressin injection induces pair bonding in prairie, not meadow vole

  In situ hybridisation - male prairie vole has much higher vasopressin receptor conc in ventral pallidum than meadow (VP associated with DA reward system)

  Viral expression of V1a receptor in meadow vole VP makes it monogamous - single gene affecting social behaviour
• Difference in vasopressin receptor genes and the effect on behaviour?

  Prairie but not meadow voles have a microsatellite repeat in promoter - controls V1a receptor expression and behaviour in mice when do transgenic experiment - converts mice to monogamous

  Longer microsatellite repeat in humans associated with altruism - more expression of receptor

  Survey where much more likely to have marital crisis/divorce if have more RS3 alleles