The Biology of Monogamy Flashcards
What are the features of prairie and montane voles?
Prairie Vole Highly social Monogamous Biparental High selective aggression High social contact
Montane Vole Solitary Promiscuous Uniparental Low selective aggression Low social contact
How is the partner preference test performed?
Laboratory assessment of pair bonding:
- Allow them to mate
- Tether the partner and tether the stranger in cages
- Prairie vole has a high association with the individual it has mated with, whereas the montane vole prefers to sit solitary.
Describe oxytocin in female bonding
- Give them oxytocin when they meet an individual
- Hormones need to be administered directly to the brain to bypass the blood brain barrier
In females:
• Strong bond formed
• Exposued to male but do not allow mating → no bond form
• Exposure to male ad administer oxytocin → bonded
• Allow to mate and administer blocker of oxytocin → no bond formed
→ In females, oxytocin is crucial for partner bond formation.
Males:
• No such effect
• They do show partner preference in the partner preference test, but you cant mimic this with oxytocin.
Describe vasopressin in male bonding
- Vasopressin causes pair bond formation in the absence of mating
- Vasopressin antagonist blocks pair bond formation following mating
- In social voles, the male helps rear the young
- Vasopressin facilitates and block of vasopressin prevents paternal behavior
What is the key thing about oxytocin and vasopressin receptors that causes the difference between prairie and montane voles?
- Have a different distribution in montane and prairie voles.
- Only male prairie voles respond to vasopressin.
Receptors:
• Important to understand that where the receptors are located in the brain determines which cells are activated
• In other words, the behavioural effects of any hormone are defined not just by the amount of hormone, but where its receptors are located in the brain.
Importance of receptor distribution
• Difference between prairie vole and montane vole response is not too much or too little hormone
• The differences are where the receptors are
• Therefore, infusing hormone into montane voles will not induce a pair bond → the receptors are in the wrong target area of the montane vole brain
Oxytocin and vasopressin receptor fields
• Receptors in the prairie vole brain are concentrated in ‘reward’ pathways → targeting regions likely to lead to the conditioning of behaviours such as partner preference
• These areas are involved with the mesolimbic dopamine reward system → eg, NAc
→ OT and VP are synthessied in the PVN and SO nucleus of the hypothalamus
• Within the brain, there is dendritic release of OT and VP to reach distant targets
• Smaller neurons project directly to other regions In the brain eg) amygdala, hippocampus
• Vasopressin acts on two different receptor classes → primary receptor involved in this bevaviour is the V1a – a GPCR.
Why do prairie and montane voles have different OT and VP receptor distributions?
- Microsatellite expansion region in the prairie vole gene that leads to different expression patterns in the brain
- Long alleles associated with higher levels of amygdala activation during a face-viewing task,
Microsatellite expansion zone in the VA1 receptor of Praire voles
• 660 bases upstream of the transcription start site
• 500 bases of highly repetitive sequence → affects which cell types express the receptor
• Species specific expression pattern results
• To test this, we need to demonstrate that you can chance the behavior in a species by changing the nature of the expansion region.
Can monogamy be introduced in promiscuous animals?
Meadow and prairie voles
• Use of viral vectors to insert new gene into promiscuous meadow voles
• When V1a receptor levels are artificially increased within the ventral pallidum of meadow voles, they display social behavior reminiscent of that of monogamous prairie voles, preferring social contact with their partner.
→ So a small change in the promoter region of the gene is enough to full change social behavior.
Mice:
• Gene insertion so the mice now express the microsatellite region
• Vasopressin receptor expressed in the mouse introduced a pattern like that of the prairie vole
• The pattern of oxytocin receptors unaffected
• Normally, wild type mice are highly polygynous and antisocial, and don’t form pair bonds
• Inserting the receptor transfers prairie vole-like behavior to them → increasing affiliative behavior
Tests for Behaviour in Rat
Social discrimination test:
• Male rat presented with juvenile rat and time taken to investigate recorded
• Now presented with novel juvenile, plus the original. Time spent on novel rat rather than familiar rat presented as a ratio.
Social interaction test:
• Active and passive interaction of pairs of rats in either wild type or transgenic combinations.
Gene transfer enhances social recognition in rats:
• Transferred gene for vole receptor directly to rat lateral septum
• Functional V1a receptor expressed
• Long-term receptor expression achieved
• Expression of the receptor associated with improved long-term social recognition
• This can be blocked with a V1a receptor antagonist
What are the affects of OT and VP in social situations in primates and humans?
Chimps
• Common chimps are highly polygynous – don’t form any pair bonds
• These animals lack the critical microsatellite region
• The bonobo does have this expansion region – and these do form pair bonds.
Owl Monkeys
• Only nocturnal primate and only true monogamous species
• One repetitive region that has been the focus of human studies of V1a receptor diversity. ‘RS3’, is absent in these specices. This suggests that if V1a receptor modulates behavior in owl monkeys, it does so independent of this region.
Humans
The ‘look of love’ activates brain regions containing OT and VP
Vasopressin:
• 4 polymorphic microsatellite regions identified
• Genetic variation in V1a receptor associated with human behavior → altruistic behavior higher in the long variants.
• Swedish study of 552 twins tested for partner bonding and marital problems:
− One allelic variant associated with a low score for partner bonding and marital problems
− Males homozygous twice as likely to have marital problems
− Altered amydala activation in a face-matching task and link to autism proposed
Oxytocin:
• Participants given intranasal OT better at classifying emotions displayed on faces
• Intranasal OT increases gaze into the eye region of the human face
• OT increases the amount of money that an investor is willing to offer a trustee who, after the amount is amplified by the experimenter, can chose to return a smaller or larger amount back to the investor
• OT does not however, increase monetary allocation when the return on the investment is determined by a random lottery → represents a quantifiable indication of interpersonal trust
• When an investor is betrayed by a trustee who returns less money than the initial investment, investment amounts decrease for placebo controls, but not of the OC treated individuals
• Pairing a shock with a face skews the views emotional rating of the face towards a more negative assessment, unless they have been given OT – OT treated individuals rate shock-paired faces as more forgiving and sympathetic.
