As it turns out, allopregnanolone increases the basal release of
vasopressin. Don't know how V1Ar works in females, though.
<http://news.bbc.co.uk/1/hi/sci/tech/3812483.stm>
'Fidelity gene' found in voles
By Julianna Kettlewell
BBC News Online science staff
As with meadow voles, most mammal males play around
A single gene can turn the Don Juan of voles into an attentive
home-loving husband, Nature magazine has reported.
By altering the small animal's brain hormone chemistry, scientists have
made a promiscuous meadow vole faithful - just like its prairie vole
cousin.
The researchers think this will lead to a greater understanding of how
social behaviour is controlled in humans.
The same hormone activity could play a role in disorders like autism
where people can lack simple social skills.
Falling in love
Fewer than 5% of mammals are habitually monogamous. Prairie voles
(Microtus ochrogaster) are among the select few.
After mating, the males "fall in love": they stick close to their chosen
one, guard her jealously and help her raise their young.
It could be that vasopressin plays a role in normal human social
interactions
Larry Young, Emory University
Closely related meadow voles (Microtus pennsylvanicus), on the other
hand, take a more standard approach. They mate with several females and
pay little attention to their babies.
Previous studies indicated a hormone called vasopressin encourages
pair-bonding in prairie voles.
Scientists had also noticed that promiscuous voles have fewer
vasopressin (V1a) receptors, in a bit of their forebrain called the
ventral pallidum region.
To prove vasopressin has a "taming" effect, the researchers gave meadow
voles extra V1a receptors in the ventral pallidum region of their
brains.
Reward system
The results were remarkable. After the V1a receptor gene was introduced,
the former playboys reformed their ways.
Suddenly, they fixated on one female, choosing to mate with only her -
even when other females tried to tempt them.
How does one hormone have such a dramatic effect? Scientists put it down
to a particular chain of events.
They think that when the voles have sex, the hormone vasopressin is
released. This hormone is then "picked up" by the V1a receptors in the
ventral forebrain, which in turn trigger a neural "reward system".
The reward system makes them feel happy, and they associate those
feelings with the vole they have just mated with - which encourages them
to stick around.
"We think what happens is when the voles mate, vasopressin activates the
reward centre, and it really makes the animals pay attention to who they
are mating with," co-author Larry Young, from Emory University, Georgia,
US, told BBC News Online.
He continued: "It makes the voles think, 'when I'm with this partner I
feel good'. And from then on, they want to spend their time with that
particular partner."
The researchers have concluded that the male meadow voles are
promiscuous because they lack just one link in the chain: the V1a
receptors in the ventral forebrain.
Autism link?
The implications of this study extend beyond Casanova voles, however.
The strings of human behaviour might be pulled by similar hormones and
similar pathways.
"We know that vasopressin is released when humans have sex," said
Professor Young. "Sex is probably involved in maintaining the bond
between humans and vasopressin may play a role in that."
Jealous wives might want to give their husbands a hefty dose of the V1a
receptor gene, but Professor Young and his team are focussed on medical
advances.
Studies of this kind could, they say, open the lid on conditions where
our social skills go wrong, such as in autism.
The strings of human behaviour might be pulled by similar hormones and
pathways
"Part of the reason we are doing this research is that we are trying to
understand the social brain," explained Professor Young. "Why do we
interact with other people, and what could be wrong in diseases like
autism?
"In autism, people are very aloof - they don't want to interact with
others. It could be that vasopressin plays a role in normal human social
interactions.
"Two studies have already found there is a modest link between
vasopressin and autism."
Professor Joseph Piven, a psychiatry expert from the University of North
Carolina at Chapel Hill, US, agrees the voles might reveal something
interesting about autism.
"This is a model where the voles have alterations in their social
behaviours," he said. "And these alterations may be linked to the same
processes that are going awry in autism."
He continued: "No very strong links have been found yet between autism
and vasopressin, but after studies like this people may take a closer
look."