The new study by Robert Malenka suggested that oxytocin's role in one-on-one bonding probably evolved from an existing, broader affinity for group living.
Oxytocin is the focus of intense scrutiny for its apparent roles in establishing trust between people, and has been administered to children with autism spectrum disorders in clinical trials. The new study pinpoints a unique way in which oxytocin alters activity in a part of the brain that is crucial to experiencing the pleasant sensation neuroscientists call "reward."
The findings not only provided validity for ongoing trials of oxytocin in autistic patients, but also suggested possible new treatments for neuropsychiatric conditions in which social activity is impaired.
Some genetic evidence suggested the awkward social interaction that is a hallmark of autism-spectrum disorders may be at least in part oxytocin-related. Certain variations in the gene that encodes the oxytocin receptor - a cell-surface protein that senses the substance's presence - are associated with increased autism risk.
"From this observation sprang a dogma that pair bonding is a special type of social behavior tied to the presence of oxytocin receptors in the nucleus accumbens. But what's driving the more common group behaviours that all mammals engage in - cooperation, altruism or just playing around - remained mysterious, since these oxytocin receptors were supposedly absent in the nucleus accumbens of most social animals," the researchers said.
The new discovery shows that mice do indeed have oxytocin receptors at a key location in the nucleus accumbens and, importantly, that blocking oxytocin's activity there significantly diminishes these animals' appetite for socializing.
As the Stanford team found, oxytocin acting at the nucleus accumbens wasn't simply squirted into general circulation, as hormones typically are, but was secreted at this spot by another nerve tract originating in the hypothalamus, a multifunction midbrain structure.
The researchers said that they think their findings in mice are highly likely to generalize to humans because the brain's reward circuitry has been so carefully conserved over the course of hundreds of millions of years of evolution.
The study is published in the journal Nature.
--ANI (Posted on 12-09-2013)