There’s been a lot of excitement in recent years about the ways in which the powers of oxytocin might be harnessed therapeutically. The hormone is best known as the mother-infant bonding hormone since its levels rise around the time a mother gives birth. And it also seems to be similarly important in bonding romantic relationships.
Because oxytocin appears to help promote human connections, there’s been particular interest in its potential use for people with autism who often have difficulty connecting with other people.
A new study shows — in mice, anyway — exactly how social behavior changes when the oxytocin pathway is blocked. The finding may lead to a new class of drugs that ease the social isolation common to those with autism spectrum disorders (ASD).
The mice also didn’t show any preference when, rather than social stimulation, the reward in the “fun” room was cocaine, for which mice typically have a strong predilection.
“People with autism-spectrum disorders may not experience the normal reward the rest of us all get from being with our friends,” said Robert Malenka, the study's senior author in a statement. “For them, social interactions can be downright painful. So we asked, what in the brain makes you enjoy hanging out with your buddies?”
Because the team had to use a mouse model to try to answer this question, they needed to devise some new ways of measuring social engagement. After all, said Malenka, “You can't ask a mouse, ‘Hey, did hanging out with your buddies a while ago make you happier?’”
Mice spent a day in a room with their littermates and then a day in another room by themselves. When researchers connected the two rooms and allowed the mice to make a choice, they generally chose to spend time in the room they’d been in with their siblings.
That choice is similar to humans, who also tend to prefer to spend time in places associated with fonder memories.
The finding underlines the link between social interaction (oxytocin) and pleasure (serotonin).
When the researchers blocked the activity of oxytocin, the mice didn’t show the same preference. They also didn’t show any preference when, rather than social stimulation, the reward in the “fun” room was cocaine, for which mice typically have a strong predilection.
These results suggest that oxytocin really is responsible for the pleasure mice get from social interaction, as opposed to some other substance. In fact, in another series of molecular experiments, the researchersd found that oxytocin affects the release of serotonin, a brain chemical known to be important in feeling happy, and which is the neurotransmitter influenced by many SSRI (serotonin reuptake inhibitor) antidepressants. The finding underlines the link between social interaction (oxytocin) and pleasure (serotonin).
Because the human and mouse brain networks underlying reward are very much the same, the authors suspect that similar mechanisms occur in humans, and that understanding these fully could lead to new treatments.
Perhaps medications that affect the function of the serotonin receptor via oxytocin could help people with autism or other social interaction disorders. “Drugs that selectively act on this receptor aren't clinically available yet, but our study may encourage researchers to start looking at drugs that target it for the treatment of diseases such as autism, where social interactions are impaired,” said lead author, Gul Dolen in a press release.
The research was carried out by a team at Stanford University School of Medicine and published in the journal Nature.