A hormone called kisspeptin has been found to link emotions and the release of sex hormones in humans, boosting activity in brain regions involved in sexual and emotional processing.
The only other hormone known to play a role in linking emotions and sex hormone release is the 'cuddle hormone' oxytocin.
In the study, published in the Journal of Clinical Investigation, 29 healthy men had fMRI scans while they were given kisspeptin solution. They were shown images that were intended to stimulate an emotional response, a sexual response, a negative response or to be neutral.
The scans showed that the men had more activity in the limbic system for the emotional response – a picture of a couple holding hands, for example – and to the sexual images when they were receiving extra kisspeptin. The men were also shown the same images while on a saline drip, to act as a baseline.
The study participants were receiving a higher dose of kisspeptin than an adult male would naturally have in his system, but it was within the range that humans can produce. Kisspeptin levels surge during puberty for both men and women, and it is also produced in large quantities by women during pregnancy.
The finding is significant because links between emotional responses and hormonal responses that are needed for reproduction are few and far between. Neuroscientists first discovered the roles that kisspeptin had in stimulating reproductive hormones in 2003.
The presence of kisspeptin and its receptors in parts of the brain involved in emotional processing were what prompted study author Waljit Dhillo of Imperial College London to see if kisspeptin played a more complex role in the reproductive system.
"It would make biological sense if kisspeptin was stimulating the hormones that it also had a role in sexual and emotional processing," Dhillo told IBTimes UK. "This is really linking the hormones with the reproductive behaviours."
It is possible that with further research kisspeptin could be used as a treatment for people who have certain psychosexual disorders, Dhillo said.
"If we're able to manipulate and heighten someone's brain activity when looking at non-sexual images, then if you've got a problem in that area, this could be one way to treat it.
"We've just done this study on healthy young men, who didn't report any sexual problems. This is proof of principle that kisspeptin could manipulate that system."