Famous for its ability to make people fall in love, oxytocin plays a pretty important role in our durability as a species. Yet while its impact on the emotional aspect of courtship is well established, new research suggests that this so-called ‘love hormone’ may also provide some magic sauce in the bedroom by controlling sexual function in males.
When it comes to the physical side of love, males rely on a specialized piece of neural equipment known as the spinal ejaculation generator (SEG), which is to be found in the lumbosacral spinal cord. From here, nerve cells called gastrin-releasing peptide (GRP) neurons control those all-important penile reflexes that allow a man to perform between the sheets.
Because previous studies have indicated that certain oxytocinergic neurons in the brain communicate with this region of the spinal cord, researchers from Okayama University decided to investigate if this neurotransmitter plays a role in coordinating the activity of the SEG.
Writing in the journal Current Biology, the study authors explain how they injected oxytocin directly into the SEG of male rats, which boosted the rodent’s libido, causing them to increase their mating efforts with nearby lady rats and enhancing their ability to ejaculate. When the researchers then injected the animals with a compound that blocks oxytocin, they saw a marked decrease in sexual activity.
While this finding alone could be seen as pretty clear evidence for the role of oxytocin on male sexual function, the researchers needed to know exactly how the hormone alters the activity of GRP neurons within the SEG. To investigate, they removed these cells and analyzed them using a technique called electron microscopy.
Novel roles of the love hormone oxytocin in controlling male sexual activity. Image: Okayama University
Results indicated that the oxytocin had locked on to receptor sites on the GRP neurons, thereby increasing their activity. However, because many of these cells were located in areas in which there were no neural connections – known as synapses – the study authors conclude that oxytocin stimulates these neurons not by synaptic transmission, but by a more passive type of diffusion through extracellular spaces.
In other words, oxytocin is simply released from cells by a process called exocytosis, and then drifts through the cerebrospinal fluid in the lumbar spine until it reaches a GRP neuron, triggering an increase in desire for rat loving.
Explaining how these findings may be relevant to humans, study author Hirotaka Sakamoto said in a statement “now that we have uncovered a novel neural mechanism, the ‘localized volume transmission’ of oxytocin from axons-involved in controlling male sexual function in the spinal cord, we can hope that this may lead to the development of treatments for male sexual dysfunction.”
