Your sensitivity to certain drugs may be determined by the amount of sex you have, which could partially explain why some people are more susceptible to addiction than others. More specifically, those who have lots of sex may be at risk of developing a tolerance to some drugs, although when these people hit a rough patch in their love lives and experience too many lonely nights, their sensitivity to these substances can dramatically increase.
As is often the case with experiments involving illegal substances, the study that gave rise to these conclusions was conducted on rats rather than people. Publishing their findings in the Journal of Neuroscience, the researchers attempt to build on previous work that has shown that when rats are over-sexed, the dopamine-releasing neurons in a part of the brain called the ventral tegmental area (TVA) shrink.
Since the TVA is part of the brain’s reward circuit, it is largely responsible for generating feelings of pleasure, so when these neurons are diminished, so too are these gratifying sensations. Interestingly, a similar effect is seen in opiate addicts, many of whom therefore build up a tolerance to their drug of choice. Likewise, overly promiscuous rats have been found to show a level of tolerance to drugs like amphetamine, requiring larger doses in order to satisfy their need for a buzz.
Not getting enough sex could increase a person's sensitivity to certain drugs. maxriesgo/Shutterstock
In the latest study, the researchers allowed rats to mate to their heart’s content, before then forcing them to remain celibate for a period of time. Following this abstinent interlude, the rats began to show an increased sensitivity for amphetamines, craving the drug and displaying a high vulnerability for addiction.
To figure out what drives this effect, the researchers chemically blocked the activity of VTA dopamine neurons while allowing the rats to mate like rabbits, before once again forcing them to remain abstinent for a week. This time, they found that having sex had no effect on the size of these neurons, and therefore caused no changes to the rats’ sensitivity to amphetamines.
The study authors note that blocking dopamine during sex suppressed the expression of a transcription factor called ΔFosB, which they suspect may be responsible for the changes in neuronal plasticity that are seen under normal conditions.
As such, they conclude that the activation of dopamine neurons in the TVA during sex results in changes to neuron size and sensitivity, which, when followed by a period of abstinence, causes rats – and possibly people – to become particularly receptive to the effects of certain drugs, therefore increasing their susceptibility to addiction.