Sex apparently, or a lack thereof.
Science 16 March 2012:
Vol. 335 no. 6074 pp. 1351-1355
Sexual Deprivation Increases Ethanol Intake in Drosophila
K. R. Kaun1,2,
+ Author Affiliations
1Department of Anatomy, University of California, San Francisco, CA 94143-2822, USA.
2Present address: Howard Hughes Medical Institute, Janelia Farm Research Center, Ashburn, VA 20174, USA.
The brain’s reward systems reinforce behaviors required for species survival, including sex, food consumption, and social interaction. Drugs of abuse co-opt these neural pathways, which can lead to addiction. Here, we used Drosophila melanogaster to investigate the relationship between natural and drug rewards. In males, mating increased, whereas sexual deprivation reduced, neuropeptide F (NPF) levels. Activation or inhibition of the NPF system in turn reduced or enhanced ethanol preference. These results thus link sexual experience, NPF system activity, and ethanol consumption. Artificial activation of NPF neurons was in itself rewarding and precluded the ability of ethanol to act as a reward. We propose that activity of the NPF–NPF receptor axis represents the state of the fly reward system and modifies behavior accordingly.
So here's the thing. Apparently those male fruit flies who did the deed had more of a brain chemical called neuropeptide F than comrades who didn’t have sex. Frustrated male fruitflies drank more. Sexually satisfied male fruit flies who had their neuropeptide F artificially suppressed also drank more.
Why do people do research like this? Among other reasons, they're looking for neurochemical bases for addiction. Find these trigger points and maybe you can find a pharmaceutical which can manipulate said biochemical pathways.
Or... we can ask for more sex and inform our partner that it's for our own good.