Research by University of Michigan student Stephen Mahler has shed light on how marijuana may hijack the brain's reward system--a finding that could have implications for future obesity drugs.
Mahler focused his research on endogenous cannaboids--the marijuana-like substances produced naturally in the brain--which can make good food taste even better. He and his colleagues injected the brains of 62 rats with anandamide--an endogenous cannaboid--or with a saline solution. They then gave the animals a taste of sugar water or bitter-tasting quinine and watched the rats' reactions.
When animals like a taste, they respond by repeatedly licking their lips. The rats in the study always licked their lips after tasting the sugar solution, but did so even more vigorously if they had been recently injected with anandamide. The drug did not, however, affect how the animals responded to bitter tastes--they always showed an equal amount of disgust and gaping in response.
The results suggest that cannaboids make sweet food taste even better, but they have no effect for other tastes, says Mahler. This may be the reason marijuana smokers generally binge on sweets but not vegetables, he notes.
After recording the rats' reactions, the researchers dissected their brains to see exactly where the anandamide took effect. Mahler found that when the drug had been injected into a 1 millimeter "hot spot" in the dorsal medial part of the nucleus accumbens shell, the rats particularly enjoyed the sweet taste.
This line of research could contribute to the development of drugs that have the opposite effect--blocking the pleasure of food-which could be useful in treating obesity, Mahler notes.
-S. Dingfelder