Cannabis and endocannabinoids — cannabis-like molecules that occur naturally in the brain — are known to stimulate appetite. In the 12 April Nature, George Kunos and colleagues of the National Institute on Alcohol Abuse and Alcoholism, Bethesda, USA, show that CB1 (a cannabinoid receptor) knock-out mice eat less than their wild-type littermates, even after 18 hours of fasting. In addition, SR141716A, a specific antagonist of CB1, caused wild-type mice to reduce their food intake. This suggests endocannabinoids acting on the CB1 receptor may be involved in stimulating appetite (Nature 2001, 410:822-825).

When normal rats were injected with leptin levels of endocannabinoids in the hypothalamus were reduced by 40–50%, suggesting that leptin, the primary signal through which the hypothalamus senses nutritional state and modulates food intake, also plays a role in the regulation of the cannabinoid pathway. Consistent with this, Di Marzo et al found that obese...

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