Observational analysis of feeding induced by Δ9-THC and anandamide

Endogenous cannabinoid systems have been implicated in the physiological regulation of appetite by the ability of cannabinoid receptor agonists to induce hyperphagia. Both the exogenous cannabinoid Δ9-THC and the endocannabinoid arachidonoyl ethanolamide (anandamide) stimulate eating in rats. However, there has been no detailed analysis of the adjustments to feeding behaviour underlying this action. We used observational methods to determine the specific components of feeding affected by these compounds. Two groups (n=6) of presatiated, male, Lister hooded rats received either Δ9-THC (0, 0.5, 1.0 or 2.0 mg/kg) or anandamide (0, 1.0, 5.0 or 10.0 mg/kg sc), and their behaviour in an open field was recorded for 45 min. Behaviour (eating, drinking, rearing, grooming, sniffing, locomotion, resting/inactivity, sleeping) was continuously monitored to provide data on the latency, temporal distribution, duration and frequency of each category. Under control conditions, a minority of animals ate small quantities of lab chow, with feeding beginning only after a long latency. Both Δ9-THC and anandamide selectively stimulated feeding, with a marked reduction in latency. Apart from its rapid onset, cannabinoid-induced eating retained the normal, species-typical sequence, characteristic of untreated, free-feeding rats. Our data suggest that exogenously administered cannabinoids promote eating by increasing the incentive value of food and support a role for endocannabinoids in the regulation of the appetitive aspects of feeding motivation