Concurrent facilitory and inhibitory effects of amphetamine on stimulation-induced eating.

At low doses (0.125 and 0.25 mg/kg, i.p.), amphetamine facilitated eating induced by lateral hypothalamic electrical stimulation. It decreased the frequency threshold for the behavior and it increased the probability of eating across a range of suprathreshold stimulation frequencies; it also accelerated eating, decreasing the average time to eat three 45-mg food pellets across the range of stimulation frequencies tested. At high doses (1.0 and 2.0 mg/kg), amphetamine increased the frequency threshold and decreased the probability of eating across the range of suprathreshold stimulation frequencies; on those trials where eating was observed, however, even these doses of amphetamine accelerated feeding. Several lines of evidence suggest that amphetamine influences feeding through multiple mechanisms, and that present data may be explained by independent facilitory and inhibitory mechanisms, with the inhibitory mechanism less sensitive to low doses but generally dominant when the two mechanisms are both activated by higher doses. Another possibility is that the well-known anorexic effects of amphetamine result at least in part from over-stimulation of the same mechanism as is involved in the more subtle facilitory effects of the drug.