Diazepam-induced hyperphagia in mice is sensitive to quinpirole

The present trial examined the possibility that diazepam (DZP, 1 mg/kg) induces hyperphagia by acting on the dopaminergic system. Quinpirole (QP), dopamine D-2 receptor agonist, was used for this purpose. Mice fasted for 24 hr were treated with QP 1 (QP-1) or 2 (QP-2) mg/kg 30 min prior to termination of the starvation. DZP was given to untreated mice and half of the QP-1 and QP-2 treated mice 10 min before the termination of the starvation. Food consumed during six 30 min intervals (30 min-feeding), food consumed for 3 hr (total feeding), time required to enter the room containing food by passing through a maze with four multiple routes (time to banquet), latent period to commencement of eating food after entering the banquet room (latent period), and feeding frequency for the 30 min intervals as well as for 3 hr were measured. DZP stimulated feeding, shortened the latent period without affecting the time to banquet and increased the feeding frequency. The hyperphagic effect was restricted to the first 30 min interval only. Both QP-1 and QP-2 first reduced, then progressively stimulated, and finally reduced feeding without modifying total feeding, thus making a bell-shaped profile. They also prolonged both the time to banquet and the latent period, and reduced the feeding frequency of the first 30 min interval but not that for 3 hr. Both QP-1 and QP-2 canceled all the effects of DZP. These results imply that dopamine D2 receptor is involved in the induction of hyperphagia by DZP.