Caffeine and chlordiazepoxide: effects on motor activity in the chronic thalamic rat.

The effects of three doses of caffeine and of chlordiazepoxide (CDX) on motor activity were tested in the chronic thalamic rat. In this preparation virtually all cortical, striatal and limbic structures were ablated. A small dose of caffeine had only a weak motor stimulant effect which was succeeded by sedation. Larger doses that are stimulatory in intact animals, depressed motor activity in the thalamic rat. Amphetamine, in contrast to caffeine, produced a substantial motor stimulation. CDX caused a dose-dependent reduction of motor activity, similar to its effect in the intact rat. It is concluded that (a) telencephalic structures are involved in mediating the stimulatory action of caffeine; (b) a sedative component of caffeine may be present, but masked, in the intact animal, and may be due to serotoninergic mechanisms; (c) the presence of limbic structures is not necessary for the sedative effect of CDX.