The action of d-amphetamine on spontaneous activity in the caudate nucleus and reticular formation of the rat

Dextro-amphetamine sulfate injected intraperitoneally in paralyzed, locally anesthetized rats, resulted in a biphasic alteration in spontaneous activity in the caudate nucleus. An initial dose-dependent potentiation of activity occurs 510 min after injection followed by a prolonged dose-dependent depression of activity which may last as long as several hours. Similar injections result in a different time-course of alterations in the mesencephalic reticular formation consisting of a prolonged increase followed by a depression of spontaneous activity. Spontaneous activity in the caudate nucleus was relatively unaffected by mephentermine sulfate, a peripheral sympathomimetic. The depression of activity produced by amphetamine could be reversed by haloperidol, a dopaminergic blocking agent. Haloperidol injected alone produced a transient potentiation of activity followed by a return to control firing rate. These results provide electrophysiological support for the inhibitory synaptic function of dopamine in the caudate-putamen and for the alleged action of amphetamine and haloperidol at these sites. Both the differential biochemical and neurophysiological effects of amphetamine on the caudate nucleus and reticular formation may have functionally significant behavioral consequences.