DIFFERENTIAL REGIONAL EFFECTS OF KETAMINE ON SPONTANEOUS AND GLUTAMATE-INDUCED ACTIVITIES OF SINGLE CNS NEURONS IN RATS

Ketamine and L-glutamate were applied microiontophoretically to neuron es of several central nervous system (CNS) structures in urethane anae sthetized Wistar rats. The spontaneous single unit activities of all t he hippocampal CA1 and CA3 neurones were suppressed by ketamine in an iontophoretic current-dependent manner. The spontaneous single-unit ac tivities of eight of nine neurones in the thalamus were not affected b y ketamine and suppressed in one. Spontaneous neurone activities in th e midbrain reticular formation were not significantly affected by keta mine. Spontaneous activities of the cerebellar Purkinje cell were supp ressed by ketamine in four of eight neurones. L-Glutamate excited all 13 hippocampal and nine thalamic neurones in a current-dependent manne r. L-Glutamate-induced excitation of all CA1, CA3 and thalamic neurone s was inhibited by ketamine. The inhibitory effects of ketamine on L g lutamate-induced excitation were dependent on the injection current in tensity, although the sensitivity of thalamic neurones to the injectio n current was approximately three times that of hippocampal neurones. We conclude that the effects of ketamine on spontaneous activities of neurones vary according to the brain region, probably because of the d istribution of NMDA receptors. Moreover, the actions of the drug on NM DA receptors appear to differ between the hippocampus and thalamus. Th ese regionally differential actions of ketamine may reflect characteri stics of anaesthesia induced by this drug.