Differential regional effects of ketamine on spontaneous and glutamate-induced activities of single CNS neurones in rats

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Abstract
Ketamine and L-glutamate were applied microiontophoretically to neurones of several central nervous system (CNS) structures in urethane anaesthetized Wistar rats. The spontaneous single-unit activities of all the hippocampal CA1 and CA3 neurones were suppressed by ketamine in an iontophoretic current-dependent manner. The spontaneous single-unit activities of eight of nine neurones in the thalamus were not affected by ketamine and suppressed in one. Spontaneous neurone activities in the midbrain reticular formation were not significantly affected by ketamine. Spontaneous activities of the cerebellar Purkinje cell were suppressed by ketamine in four of eight neurones. L-Glutamate excited all 13 hippocampal and nine thalamic neurones in a current-dependent manner. L-Glutamate-induced excitation of all CA1, CA3 and thalamic neurones was inhibited by ketamine. The inhibitory effects of ketamine on L-glutamate-induced excitation were dependent on the injection current intensity, although the sensitivity of thalamic neurones to the injection 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 distribution of NMDA receptors. Moreover, the actions of the drug on NMDA receptors appear to differ between the hippocampus and thalamus. These regionally differential actions of ketamine may reflect characteristics of anaesthesia induced by this drug.
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