PCP and ketamine inhibit non-NMDA glutamate receptor mediated hsp70 induction

Abstract

The physiological model for glutamate receptor mediated excitotoxicity entails elevation of intraneuronal calcium levels. Excessive activation of the NMDA receptor leads to excitotoxicity by prolonged calcium influx via its calcium channel. The purpose of this research was to examine the mechanism of non-NMDA glutamate receptor mediated excitotoxicity. Mammalian AMPA receptors do not show significant calcium conductance. However, some kainate receptors show significant calcium conductance. The hypothesis of this research states that non-NMDA glutamate agonists (quisqualate (5 μ1 of 2 mg/ml i.c.v.), AMPA (4 μ1 of 1 mg/ml i.c.v.), and kainate (15 mg/kg i.p.)) produce significant heat shock gene, hsp70, induction via glutamate release with subsequent opening of the NMDA receptor calcium channel. PCP (phencyclidine) and ketamine are noncompetitive blockers of the NMDA calcium channel. They act to prevent significant NMDA receptor excitotoxicity. PCP (20 mg/kg i.p.) and ketamine (60 mg/kg i.p.) both diminished quisqualate and AMPA hsp70 induction in the CA1, CA2, CA3 areas of the hippocampus, in the polymorph area of the dentate gyrus, and in the parietal neocortex. PCP significantly ( P < 0.05) diminished kainate hsp70 induction only in the CA1 area and the neocortex. Ketamine failed to reduce kainate hsp70 induction. AMPA receptors appear to result in excitotoxic damage via glutamate release. Glutamate opens NMDA receptor calcium channels which increases intraneuronal calcium levels. Kainate receptors probably mediate excitotoxicity via direct calcium conductance with glutamate release being important in the CA1 area and neocortex.