DIRECT AND CONTINUOUS MONITORING OF INTRAHIPPOCAMPAL NITRIC-OXIDE (NO) BY AN NO SENSOR IN FREELY MOVING RAT AFTER N-METHYL-D-ASPARTIC ACID INJECTION

We directly and continuously monitored the endogenous nitric oxide (NO ) in the rat hippocampus after intraperitoneal (i.p.) administration o f N-methyl-D-aspartic acid (NMDA) in freely moving state. The sensor u sed here was Malinski-type porphyrinic probe modified so as to measure in the freely moving animals. When the rats received the subconvulsiv e dose of NMDA (20 mg/kg), a significant increase of the NO concentrat ion in the hippocampus was continuously observed, The increase was up to 1 mu M at 25-30 min past administration. This elevation in NO conce ntration was totally blocked by pretreatment with an NO synthase inhib itor, N-G-monomethyl-L-arginine (30 mg/kg, i.p.). These findings indic ate that our sensor successfully measured the NMDA-induced NO in the h ippocampus catalyzed by NO synthase.