N-METHYL-D-ASPARTATE, QUISQUALATE AND KAINATE RECEPTORS ARE ALL INVOLVED IN TRANSMISSION OF PHOTIC-STIMULATION IN THE SUPRACHIASMATIC NUCLEUS IN RATS

In order to clarify the neuronal transmission mechanism of photic stimulation in the suprachiasmatic nucleus (SCN), the effects of agonists and antagonists for excitatory amino acid receptors on N-aceytltransferase (NAT) activity in the pineal gland were observed following the microinjection of drugs into both sides of the nuclei. N-Methyl-D-aspartate (NMDA), alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate, and kainate (which are selective agonists for three different subtypes, i.e. NMDA, quisqualate and kainate receptors, respectively) significantly decreased NAT activity similarly to the suppressive effect of light Moreover, compared with a control group, all the groups pretreated with a selective competitive antagonist for NMDA receptor (D-2-amino-5-phosphonovalerate or 3-((+/-)-2-carboxypiperazine-4-yl)-propyl-1-phosphonate), or a selective non-competitive antagonist for non-NMDA receptors (Joro spider toxin-3 or 1-naphthylacetyl spermine) partially blocked the suppressive effect of photic stimulation on NAT activity. These results suggest that NMDA, quisqualate and kainate receptors are all involved in mediating photic stimulation in the SCN.