N-methyl-D-aspartate receptors are indispensable for the formation of long-term potentiation in the rat suprachiasmatic nucleus in vitro.

Optic nerve (ON) stimulation caused a postsynaptic field potential in the suprachiasmatic nucleus (SCN) of rat hypothalamic slices. The postsynaptic field potential was suppressed by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), a non-NMDA receptor antagonist, in a concentration-dependent manner, but not affected by D-amino-5-phosphonovaleric acid (APV), a competitive NMDA receptor antagonist. Tetanic stimulation to the ON induced long-term potentiation (LTP) in the SCN. Application of APV at 50 microM inhibited the induction of LTP by tetanic stimulation but CNQX at lower dose (5 microM) didn't inhibit it. These results suggest that NMDA receptors are indispensable for the induction of LTP after tetanic stimulation.