METHYLCOBALAMIN INDUCES A LONG-LASTING ENHANCEMENT OF THE FIELD POTENTIAL IN RAT SUPRACHIASMATIC NUCLEUS SLICES

Optic nerve stimulation has been reported to evoke a field potential ( FP) in rat suprachiasmatic nucleus (SCN) slices. ta-(5,6-dymethylbenzi midazolyl)-Co-methyl-cobamide (Me-B-12) enhanced this FP and the enhan cement lasted more than 1 h after washing out. Maximal enhancement (14 3.6 +/- 9.8%) was achieved at a concentration of 10 mu M. BY contrast, cyanocobalamin containing CN- instead of CH3- showed no enhancement o f the amplitude in the FP. Me-B-12 induced enhancement of FP was stron gly blocked by an N-methyl-D-aspartate (NMDA) receptor antagonist, DL- 2-amino-5-phosphonovaleric acid (APV). These results indicate that CH3 - in the Me-B-12 is required to modulate the FP amplitude and the NMDA receptor is involved in the long-lasting FP enhancement induced by Me -B-12. The present results suggest that Me-B-12 modifies the Photic en trainment of the circadian clock in the suprachiasmatic nucleus via an activation of NMDA receptors. (C) 1996 Elsevier Science Ireland Ltd.