Activation of NMDA and non-NMDA receptors by L-aspartate in the suprachiasmatic nucleus of the rat.

The receptors mediating the responses of neurons in the rat suprachiasmatic nucleus (SCN) to focal application of L-aspartate were studied in coronal slices by whole-cell patch clamp electrophysiology. Neurons in the SCN showed inward currents in response to both L-aspartate and L-glutamate. Responses to L-aspartate were only partially blocked by D-2-amino-5-phosphonovalerate (D-AP5) and by 10 mM Mg+2 at resting membrane potentials, suggesting an action upon-NMDA glutamate receptors. The remaining currents were blocked by the quinoxalines CNQX (6-cyano-7-nitroquinoxaline-2,3-dione), DNQX (6,7-dinitroquinoxaline-2,3-dione), and NBQX (2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(f)quinoxaline1), indicating an action of L-aspartate upon non-NMDA receptors. We conclude that cells in the SCN are among the relatively few types in which an action of L-aspartate upon non-NMDA receptors has been demonstrated.