CHANNEL PROPERTIES OF NMDA RECEPTORS ON MAGNOCELLULAR NEUROENDOCRINE CELLS CULTURED FROM THE RAT SUPRAOPTIC NUCLEUS

Application of N-methyl-D-aspartate (NMDA) to the supraoptic nucleus o f the hypothalamus (SON) generates clustered firing that may be import ant in hormone release. However, synaptically evoked EPSPs recorded fr om SON neurons exhibit varying contributions from NMDA receptors. We u sed the high resolution of single-channel recording to examine the rec eptor and ion channel properties of NMDA receptors expressed by SON ne urons in 'punch' culture. Biocytin introduced into individual neurons during patch clamp recording revealed large (32.1 +/- 3.3 mu m), oblon g somas and bipolar extensions typical of magnocellular neuroendocrine cells (MNCs). Rapid application of NMDA (100-300 mu M) in the presenc e of 10 mu M glycine to outside-out macropatches resulted in openings with an average conductance of 46.9 pS and reversal potential of +3.9 mV. Increasing glycine from 0.03 to 30 mu M increased the apparent fre quency, duration and occurrence of overlapping NMDA-elicited openings. NMDA responses were inhibited by Mg2+ in a voltage-dependent manner a nd by the NMDA-site antagonist, D-(-)-2-amino-5-phosphonovaleric acid (D-APV). Application of saturating NMDA or glycine alone with the glyc ine-site antagonist, 5,7-dichlorohynurenate (DCK) or with D-APV, respe ctively, did not result in agonist-induced openings. NR1 immunoreactiv ity was observed in large neurons (> 25 mu m) with MNC-like morphology . These single-channel and immunocytochemical data confirm the presenc e of functional NR1-containing NMDA receptors in MNCs. (C) 1998 Elsevi er Science B.V.