NMDA RECEPTOR PROPERTIES IN RAT SUPRAOPTIC MAGNOCELLULAR NEURONS - CHARACTERIZATION AND POSTNATAL-DEVELOPMENT

Hypothalamo-neurohypophysial magnocellular neurons display specific el ectrical activities in relation to the mode of release of their hormon al content (vasopressin or oxytocin). These activities are under stron g glutamatergic excitatory control. The implication of NMDA receptors in the control of vasopressinergic and oxytocinergic neurons is still a matter of debate. We here report the first detailed characterization of functional properties of NMDA receptors in voltage-clamped magnoce llular neurons acutely dissociated from the supraoptic nucleus. All ce lls responded to NMDA with currents that reversed polarity around 0 mV and were inhibited by D-2-amino-5-phosphonovalerate (D-APV) and by 10 0 mu M extracellular Mg2+ (at -80 mV). Sensitivity to the co-agonist g lycine (EC50, 2 mu M) was low compared with most other neuronal prepar ations. The receptors displayed low sensitivity to ifenprodil, were in sensitive to glycine-independent potentiation by spermine, and had a u nitary conductance of 50 pS. No evidence was found for two distinct ce ll populations, suggesting that oxytocinergic and vasopressinergic neu rons express similar NMDA receptors. Characterization of NMDA receptor s at different postnatal ages revealed a transient increase in density of NMDA currents during the second postnatal week. This was accompani ed by a specific decrease in sensitivity to D-APV, with no change in N MDA sensitivity or any other properties studied. Supraoptic NMDA recep tors thus present characteristics that strikingly resemble those of re constituted receptors composed of NR1 and NR2A subunits. Understanding the functional significance of the development of NMDA receptors in t he supraoptic nucleus will require further knowledge about the maturat ion of neuronal excitability, synaptic connections and neurohormone re lease mechanisms.