VASOPRESSIN-INDUCED CURRENTS IN RAT NEONATAL SPINAL LATERAL HORN NEURONS ARE G-PROTEIN MEDIATED AND INVOLVE 2 CONDUCTANCES

Arginine vasopressin (AVP) receptors are expressed early in the develo ping spinal cord. To characterize AVP-induced conductances in lower th oracic sympathetic preganglionic (SPN) and other lateral horn neurons, we used patch-clamp recording techniques in neonatal (11-21 days) rat spinal cord slices. Most (90%) of 273 neurons, including all 68 SPNs, responded to AVP with membrane depolarization and/or a V-1 receptor-m ediated, dose-dependent (0.01-1.0 mu M) and tetrodotoxin (TTX)-resista nt inward current. A role for G-proteins was indicated by persistence of this inward current after intracellular dialysis with GTP-gamma-S o r GMP-PNP, its marked reduction with GDP-P-S, and significant reductio n, but not abolition, after preincubation with pertussis toxin or in t he presence of N-ethylmaleimide. Analysis of individual current-voltag e (I-V) relationships in 57 cells indicated the presence of two differ ent membrane conductances. In 21 cells, net AVP-induced currents rever sed around -103 mV, reflecting reduction in one or more barium-sensiti ve potassium conductances; in 12 cells, net AVP-induced current revers ed around -40 mV and was not significantly sensitive to several potass ium channel blockers including barium, tetraethylammonium chloride (TE A), 4-aminopyridine (4AP), cesium, or glibenclamide, suggesting increa se in a nonselective cationic conductance that was separate from I-h; in 24 cells where I-V lines shifted in parallel, AVP-induced inward cu rrents were significantly greater and probably involved both conductan ces. These data indicate that SPNs and a majority of unidentified neon atal lateral horn neurons possess functional G-protein-coupled V-1-typ e vasopressin receptors. The wide distribution of AVP receptors in neo natal spinal lateral column cells suggests a role that may extend beyo nd involvement in regulation of autonomic nervous system function.