Effects of vasopressin on the somatic membrane of spinal ganglia neurons

Abstract

The application of vasopressin (VP) in the isolated perfused dorsal root ganglia of 22-36 days old rats was studied by means of intracellular technique. 86.76% of cells have responded to the VP application. Depolarization was observed in 67.8% responded cells, the mixed response--in 16.95% cells, hyperpolarization--in 15.25% cells. All responses were dose-dependent and reversible. Input resistance (Rm) of the cell membrane decreased during depolarization and increased during hyperpolarization. The VP-evoked depolarization was accompanied by an increase in the action potential (AP) duration and decrease in the AP amplitude and after-hyperpolarization. Neurons with slow conduction velocity, high Rm and prolonged AP (small cells) had the lowest threshold of the sensitivity to VP (1.10(-11) M) and prolonged high-amplitude responses. Cells with the rapid conduction velocity, low Rm and rapid AP (large cells) responded to 1.10(-8) M, but sometimes even 1.10(-6) M had no effect. Depolarization in these neurons had smaller duration and low amplitude: sometimes hyperpolarization was observed. These results confirm the possibility that VP has effect on small neurons predominantly.