Inhibitory effect of somatostatin on vagal motoneurons in the rat brain stem in vitro.

Effects of somatostatin-14 (SRIF) on membrane electrical properties were studied in rat brain stem slice preparations maintained in vitro. SRIF hyperpolarized the resting membrane potential and decreased the input resistance of more than two-thirds of the 85 vagal motoneurons tested in the dorsal motor nucleus of the vagus. These effects persisted under synaptic blockade caused by perfusion with a solution containing tetrodotoxin or a Ca2+-free/high-Mg2+ solution and were dependent on the extracellular SRIF concentration (5 X 10(-8) to 1 X 10(-8) M). The Hill coefficient was estimated to be 2. The reversal potential of SRIF-induced hyperpolarization was affected by changing external K+ concentration. The results suggest that, in addition to its well-known peripheral action, SRIF may inhibit secretomotor functions of visceral organs by reducing vagal output in the central nervous system.