Electrophysiology of Oxytocin Actions on Central Neurons a

The action of oxytocin on neurons located in the dorsal motor nucleus of the vagus nerve was studied in brain slices in vitro. It acted postsynaptically and caused a reversible, concentration-dependent excitation of vagal motoneurons in rats. This effect is specific, since it could be mimicked by a selective agonist and suppressed by an oxytocin antagonist. Single-electrode voltage-clamp recordings from rat vagal motoneurons indicated that oxytocin generates a noninactivating inward current, whose amplitude increased as the membrane was depolarized. This current was insensitive to TTX, to a reduction of membrane calcium currents, and to a reversal in the transmembrane chloride gradient; and it was unaffected by several potassium channel blockers. By contrast, it was reversibly reduced by partially substituting extracellular sodium with equimolar N-methyl-D-glucamine. These results suggest that oxytocin exerts its neuronal action in the rat brainstem by generating a sustained voltage-dependent sodium current. Vasopressin activates a similar current when acting on motoneurons located in the facial nucleus of newborn rats. These fast, neurotransmitter-like actions of oxytocin and of vasopressin may provide an explanation--though not necessarily the sole explanation--for their central effects on maternal, sexual, and social behaviors.