MODULATION BY DIVALENT-CATIONS OF THE CURRENT GENERATED BY VASOPRESSIN IN FACIAL MOTONEURONS

Vasopressin generates a voltage-gated, sodium-dependent current in fac ial motoneurons in brainstem slices. Reducing the extracellular calciu m concentration from 2 to 0.01 mM caused a 30 to 120% increase in the amplitude of this current. Lowering extracellular magnesium also enhan ced it, but less efficiently. In the physiological solution, the respo nse of facial neurons to vasopressin is thus partially blocked. Increa sing extracellular calcium was without effect. Current-voltage curves indicate that the vasopressin current reversed at around 0 mV and sugg est that the low-calcium-induced potentiation was due to an attenuatio n of the region of negative slope conductance.