Effects of GRF on paraventricular neurons in slices of guinea-pig hypothalamus.

Growth hormone releasing factor (GRF) applied by iontophoresis, pressure, and in the perfusate, increased (14.81%) or decreased (45.92%) the firing of paraventricular neurons extracellularly recorded from guinea-pig hypothalamic slices. Effects were similar whatever the mode of application and were elicited in the nanomolar range. They persisted in high Mg2+ medium, indicating a post-synaptic action of the peptide. Of the neurons 27.40% had a phasic activity suggestive of vasopressin neurons and were recorded in the vasopressinergic parts of the paraventricular nucleus. The effect of GRF on these phasic neurons was a reduction of firing. The present results demonstrate the action of GRF on paraventricular neurons and suggest that this action is inhibitory on vasopressin neurons.