Action of gamma-aminobutyric acid on hypothalamo-neurohypophysial axons.

gamma-Aminobutyric acid (GABA) and the related compound, muscimol, were bath-applied to a preparation containing the rat median eminence, pituitary stalk and neurohypophysis, and are shown to reversibly reduce the amplitude, and increase the latency, of the antidromic compound action potential recorded from hypothalamoneurohypophysial axons in response to electrical stimulation of the posterior pituitary lobe. Both actions were antagonized by bicuculline, but were unaffected by strychnine. The data suggest that the peptidergic axons of the hypothalamo-neurohypophysial tract are endowed with receptors for GABA, which is believed to be synthesized and released by neurohypophysial glial cells.