Gaba Uptake by Gat1 Modulates Long-Term Optical Changes Following Electrical Stimulation of the Pituitary Gland Neurointermediate Lobe

Abstract

Intrinsic optical changes that follow infundibular stalk stimulation of the neurointermediate lobe of the mouse pituitary gland exhibit three di®erent phases that re°ect three distinct physiological events. The¯rst (E-wave) is the rapid light-scattering increase that is associated with a nerve terminal volume increase (mechanical spike), and that accompanies excitation of the neurohypophysial terminals by the invading action potential; the second (S-wave) is the slower lightscattering decrease that is tightly correlated with the secretion of the peptide hormones oxytocin and arginine vasopressin, and the third is the long-duration response (R-wave) that re°ects cell volume changes in the pars intermedia. We have studied the E-wave and the S-wave in earlier publications. The R-wave, considered here, is sensitive to chloride replacement as well as to blockade of chloride channels. By blocking GABA A receptors (which are ligand-gated chloride channels) with pharmacological agents, and by applying GABA directly into the bathing solution, or evoking its release from GABAergic inputs, we have demonstrated that this long-duration optical response is sensitive to chloride movements and re°ects GABA-induced changes in the intrinsic optical properties of the pars intermedia. The full time-course of this optical response takes minutes and, therefore, has to embody some other process (or processes) related to the restoration of resting physiological chloride concentrations, following the opening and closing of GABA A -receptor channels. Here we demonstrate that the shape of the R-wave, the long-lasting