Electrophysiological Actions of Norepinephrine in Rat Lateral Hypothalamus. 2. An In Vitro Study of the Effects of Iontophoretically Applied Norepinephrine on LH Neuronal Responses to Gamma-Aminobutyric Acid (GABA)

摘要

Many previous studies have demonstrated modulatory effects of norepinephrine (NE) on neuronal responsiveness in local circuits of mammalian brain including the cerebellum, cerebral cortex, hippocampus, lateral geniculate nucleus and facial motor nucleus. In the preceding paper, we reported that iontrophoretically applied NE could consistently augment synaptically mediated (70%) and gamma amino-butyric acid (GABA)-induced (69%) inhibitory responses of lateral hypothalamic (LH) neurons recorded in vivo. In the present experiments, we studied the effects of NE and other sympathomimetic drugs on LH neuronal responses to direct ionotophoretic application of GABA in the hypothalamic tissue slice preparation. The objectives of the study were two-fold: (1) to validate the slice preparation as a model for further in vitro study of NE modulatory phenomena, and (2) to characterize NE-facilitating effects on GABA inhibition in terms of alpha and beta-adrenoceptor mechanisms. The results indicate that augmentation of GABA-depressant responses by NE can be demonstrated in LH tissue slices. However, in contrast to the results obtained in vivo, NE exerted an alpha-like antagonistic effect on GABA-mediated inhibition in a high percentage of LH neurons, suggesting that under tissue slice conditions a major shift from beta-to-alpha type responsiveness of LH neurons may occur. A preliminary report of this work has appeared previously. Reprints. (kt)