GABA-A and GABA-B receptors in the cuneate nucleus of the rat in vivo

Abstract

Electric stimulation of the rat forepaw evokes a negative potential (N-wave) at the ipsilateral cuneate nucleus.The responses of the N-wave to microiontophoretically applied GABA agonists and antagonists have been studied.Applications of GABA-A agonists (3-amino-propanesulfonic acid and muscimol) reduce the amplitude of the N-wave.This effect decreases during prolonged application, suggesting a desensitization of GABA-A receptors.In addition the effect of muscimol is reduced by (-)-bicuculline methiodide.Baclofen (a GABA-B agonist) also depresses the N-wave but its action lasts longer, is less reversible, shows no desensitization and is not blocked by (-)-bicuculline methiodide.The different responses of the N-wave to GABA-A and GABA-B agonists are compatible with the existence of different types of functional receptors for them in the cuneate nucleus of the rat.The receptors activated by muscimol (GABA-A) are clearly not the same as the ones activated by baclofen (conceivably GABA-B).