(3H)-muscimol, (3H)-nipecotic acid and (3H)-isoguvacine as autoradiographic markers for GABA neurotransmission

Abstract

Summary Retinas from rabbit, goldfish and guinea-pig were exposed to (³H) GABA, (³H)-muscimol, (³H)-nipecotic acid and (³H)-isoguvacine either by intravitreal injectionin vivo or by incubations in a balanced salt solution and the distribution of radioactivity was then studied with autoradiography. All substances labelled a similar set of presumed amacrine cells. Incubating at 0 °C, in 10⁻⁵ M ouabain, or in 10⁻³ M GABA inhibited the labelling by (³H)-muscimol whereas bicuculline (10⁻⁴ M), and glycine (10⁻³ M) were less efficient blockers. The result is interpreted as a neuronal uptake of (³H)-muscimol rather than as a GABA receptor binding. All the substances except (³H)-isoguvacine also labelled glia to such a degree that neuronal labelling was often disguised in rabbits and goldfish. Glial labelling by muscimol was less pronounced in guinea-pig. (³H)-isoguvacine (tested only in rabbits) gave a strong labelling of cells with the distribution of GABA neurons and only little glial labelling.