Immunocytochemical localisation of L-glutamic acid decarboxylase in the goldfish retina

Abstract

A DIRECT way to examine whether certain neurones may use γ-aminobutyric acid (GABA) as a neurotransmitter is to determine by immunocytochemistry if L-glutamic acid decarboxylase (GAD), the enzyme responsible for GABA synthesis, is localised in these cells. We have been studying GABA-ergic pathways in the goldfish retina by autoradiographic and biochemical methods^1–3. It would therefore be of interest to localise the GAD-containing cells in this system immunocytochemically. However, although GAD has been purified from mouse brain⁴ and antibodies against the enzyme have been obtained, these antibodies do not cross-react with the GAD found in neural tissues of teleosts⁵. Thus, before immunocytochemical studies of GAD-containing neurones in the goldfish retina were possible, we had to purify GAD from teleost brain and obtain a specific antibody against this enzyme. Such an antibody has now been obtained⁶. We show here that in the goldfish retina, GAD is localised in specific interneurones: type H1 horizontal cells and probably type Ab pyriform amacrine cells. These cell types have been shown to be both pre- and postsynaptic to red-sensitive cones and red-sensitive centre-depolarising bipolar cells, respectively^3,7–9.