Immunocytochemical localization of GABAA receptor beta 2/beta 3-subunits in the brain of Atlantic salmon (Salmo salar L)

Abstract

In order to obtain a basis for future investigations concerning the possible interactions between melatonin, GABA and benzodiazepines in the central nervous system of a teleost fish, the Atlantic salmon, we have studied the expression of immunoreactivity with a monoclonal antibody against the GABAA-receptor beta 2/beta 3-subunits (bd-17) in the salmon brain. Immunoreactivity was found in all parts of the brain, mostly as a diffuse labelling of discrete neuropil areas but in some instances as a granular perikaryal labelling. Strong neuropil labelling is located in the telencephalon, dorsal thalamus/pretectum, optic tectum, torus semicircularis, and ventrolateral tegmentum. Perikaryal labelling was observed in the stratum periventriculare of the optic tectum, torus longitudinalis, torus semicircularis, ventrolateral tegmentum, and in the granular layer of the cerebellum. The general pattern of distribution is similar to that observed in mammals, in which high receptor densities are found in the telencephalon (cerebral cortex), superior and inferior colliculi, and cerebellum. There is a good correlation with the distribution of melatonin binding sites, observed in a previous study, in areas receiving visual input such as the optic tectum, pretectum, and torus semicircularis. Moreover, a correlation was found in the inferior lobes and regions connected with them. Regions containing both bd-17-immunoreactivity and melatonin binding sites may constitute areas of functional interaction between melatonin, GABA and benzodiazepines in the central nervous system.