[3H] muscimol receptors sites in the carp (Cyprinus carpio L.) brain: Binding assay and autoradiographic distribution

Autoradiographic and binding techniques were used to study the presence of [3H]muscimol receptors sites in the carp brain. The radioligand was distributed with an high degree of anatomical selectivity. We found abundant labelling in the cerebellum, in the nucleus diffusus lobi inferioris, and in the torus longitudinalis. No labelling was detected within the epithalamus, thalamus and hypothalamus, while the telencephalon and the rhombencephalon displayed a low density of [3H]muscimol receptors sites. Binding assay showed the highest concentration of receptor sites in the nucleus diffusus lobi inferioris and the lowest in the medulla oblongata. Presence of [3H]muscimol binding sites within the visceral sensory area was noted. The rank order of displacement efficacy of unlabelled ligands observed, suggested that in brain membranes of carp the receptor binding of [3H]muscimol has the same pharmacological specificity previously reported in a large number of experiments with tissue homogenates. A general agreement in binding and autoradiography was observed. The present findings suggested that muscimol receptor could be involved in neuronal pathway controlling basic central actions like gustatory signal processing or spatial learning acquisition and retention.