SUBCELLULAR-LOCALIZATION OF GABAA/BENZODIAZEPINE RECEPTOR-LIKE IMMUNOREACTIVITY IN THE SUPERFICIAL GRAY LAYER OF THE RAT SUPERIOR COLLICULUS

The monoclonal antibody bd-17, which recognizes the beta-2 and beta-3-subunits of GABA(A)/benzodiazepine receptors, was used to determine the cellular and subcellular localization of receptor-like immunoreactivity in the superficial gray layer of the rat superior colliculus. In numerous dendrites, very strong immunostraining was present in the cytoplasm and on the postsynaptic dendritic membrane of synaptic junctions. The extrasynaptic portion of the dendritic membrane also very often showed [beta-2 + beta-3]-like immunoreactivity. However, due to methodological limitations, it could not be stated with certainty whether presynaptic beta-2- and beta-3-subunits of GABA(A)/benzodiazepine receptors actually occur in this mesencephalic visual structure. In conclusion, these results strongly suggest that synaptic and non-synaptic GABA(A)/benzodiazepine receptors are present in the superficial gray layer of the rat superior colliculus. These receptors may modulate neuronal cell activity in different ways, depending on their location.