Distinct cellular distribution of GABA(B)R1 and GABA(A)alpha 1 receptor immunoreactivity in the rat substantia nigra

GABA is one of the most important inhibitory neurotransmitters in the subst antia nigra. Functions of GABA are mediated by two major types of GABA rece ptors, namely the GABA(A) and GABA(B) receptors. Subunits of both the GABA( A) and GABA(B) receptors have been cloned and functional characteristics of the receptors depend on their subunit compositions. In order to characteri ze the cellular localization of GABA(B)R1 and GABA(A)alpha 1 subunit immuno reactivity in subpopulations of neurons in the rat substantia nigra, double and triple immunofluorescence was employed. Over 90% of tyrosine hydroxyla se-immunoreactive neurons in the substantia nigra pars compacta were found to display immunoreactivity for GABA(B)R1. In contrast, immunoreactivity fo r GABA(A)alpha 1 was found to be primarily displayed by neurons in the subs tantia nigra pars reticulata. Around 85% of the GABA(A)alpha 1-immunoreacti ve reticulata neurons were found to display parvalbumin immunoreactivity an d some GABA(A)alpha 1-positive reticulata neurons were found to be parvalbu min negative. In addition, triple-labeling experiments revealed that at the single cell level, the tyrosine hydroxylase-positive, i.e. the dopaminergi c neurons in the compacta displayed intense immunoreactivity for GABA(B)R1 but not GABA(A)alpha 1 receptors. The parvalbumin-positive neurons in the r eticulata displayed intense immunoreactivity for GABA(A)alpha 1 but not GAB A(B)R1 receptors. The present results demonstrate in the same sections that there is a distin ct pattern of localization of GABA(B)R1 and GABA(A)alpha 1 receptor immunor eactivity in different subpopulations of the rat substantia nigra and provi de anatomical evidence for GABA neurotransmission in the subpopulations of nigral neurons. (C) 2000 IBRO. Published by Elsevier Science Ltd. All right s reserved.