Subpopulations of neurons in rat substantia nigra display GABA_BR2 receptor immunoreactivity

A functional gamma-aminobutyric acid (GABA) B receptor is the first metabotropic receptor known to be composed of two heteromeric subunits, GABA_BR1 and GABA_BR2. Our previous report [Neuroscience 99 (2000) 65] has demonstrated that subpopulations of neurons in the rat substantia nigra display distinct patterns of distribution of GABA_BR1 receptor immunoreactivity. A robust level of GABA_BR1 receptor is only found in the dopaminergic neurons of the substantia nigra pars compacta (SNc). The objective of the present study was to determine the precise cellular localization of GABA_BR2 subunit in the rat substantia nigra using double immunofluorescence. Neuropilar elements in the SNc and the substantia nigra pars reticulata (SNr) were found to display GABA_BR2 immunoreactivity. In addition, the tyrosine hydroxylase-immunoreactive dopaminergic neurons and the parvalbumin-immunoreactive GABAergic neurons in the SNr were also found to display GABA_BR2 immunoreactivity. The present results thus demonstrate that a functional GABA_B receptor may be expressed by the dopaminergic neurons in the SNc. It is less clear whether neurons in the SNr express a functional GABA_B receptor. The present findings have important functional implications in GABA neurotransmission in the substantia nigra. Copyright © 2001 Elsevier Science B.V. All rights reserved.