Identification of a subpopulation of substantia nigra pars compacta gamma-aminobutyric acid neurons that is regulated by basal ganglia activity

In this report, the authors provide a novel description of a population of gamma-aminobutyricacid-containing neurons in the substantia nigra, pars com pacta (SNC). By using metabolic mapping of the immediate-early gene, c-fos, the activation pattern of these cells was characterized with respect to ba sal ganglia stimulation. Dopaminergic stimulation with d-amphetamine or apo morphine induced Fos expression in the central region of the SNC. However, lesions of the nigrostriatal dopamine pathway significantly reduced d-amphe tamine- and apomorphine-induced Fos expression in the ipsilateral and contr alateral SNC, respectively Suppression of stimulant-induced Fos expression in the striatum, using antisense oligodeoxynucleotides, also eliminated Fos expression in the ipsilateral SNC, indicating that striatal efferent proje ctions are involved in the activation of these cells. Double-labeling immun ohistochemistry revealed that the Fos-positive cells did not express tyrosi ne hydroxylase but were immunoreactive for glutamic acid decarboxylase. Ret rograde labeling of nigrostriatal neurons, combined with Fos immunofluoresc ence, revealed that these Fos-positive cells did not project to the striatu m. Thus, these neurons do not appear to comprise a nondopaminergic nigrostr iatal circuit but likely represent locally-projecting interneurons of the s ubstantia nigra. J. Comp. Neurol. 416:30-44, 2000. (C) 2000 Wiley-Liss, Inc .