PARVALBUMIN-CONTAINING GABAERGIC NEURONS IN THE BASAL GANGLIA OUTPUT SYSTEM OF THE RAT

The output of the basal ganglia is directed through the entopeduncular nucleus (EPN) and the substantia nigra pars reticulata (SNR) and pars lateralis (SNL), which provide a gamma-aminobutyric acidergic (GABAer gic) projection to various nuclei of the thalamus and brainstem. Altho ugh many neurons within the SNR and EPN have been described as modalit y specific, the morphological and neurochemical similarities preclude their precise identification. In the present study, the immunocytochem ical localization of parvalbumin, a calcium-binding protein, is used i n combination with axonal tracing to verify neuronal heterogeneity wit hin the SNR, SNL, and EPN. The results reveal that the majority of neu rons in all three centers contain parvalbumin. The parvalbumin-contain ing neurons are distributed in the caudal two-thirds of the EPN, the r ostral part of the SNL, and the lateral two-thirds of the entire rostr ocaudal extent of the SNR, the areas involved in sensorimotor function of the basal ganglia. Moreover, the nigrothalamic, nigrocollicular, a nd EPN-thalamic neurons possess parvalbumin immunoreactivity, whereas the EPN-habenular neurons are devoid of parvalbumin immunoreactivity. The results indicate a neurochemical heterogeneity within the GABAergi c output neurons of the basal ganglia and suggest that the parvalbumin -containing neurons of the SNR, SNL, and EPN are the tonically active output neurons that form a major link in the disinhibitory neuronal ci rcuit of the basal ganglia, especially that concerned with sensorimoto r function. (C) 1994 Wiley-Liss, Inc.