Control of substantia nigra pars reticulata neurons by the nucleus accumbens

In alpha-chloralose anesthetized, immobilized and ventilated cats stimulation of the nucleus accumbens (NA) evokes either inhibition or brief excitation followed by inhibition of extracellularly recorded spontaneously active or sural driven units in substantia nigra pars reticulata (SNpr). Inhibition peaked 50-80 msec following the onset of NA stimulation and persisted for about 300 msec. Pharmacologic interventions designed to characterize this inhibition were performed. Bicuculline, 0.01 to 0.1 mg/kg IV, consistently antagonized NA elicited suppression of SNpr cells. Diazepam 0.5 mg/kg effectively reversed bicuculline actions. Inhibition of spontaneously active units as well as sural excited units was blocked by bicuculline. Strychnine 0.1 to 0.5 mg/kg IV failed to affect inhibition arising from NA. These data suggest that, analogous to the GABAergic striatonigral pathway, inhibition of SNpr cells arising from NA utilizes GABA as a transmitter.