Characterization of substantia nigra pars reticulata neurons based on response to iontophoretically applied GABA and flurazepam.

Previous work had suggested that neurons in the pars reticulata of the substantia nigra (SNpr) might be differentiated based on responsiveness to GABA and benzodiazepines (BZs). To evaluate this possibility, multi-barreled glass capillary assemblies were used to examine the effects of GABA and a BZ, flurazepam (FZP), on the spontaneous activity of single SNpr neurons in chloral hydrate anesthetized rats. Both FZP and GABA, as a function of increasing ejection current, decreased the rate of neuronal discharge. SNpr neurons differed according to the maximum effect of each agent. For over half of the cells, the spontaneous discharge could be inhibited at least 90% by GABA, while the maximum FZP effect in the same cells ranged from 20 to 100% inhibition. Except for 3 neurons, the maximum inhibition produced by GABA was about the same or greater than that produced by FZP. No clear anatomical segregation according to BZ effect was found.