Effects of bilateral injection of GABA into the substantia nigra on spontaneous behavior and measures of analgesia

Bilateral injection of gamma-aminobutyric acid (GABA, 10–300 μg) into the substantia nigra (pars reticulata) of rats produced stereotyped sniffing and had an analgesic-like effect on the hot-plate but not on the tail-flick test. These effects of GABA (30 μg) were suppressed by simultaneous administration of a sub-convulsant dose of bicuculline methiodide (100 ng). Significant increases in locomotion occurred when GABA (300 μg) was injected along with the inhibitor of GABA-transaminase, d, l/-gamma-vinyl-GABA (GVG; 5 μg) and the inhibitor of the uptake of GABA, 1-2,4-diaminobutyric acid (DABA; 5 μg). No other behavioral effects were observed following injection of GABA into the nigra, either alone or in combination with GVG and DABA. Bilateral injection of bicuculline (100–600 ng) into the nigra had strong convulsant actions. When injected simultaneously with bicuculline, GABA reduced bicuculline-induced seizures. These results are discussed in terms of their relevance to understanding the mechanisms that underlie the behavioral effects produced by injection of muscimol into the nigra.