GABAergic and opioid regulation of the substantia nigra innominata-cortical cholinergic pathway in the rat.

The decrease in cortical acetylcholine turnover (TRACh) observed after parenteral GABA agonists is also replicated by local drug injections into the cholinergic cell body region, the substantia innominata. The decrement in cortical TRACh induced by opiates and opioid peptides is not replicated by local drug injections into the substantia innominata. These data indicate that the cholinergic cell bodies of the substantia innominata receive a direct inhibitory GABAergic input while opioid regulatory influences are not at the level of the cell bodies of these cholinergic neurons.