GABAergic control of the cholinergic projections to the frontal cortex is not tonic.

The turnover rate of acetylcholine was measured in the frontal cortex of rats after either microinjection of bicuculline into the substantia inominata (the source of the cortical cholinergic innervation) or kainic acid lesioning of the nucleus accumbens (the source of GABAergic innervation of the substantia inominata). Neither treatment affected cortical acetylcholine metabolism, suggesting that the GABAergic inhibition of the substantia inominata-cortical cholinergic pathway is not tonic.