Changes in cortical acetylcholine output induced by modulation of the nucleus basalis

The modulatory inputs of the cholinergic neurons of the nucleus basalis have been investigated in midpontine transected and freely moving rats by measuring acetylcholine release from the cerebral cortex using the cortical cup technique. Acetylcholine release was found to be the same in both groups of rats indicating similar levels of activity of the cholinergic neurons ascending to the cortex. The electrical stimulation of the nucleus basalis was always followed by an increase in acetylcholine release. Conversely, in some experiments only the stimulation of the midbrain reticular formation enhanced acetylcholine output. The stimulation of the nucleus accumbens prevented the increase in acetylcholine release elicited by amphetamine. The dose-dependent increase in acetylcholine output following IP administration of amphetamine was also prevented by the 6-hydroxydopamine induced degeneration of the dopaminergic fibres. However injection of apomorphine in the nucleus basalis did not modify acetylcholine output. Direct injection of the GABAergic agonist muscimol resulted in a decrease in acetylcholine output which was prevented by picrotoxin. In conclusion, the cholinergic neurons ascending to the cortex can be inhibited by GABA receptors located in the nucleus basalis and stimulated indirectly by dopaminergic fibres.