Pharmacological evaluation of GABAergic and glutamatergic inputs to the nucleus basalis--cortical and the septal-hippocampal cholinergic projections.

The presence of different receptor populations within a given brain area can be effectively evaluated via the local injections of defined receptor agonists and antagonists. Using this approach, it has become evident that the nucleus basalis - cortical cholinergic pathway possesses an inhibitory GABAergic input to the nucleus basalis from the nucleus accumbens as well as a positive glutamatergic feedback from the cortex. The septal-hippocampal cholinergic pathway also possesses an inhibitory GABAergic regulation which consists of a large GABAergic interneuron population in the septum. A glutamatergic feedback from the hippocampus is also present. These regulatory inputs to cholinergic cells are not tonically active but appear to function as phasic modulators of cholinergic transmission in both pathways.