Three-dimensional representation and cortical projection topography of the nucleus basalis (Ch4) in the macaque: concurrent demonstration of choline acetyltransferase and retrograde transport with a stabilized tetramethylbenzidine method for horseradish peroxidase.

Ninety-six percent of the nucleus basalis neurons that project to the neocortex contain choline acetyltransferase. These projections from the cholinergic component of the nucleus basalis (Ch4) are topographically organized so that each cortical area receives most of its cholinergic input from a different Ch4 sector. The three-dimensional reconstruction of these sectors reveals the presence of a complex structure. A stabilization procedure that was used in these experiments maintains all the advantages of the tetramethylbenzidine method for horseradish peroxidase while eliminating the vulnerability of the reaction-product to high pH and dehydrating agents.