Morphological characterization of cholinergic neurons in the horizontal limb of the diagonal band of Broca in the basal forebrain of the rat

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Abstract
A monoclonal antibody against choline acetyltransferase (ChAT), the acetylcholine synthesizing enzyme, was used to identify cholinergic neurons in the nucleus of the horizontal limb of the diagonal band of Broca at the light and electron microscopic levels. ChAT-labelled somata were fusiform, triangular or round in shape and varied considerably in size. Depending on the type of the cell, one to four dendrites emerged from the soma, but an axon could rarely be seen. The nuclei of most cells were round or oval, showed invaginations and displayed prominent nucleoli. The karyoplasm of the larger fusiform and triangular neurons contained abundant organelles including parallel arrays of granular endoplasmic reticulum. The synaptic input to labelled perikarya and proximal dendrites was sparse. It consisted chiefly of asymmetrical synaptic contacts, sometimes with postjunctional densities, but a few symmetrical synapses were also noted. ChAT-positive axon terminals were not identified which suggests that axon collaterals are rare within the nucleus of the horizontal limb of the diagonal band of Broca.