1.7. Distribution and cellular anatomy of BFC neurons
Basal forebrain cholinergic projection (BFC) neurons in the rat are dispersed across a number of classically defined territories of the basal forebrain, as illustrated from a series of coronal sections in * (Fig.1.7-1) However, using a manual reconstruction from camera lucida drawings (Fig.1.7-2) or computer graphic three-dimensional reconstruction technique (Fig.1.7-3.), it is evident that BFC neurons form a continuum, rather than being arranged as distinct nuclear groups.
Cholinergic cell bodies are multipolar, round-to-oval or fusiform; the 2-5 primary dendrites are long, rectilinear with sparse branching. The primary dendrites are smooth, however, secondary or tertiary dendrites often showed beaded appearance (Fig.1.7-4). The long dendrites form a continuum of overlapping dendritic fields (Fig.1.7-5). The dendritic organization of BFC neurons resemble that of the isodendritic type of neurons (Ramon-Moliner and Nauta, 1966) or the interstitial neurons characterized by Das and Kreutzberg (l968). Cholinergic neurons often form cluster consisting of 5-10 tightly packed cell bodies. The dendrites of such clusters seem to radiate to all directions in more ventral and medial parts of the horizontal limb of the diagonal band (HDB), however, they often form bundles in the more dorsal part of the substantia innominata (SI) in which the predominant orientation of the dendrites is in an oblique dorso-ventral direction ( Fig.1.7-5);( Fig.1.7-6A,B,CD).