DENDRITIC REORGANIZATION IN THE BASAL FOREBRAIN UNDER DEGENERATIVE CONDITIONS AND ITS DEFECTS IN ALZHEIMERS-DISEASE .1. DENDRITIC ORGANIZATION OF THE NORMAL HUMAN BASAL FOREBRAIN

In the present study, the dendritic organisation of neurones in the no rmal human basal forebrain was analysed as a prerequisite for the eval uation of pathological changes occurring in Alzheimer's disease and re lated conditions (see other Arendt et al. papers in this issue). Neuro nes in the basal nucleus of Meynert (NbM), the nucleus of the vertical limb of the diagonal band, and the medial septal nucleus were examine d after Golgi impregnation. Cells were classified according to the den dritic branching pattern and soma shape as either reticular neurones o r multipolar giant neurones. The reticular type of neurones constitute s more than 90% of neurones in the NbM. Cholinergic neurones also belo ng to this cell type. Reticular neurones were further subdivided into four subtypes. Morphological features and arrangement of reticular bas al forebrain neurones were identical to those described for ''reticula r formation cells'' or ''isodendritic'' neurones. Dendritic trees of r eticular neurones show a spatial orientation perpendicular to passing fibres as well as a high degree of overlap, both of which are hallmark s of ''open nuclei.'' The qualitative classification of Golgi-impregna ted basal forebrain neurones was substantiated by a computer-based thr ee-dimensional analysis. Topologic and metric parameters of the dendri tic tree were calculated for each type of neurone to characterise the degree of dendritic branching, the shape and orientation of the dendri tic arborisation, the spatial extension of the dendritic tree, and som a size. The classification criteria were evaluated according to their power of discrimination between different cell types by means of a dis criminant analysis. The quantitative approach applied in the present s tudy not only provides an objective measure for the description and co mparison of the structure of various types of neurones but also makes it possible to elucidate fine structural changes that might occur unde r pathologic conditions and that are not evident during qualitative st udies alone. (C) 1995 Wiley-Liss, Inc.