Changes within the basal nucleus in Parkinson's disease

The magnocellular nuclei in the basal forebrain--the medial septal nucleus, the nucleus of the diagonal band, and the basal nucleus within the substantia innominata--are tightly connected with each other. Large multipolar neurons clearly predominating in number can be differentiated from a spindle-shaped and a small globular type of neuron on account of their typical pattern of lipofuscin pigmentation. As an additional feature some of the multipolar neurons exhibit intracytoplasmic acidophilic granules. At the ultrastructural level, these granules reveal a homogeneous substructure, and they are occasionally located within mitochondria. The percentage of large multipolar neurons displaying acidophilic granules varies in a topographical manner (medial septal nucleus and vertical limb nucleus of the diagonal band: 10%, horizontal limb nucleus of the diagonal band and anteromedial subnucleus of the basal nucleus: 36%, posterolateral subnucleus of the basal nucleus: 54%). In parkinsonian cases a significant decrease of granule-bearing neurons within the posterolateral subnucleus of the basal nucleus is noted. This decrease might be associated with the appearance of neurons containing Lewy-bodies. It is also conceivable that the granule-bearing neurons show a higher vulnerability and underlie neuronal death. Analyzing the lipofuscin pigmentation within the two subnuclei of the basal nucleus in parkinsonian cases, one notices that the number of large multipolar neurons displaying pigment granules in a dendritic stem is significantly higher than in controls. Moreover, it is apparent that the degree of this pigment penetration is more pronounced in cases of Parkinson's disease. These alterations may be interpreted as a sign of plasticity of this neuronal population.