Anterograde vs. retrograde degeneration of the nucleus basalis medialis in Alzheimer's disease.

The evidence that degeneration in the basal forebrain cholinergic nuclei in Alzheimer's disease is a secondary phenomenon is reviewed. Experimental retrograde degeneration in these nuclei shares some common features with the degeneration actually observed in the disease, and can occur without direct damage to the cholinergic axons within the cortex. The neuroanatomical distribution of the pathological changes typical of Alzheimer's disease in the neocortex suggests a progression of the disease process, from the medial temporal cortex and amygdala out into the parieto-temporal association areas. Neurochemical evidence also points to the early and severe involvement of the amygdala in the disease. The close reciprocal relationship between the amygdala and the basal nucleus may underly the degeneration seen in the basal nucleus in Alzheimer's disease.