Morphometric and dendritic analysis of fascia dentata granule cells in human aging and senile dementia

Abstract

In this study the cellular morphology in the human fascia dentata of 5 very old demented cases (4 Alzheimer's disease and 1 multi-infarct dementia patients) was compared with 5 (very) old control cases. The postmortem delay in fixation was for all cases within 3.5 h. In the demented group, a significant reduction in thickness of the molecular layer, density of dendritic spines in the middle third of the molecular layer and total dendritic length (±30%) was found. The number of dendritic segments, indicative of the branching frequency showed no difference. In both the control and the demented group, three-quarters of all dendritic bifurcations of granule cells occurred in the inner third of the molecular layer in which the commissural and associational fibers terminate. The size of the dendrites in the demented group could be the result of at least 3 independent processes: (a) a regressive change due to partial denervation of the outer two-thirds of the molecular layer as axons from the perforant pathway are lost; (b) a dendritic regrowth in response to sprouting of the commissural-associational fiber systems and septal afferents, which is presumed to occur in response to degeneration of perforant path axons; (c) a dendritic regrowth in response to the loss of the dendrites of neighboring cells which have died. Analysis of our material suggests that dendritic degeneration is the predominant factor in the demented group.