Immunocytochemical localization of enkephalin-like immunoreactivity in neurons of human hippocampal formation: effects of ageing and Alzheimer's disease.

The localization of neurons containing enkephalin-like immunoreactivity was studied within the human hippocampal formation. It was present in numerous dentate granule cells and a few larger neurons within the dentate molecular layer. In hippocampus proper, numerous pyramidal cells also demonstrated it, especially in field H1 of Rose (1926) and subiculum. No difference attributable to ageing or to dementia of the Alzheimer type was seen in this distribution. Post-mortem delay was the major factor affecting the intensity of its immunocytochemical localization to hippocampal cells and nonspecific background staining, due to binding of the secondary antiserum, increased directly with this. Some dendrites of dentate granule cells with immunoreactivity were found entering senile (neuritic) plaques in tissue from cases of Alzheimer's disease. These dendrites appeared morphologically normal.