Alteration in the pattern of nerve terminal protein immunoreactivity in the perforant pathway in Alzheimer's disease and in rats after entorhinal lesions.

Neurons in layer II of the entorhinal cortex consistently develop neurofibrillary tangles in Alzheimer's disease (AD). Experimental neuroanatomical studies have shown that these neurons give rise to the perforant pathway, a major excitatory projection to the hippocampal formation, which terminates in a discrete pattern in the outer portion of the molecular layer of the dentate gyrus. The distribution of two nerve terminal associated proteins, synaptophysin and NT75, was studied in the molecular layer of the dentate gyrus in AD and control cases to determine whether Alzheimer neuronal pathology is associated with loss of synaptic markers. In parallel studies, the effect of ablation of the entorhinal cortex in rats was evaluated. In AD as compared to controls, a decrease in synaptophysin immunostaining was evident in the terminal zone of the perforant pathway. NT75 nerve terminal immunostaining was too weak to interpret in the human hippocampal formation. Both synaptophysin and NT75 immunoreactivity were found in association with some neuritic plaques. In rats, entorhinal lesions resulted in diminished immunoreactivity for both synaptophysin and NT75 in the perforant pathway terminal zone. These results suggest that nerve terminal protein loss is a concomitant feature of neuronal pathology in AD.