Hemisynaptic distribution patterns of presenilins and β‐APP isoforms in the rodent cerebellum and hippocampus

Healthy brain neurons co-express Alzheimer's disease (AD) related proteins presenilins (PS) and β-amyloid precursor protein (β-APP). Deposition of β-amyloid and PS in the senile plaques of AD brain and their ability to interact in vitro suggest that AD pathology could arise from a defect in the physiological interactions between β-APP and PS within and/or between neurons. The present study compares the immunocytochemical distribution of PS (1 and 2) and β-APP major isoforms (695 and 751/770) in the synapses of the cerebellum and hippocampus of the adult rat and mouse. In the cerebellar cortex of both species, the four molecules are immunodetected in the presynaptic or the postsynaptic compartments of synapses, suggesting that they are involved in interneuronal relationships. In contrast, PS and β-APP are postsynaptic in almost all the immunoreactive synapses of the hippocampus. The different distribution patterns of these proteins in cerebellar and hippocampal synapses may reflect specific physiological differences, responsible for differential vulnerability of neurons to AD synaptic pathology. Defective interactions between β-APP and PS at the synapses could impede the synaptic functions of β-APP, inducing the selective loss of synapses that accounts for cognitive impairment in AD. Synapse 35:96–110, 2000. © 2000 Wiley-Liss, Inc.