Reactive synaptogenesis in aging and Alzheimer's disease: lessons learned in the Cotman laboratory.

Early experiments resulting in partial deafferentation of the rodent hippocampus demonstrated a robust reactive plasticity response that includes the replacement of lost synaptic contacts. Similar experiments carried out in the hippocampus of aged animals produced an alteration in the temporal sequence of the reactive plasticity response and a slowing of synaptic replacement. In Alzheimer's disease, one observes a marked reduction in the number of synaptic contacts in important association areas of the cortex and hippocampus. This reduction may be the result of an altered reactive plasticity response.