Compensatory synapse growth in aged animals after neuronal death.

The capacity of neurons to grow new synapses following partial denervation has been studied in the brain of aged rats and compared to that of younger animals. Lesion induced synapse formation is reduced in aged rats in the hippocampus and septum, two brain areas which show particularly robust growth responses in younger animals. The rate of growth as well as the final magnitude of the response is diminished in aged animals. A possible mechanism for the decreased growth response in aged animals is discussed in light of current models of reactive synaptogenesis. The loss of a compensatory growth response in the aged animal may be one of the factors which contribute to decreased brain plasticity and the slower and poorer recovery from brain damage following injury.