Loss of synapses in the cerebellar cortex of the senescent rat.

Numbers of synapses were compared in the cerebellar cortex of adult (12 months of age) and senescent (25 months of age) male rats of the Fisher-344 strain. The total number of axodendritic synapses was found to be 24% lower in the senescent rats as compared with adults. A differential analysis of synapses involving dendritic shafts and spines showed no significant change in numbers of synapses involving shafts, but a highly sigificant 33% decrease in numbers involving spines in senescent rats. These data suggest that the selective age-related loss of synapses involving dendritic spines (but not shafts) in the cerebellar cortex results from the impairment with advanced age of specific afferent neurons and/or a selective age-related vulnerability of dendritic spines.