Environmental conditions modulate degeneration and new dendrite growth in cerebellum of senescent rats

Spiny branchlets of cerebellar Purkinje neurons, thought to be sites of synaptic efficacy change during motor learning, degenerate during aging. To examine effects of behavioral experience on degeneration, Purkinje neurons were studied in aging rats housed for 4.5 months either under complex environment conditions promoting sensory-motor activity or in pairs in standard cages. Their data were compared with those of a baseline group of rats from standard cages sacrificed at the age of onset of differential housing for the older groups. Rats housed in the complex environment had more spiny branchlets than the other groups, indicating that new branches had formed. There was a net loss of summed total spiny branchlet material per Purkinje cell in both the laboratory cage and complex environment older groups, although the complex environment group had more spiny branchlet per cell than the laboratory cage group. Thus, dendrite loss in the aging cerebellum can be partly offset by appropriate experience. There was no net loss of Purkinje cell main branch dendrite with aging, as indicated by previous studies, and there was no effect of differential housing upon main branches in the older groups. However, changes in the pattern of branching in the main dendritic field suggested that this region undergoes reorganization with aging.