LEARNING-DEPENDENT SYNAPTIC MODIFICATIONS IN THE CEREBELLAR CORTEX OFTHE ADULT-RAT PERSIST FOR AT LEAST 4 WEEKS

Several experiments have demonstrated increased synapse number within the cerebellar cortex in association with motor skill learning but not with motor activity alone. The persistence of these synaptic changes in the absence of continued training was examined in the present exper iment, Adult female rats were randomly allocated to either an acrobati c condition (AC) or a motor activity condition (MC). The AC animals we re trained to traverse a complex series of obstacles, and each AC anim al was pair-matched with an MC animal that traversed an obstacle-free runway. These animals were further assigned to one of three training c onditions. Animals in the EARLY condition were trained for IO consecut ive days before being killed, animals in the DELAY condition received the same 10 d of training followed by a 28 d period without training, and animals in the CONTINUOUS condition were trained for the entire 38 d. Unbiased stereological techniques were used to obtain estimates of the number of synapses per Purkinje cell within the cerebellar parame dian lobule. Results showed the AC animals to have significantly more synapses per Purkinje cell than the MC animals in all three training c onditions. There were no differences in the number of synapses per Pur kinje cell among the EARLY, DELAY, and CONTINUOUS conditions. These da ta demonstrate that both the motor skills and the increases in synapse number presumed to support them persist in the absence of continued t raining.