MOTOR-SKILL LEARNING - CHANGES IN SYNAPTIC ORGANIZATION OF THE RAT CEREBELLAR CORTEX

Rats trained on motor-skill learning tasks for 30 days were previously found to have more synapses in the volume of tissue proportional to a Purkinje cell than rats that exercised or were inactive. In the motor learning tasks, hooded rats were required to traverse an obstacle cou rse requiring balance and coordination. Rats in two exercise groups we re required to walk rapidly or allowed to run in activity wheels. Cont rols were relatively inactive in standard housing and handled once dai ly. Synapses were classified to determine which synaptic types changed in number across levels of the molecular layer in the paramedian lobu le. The motor learning group had significantly more parallel fiber syn apses and climbing fiber synapses per unit Purkinje cell reference vol ume than all other groups. There were also more synapses and more para llel fiber synapses per reference volume in the outermost than in the innermost molecular layer. The plasticity reported here occurs in vivo under normal physiological conditions. Excitatory synapses account fo r at least 80% of the synapses in the molecular layer. The results sup port prior predictions that parallel fiber synapses are modifiable dur ing conditions of learning. (C) 1996 Academic Press, Inc.