Motor skills and learning in the rats: role of the ponto-cerebellar pathway

Many evidences support the role of the cerebellum (Cb) in motor learning and memory. Previous studies showed that olivary projections to the Cb are involved in motor learning. Since the pontine nuclei are the other main relay in the cerebro-cerebellar pathway, our purpose is to verify the involvement of the ponto-cerebellar projection in motor skills and spatial learning, by comparing sham-operated animals and rats with selective lesion of the inferior olivary complex (IOC) or middle cerebellar peduncle (mcp). Two groups of male Wistar rats were used: in order to destroy the IOC, the first group was treated with 3-acetylpiridine (3-AP) i. p. ; the second group received electrolytic lesions of the mcp, to interrupt the ponto-cerebellar pathway. Different groups of lesioned and sham-operated animals were then submitted to 3 tasks: unrotated-rod, rota rod at 20 r. p. m., and Morris water maze (MWM). When trained on the unrotated-rod, either 3-AP-treated or mcp lesioned rats showed at the beginning some static equilibrium deficiencies but, with training, they were able to reach the maximal scores attained by the controls. The rats submitted to the rota-rod at 20 r. p. m. obtained scores significantly lower than the controls. In fact, they were unable to improve their performance by training. Therefore, our results suggest that either the lesion of the IOC or the lesion of the mcp prevent learning of complex motor sequences. Finally, the animals were submitted to a MWM (spatial version) : the results indicate that both the lesion of the IOC and mcp alter learning of spatial tasks. These findings show that both the ponto- and the olivo-cerebellar pathways are involved in learning complex motor sequences and spatial tasks. Since both projections converge onto Purkinje cells, our data suggest that motor learning is supported in the cerebellum by anatomical re-arrangement of synaptic interactions of Purkinje cells with both climbing and parallel afferent fibers