Effects of cerebellectomy at day 15 on the ontogenesis of the equilibrium behavior in the rat

Young cerebellectomized and control (sham-operated) DA/HAN strained rats, 1 day to 1 month old, were submitted to an equilibrium test consisting for the animals in maintaining their equilibrium when placed on a horizontal mast rotating around its longitudinal axis at 10 or 20 rpm (slow and fast rotation rates, respectively). Cerebellectomized animals, operated when 15 days old, were either naive (tested at one given day) or trained; these last ones were trained before and after the operation, or only before, or only after, according to a slow or a fast rotation rate. Control rats were also either naive or trained in conditions similar to those given to operated animals. Relevant comparisons show that: (1) rats cerebellectomized at day 15 which have not been trained before the operation are unable to learn a given motor pattern. (2) When trained before the operation, the animals learn the motor patterns that they use to maintain their equilibrium upon the rotating mast as well as controls. (3) Postoperative training is inefficient in the acquisition of the equilibrium behavior whether the animals were trained preoperatively or not. (4) Compared to the slow rotation rate (10 rpm), theevolution of the equilibrium behavior in cerebellectomized rats is not altered when the rotation rate is increased to 20 rpm, that is when the task is more difficult. From these results it can be concluded that whatever the difficulty of the task the cerebellum is involved in the learning processes especially between the 10th and the 15th day, that is when the rat's cerebellum becomes mature and when due to growing of parallel fibers, Purkinje cells of the cerebellar cortex which were polyinnervated by climbing fibers become monoinnervated.