EFFECTS OF LESION OF THE INFERIOR OLIVARY COMPLEX IN LEARNING OF THE EQUILIBRIUM BEHAVIOR IN THE YOUNG-RAT DURING ONTOGENY .1. TOTAL LESIONOF THE INFERIOR OLIVE BY 3-ACETYLPYRIDINE

Young DA/HAN strain rats were submitted to an equilibrium test consist ing in maintaining equilibrium upon a rotorod rotating at 10 or 20 rpm . They were either intact or lesioned, the lesion consisting in destru ction of the inferior olivary complex (IOC) by 50-95 mg/kg i.p. admini stration of 3-acetylpyridine (3-AP) at day 15, followed, 2 to 4 h late r, by i.p. injection of niacinamide (300 mg/kg). All the 3-AP-treated animals included in this study were completely lesioned, the extent of the lesion being estimated by both the response of the rats to harmal ine and histological controls at the end of the experiments. The IOC l esioned rats were either naive (tested at one given day) or trained ev ery day (10 trials per day); among the latters, some were trained befo re and after the lesion, the others being trained either before or onl y after. Control rats were submitted to the same training schedule. Bo th quantitative (time during which the animals maintained the equilibr ium upon the rotating rod) and behavioral data (strategy used by the a nimals to maintain equilibrium) were obtained. The results demonstrate that, compared to those of control rats, the quantitative and behavio ral scores of the IOC lesioned animals were altered. Comparison of nai ve and trained animals shows that the impairment of the equilibrium be havior is not only due to the ataxia provoked by the IOC lesion but is also due to cognitive deficits. However, prelesion training facilitat es the acquisition of a more efficient postlesion equilibrium behavior . From these results, it can be concluded that the olivo-cerebellar pa thway is involved in the adaptation of motor behavior to the environme ntal conditions.