Progressive impairment in motor skill learning at 12 and 20 weeks post 6-OHDA- SNc lesion in rats

Deficiency in skilled motor activity is primarily attributed to the loss of dopaminergic neurons in the pars compacta of substantia nigra (SNc), which can be detected by performance of the rotarod test. Previous reports have demonstrated impaired skilled motor behavior in rats during the pre-motor stage of Parkinson's disease (PD) (3-8 weeks post 6-OHDA lesion of striatum). We studied skilled motor learning in 6-hydroxydopamine (6-OHDA) SNc lesion rats at 12 and 20 weeks by rotarod task after providing sufficient training to give allowance for ageing (3 sessions/day for 14 consecutive days). On each day, the stay duration on rotarod was noted and compared between the groups (Group 1 = Control, Group 2 = Post lesion (PL) week 12, Group 3 = PL week 20). In Group 2 rats, the duration of stay on rotarod gradually increased from day 1 through 7 {day 7 = 193.1 (81.8-247.4) vs. control group day 7 = 202.1 (87.7-279.8), p = 0.771} and declined thereafter. While, the stay duration in Group 3 rats remained lower {day 7 = 32.5 (20.4-52.1), p = 0.011} than that of the control rats throughout the study period. The results of our study suggest a slower brief learning of skilled motor tasks at post lesion week 12 whereas no learning at all at post-lesion week 20.