Changes Of Motor Coordination, Spatial Learning And Memory Abilities In Mice By Intragastric Administration Of Rotenone

Parkinson’s disease (PD) is a prevalent neurodegenerative disease. Until recently, PD is considered to affect not only substantia nigra-striatum dopaminergic system, but also the peripheral nervous system and other nuclei of the central nervous system. A high rate as84%in cognitive decline was reported in PD patients.The cause of PD is largely unknown up to now. Although genetic and environmental factors all contribute to its etiology, more than90%of PD patients are sporadic. There is growing evidence that environmental toxicants, such as pesticides, are associated with an increased risk of PD. Rotenone, which is commonly used as a liposoluble insecticide, is widely believed to be a high-affinity, specific inhibitor of mitochondrial complex I. It is widely used in copying the pathological changes of PD by inducing energy repletion of dopaminergic neurons in the substantia nigra. Rotenone-induced PD model seems to replicate almost all of the hallmarks of PD including alpha-synuclein aggregation, Lewy body formation and nigral dopaminergic neurons loss.Since most of the researches are concentrated on the substantia nigra-striatum dopaminergic system in rotenone-intoxicated PD model, the changes of spatial learning and memory ability have not yet been reported. In the present study, we aim to observe the changes of cognitive function in PD, as well as the underlying mechanisms. Intragastrical delivery of rotenone was administered to one-year old C57BL/6mice for1or3months. Using immunofluorescent and Thioflavine T staining, we observed the number of the nigral dopaminergic neurons and alpha-synuclein inclusions in dopaminergic neurons. Then, we evaluated the changes of motor coordination by rotarod test. Spatial learning and memory abilities were evaluated by Morris water maze task. Proliferating cell nuclear antigen and doublecortin antibodies were applied to detect hippocampal neurogenesis by double immunofluorescent staining. The results were as follows:1. The number of dopaminergic neurons reduced24%(P<0.05) in the substantia nigra of3-month-treated mice, compared with the vehicle group, whereas the number of dopaminergic neurons did not change in1-month-treated mice. Alpha-synuclein aggregation was observed in3-month-treated mice, despite the absence of obvious alpha-synuclein aggregation in the substantia nigra dopaminergic neurons of1-month-treated mice. 2. The residence time of mouse on rotarod treadmills was35%shorter in mice with rotenone administration for3months (P<0.05). There were no variations observed in1-month-rotenone-treated group compared with the vehicle group.3. The latency to escape on the hidden platform reduced in mice with rotenone administration for3months compared with the corresponding vehicle group (P<0.05). Although there was a tendency of the latency to escape to be delayed in mice with rotenone administration for1month, no significant difference was observed compared with the corresponding vehicle group.4. In rotenone-intoxicated mice for3months, we observed times of platform crossings and relative time in the training quadrant ameliorated144%and33.4%(P<0.05), respectively, nonetheless, average proximity and relative time in the opposite quadrant declined16.0%and34.5%(P<0.05), respectively, on the fifth day. There was no variations in the other parameters of the probe trial, for instance, average speed and time to destination. However, time to destination, average proximity, and relative time spent in the opposite quadrant reduced54.9%,22.2%and37.3%(P<0.05), respectively on the seventh day, whereas relative time spent in the training quadrant improved41.4%(P<0.05). These data suggested that intragastrical administration of rotenone for3months enhanced spatial memory ability in mice.5. No changes were detected in1-month-treated group in any of the parameters (average speed, time to destination, average proximity, times of platform crossings, relative time in the training and opposite quadrant) of the probe session on the fifth day. Average proximity elevated19.8%(P<0.05), nevertheless, relative time spent in the training quadrant decreased26.4%(P<0.05) on the seventh day. This indicated a deficit of spatial memory ability in rotenone-intoxicated-mice for1month.6. We labeled proliferating cell nuclear antigen positive cells and doublecortin positive cells in hippocampus by double immunofluorescent staining. Nevertheless, no obvious difference was observed in the hippocampus between the vehicle and rotenone-treated groups, indicating the lack of neurogenesis in this region.These results suggest that chronic intragastrically administration of rotenone for3months could successfully replicate classical features of PD in mice, which could be indicated by the reduced number of dopaminergic neurons, alpha-synuclein inclusions in the dopaminergic neurons of the substantia nigra, and the impairment of motor coordination mice. Interestingly, this study for the first time reports that both spatial learning and memory abilities are improved in mice with intragastrical rotenone treatment for3months, however, space memory ability was disturbed in rotenone-intoxicated mice for1month. There seems no evidence for hippocampal neurogenesis in rotenone-intoxicated mice. The underlying mechanism remains to be further discussed. This study provides a reliable experimental evidence for disturbance of learning and memory abilities in PD.