Abstract: Objective To explore the effect of exercise training on learning and memory ability in rats with focal cerebral ischemia, and to analyze the changes of brain tissue structure of rats after exercise training through diffusion tensor imaging (DTI). Methods Twenty-four SPF male Sprague-Dawley rats were randomly divided into sham operation group (n=8), natural recovery group (n=8) and exercise training group (n=8). The left middle cerebral artery occlusion (MCAO) model was established. The exercise training group received running wheel training 24 hours after modeling, for 14 days. All groups were tested by the Morris water maze 15 days after modeling. The latency in the navigation experiment, as well as the first latency, boundary swimming time ratio, the boundary swimming distance ratio, the average speed and the swimming path in the space exploration experiment were recorded. Four rats with similar Longa scores in each group received routine magnetic resonance imaging and DTI scanning, the fractional anisotropy (FA), axial diffusivity (λ‖), and radial diffusivity (λ⊥) of isch-emic cortex and hippocampal lesion and contralateral side were measured. Results In the navigation experiment, the latency of three groups showed a downward trend along with training days (P<0.05). The latency was longer in all the time points in the natural recovery group than in the sham operation group (P<0.05), and was longer in the first three days in the exercise training group than in the sham operation group (P<0.05), however, there was no significant difference between them in the last two days (P>0.05), while it was shorter in the exercise training group than in the natural recovery group in the same time (P<0.05). In the space exploration experiment, the latency, the boundary swimming time ratio and the boundary swimming distance ratio were more in the natural recovery group than in the sham operation group (Z> 2.627, P<0.01), and the latter two indexes were also higher in the natural recovery group than in the exercise training group (Z>2.521, P< 0.05). No significant difference was found in the average speed among three groups (P>0.05). The swimming paths in the exercise training group and the sham operation group were better than that of the natural recovery group. The FA and rFA in the left cortical area were higher in the sham operation group than in the exercise training group and the natural recovery group (P<0.05), however, no significant difference was found between the exercise training group and the natural recovery group (P>0.05). There was no significant difference in the FA in the right cortical area among three groups (F=0.532, P=0.607). The λ⊥, λ‖, rλ‖ and rλ⊥ in the left cortical area were lower in the sham operation group than in the natural recovery group (P<0.05), and no significant difference was found from the exercise training group to the natural recovery group, nor to the sham operation group (P>0.05). There was no significant difference in the λ⊥ and λ‖ in the right cortical area among three groups (F<1.030, P>0.05). There was no significant difference in the FA, λ⊥, λ‖ and rFA, rλ⊥ and rλ‖ in the bilateral hippocampal interest area among three groups (F<1.845, P>0.05). The rFA, rλ‖, rλ⊥ and left λ⊥ were correlated with the latency in the space exploration experiment in the Morris water maze test (P<0.05), in which the correlation coefficient of rλ⊥ was the highest (r=0.761, P<0.01). Conclusion Proper exercise training can improve the learning and memory ability of rats with focal cerebral ischemia, and can promote the repair of nerve fiber damage and reduce the vascular edema. In addition, the rFA, rλ‖, rλ⊥ and λ⊥ of ischemic cortex may be predictors of cognitive function recovery in rats after focal cerebral ischemia, especially rλ⊥.

Key words: focal cerebral ischemia, exercise training, learning and memory ability, diffusion tensor imaging