Background:
Ischemic preconditioning can be protective against lethal forebrain ischemia. Ageing may increase ischemic susceptibility and reduce brain plasticity. Magnetic resonance diffusion tensor imaging (DTI) is known a sensitive method for detecting brain integrity and white matter architecture. The present study used DTI to investigate the influence of ageing on the protective effect of ischemic preconditioning.
Methods:
Adult (16-20 wk) and aged (51-55 wk) male Mongolian gerbils were subjected to nonlethal 5-min forebrain ischemia (ischemic preconditioning) or a sham operation, followed by 3 days of reperfusion, and then lethal 15-min forebrain ischemia. A 9.4-Tesla MR imaging system was used to study DTI indices, namely fractional anisotropy (FA), mean diffusivity (MD), and intervoxel coherence (IC), and in situ expression of microtubule-associated protein 2 (MAP2) and apoptosis were also examined in the hippocampal CA1 and dentate gyrus (DG) areas. 
Totally, 3 experimental groups in adult and aged gerbils were studied including the followings.
5-min ischemia group
5-min + 15-minute ischemia group
Sham + 15-minute ischemia group
Results:
Ischemic preconditioning for 5 min significantly reduced IC in the aged gerbils and MAP2 immunoreactivity in both the adult and aged gerbils compared with sham controls. Compared with sham controls, gerbils with ischemic preconditioning, particularly adults, exhibited less apoptosis in CA1 area and less ischemic injury, as represented by higher dendritic integrity in DTI (Figure 1) and preservation of MAP2 immunoreactivity (Figure 2) in both the hippocampal CA1 and DG areas.
Conclusion:
The present study suggested that ischemic preconditioning could protect ischemic neuron and recover neural fiber integrity in ischemia-vulnerable CA1 area and ischemia-resistant DG area. There was a temporal correlation between MAP2 and DTI with earlier reduction in MAP2. Ageing may diminish the effectiveness of ischemic preconditioning with injury in both dendrite and neuron.

AGEING MAY REDUCE THE PROTECTIVE EFFECT OF ISCHEMIC PRECONDITIONING AGAINST FOREBRAIN ISCHEMIA IN GERBILS— DIFFUSION TENSOR IMAGING AND HISTOPATHOLOGICAL STUDY