Induction of ischaemic tolerance in gerbil hippocampus by pretreatment with focal ischaemia.

We investigated the induction of ischaemic tolerance in the hippocampal CA1 neurones to transient forebrain ischaemia following pretreatment with unilateral middle cerebral artery occlusion (MCAO) in gerbils. Histological evaluation was carried out after 5 min bilateral carotid artery occlusion (5BCO) in the gerbils with no MCAO pretreatment, MCAO pretreatment 3 days prior to 5BCO (MCAO-3d-5BCO), MCAO pretreatment 7 days prior to 5BCO and sham MCAO pretreatment 3 days prior to 5BCO. CA1 neurones were preserved at > 40% of normal controls only in the left hippocampus in the MCAO-3d-5BCO gerbils. CA1 neurones in the right side of MCAO-3d-5BCO gerbils as well as in both sides of animals in the other pretreatment groups almost completely disappeared after 5BCO. While the exact mechanism remains to be resolved, pretreatment with focal ischaemia seems to induce ischaemic tolerance in neurones outside of the primary ischaemic lesion.