Persistent behavioral impairments and neuroinflammation following global ischemia in the rat

Cognitive deficits associated with cardiac arrest have been well documented; however, the corresponding deficits in animal models of global ischemia have not been comprehensively assessed, particularly after long-term, clinically relevant survival times. We exposed male Sprague-Dawley rats to 10 min of bilateral carotid artery occlusion + systemic hypotension (40-45 mmHg) or sham surgery, and used histopathological assessments for short-term survival animals (16 days) and both behavioral and histopathological assessments for long-term survival animals (270 days). Analyses revealed significant long-term deficits in ischemic animals' learning, memory (T-maze, radial arm maze), working memory (radial arm maze), and reference memory (Morris water maze, radial arm maze) abilities that were not associated with a general cognitive decline. Histological results showed significant increases in glial fibrillary acidic protein, neuron glia 2, OX-42 and ED-1 staining, as well as significant decreases in microtubule-associated protein 2 staining and cornu ammonis area 1 (CA1) cell counts 16 days post-ischemia. The pattern at 270 days was similar, but notably there was a persistent elevation of ED-1 staining, suggesting recent cell death as well as significant atrophy of CA1. Whereas previous work has primarily reported transient changes in behavior after global ischemia, this study describes disturbances in several different functional domains following CA1 cell loss at clinically relevant survival times. Moreover, the histopathological outcome is suggestive of a spontaneous repopulation of CA1, but this was not sufficient to offset the behavioral impairments arising from the ischemic insult.