Hibernation, a model of neuroprotection

Hibernation, a natural model of tolerance to cerebral ischemia, represents a state of pronounced fluctuation in cerebral blood flow where no brain dam age occurs. Numerous neuroprotective aspects may contribute in concert to s uch tolerance. The purpose of this study was to determine whether hibernati ng brain tissue is tolerant to penetrating brain injury modeled by insertio n of microdialysis probes. Guide cannulae were surgically implanted in stri atum of Arctic ground squirrels before any of the animals began to hibernat e. Microdialysis probes were then inserted in some animals after they enter ed hibernation and in others while they remained euthermic. The brain tissu e from hibernating and euthermic animals was examined 3 days after implanta tion of microdialysis probes. Tissue response, indicated by examination of hematoxylin and eosin-stained tissue sections and immunocytochemical identi fication of activated microglia, astrocytes, and hemeoxygenase-1 immunoreac tivity, was dramatically attenuated around probe tracks in hibernating anim als com pared to euthermic controls. No difference in tissue response aroun d guide cannulae was observed between groups. Further study of the mechanis ms underlying neuroprotective aspects of hibernation may lead to novel ther apeutic strategies for stroke and traumatic brain injury.