Dynamic changes in CA1 dendritic spines associated with ischemic tolerance.

Hippocampal CA1 neurons are particularly vulnerable to 5-10 min durations of global ischemia. These cells can develop tolerance to ischemia through prior exposure to brief episodes of ischemia (ischemic preconditioning, IP). Dendritic spines are implicated in various forms of neuroplasticity including memory and recovery of function. Here we characterized the changes in hippocampal CA1 dendritic spines during the development of ischemic tolerance and the subsequent postischemic recovery period. Gerbils received 5 min, bilateral carotid artery occlusions preceded by two 1.5 min occlusions each of which were 24 h apart (tolerance groups). Spine densities were calculated from CA1 apical and basilar dendrites in tolerant animals that survived 3 (IP3), 10 (IP10) or 30 (IP30) days as well as sham-operated animals and those that received only the two preconditioning episodes (PO). Habituation to a novel open-field was assessed 3, 7, 10 and 30 days after ischemia to gauge CA1 functional integrity. Dendritic spines were quantified from Golgi-Cox stained sections of the CA1 subfield. IP10, IP30 and PO animals had significantly higher CA1 basilar and apical spine densities than all other groups. Tolerant animals initially displayed open-field habituation impairments at a time when spine densities were reduced. Behavioral impairments gradually subsided over time in coincidence with an increase in CA1 spine densities. These findings suggest that dendritic spines may play a role in recovery of function associated with ischemic tolerance and stroke.