Time‐course of neuropeptide changes in peri‐ischemic zone and amygdala following focal ischemia in rats

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Abstract
Previously, using a middle cerebral artery occlusion model in Wistar rat, we showed autonomic disturbances similar to those seen clinically and observed striking neurochemical changes in cortical and subcortical sites at 5 days following stroke. The neurochemical changes may account for functional recovery and/or autonomic disturbances after focal ischemia. To understand the possible mechanisms and to facilitate future studies, it is necessary to define the time‐courses of these changes. Using immunohistochemical staining with the peroxidase‐antiperoxidase reaction, the changes in several neuropeptides over the peri‐ischemic region and the ipsilateral central and basolateral nucleus of the amygdala were investigated at different times after middle cerebral artery occlusion. In the experimental group, neuropeptide Y immunoreactivity appeared to increase by 6 hours in the peri‐ischemic region. Using image analysis to quantify the staining intensity, the change became statistically significant at 1 day, peaked around 3 days, and subsided at 10 days. There was a delayed increase in neuropeptide Y in the ipsilateral basolateral nucleus of the amygdala with a peak around 3 days. Immunoreactive staining for leucine‐enkephalin, dynorphin, and neurotensin demonstrated an increase that was localized to the ipsilateral central nucleus of the amygdala with a peak around 3 days and a return to baseline levels by 10 days. The results support a specific time‐course for each of the neuropeptides studied and indicate that a survival time of 3 days after focal ischemia is the critical period for examining the relationship between neuropeptide responses and neuronal or functional recovery.