Temporal profile of nerve growth factor-like immunoreactivity after transient focal cerebral ischemia in rats

We studied the temporal profile of nerve growth factor-like immunoreactivity (NGF-LI) in the rat brains following 30 min of middle cerebral artery occlusion. The rats were decapitated at 4 h, 1, 3, 7, and 14 days of recirculation. Brain sections at the level of striatum were immunostained against NGF as well as a stress protein, HSP70. Also, double immunostaining of NGF and glial fibrillary acidic protein was performed. In the sham-control rats, NGF-LI was normally present in the cortical and striatal neurons. However, at 4 h of recirculation, there was a significant decrease of NGF-LI in the ischemic cortex and striatum. From 1 day, NGF-LI was absent completely in the ischemic striatum. However, in the ischemic cortex, NGF-LI decreased to the lowest level at 1 day, but it recovered gradually from 3 days and increased significantly to above sham-control level at 7 days. At 14 days of recirculation, NGF-LI returned to a near sham-control level. In the non-ischemic cortex, NGF-LI increased gradually from 4 h with a peak at 7 days, and returned to the sham-control level at 14 days of recirculation. A HSP70 was induced in the ischemic cortex at 1 and 3 days, when there was a significant reduction of NGF-LI. The number of reactive astrocytes increased gradually and NGF-LI in the reactive astrocytes became gradually intense after ischemia. The present finding showing that NGF-LI can be recovered in the stressed cortical neurons suggests a possible involvement of NGF in the process of neuronal survival after focal cerebral ischemia. The expression of NGF in reactive astrocytes indicates that astrocyte may also play a role in supporting neuronal survival after ischemia.