The fate of Nissl-stained dark neurons following traumatic brain injury in rats: difference between neocortex and hippocampus regarding survival rate

We studied the fate of Nissl-stained dark neurons (N-DNs) following traumatic brain injury (TBI). N-DNs were investigated in the cerebral neo- cortex and the hippocampus using a rat lateral Xuid percussion injury model. Nissl stain, acid fuchsin stain and immunohistochemistry with phosphorylated extra- cellular signal-regulated protein kinase (pERK) anti- body were used in order to assess posttraumatic neurons. In the neocortex, the number of dead neurons at 24 h postinjury was signiWcantly less than that of the observed N-DNs in the earlier phase. Only a few N-DNs increased their pERK immunoreactivity. On the other hand, in the hippocampus the number of dead neurons was approximately the same number as that of the N-DNs, and most N-DNs showed an increased pERK immunoreactivity. These data suggest that not all N-DNs inevitably die especially in the neo- cortex after TBI. The fate of N-DNs is thus considered to diVer depending on brain subWelds.