ABSTRACT
Previous studies have demonstrated that cortical spreading depression (CSD) increases the expression of putative neuroprotective proteins. The objective of the present study was to elucidate the relationship between the number of episodes of CSD and steady-state levels of mRNAs encoding brain-derived neurotrophic factor (BDNF), heat-shock protein-72 (hsp72) and c-fos. Wistar rats were administered one, five, or twenty-five episodes of CSD evoked by application of 2 M KCl to the frontal cortex of one hemisphere. Animals were permitted to recover for 30 min, 2 h or 24 h prior to sacrifice. Total RNA was isolated from the parietal cortex of each hemisphere and analyzed using Northern blots. At 30 min recovery, levels of BDNF mRNA were not significantly elevated after 1 episode of CSD, but were increased 4-fold after five episodes of CSD and 11-fold after twenty-five episodes of CSD, relative to levels in the contralateral hemisphere. At 2 h recovery, BDNF mRNA levels increased 2-, 3- and 9-fold, respectively. At 24 h, BDNF mRNA had returned to control levels in all groups. Thus, CSD increased levels of BDNF mRNA in a dose-dependent fashion at the early recovery times. Hsp72 mRNA was below the level of detection after 1 and 5 episodes of CSD. However, after twenty-five episodes of CSD, hsp72 mRNA levels were increased in the ipsilateral hemisphere at 30 min and 2 h recovery. Unlike levels of BDNF and hsp72 mRNA, levels of c-fos mRNA were increased nearly to the same extent at 30 min and 2 h after one, five or twenty-five episodes of CSD before returning to control by 24 h recovery. These results demonstrate that CSD triggers a dose-dependent increase in the expression of genes encoding neuroprotective proteins, which may mediate tolerance to ischemia induced by CSD.
Subject(s)
Brain-Derived Neurotrophic Factor/genetics , Cortical Spreading Depression/physiology , Heat-Shock Proteins/genetics , Animals , Blotting, Northern , Brain Chemistry/genetics , Brain Ischemia/physiopathology , Cerebrovascular Circulation/physiology , HSP72 Heat-Shock Proteins , Laser-Doppler Flowmetry , Male , Proto-Oncogene Proteins c-fos/genetics , RNA, Messenger/metabolism , Rats , Rats, Wistar , Time FactorsABSTRACT
Previous studies have demonstrated that cortical spreading depression (CSD) induces neuronal tolerance to a subsequent episode of ischemia. The objective of the present investigation was to determine whether CSD alters levels of mRNA coding for putative neuroprotective proteins. Unilateral CSD was evoked in male Wistar rats by applying 2 mol/L KCl over the frontal cortex for 2 hours. After recovery for 0, 2, or 24 hours, levels of several mRNA coding for neuroprotective proteins were measured bilaterally in parietal cortex using Northern blot analysis. Levels of c-fos mRNA and brain-derived neurotrophic factor (BDNF) mRNA were markedly elevated at 0 and 2 hours, but not 24 hours after CSD. Tissue plasminogen activator (tPA) mRNA levels were also significantly increased at 0 and 2 hours, but not 24 hours after CSD. Levels of the 72-kDa heat-shock protein (hsp72) mRNA were not significantly increased by CSD, except for a small elevation (20%) at 2 hours recovery. Levels of the 73-kDa heat-shock cognate (hsc73) mRNA were slightly, but significantly, increased at 2 and 24 hours of recovery. Finally, levels of mRNA for protease nexin-1 and glutamine synthetase were not significantly altered by CSD at any time studied. The current results support the hypothesis that neuronal tolerance to ischemia after CSD may be mediated by increased expression of FOS, BDNF, or tPA, but not by increased expression of hsp72, hsc73, nexin-1, or glutamine synthetase.
