Growing evidence from in vitro studies supports that valproic acid (VPA), an anti-convulsant and mood-stabilizing drug, has neuroprotective effects. The present study investigated whether VPA reduces brain damage and improves functional outcome in a transient focal cerebral ischemia model of rats. Subcutaneous injection of VPA (300 mg/kg) immediately after ischemia followed by repeated injections every 12 h, was found to markedly decrease infarct size and reduce ischemiainduced neurological deficit scores measured at 24 and 48 h after ischemic onset. VPA treatment also suppressed ischemia-induced neuronal caspase-3 activation in the cerebral cortex. VPA treatments resulted in a time-dependent increase in acetylated histone H3 levels in the cortex and striatum of both ipsilateral and contralateral brain hemispheres of middle cerebral artery occlusion (MCAO) rats, as well as in these brain areas of normal, non-surgical rats, supporting the in vitro finding that VPA is a histone deacetylase (HDAC) inhibitor. Similarly, heat shock protein 70 (HSP70) levels were timedependently up-regulated by VPA in the cortex and striatum of both ipsilateral and contralateral sides of MCAO rats and in these brain areas of normal rats. Altogether, our results demonstrate that VPA is neuroprotective in the cerebral ischemia model and suggest that the protection mechanisms may involve HDAC inhibition and HSP induction. Keywords: acetylated histone 3, cerebral ischemia, heat shock protein 70, neuroprotection, rat, valproic acid. (De Sarno et al. 2002). In rat cortical neurons, long-term VPA treatment blocks glutamate-induced excitotoxicity (Hashimoto et al. 2002) and prolongs life span of these cortical cultures (Jeong et al. 2003). Similar to the effect of another mood stabilizing drug, lithium, VPA protects mature rat cerebellar granule cells in cultures from NMDA receptor-mediated excitotoxicity and this action is mimicked by other histone HDAC inhibitors such as butyrate and trichostatin A (Kanai et al. 2002). A growing body of reports also demonstrate that VPA is neuroprotective against a variety of other insults (Mark et al. 1995;Mora et al. 1999;Bown et al. 2000;Wang et al. 2003).Stroke is one of the leading causes of mortality and morbidity world-wide. Although our knowledge concerning the molecular and cellular pathophysiology of brain injury after focal ischemia has advanced greatly, the development of new treatment drugs for acute ischemic stroke has not progressed as rapidly. The use of intravenous recombinant Abbreviations used: HDAC, histone deacetylase; HSP70, heat shock protein 70; GSK-3b, glycogen synthase kinase-3b; MCAO, middle cerebral artery occlusion; rt-PA, recombinant tissue-type plasminogen activator; TTC, 2,3,5-triphenyltetrazolium chloride; VPA, valproic acid.

In the healthy adult brain, neurogenesis normally occurs in the subventricular zone (SVZ) and hippocampal dentate gyrus (DG). Cerebral ischemia enhances neurogenesis in neurogenic and non‐neurogenic regions of the ischemic brain of adult rodents. This study demonstrated that post‐insult treatment with a histone deacetylase inhibitor, sodium butyrate (SB), stimulated the incorporation of bromo‐2′‐deoxyuridine (BrdU) in the SVZ, DG, striatum, and frontal cortex in the ischemic brain of rats subjected to permanent cerebral ischemia. SB treatment also increased the number of cells expressing polysialic acid–neural cell adhesion molecule, nestin, glial fibrillary acidic protein, phospho‐cAMP response element‐binding protein (CREB), and brain‐derived neurotrophic factor (BDNF) in various brain regions after cerebral ischemia. Furthermore, extensive co‐localization of BrdU and polysialic acid–neural cell adhesion molecule was observed in multiple regions after ischemia, and SB treatment up‐regulated protein levels of BDNF, phospho‐CREB, and glial fibrillary acidic protein. Intraventricular injection of K252a, a tyrosine kinase B receptor antagonist, markedly reduced SB‐induced cell proliferation detected by BrdU and Ki67 in the ipsilateral SVZ, DG, and other brain regions, blocked SB‐induced nestin expression and CREB activation, and attenuated the long‐lasting behavioral benefits of SB. Together, these results suggest that histone deacetylase inhibitor‐induced cell proliferation, migration and differentiation require BDNF–tyrosine kinase B signaling and may contribute to long‐term beneficial effects of SB after ischemic injury.

Valproic acid (VPA), a histone deacetylase (HDAC) inhibitor, is known to protect against cerebral ischemia. The effects of VPA on blood-brain barrier (BBB) disruption were investigated in rats subjected to transient middle cerebral artery occlusion (MCAO). Postischemic VPA treatment remarkably attenuated MCAO-induced BBB disruption and brain edema. Meanwhile, VPA significantly reduced MCAO-induced elevation of matrix metalloproteinase-9 (MMP-9), degradation of tight junction proteins, and nuclear translocation of nuclear factor-jB (NF-jB). Sodium butyrate, another HDAC inhibitor, mimicked these effects of VPA. Our findings suggest that BBB protection by VPA involves HDAC inhibition-mediated suppression of NF-jB activation, MMP-9 induction, and tight junction degradation.