Expression of sphingomyelin synthase 1 gene in rat brain focal ischemia.

Metabolites of the sphingomyelin cycle are reported to play an important role in neuronal death after ischemia. To elucidate the involvement of the key enzyme of this cycle, sphingomyelin synthase (SMS), in the mechanism underlying cerebral ischemia, we, for the first time, investigated changes in the mRNA expression of the SMS1 gene in rats after focal cerebral ischemia. According to our histological analysis, the damaged area is localized only in the ipsilateral cortex. In the ischemic cortex, the level of SMS1 transcripts was decreased at 3 and 24 h after occlusion, and at 72 h it had returned to the control level. A reduced level of SMS1 mRNA expression in the subcortex of rats with occlusion and sham-operated animals also was appeared during the first 24 h after surgery. This could be attributed to the effect of surgical stress. Seventy-two hours after occlusion, SMS1 mRNA expression in subcortex of ischemic rats was still at a decreased level; this may be considered to be a somewhat distant extended effect. Our results show the early response of the SMS1 gene that can be induced by both ischemia and stress. The results also suggest that inhibition of SMS1 mRNA expression may contribute to ceramide accumulation in a damaged cortex.