The influence of focal ischemic brain injury on tail-flick latency in the rat

Tail-flick latency (TFL), a measure of response threshold to pain, was investigated in rats with focal ischemic brain injury resulting from middle cerebral artery occlusion (MCAO) as compared to sham and non-operative (non-op) groups on the 1st, 7th, 14th, 21st and 28th days following surgery or anesthesia. No significant differences were observed between MCAO and sham groups postoperatively, indicating focal ischemic insult induced by this model had no significant influence on TFL. Increased sensitivity to TFL in early postoperative period was shown when compared sham or MCAO with non-op group. The correlation between TFL and the time from surgery was statistically significant on the 1st and 7th days in sham group and the 1st, 7th and 14th days in MCAO group. We conclude that the focal ischemic injury resulting from middle cerebral artery occlusion that has no obvious neurologic effects does not alter pain threshold; however, surgical procedure increases postoperative sensitivity to pain stimulation.