Effect Of General Anesthetics On The Anxiety-like Behavior In Acute Inflammatory Pain And The Activation Of ERK1/2in Anterior Cingulate Cortex

Objective:The present study was aimed to use the formalin acute inflammatory pain model to observe the different influence of anesthetics including sevoflurane, propofol and pentobarbital on pain-related anxiety-like behavior and the expression of extracellular signal-regulated kinase (ERK1/2) in anterior cingulate cortex.Methods:Adolescent male Sprague-Dawley rats (4-6weeks old, weighting15-200g) was divided to5groups (n=12) randomly. In the naive control group (group C), no experimental procedure were performed; in formalin group (group F), rats were received1%formalin right intra-plantar injection; and in group S, group B or group P, formalin hind paw injection was performed under the anesthesia with sevolurane (Group S), propofol (Group B) or pentobarbital (Group P) maintaining for1h, respectively. Anxiety-like behavior and depression-like behavior was determined by open field test, elevated plus maze test and sucrose consumption preference experiment at24h and72h post-formalin injection. Immunohistochemistry was applied to examine the expression of p-ERK in ACC at1h and24h after formalin injection.Result:Formalin intra-plantar injection caused a biphasic nociceptive response as described previously. The paw withdrawal threshold (PWT) was decreased at3h and6h after formalin injection (P<0.05) as compared to baseline or control group. The decreased PWT was returned to the baseline24h after formalin injection. Formalin acute inflammatory pain can induce anxiety-like behaviors at24h (P<0.05) post-formalin injection and would last to72h (P<0.05), concomitant with the increased expression of ERK1/2in ACC. At1hour post-injection when the animals was still under anesthesia, the expression of p-ERK in the ACC was dramatically lower in the groups S, B and P than that in the control group. At24h post-formalin injection, the expression of p-ERK was still low in group S whereas the expression of p-ERK in groups B and P was highly expressed.Conclusion:The present study suggested that inhaled anesthetics, but not intravenous anesthetics may inhibit the development of pain-related anxiety through inhibiting ERK1/2activation in ACC. Administration of inhaled anesthetics intra-operatively may be an ideal anesthetic to reduce postoperative anxiety in clinical practice.