Objective To observe the effect of electroacupuncture(EA)on cytotoxic activity of splenic natural killer(NK)cells after surgical trauma via extracellular signal-regulated kinase(ERK)5pathway in the rats' hypothalamus

so as to explore its mechanism underlying improving immune disorders after surgery.Methods Sprague-Dawley rats were randomly divided into the following 6groups:control

trauma model

EA

sham EA

4nmol-BIX 02188(an inhibitor for ERK 5catalytic activity)and 20nmol-BIX 02188(n=6rats per group).The surgical trauma model was established by making a longitudinal incision(6cm in length)along the median line of the back to expose the spinal column and another longitudinal incision along the abdominal median line.EA(2Hz/15 Hz

1-2mA)was applied to bilateral"Zusanli"(ST 36)for 30 min immediately after surgery.For rats of the BIX groups

intra-lateral ventricular microinjection of BIX 02188(10μL

4nmol or 20 nmol

or saline for control rats)was conducted 30 min before the surgery.The expression level and protein of phosphorylated ERK 5(p-ERK 5)and corticotropin-releasing factor(CRF)protein were measured by immunohistochemistry and Western blot

respectively.The cytotoxicity of splenic NK cells and the expression of splenic Perforin and Granzyme-B genes were measured by lactate dehydrogenase(LDH)release assay and real-time PCR

respectively.Results In comparison with the control group

hypothalamic p-ERK 5immunoactivity

p-ERK5 protein and CRF protein expression levels were significantly up-regulated in the model group(P<0.01

P<0.05)

while splenic NK cell cytotoxicity and Perforin mRNA and Granzyme-B mRNA expression levels were notably down-regulated in the model group(P<0.05

P<0.01).Following EA and administration of ERK 5antagonist

the increased expression levels of p-ERK 5immunoactivity in the EA group

and p-ERK 5and CRF proteins in both EA and 20nmol-BIX 02188 groups were obviously down-regulated(P<0.05

P<0.01)

without changes in the sham EA and 4nmol-BIX 02188groups(P>0.05)except the increased p-ERK 5protein in the 4nmol-BIX 02188 group.In addition

the down-regulated NK cell activity

Perforin mRNA and Granzyme-B mRNA expression levels were significantly reversed in the EA and 20nmol-BIX 02188groups(P<0.05

P<0.01).No significant differences were found between the EA group and 20nmol-BIX 02188 group in down-regulating hypothalamic p-ERK 5and CRF protein expression and up-regulating splenic NK cytotoxicity and Perforin and Granzyme-B gene expression(P>0.05).Conclusion EA can promote the cytotoxicity of splenic NK cells in surgical trauma rats

which may be closely associated with its functions in down-regulating trauma-induced activation of ERK 5pathway and production of CRF in the hypothalamus.