Effects Of Acupuncture Preconditioning On NO Distribution And C-fos Expression In Spinal Cord Of Adult And Aged Rats With Formalin-induced Pain

ObjectiveTo compare the difference of the response to Inflammatory pain of adult and aged rats,and the effects of acupuncture preconditioning(AP)on Nitric oxide(NO)distribution and c-fos expression in the spinal cord of adult and aged rats with formalin injection.MethodsThe 4 and 21 months old male Dawley Sprague(SD)rats were randomly divided into control group(CTL,with nothing treated),formalin-injection-only group(For),formalin injection following AP at the acupoint ST36 group(ST36+For),and formalin injection following AP at a non-acupoint group(NA+For),respectively.Six rats in each group.After acupuncture treatment,all rats were injected with formalin to the same side of acupuncture site except the control groups.To observe the behavioral responses of rats,and record the flinching number and licking time(sec)in 1 hour after formalin injection.The segment of 4th lumbar spinal cord to 5th lumbar spinal cord were obtained 1.5 hours after formalin injected.The distribution of Nitric oxide(NO)and the Fos-immunoreactive(Fos-ir)neurons were detected with enzymehistochemical and immunohistochemical techniques.Results1.In control groups: the number of NO were low and lower than adult rats in aged ones(P < 0.01);the basic level of Fos-ir positive neurons were low and there is no difference in adult and aged rats(P > 0.05);there are no double labeled neurons of NO and Fos in adult and aged rats.2.In formalin-injection-only groups: the flinching number in the late phase were higher in aged rats than in adult ones(P < 0.05);compared to control groups,marked increase of NO positive neurons,Fos positive neurons and double labeled neurons of NO and Fos were observed in the spinal cord of both adult and aged rats(P < 0.01).The number of NO positive neurons(P < 0.05,dorsal horn;P < 0.01,central canal)and Fos positive neurons(P < 0.01)were higher in aged rats than in adult ones.3.In formalin injection following AP at the acupoint ST36 groups: the flinching number(P < 0.01)and licking time(adult,P < 0.05;aged,P < 0.01)in the late phase of adult and aged rats were lower than formalin-injection-only groups;the number of NO positive neurons,Fos positive neurons and double labeled neurons of NO and Fos in adult and aged rats were both lower than formalin-injection-only groups(P < 0.01).Compared to formalin-injection-only groups,the range of decline of the number of NO positive neurons and Fos positive neurons were higher in aged rats than in adult ones(P < 0.01).4.In formalin injection following AP at a non-acupoint groups: there is no difference in flinching number,licking time,the number of NO positive neurons,Fos positive neurons and double labeled neurons of NO and Fos compared to formalin-injection-only groups in both adult and aged rats(P > 0.05).ConclusionsThe response to Inflammatory pain was elevated in aged rats compared to adult ones.Further,AP at the acupoint ST36 can improve the pain threshold,relieve the pain reaction,and reduce the number of NO and the expression of c-fos in spinal cord which with more potential in aged rats.