Effect of intrathecal co-administration of ketamine and L-NAME on formaldehydum-induced c-fos expression in the spinal dorsal horn in rats

Objective To observe the effect of intrathecal administration of L-NAME,a non-selective NOS inhibitor,on the suppression of formaldehydum-induced c-fos expression in the spinal dorsal horn in rats elicited by ketamine. Methods Twenty-four female Sprague-Dawley rats without signs of neurological deficiency after intrathecal cathetrization were randomly divided into 4 groups with 6 rats each. All animals received hypodermal injection of 5% formaldehydum 40 μl in the right foot 20 min following intrathecal administration of normal saline(group K0),ketamine 25 μg(group K1),ketamine 150 μg(group K2),and ketamine 25 μg + L-NAME 100 μg (group KL),respectively,which were all diluted into the volume of 10 μl with normal saline. Normal saline of similar volume was injected hypodermally in the right foot as the control in another 4 rats (group N). Their pain behaviors were observed,while the c-fos expression in the spinal dorsal horn was measured by immunohistochemical method. Results As compared to group K0,the total numbers of FIL neurons located in the ipsilateral spinal dorsal horn in group K1, K2 and KL decreased by 32.4%,48.5% and 39.1%,respectively. The numbers of FIL neurons in the laminae Ⅰ-Ⅱ and laminae Ⅴ-Ⅵ/Ⅹ of spinal dorsal horn in group K1 and group K2 were significantly lower than those in group K0 (P0.05). In the number of FIL neurons in the laminae Ⅴ-Ⅵ/Ⅹ of spinal dorsal horn,there appeared a significant more decrease in group KL than that in group K1(P0.05). Conclusions Intrathecal administration of ketamine could inhibit formaldehydum-induced c-fos expression in the spinal dorsal horn of rats in a dose-dependent manner,while co-administration of L-NAME selectively enhanced ketamine-elicited suppression of c-fos expression in the deeper laminae of the spinal dorsal horn.