C-FOS EXPRESSION IN ISOLATED RAT SPINAL-CORD

Expression of c-Sos-immunoreactivity (c-fos-ir) has been demonstrated in the dorsal horn of lumbar segments of an isolated spinal cord prepa ration from 3 week old rats. The method of preparation generated a low level of c-fos-ir activity which was not significantly altered by low intensity (1.5 times threshold) dorsal root stimulation, but was sign ificantly increased by high intensity (20 times threshold) stimulation . Replacement of the calcium in the bathing medium by 2 mM manganese s uppressed all detectable c-fos-ir, whereas inclusion of 0.5 mu M capsa icin caused intense c-fos-ir expression in the absence of stimulation. The number of dorsal horn cells exhibiting c-fos-ir increased between 0.5 and 1 h after stimulation, reaching a maximum at 2 h, with no fur ther increase at longer intervals. Few positive cells were found when the incubation temperature was reduced from 27 to 20 degrees C. The st rongest increase in c-fos-ir was found in the dorsal horn ipsilateral to the stimulated dorsal root and a smaller, but significant, increase was also seen in the contralateral dorsal horn. Cords obtained from a nimals treated at 1 day old with capsaicin to destroy afferent C fibre s showed a reduction in the number of c-fos-ir positive cells induced by high intensity dorsal root stimulation. This preparation will aid d etailed investigation of the pharmacology of nociceptive pathways. (C) 1998 Elsevier Science B.V.