Inhibitory effects of intrathecally administered interleukin-1β on carrageenan-induced hyperalgesia and spinal c-Fos expression in rats

The present study investigated the effects of interleukin-1beta (IL-1beta) injected intrathecally (i.t.) on carrageenan-induced thermal hyperalgesia and spinal c-Fos expression. The paw withdrawal latency (PWL) by the thermal stimulus was taken as an index of the thermal hyperalgesia of rats. I.t. injection of 10 ng IL-1beta significantly increased the PWL of the carrageenan-injected paw. Expression of c-Fos induced by intraplantar (i.pl.) injection of carrageenan was examined in the spinal cord with immunohistochemical methods. Three hours after i.pl. injection of carrageenan, the number of c-Fos-like immunoreactive (c-Fos-LI) neurons was significantly increased in laminae I-II, III-IV and V-VI of the ipsilateral spinal cord at L4-5 with the higher density in laminae I-II and V-VI. I.t. pre-injected IL-1beta significantly decreased the number of carrageenan-induced c-Fos-LI neurons in laminae I-II in the ipsilateral spinal cord and also inhibited the hyperalgesia induced by i.pl. carrageenan. These results suggested that i.t. injection of IL-1beta suppressed the central nociceptive input into laminae I-II and produced an antinociceptive effect. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.