Selective blockade by yohimbine of descending spinal inhibition from lateral reticular nucleus but not from locus coeruleus in rats

Abstract

The present study was undertaken to compare the effects of the α 2-adrenoceptor antagonist yohimbine on inhibition of C-fiber-evoked responses of dorsal horn neurons produced by electrical stimulation of the lateral reticular nucleus (LRN) and the Locus coeruleus (LC) in the rat. In the majority of neurons, C-fiber-evoked responses were significantly inhibited by 53.84±5.02% and 57.63±5.79% of control by LRN and LC stimulation, respectively, whereas in less than half of the neurons, A-fiber-evoked responses were reduced by 20.99±6.06% and 21.78±4.48% of control, respectively. After systemic or spinal administration of yohimbine, LC-induced inhibition of C-fiber-evoked responses was not affected. In contrast, LRN-induced inhibition was markedly attenuated by yohimbine. The results suggest that α 2-adrenoceptors may be involved in mediation of inhibition of spinal nociception induced by stimulation of LRN but not by LC.