19. A comparison of visceral and noxious somatic influences on neurons in rat nucleus raphe magnus

The activities of certain neurons in the spinal dorsal horn can be depressed by widespread noxious stimuli (Le Bars et al. 1979), A phenomenon usually referred to as ‘diffuse noxious inhibitory controls’ (d.n.i.c.). Similar effects have been demonstrated following distension of the urinary bladder or colon (Cadden, this meeting). D.n.i.c. are thought to be mediated by a pathway which relays in the medullary nucleus raphe magnus (n.r.m.) (Dickenson et al. 1980). The aims of the present study were to determine whether neurons in n.r.m. could be influenced by visceral and somatic stimuli that produce d.n.i.c., and whether any such neurons have spinally projecting axons.