[Diffuse noxious inhibitory controls: theoretical aspects applied to the effects of regional administration of...

Assuming a relatively high background activity of convergent neurons, we have suggested that their pain-signalling message could consist in the contrast between the high rate of firing in the segmental neuronal pool induced by the painful focus and the D.N.I.C.-mediated silence of the remaining neuronal population. This notion is substantiated by several observations in the rat regarding morphine analgesia: a clear lifting of D.N.I.C. is observed following systemic (0.1-1 mg/kg; i.v.), intraventricular (0.6-2.5 micrograms) or intrathecal (15 micrograms) morphine. All these procedures could restore the initial level of background activity, analgesia resulting from the attenuation of the postulated contrast.