Intracerebroventricular morphine restores the basic somesthetic activity of dorsal horn convergent neurones in the rat.

We have proposed that a painful focus will disturb the global activity of spinal and trigeminal convergent neurones in two complementary ways: by activation of the corresponding segmental pool of neurones and by an inhibition mediated by diffuse noxious inhibitory controls of the remaining neuronal population. Morphine (10 micrograms) administered within the third ventricle blocks diffuse noxious inhibitory controls acting on a basic somesthetic activity simulated by responses of convergent neurones to innocuous stimuli. It is proposed that analgesia induced by intracerebroventricular morphine could result, at least in part, from restoration of the basic somesthetic activity.