Descending control of spinal nociceptive transmission. Actions produced on spinal multireceptive neurones from the nuclei locus coeruleus (LC) and raphe magnus (NRM)

Summary The effects of electrical stimulation in the nuclei locus coeruleus (LC) and raphe magnus (NRM) were examined on the background and/or evoked discharge of neurones in the spinal dorsal horn of anaesthetized cats. These were qualitatively, and in most cases quantitatively similar, in their action on multireceptive neurones. In these neurones an inhibitory action on the discharge evoked by noxious cutaneous stimuli or by activation of A and C fibres was most prominent although in some neurones (22%) an initial excitation lasting up to 100 ms preceded the inhibition which could last up to 1 s. Excitation alone was observed in only 3% of multireceptive neurones. Electrical stimulation also produced an inhibitory action on the discharge of low threshold mechanoreceptive neurones (80%). In four of ten multireceptive neurones examined in detail, LC stimulation produced a selective inhibitory action on the discharge evoked by noxious cutaneous stimuli. In the remaining six multireceptive neurones it was partially selective against noxious as compared with non-noxious inputs. The inhibitory action was also more pronounced on the discharge evoked by activity in A and C fibres than fast conducting afferents. The inhibitory action evoked by electrical stimulation in LC on nociceptive transmission in the spinal cord is suggested to play a part in mediating analgesia from LC.Abbreviation for Structures 6 Abducens nucleus - BC Brachium Conjunctivum - BP Brachium Pontis Dorsal Nucleus of Raphe - DRM Medial division - TD Dorsal Tegmental nucleus - 7L Facial Nucleus lateral division - 7M Facial Nucleus medial Division - V4 Fourth ventricle - 7G Genu of the Facial Nerve - IC Inferior Colliculus - SOL, SOM Lateral, Medial Nucleus of Superior Olive - BCM Marginal Nucleus of the Brachium conjunctivum - 5ME Mesencephalic trigeminal nucleus - 5M Motor Trigeminal Nucleus - LC Nucleus locus coeruleus - PH Nucleus praepositus hypoglossi - NRM Nucleus Raphe Magnus - P Pyramidal tract - PPR Postpyramidal Nucleus of the Raphe - SC Subcoeruleus - CS Superior Central Nucleus - TB trapezoid body