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Brain stem anti-nociceptive areas are activated via a spinal-raphe-spinal positive feed-back loop
s222 BRAIN STEM CONTROL OF SPINAL NOCICEPTIVE TRiW34ISSION: AN INTRACELLULAR mazms OF SYNAPTIC MECHANISMS. S.S. Mokha+ ~ ;;f ‘;?$ and A. Iggo, Department of Veterinary Physiology, R.D.S.V.S. Vashon University of Edinburgh, EH9 lQH, U.K. Previous work from our laboratory has shown that the nuclei locus coeruleus (LC) and raphe magnus (NRM) exert a predominantly inhibitory action on nociceptive transmission in the spinal cord. The present investigation examined synaptic mechanisms mediating descending control from the brain-stem (e.g. LC, NRM, pontine and medullary reticular formation) on neurones located in the superficial and deeper laminae of the dorsal horn. Experiments were performed on paralysed cats under chloralose anaesthesia. Concentric bipolar stainless steel electrodes were used for stimula-
tion in the brain-stem. Glass microelectrodes filled with 3M Kc1 or 2M Potassium Acetate were employed for intracellular recordings in the lumbar dorsal horn. Stimuli in Ix:that produced an inhibitory action on the discharge of multireceptive neurones also evoked DRPs on both the ipsi- and contralateral side. Hyperpolarisation was produced from LC only in some multireceptive neurones. Pontine and medullary reticular nuclei produced long lasting hyperpolarisation on multireceptive neurones located in the superficial and medullary reticular dorsal horn. Brain-stem (LC, raphe nuclei,pontine formation) stimulation did not affect the discharge of neurones in the superficial dorsal horn that in addition to receiving excitatory inputs were inhibited by thermal stimuli. LOW threshold mechanoreceptive neurones having wide receptive fields received powerful excitation from LC. There was a predominance of depolarisation produced from LC in the ventral horn but sometimes a sequence of hyperpolarisation-depolarisation was also observed. The results indicate the widespread actions of brain-stim nuclei in the dorsal horn which are mediated via pre- and post-synaptic mechanisms. t Present address: National Institute for Medical Research, The Ridgeway, Mill Hill, London, NW7 1AA.
BRAIN STEM ANTI-NOCICEPTIVE AREAS ARE ACTIVATED VIA Al SPINAL-RAPHE-SPINALPOSITIYE FEED-BACK LOOP. F.Cervero and the late J.H. Wolstencroft .Department of Physiology, Edinburgh University1 and Department of Physiology, Aim of investigation:Nucleus raphe magnus (NRM) and the adjacent areas of the reticular formation (RF) have been implicated in mechanisms of pain modulation as their stimulation results in behavioural analgesia and inhibition of nociceptive neurones in the spinal cord. Ascending projections from the spinal cord to NRM and BF were studied in order to examine the kinds of peripheral input that may influence the activity of neurones projecting to these brain stem areas. Methods: Electrical activity was recorded from neurones in L6 and L7 segments of the spinal cord of decerebrate cats. An array of nine electrodes was placed in the brain stem to stimulate NPM and the adjacent RF. Stimulating electrodes were also placed in the four quadrants of the cervical spinal cord to locate projection pathways. Results: Spinal cord neurones driven from NRM and the RF were located in E VII/VIII of the grey matter and were all excited by noxious stimulation of deep tissues in the ipsilateral and/or contralateral hindlimb. Fifty percent had long ascending axons, most of which projected to NPM, the RF or both. Pathways of projection were located in the ipsilateral ventrolateral quadrant of the cord. All neurones studied were excited by electrical stimulation of NRM, the RF or most commonly, of both. Stimulation of Lamina VIII was shown to excite cells in NRM and the RF. Conclusions: There is a population of neurones in or around Lamina VIII of the cord that project to NRM and the RF and receive an excitatory drive from the same areas. This system could act as a positivefeed-back loop to produce descending inhibition onto other sensory pathways in the spinal cord.
tion in the brain-stem. Glass microelectrodes filled with 3M Kc1 or 2M Potassium Acetate were employed for intracellular recordings in the lumbar dorsal horn. Stimuli in Ix:that produced an inhibitory action on the discharge of multireceptive neurones also evoked DRPs on both the ipsi- and contralateral side. Hyperpolarisation was produced from LC only in some multireceptive neurones. Pontine and medullary reticular nuclei produced long lasting hyperpolarisation on multireceptive neurones located in the superficial and medullary reticular dorsal horn. Brain-stem (LC, raphe nuclei,pontine formation) stimulation did not affect the discharge of neurones in the superficial dorsal horn that in addition to receiving excitatory inputs were inhibited by thermal stimuli. LOW threshold mechanoreceptive neurones having wide receptive fields received powerful excitation from LC. There was a predominance of depolarisation produced from LC in the ventral horn but sometimes a sequence of hyperpolarisation-depolarisation was also observed. The results indicate the widespread actions of brain-stim nuclei in the dorsal horn which are mediated via pre- and post-synaptic mechanisms. t Present address: National Institute for Medical Research, The Ridgeway, Mill Hill, London, NW7 1AA.
BRAIN STEM ANTI-NOCICEPTIVE AREAS ARE ACTIVATED VIA Al SPINAL-RAPHE-SPINALPOSITIYE FEED-BACK LOOP. F.Cervero and the late J.H. Wolstencroft .Department of Physiology, Edinburgh University1 and Department of Physiology, Aim of investigation:Nucleus raphe magnus (NRM) and the adjacent areas of the reticular formation (RF) have been implicated in mechanisms of pain modulation as their stimulation results in behavioural analgesia and inhibition of nociceptive neurones in the spinal cord. Ascending projections from the spinal cord to NRM and BF were studied in order to examine the kinds of peripheral input that may influence the activity of neurones projecting to these brain stem areas. Methods: Electrical activity was recorded from neurones in L6 and L7 segments of the spinal cord of decerebrate cats. An array of nine electrodes was placed in the brain stem to stimulate NPM and the adjacent RF. Stimulating electrodes were also placed in the four quadrants of the cervical spinal cord to locate projection pathways. Results: Spinal cord neurones driven from NRM and the RF were located in E VII/VIII of the grey matter and were all excited by noxious stimulation of deep tissues in the ipsilateral and/or contralateral hindlimb. Fifty percent had long ascending axons, most of which projected to NPM, the RF or both. Pathways of projection were located in the ipsilateral ventrolateral quadrant of the cord. All neurones studied were excited by electrical stimulation of NRM, the RF or most commonly, of both. Stimulation of Lamina VIII was shown to excite cells in NRM and the RF. Conclusions: There is a population of neurones in or around Lamina VIII of the cord that project to NRM and the RF and receive an excitatory drive from the same areas. This system could act as a positivefeed-back loop to produce descending inhibition onto other sensory pathways in the spinal cord.