- Email: [email protected]
Deafferentation pain: Does intravenous morphine influence dorsal horn neuronal spontaneous hyperactivity?
DEAFFERENTATION DORSAL HORN
PAIN: DOES INTRAVENOUS MORPHINE INFLUENCE NEURONAL SPONTANEOUS HYPERACTIVITY? M
Lombard and J. M. Hesson. and INSERM
Ecole
Pratique
des Ha&es
Etude
(U161), 2, rue d’Al&ia 75014, PARIS, FRANCE. investioation: To study in the rat, after section
of brachial Aim of dorsal roots. the action of morohine on dorsal horn soontaneous hvoer,. activity which may be responsible for the self-mutilatioh and scratching behaviours observed in such animals. Methods: 28 rats underwent dorsal rhizotomy (C5-Thl). 11 to 41 deys later they were prepared for acute experiments. Unit recordings were performed at C7 level in 24 spinal unanaesthetized decerebrate rats and in 4 anaethetized intact rats where the neurones were characterized as non specific nociceptive on the basis of their reactivity to DNIC. Results: All the rats developed scratching and/or self(n=20) mutilation (n=lO) behaviours. None of the 28 selected cells, mainly located in lamina V, could be driven by peripheral ipsilateral stimulation but all of them displayed high frequency spontaneous bursting activity and/or paroxysmal long lasting discharges. Morphine 2mg/kg I.V. had little effect on this hyperactivity. The spontaneous firing rate was moderately decreased in 6 and briefly increased in 5 of the 28 neurones. Additionnal cumulative doses (6mg/kg total) enhanced the depressive effect for 3 of the 6 already slightly depressed neurones and depressed 5 of 17 others. In most cases naloxone (0.6mg/kg) reversed the depression. In contrsst, the hyperactivity was strongly reduced after low doses of thiopental or clonazepam. Conclusions: These weak effects of morphine are consistent with the fact that dorsal rhizotomy induces a dramatic decrease of opioid receptors in the dorsal horn, they could be due to a postsynaptic site of action of the drug. These findings tend to suggest that morphine is not a very effective analgesic for the relief of deafferentation pain. Ascending pain pathways CELLSOF ORIGIN OF THE SPINOTRALAMIC PATHWAYS IN THE PRIMATE. A.V. Aokarian*, R.T. Stevens*, M.W. Jones*, and C.J. Hodge, II Department of Neurosugery, SUNYHealth Science Center, Syracuse, NY 13210, USA. Recent experiments have demonstrated two distinct spinothalamic pathways A dorsolateral spinothalaaic tract (DSTT) comprised of lamina (STT) in cat. I cell axons travels in the contralateral dorsolateral funiculus (DLP), and a ventral spinothalamic tract (VSTT) comprised of axons of cells located in laminae IV-VIII crosses and ascends in the ventral quadrant (VQ). This study examines whether a similar segregation of the STT exists in primates. Injections of WSA-HRPwere made in the somatosensory thalamus of squirrel ronkeys, and in some animals, ipsilateral thoracic spinal cord lesions were made prior to the injections to block HRP transport through the DLP or the and the tissue VQ. After a 5 day survival the aniaals were sacrificed processed for HRP histochemistry. Retrogradely labeled neurons were mapped from the first cervical to the caudal segments of the spinal cord. In animals with no spinal lesions: labeled cells in Cl-C2 were found in contralateral laaina I and larinae V-VIII bilaterally, labeled cells in the cervical enlargement were found mainly in contralateral laminae I and V, labeled cells in the thoracic cord were found in contralateral laminae I, V, and VII-VIII, labeled cells in the lumbar enlargement were found in contralateral larinae I, IV-VIII, label in the caudal segments was bilateral and located in lanina VII. In monkeys with a thoracic DLF lesion label in the luwbar enlargement was limited to cells in lawinae V-VIII. In aonkeys with a thoracic VQ lesion label in the lumbar enlargment was limited to cells in laainae I and V. The cells of origin of the spinothalamic tract in the squirrel monkey vary considerably between the cervical, thoracic, lumbar and caudal segments of the spinal cord. DSTT and VSTT are present in the squirrel monkey suggesting their existence in higher primates.
PAIN: DOES INTRAVENOUS MORPHINE INFLUENCE NEURONAL SPONTANEOUS HYPERACTIVITY? M
Lombard and J. M. Hesson. and INSERM
Ecole
Pratique
des Ha&es
Etude
(U161), 2, rue d’Al&ia 75014, PARIS, FRANCE. investioation: To study in the rat, after section
of brachial Aim of dorsal roots. the action of morohine on dorsal horn soontaneous hvoer,. activity which may be responsible for the self-mutilatioh and scratching behaviours observed in such animals. Methods: 28 rats underwent dorsal rhizotomy (C5-Thl). 11 to 41 deys later they were prepared for acute experiments. Unit recordings were performed at C7 level in 24 spinal unanaesthetized decerebrate rats and in 4 anaethetized intact rats where the neurones were characterized as non specific nociceptive on the basis of their reactivity to DNIC. Results: All the rats developed scratching and/or self(n=20) mutilation (n=lO) behaviours. None of the 28 selected cells, mainly located in lamina V, could be driven by peripheral ipsilateral stimulation but all of them displayed high frequency spontaneous bursting activity and/or paroxysmal long lasting discharges. Morphine 2mg/kg I.V. had little effect on this hyperactivity. The spontaneous firing rate was moderately decreased in 6 and briefly increased in 5 of the 28 neurones. Additionnal cumulative doses (6mg/kg total) enhanced the depressive effect for 3 of the 6 already slightly depressed neurones and depressed 5 of 17 others. In most cases naloxone (0.6mg/kg) reversed the depression. In contrsst, the hyperactivity was strongly reduced after low doses of thiopental or clonazepam. Conclusions: These weak effects of morphine are consistent with the fact that dorsal rhizotomy induces a dramatic decrease of opioid receptors in the dorsal horn, they could be due to a postsynaptic site of action of the drug. These findings tend to suggest that morphine is not a very effective analgesic for the relief of deafferentation pain. Ascending pain pathways CELLSOF ORIGIN OF THE SPINOTRALAMIC PATHWAYS IN THE PRIMATE. A.V. Aokarian*, R.T. Stevens*, M.W. Jones*, and C.J. Hodge, II Department of Neurosugery, SUNYHealth Science Center, Syracuse, NY 13210, USA. Recent experiments have demonstrated two distinct spinothalamic pathways A dorsolateral spinothalaaic tract (DSTT) comprised of lamina (STT) in cat. I cell axons travels in the contralateral dorsolateral funiculus (DLP), and a ventral spinothalamic tract (VSTT) comprised of axons of cells located in laminae IV-VIII crosses and ascends in the ventral quadrant (VQ). This study examines whether a similar segregation of the STT exists in primates. Injections of WSA-HRPwere made in the somatosensory thalamus of squirrel ronkeys, and in some animals, ipsilateral thoracic spinal cord lesions were made prior to the injections to block HRP transport through the DLP or the and the tissue VQ. After a 5 day survival the aniaals were sacrificed processed for HRP histochemistry. Retrogradely labeled neurons were mapped from the first cervical to the caudal segments of the spinal cord. In animals with no spinal lesions: labeled cells in Cl-C2 were found in contralateral laaina I and larinae V-VIII bilaterally, labeled cells in the cervical enlargement were found mainly in contralateral laminae I and V, labeled cells in the thoracic cord were found in contralateral laminae I, V, and VII-VIII, labeled cells in the lumbar enlargement were found in contralateral larinae I, IV-VIII, label in the caudal segments was bilateral and located in lanina VII. In monkeys with a thoracic DLF lesion label in the luwbar enlargement was limited to cells in lawinae V-VIII. In aonkeys with a thoracic VQ lesion label in the lumbar enlargment was limited to cells in laainae I and V. The cells of origin of the spinothalamic tract in the squirrel monkey vary considerably between the cervical, thoracic, lumbar and caudal segments of the spinal cord. DSTT and VSTT are present in the squirrel monkey suggesting their existence in higher primates.