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Epidural opioid analgesia in infant rats - I: mechanical and heat responses

Marsh, D; Dickenson, A; Hatch, D; Fitzgerald, M; (1999) Epidural opioid analgesia in infant rats - I: mechanical and heat responses. PAIN , 82 (1) 23 - 32.

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Abstract

The aim of this study was to investigate the analgesic effects of epidural opioids in neonatal rat pups. The contribution of individual opioid receptor subtypes in the spinal cord to analgesia at different developmental stages was investigated using epidural mu (morphine sulphate), delta (DPDPE) and kappa (U69593) opioid receptor agonists in neonatal rats aged postnatal day (P) 3, 10 and 21. Thresholds for flexion withdrawal reflexes to mechanical stimuli (von Frey hairs) and to noxious heating of the hind paw were low in neonates and increased with postnatal age. The analgesic action of each opioid receptor agonist followed an individual developmental pattern. In mechanical tests, all three opioid agonists were considerably more efficacious analgesics in younger animals and ED50s at P3 were always lower than at P21. In heat tests, the pattern differed. The efficacy of the kappa opioid agonist decreased with postnatal age, morphine efficacy increased over the same period and the effects of the delta agonist remained relatively unchanged. The distribution and concentration of tritiated morphine in the spinal cord following epidural administration did not alter significantly with postnatal age, suggesting that opioid access is not a major determinant of the effects reported here. It is concluded that whereas heat pain is particularly sensitive to spinal kappa opioids in neonates, mechanical sensory thresholds are generally sensitive to all spinal opioids in the newborn. The differing epidural opioid requirements compared to older subjects is likely to be due to developmental changes in spinal cord opioid receptor distribution or pharmacology. (C) 1999 International Association for the Study of Pain. Published by Elsevier Science B.V.

Type: Article
Title: Epidural opioid analgesia in infant rats - I: mechanical and heat responses
Keywords: paediatric pain, analgesia, development, opioid, epidural, spinal cord, OPIATE RECEPTOR SUBTYPES, SPINAL-CORD, NEONATAL RAT, DORSAL HORN, NEWBORN RAT, POSTNATAL-DEVELOPMENT, NOCICEPTIVE NEURONS, MORPHINE, STIMULATION, AGONISTS
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences > Div of Biosciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences > Div of Biosciences > Neuro, Physiology and Pharmacology
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Pop Health Sciences > UCL GOS Institute of Child Health
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Pop Health Sciences > UCL GOS Institute of Child Health > ICH Infect, Imm, Infla. and Physio Med
URI: http://discovery.ucl.ac.uk/id/eprint/186643
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