Glia: novel counter-regulators of opioid analgesia.
Development of analgesic tolerance and withdrawal-induced pain enhancement present serious difficulties for the use of opioids for pain control. Although neuronal mechanisms to account for these phenomena have been sought for many decades, their bases remain unresolved. Within the past four years, a novel non-neuronal candidate has been uncovered that opposes acute opioid analgesia and contributes to development of opioid tolerance and tolerance-associated pain enhancement. This novel candidate is spinal cord glia. Glia are important contributors to the creation of enhanced pain states via the release of neuroexcitatory substances. New data suggest that glia also release neuroexcitatory substances in response to morphine, thereby opposing its effects. Controlling glial activation could therefore increase the clinical utility of analgesic drugs.
Watkins
Linda R
LR
Department of Psychology and the Center for Neuroscience, University of Colorado at Boulder, Boulder, CO 80309-0345, USA. linda.watkins@colorado.edu
Hutchinson
Mark R
MR
Johnston
Ian N
IN
Maier
Steven F
SF
D000701:Analgesics, Opioid / Q000008:administration & dosage*; D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism; D004361:Drug Tolerance; D006801:Humans; D009457:Neuroglia / Q000187:drug effects / Q000378:metabolism*; D018377:Neurotransmitter Agents / Q000378:metabolism*; D009619:Nociceptors / Q000187:drug effects / Q000378:metabolism; D010146:Pain / Q000378:metabolism* / Q000517:prevention & control*; D013116:Spinal Cord / Q000187:drug effects* / Q000378:metabolism*
D000701:Analgesics, Opioid; D018377:Neurotransmitter Agents