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Exogenous melatonin abolishes mechanical allodynia but not thermal hyperalgesia in neuropathic pain. The role of the opioid system and benzodiazepine-gabaergic mechanism.

Journal of physiology and pharmacology : an official journal of the Polish Physiological Society
December 1, 2012
D Zurowski et al. (5 authors)
Journal ArticleAnimal Study
Extracted Claims (8)
InterventionDirectionEndpointPopulationDosageImpactClaim #
melatonin
increase
pain threshold of the mechanical allodynia
rats with CCI
-
caused the increase
#1
melatonin
increase
threshold of the thermal hyperalgesia
rats with CCI
-
caused the slight increase
#2
pre-treatment with naloxone
decrease
antinociceptive effects of melatonin
rats with CCI
-
completely abolished
#3
pre-treatment with naloxone
no change
thermal sensation
rats with CCI
-
did not abolish
#4
prazosin
no change
antinociceptive effect of melatonin
rats with CCI
-
did not have any effects
#5
administration of luzindole
decrease
antinociceptive effect of melatonin
rats with CCI
-
significantly suppressed
#6
flumazenil
decrease
antiallodynic effect of MT
rats with CCI
-
abolished
#7
picrotoxin
decrease
antiallodynic effect of MT
rats with CCI
-
abolished
#8
Abstract

Melatonin (MT) is a neurohormone synthesized and secreted by the pineal gland. MT plays an important role in the regulation of physiological and neuroendocrine functions. The purpose of this study was to assess the overall effect of melatonin on neuropathic pain, the type of melatonin receptor involved, and potential role of the opioid system and GABA(A) receptors. The experiments were conducted by using the animal neuropathic pain model (CCI). The rats with CCI showed the characteristic for the mechanical allodynia and thermal hyperalgesia signs that were calculated by using the von Frey's and Hargreaves' tests. The conducted studies measured the effects of intraperitoneal administration of naloxone (opioid antagonist), prazosin (MT3 antagonist), luzindole (MT1/MT2 receptor antagonist), picrotoxin (GABA(A) antagonist) and flumazenil (benzodiazepine antagonist) on the antinociceptive effects caused by melatonin. Melatonin caused the increase in the pain threshold of the mechanical allodynia and the slight increase in the threshold of the thermal hyperalgesia. The pre-treatment with naloxone completely abolished the antinociceptive effects of melatonin in von Frey's test, but not thermal sensation in the Hargreaves's test. Prazosin did not have any effects, while administration of luzindole significantly suppressed the antinociceptive effect of melatonin. The antiallodynic effect of MT was also abolished by flumazenil and picrotoxin. Melatonin influences the mechanical allodynia but not thermal hyperalgesia via activation of opioid system and benzodiazepine-GABAergic pathway. Antinociceptive effects of melatonin are mostly related to the MT1/MT2 receptors interaction.

Medical Subject Headings (MeSH)
AnalgesicsAnimalsBehavior, AnimalCarrier ProteinsDisease Models, AnimalGABA-A Receptor AntagonistsHot TemperatureHyperalgesiaMaleMelatoninNarcotic AntagonistsPain MeasurementPain PerceptionPain ThresholdPressureRatsRats, WistarReceptors, GABA-AReceptors, MelatoninReceptors, OpioidSciatic NeuropathySciaticaTime Factors
Study Links
PubMed ID23388480
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Exogenous melatonin abolishes mechanical allodynia but not t... | Panacea Index