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Effects of opioid receptor and alpha2-adrenoceptor agonists on slow ventral root potentials and on capsaicin and formalin tests in neonatal rats.
Brain Res Dev Brain Res. 2005 Aug 08; 158(1-2):50-8.BR

Abstract

The inhibitory effects of morphine and alpha2-adrenoceptor agonists on slow ventral root potentials (slow VRP) following ipsilateral dorsal root stimulation in neonatal rat spinal cord were compared with the analgesic effects of these drugs on formalin and capsaicin tests in neonatal rats. Morphine, (D-Phe2, D-Pen5)-enkephalin (DPDPE), dexmedetomidine, clonidine and xylazine showed concentration-related inhibition of slow VRP. The order of potency was dexmedetomidine>morphine=DPDPE>clonidine>xylazine. The inhibitory effects of opioid agonists and alpha2-adrenoceptor agonists were abolished by naloxone, an opioid antagonist, and atipamezole, an alpha2-adrenoceptor antagonist, respectively. There was no cross antagonism. Morphine, dexmedetomidine and xylazine dose-dependently inhibited body movement induced by formalin or capsaicin. The order of potency was dexmedetomidine>morphine>xylazine. Although morphine and dexmedetomidine inhibited formalin- and capsaicin-induced body movement in the same dose range, xylazine inhibited formalin-induced body movement at lower concentrations than capsaicin-induced one. The inhibitory potency for slow VRP by these drugs seems to be correlated with that for capsaicin-induced body movement but not that for formalin-induced one. Dexmedetomidine and morphine in combination inhibited slow VRP and body movement induced by capsaicin in an additive manner. It is suggested that the antinociceptive effects of dexmedetomidine and morphine but not xylazine on the capsaicin test are mainly due to spinal effects and that there is no synergistic interaction between dexmedetomidine and morphine in the neonatal rat.

Authors+Show Affiliations

Laboratory of Pharmacology, Graduate School of Veterinary Medicine, Hokkaido University, Kita 18, Nishi 9, Sapporo 060-0818, Japan.No affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Comparative Study
Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

16023221

Citation

Otsuguro, Ken-ichi, et al. "Effects of Opioid Receptor and Alpha2-adrenoceptor Agonists On Slow Ventral Root Potentials and On Capsaicin and Formalin Tests in Neonatal Rats." Brain Research. Developmental Brain Research, vol. 158, no. 1-2, 2005, pp. 50-8.
Otsuguro K, Yasutake S, Ohta T, et al. Effects of opioid receptor and alpha2-adrenoceptor agonists on slow ventral root potentials and on capsaicin and formalin tests in neonatal rats. Brain Res Dev Brain Res. 2005;158(1-2):50-8.
Otsuguro, K., Yasutake, S., Ohta, T., & Ito, S. (2005). Effects of opioid receptor and alpha2-adrenoceptor agonists on slow ventral root potentials and on capsaicin and formalin tests in neonatal rats. Brain Research. Developmental Brain Research, 158(1-2), 50-8.
Otsuguro K, et al. Effects of Opioid Receptor and Alpha2-adrenoceptor Agonists On Slow Ventral Root Potentials and On Capsaicin and Formalin Tests in Neonatal Rats. Brain Res Dev Brain Res. 2005 Aug 8;158(1-2):50-8. PubMed PMID: 16023221.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Effects of opioid receptor and alpha2-adrenoceptor agonists on slow ventral root potentials and on capsaicin and formalin tests in neonatal rats. AU - Otsuguro,Ken-ichi, AU - Yasutake,Sumiko, AU - Ohta,Toshio, AU - Ito,Shigeo, PY - 2004/12/11/received PY - 2005/05/30/revised PY - 2005/06/01/accepted PY - 2005/7/19/pubmed PY - 2005/10/28/medline PY - 2005/7/19/entrez SP - 50 EP - 8 JF - Brain research. Developmental brain research JO - Brain Res. Dev. Brain Res. VL - 158 IS - 1-2 N2 - The inhibitory effects of morphine and alpha2-adrenoceptor agonists on slow ventral root potentials (slow VRP) following ipsilateral dorsal root stimulation in neonatal rat spinal cord were compared with the analgesic effects of these drugs on formalin and capsaicin tests in neonatal rats. Morphine, (D-Phe2, D-Pen5)-enkephalin (DPDPE), dexmedetomidine, clonidine and xylazine showed concentration-related inhibition of slow VRP. The order of potency was dexmedetomidine>morphine=DPDPE>clonidine>xylazine. The inhibitory effects of opioid agonists and alpha2-adrenoceptor agonists were abolished by naloxone, an opioid antagonist, and atipamezole, an alpha2-adrenoceptor antagonist, respectively. There was no cross antagonism. Morphine, dexmedetomidine and xylazine dose-dependently inhibited body movement induced by formalin or capsaicin. The order of potency was dexmedetomidine>morphine>xylazine. Although morphine and dexmedetomidine inhibited formalin- and capsaicin-induced body movement in the same dose range, xylazine inhibited formalin-induced body movement at lower concentrations than capsaicin-induced one. The inhibitory potency for slow VRP by these drugs seems to be correlated with that for capsaicin-induced body movement but not that for formalin-induced one. Dexmedetomidine and morphine in combination inhibited slow VRP and body movement induced by capsaicin in an additive manner. It is suggested that the antinociceptive effects of dexmedetomidine and morphine but not xylazine on the capsaicin test are mainly due to spinal effects and that there is no synergistic interaction between dexmedetomidine and morphine in the neonatal rat. SN - 0165-3806 UR - https://www.unboundmedicine.com/medline/citation/16023221/Effects_of_opioid_receptor_and_alpha2_adrenoceptor_agonists_on_slow_ventral_root_potentials_and_on_capsaicin_and_formalin_tests_in_neonatal_rats_ L2 - https://linkinghub.elsevier.com/retrieve/pii/S0165-3806(05)00170-7 DB - PRIME DP - Unbound Medicine ER -