title: Stimulus intensity and the comparative efficacy of mu- and kappa-opioid agonists on nociceptive spinal reflexes in the rat.
abstract: The influence of stimulus intensity was tested on the relative spinal efficacy of intravenously administered mu- (fentanyl) and kappa-opioid (U-50,488) agonists. Spinal reflexes were generated by different intensities of noxious electrical stimuli in alpha-chloralose anaesthetized, spinalized rats. Both drugs became less effective as the intensity of C-fibre generated responses was increased, but U-50,488 retained the ability to reduce responses to the same degree as fentanyl. The effects were naloxone reversible. The results indicate that kappa-opioid receptor activation has similar potential for spinal analgesia as does activation of mu-opioid receptors.
authors.affiliation: Department of Physiology, University of Bristol, School of Medical Sciences, University Walk, UK.
authors.forename: S A
authors.initials: SA
authors.lastname: Thorn
authors.forename: J F
authors.initials: JF
authors.lastname: Herrero
authors.forename: P M
authors.initials: PM
authors.lastname: Headley
mesh_terms: D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; D000818:Animals; D004558:Electric Stimulation; D005283:Fentanyl / Q000494:pharmacology; D008297:Male; D010146:Pain / Q000503:physiopathology*; D011759:Pyrrolidines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D017473:Receptors, Opioid, kappa / Q000819:agonists*; D017450:Receptors, Opioid, mu / Q000819:agonists*; D012018:Reflex / Q000187:drug effects*; D013116:Spinal Cord / Q000187:drug effects*
chemical_list: D011759:Pyrrolidines; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu; D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; D005283:Fentanyl