Inhibition of nociceptive responses of dorsal horn neurones in the cat spinal cord by ohmefentanyl, a preferring mu opioid receptor agonist [corrected].

An action of ohmefentanyl (OMF), a novel preferring mu opioid receptor agonist, on nociceptive response of the dorsal horn neurone, has been studied in the spinal cat. OMF (0.5-2 micrograms/kg, i.v.) produced a potent naloxone-reversible inhibition of firing of dorsal horn neurones in response to noxious heating of glabrous hindpaw or to impulses in C primary afferents. When ejected into the substantia gelatinosa, OMF produced a relatively selective inhibition of C response, but not A response to excitation of myelinated afferent fibres, of the dorsal horn neurone. An interaction between ohmefentanyl and mu opioid receptors is discussed.