Opioid receptor subtypes in the rat spinal cord: electrophysiological studies with mu- and delta-opioid receptor agonists in the control of nociception.
We have compared the ability of selective mu- and delta-opiate agonists to modulate nociceptive transmission at the level of the rat dorsal horn using electrophysiological approaches. Single-unit extracellular recordings were made from neurones in the lumbar dorsal horn of the intact rat under halothane anaesthesia. Neurones could be activated by both A- and C-fibre electrical stimulation (and by natural innocuous and noxious stimuli). Agonists were applied directly onto the cord in a volume of 50 microliters. The intrathecal administration of 3 agonists, Tyr-D-Ala-Gly-MePhe-Gly-ol (DAGO) (mu-selective) (2 X 10(-3)-10 nmol) Tyr-D-Thr-Gly-Phe-Leu-Thr (DTLET) (mu/delta) (7 X 10(-4)-70 nmol), and cyclic Tyr-D-Pen-Gly-Phe-D-Pen (DPDPE) (delta) (2 X 10(-2)-100 nmol) produced dose-dependent inhibitions of C-fibre-evoked neuronal activity whilst A-fibre activity was relatively unchanged. DAGO produced near-maximal inhibitions which could be completely reversed by naloxone (1.5 nmol) whilst DPDPE causes less marked inhibitions which could only be partially reversed by naloxone (1.5-13.5 nmol). DTLET produced effects intermediate to those of DAGO and DPDPE. The results suggest that both mu- and delta-opioid receptors can modulate the transmission of nociceptive information in the rat spinal cord.
D000818:Animals; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D020881:Enkephalin, D-Penicillamine (2,5)-; D004745:Enkephalins; D008297:Male; D009842:Oligopeptides; D010146:Pain / Q000503:physiopathology*; D051381:Rats; D011919:Rats, Inbred Strains; D011957:Receptors, Opioid / Q000502:physiology*; D017465:Receptors, Opioid, delta; D017450:Receptors, Opioid, mu; D013116:Spinal Cord / Q000503:physiopathology*; D009435:Synaptic Transmission
D004745:Enkephalins; D009842:Oligopeptides; D011957:Receptors, Opioid; D017465:Receptors, Opioid, delta; D017450:Receptors, Opioid, mu; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; C037653:deltakephalin; D020881:Enkephalin, D-Penicillamine (2,5)-