Electrophysiological studies on the effects of opiates on dorsal horn nociceptive neurones at 51 atmospheres absolute.
The purpose of this study was to investigate the effects, if any, of high pressure on opiate analgesia. The interaction of high pressure with intrathecal morphine (2.5-15 micrograms) and pethidine (10-145 micrograms) was studied on the responses of 51 dorsal horn neurones in the intact rat under urethane anaesthesia to electrical stimulation applied to their receptive fields. Two types of response to the addition of the opiates were found. Cells were either rapidly and maximally inhibited by the lowest dose of morphine (2.5 micrograms) or pethidine (10 micrograms) or slowly inhibited in a dose-dependent manner with an ED50 of 13.6 nmol for morphine and 401 nmol for pethidine. Pressure did not significantly affect the time-response curves for these two types of response but did change the relative numbers of each type recorded. The number of cells totally inhibited by the lowest of drug concentrations was increased for morphine at pressure but decreased for pethidine.
HPNS Group, Division of Anaesthesia, Clinical Research Centre, Watford Road, Harrow, Middx HA1 3UJ U.K. Department of Pharmacology, University College London, Gower Street, London WC1E U.K.
Karen
K
Smallman
Anthony H
AH
Dickenson
Michael J
MJ
Halsey
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001274:Atmospheric Pressure; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D005260:Female; D007278:Injections, Spinal; D008614:Meperidine / Q000494:pharmacology*; D009020:Morphine / Q000494:pharmacology*; D009433:Neural Inhibition / Q000187:drug effects*; D009619:Nociceptors / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D013116:Spinal Cord / Q000187:drug effects / Q000503:physiopathology*
D009020:Morphine; D008614:Meperidine