A peripheral, intracerebral, or intrathecal administration of an opioid receptor antagonist blocks illness-induced hyperalgesia in the rat.
We used the tail-flick response of rats to study the role of opioid receptors in illness-induced hyperalgesia. An intraperitoneal injection of lithium chloride (LiCl) produced hyperalgesia that was blocked in a dose-dependent manner by subcutaneous injection of the opioid antagonist naloxone. Neither hyperalgesia nor its blockade by naloxone were due to variations in tail-skin temperature induced by LiCl. Hyperalgesia was also blocked when opioid receptor antagonism was restricted to (a) the periphery, by intraperitoneal administration of the quaternary opioid receptor antagonist naloxone methiodide; (b) the brain, by intracerebroventricular microinjection of naloxone; or (c) the spinal cord, by intrathecal microinjection of naloxone. These results document a pain facilitatory role of opioid receptors in both the peripheral and central nervous systems and are discussed with reference to their analgesic and motivational functions.
McNally
G P
GP
School of Psychology, University of New South Wales, Sydney, Australia. g.mcnally@unsw.edu.au
Johnston
I N
IN
Westbrook
R F
RF
D000818:Animals; D001921:Brain / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D007276:Injections, Intraventricular; D007278:Injections, Spinal; D007279:Injections, Subcutaneous; D018021:Lithium Chloride / Q000633:toxicity*; D008297:Male; D009270:Naloxone / Q000031:analogs & derivatives* / Q000494:pharmacology*; D017288:Pain Threshold / Q000187:drug effects*; D010525:Peripheral Nerves / Q000187:drug effects*; D000644:Quaternary Ammonium Compounds; D051381:Rats; D017208:Rats, Wistar; D011957:Receptors, Opioid / Q000187:drug effects*; D013116:Spinal Cord / Q000187:drug effects*
D000644:Quaternary Ammonium Compounds; D011957:Receptors, Opioid; D009270:Naloxone; C041269:N-methylnaloxone; D018021:Lithium Chloride