Primary sensory neurones and naloxone-precipitated morphine withdrawal.
1. The C-fibre-evoked depressor reflex following i.a. injection of capsaicin and the wiping movements following chemical irritation of the cornea by capsaicin were both found to be augmented in the naloxone-precipitated morphine withdrawal phase. 2. The in vitro capsaicin-evoked release of substance P from central terminals of C-fibre afferents in the spinal cord was decreased in morphine-treated rats. Following naloxone, the release in the morphine-treated group was as large as in the control group. 3. The C-fibre mediated plasma extravasation in the rat paw after naloxone was found to be the same in morphine-treated and control rats. 4. It is concluded that C-fibre-evoked reflex reactions are augmented during morphine withdrawal, but that the mechanisms responsible are either located postsynaptically to the primary sensory neurone or further centrally.
Donnerer
J
J
Department of Experimental and Clinical Pharmacology, University of Graz, Austria.
D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002211:Capsaicin / Q000494:pharmacology; D005260:Female; D008297:Male; D009021:Morphine Dependence / Q000503:physiopathology*; D009270:Naloxone / Q000494:pharmacology*; D009412:Nerve Fibers / Q000187:drug effects*; D009475:Neurons, Afferent / Q000187:drug effects*; D051381:Rats; D011919:Rats, Inbred Strains; D012018:Reflex / Q000187:drug effects; D013373:Substance P / Q000494:pharmacology; D013375:Substance Withdrawal Syndrome / Q000503:physiopathology*; D013997:Time Factors
D013373:Substance P; D009270:Naloxone; D002211:Capsaicin