Changes in brain and spinal tryptophan and 5-hydroxyindoleacetic acid levels following acute morphine administration in normal and arthritic rats.
The effects of morphine (10 mg/kg/s.c.) on tryptophan (TRP), 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) levels were studied in normal and arthritic rats. (1) In normal rats morphine induced a discrete but significant increase of 5-HIAA levels in the forebrain and the spinal cord. (2) By contrast, in rats suffering from experimentally induced arthritis large modifications were apparent. The basal levels of TRP, 5-HT and 5-HIAA were significantly higher than in normal rats. Morphine induced clear increases of 5-HIAA and TRP in the forebrain, the brain stem and the spinal cord, without any modification of 5-HT. The effects were dose-dependent and suppressed by naloxone (1 mg/kg/i.m.). Statistical analysis clearly revealed that arthritic rats were much more sensitive to morphine. The results support the hypothesis of an activation of a 5-HT descending pathway by morphine which parallels the activation of the ascending pathway previously demonstrated by several authors and confirmed here.
D000818:Animals; D001168:Arthritis / Q000378:metabolism*; D001169:Arthritis, Experimental / Q000378:metabolism*; D001921:Brain / Q000187:drug effects*; D001933:Brain Stem / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D006897:Hydroxyindoleacetic Acid / Q000378:metabolism*; D007031:Hypothalamus / Q000378:metabolism; D008297:Male; D008636:Mesencephalon / Q000378:metabolism; D009270:Naloxone / Q000494:pharmacology; D051381:Rats; D012701:Serotonin / Q000378:metabolism; D013116:Spinal Cord / Q000187:drug effects* / Q000378:metabolism; D014364:Tryptophan / Q000378:metabolism*
D012701:Serotonin; D009270:Naloxone; D006897:Hydroxyindoleacetic Acid; D014364:Tryptophan