A comparison of the effects of morphine on 5-HT metabolism in the periaqueductal gray, ventromedial medulla and medullary dorsal horn: in vivo electrochemical studies in freely moving rats.
The effect of systemic morphine on serotonin (5-HT) metabolism within the dorsal raphe nucleus (DRN) has been investigated by in vivo 5-hydroxyindole electrochemical (peak '3') detection in freely moving rats. Morphine caused a weak and delayed, but naloxone-reversible, increase in peak '3'. This increase was poorly, if at all, correlated with the morphine-induced analgesia. Finally, stress and/or noxious stimulation had no effect on this signal. These results are compared with our previous studies using the same methodological approaches and show that morphine caused a significant and specific increase in 5-HT metabolism at the levels of nucleus raphe magnus (NRM) and medullary dorsal horn. Furthermore, as shown in the present paper, there was also a good correlation between the time course of such increases and the analgesic effect of morphine. These findings are discussed with reference to the involvement of 5-HT mechanisms in the so-called DRN-NRM-dorsal horn 'intrinsic analgesic system'.
Unité de Recherches de Physiopharmacologie du Système Nerveux (INSERM U. 161), Paris, France.
J P
JP
Rivot
D
D
Pointis
J M
JM
Besson
D000818:Animals; D004563:Electrochemistry; D008297:Male; D008526:Medulla Oblongata / Q000187:drug effects / Q000378:metabolism*; D009020:Morphine / Q000494:pharmacology*; D011903:Raphe Nuclei / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012701:Serotonin / Q000378:metabolism*; D013116:Spinal Cord / Q000187:drug effects / Q000378:metabolism*
D012701:Serotonin; D009020:Morphine