Morphine depresses the transmission of noxious messages in the spino(trigemino)-ponto-amygdaloid pathway.
We had recently demonstrated that a subregion of the parabrachial area relays nociceptive information in the spino(trigemino)-ponto-amygdaloid pathway. The aim of the present study was to investigate, in halothane-anesthetized rats, the effect of i.v. administration of morphine on nociceptive specific neurons located in the parabrachial area with some cells being antidromically driven from the amygdala. Morphine induced a marked depression of responses elicited by noxious thermal stimuli (waterbath, 50 degrees C) dose relatedly (1, 3, 9 mg/kg) and naloxone reversibly, with an ED50 = 1.8 mg/kg. This effect of morphine probably not only reflects the direct action of this drug at the spinal level, but could also involve a direct action at the parabrachial level. These results could account at least in part for the effect of morphine on the emotional-affective aspects of pain.
Huang
G F
GF
Unité de Recherches de Physiopharmacologie du Système Nerveux and EPHE, INSERM U.161, Paris, France.
Besson
J M
JM
Bernard
J F
JF
D000679:Amygdala; D000818:Animals; D006358:Hot Temperature; D007275:Injections, Intravenous; D008297:Male; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology*; D009270:Naloxone / Q000494:pharmacology; D009434:Neural Pathways / Q000187:drug effects*; D009474:Neurons / Q000187:drug effects; D010146:Pain / Q000503:physiopathology*; D011149:Pons; D051381:Rats; D017207:Rats, Sprague-Dawley; D014279:Trigeminal Nucleus, Spinal
D009270:Naloxone; D009020:Morphine