The modification by systemic morphine of the responses of serotonergic and non-serotonergic neurons in nucleus raphe magnus to heating the tail.
In anaesthetised rats, 63 raphe-spinal units in nucleus raphe magnus (NRM) have been identified by means of electrophysiological methods and further classified into serotonergic (5-HT) and non-5-HT units according to their conduction velocity and spontaneous discharge rate. All units, except one, showed either excitatory (n = 39) or inhibitory (n = 23) responses to noxious heating of the tail with hot water at 52 degrees C. The threshold temperature was around 44 degrees C and both types of responses increased with stepwise increases in temperature. The excitatory or inhibitory responses of raphe-spinal units induced by noxious heating of the tail correlated well with those elicited by noxious pinching, but did not correlate with the different transmitter populations (5-HT or non-5-HT) of the NRM unit. The effects of morphine or Fentanyl administration on the heat-induced responses of NRM units was observed. The possible involvement of NRM raphe-spinal units in 'diffuse noxious inhibitory controls' (DNICs) was discussed, particularly in relation to the 'lifting of DNICs' produced by morphine.
D000818:Animals; D005283:Fentanyl / Q000494:pharmacology; D006358:Hot Temperature; D008297:Male; D009020:Morphine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D009270:Naloxone / Q000494:pharmacology; D009431:Neural Conduction / Q000187:drug effects; D009474:Neurons / Q000502:physiology*; D011903:Raphe Nuclei; D051381:Rats; D011919:Rats, Inbred Strains; D012701:Serotonin / Q000378:metabolism*; D009435:Synaptic Transmission; D013623:Tail
D012701:Serotonin; D009270:Naloxone; D009020:Morphine; D005283:Fentanyl