Differential responses of serotonergic and non-serotonergic neurons in nucleus raphe magnus to systemic morphine in rats.
Forty-eight raphe-spinal units in nucleus raphe magnus were identified by antidromic stimulation and further classified into serotonergic and non-serotonergic populations according to their conduction velocity and spontaneous discharge rate. Following morphine administration (5 mg/kg, i.p.) they showed different responses: excitatory, depressive or non-responsive. It was found that 6 of 7 non-responsive, 3 of 20 depression-responsive and only 1 of 21 excitation-responsive units proved to be serotonergic neurons, indicating that the involvement of serotonergic neurons in morphine analgesia is probably insignificant. It is suggested that the raphe-spinal fiber systems, both excitatory and inhibitory are originated mainly from the non-serotonergic neurons.
D000818:Animals; D004558:Electric Stimulation; D004594:Electrophysiology; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009474:Neurons / Q000145:classification*; D011903:Raphe Nuclei / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains; D012701:Serotonin / Q000502:physiology*
D012701:Serotonin; D009020:Morphine