Effects of intrathecal monoamine antagonists and naloxone on the descending inhibition of the spinal transmission of noxious input in rats: study with a new experimental model.
An electrophysiological model has been developed to explore the transmitters and their relationships in the descending control of spinal transmission of noxious inputs. Nociceptive discharges were recorded extracellularly in parafascicular (Pf) neurons, and the caudal stump of longitudinally isolated dorsal half of the lower thoracic spinal cord was stimulated to simulate the descending volleys coming from the supraspinal structures. Nociceptive discharges in 34 Pf cells were markedly suppressed (83.2 +/- 13.9%) by the preceding spinal stimulation. Phentolamine, methysergide and naloxone were separately administered with random sequence in each of 25 cells by an intrathecal route to observe if the descending inhibition could be blocked by these drugs. The results suggested that in the dorsal spinal cord there exist at least two neurochemically different descending inhibitory fiber systems which comprise either the long descending adrenergic or serotonergic fibers and, most of the adrenergic fibers are succeeded by a propriospinal opioidergic neuron while a few of the serotonergic fibers have such a succession.
Li
Y J
YJ
Department of Neurobiology, Shanxi Medical College, People's Republic of China.
Xie
Y F
YF
Qiao
J T
JT
D000818:Animals; D005260:Female; D007278:Injections, Spinal; D008297:Male; D008784:Methysergide / Q000008:administration & dosage / Q000494:pharmacology*; D009270:Naloxone / Q000008:administration & dosage / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D010146:Pain / Q000503:physiopathology*; D010543:Peroneal Nerve / Q000187:drug effects / Q000502:physiology / Q000503:physiopathology*; D010646:Phentolamine / Q000008:administration & dosage / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D013116:Spinal Cord / Q000187:drug effects / Q000502:physiology / Q000503:physiopathology*
D009270:Naloxone; D008784:Methysergide; D010646:Phentolamine