title: Spinal alpha 1- and alpha 2-adrenoceptors mediate facilitation and inhibition of spinal motor transmission, respectively.
abstract: The role of descending noradrenergic fibers in the spinal motor systems was investigated using spinal reflexes in acutely spinalized rats. In rats pretreated with the MAO inhibitor clorgyline-HCl (1 mg/kg, i.v.), L-3,4-dihydroxyphenylalanine (L-dopa) (5 mg/kg, i.v.), a precursor of dopamine and noradrenaline, markedly potentiated the mono- (MSR) and polysynaptic reflexes (PSR). Selective blockade of alpha 1-adrenoceptors by pretreatment with prazosin-HCl abolished these facilitatory effects on the MSR and the PSR and revealed the inhibitory effect of L-dopa on the PSR. The depression of PSR was antagonized by the alpha 2-antagonist piperoxan. Clonidine-HCl (0.05 mg/kg, i.v.), a so-called alpha 2-agonist, and tizanidine-HCl (0.1 mg/kg, i.v.) decreased the MSR and the PSR in rats pretreated with prazosin. These inhibitions were antagonized by piperoxan. These results suggest that alpha 1- and alpha 2-adrenoceptors mediate facilitation and attenuation of motor transmission in the rat spinal cord, respectively.
authors.affiliation: Department of Toxicology and Pharmacology, Faculty of Pharmaceutical Sciences, University of Tokyo, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Tanabe
authors.forename: H
authors.initials: H
authors.lastname: Ono
authors.forename: H
authors.initials: H
authors.lastname: Fukuda
mesh_terms: D000818:Animals; D003000:Clonidine / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D003010:Clorgyline / Q000494:pharmacology; D007980:Levodopa / Q000494:pharmacology*; D008297:Male; D009046:Motor Neurons / Q000502:physiology; D010883:Piperoxan / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D011292:Premedication; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D012023:Reflex, Monosynaptic / Q000187:drug effects* / Q000502:physiology; D013116:Spinal Cord / Q000502:physiology*; D009435:Synaptic Transmission / Q000187:drug effects*
chemical_list: D011942:Receptors, Adrenergic, alpha; D007980:Levodopa; C023754:tizanidine; D010883:Piperoxan; D003010:Clorgyline; D003000:Clonidine; D011224:Prazosin