Interaction of thyrotropin-releasing hormone and methysergide on the monosynaptic reflex in isolated mammalian spinal cord.
The interaction between thyrotropin-releasing hormone (TRH) and methysergide (MeSG) on reflex activity was examined in spinal cords from neonatal rats. MeSG depressed the monosynaptic reflex (MSR) by nearly 90% at 0.03 microM but had no effect on the dorsal root reflex at 0.003-3.0 microM. Neither spiperone, ketanserin, cyproheptadine nor ICS 205-930 (3-tropanyl-indole-3-carboxylate) depressed the MSR nor did they affect the potentiation elicited by TRH. TRH reversed the depression of the MSR by MeSG in a concentration-dependent manner without affecting the dorsal root reflex. MeSG-induced depression of the MSR was also reversed by 3,4-diaminopyridine which simultaneously increased the magnitude and duration of both reflexes. It appears that neither MeSG-induced depression nor TRH-induced potentiation of the MSR involves the spinal serotonergic system or blockade of K+ channels.
Deshpande
S B
SB
Department of Pharmacology and Experimental Therapeutics, University of Maryland School of Medicine, Baltimore 21201.
Warnick
J E
JE
D015116:5,7-Dihydroxytryptamine / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D003533:Cyproheptadine / Q000494:pharmacology; D004347:Drug Interactions; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology; D007650:Ketanserin / Q000494:pharmacology; D008297:Male; D008784:Methysergide / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D012018:Reflex / Q000187:drug effects*; D012702:Serotonin Antagonists / Q000494:pharmacology; D013116:Spinal Cord / Q000187:drug effects / Q000502:physiology*; D013134:Spiperone / Q000494:pharmacology; D013569:Synapses / Q000187:drug effects / Q000502:physiology*; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*; D000077526:Tropisetron
D007211:Indoles; D012702:Serotonin Antagonists; D003533:Cyproheptadine; D015116:5,7-Dihydroxytryptamine; D013134:Spiperone; D013973:Thyrotropin-Releasing Hormone; D000077526:Tropisetron; D007650:Ketanserin; D008784:Methysergide