Thyrotropin-releasing hormone reverses the supersensitively depressed monosynaptic transmission by serotonin in 5,7-dihydroxytryptamine-treated neonatal rats in vitro.
The interaction of serotonin and thyrotropin-releasing hormone (TRH) on monosynaptic reflex (MSR) in isolated neonatal spinal cords was examined. Superfusion of serotonin (1-30 microM) in untreated cords, depressed the MSR in a dose-dependent manner. The depression was about 25% at 10 microM of serotonin, in either control or vehicle-treated groups. While for the same concentration of serotonin, the depression was 97 +/- 2.1% of the control in cords from 5,7 dihydroxytryptamine (5,7-DHT)-treated animals. The inhibition of the reflex seen in cords obtained from 5,7-DHT-treated animals could not be reversed by washing with normal physiological solution (> 60 min) or in presence of serotonin antagonists. TRH (0.03-1.0 microM) reversed the depression in a concentration-dependent manner and complete reversal could be seen with 1 microM of TRH. These observations indicate that, serotonin and TRH act dissimilarly on the spinal synaptic transmission though they are known to coexist in the descending bulbospinal tracts.
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; D007211:Indoles / Q000494:pharmacology; D008784:Methysergide / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D012023:Reflex, Monosynaptic / Q000187:drug effects; D012701:Serotonin / Q000494:pharmacology*; D012702:Serotonin Antagonists / Q000494:pharmacology; D013116:Spinal Cord / Q000166:cytology / Q000187:drug effects; D013569:Synapses / Q000187:drug effects*; D009435:Synaptic Transmission / Q000187:drug effects*; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*; D000077526:Tropisetron
D007211:Indoles; D012702:Serotonin Antagonists; D015116:5,7-Dihydroxytryptamine; D012701:Serotonin; D013973:Thyrotropin-Releasing Hormone; D000077526:Tropisetron; D008784:Methysergide