Effects of 5-HT alone and its interaction with TRH on neurons in rat dorsal motor nucleus of the vagus.
The purpose of this study was to determine whether exposure to thyrotropin-releasing hormone (TRH) enhances the excitatory effect of 5-hydroxytryptamine (5-HT) on motoneurons of the dorsal motor nucleus of the vagus (DMV) as described in whole animal studies. For this purpose we used the patch-clamp technique applied to rat brain stem slices. Exposure of DMV motoneurons to concentrations of 5-HT (0.1-3 microM) resulted in a concentration-related increase in spontaneous firing rate. As previously described by Travagli et al. [Am. J. Physiol. 263 (Gastrointest. Liver Physiol. 26): G508-G517, 1992], TRH (1-30 microM) increased action potential firing rate. Indeed, when TRH perfusion increased the firing rate, addition of 5-HT to the perfusing solution exerted no further excitation of the DMV motoneuron, indicating that there was no summation of response. Studies using whole cell current recordings showed a common action of 5-HT and TRH in antagonizing the Ca(2+)-dependent afterhyperpolarizing current (IAHP). Again, interaction studies between TRH and 5-HT indicated no enhancing effect of TRH on 5-HT-induced antagonism of IAHP. In conclusion, our data indicated that the enhancement of 5-HT-induced excitation of DMV motoneurons by TRH described by in vivo rat experiments is not due to an interaction of TRH and 5-HT directly on the DMV motoneuron.
Travagli
R A
RA
Department of Pharmacology, Georgetown University School of Medicine, Washington, DC 20007.
Gillis
R A
RA
D000818:Animals; D004347:Drug Interactions; D004594:Electrophysiology; D066298:In Vitro Techniques; D008526:Medulla Oblongata / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D009474:Neurons / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012701:Serotonin / Q000494:pharmacology*; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*; D013997:Time Factors; D014630:Vagus Nerve / Q000502:physiology*
D012701:Serotonin; D013973:Thyrotropin-Releasing Hormone