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 μM) 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 μM) 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 Ca2+-dependent after hyperpolarizing current (I(AHP)). Again, interaction studies between TRH and 5-HT indicated no enhancing effect of TRH on 5-HT-induced antagonism of I(AHP). 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.
|Original language||English (US)|
|Journal||American Journal of Physiology - Gastrointestinal and Liver Physiology|
|Issue number||2 31-2|
|State||Published - 1995|
All Science Journal Classification (ASJC) codes
- Physiology (medical)