抄録
5-HT in the hypoglossal motor nucleus stimulates the activity of the genioglossus muscle, which is mediated via 5-HT2 receptors. In the present study, the role of 5-HT2 receptors in the dorsomedial medulla oblongata (DMM) in airway resistance to CO2 was studied. Each mouse was anesthetized with pentobarbital sodium i.p., for insertion of a microdialysis probe in the DMM, and placed in a double chamber plethysmograph for at least 1.5 hour to recover from anesthesia and to acclimatize to the chamber. Two respiratory flow curves were recorded from the body and head chambers to obtain specific airway resistance, while extracellular fluid was collected at 1.2 μl/minute every 25 minutes. Extracellular 5-HT concentrations were analyzed with ECD-HPLC. 1 x 10−5M fluoxetine and LY-53857 were dialyzed via a microdialysis probe in the DMM. CO2 in O2 was changed every 8 minutes in a stepwise series of 5, 7 and 9%. Positions of the microdialysis probes were identified by coronal sections stained with neutral red. The 5-HT concentration in the DMM during 100% O2 inhalation with fluoxetine plus LY-53857 co-perfusion was similar to that with fluoxetine perfusion. However, specific airway resistance during 100% O2 inhalation with fluoxetine plus LY-53857 co-perfusion was significantly higher than that with fluoxetine perfusion, which was suppressed by CO2 gas inhalation. These results suggest that 5-HT in the DMM increases airway patency via 5-HT2 receptors, and that interference of 5-HT2 receptors in the DMM causes accumulation of CO2 and stimulates airway patency through other pathways. [Jpn J Physiol 55 Suppl:S108 (2005)]
