Abstract
We have reported that serotonin (5-HT) type 2 receptors in the dorsomedial medulla oblongata (DMM) influence ventilation and airway resistance in mice. In the present study, the role of 5-HT2 receptors in the DMM in respiration to hypoxia was investigated. Each male mouse was anesthetized with pentobarbital sodium i.p. for insertion of a microdialysis probe into the DMM. The mouse was placed into a double chamber plethysmograph to obtain two respiratory flow curves to calculate respiratory variables, while extracellular fluid was collected at 1.2 microL/minute every 5 minutes. Extracellular fluid via the microdialysis probe was analyzed with an ECD-HPLC. Artificial cerebrospinal fluid (aCSF) or 1 x 10−5M LY-53857 (a 5-HT2 receptor antagonist) was perfused via the microdialysis probe in the DMM with air or hypoxic gas (7% O2 in N2) inhalation. Changes in respiratory variables and the 5-HT concentration in the DMM were analyzed every 5 minutes. Respiratory variables during hypoxia in a LY-53857-perfused group were not different from those in an aCSF-perfused group. Post-hypoxia frequency in the LY-53857-perfused group was decreased compared to that in the aCSF-perfused group, while the 5-HT concentration in the DMM was significantly increased under hypoxia in both the aCSF-perfused group and the LY-53857-perfussed group. We discuss whether or not the post-hypoxia frequency decline with LY-53857 perfusion in the DMM is a result of respiratory hypoxic excitation with a more detailed analysis of respiration variables. [J Physiol Sci. 2006;56 Suppl:S138]
