抄録
5-HT release in the dorsomedial medulla oblongata (DMM), especially in the hypoglossal nucleus, affects genioglossus muscle activity. We previously showed that 5-HT release in the DMM is increased by CO2 inhalation and that 5-HT2 activity in the DMM increases airway dilation and ventilatory volume in adult mice. However, whether there was dose dependency for inspired-CO2-induced increase in 5-HT release in the DMM was not clear. Prematurity of medullary 5-HT neurons has been associated with sudden infant death syndrome. In the present study, 5-HT release in the DMM, airway and respiratory responses to CO2 inhalation were investigated in infant rats. Infant Wister rats were anesthetized with pentobarbital sodium (0.5 mg/0.1 ml saline/10 g body wt i.p.) and locally anesthetized with 0.5% Marcain for insertion of a microdialysis probe in the DMM and placed in a double-chamber plethysmograph to record respiratory variables. After recovery from anesthesia, extracellular fluid was collected at 1.2 μl/min every 10 min. 5-HT was analyzed with an ECD-HPLC. Infant rats were exposed to 0, 5, 7 and 9% CO2 in O2 at intervals of 10 min. The 5-HT increase induced by CO2 inhalation in the DMM of infant rats was dose-dependent. Specific airway resistance was increased by CO2 inhalation in infant rats, as were tidal volume, respiratory rate, minute ventilation and mean inspiratory flow. Our results suggest that inspired-CO2-induced increases in 5-HT release in the DMM were dose-dependent and occurred with airway narrowing and ventilatory augmentation in infant rats. The airway response differed from that seen in adult mice. [J Physiol Sci. 2008;58 Suppl:S119]
