Selective augmentation of genioglossus electromyographic activity by L-5-hydroxytryptophan in the rat

The present study was undertaken to determine the effects of intravenous L-5 hydroxytryptophan (5HTP), the immediate precursor of serotonin, on the electromyographic (EMG) activity of the genioglossus (gEMG) and diaphragm (dEMG) in the spontaneously breathing, vagotomized anesthetized male Sprague-Dawley rats (urethane 1.2-1.4 g/kg). Sequential administration of saline and 0.05-, 0.1-, 0.2-, 1-, and 5-mg/kg doses of 5HTP were given intravenously every 15 min. There was a significant increase (percent change from predrug) in both gEMG and dEMG amplitude at 1.0 and 5.0 mg/kg of 5HTP compared to saline. The percent increase in gEMG induced by 1.0 and 5.0 mg/kg 5HTP however was significantly greater than the increase in dEMG. There was no significant change in heart rate (HR), mean arterial blood pressure (MAP), or respiratory rate at any of the doses of 5HTP tested. These results suggest that intravenous 5HTP at doses of 1 and 5 mg/kg preferentially increased the gEMG in the anesthetized rat compared to the dEMG. We hypothesize that at appropriate doses serotonin precursors could increase genioglossus activity in humans during sleep and help maintain upper-airway patency.