Arousal effects of orexin-A correlate with GLU release from the locus coeruleus in rats

Although orexin was found to promote food intake, recent reports proposed its involvement in the regulation of vigilance. To study the mechanism of how orexin affects arousal, we analyzed glutamate (GLU) release from the locus coeruleus (LC) in rats after systemic injection of orexin-A. Baseline levels of orexin-A in the LC were significantly higher during the dark period than the light period. Intravenous administration of orexin-A increased GLU levels as well as orexin in the LC, simultaneously promoting wakefulness. These results suggest that increases in GLU release may reflect the arousal-inducing effects of orexin.