The endogenous rise in glucose appearance (Ra) during ICV vehicle administration is shown in the left panel. ICV administration of the orexin antagonist, during the latter part of the light period, prevents the endogenous rise of Ra before the onset of darkness (ZT11–ZT12), and during the onset of the dark period (ZT12–ZT15) (right panel). The orexin antagonist SB-408124 was administered ICV from ZT4 – ZT12. IV administration of the orexin antagonist had no effect on glucose appearance. Food intake was not changed by ICV orexin. O and Δ, P<0.05 compared with ZT4–6 and ZT6–11, respectively. *, P<0.05 compared with comparable time points in the vehicle group.