Hypocretin immunoreactivity. A, Immunocytochemical staining revealed high densities of axons in both the lateral hypothalamus (A, B,LH) and arcuate nucleus (C,D, ARC) of the hypothalamus. Around immunoreactive cells in the LH, a high density of immunoreactive axons was found. E, Immunoreactive axons were not found in the external zone of the median eminence (ME), in which neurosecretory axons release pituitary tropins that are carried to the anterior pituitary by the portal blood system. Scale bars:A, 25 μm; B, 12 μm; C, 25 μm; D, E, 12 μm.