Fig. 8.

Photomicrographs of hypothalamic sections depicting Hcrt receptor mRNA (A, D), Hcrt-ir neurons (B, E), and Hcrt-ir fibers in the locus ceruleus (C,F). In A–C, tissue from saline-treated rats is depicted. D–F depict tissue from a representative rat with Hcrt2-SAP administered to the LH.A depicts an autoradiogram image of Hcrt receptor mRNA labeling in the LH (coronal section). The region outlined by thebox in A represents the area in which Hcrt-ir neurons are present (B). Images inB and F are presented in reverse contrast. Hcrt2-SAP applied to the LH eliminated Hcrt receptor mRNA labeling (D) and Hcrt-ir neurons (E). Elimination of the Hcrt-ir neurons produced a loss of Hcrt-ir fibers at target sites such as the locus ceruleus (LC). In control rats, the LC is heavily innervated by Hcrt-ir fibers (C), but this innervation is lost after Hcrt2-SAP lesions of the Hcrt-ir neurons in the LH (F). 3V, Third ventricle;4V, fourth ventricle; Amyg, amygdala;f, fornix; MHb, medial habenula;mt, mammillothalamic tract; PeF, perifornical nucleus.