Dual labeling of CTB retrograde transport (brown) and Fos expression (black) in cells within the extended VLPO and VLPO cluster (B,E, H) after the injections of CTB into the central DRN (A, experiment R2049), LDT (D, experiment R1969), and LC (G, experiment R2219), respectively, in the rats exposed to 3 hr of darkness. In B, E, and H, the VLPO cluster is identified by a large arrow and the extended VLPO by a large double-headed arrow. Therectangular boxes identify the fields that are magnified in C, F, and I, respectively. Double-labeled cells in the extended VLPO and VLPO cluster are indicated by small arrows and single CTB labeled cells are indicated by small arrowheads.