Figure 6.

DAMGO induces c-Fos in hypothalamic orexin neurons, and DAMGO-responsive sites project to the hypothalamic orexin field in rats. a, b, DAMGO (250 ng) but not saline administered to the nucleus accumbens increases c-Fos expression in the perifornical hypothalamus. Rectangular boxes indicate the areas selected for quantitative analysis in Figure 4. c, DAMGO induces c-Fos expression (black nuclei) in many orexin-immunoreactive neurons (red cytoplasm). Examples of double-labeled neurons are indicated by arrows. d, e, Retrograde tracing of axonal projections from DAMGO-responsive nucleus accumbens site to the perifornical hypothalamus. Lower- and higher-magnification images of BDA-labeled axon profiles (red) in close anatomical apposition to orexin-IR neurons (green) in perifornical area of hypothalamus. fx, Fornix. Scale bars: a, b, 200 μm; c–e, 50 μm.