Neuropeptide Y (NPY) or cocaine- and amphetamine-regulated transcript (CART) fiber innervation on central and medial amygdaloid neurons that project to the locus coeruleus and dorsal raphe in the rat.

The amygdaloid nuclear complex has been linked to the regulation of emotional behavior and energy regulation in that emotional stress might cause either reduction or enhancement of eating. We examined hypothalamic neuronal origin of feeding/arousal-related peptidergic fibers containing cocaine- and amphetamine-regulated transcript (CART) and neuropeptide Y (NPY) located in the rat amygdala along with its efferent projections to the brainstem monoaminergic nuclei. First, central (CeA) as well as medial (MeA) amygdala, among several amygdaloid subdivisions, exhibited the most prominent NPY or CART immunostaining which consisted of a substantial number of somata as well as labeled fibers. When we examined hypothalamic neuronal origin of NPY or CART fibers projecting to the CeA and MeA, medial and lateral arcuate nuclei were neuronal origins of NPY and CART fibers, respectively. However, the majority (>70%) of amygdala-projecting CART neurons which co-contained melanin-concentrating hormone (MCH) originated from the lateral hypothalamus (LH), zona incerta (ZI), and dorsal hypothalamic area (DA). This observation implied that the CeA as well as the MeA might receive potent second-order (and downstream) feeding-related CART input from the lateral hypothalamic regions in addition to first-order CART or NPY input from the Arc. Second, a large number of CeA neurons projected to the locus coeruleus (LC), whereas only a small number of MeA cells projected to the dorsal raphe (DR); none of the CeA or MeA cells provided dual projections to the LC and DR. Finally, a portion of MCH cells in the LH, ZI, and DA sent divergent axon collaterals to the CeA and LC. Considering that the CeA sends substantial GABAergic input to the LC, the present observation might serve as an anatomical substrate to support the potent hypnogenic role of MCH neurons in the LH regions during cataplexy and REM sleep.