Projection-dependent differentiation of melanin-concentrating hormone-containing neurons.

1. Melanin-concentrating hormone (MCH)-containing neurons within the lateral hypothalamus affect a broad spectrum of physiological and behavioral processes. The aim of this study was to examine a differentiation of rat MCH neurons dependent on their functionally related projections to the intermediolateral column (IML) of the spinal cord, the midbrain periaqueductal gray (PAG), and the brainstem locus coeruleus (LC). 2. A combination of retrograde fluorescent neuronal tracing and immunocytochemical identification revealed MCH neurons that project to IML, PAG, and LC. Subsequent to isolation of these single neurons by laser microdissection, multi-transcriptional profiling by means of real-time RT-PCR demonstrated different expression patterns between sympathetically projecting MCH neurons and those targeting the PAG or LC. 3. These results provide evidence for the existence of projection-dependent MCH neuronal subpopulations with functional differentiation in the context of controlling energy homeostasis, autonomic functioning, and arousal.