Peptides, Vol. 10, pp. 375-382. © Pergamon Press plc, 1989. Printed in the U.S.A. 0196-9781/89 $3.00 + .00 Melanin-Concentrating Hormone (MCH) Immunoreactivity in the Brain and Pituitary of the Dogfish Scyliorhinus canicula. Colocalization With Alpha-Melanocyte-Stimulating Hormone (a-MSH) in Hypothalamic Neurons M. VALLARINO,* A. C. ANDERSEN,t C. DELBENDE,t I. OTTONELLO,* A. N. EBERLE$ AND H. VAUDRYt *lstituto di Anatomia Comparata, Universit~ Degli Studi di Genova Viale Benedetto XV, 5, 16132 Genova, Italy tGroupe de Recherche en Endocrinologie Moldculaire, URA CNRS 92 Unit( affili(e ?t I'INSERM, Universit( de Rouen, 76134 Mont-Saint-Aignan, France SDepartment of Research (ZLF), University Hospital and University Children's Hospital CH-4031 Basel, Switzerland Received 10 June 1988 VALLARINO, M., A. C. ANDERSEN, C. DELBENDE, I. OTTONELLO, A. N. EBERLE AND H. VAUDRY. Melanin- concentrating hormone (MCH) immunoreactivity in the brain and pituitary of the dogfish Scyliorhinus canicula. Colocaliza- tion with alpha-melanocyte-stimulating hormone (c~-MSH)in hypothalamic neurons. PEPTIDES 10(2) 375-382, 1989.-The distribution of melanin-concentrating hormone (MCH) in the central nervous system of the dogfish Scyliorhinus canicula was determined by indirect immunofluorescence and peroxidase-anti-peroxidase techniques, using an antiserum raised against synthetic salmon MCH. Three groups of MCH-positive cell bodies were localized in the posterior hypothalamus. The most prominent cell group was detected in the nucleus sacci vasculosi. Scattered MCH-immunoreactive cells were observed in the nucleus tuberculi posterioris and in the nucleus lateralis tuberis. At the pituitary level, the caudal part of the median lobe of the pars distalis contained strongly MCH-positive perikarya. Some of these cells were liquor-contacting-type. Immunoreactive fibers originating from the hypothalamic perikarya projected throughout the dorsal wall of the posterior hypothalamus. Pos- itive fibers were also detected within the thalamus and the central gray of the mesencephalon. The distribution of MCH- containing neurons was compared to that of c~-MSH-immunoreactive elements using consecutive, 5-~m thick sections. Both MCH- and u-MSH-immunoreactive peptides were found in the same neurons of the nucleus sacci vasculosi. These data suggest that MCH and t~-MSH, two neuropeptides which exert antagonistic activities on skin melanophores, may also act in a coordinate manner in the central nervous system of cartilaginous fish. Melanin-concentrating hormone Alpha-melanocyte-stimulating hormone Pituitary Neuropeptides Dogfish Immunocytochemistry Hypothalamus MANY cold-blooded vertebrates possess the remarkable abil- ity to adapt the color of their skin in response to variations of the coloration of their background (3). Skin color adaptation results from the dispersion or aggregation of the black pigment melanin in dermal melanophores. In fish, expansion or concen- tration of melanin is controlled by two antagonistic pitui- tary hormones, the tridecapeptide alpha-melanocyte-stimulating hormone (ct-MSH) (17) and the cyclic heptapeptide melanin- concentrating hormone (MCH) (20). Besides its direct melano- some-aggregating activity at the skin level (9, 15, 27, 28), MCH also exerts an indirect action on melanin dispersion by inhibit- ing melanotrophs (5). Several studies have demonstrated that t~-MSH is also a neu- ropeptide found in the central nervous system of mammals (8, 375