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Notes: The distribution of α-melanocyte-stimulating hormone (α-MSH)-like immunoreactivity in the central nervous system of the rainbow trout Salmo gairdneri was investigated by indirect immunofluorescence and peroxidase-antiperoxidase techniques, using a highly specific antiserum generated in rabbits against synthetic α-MSH. Immunoreactive perikarya were exclusively observed in the basal hypothalamus within the pars anterioris of the nucleus lateralis tuberis. In this region, a moderate number of small stained cell bodies were observed surrounding the dorsal wall of the anterior infundibular recess. These immunoreactive cells were organized in rostro-caudal rows extending over the whole portion of the nucleus. Positive fibres originating from these perikarya were visualized in the dorsal posterior lobe and the ventral hypothalamus. A dense tract of immunoreactive fibres projected ventrally through the pituitary stalk and terminated in the neurohypophysis. The concentrations of α-MSH in different regions of the brain were measured by means of a sensitive and specific radioimmunoassay. The dilution curves obtained with synthetic α-MSH and serial dilutions of diencephalon, mesencephalon, medulla oblongata, telencephalon or pituitary extracts were strictly parallel. The highest concentration of α-MSH in brain was found in the diencephalon (1.31 ± 0.07 ng/mg protein). In contrast α-MSH was not detectable in cerebellar extracts. Reverse-phase high-performance liquid chromatography and radioimmunoassay were used to characterize α-MSH-like peptides in the trout brain and pituitary. Two major forms of immunoreactive α-MSH were resolved by high performance liquid chromatography in hypothalamic extracts; these peptides exhibited the same retention times as des-Na-acetyl α-MSH and its sulfoxide derivative, respectively. Additional peaks of α-MSH immunoreactive material were detected in pituitary extract. These latter peptides coeluted with authentic α-MSH, diacetyl α-MSH and their sulfoxide forms. These results provide the first evidence for the presence of α-MSH in the brain of a teleostean fish. Our data indicate that, in the brain, the immunoreactivity corresponds to the non-acetylated form of α-MSH, while three different types of α-MSH-like molecules (namely deacetylated, monoacetylated, and diacetylated forms) coexist in the pituitary. It thus appears that, in salmonoid fish, mono- or diacetylation of the N-terminal serine residue of aL-MSH only occurs at the pituitary level.

Notes: Summary Using the peroxidase-antiperoxidase technique, we showed the presence of peptides which are immunologically resembling mammalian corticotropin releasing hormone (CRF)-, adrenocorticotropic hormone (ACTH)-, β-endorphin (β-END)-, α-melanocyte stimulating hormone (α-MSH)-, methionine-enkephaline (met-ENK)- and leucine enkephaline (leu-ENK)- like immunoreactivity in hundreds to thousands of endocrine cells and nerve fibers in the midgut of the American cockroach Periplaneta americana. In the cockroach hindgut no immunoreactive cell bodies could be observed, although nerve fibers were clearly noticed to be recognized by antisera to CRF, ACTH1–24, ACTH11–24 and β-END. Nothing is exactly known as to the function(s) of the demonstrated materials, but one can speculate that these numerous immunoreactive cells, might have important paracrine and/or endocrine functions in the insect physiology.