UROTENSIN-II IN THE CENTRAL-NERVOUS-SYSTEM OF THE FROG RANA-RIDIBUNDA- IMMUNOHISTOCHEMICAL LOCALIZATION AND BIOCHEMICAL-CHARACTERIZATION

Urotensin II (UII) is traditionally regarded as a product of the neuro secretory cells in the caudal portion of the spinal cord of jawed fish es. A peptide related to UII has been recently isolated from the frog brain, thereby providing the first evidence that UII is also present i n the central nervous system of a tetrapod. In the present study, we h ave investigated the distribution of UII-immunoreactive elements in th e brain and spinal cord of the frog Rana ridibunda by immunofluorescen ce using an antiserum directed against the conserved cyclic region of the peptide. Two distinct populations of UII-immunoreactive perikarya were visualized. The first group of positive neurons was found in the nucleus hypoglossus of the medulla oblongata, which controls two stria ted muscles of the tongue. The second population of immunoreactive cel l bodies was represented by a subset of motoneurons that were particul arly abundant in the caudal region of the cord (34% of the motoneuron population). The telencephalon, diencephalon, mesencephalon, and meten cephalon were totally devoid of UII-containing cell bodies but display ed dense networks of UII-immunoreactive fibers, notably in the thalamu s, the tectum, the tegmentum, and the granular layer of the cerebellum . In addition, a dense bundle of long varicose processes projecting ro strocaudally was observed coursing along the ventral surface of the br ain from the midtelencephalon to the medulla oblongata. Reversed-phase high-performance liquid chromatography analysis of frog brain, medull a oblongata, and spinal cord extracts revealed that, in all three regi ons, UII-immunoreactive material eluted as a single peak which exhibit ed the same retention time as synthetic frog UII. Taken together, thes e data indicate that UII, in addition to its neuroendocrine functions in fish, is a potential regulatory peptide in the central nervous syst em of amphibians. (C) 1996 Wiley-Liss, Inc.