Immunohistochemistry and spinal projections of the reticular formation in the northern leopard frog, Rana pipiens

Over 30 nuclei have been identified in the reticular formation of rats, but only a small number of distinct reticular nuclei have been recognized in f rogs. We used immunohistochemistry, retrograde tracing, and cell morphology to identify nuclei within the brainstem of Rana pipiens. FluoroGold was in jected into the spinal cord, and, in the same frogs, antibodies to enkephal in, substance P, somatostatin, and serotonin were localized in adjacent sec tions. We identified many previously unrecognized reticular nuclei. The rho mbencephalic reticular formation contained reticularis (r.) dorsalis; r. ve ntralis, pars alpha and pars beta; r. magnocellularis; r. parvocellularis; r. gigantocellularis; r. paragigantocellularis lateralis and dorsalis; r. p ontis caudalis, pars alpha and pars beta; nucleus visceralis secundarius; r . pontis oralis, pars medialis and pars lateralis; raphe obscurus; raphe pa llidus; raphe magnus; and raphe pontis. The mesencephalic reticular formati on contained locus coeruleus-subcoeruleus, r. cuneiformis, r. subcuneiformi s, raphe dorsalis-raphe centralis superior, and raphe linearis. Thus, the r eticular formation of frog, which is an anamniote, is organized complexly a nd is similar to the reticular formation in amniotes. Because many of these nuclei may be homologous to reticular nuclei in mammals, we used mammalian terminology for frog reticular nuclei. (C) 1999 Wiley-Liss, Inc.