BASAL GANGLIA ORGANIZATION IN AMPHIBIANS - EFFERENT CONNECTIONS OF THE STRIATUM AND THE NUCLEUS-ACCUMBENS

As a further step in unraveling the organization of the basal ganglia of amphibians, the efferent connections of the striatum and the nucleu s accumbens have been studied in the brains of the anurans, Rana perez i and Xenopus laevis, and the urodele, Pleurodeles waltl, by using bio tinylated or fluorescent dextran amines as anterograde tracers. A comm on pattern of efferent connections was observed in both groups of amph ibians, but those in the anurans were more elaborate. Striatal efferen t fibers were found to reach the lateral and medial amygdala, the ante rior and posterior entopeduncular nuclei, several thalamic nuclei, the dorsomedial posterior tubercle, the pretectum, the optic tectum, the torus semicircularis, the pontomesencephalic reticular formation, and the caudal brainstem. Efferent fibers of the nucleus accumbens project to the medial amygdala, the preoptic area, the ventral hypothalamic n ucleus, the dorsomedial posterior tubercle, the medial tegmental area, the pontomesencephalic reticular formation, and the raphe. In additio n, the study has revealed the existence of intrinsic connections withi n the ventral telencephalic wall, suggesting a possible further compar tmentalization of the amphibian basal forebrain. In conclusion, the re sults of the present study corroborate the notion that the basal gangl ia of amphibians share many features with their presumed homologues in amniotes. (C) 1997 Wiley-Liss, Inc.