Evidences for shared features in the organization of the basal ganglia in tetrapods: studies in amphibians.

In a series of recent studies, the organization of the basal ganglia of amphibians, more in particular their connectivity and chemoarchitecture, has been thoroughly analyzed. The pattern of organization found for the amphibian basal ganglia includes dorsal and ventral striatopallidal systems, reciprocal connections between the striatopallidal complex and structures derived from the diencephalic and mesencephalic parts of the basal plate (striatonigral and nigrostriatal projections), and descending pathways from the striatopallidal system to the midbrain tectum and the reticular formation of the brain stem. A comparative analysis of the organization of the basal ganglia in tetrapods strongly supports the notion that a primitive pattern was most likely present in ancestral tetrapods, and that many features can still be recognized in extant amphibians and amniotes.