A new subdivision of mammalian neostriatum with functional implications tolearning and memory

A new subdivision with distinctive morphological and functional attributes has been identified at the caudo-medial margin of the neostriatum and surro unding the rostrolateral border of the globus pallidus in the brains of the rat, cat, monkey, and human. The subdivision is termed marginal division ( MrD) based on its location. It is readily distinguishable from the rest of striatum by consisting of spindle-shaped neurons, special connections, and intensely expressed immunoreactivities of many neuropeptides and some monoa mines in the fibers, terminals, and neuronal somata. Three-dimensional reco nstruction from Nissl-stained sections of the rat brain revealed that the M rD is a Rat, pan-shaped zone between the neostriatum and globus pallidus. F unctional neuronal connections were delineated by chemical-induced c-Fos ex pression between the MrD and hippocampus, amygdala, as well as the basal nu cleus of Meynert. In rats with chemical lesions of bilateral MrD, learning and memory functions were severely impaired as demonstrated by double blind Y-maze test. Our results thus suggested that the MrD is a distinct part an d a universal structure in the neostriatum of the mammalian brain and might play an important role in the mechanism of learning and memory. (C) 1999 W iley-Liss, Inc.