Efferent projections of the nucleus accumbens in the rat with special reference to subdivision of the nucleus: biotinylated dextran amine study

The nucleus accumbens (Acb) of the rat has been divided immunohistochemically into shell and core, and further, it was subdivided into several portions in relation to functional significance. In this report, the efferent projection of each subdivision of the Acb was examined using biotinylated dextran amine as an anterograde tracer. In rostral Acb, the dorsomedial shell mainly projected to the dorsomedial ventral pallidum (VP), lateral hypothalamus (LH) and substantia nigra pars compacta (SNc), while the ventromedial shell projected to the ventromedial VP, lateral preoptic area, LH and ventral tegmental area (VTA). The dorsal core of rostral Acb projected to the caudate putamen, dorsolateral VP, globus pallidus (GP), LH, and substantia nigra pars reticulata (SNr). In the middle to caudal Acb, the dorsomedial shell mainly projected to the dorsomedial VP, LH and VTA, the ventromedial shell projected to the ventromedial VP, substantia innominata, VTA, SNc and retrorubral area, and the ventrolateral shell projected to the ventrolateral VP and SNc. Furthermore, the ventromedial shell projected to the parabrachial nucleus (PB). The dorsomedial core projected to the dorsal VP, LH, SNc and SNr, and the ventral and lateral core sent axons to the dorsolateral VP, GP and SNc. From the point of view of projection patterns, shell and core are distinct throughout the rostro-caudal extent of the Acb. The ventrolateral shell at the caudal Acb was clearly differentiated. A direct projection from the ventromedial shell of the Acb to PB was also recognised.