Efferent connections of nucleus accumbens subdivisions of the domestic chicken (Gallus domesticus): an anterograde pathway tracing study.

Envisaged as a limbic-motor interface, the mammalian nucleus accumbens (Ac) is responsible for motivation, emotionality, and reward mechanisms. As in mammals, Ac of the domestic chick has three subdivisions: the rostral pole (AcR) lying in the rostral part of basal telencephalon, the core (AcC), corresponding to the ventromedial medial striatum, and the shell (AcS), lying ventrally and ventrolaterally to the AcC. Less well known is the connectivity of subdivisions. Here we report on the efferents of Ac subregions, using biotinylated dextran amine as anterograde tracer, deposited into the AcR, AcS, and AcC. The projections of the accumbens subregions mainly overlap in the telencephalon and the diencephalon but differ in the brainstem. In the telencephalon, the main projection sites are the ventral pallidum, the basal nucleus (Meynert), and the nucleus of the diagonal band. The lateral hypothalamus and lateral preoptic area receive strong projections from the AcR and AcS, and weaker projections from the AcC. The AcR and AcC massively innervate the subthalamic nucleus. In the brainstem the bulk of accumbens fibers were found in the compact part of the substantia nigra. All subregions project to the parabrachial region, reticular formation, periaqueductal gray, and the raphe nuclei, with some differences in the weights and subregional distributions. AcR and AcS project extensively to the ventral tegmental area, while AcC sends massive innervation to the solitary and vagal motor nuclei. Overall, the results seem to support the previously suggested distribution of Ac subregions, emphasizing similarities and differences with mammals.