The efferent connections of the nucleus accumbens in the lizard Gekko gecko. A combined tract-tracing/transmitter-immunohistochemical study.

The present investigation of connections in the basal ganglia of the lizard Gekko gecko has revealed that the efferent projections of the nucleus accumbens are far more elaborate than previously thought. The projections reach not only the ventral pallidum, the preoptic area, the lateral hypothalamic area and the ventral tegmental area, but also the bed nucleus of the stria terminalis, the dorsomedial thalamic nucleus, the substantia nigra and the retrorubral dopaminergic cell group. Additional projections were observed within the nucleus accumbens and, caudally, to the peribrachial region and the superior raphe nucleus. Moreover, the results of the present study indicate that the accumbal projections to both the ventral pallidum and midbrain dopaminergic cell groups have a medial-to-lateral topographical organization. This expanded view of the efferent projections of the nucleus accumbens of Gekko gecko suggests a great resemblance in accumbal output systems between reptiles and mammals. A notable difference, however, is observed in the "limbic loop", which in reptiles, in contrast to mammals, seems to lack a cortical involvement.