Topographical organization of amygdaloid projections to the caudatoputamen, nucleus accumbens, and related striatal-like areas of the rat brain

Abstract

The topographical organization of amygdaloid projections to the caudatoputamen, nucleus accumbens, and lateral portions of the bed nucleus of the stria terminalis and central amygdaloid nucleus was investigated, in the rat, using the retrograde transport of wheat germ agglutinin-conjugated horseradish peroxidase. Although the caudatoputamen and nucleus accumbens are the principal components of the striatum, there is evidence that lateral portions of the bed nucleus of the stria terminalis and central amygdaloid nucleus may be striatal-like structures. The basolateral nucleus was the main source of amygdaloid fibers to all of these structures. In many instances labeled areas of the basolateral nucleus were continuous with labeled areas in the adjacent lateral and basomedial nuclei. Amygdaloid neurons projecting to the striatum and striatal-like areas exhibited an overlapping topographical organization. In general, the medial-to-lateral coordinate in the striatum corresponds to the medial-to-lateral coordinate in the basolateral nucleus. There was also a partial reversed sagittal topography in that the caudal caudatoputamen receives its principal projection from the rostral basolateral nucleus. However, the rostral basolateral nucleus had a stronger projection to the rostral caudatoputamen and lateral nucleus accumbens than the caudal basolateral nucleus. The principal striatal projection of the caudal basolateral nucleus was to the medial nucleus accumbens. Amygdaloid labeling produced by injections into the medial nucleus accumbens was very similar to that seen with injections into the lateral portions of the bed nucleus of the stria terminalis and central amygdaloid nucleus. The retrograde amygdaloid labeling seen in this investigation, when compared to labeling seen with cortical injections in previous studies, suggests that specific amygdaloid domains project to particular cortical areas as well as to the principal striatal targets of the same areas.