TOPOGRAPHICAL ORGANIZATION OF SUBICULAR NEURONS PROJECTING TO SUBCORTICAL REGIONS

Direct projections from the subiculum to the septum, thalamus, and hyp othalamus were studied in the rat by the fluorescent retrograde double -labeling technique with Fast blue and Diamidino yellow. The results c onfirm and extend the previously reported findings. The dorsal subicul um projects primarily to the lateral septum, anterior and midline thal amus, and mammillary complex. The distribution areas of cell bodies of these projection neurons are substantially segregated, depending on t heir target region, and few single neurons project to two of the targe t regions by way of axon collaterals. The ventral subiculum projects m ainly to the lateral septum, midline thalamus, and ventromedial hypoth alamic area. The distribution areas of cell bodies of these projection neurons are considerably overlapped with one another, and a number of single neurons send axon collaterals to two of the lateral septum, mi dline thalamus, and ventromedial hypothalamic area. It is, thus, indic ated that the populations of subicular neurons projecting to each of t he subcortical structures examined are more distinctly segregated in t he dorsal subiculum than in the ventral subiculum.