PROJECTIONS FROM THE ANTERODORSAL AND ANTEROVENTRAL NUCLEUS OF THE THALAMUS TO THE LIMBIC CORTEX IN THE RAT

The present study characterized the projections of the anterodorsal (A D) and the anteroventral (AV) thalamic nuclei to the limbic cortex. Bo th AD and AV project to the full extent of the retrosplenial granular cortex in a topographic pattern. Neurons in caudal parts of both nucle i project to rostral retrosplenial cortex, and neurons in rostral part s of both nuclei project to caudal retrosplenial cortex. Within AV, th e magnocellular neurons project primarily to the retrosplenial granula r a cortex, whereas the parvicellular neurons project mainly to the re trosplenial granular b cortex. AD projections to retrosplenial cortex terminate in very different patterns than do AV projections: The AD pr ojection terminates with equal density in layers I, III, and IV of the retrosplenial granular cortex, whereas, in contrast, the AV projectio ns terminate very densely in layer Ia and less densely in layer IV. Fu rther, both AD and AV project densely to the postsubicular, presubicul ar, and parasubicular cortices and lightly to the entorhinal (only the most caudal part) cortex and to the subiculum proper (only the most s eptal part). Rostral parts of AD project equally to all three subicula r cortices, whereas neurons in caudal AD project primarily to the post subicular cortex. Compared to AD, neurons in AV have a less extensive projection to the subicular cortex, and this projection terminates pri marily in the postsubicular and presubicular cortices. Further, the AD projection terminates in layers I, II/III, and V of postsubiculum, wh ereas the AV projection terminates only in layers I and V. (C) 1995 Wi ley-Liss, Inc.