Rostral Reticular Nucleus of the Thalamus Sends a Patchy Projection to the Pulvinar Lateralis-Posterior Complex of the Cat

Abstract

The pulvinar lateralis posterior complex (Pul-LP) and the reticular nucleus of the thalamus (RE) are thought to be involved in visual and attention-related tasks. This report provides data on the anatomical connections between these two nuclei following the analysis of injections of horseradish peroxidase (HRP) + [3H]leucine into the Pul-LP and RE of the cat. Following the retrograde transport of HRP from the Pul-LP, labeled cells were distributed in regions of the RE ventral to the caudate nucleus and adjacent to the stria terminalis between Horsley-Clarke anterior-posterior (AP) coordinates 13.0 and 9.5 and more caudally in areas dorsal and ventral to the lateral geniculate nucleus (LGN) between AP 9.0 and 4.5. The majority of the cell labeling within the RE following injections within the Pul-LP was seen dorsal to the lateral geniculate nucleus around AP 6.5-6.0. Cell labeling was heaviest following injections within the lateral LP in contrast to injections within the Pul which resulted in fewer labeled cells. Autoradiographic analysis of the anterograde transport of leucine showed that the labeled Pul-LP fibers within the RE did not completely coincide with the distribution of HRP-labeled reticular cells from the same injection site. This indicated a lack of strict reciprocity between these two nuclei. In addition, injections of [3H]leucine into dorsomedial areas of the RE near the rostral pole of the LGN resulted in a patchy distribution of label within the Pul-LP which was most prominent as oblique dorsoventral slabs across the thalamus. It was inferred that this distribution was along the borders between different subdivisions within the Pul-LP. The lack of strict reciprocity between the thalamic relay nuclei and the reticular nucleus implies that areas of the Pul-LP may receive inhibition from RE regions which they do not directly influence; this anatomical feature may provide a basis for selective inhibition of thalamic nuclei.