Neurochemical subdivisions of the inferior pulvinar in macaque monkeys

Abstract

The architecture of the pulvinar of rhesus monkeys was investigated by acetylcholinester ase (AChE) histochemistry, and by immunocytochemiatry for calbindin-D_28k and the SMI-32 antibody. The presence of four inferior subdivisions, comparable to those found in architectonic connectional studies in squirrel monkeys (C. G. Cusick, J Scripter, J. G. Darensbourg, and J. T. Weber, 1993, J. Comp. Neurol. 336:1–30), provided a basis for a proposed revised terminology for visual sectors of the macaque pulvinar. In the present study, the inferior pulvinar (PI) was identified as a neurochemically distinct region that included the traditional cytoarchitectonic nucleus PI and adjacent portions of the lateral and medial pulvmar nuclei, PL and PM. In calbindin-D_28k stains, the lateral. subdivision of the inferior pulvinar (PI_L) had less intense neuropil staining than the adjacent central division, PI_c. The PI_L was characterized by large, intensely immunopositive neurons seldom found within Pl_c. PI_L occupied the traditional PL and PI and exhibited a shell zone, PI_L-S, restricted to PL. The medial division of the inferior pulvinar (PI_M) was in a location previously shown to be strongly connected with the middle temporal visual area (MT) in macaques. PI_M was found in the medial one-half of the traditional PI and extended into adjacent portions of the traditional PM and PL. PI_M was distinguished by less intense staining for calbindin and many cells stained with the SMI-32 antibody for neurofilament protein. In AChE stains, PI_L was moderately dark, Pl_c appeared lighter, and PI_M was characterized by small, intensely stained patches. The small posterior division (PI_P) stained darkly for calbindin, lightly for AChE, and was unstained with the SMI-32 antibody. Thus, neurochemical, and perhaps connectional, subdivisions exist within PI, the region of the pulvinar that relays information to striate, “lower order” extrastriate, and inferotemporal visual cortex.