Parcellation of the human pretectal complex: a chemoarchitectonic reappraisal

The pretectum is composed of numerous small nuclei that control various oculomotor functions. In all the non-human mammals investigated, the different pretectal nuclei have been named uniformly according to their structural and functional homology. However, the human pretectal nuclei still bear their traditional, in most cases misleading, nomenclature.In order to reveal the presumed chemoarchitectonic similarities between human and non-human pretectal nuclei, neuropeptide Y (NPY)- and vasoactive intestinal polypeptide (VIP)-immunohistochemistry was performed in the human pretectum, after being utilised successfully for the identification of different pretectal nuclei in the cat. No VIP neurones were observed in the human pretectal area, but numerous NPY cells were found in the 'nucleus lentiformis', and in the anterior bulge of the pretectum, while the 'nucleus sublentiformis' contained an abundant NPY fibre network. Some NPY neurones were present in the 'principal pretectal nucleus' as well. The olivary pretectal nucleus possessed NPY fibres, too. In the accessory optic system, the lateral terminal nucleus contained both NPY and VIP neurones, while in the dorsal terminal nucleus only NPY neurones were found. Our chemoanatomical findings were compared to the standard cytoarchitecture as well. Based on the homotopies in the spatial distribution pattern of NPY neurones in the cat and human pretectum, the current, widely accepted non-human anatomical nomenclature was applied to the morphologically homologous nuclei of the human pretectum. Accordingly, the 'nucleus lentiformis' (which contains numerous NPY cells) corresponds to the nucleus of the optic tract, the 'nucleus sublentiformis' (containing a dense network of NPY fibres) to the posterior pretectal nucleus, and the 'nucleus of the pretectal area' corresponds to the medial pretectal nucleus. We identified the anterior part of the pretectum as the human equivalent of the anterior pretectal nucleus in non-humans, including its two compact and reticular subdivisions. In addition, two accessory optic nuclei were verified chemoarchitectonically in the human brain.