A stereometric pattern of distribution of acetylthiocholinesterase in the deep layers of the superior colliculus

Abstract

THE superior colliculus, although a layered structure, is not classified as a cortex because most of its neurones lack long apical dendrites. The colliculus, nevertheless, seems to share with the neocortex some of the features of columnar organisation. In particular, a periodic segmentation of certain afferent connections has been found, in which incoming fibres are arranged in the colliculus in bands or slabs, much like the ocular dominance columns in the striate cortex^1–6. The possibility that such a distribution pattern might be evident also in a histochemical analysis of the superior colliculus was raised by Ramon–Moliner's finding⁷, in a survey of acetylthiocholinesterase activity in the cat's brain stem, that this enzyme is distributed in a series of regularly spaced clumps in the deep collicular layers. Evidence is presented here that such enzyme-positive clumps are also seen in the monkey and that, in the cat at least, these clumps do indeed form longitudinal bands.