Acetylcholinesterase in the developing forebrain.

Abstract

A histochemical study has been made of the development of forebrain cholinesterase in cat embryos,. At the earliest stage, cholinesterase is only found in the striatal primordium, particularly in or close to the germinal layer in the ependyma. AChE-containing cells migrate from the striatal ependyma to form the lenticular nucleus. Later. AChE-containing fibers grow from this nucleus into the lateral half of the cerebral hemisphere. Similar fibers from the strongly stained septal area penetrate the medial wall of the hemisphere. Some of these fibers are found below the ependyma where they form the 'subcallosal band'. At every stage, AChE-containing fibers remain distinct from the unstained fibers of the internal capsule, corpus callosum and anterior commissure. Since the primitive cortex contains no stained cells or fibers, it is probably free of cholinergic elements. Stained lenticular and septal fibers only begin to penetrate the neocortex relatively late, mostly just before birth. At about the same time, stained cells are seen in the subcortical white matter. They resemble migrating cells and are later found in the deepest layer of the cortex. It is suggested that these cells are the precursors of the adult polymorph cells of layer VI which probably give rise to cortical U-fibers. Since the initial focus of staining in the striatal eminence appears to be independent of diencephalic and mesencephalic foci, it is probable that forebrain AChE-containing elements have a purely telencephalic origin. The telencephalic, diencephalic and mesencephalic areas of strong AChE activity are later linked by stained fibers.