Localization and possible role of molecules associated with the cholinergic system during "non-nervous" developmental events.

Data on the non-nervous location of cholinergic molecules are reviewed to give a general indication of their possible functions. Cholinergic or immunologically related molecules were detected and localized mainly in three classes of differentiative events supported by intracellular ion concentration changes. I: during gamete maturation, activation and interaction; II: during the early development of invertebrate and vertebrate embryos. In this case cholinergic molecules are located mainly in moving cells and tissues engaged in relevant morphogenetic events, such as gastrulation and limb bud differentiation, and are often codistributed with special extracellular matrix molecules (fibronectin); III: during inductive communications between mesenchyme and other tissues. The cholinergic system thus seems to be a multifunctional cell communication system. It appeared early during evolution as a regulator of intercellular communications mediated by ion dynamics, before becoming involved in highly specialized communication structures, such as synapses and nerve endings.