Molecules involved in the formation of synaptic connections in muscle and brain

Synapses are highly specialized structures designed to guarantee precise an d efficient communication between neurons and their target cells. Molecules of the extracellular matrix have an instructive role in the formation of t he neuromuscular junction, the best-characterized synapse. In this review, the molecular mechanisms underlying these instructive signals will be discu ssed with particular emphasis on the receptors involved. Additionally. rece nt evidence for the involvement of specific adhesion complexes in the forma tion and modulation of synapses in the central nervous system will be revie wed. Synapses are specialized junctions between neurons and their target ce lls where information is transferred from the pre- to the postsynaptic cell . At most vertebrate synapses, this transfer is accomplished by the release of a specific neurotransmitter from the presynaptic nerve terminal. The re lease of neurotransmitter is initiated by the action potential acid the sub sequent influx of Ca2+ into the presynaptic nerve terminal. This results in the rapid fusion of vesicles with the nerve membrane and the release of th e neurotransmitter into the synaptic cleft. The neurotransmitter then diffu ses across the cleft and binds to specific postsynaptic receptors, resultin g in a change in the membrane potential of the postsynaptic cell. This can result in the generation of an action potential. The high precision of syna ptic transmission requires that pre- and postsynaptic structures are both h ighly organized and in juxtaposition to each other. In addition, alteration s in synaptic transmission are the basis of learning and memory and are lik ely to be accompanied by the remodeling of synaptic structures (Toni et al. , 1999). Thus; the study of how synapses are formed during development is a lso of relevance for the understanding of the cellular and molecular proces ses involved in learning and memory. This review focuses on the molecular m echanisms involved in the formation and the function of synapses. (C) 2001 Elsevier Science B.V. International Society of Matrix Biology. All rights r eserved.