| Summary: | This paper surveys two different mechanisms by which a presynaptic cell can modulate the structure and function of the postsynaptic cell. We first present the evidence that this occurs, and then discuss two mechanisms that could bring this about. The first hypothesis relates to the long lasting effects that the spike patterns of presynaptic axons may exert by modulating activity–inducible large molecular signaling programs in post-synaptic cells. The second hypothesis is based on evidence has recently been obtained that the afferent neuron at the neuromuscular junction buds off exosomes at its synapse that carry a cargo of Wg and Evi, that are large molecular transsynaptic signaling agents (LMTSAs). Further evidence indicates that many types of neuron bud off exosomes that carry cargoes of various lipids, proteins and various types of RNA. These may be transmitted across the synapse and taken up by the postsynaptic structure either by perisynaptic or exosynaptic mechanisms, thus mediating information transfer between neurons. To date the molecular hypothesis has been limited to local interactions in the synapse concerned. In this paper we explore the possibility that this represents a mechanism for information transfer involving the postsynaptic neuron as a whole. This entails a review of the known functions of these molecules in neuronal function, together with an estimate of the possible types of information they could carry and how they might affect neurocomputations.
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