Molecular heterogeneity of central synapses: afferent and target regulation

Electrophysiological recordings show a functional spectrum even within a single class of synapse, with individual synapses ranging widely in fundamental properties, including release probability, unitary response and effects of previous stimulation on subsequent response. Molecular and cellular biological approaches have shown a corresponding diversity in the complement of ion channels, receptors, scaffolds and signal transducing proteins that make up individual synapses. Indeed, we believe that each individual synapse is unique, a function of presynaptic cell type, postsynaptic cell type, environment, developmental stage and history of activity. We review here the molecular diversity of glutamatergic and GABAergic synapses in the mammalian brain in the context of potential cell biological mechanisms that may explain how individual cells develop and maintain such a mosaic of synaptic connections.