Control of Presynaptic Function by Axonal Dynamics

Neuronal transmission at a synaptic contact is determined by the number of synaptic vesicles exocytosed from the presynaptic bouton and the postsynaptic responsiveness to transmitter released from a single synaptic vesicle. The signal arriving at individual presynaptic compartments along an axon, the action potential, has traditionally been considered as an all-or-none type of stable digital information, equally activating individual presynaptic structures. However, accumulating evidence challenges this view and suggests that the axon performs rich computations that influence neuronal integration, signal transmission, synaptic efficacy and plasticity. Although the technical difficulties arising from the small size and complex anatomy of the axon/presynaptic terminals have impeded the study of axonal physiology, recent technical advances to directly record from axonal compartments have contributed to unveil the detailed mechanisms of axonal dynamics, such as the unique membrane excitability of the axon, the analogue-type of signal propagation from somatodendritic compartments to presynaptic terminals, the local activation of axonal iono- and metabotropic receptors, and the activity-dependent modulation of action potentials. Furthermore, recent improvements of fluorescent imaging techniques are shedding light on the spatiotemporal dynamics of axonal signal propagation and the exocytosis of individual synaptic vesicles. Together with the identification of the molecular components of release sites in small presynaptic structures, these advances are giving rise to a comprehensive understanding of the functional design of the presynaptic release machinery.

In this Research Topic, recent findings on the dynamic modulation of axonal and presynaptic function will be highlighted by the methodological tour de force of direct patch-clamp recordings from a variety of axonal compartments in the central nervous system. In addition to electrophysiological techniques, an attempt to directly visualize the dynamics of presynaptic function with fluorescent imaging methods will also be highly appreciated. We welcome any type of contribution including original research, review, and perspective.