Functional roles of microtubules in a giant presynaptic terminal

The functional roles of cytoskeletal elements actin and microtubule are well established in various cellular processes. However, their role in axon terminals is still unclear. Here, I started my thesis study by questioning the role of actin filaments at the calyx of Held presynaptic terminals in developing rats before and after hearing onset. Having observed that actin filaments are involved in synaptic vesicle recruitment in pre-hearing rats, but not in post-hearing rats, I then proceeded to address the functional roles of the other cytoskeletal element, namely microtubules in rats after hearing onset. I have used a combination of tools to address both the functional and morphological aspects. I found that both cytoskeletal elements play significant roles in regulating synaptic transmission.Okinawa Institute of Science and Technology Graduate Universit

Microtubule and actin differentially regulate synaptic vesicle cycling to maintain high-frequency neurotransmission

Cytoskeletal filaments such as microtubules (MTs) and filamentous actin (F-actin) dynamically support cell structure and functions. In central presynaptic terminals, F-actin is expressed along the release edge and reportedly plays diverse functional roles, but whether axonal MTs extend deep into terminals and play any physiological role remains controversial. At the calyx of Held in rats of either sex, confocal and high-resolution microscopy revealed that MTs enter deep into presynaptic terminal swellings and partially colocalize with a subset of synaptic vesicles (SVs). Electrophysiological analysis demonstrated that depolymerization of MTs specifically prolonged the slow-recovery time component of EPSCs from short-term depression induced by a train of high-frequency stimulation, whereas depolymerization of F-actin specifically prolonged the fast-recovery component. In simultaneous presynaptic and postsynaptic action potential recordings, depolymerization of MTs or F-actin significantly impaired the fidelity of high-frequency neurotransmission. We conclude that MTs and F-actin differentially contribute to slow and fast SV replenishment, thereby maintaining high-frequency neurotransmission