We have shown a potential link between mechanical tension in neurons, and memory and learning in animals. It has so far been believed that biochemical signaling is the basis for memory formation and learning process. Mechanical force in neurons has never been considered as a possible player. It is well understood today that memory and learning are mediated by neurotransmitters that are released from vesicles clustered at the synaptic terminal (end point of axon – a long arm of the neuron). As a synapse is used more frequently, its neurotransmission efficiency increases, partly because of increased vesicle clustering in the synapse, i.e., the synapse remembers its past usage, which offers the basis for understanding memory. We (together with Chiba lab, University of Maimi) conducted in vivo experiments on embryonic Drosophila (fruit fly) nervous system and showed that vesicle clustering at the neuromuscular synapse depends on mechanical tension within the axons. Vesicle clustering vanishes upon severing the axon from the cell body, but is restored when mechanical tension is applied to the severed end of the axon. Clustering increases when intact axons are stretched mechanically. Using nano mechanical force sensors that touch single neurons of the embryos, we found that embryonic axons that have formed neuromuscular junctions maintain a rest tension of about one nano Newton, which appears to be essential for neurotransmission. The study thus adds a new paradigm in the understanding of memory and learning.
Currently, we are addressing the following questions: (1) What is the mechanism of force generation in embryonic fly axons? (2) What is the role of axonal tension in post synaptic excitation? (3) How does tension in axons modulate short and long term potentiation? (4) What is the role of tension in axonal transport? We are using embryonic fruit flies, adult cray fish, and rat brain slices to address these questions.