Motor neurons that multitask

Can repetitive mechanical motion cause structural damage to axons?

Biological structures have evolved to very efficiently generate, transmit, and withstand mechanical forces. These biological examples have inspired mechanical engineers for centuries and led to the development of critical insights and concepts. However, progress in mechanical engineering also raises new questions about biological structures. The past decades have seen the increasing study of failure of engineered structures due to repetitive loading, and its origin in processes such as materials fatigue. Repetitive loading is also experienced by some neurons, for example in the peripheral nervous system. This perspective, after briefly introducing the engineering concept of mechanical fatigue, aims to discuss the potential effects based on our knowledge of cellular responses to mechanical stresses. A particular focus of our discussion are the effects of mechanical stress on axons and their cytoskeletal structures. Furthermore, we highlight the difficulty of imaging these structures and the promise of new microscopy techniques. The identification of repair mechanisms and paradigms underlying long-term stability is an exciting and emerging topic in biology as well as a potential source of inspiration for engineers.

Developmental and genetic mechanisms of neural circuit evolution

Regardless of how a nervous system is genetically built, natural selection is acting on the functional outcome of its activity. To understand how nervous systems evolve, it is essential to analyze how their functional units - the neural circuits - change and adapt over time. A neural circuit can evolve in many different ways, and the underlying developmental and genetic mechanisms involve different sets of genes. Therefore, the comparison of gene expression can help reconstructing circuit evolution, as demonstrated by several examples in sensory systems. Functional constraints on neural circuit evolution suggest that in nervous systems developmental and genetic variants do not appear randomly, and that the evolution of neuroanatomy might be biased. Sensory systems, in particular, seem to evolve along trajectories that enhance their evolvability, ensuring adaptation to different environments.