Supporting synapse formation of regenerating axons by microtubule stabilization
After spinal cord injury, severed central axons fail to regenerate past the injury site. The loss of activating and modulating inputs below the lesion leads to loss of sensation and motor function below the lesion. In the past years several strategies have been developed to induce regeneration of injured axons in the central nervous system. Even though regenerating axons fail to reach their original target and form connections with other neurons in close proximity, the improvement of motor function is remarkable. While the regeneration-induced newly formed synaptic micronetworks in the injury site and below the lesion seem to play a major role in behavioral recovery, the nature of these circuits is undefined. We have recently shown that systemic administration of epothilone B treatment, a microtubule stabilizing drug, induces axon regeneration and functional recovery after a spinal cord injury. The next step is to elucidate the physiological role of the newly formed connections within the spinal microcircuitry. How do regenerating axons integrate into locomotion controlling microcircuits? In particular, we will describe the formation of the micronetworks after injury by using whole tissue imaging, which allows imaging of the whole lesioned area in three dimensions and tracking of fluorescently labeled axons, to identify and study presynaptic as well as postsynaptic sites. Finally, we will assess the functionality of the synapses. Cell types identified by transsynaptic markers as target cells of regenerating fibers will be characterized and the synaptic strength of the newly formed connections will be investigated with electrophysiological, optical and optogenetical tools. Together, this project will give us key insights into how lesioned axons regenerate and re-integrate into micronetworks to enhance functional recovery in the central nervous system.