In Vivo Visualization of Single Axons and Synaptic Remodeling in Normal and Pathological Conditions

Charting the trajectory of individual axons within the intact central nervous system during development into maturity and into the normal aging process has long been the holy grail of neuroimaging. We review a range of approaches that have historically been used to visualize axons, which culminate in the powerful combination of transgenic technologies and microscopy techniques allowing direct observation of axonal dynamics in the intact cerebral cortex. Using animal models of health and disease, the visualization of axons and their connectivity over extended periods of time has become a reality. In this chapter, we review our current knowledge of axonal dynamics in the healthy brain, as well as in a range of neurodevelopmental disorders, neurodegenerative pathologies including dementia, and in response to sensory manipulations and trauma.