TY - JOUR T1 - <em>In Vivo</em> Nerve–Macrophage Interactions Following Peripheral Nerve Injury JF - The Journal of Neuroscience JO - J. Neurosci. SP - 3898 LP - 3909 DO - 10.1523/JNEUROSCI.5225-11.2012 VL - 32 IS - 11 AU - Allison F. Rosenberg AU - Marc A. Wolman AU - Clara Franzini-Armstrong AU - Michael Granato Y1 - 2012/03/14 UR - http://www.jneurosci.org/content/32/11/3898.abstract N2 - In vertebrates, the peripheral nervous system has retained its regenerative capacity, enabling severed axons to reconnect with their original synaptic targets. While it is well documented that a favorable environment is critical for nerve regeneration, the complex cellular interactions between injured nerves with cells in their environment, as well as the functional significance of these interactions, have not been determined in vivo and in real time. Here we provide the first minute-by-minute account of cellular interactions between laser transected motor nerves and macrophages in live intact zebrafish. We show that macrophages arrive at the lesion site long before axon fragmentation, much earlier than previously thought. Moreover, we find that axon fragmentation triggers macrophage invasion into the nerve to engulf axonal debris, and that delaying nerve fragmentation in a Wlds model does not alter macrophage recruitment but induces a previously unknown ‘nerve scanning’ behavior, suggesting that macrophage recruitment and subsequent nerve invasion are controlled by separate mechanisms. Finally, we demonstrate that macrophage recruitment, thought to be dependent on Schwann cell-derived signals, occurs independently of Schwann cells. Thus, live cell imaging defines novel cellular and functional interactions between injured nerves and immune cells. ER -