Imaging of Radicals Following Injury or Acute Stress in Peripheral Nerves with Activatable Fluorescent Probes

Peripheral nerve injury evokes a complex cascade of chemical reactions including generation of molecular radicals. Conversely, the reactions within nerve induced by stress are difficult to directly detect or measure to establish causality. Monitoring these reactions in vivo would enable deeper understanding of the nature of the injury and healing processes. Here, we utilized near-infrared fluorescence molecular probes delivered via intra-neural injection technique to enable live, in vivo imaging of tissue response associated with nerve injury and stress. These initially quenched fluorescent probes featured specific sensitivity to hydroxyl radicals and become fluorescent upon encountering reactive oxygen species (ROS). Intraneurally delivered probes demonstrated rapid activation in injured rat sciatic nerve but minimal activation in normal, uninjured nerve. In addition, these probes reported activation within sciatic nerves of living rats after a stress caused by a pinprick stimulus to the abdomen. This imaging approach was more sensitive to detecting changes within nerves due to the induced stress than other techniques to evaluate cellular and molecular changes. Specifically, neither histological analysis of the sciatic nerves, nor the expression of pain and stress associated genes in dorsal root ganglia could provide statistically significant differences between the control and stressed groups. Overall, the results demonstrate a novel imaging approach to measure ROS in addition to the impact of ROS within nerve in live animals.