carbocyanines and Peripheral-Nerve-Injuries

Motor endplates (MEPs) are the important interfaces between peripheral nerves and muscle fibers. Investigation of the spatial distribution of MEPs could help us better understand neuromuscular functional activities and improve the diagnosis and therapy of related diseases.

Topics: Action Potentials; Animals; Bungarotoxins; Carbocyanines; Imaging, Three-Dimensional; Mice; Mice, Inbred C57BL; Microscopy, Confocal; Microscopy, Fluorescence; Motor Endplate; Muscle Denervation; Muscle, Skeletal; Peripheral Nerve Injuries

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.

Topics: Animals; Carbocyanines; Fluorescent Dyes; Ganglia, Spinal; Hydroxyl Radical; Injections, Intralesional; Male; Optical Imaging; Peripheral Nerve Injuries; Rats; Rats, Sprague-Dawley; Sciatic Nerve

It is generally believed that nerve injury results in neuronal hyperexcitability that reflects in part a change in Na+ currents. However, there are conflicting data on the nature of Na+ current changes and the association between alterations in Na+ currents and increases in excitability. One potential source of conflicting data is that injured and spared neurons may respond differently to nerve injury; these subpopulations of neurons have not been distinguished in previous studies with the axotomy model of nerve injury (complete transection of the sciatic nerve). The present study was performed to determine the relationship between changes in Na+ channels and changes in neuronal excitability in identified injured dorsal root ganglion neurons post-axotomy. Small (< 45 pF) neurons labeled with a DiI injection into the sciatic nerve were studied 10 days and 4 weeks post-axotomy. Ten days post-axotomy, tetrodotoxin-resistant (TTX-R) Na+ current (INa) was decreased and TTX-sensitive (TTX-S) INa was increased, however, excitability was unchanged. Four weeks post-axotomy, neurons had become hyperexcitable while TTX-R INa remained reduced and TTX-S INa had returned to control levels. Thus, axotomy-induced changes in Na+ currents were not correlated with an axotomy-induced change in excitability. Additional analysis of axotomized neurons suggested that concomitant changes in other ionic currents occurred. These results suggest that neuronal excitability following axotomy is dependent on the sum of changes in ionic currents, and the overall effect on excitability may not always correspond to that predicted by a change in a single class of voltage-gated ion channel.

Topics: Action Potentials; Animals; Axotomy; Carbocyanines; Cell Membrane; Cells, Cultured; Ganglia, Spinal; Male; Membrane Potentials; Neural Conduction; Neurons, Afferent; Patch-Clamp Techniques; Peripheral Nerve Injuries; Peripheral Nerves; Rats; Rats, Sprague-Dawley; Sciatic Neuropathy; Sodium Channel Blockers; Sodium Channels; Tetrodotoxin