Superfast Electrophoretic Transport of Carbocyanine Dyes In Situ: An Improved Method in Nerve Pathway Tracing

Carbocyanine dyes are an important tool used to trace the innervations to specific structures, and although the rate of dye transport has improved, faster rates are required to make these dyes effective especially in fixed tissues. We applied a direct electrical current to the sciatic nerve of a cat to electrophoretically transport pastes of DiI and DiD in situ , using a sodium borate (SB) buffer ‐ filled anode apparatus and hypodermic needle as a cathode. Dye labeling was visualized using a Bio‐Rad Radience 2100MP confocal microscope. DiI was transported at an average rate of 60.2 ± 4.1 mm/hr, which was >5,000 X faster than previously reported for crystal diffusion (Lukas et al. 1998, Swift et al. 2005) and 50 X faster than using a DC field in vitro . The average electrophoretic transport rate of DiD (60.9 ± 7.0 mm/hr) was similar to DiI. Lower crystal solubility and reverse micelle formation may be responsible for the slower diffusion rates reported previously. Use of the paste form with a lower alcohol content together with SB buffer solution, could reduce reverse micelle formation, and improve diffusion. Initial counter‐ion distribution at the anode may facilitate development of superfast electrophoresis in a weak field (5mA). This could allow the small ions to facilitate superfast electrophoretic transport of the carbocyanine dyes at low currents. Grant Funding Source : Palmer College of Chiropractic