Comparison of techniques for retrograde labeling using the rat's facial nucleus

This comparison of retrograde labeling substances was designed to define parameters which would produce the largest number of labeled neurons. The tracers are, horseradish peroxidase (HRP), wheat germ agglutinin (WGA), cholera toxin subunit B (CTB), wheat germ agglutinin-horseradish peroxidase conjugate (WGA-HRP), cholera toxin subunit B-horseradish peroxidase conjugate (CTB-HRP), Fast blue (FB), Diamidino yellow (DY), and Rhodamine microspheres (RH). The whiskerpad of 29 adult rats was injected with 50 microliters of one of these tracers. The animals were anesthetized and perfused with various concentrations of fixatives to determine the labeling efficiency of the tracers (number of neurons labeled irrespective of their individual mode(s) of transport). All labeled neurons were counted and the averages of the 5 largest counts from every third section of the facial nucleus were compared based on changes in the procedures. The largest number of neurons labeled occurred when WGA was used as the tracer. WGA-HRP and CTB were better than HRP and twice as effective as CTB-HRP. Fast blue and HRP were equally effective. DY did not label as many neurons as CTB-HRP. Rhodamine microspheres did not label any neurons of this peripheral system. Glutaraldehyde reduced the number of neurons labeled.