Retrograde labeling of RNs in hemisected animals.

<p>Animals were subjected to spinal cord unilateral hemi-TX followed by complete TX caudal to the hemi-TX, as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0137670#pone.0137670.g001" target="_blank">Fig 1</a>. <b>A,</b> DAF 488-labeled RNs, whose axons were not originally injured by a right-sided hemi-TX. The right Mauthner (Mth) neuron is labeled because its axon decussates in the brainstem and projects to the contralateral spinal cord. In this case, its axon (arrowhead) had rapidly retracted to just below its decussation in the floor of the 4th ventricle. <b>B</b>, dual retrograde labeling of RNs. Those axotomized by a right-sided hemi-TX were back-labeled with DTMR (red), while those that were spared are labeled by DAF 488 (green) applied to a complete TX 5 weeks later. Mth and auxiliary Mauthner (mth) neurons have decussating axons and are labeled contralateral to other large (Müller) neurons. (The left M3 and M2 neurons were unintentionally labeled red because their axons are located near the spinal cord midline and were injured by the hemi-TX.) A Mth axon severed by the original hemi-TX (labeled red) had retracted to the 4^th ventricle and looped rostrally (arrowhead). This is shown at higher magnification in <b>C</b> and <b>C’</b>, in which the rostrally oriented axon and its terminal branches are followed at two focal planes. Numbers identify the same neurons, while the * indicates the same point on the axon. The point of axon looping is indicated by the arrowhead in <b>C’</b>. Arrows in <b>C</b> and <b>C’</b> point to terminal branches and sprouts emanating from the looping point, respectively.