Evaluation of the effects of various additives on retrograde labelling by horseradish peroxidase applied to intact and transected hindlimb nerves of rat and rabbit

The numbers of retrogradely labelled motor, sensory and sympathetic neurons were determined after application of concentrated solutions of horseradish peroxidase to transected rat sural and medial gastrocnemius nerves and rabbit sural nerves. In some experiments, the number of labelled cell bodies approached the number of axons counted from electronmicrographs of the nerve trunk. In the other experiments, deficits apparently resulted from failure to label some small neurons, because the mean size of labelled somata was higher. Incorporation of dimethylsulphoxide, poly- l-ornithine or a detergent (Teric-X8) in the applied solution did not significantly increase the number of labelled neurons. When horseradish peroxidase was applied outside nerves that were not transected, only the inclusion of Teric-X8 consistently produced labelling, but of