Labelling of restricted numbers of axons by solid rhodamine implantation into nerve trunks

Solid rhodamine B isothiocyanate microsurgically implanted into mammalian peripheral nerve labels a small number of axons within that nerve. These axons can be observed in whole mounts or slices following fixation of the tissue approximately 16 h after the rhodamine is applied. The labelling appears to involve axoplasmic transport in both directions, for axons can be followed over long distances in the whole mounts. Since only some axons are labelled, their structure can be observed within large populations of cells in a whole nerve. This is valuable in interpreting axon counts in developmental and regenerative studies, and in observing the pattern of sprouting at regenerating axon terminals.