Double and triple labeling of neurons with fluorescent substances; the study of collateral pathways in the ascending raphe system.

A retrograde labeling procedure utilizing fluorescent substances (Granular Blue, Nuclear Yellow and propidium iodide) was used to establish the presence of branching axons in the ascending raphe system of young rats. After injections in septum, medial thalamus and olfactory cortex, the number of double-labeled cells in various combinations was found to be relatively large in the dorsal raphe nucleus, whereas triple-labeled cells occurred more rarely. Each class of neurons, i.e. single-, double- and triple-labeled, were shown to have a predominant distribution within specific parts of the nucleus.