Comparisons between the use of true blue and diamidino yellow as retrograde fluorescent tracers.

The retrogradely transported fluorescent tracers True Blue and Diamidino Yellow were compared. They were found similar in the following respects: spread at injection sites; uptake from fibres of passage; fading of fluorescence and absence of retrograde transneuronal transport. Their fluorescence properties were, however, dissimilar and this, rather than differences in their sensitivity or efficiency, appears to account for their differences in respect of the intensities of fluorescence in such labelled neurones.