Variation between different samples of SITS with respect to axonal transport and toxicity.

Retrograde axonal transport of the fluorescent compound SITS has been described as occurring only from axon terminals and not from axons of passage. Injection of 4 different commercially available samples of SITS into terminations of cerebellar pathways in the rat revealed that only one sample produced retrogradely labelled neurones. Chemical analysis suggested that this was due to a unique fluorescent component (not SITS). This sample also contained other fluorescent components one of which, present in two other samples, produced paroxysmal motor disturbances. All of the samples examined contained several other fluorescent compounds.