The time course of retrograde transsynaptic transport of tetanus toxin fragment C in the oculomotor system of the rabbit after injection into extraocular eye muscles.

The aim of this study was to determine the optimal survival time for labelling those neurons that monosynaptically terminate on extraocular motoneurons, i.e. the premotor neurons, after an injection of tetanus toxin fragment C, a retrograde transsynaptic tracer substance, into the eye muscle of the rabbit. Concentrated fragment C was injected into the inferior rectus or inferior oblique muscle and detected immunocytochemically in the brain after survival times of 8 h, 17 h, 2 d, 3 d, 4 d, 5 d, 6 d, 8 d, and 12 d. Immunoreactivity was confined to granules within motoneuronal and premotor neuronal cell bodies, but became associated with punctate profiles outlining the somata with longer survival times. The strongest and most consistent labelling of premotor cell bodies was seen after 4 days survival time. The transsynaptic labelling pattern was shown to vary for individual premotor pathways.