Biotinylated dextran amine and biocytin hydrochloride are useful tracers for the study of retinal projections in the...

Anatomical study of the topographic organization of retinal projections requires a tracer capable of resolving fine morphological detail and permitting analysis of the projection from either the whole retina or selected areas. To obtain a permanent record of the experiments and to have access to ultrastructural data, it is preferable for the tracer to be compatible with both brightfield microscopy and electron microscopy. Biotinylated dextran amine and biocytin hydrochloride, as employed in the present experiments, meet these needs exceptionally well for anterograde tracing studies on the frog visual system. Both tracers labeled axons and terminal arbors more prominently than comparable material studied by the widely used methods of anterograde fiber-filling with horseradish peroxidase or cobalt. When used to trace the projections from small sectors of retina, the finest unmyelinated fibers in layers A, C and E of the frog optic tectum and their synaptic boutons were made readily visible by the new tracers.