BIOTINYLATED DEXTRAN-AMINE AND BIOCYTIN HYDROCHLORIDE ARE USEFUL TRACERS FOR THE STUDY OF RETINAL PROJECTIONS IN THE FROG

Anatomical study of the topographic organization of retinal projection s 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 t o have access to ultrastructural data, it is preferable for the tracer to be compatible with both brightfield microscopy and electron micros copy. Biotinylated dextran amine and biocytin hydrochloride, as employ ed in the present experiments, meet these needs exceptionally well for anterograde tracing studies on the frog visual system. Both tracers l abeled axons and terminal arbors more prominently than comparable mate rial studied by the widely used methods of anterograde fiber-filling w ith horseradish peroxidase or cobalt. When used to trace the projectio ns from small sectors of retina, the finest unmyelinated fibers in lay ers A, C and E of the frog optic tectum and their synaptic boutons wer e made readily visible by the new tracers. (C) 1997 Elsevier Science B .V.