3-D TRACING OF BIOCYTIN-LABELED PALLIDO-THALAMIC AXONS IN THE MONKEY

THIS study presents three-dimensional tracings of axons and axonal end ings of associative pallido-thalamic axons in the monkey (Macaca mulat ta, M. irus). Injections of the anterograde tracer biocytin were made in the dorsal, associative region of the medial pallidum. Numerous axo nal endings were observed throughout the pallidal territory of the tha lamus. Four individual axons were reconstructed from serial sections a nd traced in three dimensions. The initial branch of each axon subdivi ded successively, each new branch ending in a different part of the pa llidal territory. Each of the latter branches ended in a characteristi c, extremely dense terminal arborization, that we called a bunch. Asso ciative medial pallidal information may therefore be distributed throu ghout the pallidal territory by means of numerous branches and bunches .