2 MORPHOLOGICALLY DIFFERENT TYPES OF RETINAL AXON TERMINALS IN THE RATS DORSAL LATERAL GENICULATE-NUCLEUS AND THEIR RELATIONSHIPS TO THE X-CHANNEL AND Y-CHANNEL

In the rat''s dorsal lateral geniculate nucleus (dLGN) 2 types of retino-geniculate axon terminals were visualized using EM in adult and juvenile material and in Golgi-Kopsch and Golgi-Rapid impregnated sections. The 2 types differ in size and number of boutons. 2a-terminals have large, sparse boutons, mainly connected with branching zones of geniculo-cortical relay cells (GCR cells). 2b-terminals bear numerous small boutons forming simple contacts with more distal segments of GCR cell dendrites. After horseradish peroxidase (HRP) injection in the superior colliculus optic tract, fibers and lateral fiber bundles in the dLGN are labeled with reaction product. Beside these tracts the terminal branching zones of retino-tectal fiber collaterals in the dLGN also show reaction product. As a result of the good visualization of these retinal terminals by the HRP-method they are identified as 2a-terminals. 2a-terminals may represent the Y-channel projecting from the retina to both the superior colliculus and the dLGN.