Experimental evidence for climbing fibers in the avian cerebellum

This study identifies climbing fibers in the cerebellar cortex following brain stem lesions. Antegrade nerve fiber degeneration was studied after electrolytic destruction of rhombencephalic structures in 24 domestic fowl. Direct damage to the cerebellum was precluded by a retropharyngeal surgical approach. Only lesions that include the inferior olivary nucleus were compatible with Fink-Heimer staining of degeneratin nerve fibers in the Purkinje cell and molecular layer. Degenerating axons were identified as climbing fibers from their trajectory in association with Purkinje cell soma and dendrites. Terminal nerve endings were observed only in the basal one-third to one-half of the molecular layer. The presence of climbing fibers in only the contralateral molecular layer was observed in autoradiographic preparation subsequent to unilateral injection of tritiated leucine into the inferior olivary nucleus of three hens. The morphology of the labeled and impregnated degenerating nerve fibers closely coincides with information provided by previous investigators using Golgi stained histological preparations and electron microscopy.