Further observations on cerebellar climbing fibers. A study by means of light microscopy, confocal laser scanning microscopy and scanning and transmission electron microscopy

The intracortical pathways of climbing fibers were traced in several verteb rate cerebella using light microscopy, confocal laser scanning microscopy, scanning and transmission electron microscopy. They were identified as fine fibers up to 1(mum thick, with a characteristic crossing-over bifurcation pattern. Climbing fiber collaterals were tridimensionally visualized formin g thin climbing fiber glomeruli in the granular layer. Confocal laser scann ing microscopy revealed three types of collateral processes at the interfac e between granular and Purkinje cell layers. Scanning electron microscopy s howed climbing fiber retrograde collaterals in the molecular layer. Asymmet ric synaptic contacts of climbing fibers with Purkinje dendritic spines and stellate neuron dendrites were characterized by transmission electron micr oscopy. Correlative microscopy allowed us to obtain the basic three- dimens ional morphological features of climbing fibers in several vertebrates and to show with more accuracy a higher degree of lateral collateralization of these fibers within the cerebellar cortex. The correlative microscopy appro ach provides new views in the cerebellar cortex information processing.