An autoradiographic identification of Purkinje axon terminals in the cat

Summary The Purkinje axon boutons terminating in nuclei fastigii and interpositus in the cat have been identified after injection of³H leucine into the cerebellar cortex overlying the nuclei. The animals survived from 4–48 h after injection of the isotope. Semithin and ultrathin sections were coated and exposed for 3 and 14 weeks, respectively. The electron micrographs showed labelling over myelinated axons down to a diameter of 0.8 m, and over boutons.Fifty labelled boutons were used for identification of the shape of their synaptic vesicles. The statistical analysis including the test for skewness showed that 39 boutons (78%) fall in one group. Most of the synaptic vesicles in this group are elliptical (ration from 11.1 – 11.7). Slightly ovoid vesicles (ration up to 11.3) are frequent, but flattened vesicles (ration above 11.7) are relatively few in this group of boutons. 8% of the boutons have a rather homogeneous vesicle population (prevalence of round vesicles, ratio 11).Synaptic specializations of Gray's type II or of an intermediate type were found in the boutons belonging to the first group (78% of the boutons). Specializations of Gray's type I were found in the other bouton groups (8% of the boutons).