Tilt analysis of pleomorphic vesicles in the superficial layers of the superior colliculus of Galago and chimpanzee.

Pleomorphic vesicles in two different classes of 'flat-vesicle-containing profiles'(F-profiles) from the superficial layers of the superior colliculus of Galago and chimpanzee were found to be disk-like in shape as revealed by tilt analysis. In both primates, presynaptic dendrites, postsynaptic F-profiles and exclusively presynaptic F-profiles cannot be distinguished on the basis of vesicle morphology. This lends to support to the notion that F-profiles originate from one type of neuron. Modifications of the basic disk shape are interpreted as manifestations of different stages in the life cycle of individual vesicles.