A comparative morphometric study of synaptic vesicles and other organelles in mossy fiber endings of the pigeon and the rat.

The mossy fiber ending organelles of 4 rats and 4 pigeons were studied using ultrastructural morphometric methods. The number of agranular vesicles per square micrometer of synaptic surface, as well as the number of agranular vesicles per synapse, were found to be greater in the rat than in the pigeon, while no significant differences were found in coated and dense core vesicles. A highly positive correlation was found, in both species, between the synaptic surface and the number of agranular vesicles per unit volume of mossy fiber endings, while no correlation was found between the synaptic surface and numerical densities of coated and dense core vesicles.