Quantitative analysis of axodendritic and axosomatic collateral terminals of two feline spinocervical tract cells

The initial axon collaterals of two feline spinocervical tract cells have been ultrastructurally investigated after intracellular injection with horseradish peroxidase. A total of 200 axodendritic and 43 axosomatic terminals were analysed in serial section. The following variables were measured: the diameter and area of the bouton profiles, the areal densities of synaptic vesicles and mitochondria of the bouton profiles, the width and length of the synaptic clefts, the width of the postsynaptic densities, the width of the postsynaptic dendrites, and the width and length of axons between the boutons. Ten boutons were reconstructed for an investigation of the relation between measurements in two and three dimensions. All the measured variables showed wide ranges of variation. They were analysed statistically for significant differences between the cells and between the axodendritic and axosomatic boutons of each and both cells. Significant differences were mainly observed in the former comparison but they were also found between the axodendritic and axosomatic terminals of the individual cells.