5360 Average Synapses formed per axon 40 Number of corticostriatal axons participating 381180 a. Based on a spherical dendritic tree of 400 m diameter. Based on Oorschot, 1996. Based on Ingham et al., 1996. Based on the assumption that corticostriatal inputs form half of the total asymmetric synapses.
Synapses occur exclusively at varicosities on corticostriatal axons.
The diameters of the intervaricose regions cannot be measured accurately, but the varicosities were as large as 1 m in diameter. B. High Voltage Electron Micrograph from a 4 m thick section through axons as in A. Intervaricose segments were resolved, and could be measured to be approximately 0.1 m in diameter. Varicosities were between 0.2 and 1.0 m. C. Thin section conventional electron micrograph through a varicosity on a BDA labeled corticostriatal axon. A single synapse was formed with a an unlabeled dendritic spine.