Figure 6

Ultramicroscopy of mossy fiber boutons reveal severe synaptic vesicle reduction in mice expressing pro-aggregant Tau ^RDΔ . (a-b) Electron micrographs of mossy fiber synapses from a control littermate (a) and pro-aggregant Tau^RDΔ transgenic mouse (b). While the presynaptic mossy fiber bouton of the control animal is densely filled with clear synaptic vesicles (a, arrow), vesicle accumulations are rare in presynaptic mossy fiber boutons from pro-aggregant Tau^RDΔ mice (b, arrow). Rather, large parts of the presynaptic bouton area in the mutant are almost free of vesicles (asterisks). S = postsynaptic complex spines protruding into the presynaptic bouton. Scale bar: 300 nm. (c) Length of active zones and (d) number of synaptic vesicles/μm² in mossy fiber synapses from control (Ctrl) and Tau^RDΔ transgenic animals. While there is no statistically significant difference in the length of active zones of mossy fiber synapses between control mice and mutants, the number of vesicles/μm² bouton area is dramatically decreased in Tau^RDΔ transgenic mice. Data expressed as mean ± standard deviation. 4 animals per group ***p < 0.001; n.s. not significant; az = active zone.