Unique synaptic topography of crest-type synapses in the interpeduncular nucleus.

Neurons in the central nervous system display a great diversity of synaptic architecture. While much of our knowledge on the excitatory synapse morphology derives from the prototypical asymmetric synapses, little has been studied about the atypical crest-type synapse that exists in the restricted brain regions. Here, we used focused ion beam scanning electron microscopy (FIB/SEM) to image a neuropil volume of interpeduncular nucleus (IPN) and manually reconstructed several dendrites to obtain an insight about the topography and quantitative features of crest synapses. Three-dimensional reconstruction showed numerous U-shaped structures protruding from the IPN dendrites. On either faces of the U-shaped structure, a pair of crest synapses are aligned in parallel such that there exists a positive correlation between the postsynaptic density (PSD) area of synapses that participate in pair formation. Interestingly, mitochondria are excluded from the site of crest synapses. Several presynaptic axons run through the hollow, cylindrical space of the U-shape grooves such that the plasma membrane of the axon and the dendrite are organized in a tight opposition without any intervening glial membrane. Unlike the peculiar dendritic morphology, IPN neurons possess typical somatic morphology with an oval, centrally located nucleus. In conclusion, our data reveals a hitherto unknown unique topographical feature of crest synapses in the IPN.

Developmental Changes in Dendritic Spine Morphology in the Striatum and Their Alteration in an A53T α-Synuclein Transgenic Mouse Model of Parkinson's Disease.

The aging process is accompanied by various neurophysiological changes, and the severity of neurodegenerative disorders such as Parkinson's disease (PD) increases with aging. However, the precise neuroanatomical changes that accompany the aging process in both normal and pathologic conditions remain unknown. This is in part because there is a lack of high-resolution imaging tool that has the capacity to image a desired volume of neurons in a high-throughput and automated manner. In the present study, focused ion beam/scanning electron microscopy (FIB/SEM) was used to image striatal neuropil in both wild-type (WT) mice and an A53T bacterial artificial chromosome (BAC) human α-synuclein (A53T-BAC-SNCA) transgenic (Tg) mouse model of PD, at 1, 3, 6, and 22 months of age. We demonstrated that spine density gradually decreases, and average spine head volume gradually increases with age in WT mice, suggesting a homeostatic balance between spine head volume and spine density. However, this inverse relationship between spine head volume and spine density was not observed in A53T-BAC-SNCA Tg mice. Taken together, our data suggest that PD is accompanied by an abnormality in the mechanisms that control synapse growth and maturity.