EM 3D-Reconstruction Technique And Study On Synaptic Ultrastructure In The Mouse

The study of synapse is one of the focuses in neurobiology and an important basis for functional study of neural system. Synaptic development and plasticity are involved in learning, memory, intelligence development of children, aging, neural trauma, neural repair and regeneration, and, various neural diseases such as Alzheimer's disease. The quantity, morphology and functional state of synapses are important indications for the function of neural system. In this work, the synaptic ultrastructure variations in submandibular ganglion (SMG) of wild type mice in the development process and that of APP/APLP2 double knockout mice were investigated. 3D-EM method based on ultrathin section and 3D image reconstruction is mastered by few laboratories in the world. In this method, a series of parallel sections are obtained from sample and their pictures were taken. The serial pictures are then positionally normalized and some subcellular structural objects (organelles) are traced and 3D images of the structures are reconstructed. The purposes of this work include setup of the 3D-EM platform and study of synaptic ultrastructure based on the platform. An improved method of sample-block trimming was developed. With this novel method, qualified sample-block of sizes less than 100 μm can be obtained quickly and conveniently with no need of expensive block-trimming machine and the required ultrathin sectioning can be obtained following the block trimming. The ultrstructural changes in the synapses of SMG of mice in development were investigated. Most of the axons around SMG cell body were short rod-like and few synaptic boutons were observed in neonatal mice. In contrast, most of the axons around SMG cell body show spherical heads in the 1-year mice. The number of non-synaptic axonal sections per unit area of SMG in neonatal mice was obviously larger than that in mature nice. Both the axon bundle and single axon were observed in neonatal mice while there was no axon bundle observed in matured ones. It is suggested that the number of axons connecting SMG cell body is decreasing in the mature process. The 3D synaptic structures of SMG in APP/APLP2 double knockout mice were reconstructed and investigated preliminarily. The obtained 3D images need further localized and quantified analysis to derive further conclusion.