Fluorescent Imaging and Microscopy for Dynamic Processes in Rats.

The rat is a favored model organism to study physiological function in vivo. This is largely due to the fact that it has been used for decades and is often more comparable to corresponding human conditions (both normal and pathologic) than mice. Although the development of genetic manipulations in rats has been slower than in mice, recent advances of new genomic editing tools allow for the generation of targeted global and specific cell type mutations in different rat strains. The rat is an ideal model for advancing imaging techniques like intravital multi-photon microscopy or IVMPM. Multi-photon excitation microscopy can be applied to visualize real-time physiologic events in multiple organs including the kidney. This imaging modality can generate four-dimensional high resolution images that are inherently confocal due to the fact that the photon density needed to excite fluorescence only occurs at the objective focal plane, not above or below. Additionally, longer excitation wavelengths allow for deeper penetration into tissue, improved excitation, and are inherently less phototoxic than shorter excitation wavelengths. Applying imaging tools to study physiology in rats has become a valuable scientific technique due to the relatively simple surgical procedures, improved quality of reagents, and reproducibility of established assays. In this chapter, the authors provide an example of the application of fluorescent techniques to study cardio-renal functions in rat models. Use of experimental procedures described here, together with multiple available genetically modified animal models, provide new prospective for the further application of multi-photon microscopy in basic and translational research.

In vivo microscopic voxel-based morphometry with a brain template to characterize strain-specific structures in the mouse brain.

Hundreds of inbred mouse strains are established for use in a broad spectrum of basic research fields, including genetics, neuroscience, immunology, and cancer. Inbred mice exhibit identical intra-strain genetics and divergent inter-strain phenotypes. The cognitive and behavioral divergences must be controlled by the variances of structure and function of their brains; however, the underlying morphological features of strain-to-strain difference remain obscure. Here, in vivo microscopic magnetic resonance imaging was optimized to image the mouse brains by using an isotropic resolution of 80 µm. Next, in vivo templates were created from the data from four major inbred mouse strains (C57Bl/6, BALB/cBy, C3H/He, and DBA/2). A strain-mixed brain template was also created, and the template was then employed to establish automatic voxel-based morphometry (VBM) for the mouse brain. The VBM assessment revealed strain-specific brain morphologies concerning the gray matter volume of the four strains, with a smaller volume in the primary visual cortex for the C3H/He strain, and a smaller volume in the primary auditory cortex and field CA1 of the hippocampus for the DBA/2 strain. These findings would contribute to the basis of for understanding morphological phenotype of the inbred mouse strain and may indicate a relationship between brain morphology and strain-specific cognition and behavior.