Abstract
Three-dimensional neuroimaging at high resolution for visualization of complex nerve circuits in the whole brain is the dream of many neuroscientists. In order to study brain functions and apply to clinical neuroscience, precise three-dimensional knowledge of the topography and localization of brain structures and neurofunctional systems is very important. Several medical-imaging techniques such as MRI and PET have already been widely used to generate series of images for 3D reconstruction of the whole brain. However, connections between nerve fibers within the brain are too fine to be visualized with those conventional medical-imaging techniques. In contrast, confocal microscopy may provide sub-micron resolution for mapping brain circuits, but its field of view is limited by the objective lens used. Here, I use the brain of the fruitfly, Drosophila melanogaster, as a model system to establish methods allowing high-resolution imaging of the whole brain and comparisons of topographic variations of the brains among different flies. The ?D montage" technique was developed to combine two stacks of confocal images derived from each of the two brain hemispheres. As a result, fine structural details of the whole brain could be observed with high-resolution objective lens, recorded separately with confocal microscopy, combined into a single volume database and then three-dimensionally reconstructed. Several 3D models of Drosophila's brain showing all major neuropilar structures were created and morphometrically analyzed. The 3D models of mushroom bodies derived from different flies were three-dimensionally aligned using the "brain warping" technique based on external and internal 3D landmarks. Results of "brain warping" indicate that although the structures of mushroom bodies are extremely complicated their topography and volumetric parameters are invariant among different flies. The ideal of warping and combining two sets of brain neurons expressing different neuropeptides, allatostatin (AST) and leucokinine (LK) in two flies, is also practiced. The developed ?D montage" and "brain warping" techniques should be readily applicable for confocal imaging of larger brains such as rat or even human brains.