A computer-aided light microscopy system for three-dimensional reconstruction of axonal projections

Axons allow nerve cells (neurons) to signal each other over long distances. Axonal projection patterns determine the organization of the central nervous system. Morphological techniques to analyse axonal projections systematically include tracing the trajectory of labelled axons, mapping the distribution of labelled axonal terminals and nerve cell bodies and reconstructing their original spatial arrangement. The camera lucida apparatus, in combination with the microscope, has been used for mapping and tracing labelled microscopic structures such as axons, terminals, and cell bodies for more than a century. Although two-dimensional mapping and tracing can be done efficiently with the camera lucida apparatus in single histological sections of the central nervous system, reconstruction of the three-dimensional nature of axonal projections and microscopic organization of the central nervous system has been too difficult or expensive to be generally performed using this technique. We have been developing a computer-aided light microscopy system with commercially available software for personal or industrial use (Adobe Illustrator and Robert McNeel Rhinoceros). In this system, a computer monitor is connected to the camera lucida apparatus, so that one can directly draw labelled structures viewed under the microscope with the software. This system enables efficient tracing, mapping and reconstruction of microscopic structures in three-dimensional space from serial sections. The technical aspects of this system are described in this chapter.