3-DIMENSIONAL RECONSTRUCTIONS OF AUTONOMIC PROJECTIONS TO THE GASTROINTESTINAL-TRACT

Three-dimensional reconstruction protocols in confocal microscopy are typically considered in terms of rendering separate stacks of optical sections. Single stacks, however, include volumes that are often too s mall to permit descriptions of entire neurons, complete axonal arbors, or complex neural networks. Furthermore, traditional tissue preparati on protocols generally yield specimens too limited to permit reconstru ctions of complex neural systems. For 3-D analyses of extensive networ ks such as the autonomic nervous system projections within the viscera , it is critical to incorporate appropriate tissue techniques, includi ng suitable tracer protocols, into the reconstruction strategy. This r eport summarizes complementary technologies, including whole mount pro cedures, tracer techniques for identifying single fibers in situ, and methods of examining stacks of optical images, which make it practical to describe the complete terminal field of an individual axon in the gastrointestinal tract. Such methods establish that vagal motor axons travel long distances within their target organs, collateralize freque ntly, and ramify extensively. Vagal afferents have extensive, complex, and, in some cases, polytopic arbors within target tissues. (C) 1994 Wiley-Liss, Inc.