Glioanatomy assessed by cell-cell interactions and phagocytotic labelling

In the last three decades of research in neuroscience, fluorescent probes h ave gone from technical tools in the studies of physicochemical reactions, to being versatile tools in developmental neurobiology, neuroanatomy, angio graphy, neuromorphology, connectivity, cell death and even photodynamic the rapy. Fluorescent dyes belong to heterogeneous groups of substances, but th e feature to emit light of a certain wavelength depends on the energy statu s of the corresponding chemical bond. Therefore, light emission can range f rom the blue to the infrared spectrum, thus allowing multiple stains of the same cell, or event. The heterogeneity in their structure allows applicati on of some fluorescent dyes for anterograde long-tract labelling, whereas o thers can be used for retrograde tracing. Lipophilic dyes are suitable for intramembraneous diffusion along cell membranes post-mortem, whereas hydrop hilic stains seem more suitable for genealogic cell studies over several ce ll divisions. In the same time, less attention has been paid by most resear chers to the use of fluorescent dyes to monitor neuroglial interactions and glioanatomy in the healthy and diseased brain. Studies of cell-cell-intera ctions during apoptosis can now be carried out with sequestration and subse quent phagocytosis of intracellular dyes. The present review focuses on rec ent developments that include the use of fluorescent probes. These probes m ake it possible to transneuronally assess functions of glial cells during p rogrammed cell death, or induced degeneration. The high variety of availabl e dyes, and their particular accumulation within subcellular compartments, is promising to shed light on some glial cell geometry and functions. The l essons obtained from the vast number of studies in neurons are of increasin g importance for cells too, as their functions are not directly accessible. In short, some glial-glial and neuroglial negotiations will be analysed in near future by developing new, or by modifying existing fluorescent probes . (C) 2000 Elsevier Science B.V. All rights reserved.