EFFECTS OF THE NEUROTROPHINS NERVE GROWTH-FACTOR, NEUROTROPHIN-3, ANDBRAIN-DERIVED NEUROTROPHIC FACTOR (BDNF) ON NEURITE GROWTH FROM ADULTSENSORY NEURONS IN COMPARTMENTED CULTURES

We used compartmented cultures to study the regulation of adult sensor y neurite growth by neurotrophins. We examined the effects of the neur otrophins nerve growth factor (NGF), neurotrophin-3 (NT3), and BDNF on distal neurite elongation from adult rat dorsal root ganglion (DRG) n eurons. Neurons were prated in the center compartments of three-chambe red dishes in the absence of neurotrophin, and neurite extension into the distal (side) compartments containing NGF, BDNF, or NT3 was quanti tated. Initial proximal neurite growth did not require any of the neur otrophins, while subsequent elongation into distal compartments requir ed NGF. After neurites had extended into NGF-containing distal compart ments, removal of NGF by treatment with anti-NGF resulted in the cessa tion of growth with minimal neurite retraction. In contrast to the eff ects of NGF, no distal neurite elongation was observed into compartmen ts with BDNF or NT3. To examine possible additive influences, neurite extension into compartments containing BDNF plus NGF or NT3 plus NGF w as quantitated. There was no increased neurite extension into NGF plus NT3 compartments, while the combination of BDNF plus NGF resulted in an inhibition of neurite extension compared with NGF alone. We then in vestigated whether the regrowth of neurites that had originally grown into NGF subsequent to in vitro axotomy still required NGF. The result s demonstrated that unlike adult sensory nerve regeneration in vivo, t he in vitro regrowth did require NGF, and neither BDNF nor NT3 was abl e to substitute for NGF. Since the initial growth from neurons after d issociation (which is also a regenerative response) did not require NG F, it would appear that neuritic growth and regrowth of adult DRG neur ons in vitro includes both NGF-independent and NGF-dependent component s. The compartmented culture system provides a unique model to further study aspects of this differential regulation of neurite growth. (C) 1997 John Wiley & Sons, Inc.