Submitted to: Journal of Neuroscience
Publication Type: Proceedings
Publication Acceptance Date: December 1, 1997
Publication Date: N/A
Abstract. In the adult songbird forebrain, neurons continue to be produced in the subependymal zone (SZ) from which they migrate upon radial guide fibers. We have previously found that neuronal recruitment into the adult canary neostriatum is modulated by gonadal steroids, while neuronal outgrowth in culture is preferentially colocalized with ependymal and radial cell outgrowth. We therefore asked whether radial cells might provide neurotrophic support to their newly generated neuronal siblings. To this end, we focused upon the role of IGF-I, a trophic agent for neurons and their precursors, and a known estrogen-modulated agent, in the adult zebra finch forebrain. We found that IGF-I immunoreactivity (IGF-I IR) was expressed heavily by radial cells and their fibers; indeed most neostriatal IGF-I immunostaining was radial cell associated. Whether radial cell IGF-I was synthesized by these cells or sequestered by them after production elsewhere was unclear. Yet IGF-I's trophic effect upon adult SZ-derived neurons was unambiguous. When added to cultured explants of the adult zebra finch SZ, IGF-I increased neuronal outgrowth to greater than twice that observed in IGF-I deficient media. However, IGF-I neither accelerated neuronal outgrowth nor extended neuronal survival. These results suggest that in neurogenic regions of the adult avian forebrain, IGF-I might act as a radial cell-associated neuronal differentiation factor which may serve to regulate neuronal recruitment into the adult forebrain.