SURVIVAL, REGENERATION AND SPROUTING OF CENTRAL NEURONS - THE RAT SEPTOHIPPOCAMPAL PROJECTION AS A MODEL

The septohippocampal projection was used to study the survival followi ng axotomy, axonal regeneration, and sprouting of a defined group of c entral neurons. Septohippocampal projection neurons in adult rats were axotomized by bilateral lesions of the fimbria-fornix. Using prelabel ing prior to axotomy, intracellular staining, electron microscopy, and immunocytochemical and in situ hybridization techniques, we were able to demonstrate that the majority of septohippocampal neurons survived after axotomy. At least in young postnatal rats, these axotomized neu rons have the capacity to regenerate an axonal process that reinnervat es its appropriate target tissue, the hippocampus. We demonstrated thi s by axotomizing young septohippocampal neurons and co-culturing them with sections of hippocampus. Septohippocampal neurons appear to retai n their capacity for axonal growth in adulthood, since they are able t o sprout within hippocampal layers partially denervated by removing en torhinal afferents. In this paradigm the terminals of septohippocampal neurons themselves were not lesioned. Our results point to a previous ly underestimated capacity of septohippocampal neurons for survival fo llowing axotomy, regeneration, and sprouting.