Target regulation of sympathetic sprouting in the rat hippocampal formation

Sympathetic fibers appear in the rat hippocampal formation after lesions of the medial septal nucleus. The distribution of sympathetic axons correlates most closely with the distribution of dentate granule cells and their axons. To test the hypothesis that granule cells are the targets of sympathetic fibers, neurotoxins were injected to destroy either the granule cells (colchicine) or the pyramidal cells (kainic acid) in the hippocampal formation 1 month prior to placing septal lesions. Sympathetic fibers appeared in animals with kainic acid lesions but not in regions lacking granule cells in animals treated with colchicine. These results support the hypothesis that the granule cells of the dentate gyrus are the targets of sprouting sympathetic fibers.