Sympathetic sprouting and recovery of a spatial behavior

After lesions of the medial septum, peripheral sympathetic fibers from the superior cervical ganglion appear in the hippocampal formation. To assess the functional significance of this neuronal rearrangement, we analyzed behavior on a spatial/memory task sensitive to hippocampal dysfunction, the radial eight-arm maze. The procedure allowed evaluation of both working and reference memory. All rats were able to master the task. Half of the rats then underwent either medial septal lesions and ganglionectomy or sham neurosurgery and ganglionectomy, and the other half underwent medial septal lesions or sham neurosurgery followed by ganglionectomy after further behavioral testing. Medial septal lesions in both groups disrupted taks performance with recovery of performance occurring with time. However, the rate of recovery was significantly enhanced in rats which had septal lesions and ganglionectomies simultaneously. Removal of the ganglion after recovery produced no effects on maze performance. Our results suggest that sympathetic ingrowth retards recovery processes.