Hippocampal sympathetic ingrowth in rats and guinea pigs: quantitative morphometry and topographical differences.
Sympathetic ingrowth is an unusual neural rearrangement in response to damage of the septohippocampal pathway in which peripheral noradrenergic nerves grow into the hippocampal formation. Hippocampal ingrowth has been extensively studied in rats and has been suggested to be regulated by the mossy fibers of the dentate granule cells, hippocampal interneurons, or glial cells. Sympathetic ingrowth was found to occur in both rats and guinea pigs; however, a discrepancy between the species was observed in the topographical distribution of sympathetic ingrowth. Ingrowth fibers were found in the dentate hilus and area CA3 of guinea pigs and rats. However, in the guinea pig fibers extended into area CA1. Quantitative estimates of fiber number confirmed these observations and identified significant differences between the species in the intrahippocampal lamellar distribution of ingrowth fibers. The topographical differences in sympathetic ingrowth could not be explained by differences in the distribution of the mossy fibers (Timms stain), cholinergic septal afferents (anterograde HRP), or in hippocampal interneurons (GAD-immunoreactive neurons). These species differences are challenging to current theories concerning the regulation of sympathetic ingrowth and may provide a useful model for testing further hypotheses about axonal guidance and target selection.
D000818:Animals; D002799:Cholinergic Fibers / Q000502:physiology; D005968:Glutamate Decarboxylase / Q000378:metabolism; D006168:Guinea Pigs; D006624:Hippocampus / Q000201:enzymology / Q000502:physiology*; D007395:Interneurons / Q000201:enzymology; D008297:Male; D009473:Neuronal Plasticity; D051381:Rats; D012688:Septum Pellucidum / Q000502:physiology; D013045:Species Specificity; D013564:Sympathetic Nervous System / Q000502:physiology*
D005968:Glutamate Decarboxylase