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Commissurally projecting inhibitory interneurons of the rat hippocampal dentate gyrus: A colocalization study of neuronal markers and the retrograde tracer fluoro‐gold
Author(s) -
Zappone Colin A.,
Sloviter Robert S.
Publication year - 2001
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.1415
Subject(s) - dentate gyrus , hippocampal formation , granule cell , neuroscience , biology , inhibitory postsynaptic potential , entorhinal cortex , neocortex , pyramidal cell , granule (geology) , parvalbumin , calretinin , anatomy , immunohistochemistry , paleontology , immunology
Improved methods for detecting neuronal markers and the retrograde tracer Fluoro‐Gold (FG) were used to identify commissurally projecting neurons of the rat hippocampus. In addition to the dentate hilar mossy cells and CA3 pyramidal cells shown previously to transport retrograde tracers after injection into the dorsal hippocampus, FG‐positive interneurons of the dentate granule cell layer and hilus were detected in numbers greater than previously reported. FG labeling of interneurons was variable among animals, but was as high as 96% of hilar somatostatin‐positive interneurons, 84% of parvalbumin‐positive cells of the granule cell layer and hilus combined, and 33% of hilar calretinin‐positive cells. By comparison, interneurons of the dentate molecular layer and all hippocampal subregions were conspicuously FG‐negative. Whereas hilar mossy cells and CA3 pyramidal cells were FG‐labeled throughout the longitudinal axis, FG‐positive interneurons exhibited a relatively homotopic distribution. “Control” injections of FG into the neocortex, septum, and ventral hippocampus demonstrated that the homotopic labeling of dentate interneurons was injection site‐specific, and that the CA1‐CA3 interneurons unlabeled by contralateral hippocampal FG injection were nonetheless able to transport FG from the septum. These data suggest a hippocampal organizing principle according to which virtually all commissurally projecting hippocampal neurons share the property of being monosynaptic targets of dentate granule cells. Because granule cells innervate their exclusively ipsilateral target cells in a highly lamellar pattern, these results suggest that focal granule cell excitation may result in commissural inhibition of the corresponding “twin” granule cell lamella, thereby lateralizing and amplifying the influence of the initiating discharge. J. Comp. Neurol. 441:324–344, 2001. © 2001 Wiley‐Liss, Inc.