title: Characterization of medial septal glutamatergic neurons and their projection to the hippocampus.
abstract: The two neuronal populations that have been typically investigated in the septum use acetylcholine and GABA as neurotransmitters. The existence of noncholinergic, non-GABAergic, most likely glutamatergic septal neurons has recently been reported. However, their morphological characteristics, numbers, distribution, and connectivity have not been determined. Furthermore, the projection of septal glutamatergic neurons to the hippocampus has not been characterized. To address these issues, subpopulations of cholinergic and GABAergic neurons were identified by immunohistochemistry. In addition, the retrograde tracer fluorogold was injected into the hippocampus to determine the characteristics of a glutamatergic septo-hippocampal projection. Our work revealed that although glutamatergic neurons are found throughout the septum, they concentrate in medial septal regions. Using stereological probes, approximately 16,000 glutamatergic neurons were estimated in the medial septal region. Triple immunostaining showed that most glutamatergic neurons do not immunoreact with cholinergic or GABAergic neuronal markers (anti-ChAT or anti-GAD67 antibodies, respectively). Fluorogold injections into CA1, CA3, and dentate gyrus of the hippocampus showed that septal glutamatergic neurons project to each of these hippocampal regions, forming approximately 23% of the septo-hippocampal projection. Most cell bodies of septo-hippocampal glutamatergic neurons were located in the medial septum. The remaining cell bodies were found in the diagonal band. This data shows that glutamatergic neurons constitute a significant neuronal population in the septum and that a subpopulation of these neurons projects to hippocampal regions. Thus, the septo-hippocampal projection needs to be reconsidered as a three neurotransmitter pathway.
authors.affiliation: Department of Biological Sciences, University of Texas at Brownsville/Texas Southmost College, Brownsville, Texas. luis.colom@utb.edu
authors.forename: Luis V
authors.initials: LV
authors.lastname: Colom
authors.forename: Maria T
authors.initials: MT
authors.lastname: Castaneda
authors.forename: Tania
authors.initials: T
authors.lastname: Reyna
authors.forename: Sofia
authors.initials: S
authors.lastname: Hernandez
authors.forename: Emilio
authors.initials: E
authors.lastname: Garrido-Sanabria
mesh_terms: D000109:Acetylcholine / Q000378:metabolism; D000818:Animals; D001370:Axonal Transport / Q000502:physiology; D002452:Cell Count; D048429:Cell Size; D002795:Choline O-Acetyltransferase / Q000378:metabolism; D018891:Dentate Gyrus / Q000166:cytology / Q000378:metabolism; D005968:Glutamate Decarboxylase / Q000378:metabolism; D018698:Glutamic Acid / Q000378:metabolism*; D006624:Hippocampus / Q000166:cytology / Q000378:metabolism*; D007150:Immunohistochemistry; D007527:Isoenzymes / Q000378:metabolism; D008297:Male; D009434:Neural Pathways / Q000166:cytology / Q000378:metabolism*; D009474:Neurons / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012686:Septal Nuclei / Q000166:cytology / Q000378:metabolism*; D013266:Stilbamidines; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
chemical_list: C049774:2-hydroxy-4,4'-diamidinostilbene, methanesulfonate salt; D007527:Isoenzymes; D013266:Stilbamidines; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; D002795:Choline O-Acetyltransferase; D005968:Glutamate Decarboxylase; C402565:glutamate decarboxylase 1; D000109:Acetylcholine