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Organization of the GABAergic system in the rat hippocampal formation: A quantitative immunocytochemical study
Author(s) -
Woodson Walter,
Nitecka Liliana,
BenAri Yehezkel
Publication year - 1989
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.902800207
Subject(s) - neuropil , fascia dentata , hippocampal formation , granule cell , biology , gabaergic , glutamate decarboxylase , pyramidal cell , population , neuroscience , gamma aminobutyric acid , anatomy , central nervous system , dentate gyrus , inhibitory postsynaptic potential , biochemistry , receptor , enzyme , demography , sociology
Specific antibodies against gamma aminobutyric acid (GABA) and glutamic acid decarboxylase (GAD) were used to study the organization of the GABAergic system in the rat hippocampal formation. Both the number of GABA‐like‐immunoreactive (Li) somata and neuropil density were assessed in semithin sections. Cell counts revealed that approximately 11% of the hippocampal neuronal population showed GABA‐Li within the various planes of section. Each layer in the hippocampal formation had a characteristic organization of GABA‐Li elements. In Ammon's horn, 80–95% of the neuronal somata within the apical and basal dendritic regions were GABA‐Li positive. Within the pyramidal cell layer 5–8% of the cells were GABA‐Li in the CA1 to CA3 subfields of Ammon's horn and only 3% were GABA‐Li within that portion of the pyramidal cell layer that inserts into the hilus. Only slight differences in the density of the GABA‐Li neuropil were observed within the CA1‐CA3 dendritic regions. Restricted to the stratum lucidum was a dense band of GABA‐Li label. Counts of immunoreactive grains localized on the perimeter of pyramidal (CA1‐CA3) and granule somata revealed more terminal boutons on the CA3 cells than on CA1 and granule neuronal somata. A topographical distribution of GABA‐Li somata and neuropil was found in the fascia dentata: There the label particularly concerned its suprapyramidal and rostrolateral portions. Approximately 40% of neurons in the molecular layer, 60% in the polymorph layer, and 18% within the hilar region were GABA‐Li. Within the granule cell layer only 2% of the neurons were GABA‐Li positive. Distinct differences in the density of the GABA‐Li neuropil were present in the molecular, pericellular granular, and hilar regions of the fascia dentata. While the morphology of GABA‐Li neuronal somata varied according to their hippocampal layer, the most heterogeneous cell types were found in the regio inferior of the hippocampus. There we have identified neurons that are reminiscent of the inferior region interneuron described in Golgi material by Amaral and Woodward (Brain Res. 124: 225–236, '77). Moreover, particularly in the sagittal plane, we have identified oval, triangular, and round cells and that have processes oriented in a parallel arrangement, appearing to be aligned along the granule cell mossy fibers.