Number and regional distribution of GAD65 mRNA-expressing interneurons in the rat hippocampal formation
2013
Czéh, B. | Ábrahám, Hajnalka | Tahtakran, Siroun | Houser, Carolyn R. | Seress, L.
In rodent models for neuropsychiatric disorders reduced number of hippocampal interneurons have been reported, but the total number of GABAergic neurons in the normal rat hippocampus is yet unknown. We used <i>in situ</i> hybridization method to label the 65 isoform of glutamic acid decarboxylase (GAD65) and counted the number of GAD65 mRNA-expressing neurons along the entire septo-temporal axis of the hippocampus. We found that 2/3 of the interneurons were in Ammon’s horn (61,590) and 1/3 in the dentate gyrus (28,000). We observed the following numbers in Ammon’s horn: CA3 area 33,400, CA2 area 4,190, CA1 area 24,000 and in the dentate gyrus: 6,000 in the molecular and 9,000 in the granule cell layers and 13,000 in the hilus. GAD65 mRNA-expressing neurons were significantly more numerous in dorsal than in ventral hippocampus. The ratio between interneurons and principal cells was lowest in the granule cell layer (0.9%) and highest in hilus (21%). In Ammon’s horn this ratio was constant being 13% in CA3 and 8% in CA1-2 areas. In the entire hippocampal formation, the interneuron/principal cell ratio was 6%, with a significant difference between Ammon’s horn (9.5%) and the dentate gyrus (2.8%) including the hilus. Such low ratios could suggest that even a limited loss of GABAergic neurons in the hippocampus may have a considerable functional impact.
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