Hilar granule cells of the mouse dentate gyrus: effects of age, septotemporal location, strain, and selective deletion of the proapoptotic gene BAX

Abstract

The dentate gyrus (DG) principal cells are glutamatergic granule cells (GCs) and they are located in a compact cell layer. However, GCs are also present in the adjacent hilar region, but have been described in only a few studies. Therefore we used the transcription factor prospero homeobox 1 (Prox1) to quantify GCs at postnatal day (PND) 16, 30 and 60 in a common mouse strain, C57BL/6J mice. At PND16, there was a large population of Prox1-immunoreactive (ir) hilar cells, with more in the septal than temporal hippocampus. At PND30 and 60, the size of the hilar Prox1-ir cell population was reduced. Similar numbers of hilar Prox1-expressing cells were observed in PND30 and 60 Swiss Webster mice. Prox1 is usually considered to be a marker of postmitotic GCs. However, many Prox1-ir hilar cells, especially at PND16, were not double-labeled with NeuN, a marker typically found in mature neurons. Most hilar Prox1-positive cells at PND16 co-expressed doublecortin (DCX) and calretinin, markers of immature GCs. Double-labeling with a marker of actively dividing cells, Ki67, was not detected. These results suggest that, surprisingly, a large population of cells in the hilus at PND16 are immature GCs (Type 2b and Type 3 cells). We also asked whether hilar Prox1-ir cell numbers are modifiable. To examine this issue we conditionally deleted the proapoptotic gene BAX in Nestin-expressing cellss at a time when there are numerous immature GCs in the hilus, PND2-8. When these mice were examined at PND60, the numbers of Prox1-ir hilar cells were significantly increased compared to control mice. However, deletion of BAX did not appear to change the proportion that co-expressed NeuN, suggesting that the size of the hilar Prox1-expressing population is modifiable. However, deleting BAX, a major developmental disruption, does not appear to change the proportion that ultimately become neurons.

Novelty and Novel Objects Increase c-Fos Immunoreactivity in Mossy Cells in the Mouse Dentate Gyrus

“…The outline of the hilus and GCL was drawn manually, and automated counts of cells based on size and circularity parameters were performed for both areas. We manually confirmed the accuracy of the threshold technique in every section, which we have previously discussed [57]. Quantification of double labeling for c-fos and GluR2/3 in the hilus was performed manually using 40x images.…”

Adult neurogenesis in the mouse dentate gyrus protects the hippocampus from neuronal injury following severe seizures

“…The background strain of these mice was a combination of C57BL6 and Sv129 (Bermudez‐Hernandez et al, ; Sahay et al, ). For breeding, Bax f/f female mice were bred with NestinCreER T2+/‐ Bax f/f male mice and the progeny were genotyped (Supporting Information Table S1) in‐house for the presence of Cre recombinase.…”

“…Immunofluorescence was conducted as described previously (Bermudez‐Hernandez et al, ). Free‐floating sections were washed in 0.1 M TB, incubated in blocking serum for 1 hr (10% goat serum, 0.025% (v/v) Triton X‐100 and 0.005% (v/v) bovine serum albumin in 0.1 M Tris buffer), followed by washes in 0.1 M TB.…”

The Dentate Gyrus and Temporal Lobe Epilepsy: An “Exciting” Era

“…53 Many years later, it was also shown that the GCs might emerge from the septohippocampal zone, 54 or the hilus itself, because progenitors and young GCs appear to be present in the hilus normally. 55 When recordings were made of the hilar "ectopic" granule cells (EGCs), it was shown that they have axons that innervate normal GCs and CA3 pyramidal cells, possibly mediating the synchronization needed for a seizure focus. 56 Therefore, there was a new reason to think of the epileptic DG and CA3 as a potential focus.…”

“…Immature GCs arise from progenitors that are mainly beneath the GCL but can be in the hilus. 55 Many types of GABAergic neurons (red) are added to the diagram because of the greater understanding that they normally are present. GABAergic neurons are named using a different classification system.…”