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

Figure 5

The majority of hilar c-fos+ cells were double labeled for a marker of glutamatergic neurons, GluR2/3, suggesting that they were MCs. (a, 1) A dorsal section from a control mouse double labeled for c-fos (black) and GluR2/3 (orange). Few double-labeled cells are present in the hilus. Calibration: 100 μm. MOL=molecular layer. (a, 2) A dorsal section of a mouse exposed to novel objects shows more double-labeled hilar cells. Calibration: 100 μm. (a, 3) Inset: at higher gain. Double-labeled cells (arrows) and cells only expressing GluR2/3 (arrowhead) are shown. Calibration: 25 μm. (b, 1) The mean value for hilar c-fos+ cells is listed for 4 controls and 4 mice exposed to novel objects (NO). The differences were significant (-test: , ; ). (b, 2) The mean value for hilar c-fos+/GluR2/3+ double-labeled cells is shown for the same mice as (b, 1). Differences were significant (-test: , ; ). (b, 3) The mean value of hilar double-labeled cells (presumably MCs) as a fraction of all hilar c-fos+ cells is expressed as a percent. Differences were significant (-test: , ; ). (c, 1) Values for c-fos+ hilar cells are plotted along the septotemporal axis for 8 sections selected at intervals throughout the axis. These data suggest that the differences in groups were mainly ventral, which was also observed in (c, 2) and (c, 3). Some control sections showed no c-fos+ cells in the hilus, so the most ventral sections and the most dorsal sections were pooled. A two-way ANOVA showed a significant effect of condition (control vs. novel object: ; ) and no effect of ventral vs. dorsal position (; ). There was a trend towards an interaction between condition and position (; ) which appeared to underlie a significant difference in post hoc tests comparing ventral location. Thus, Tukey’s post hoc test showed a significant difference in the ventral but not dorsal locations.

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