Fig. 7. DG-projecting SuM neurons exhibit increased activity in EE.

(a) Diagram of c-Fos labeling in DG-projecting SuM neurons in the EE. RetroAAV2-Cre and AAV5-DIO-eGFP were injected into the DG and SuM, respectively. Mice were in enriched environments (EE) for 15 minutes and perfused 75 minutes later for c-Fos staining. Control mice were in the home cage (HC). Scale bar = 100 µm.

(b) Representative images of c-Fos expression in the SuM in EE and HC. Yellow arrowheads indicate c-Fos+GFP+ cells. Scale bar = 20 µm.

(c) Expression of c-Fos in DG-projecting SuM neurons was significantly increased in the EE. n = 4 mice in each group, P = 0.0002 by two-sided unpaired t-test.

(d) Diagram of calcium recording of DG-projecting SuM neurons. RetroAAV2-Cre and AAV5-DIO-GCaMP7f were injected into the DG and SuM, respectively. Fiber photometry recording of free-moving mice in HC and EE for 10 minutes. Scale bar = 100 µm.

(e) Representative traces of population activity of DG-projecting SuM neurons in the HC and EE.

(f–g) Average peak ΔF/F (f) and events (g) of calcium activity in the HC and EE. n = 8 mice in each group, two-sided paired t-test, P = 0.0772 (f), P = 0.0081(g).

(h) Diagram of in vivo multi-channel spike recording. AAV2-retro-Cre-GFP and AAV5-DIO-ChR2-mCherry were injected into the DG and SuM, respectively. Optic fiber and tetrodes were implanted above or into the SuM, respectively. Sample image showed SuM with optical tetrode locations.

(i) Peristimulus time histograms of representative single units photo-identified as SuM–DG projectors.

(j) Waveforms of spontaneous (black line for the mean, grey shadow for the standard deviation) and light-evoked (blue) spikes of the single units.

(k) Raster plots of sample neurons.

(l) Firing rate of DG-projecting SuM neurons in HC and EE. n = 12 neurons from 6 mice. P = 0.0234 by two-sided paired t-test.