Predator stress-induced depression is associated with inhibition of hippocampal neurogenesis in adult male mice

Abstract

Stress has been suggested to disturb the 5-hydroxytryptamine system and decrease neurogenesis, which contribute to the development of depression. Few studies have investigated the effect of predator stress, a type of psychological stress, on depression and hippocampal neurogenesis in adult mice; we therefore investigated this in the present study. A total of 35 adult male Kunming mice were allocated to a cat stress group, cat odor stress group, cat stress + fluoxetine group, cat odor stress + fluoxetine group, or a control group (no stress/treatment). After 12 days of cat stress or cat odor stress, behavioral correlates of depression were measured using the open field test, elevated plus maze test, and dark-avoidance test. The concentrations of hippocampal 5-hydroxytryptamine and 5-hydroxyindoleacetic acid were measured using high-performance liquid chromatography-electrochemical detection. Neurogenesis was also analyzed using a bromodeoxyuridine and doublecortin double-immunostaining method. Cat stress and cat odor stress induced depression-like behaviors; this effect was stronger in the cat stress model. Furthermore, compared with the control group, cat stress mice exhibited lower 5-hydroxytryptamine concentrations, higher 5-hydroxyindoleacetic acid concentrations, and significantly fewer bromodeoxyuridine⁺/doublecortin⁺-labeled cells in the dentate gyrus, which was indicative of less neurogenesis. The changes observed in the cat stress group were not seen in the cat stress + fluoxetine group, which suggests that the effects of predator stress on depression and neurogenesis were reversed by fluoxetine. Taken together, our results indicate that depression-like behaviors induced by predator stress are associated with the inhibition of hippocampal neurogenesis.

Keywords: 5-hydroxyindoleacetic acid; 5-hydroxytryptamine; behavioral evaluation; cat odor stress; cat stress; dark-avoidance test; depressive disorder; elevated plus maze test; hippocampal neurogenesis; nerve regeneration; neural regeneration; open field test.

Figure 1

Effect of cat odor stress and cat stress on behavior in the open field test. The effect of cat odor stress and cat stress on (A) the number of rearing, (B) the total distance moved, (C) the central distance moved, and (D) the central time in open field test, which was implemented on day 21. Data are expressed as the mean ± SEM (n = 7 per group; one-way analysis of variance and Tukey’s post hoc tests). *P < 0.05, **P < 0.01, ***P < 0.001, vs. Con; ##P < 0.01, vs. COS; †P < 0.05, ††P < 0.01, vs. CS. Con: Control; COS: cat odor stress; COS + Fluo: cat odor stress + fluoxetine; CS: cat stress; CS + Fluo: cat stress + fluoxetine.

Figure 2

Effect of cat odor stress and cat stress on behavior in the elevated plus maze test. The effect of cat odor stress and cat stress on (A) the time spent in open arm (%) and (B) the number of entries into the open arm in the elevated plus maze test, which was implemented on day 20. Data are expressed as the mean ± SEM (n = 7 per group; one-way analysis of variance and Tukey’s post hoc tests). ***P < 0.001, vs. Con; ##P < 0.01, ###P < 0.001, vs. COS; †P < 0.05, ††P < 0.01, vs. CS. Con: Control; COS: cat odor stress; COS + Fluo: cat odor stress + fluoxetine; CS: cat stress; CS + Fluo: cat stress + fluoxetine.

Figure 3

Effect of cat odor stress and cat stress on behavior in the dark-avoidance test. The effect of cat odor stress and cat stress on (A) movement (the representative trace of an individual mouse), (B) the latency to enter the dark compartment, (C) the number of entries into the dark compartment, and (D) the total time spent in the dark compartment in dark-avoidance test, which was implemented on day 22. Data are expressed as the mean ± SEM (n = 7 per group; one-way analysis of variance and Tukey’s post hoc tests). *P < 0.05, **P < 0.01, vs. Con; #P < 0.05 vs. COS; †P < 0.05, vs. CS. Con: Control; COS: cat odor stress; COS + Fluo: cat odor stress + fluoxetine; CS: cat stress; CS + Fluo: cat stress + fluoxetine.

Figure 4

Effect of cat stress on 5-HT and 5-HIAA levels in the hippocampus of mice on day 23. (A) The levels of 5-HT and 5-HIAA in the standards and control. (B, C) The hippocampal 5-HT and 5-HIAA levels in control, cat stress, and cat stress + fluoxetine mice. Data are expressed as the mean ± SEM (n = 7 per group; one-way analysis of variance and Tukey’s post hoc tests). **P < 0.01, vs. Con; †P < 0.05, vs. CS. Con: Control; CS: cat stress; CS + Fluo: cat stress + fluoxetine; 5-HIAA: 5-hydroxyindoleacetic acid; 5-HT: 5-hydroxytryptamine.

Figure 5

Effects of cat stress on neuronal cell proliferation in the dentate gyrus. (A) Microscopy images of sections of the dentate gyrus stained for BrdU. The fluorescent signals for Alexa 488 labeling (green) and PE (red) were used to detect BrdU and DCX, respectively. DAPI (blue) was used to stain nucleus DNA, so that the dentate gyrus of the hippocampus could be seen clearly. All micrographs are at the same magnification. Scale bar: 200 μm. (B) The number of BrdU and DCX co-expressing cells in the dentate gyrus was quantitatively analyzed. Data are expressed as the mean ± SEM (n =7 per group; analysis of variance and Tukey’s post hoc tests). **P < 0.01, vs. Con; †P < 0.05, vs. CS. BrdU: 5-bromodeoxyuridine; Con: control; CS: cat stress; CS + Fluo: cat stress + fluoxetine; DAPI: 4′,6-diamidino-2-phenylindole; DCX: doublecortin.