Article Figures & Data
Figures
- Figure 1.
Maladaptive behavioral responses to SD stress are prevented by ADX. A, An acute and prolonged elevation in plasma CORT was observed after SD exposure during each sampling day (D1, D7, and D14). *p < 0.05 versus baseline (Pre) (post hoc test). ADX prevented SD-induced increases in CORT (n = 8 for intact, 6 for ADX). B, Diagram depicting experimental groups and study design. C, Lit compartment exploration was significantly reduced in defeated mice during the L/D (stress effect, F(1,50) = 34.3, p < 0.0001). D, The significant reduction in transitions between light and dark compartments observed in defeated mice was abrogated by prior ADX (interaction, F(1,50) = 16.78, p < 0.001; stress effect, F(1,50) = 10.52, p < 0.005; surgery effect, F(1,50) = 5.99, p < 0.01). E, ADX prevented the defeat-induced avoidance of open arms exhibited by defeated shams in the EZM (interaction, F(1,50) = 10.33, p < 0.01). F, ADX before SD prevented the stress-induced increase in floating time in the FST (interaction, F(1,50) = 4.69, p < 0.05; stress effect, F(1,50) = 35.85, p < 0.0001). G, Strong social aversion displayed by defeated sham mice was significantly reduced in mice ADX before defeat stress (interaction quotient; duration on mouse (s)/duration on object; interaction, F(1,50) = 7.74, p < 0.01; stress effect, F(1,50) = 29.47, p < 0.0001). H, Heat maps representing time spent exploring CD-1 mouse chamber and empty chamber. Error bars indicate mean ± SE (n = 12–14). *p < 0.05 versus control group (post hoc test). **p < 0.01 versus control group (post hoc test). ***p < 0.001 versus control group (post hoc test).
- Figure 2.
Clamping adrenal hormone secretions during SD stress prevents a reduction in neurogenesis in the caudal DG. A, Experimental design testing the interaction between ADX and SD exposure on newborn cell survival in the DG. Mice administered BrdU were adrenalectomized or given sham surgery and then housed in HC or SD for 2 weeks. B, Quantification of BrdU+ cells in the rostral and caudal subdivisions of the DG. Quantification was made in fluorescently labeled tissue. SD significantly reduced survival of BrdU+ cells in the caudal DG. Mice adrenalectomized before SD showed a robust increase in BrdU+ cells compared with sham defeated mice and nondefeated ADX mice (interaction, F(1,20) = 27.05 p < 0.0001; surgery effect, F(1,20) = 9.89, p < 0.005). C, Representative photomicrographs of Ni-DAB-stained BrdU+ cells in the rostral and caudal DG of sham and ADX mice exposed to SD (counterstained with eosin Y) are shown for clarity. D, Confocal photographs of caudal DG BrdU and NeuN double immunostaining in defeated mice with intact adrenals (Sham-SD) and mice ADX before SD (ADX-SD); arrows indicate BrdU+ cells. E, Example of NeuN+ neuron colabeled with BrdU. Error bars indicate mean ± SE (n = 6). **p < 0.01 (significant post hoc comparisons to respective control groups). ***p < 0.001 (significant post hoc comparisons to respective control groups). Scale bars: C, 100 μm; D, 40 μm; E, 10 μm. GCL, Granule cell layer; HIL, hilus.
- Figure 3.
Conditional genetic ablation of adult neurogenesis has no effect on baseline behavior and has no effect on the induction of maladaptive behaviors after SD. A, The DG of control mice (NG+) contains many DCX+ neuroblasts (green), whereas these cells are virtually abolished in hGFAPtk mice treated with VGCV for 3 weeks (NG−). B, Experimental design testing the interaction between adult neurogenesis and SD exposure on behavior. Defeated mice with intact (NG+) and ablated (NG−) neurogenesis showed similar and significant increases in anxiety- and depressive-like behavior. Anxiety-like behaviors were measured in the L/D and EZM. SD significantly reduced (C) light compartment exploration (stress effect, F(1,26) = 13.56), (D) transitions between light and dark compartments (stress effect, F(1,26) = 30.49), and (E) open-arm exploration in the EZM (stress effect, F(1,26) = 113.1). Defeated mice (F) showed increased immobility in the FST (stress effect, F(1,26) = 23.66) and (G) spent significantly less time with the aggressor mice in the SI task (stress effect, F(1,26) = 22.41). H, Heat maps representing time spent exploring CD-1 mouse chamber and empty chamber. Scale bar: A, 50 μm. Error bars indicate mean ± SE (n = 7 or 8). **p < 0.01, ***p < 0.001.
- Figure 4.
Adrenalectomy does not confer stress resiliency to mice lacking neurogenesis. A, Experimental design testing the interaction between ADX and neurogenesis on behavior in mice exposed to chronic SD. ADX reduced anxiety- and depressive-like behaviors in defeated NG+ mice but had no effect in defeated NG− mice. B, C, In the L/D test, ADX NG+ mice spent more time in the light compartment compared with sham NG+ mice (B, surgery effect, F(1,22) = 6.58, p < 0.01). C, ADX NG+ mice showed an elevated number of transitions between light and dark compartments compared with all other groups (interaction effect, F(1,22) = 9.84, p < 0.005; surgery effect, F(1,22) = 12.03, p < 0.002). D, ADX increased open-arm exploration in the EZM in NG+ mice only (interaction, F(1,22) = 6.75, p < 0.02; surgery effect, F(1,22) = 6.21, p < 0.03). E, ADX reduced immobility time in NG+ mice during the FST (surgery effect, F(1,22) = 4.96, p < 0.05). F, ADX significantly increased social interaction in NG+ mice, whereas no effect of ADX was detected in NG− mice (interaction, F(1,22) = 5.02, p < 0.05; surgery effect, F(1,22) = 4.33, p < 0.05). G, Heat maps representing time spent exploring CD-1 mouse chamber and empty chamber. Error bars indicate mean ± SE (n = 6–8). *p < 0.05, **p < 0.01, ***p < 0.001.
- Figure 5.
SD and EE increase the magnitude of diurnal CORT surges. Mice exposed to HC or SD for 2 weeks were transferred to either EE or HC housing for 3 weeks. Tail blood was assayed for CORT every 7 d during the diurnal surge, 60 min before lights off. A, SD exposure markedly increased CORT during the diurnal surge (main stress effect, F(1,90) = 24.12, p < 0.0001). B, Prior stress exposure and the type of recovery housing (HC vs EE) affected diurnal CORT surges during the recovery period (2-way mixed-model ANOVA, stress × recovery housing interaction, F(6,56) = 4.272, p < 0.001; effect of prior SD, F(3,28) = 13.13, p < 0.001). During the recovery period, surge levels were significantly increased in nondefeated mice housed in EE (HC→EE) on day 7 compared with all other treatment conditions (interaction, F(1,28) = 17.61, p < 0.001; housing effect, F(1,28) = 4.28, p < 0.05). On days 14 and 21, CORT during the diurnal surge was significantly higher in both EE groups; this effect occurred independent of prior stress exposure (day 14 housing effect, F(1,28) = 18.05, p < 0.001; day 21 housing effect, F(1,28) = 24.95, p < 0.0001). Prolonged EE housing increased diurnal CORT surges in previously defeated mice (SD→EE) (repeated-measures ANOVA across days, F(2,23) = 11.55, p < 0.001) (n = 16 per group during induction, n = 8 per group during recovery). *p < 0.05 (significant post hoc comparison).
- Figure 6.
Environmental enrichment facilitates behavioral recovery in socially defeated mice through adrenal hormone secretions. A, Experimental design testing the role of adrenal activity during EE housing on recovery from SD. Clamping adrenal secretions during EE severely disrupted recovery in defeated mice (SD→ADX→EE), whereas defeated mice with intact adrenals (SD→sham→EE) showed behavioral responses comparable with nondefeated controls. Surgery had no effect on behavior in nondefeated groups. SD→ADX→EE mice showed (B) a significant decrease in light compartment activity (interaction, F(1,44) = 18.15, p < 0.0001; surgery effect, F(1,44) = 54.44, p < 0.0001) and (C) a significant decline in number of transitions between light and dark compartments (interaction, F(1,44) = 10.96, p < 0.001; surgery effect, F(1,44) = 5.39 p < 0.02). D, Likewise, SD→ADX→EE mice showed significant decreases in open-arm exploration of the EZM compared with SD→sham→EE mice and nondefeated adrenalectomized mice (interaction, F(1,44) = 8.30, p < 0.005; stress effect, F(1,44) = 20.58, p < 0.0001). E, In the FST, SD→ADX→EE mice showed a substantial increase in immobility time relative to all other groups (interaction, F(1,44) = 4.79, p < 0.05; stress effect, F(1,44) = 6.63, p < 0.02; surgery effect, F(1,44) = 9.31, p < 0.005). F, G, In the SI task, SD→sham→EE mice showed an interaction preference with a social target comparable with nondefeated controls, whereas SD→ADX→EE mice showed a significant increase in social avoidance compared with all tested groups, indicative of a strong prodepressive phenotype (interaction, F(1,44) = 10.43, p < 0.005; stress effect, F(1,44) = 21.95, p < 0.0001; surgery effect, F(1,44) = 8.55, p = 0.005). Error bars indicate mean ± SE (n = 12). *p < 0.05, **p < 0.01, ***p < 0.001.
- Figure 7.
Effects of SD and ADX on wheel running activity. A, Diagram depicting experimental groups and study design. Mice were exposed to 14 d of HC or SD. Animals then received either ADX or sham surgery (Sham) and were then housed in enriched housing with running wheels for 21 d. B, Characteristics of running activity during a 24 h period were examined every 3 d, including distance run, time spent running, and average velocity of running speed. No noticeable effects of surgery or prior stress exposure were detected.
- Figure 8.
EE enhances neurogenesis through adrenal hormones. A, Experimental design examining the interaction between ADX and prior SD on newborn cell survival in the DG during EE. B, Quantification of BrdU+ cells in the rostral and caudal subdivision of the DG. CORT secreted during EE facilitated cell survival during EE, but only in the caudal DG. ADX significantly diminished numbers of BrdU+ cells in the caudal DG of mice housed in EE during recovery (surgery effect, F(1,20) = 76.33, p < 0.001), an effect that occurred regardless of prior stress exposure (HC→EE, p < 0.001; SD→EE, p < 0.001). SD stress also significantly reduced cell survival in the rostral DG, but the effects were limited to mice with intact adrenals (stress effect, F(1,20) = 4.43, p < 0.05). C, Representative photomicrographs of BrdU+ cells in the rostral and caudal DG of defeated mice sham and ADX before housing in EE (counterstained with eosin Y). D, Experimental design examining the interaction between ADX and prior SD on newborn cell survival during HC housing recovery from SD. Mice are housed in standard control housing during recovery. E, Quantification of BrdU+ cells in the rostral and caudal subdivision of the DG. Two-way ANOVA (surgery × stress) showed no significant effect of surgery and no effect of CORT secreted during standard housing on cell survival. A significant effect of prior stress was detected in both the rostral (stress effect, F(1,20) = 4.11, p < 0.05) and caudal (stress effect, F(1,20) = 4.92, p < 0.05) subdivisions of the DG, but no significant post hoc comparisons were observed. F, Representative photomicrographs of BrdU+ cells in the rostral and caudal DG of defeated mice sham and ADX before housing in HC (counterstained with eosin Y). Quantification of BrdU+ cells was made in fluorescently labeled tissue. Ni-DAB labeled tissue is shown for clarity. Error bars indicate mean ± SE (n = 6). ∂, significantly elevated from comparable group housed in HC during recovery: *p < 0.05, **p < 0.01, ***p < 0.001. Scale bars, 100 μm.
- Figure 9.
Summary of experimental conditions, results, and conclusions made in the study.
