Prefrontal cortical circuit for depression- and anxiety-related behaviors mediated by cholecystokinin: role of ΔFosB

Abstract

Decreased medial prefrontal cortex (mPFC) neuronal activity is associated with social defeat-induced depression- and anxiety-like behaviors in mice. However, the molecular mechanisms underlying the decreased mPFC activity and its prodepressant role remain unknown. We show here that induction of the transcription factor ΔFosB in mPFC, specifically in the prelimbic (PrL) area, mediates susceptibility to stress. ΔFosB induction in PrL occurred selectively in susceptible mice after chronic social defeat stress, and overexpression of ΔFosB in this region, but not in the nearby infralimbic (IL) area, enhanced stress susceptibility. ΔFosB produced these effects partly through induction of the cholecystokinin (CCK)-B receptor: CCKB blockade in mPFC induces a resilient phenotype, whereas CCK administration into mPFC mimics the anxiogenic- and depressant-like effects of social stress. We previously found that optogenetic stimulation of mPFC neurons in susceptible mice reverses several behavioral abnormalities seen after chronic social defeat stress. Therefore, we hypothesized that optogenetic stimulation of cortical projections would rescue the pathological effects of CCK in mPFC. After CCK infusion in mPFC, we optogenetically stimulated mPFC projections to basolateral amygdala or nucleus accumbens, two subcortical structures involved in mood regulation. Stimulation of corticoamygdala projections blocked the anxiogenic effect of CCK, although no effect was observed on other symptoms of social defeat. Conversely, stimulation of corticoaccumbens projections reversed CCK-induced social avoidance and sucrose preference deficits but not anxiogenic-like effects. Together, these results indicate that social stress-induced behavioral deficits are mediated partly by molecular adaptations in mPFC involving ΔFosB and CCK through cortical projections to distinct subcortical targets.

Keywords: CCK; accumbens; amygdala; anxiety; depression; mPFC.

Figure 1.

ΔFosB induction in mPFC promotes susceptibility to stress. A, Representative photomicrographs of ΔFosB immunohistochemistry in mPFC 24 h after the last of 10 social defeat episodes. B, Induction of ΔFosB does not occur in GABAergic interneurons in PrL. C, Representative photomicrograph of HSV-ΔFosB injection into PrL (left) and IL (right). D, Overexpression of ΔFosB in PrL promotes social avoidance to submaximal defeat stress (n = 7–11; *p < 0.05, two-way ANOVA, compared with “no target”), and immobility in the forced swim test (E) (n = 8–10; *p < 0.05, one-way ANOVA, compared with “GFP”) but does not affect basal measures of anxiety (F, G), anhedonia (H), social interaction with no stress (I), or locomotor activity (J) (n = 7–11). Overexpression of ΔFosB in IL had no discernible effects in these assays (D–J) (n = 7–11). K, Overexpression of ΔFosB in mOFC did not significantly reverse social avoidance induced by chronic social defeat stress (n = 8–10; *p < 0.05, two-way ANOVA, compared with “no target,” ^#p < 0.05, t test vs GFP).

Figure 2.

Blockade of the CCKB receptor has a proresilience, antidepressant-like effect. A, Social defeat decreases CCKB receptor levels in mPFC only in resilient mice (n = 8–10). *p < 0.05, compared with control (one-way ANOVA). **p < 0.05 (t test). B, ΔFosB mRNA was only induced in susceptible mice (n = 8–10). *p < 0.05 (one-way ANOVA). ^#p < 0.05 (t test). C, Overexpression of ΔFosB in PrL of susceptible mice upregulates CCKB levels and downregulates c-Fos levels in this brain region (n = 7–11). *p < 0.05 (t test vs GFP). **p < 0.01 (t test vs GFP). D, HSV-mediated expression of ΔJunD in PrL blocked social defeat-induced CCKB protein levels in this region (n = 7). **p < 0.05 (one-way ANOVA). ^#p < 0.05 (t test vs control). E, Western blots of virus-injected PrL shown in D. F, ΔJunD promoted resilience to social defeat-induced avoidance (n = 9). ^#p = 0.05 (t test vs GFP). G, H, Infusion of the CCKB receptor antagonist CI-988 (10 ng) into PrL of susceptible mice reverses the social avoidance (n = 6; *p < 0.05, two-way ANOVA) and sucrose preference deficit induced by social defeat (n = 6; *p < 0.05, t test vs vehicle).

Figure 3.

CCK-8-induced stress susceptibility depends on specific cortical projections. A, At 24 h after submaximal social defeat and 30 min after CCK-8 infusion, mPFC projection regions were laser-stimulated during a test for social interaction. CCK-8 infusion into the PrL induced social avoidance (B, C), reduced exploratory behaviors (D, E), and decreased sucrose preference (F, G) (n = 6–8). *p < 0.05 (two-way ANOVA). ^#p < 0.05, compared with vehicle (t test). H, CCK-8 infusion decreased c-Fos mRNA levels in mPFC, suggesting decreased neuronal activity (n = 7 or 8). *p < 0.05, compared with vehicle (t test). I, Representative photomicrograph of ChR2-GFP expression in two mPFC projections areas, NAc (left) and BLA (right), 6 weeks after injection into PrL. Optogenetic stimulation of cortical projections to BLA (B–F) or NAc (C–G) had opposite effect on measures of social avoidance, sucrose preference, and anxiety-like behavior (n = 6–8). *p < 0.05 (two-way ANOVA).