Stress-induced potentiation of cocaine reward: a role for CRF R1 and CREB

Abstract

Both clinical and preclinical research have shown that stress can potentiate drug use; however, the underlying mechanisms of this interaction are unknown. Previously, we have shown that a single exposure to forced swim (FS) reinstates extinguished conditioned place preference (CPP) to cocaine and that cAMP response element binding protein (CREB) is necessary for this response. CREB can be activated by corticotropin releasing factor (CRF) receptor type 1 (CRF(R1)) binding, which mediates neuroendocrine and behavioral responses to stress as well as to drugs of abuse. The present experiments investigate whether changes in cocaine reward elicited by previous exposure to stress are mediated by CREB and/or CRF(R1). Chronic exposure to FS in advance of conditioning enhances cocaine CPP in wild-type mice, but this is blocked in CREB-deficient mice. In addition, pretreatment with the CRF(R1) antagonist, antalarmin, before FS exposure blocks this stress-induced enhancement of cocaine CPP. Furthermore, FS-induced increase in phosphorylated CREB (pCREB), specifically in the lateral septum (LS) and nucleus accumbens (NAc) is also blocked by antalarmin. Taken together, these studies suggest that both CREB and CRF(R1) activation are necessary for stress-induced potentiation of drug reward.

Figure 1. Experimental paradigm for Cocaine CPP

Preconditioning day (PRE;1): On day 1, mice were tested for initial bias. Forced swim stress: mice were exposed to forced swim stress for 6 min/day; days 2–8). Thirty minutes before each forced swim exposure separate cohorts of mice were injected with antalarmin (arrows; 10 mg/kg) or saline. Conditioning phase (days 9–16): The distinct sides of conditioning boxes were paired with either saline (S) or cocaine (C; 10 mg/kg, i.p.) injections, with one exposure to box per 24 h. Test (day 17): Mice were tested for preference.

Figure 2. Wild-type but not CREB mutant mice show augmented conditioned cocaine place preference after chronic FS

Both wild-type and mutant mice paired with cocaine (WT/NS, MUT/NS) showed a significant place preference to the cocaine-paired side on test day. Wild-type mice exposed to forced swim (WT/FS) showed increased preference scores (time on paired side minus time on unpaired side); CREB mutant mice did not show this stress-induced potentiation (MUT/FS). Data are expressed as mean±SEM; six mice per group. * p<0.05 from corresponding saline group; ** p<0.05 from cocaine non-stress group (ANOVA; Fisher's post hoc test)

Figure 3. Wildtype and CREB mutant mice show equivalent forced swim behavior and corticosterone response to FS

(a) CREB mutant mice (MUT) showed decreased immobility on days 1, 2 and 5 of the forced swim exposure. However, immobility increased over the 7 days of FS testing in both wild-type (WT) and CREB mutant mice. (b) Wild-type and CREB mutant mice exhibited similar changes in plasma corticosterone after acute as well as repeated FS stress exposures. Additionally, both groups showed similar basal levels of corticosterone in the non-stressed groups. Data are expressed as mean±SEM; 6–9 mice per group. * p<0.05 from either corresponding mutant group (a) or corresponding non-stress group (b) (ANOVA; Fisher's post hoc test).

Figure 4. Antalarmin pretreatment during repeat FS exposure blocks stress-induced potentiation of cocaine place preference

Wildtype mice were conditioned to cocaine (10mg/kg). All mice conditioned to cocaine showed a place preference regardless of pretreatment. Mice paired with cocaine and previously exposed to the forced swim showed an augmentation of place preference. Mice pretreated with antalarmin (10mg/kg) showed similar cocaine place preference regardless of previous FS exposure. Data are expressed as mean±sem; 6 mice per group. * indicates p<0.05 from preconditioning day; ** indicates p<0.05 from cocaine non stress group (ANOVA; Fisher’s PLSD post hoc test).

Figure 5. Antalarmin and vehicle treated mice show equivalent forced swim behavior and corticosterone response to FS

(a) Wild-type mice given saline injections (VEH) showed increased immobility over 7 days of repeated forced swim. Pretreatment with antalarmin (ANT) injection did not alter immobility behavior of wild-type mice at any time point. Both groups showed a significant increase in immobility over 7 days. (b) Forced swim exposure increased corticosterone levels both acutely as well as after repeated exposure. Wild-type mice injected with saline (VEH) showed increased corticosterone levels after acute FS exposure. Pretreatment with antalarmin blocked the forced swim stress-induced increase in plasma corticosterone in wild-type mice (VEH/FS; ANT/FS) after the first, but not after repeated exposures. In addition, antalarmin injection does not alter basal corticosterone levels in the non-stressed groups (NS). Data are expressed as mean±SEM; 4–6 mice per group. * p<0.05 from corresponding non-stress group (ANOVA; Fisher's PLSD post hoc test).

Figure 6. Stress-elicited pCREB expression in certain forebrain regions is dependent on CRF₁ receptor activation

(a) Representative micrographs show pCREB expression in lateral septum and nucleus accumbens core (NAc core) after chronic FS exposure (FST Sal) and antalarmin treatment (FST Ant). Saline injected mice exhibited an increase in pCREB-immunoreactive profiles after repeated stress exposure in lateral septum (LS) (b), the nucleus accumbens (NAc) core (c), and shell (d), ventral and dorsal bed nucleus of the stria terminalis (vBNST, dBNST) (e, f), and basolateral and central nuclei of the amygdala (BLA, CeA) (g, h). Mice pretreated with antalarmin did not exhibit stress-induced increases in pCREB protein expression in the LS, NAc core and NAc shell (b–d). Stress-induced increases in pCREB activation remained intact in vBNST, dBNST, BLA and CeA (e–h) after antalarmin pretreatment. Data are expressed as mean±SEM. ** p<0.01, *** p<0.001 from non stress group; #p<0.05, ###p<0.001 from saline treated group (ANOVA; Bonferroni–Dunn post hoc test).