Male and female behavioral variability and morphine response in C57BL/6J, DBA/2J, and their BXD progeny following chronic stress exposure

Abstract

Drug addiction is a multifactorial syndrome in which genetic predispositions and exposure to environmental stressors constitute major risk factors for the early onset, escalation, and relapse of addictive behaviors. While it is well known that stress plays a key role in drug addiction, the genetic factors that make certain individuals particularly sensitive to stress and, thereby, more vulnerable to becoming addicted are unknown. In an effort to test a complex set of gene x environment interactions-specifically gene x chronic stress-here we leveraged a systems genetics resource: BXD recombinant inbred mice (BXD5, BXD8, BXD14, BXD22, BXD29, and BXD32) and their parental mouse lines, C57BL/6J and DBA/2J. Utilizing the chronic social defeat stress (CSDS) and chronic variable stress (CVS) paradigms, we first showed sexual dimorphism in social and exploratory behaviors between the mouse strains. Further, we observed an interaction between genetic background and vulnerability to prolonged exposure to non-social stressors. Finally, we found that DBA/2J and C57BL/6J mice pre-exposed to stress displayed differences in morphine sensitivity. Our results support the hypothesis that genetic variation influences chronic stress-induced behavioral outcomes such as social and approach-avoidance behaviors, reward responses, as well as morphine sensitivity, and is likely to modulate the development of drug addiction.

Fig. 1

C57BL/6J, DBA/2J, and BXD mice have distinct behaviors following chronic social defeat stress. (a) Experimental timeline illustrating the CSDS paradigm followed by the social interaction test (SI) and the open-field test (OFT). (b) Behavioral assessment showing the heterogeneous impact of CSDS on SI, OFT, and locomotion by genetic background in male (blue) and female (red) stressed mice. (c) CSDS-exposed male mice display distinct SI ratio, percentage of time spent in the center of the OFT, and distance traveled in the OFT in a “no-target” context amongst C57BL/6J, BXD: 5, 8, 14, 22, 29, and 32, and DBA/2J male mice following CSDS (n = 40, 6, 9, 14, 8, 6, 8, 35). (d) Same as c in CSDS-exposed female mice, C57BL/6J, BXD: 5, 8, 14, 22, 29, and 32, and DBA/2J (n = 28, 11, 12, 10, 8, 4, 14, 26). Bars represent mean ± SEM. ANOVA or Kruskal–Wallis tests followed by post-hoc comparison to C57BL/6J mice with Bonferroni correction; see Supplementary Table S1; *P < 0.05, **P < 0.01, and ***P < 0.01.

Fig. 2

C57BL/6J, DBA/2J, and BXD mice have distinct sensitivity to non-social chronic stress. (a) Experimental timeline illustrating the chronic variable stress (CVS) paradigm followed by the novelty suppress feeding test (NSF), the sucrose preference test (SP), the elevated plus-maze test (EPM), and locomotion in an open field. (b) Behavioral assessment showing the heterogeneous impact of CVS on NSF, SP, EPM, and locomotion by genetic background. Bars represent mean ± SEM for n = 6–40 mice. (c) CVS-exposed male mice display distinct latency to feed during the NSF task, SP ratio (%), time spent as percentage in open arms of the EPM, and distance traveled in an open field in the “no-target” context amongst C57BL/6J, BXD: 8, 22, and 29 and DBA/2J male mice (n = 27, 8, 9, 15, 16). (d) CVS-exposed female mice display distinct latency to feed times during the NSF task, SP ratio (%), time spent in EPM open arms, and distance traveled in an open field in “no-target” context amongst C57BL/6J, BXD: 8, 22, and 29 and DBA/2J (n = 27, 10, 9, 15, 15). Bars represent mean ± SEM. ANOVA followed by post hoc comparison to C57BL/6 J mice with Bonferroni correction; see Supplementary Table S1; *P < 0.05, **P < 0.01, and ***P < 0.01.

Fig. 3

Parental C57BL/6J and DBA/2J mice have distinct locomotor responses to acute morphine after chronic stress exposure. (a) Experimental timeline illustrating the two procedures performed, i.e. CSDS or CVS, followed by locomotor activity monitoring for 60 min in a locomotor apparatus 15 min after the animals were given an intraperitoneal injection of 7.5 mg/kg morphine. (b) Locomotor activity counts in C57BL/6J and DBA/2J male (left) and female (right) mice (n = 8) exposed to CSDS. (c) Locomotor activity counts in C57BL/6J and DBA/2J male (left) and female (right) mice (n = 8) exposed to CVS. Bars represent mean ± SEM. Unpaired t-test; see Supplementary Table S1; *P < 0.05, **P < 0.01, and ***P < 0.01.

Fig. 4

Parental C57BL/6J and DBA/2J mice have distinct place conditioning responses to morphine after chronic stress exposure. (a) Experimental timeline illustrating the two procedures performed, i.e. CSDS or CVS, prior to performing morphine conditioned place preference (CPP). Morphine CPP was performed using an unbiased approach: one compartment was paired with saline (0.3 mL, s.c.) and the other paired with morphine (7.5 mg/kg, s.c.). Sessions were 20 min long. (b) Time spent in each compartment of the three-chamber apparatus after paired-conditioning with morphine (vs. saline) in CSDS-exposed C57BL/6J and DBA/2J male mice (n = 8) and respective percentage in the morphine-paired chamber. (c) Same as (b), in CSDS-exposed C57BL/6J and DBA/2J female mice (n = 8). (d) Time spent in each compartment of the three-chamber apparatus after paired-conditioning with morphine (vs. saline) in CVS-exposed C57BL/6J and DBA/2J male mice (n = 8) and respective percentage in the morphine-paired chamber. (e) Same as (b), in CVS-exposed C57BL/6J and DBA/2J female mice (n = 8). Bars represent mean ± SEM. Two-way ANOVA followed by post-hoc comparison to C57BL/6J mice with Bonferroni correction and non-paired t-test; see Supplementary Table S1; *P < 0.05, **P < 0.01, and ***P < 0.01.