Increased depression-related behavior during the postpartum period in inbred BALB/c and C57BL/6 strains

Abstract

Pregnancy and lactation are characterized by dramatic changes in the endocrine system and brain in mammalian females. These changes, with stress before pregnancy, are potential risk factors for the development of postpartum depression (PPD). A valid animal model of PPD is needed to understand the neurobiological basis of the depressive state of females. To explore a mouse model of PPD, we first assessed anxiety-like and depression-related behaviors in nulliparous (virgin), nonlactating primiparous, and lactating primiparous females in four inbred strains of mice (C57BL/6J, C57BL/6JJcl, BALB/cAnNCrlCrlj, and BALB/cAJcl). Pups from the nonlactating female group were removed one day after parturition to examine the effects of physical interaction with pups on the postpartum behaviors. Second, we investigated the additional effects of prepregnancy stress (restraint stress for 6 h/day for 21 days) on postpartum behaviors in the BALB/cAJcl strain. We found that females of the two BALB/c substrains showed decreased locomotor activity and increased anxiety-like and depression-related behaviors compared with females of the two C57BL/6 substrains. Behavioral differences were also observed between the two substrains of each strain. Additionally, pregnancy- and lactation-dependent behavioral differences were found in some strains: lactating BALB/cAJcl females traveled shorter distance than the females of the other reproductive state groups, while nonlactating and lactating BALB/cAJcl and C57BL/6J females showed increased depression-related behavior compared with nulliparous females. Lactating BALB/cAJcl and C57BL/6JJcl females exhibited decreased sucrose preference or anhedonia-like behavior compared with nulliparous and nonlactating females, although these results did not reach statistical significance after correction for multiple testing. An additional independent experiment replicated the marked behavioral changes in lactating BALB/cAJcl females. Moreover, increased anxiety-like behavior was observed in lactating BALB/cAJcl females that experienced prepregnancy stress. These results suggest genetic contributions to the regulation of anxiety-like and depression-related behaviors in female mice. Furthermore, this study suggests that pregnancy and lactation cause decreased locomotor activity and increased depression-related behaviors, which was consistently found in our results, and that prepregnancy stress enhances anxiety-like behavior in the BALB/cAJcl strain. The inbred strain of female mice may be used as a potential model of PPD to further study the genetic and neurobiological mechanisms underlying the development of this disorder.

Keywords: BALB/cA; C57BL/6J; Inbred substrain; Mouse model; Postpartum depression; Prepregnancy stress.

Fig. 1

Schematic diagram of the experimental procedure. Flow diagrams of the experimental procedures for (a) behavioral comparisons of nulliparous, nonlactating primiparous, and lactating primiparous females of four inbred strains (C57BL/6J, C57BL/6JJcl, BALB/cAnNCrlCrlj, and BALB/cAJcl) of mice and for (b) behavioral analysis of nulliparous and lactating primiparous BALB/cAJcl females previously exposed to chronic restraint stress (CRS, for 6 h/day for 21 days). Behavioral analysis of female mice was performed using the light/dark transition (LD) test, the open field (OF) test, the elevated plus maze (EP) test, the Porsolt forced swim (PS) test, the tail suspension (TS) test, and the sucrose preference (SP) test

Fig. 2

Locomotor activity and anxiety-like behavior of BALB/c and C57BL/6 female mice during the postpartum period in the open field test. The open field test was performed for a 30-min test period in nulliparous, nonlactating primiparous, and lactating primiparous females of C57BL/6J, C57BL/6JJcl, BALB/cAnNCrlCrlj, and BALB/cAJcl strains. a–d Open field test: a distance traveled (cm), b vertical activity, c center time (s), and d stereotypic counts during three 10-min blocks. Values are means ± SEM. The dashed enclosure in the figure indicates the results replicated in another independent experiment (see Fig. 7). In each strain, *p < 0.05 after Bonferroni correction (lactating primiparous vs.  nulliparous); †p < 0.05 after Bonferroni correction (lactating primiparous vs. nonlactating primiparous); §p < 0.05 after Bonferroni correction (nonlactating vs. nulliparous)

Fig. 3

Locomotor activity and anxiety-like behavior of BALB/c and C57BL/6 female mice during the postpartum period in the light/dark transition test. The light/dark transition test was performed for a 10-min test period in nulliparous, nonlactating primiparous, and lactating primiparous females of C57BL/6J, C57BL/6JJcl, BALB/cAnNCrlCrlj, and BALB/cAJcl strains. a–d Light/dark transition test: a distance traveled (cm) in the dark chamber, b distance traveled (cm) in the light chamber, c time spent in the light chamber (s), d number of transitions between the light and dark chambers, and e latency to enter the light chamber (s). Values are means ± SEM

Fig. 4

Locomotor activity and anxiety-like behavior of BALB/c and C57BL/6 female mice during the postpartum period in the elevated plus maze test. The elevated plus maze test was performed for a 10-min test period in nulliparous, nonlactating primiparous, and lactating primiparous females of C57BL/6J, C57BL/6JJcl, BALB/cAnNCrlCrlj, and BALB/cAJcl strains. a–f Elevated plus maze test: a distance traveled (cm), b number of total arm entries, c time spent in closed arms (s), d entries into open arms (%), e time spent in open arms (%), and f time spent in center area (s). Values are means ± SEM. Dashed enclosures in the figure indicate the results replicated in another independent experiment (see Fig. 7). *p < 0.05 after Bonferroni correction (lactating primiparous vs. nulliparous); †p < 0.05 after Bonferroni correction (lactating primiparous vs. nonlactating primiparous)

Fig. 5

Depression-related behavior in BALB/c and C57BL/6 female mice during the postpartum period in the forced swim test. The forced swim test was performed for a 10-min test period in nulliparous, nonlactating primiparous, and lactating primiparous females of C57BL/6J, C57BL/6JJcl, BALB/cAnNCrlCrlj, and BALB/cAJcl strains. a–d Porsolt forced swim test: a immobility time (%) on day 1, b distance traveled (cm) on day 1, c immobility time (%) on day 2, and d distance traveled (cm) on day 2. Values are means ± SEM. Dashed enclosures in the figure indicate the results replicated in another independent experiment (see Fig. 7). In each strain, *p < 0.05 after Bonferroni correction (lactating primiparous vs. nulliparous); §p < 0.05 after Bonferroni correction (nonlactating primiparous vs. nulliparous)

Fig. 6

Anhedonia-like behavior in BALB/c and C57BL/6 female mice during the postpartum period in the sucrose preference test. The sucrose preference test was performed in nulliparous, nonlactating primiparous, and lactating primiparous females of C57BL/6 J, C57BL/6 JJcl, BALB/cAnNCrlCrlj, BALB/cAJcl strains. Water intake and 1% sucrose intake were measured for two days, and sucrose preference (%) was calculated according to the formula: 100 × (sucrose intake/total solution intake). Values are means ± SEM. †p < 0.05 after Bonferroni correction (lactating primiparous vs. nonlactating primiparous)

Fig. 7

Replication of behavioral results in BALB/cAJcl female mice. A series of behavioral tests was performed in independent groups of nulliparous and lactating primiparous BALB/cAJcl females (n = 12, each group). a–d Open field test: a distance traveled (cm), b vertical activity, c center time (s), and d stereotypic counts during three 10-min blocks. e–i Light/dark transition test: e distance traveled (cm) in the dark chamber, f distance traveled (cm) in the light chamber, g time spent in the light chamber (s), h number of transitions between the light and dark chambers, and i latency to enter the light chamber (s). j–o Elevated plus maze test: j distance traveled (cm), k number of total arm entries, l time spent in closed arms (s), m entries into open arms (%), n time spent in open arms (%), and o time spent in center area (s). p–s Porsolt forced swim test: p immobility time (%) on day 1, q distance traveled (cm) on day 1, r immobility time (%) on day 2, and s distance traveled (cm) on day 2. t Immobility time (%) in the tail suspension test. Females showing tail-climbing behavior for more than 30 s in total during the test period were excluded from the analysis. u 1% sucrose preference (%). Values are means ± SEM. Dashed enclosures in the figure indicate the results replicated in another independent experiment (see Figs. 2, 4, and 5). *p < 0.05, compared with nulliparous females

Fig. 8

Increased anxiety-like behavior in BALB/cAJcl female mice previously exposed to chronic restraint stress. Behaviors of nulliparous and lactating primiparous BALB/cAJcl females previously exposed to chronic restraint stress were assessed (nonstressed (NS) nulliparous females, n = 14; chronic restraint-stressed (CRS) nulliparous females, n = 14; NS-lactating females, n = 13; CRS-lactating females, n = 9). a–d Open field test: a distance traveled (cm), b vertical activity, c center time (s), and d stereotypic counts during three 10-min blocks. e–i Light/dark transition test: e distance traveled (cm) in the dark chamber, f distance traveled (cm) in the light chamber, g time spent in the light chamber (s), h number of transitions between the light and dark chambers, and i latency to enter the light chamber (s). j–m) Porsolt forced swim test: j immobility time (%) on day 1, k distance traveled (cm) on day 1, l immobility time (%) on day 2, and m distance traveled (cm) on day 2. n Immobility time (%) in the tail suspension test. Females showing tail-climbing behavior for more than 30 s in total during the test period were excluded from the analysis. o 2% sucrose preference (%). Values are means ± SEM. *p < 0.05, compared with nulliparous females