Behavioral and physiological responses of female prairie voles (Microtus ochrogaster) to various stressful conditions

Figures & data

Figure 1. Testing schedule for various acute psychological and social stressors in Experiment 1.

Figure 2. Testing schedule for the predictable and unpredictable immobilization treatments in Experiment 2.

Figure 3. The source and intensity of a stressor affected the biobehavioral stress response. (a–b), Only immobilization (IMO) stress led to a (a) delay in the latency of females to enter the open arm and (b) decreased percentage of time that females spent in the open arms during the EPM test. (c) None of the stressors influenced locomotor behavior (i.e. total arm entries) during the EPM test. (d) Corticosterone remained elevated 30 min post-stress in response to IMO and prolonged social defeat (SD), but not environmental novelty (Novel) or brief SD, in comparison to handled controls (HAN). (a–d) No differences were observed between HAN controls or social controls (SC). (e) Female plasma corticosterone concentrations were negatively associated with the percentage of time females spent in the open arm in the EPM test. Bars labeled with different letters differ significantly by Gabriel’s post hoc test in which a significant main effect was detected in the ANOVA (p < 0.05). (a–d) Data are expressed as mean ± SEM.

Table 1. Effect of stressors on the frequency of arm entries in the elevated plus maze.

Groups	n	Open arm	Closed arm	% Open arm
Experiment 1. Various acute psychological and social stressors
HAN	6	5.33 ± 1.86	9.83 ± 2.24	36.59 ± 9.25
SC	6	5.33 ± 1.33	10.83 ± 1.85	30.93 ± 13.73
Novel	6	7.33 ± 1.67	7.83 ± 2.23	51.35 ± 28.09
IMO	6	1.03 ± 0.37	6.67 ± 1.65	15.83 ± 6.38
Brief SD	8	4.25 ± 1.91	8.75 ± 2.11	33.08 ± 8.89
Prolonged SD	7	3.43 ± 0.75	10.43 ± 1.17	23.99 ± 3.55
Experiment 2. Predictable versus unpredictable immobilization
HAN	11	5.55 ± 1.12	9.54 ± 1.04	34.96 ± 5.69
Acute IMO	6	1.50 ± 0.72	9.83 ± 2.83	10.99 ± 6.05
3-day pIMO	8	4.13 ± 1.01	8.13 ± 1.76	35.35 ± 8.03
7-day pIMO	6	3.50 ± 1.52	14.00 ± 1.86	17.64 ± 3.97
3-day uIMO	7	2.00 ± 1.05	7.29 ± 1.74	14.15 ± 5.50
7-day uIMO	6	2.05 ± 0.86	9.67 ± 3.40	15.16 ± 6.02

Values represent frequency of entries into the open and closed arms on the elevated plus maze as well as the percentage of open arm entries (open arm entries versus total arm entries). Behaviors are reported as means and standard errors. Groups include handled controls (HAN), social controls (SC), and females exposed to novel environment stress (Novel), immobilization (IMO or acute IMO), brief social defeat (Brief SD), prolonged social defeat (Prolonged SD), 3-day predictable IMO (3-day pIMO), 7-day predictable IMO (7-day pIMO), 3-day unpredictable IMO (3-day uIMO), and 7 day unpredictable IMO (7-day uIMO).

Figure 4. The predictability of immobilization (IMO) stress influenced the biobehavioral stress response. (a) Females exposed to 1 day IMO delayed entry into the open arm in the EPM test compared to handled control females (HAN) and females exposed to 3 or 7 day predictable IMO (pIMO). (b) The percentage of time that females spent in the open arms during the EPM test was lower after exposure to 1 day IMO, 3-day uIMO, and 7 day unpredictable IMO (uIMO) compared to HAN controls. No differences were observed between HAN control females or females exposed to 3- or 7-day pIMO. (c) None of the stressors influenced locomotor behavior (i.e. total arm entries) during the EPM test. (d) Corticosterone remained elevated 30 min post-stress in response to exposure to 1 day IMO, 3-day pIMO, 3-day uIMO, and 7-day uIMO compared to HAN controls. However, no differences were observed between HAN controls and 7-day pIMO. Females exposed to 7-day uIMO had significantly higher corticosterone levels than 1 day IMO and 7-day pIMO. (e) Female plasma corticosterone concentrations were negatively associated with the percentage of time females spent in the open arm in the EPM test. Bars labeled with different letters differ significantly by Gabriel’s post-hoc test in which a significant main effect was detected in the ANOVA (p < 0.05). (a–d) Data are expressed as mean ± SEM.