Chronic unpredictable restraint stress increases hippocampal pro-inflammatory cytokines and decreases motivated behavior in rats

Figures & data

Figure 1. Experimental design of experiments 1 and 2. SNCT: sucrose negative contrast test; NSF: novelty suppressed feeding; EPM: elevated plus maze; FST: forced swim test.

Table 1. Schedule of chronic stress by movement restraint with variable duration.

Restraint	Monday (h/day)	Tuesday (h/day)	Wednesday (h/day)	Thursday (h/day)	Friday (h/day)
First week	6	2	6	4	2
Second week	4	6	2	6	2
Third week	2	6	4	6	2

Figure 2. Chronic stress decreased body weight gain in Experiments 1 (A) and 2 (B). Experiment 1 included 10 CTL and 18 CUMR rats. Experiment 2 included 26 CTL and 33 CUMR animals. *Difference from controls, p < 0.001; ^#difference from the first week, p < 0.001; ^‡difference from the second week, p < 0.01 (two-way ANOVA repeated measures). Values are shown as mean ± s.e.m.

Figure 3. Chronic stress increased pro-inflammatory cytokine levels (normalized by total protein level in the tissue) in the hippocampus. (A) IL-1α; p < 0.2; (B) IL-1β; p = 0.003; (C) IL-2; p < 0.02; (D) IL-6; p < 0.03; (E) IL-10; p = 0.002; (F) TNF-α; p < 0.09. Values are shown as mean ± s.e.m. of 10 CTL and 18 CUMR rats. *Difference from CTL.

Table 2. Correlation matrix between hippocampal cytokines.

	IL-1α	IL-1β	IL-2	IL-6	IL-10
IL-1α	–	–	–	–	–
IL-1β	0.63	–	–	–	–
IL-2	0.86	0.90	–	–	–
IL-6	0.90	0.85	0.97	–	–
IL-10	0.63	0.96	0.89	0.84	–
TNFα	0.82	0.71	0.85	0.88	0.70

Table 3. Results of corticosterone (CORT) levels, novelty suppressed feeding (NSF) and elevated plus maze (EPM) tests.

CORT levels (ng/mL)
Control	31.85 ± 19.69
Stress	44.64 ± 28.73
p-Value	0.249
NSF	Latency (s)
Control	355.86 ± 136.73
Stress	314.65 ± 154.072
p-Value	.199
EPM	Open arms	Closed arms	% Open arms
Entries
Control	2.92 ± 2.17	7.50 ± 3.25	26.47 ± 16.33
Stress	3.12 ± 2.01	8.18 ± 2.82	24.92 ± 14.10
p-Value	0.520	0.393	0.771
Time (s)
Control	33.53 ± 27.92	218.96 ± 45.57	14.06 ± 13.79
Stress	36.20 ± 24.95	211.62 ± 42.11	15.25 ± 11.18
p-Value	0.435	0.299	0.359
Segments crossed
Control	9.46 ± 7.87	38.54 ± 13.21	18.48 ± 13.66
Stress	10.52 ± 7.89	39.76 ± 12.17	19.50 ± 13.05
p-Value	0.612	0.976	0.771

Results are presented as mean ± s.d. of 10 controls and 18 stressed animals/group for CORT levels, and 26 controls and 33 stressed animals/group for NSF and EPM. For the analysis of CORT and behavioral tests Student’s-t test and the Mann-Whitney U-test were used, respectively.

Figure 4. Chronic stress did not reduced sucrose preference for the less palatable solution rats and increased the frequency of immobility and reduced the frequency of swimming of CUMR animals in the forced swim test. (A) Sucrose preference in the Sucrose Negative Contrast Test; (B) behaviors in the forced swim test. Values are shown as mean ± s.e.m. of n = 26 CTL and 33 CUMR rats. *Difference from CTL, p < 0.001 (Student’s t test); ^‡difference from day 2 (two-way ANOVA repeated measures); p = 0.003.