Stress-induced endocrine response and anxiety: the effects of comfort food in rats

Figures & data

Table 1. Chronic unpredictable mild stress protocol (Moreau et al., 1994).

Period	Monday (Day 1/8)	Tuesday (Day 2/9)	Wednesday (Day 3/10)	Thursday (Day 4/11)	Friday (Day 5/12)	Saturday (Day 6/13)	Sunday (Day 7/14)
Morning	Restraint (60 min)	Restraint (60 min)	Food restriction*	Empty water bottle (60 min)	Restraint (60 min)	Inversion of light/ dark cycle over the weekend	Inversion of light/ dark cycle over the weekend
				Restraint (60 min)
Afternoon	Restraint (60 min)	Restraint (60 min)	Restraint (60 min)	Restraint (60 min)
Night	Light on during the night	Water/food deprivation overnight	Water deprivation overnight	Damp sawdust overnight	Inversion of light/ dark cycle over the weekend**

*after overnight water/food deprivation, on Wednesday (Day 3/10) morning a Petri plate containing 45 mg of food pellets was positioned on the floor of the cage. Two hours later, food was made available ad libitum.

**On Friday night, lights were not turned off and remained on all night. Lights were turned off Saturday morning; they were turned on again Saturday night, and so on during the weekend. On Monday morning the light/dark cycle was restored (i.e. lights were on Monday morning and off Monday night).

Figure 1. Daily food intake (mean ± sem; n = 10 rats/group) by rats submitted (CUMS) or not (control) to chronic unpredictable mild stress and given access to commercial chow only (CC). Note: On day 0, rats were not submitted to CUMS (the day before the stress protocol), on days 2 and 9, rats submitted to CUMS had access to food and water for only 12 h and restricted access for an additional 2 hours. On days 3 and 10, rats submitted to CUMS had access to water for only 12 h. *p < 0.05 versus controls (two-way ANOVA with Bonferroni test).

Figure 2. Daily intake of commercial chow (CC) and comfort food (CF) shown separately for the control group and for the chronic unpredictable mild stress group (CUMS) given the combined food choice. Hence, total daily food intake (not shown) for the control and CUMS groups can be interpolated by summing daily CC and CF intakes for each group. Data are mean ± sem, n = 10 rats/group. On day 0, rats were not submitted to CUMS (the day before the stress protocol); on days 2 and 9, rats submitted to CUMS had access to food and water for only 12 h and restrict access for an additional 2 hours. On days 3 and 10, rats submitted to CUMS had access to water for only 12 h. *p < 0.05 versus controls (two-way ANOVA with Bonferroni test).’.

Table 2. Daily food and caloric intake, initial body weight and body weight gain by rats submitted (CUMS) or not (control) to chronic unpredictable mild stress and given access either to commercial chow (CC) only or to commercial chow and comfort food (CC/CF).

	Group
Parameter	CC-control	CC-CUMS	CC/CF-control	CC/CF-CUMS
Commercial chow intake (g/day)	24.9 ± 0.3	22.9 ± 0.7^a	4.77 ± 0.02	1.06 ± 0.4^a
Comfort food intake (g/day)	–	–	19.7 ± 0.1^b	19.1 ± 0.5^a,b
Total caloric intake (kJ/day)	423 ± 5	390 ± 12^a	562 ± 2^b	428 ± 10^a,c
Initial body weight (g)	202 ± 5	192 ± 5	196 ± 4	191 ± 6
Body weight gain (g)	79 ± 2	59 ± 4^a	104 ± 4^b	74 ± 5^a

Values are means ± sem; n = 10 rats/group.

^ap < 0.05 versus CC/CF-control (Student’s t-test); ^bp < 0.05 versus the intake of commercial chow; ^cp < 0.05; versus CC-CUMS (two-way analysis of variance followed by Bonferroni test).

Figure 3. Percentage of entries into (A) and time spent in (B) the open and closed arms of the elevated plus-maze by rats submitted (CUMS) or not (control) to chronic unpredictable mild stress and given access either to commercial chow (CC) only or to commercial chow (CC) and comfort food (CF). (n = 10 rats/group). *p < 0.05, stress effect; **p < 0.05, diet effect (two-way ANOVA followed by Bonferroni test).

Table 3. Behavior in the open field test of rats submitted (CUMS) or not (control) to chronic unpredictable mild stress and given access either to commercial chow only (CC) or to commercial chow and comfort food (CC/CF).

	Group
Parameter	CC-control	CC-CUMS	CC/ CF-control	CC/ CF-CUMS
Latency to first crossing (s)	3.3 ± 0.7	3 ± 0.5	2.4 ± 0.4	3.8 ± 0.5
Time spent in centre (s)	51 ± 9.5	27 ± 5^a	42 ± 5.7	24 ± 3.8^a
Time spent in periphery (s)	249 ± 9.5	272 ± 4.5^a	258 ± 5.7	275 ± 3.8^a
Crossing	65 ± 7.4	64 ± 2.8	51 ± 2.6	64 ± 3.7
Rearing	44 ± 5.2	34 ± 3.4	30.6 ± 3.3	32 ± 3.3
Grooming	2.5 ± 0.6	2.9 ± 0.4	2.3 ± 0.5	2.4 ± 0.5

Values are means ± sem; n = 10 rats/group; ^ap < 0.05 versus. CC-control (two-way analysis of variance and Bonferroni test).

Figure 4. Serum corticosterone concentration (mean ± sem) by rats submitted (CUMS) or not (control) to chronic unpredictable mild stress and given access either to commercial chow (CC) only or to commercial chow (CC) and comfort food (CF). CC-control group: n = 8 rats/group; CC-CUMS group: n = 5 rats/group; CC/CF-control group: n = 8 rats/group; CC/CF-CUMS group: n = 4 rats/group. *p < 0.05, stress effect; **p < 0.05, interaction between stress and diet effects (two-way ANOVA with Bonferroni test).

Table 4. Serum concentrations of glucose, total cholesterol and triglycerides of rats submitted (CUMS) or not (control) to chronic unpredictable mild stress and given access either to commercial chow (CC) only or to commercial chow and comfort food (CC/CF).

	Group
Serum parameter	CC-control	CC-CUMS	CC/ CF-control	CC/ CF-CUMS
Glucose (mg/dl)	111.0 ± 3.5	116.5 ± 2.8	124.8 ± 2.18^a	120.0 ± 6.9
Total cholesterol (mg/dl)	92.0 ± 3.5	104.8 ± 7.6	132.8 ± 25.9^a	122.0 ± 8.2
Triglycerides (mg/dl)	126.1 ± 13.3	108.7 ± 11.5	125.8 ± 13.7	148.7 ± 11.7

Values are means ± sem; n = 5 rats/group; ^ap < 0.05 versus CC-control (two-way analysis of variance and Bonferroni test).