Stress-induced visceral analgesia assessed non-invasively in rats is enhanced by prebiotic diet

Table 1 Chemical composition of standard and enzyme-treated rice fiber diets

Content (g/kg)	Standard	ERF1
Casein2	146.0	140.4
Vitamin mix	10.0	10.0
Mineral mix	35.0	35.0
Choline chloride	2.0	2.0
Cellulose2	30.0	-
ERF	-	40.0
Corn oil	50.0	50.0
Corn starch	727.0	722.6

¹Enzyme-treated rice fiber (protein, 14.9%; dietary fiber, 74.5%);

²According to AIN 93G formula, protein and dietary fiber contents in two diets were adjusted to the same value using casein and cellulose, respectively. ERF: Enzyme-treated rice fiber.

Table 2 Baseline visceromotor response to colorectal distension at day 0

CRD (mmHg)	Standard diet1		ERF diet1
	No stress (n = 7) VMR (%)2	WAS (n = 7) VMR (%)2	No stress (n = 9) VMR (%)2	WAS (n = 8) VMR (%)2
10	-0.3 ± 1.2	0.9 ± 1.9	2.8 ± 2.8	0.89 ± 1.0
20	5.1 ± 1.8a	26.8 ± 12.2	30.6 ± 12.2	30.7 ± 7.0
40	71.4 ± 6.2	77.3 ± 11.8	71.1 ± 11.2	88.7 ± 7.8
60	100 ± 0	100 ± 0	100 ± 0	100 ± 0

¹Rats were fed standard or 4% enzyme-treated rice fiber (ERF) diet (2 groups each before to be assigned to no stress or water avoidance stress, WAS) starting at the weaning period for 37 d before performing the baseline visceromotor response (VMR) to colorectal distension (CRD);

²Each value represents the mean ± SE of n as indicated in parenthesis;

^aP < 0.05 vs all other groups at 20 mmHg - 2-way ANOVA, Bonferroni post test.

Table 3 Visceromotor response after water avoidance stress or no stress in rats fed standard or enzyme-treated rice fiber diet

Time1 Post WAS	CRD pressure (mmHg)	Standard diet1				ERF diet1
		No stress		WAS		No stress		WAS
		VMR (%)2	n	VMR (%)2	n	VMR (%)2	n	VMR (%)2	n
45 min day 1	40	15.8 ± 17.6	7	- 32.4 ± 15.2a	7	26.0 ± 23	8	- 29.5 ± 12.3b	8
	60	1.0 ± 9.7		- 30.0 ± 10.8a		12.9 ± 13.8		- 28.7 ± 6.0bc
45 min day 10	40	-26.4 ± 11.7	7	- 36.2 ± 17.8b	7	3.7 ± 21.3	8	- 49.3 ± 11.6bc	9
	60	-23.7 ± 18.6		- 20.6 ± 12.2		21.6 ± 23.5		- 38.9 ± 7.3b
24 h day 11	40	7.5 ± 38.7	5	- 28.2 ± 15.0	7	- 4.1 ± 21.5	6	- 49.8 ± 12.6b	9
	60	30.4 ± 15.4		- 24.3 ± 9.6c		5.8 ± 15.1		- 34.3 ± 10.8b

¹Rats were fed 4% enzyme-treated rice fiber (ERF) diet or standard control diet starting at the weaning period for 37 d, then tested for baseline visceromotor response (VMR) to colorectal distention (CRD) response (day 0) and thereafter exposed daily to 1 h water avoidance stress (WAS) for 10 consecutive d or no stress (days 1-10), while still maintained under standard or 4% ERF diet. Non-stressed animals were kept in their home cages. On days 1 (acute WAS) and 10 [repeated water avoidance stress (rWAS)], 45-50 min after the end of the stress session, and on day 11, 24 h after the last rWAS session, rats were subjected to CRD protocol and VMR was monitored in all groups;

²Each value represents the mean ± SE of % VMR changes from baseline (day 0) in number of animal indicated by n in columns). Minus values represent analgesia.

^aP < 0.05,

^bP < 0.01 vs baseline;

^cP < 0.05 vs respective diet non stressed group, 2-way ANOVA, Bonferroni post hoc test.