HPA axis dampening by limited sucrose intake: reward frequency vs. caloric consumption

Abstract

Individuals often cope with stress by consuming calorically-dense, highly-palatable 'comfort' foods. The present work explores the stress-relieving properties of palatable foods in a rat model of limited sucrose intake. In this model, adult male rats with free access to chow and water are given additional access to a small amount of sucrose drink (or water as a control). A history of such limited sucrose intake reduces the collective (HPA axis, sympathetic, and behavioral-anxiety) stress response. Moreover, the stress-dampening by sucrose appears to be mediated primarily by its rewarding properties, since beneficial effects are reproduced by the noncaloric sweetener saccharin but not oral intragastric gavage of sucrose. The present work uses an alternate strategy to address the hypothesis that the rewarding properties of sucrose mediate its stress-dampening. This work varies the duration, frequency, and/or volume of sucrose and assesses the ability to attenuate HPA axis stress responses. The data indicate that HPA-dampening is optimal with a greater duration and/or frequency of sucrose, whereas increasing the volume of sucrose consumed is without effect. This finding suggests that the primary factor mediating stress-dampening is the number/rate of reward (i.e., sucrose) exposures, rather than the total sucrose calories consumed. Collectively, these data support the hypothesis that stress relief by limited palatable food intake is mediated primarily by its hedonic/rewarding properties. Moreover, the results support the contention that naturally rewarding behaviors are a physiological means to produce stress relief.

Figure 1. For all durations of sucrose exposure, sucrose-drinking rats readily learned to drink the sucrose, and decreased their chow intake such that body weight was not altered

(A) Intake of rats given up to 4 ml of water or 30% sucrose twice daily for 7, 14, or 28 days. Not noted on figure: all sucrose values are greater than their respective water controls. (B) Chow intake for rats given water or sucrose drink for 7, 14, or 28 days. Not noted on figure: all sucrose values are less than their respective water controls. (C) Body weight of rats given water or sucrose drink for 7, 14, or 28 days. *p < 0.05 vs. respective water control.

Figure 2. Sucrose decreased the plasma corticosterone, but not the plasma ACTH, response to restraint stress

(A) The time course of restraint-stress-induced plasma ACTH for rats receiving sucrose or water twice daily for 4 (top), 2 (middle) or 1 (bottom) weeks. (B) The time course of restraint-stress-induced plasma corticosterone for rats receiving sucrose or water twice daily for 4 (top), 2 (middle) or 1 (bottom) weeks. Please note that for each hormone, the statistics depicted on the figure resulted from a three-way ANOVA comparing DRINK, DURATION, and TIME POST-STRESS. Not noted on figure: all values at 20, 40, and 60 min are greater than 0 min. #p < 0.05 vs.4 weeks, *p < 0.05 vs. water.

Figure 3. At least 2 weeks of twice daily sucrose exposure was required to reduce the integrated plasma corticosterone response to restraint

*p < 0.05 vs. water.

Figure 4. For all frequencies and volumes of sucrose, sucrose-drinking rats readily learned to drink the sucrose, and decreased their chow intake such that body weight was not altered

(A) Intake of rats given twice daily (up to 4 ml/session with 8 ml/day maximum) sucrose or water, or once daily (up to either 4ml/day or 8 ml/day) water or sucrose for 14 days. Not noted on figure: (1) all sucrose values are greater than their respective water controls except for the “once daily 4 ml” cohort on experiment day 1; and (2) the sucrose intake of the “once daily 4 ml” group is less than the other sucrose groups on all experimental days. (B) Chow intake for rats given twice daily (8ml/day) or once daily (either 4 ml/day or 8 ml/day) water or sucrose. Not noted on figure: all sucrose values are less than their respective water controls except for the “once daily 4 ml” cohort at experiment days 8-15. (C) Body weight of rats given twice daily (8ml/day) or once daily (either 4 ml/day or 8 ml/day) water or sucrose.

Figure 5. Sucrose decreased the plasma corticosterone response to restraint stress, and twice daily sucrose was more effective than once daily sucrose

(A) The time course of restraint-stress-induced plasma corticosterone for rats receiving 4 ml sucrose or water twice daily (top), 4 ml of sucrose or water once daily (middle), or 8 ml of sucrose or water once daily (bottom). The statistics depicted on the figure resulted from a three-way ANOVA comparing DRINK, PARADIGM, and TIME POST-STRESS. Not noted on figure: all values at 20, 40, and 60 min are greater than 0 min. #p < 0.05 vs. twice daily, *p < 0.05 vs. water. (B) Twice daily sucrose exposure was required to reduce the integrated plasma corticosterone response to restraint. *p < 0.05 vs. water.