Figure 2.

A history of limited sucrose intake reduces hypothalamic-pituitary-adrenal (HPA) axis responses to stress and is largely mediated by the pleasurable and rewarding properties of the sucrose. (A) The plasma adrenocorticotropic hormone (ACTH) response to a 20-min restraint stress is blunted by either limited sucrose (Suc; 30%) or saccharin (Sac; 0.1%; a non-caloric, artificial sweetener) drink intake, suggesting that the pleasurable or rewarding properties of these sweet drinks are sufficient for stress relief. *p < 0.05 vs. Water (Wat). (B) Rats given twice-daily sucrose (S) drink have a reduced integrated (area-under-the-curve) plasma corticosterone response to restraint relative to water-only controls (left). In contrast, those receiving twice-daily orogastric gavage of 4 ml of sucrose vs. water (to replicate many of the post-ingestive effects of the drink while minimizing taste and hedonic properties), do not have a reduced plasma corticosterone response (right), suggesting that sucrose’s hedonic/rewarding properties are necessary. *p < 0.05 vs. Water. (C) Male rats with a history of daily, limited (30 min) access to a sexually-responsive female engaged in sexual activity (Sex) and had a reduced integrated plasma corticosterone response to restraint compared to both undisturbed controls (C) and sham-sex rats (Sh; this group received a female rat in their cages, but the female was enclosed in a wire mesh box that prevented physical interactions), suggesting that other types of natural reward provide similar HPA-dampening. *p < 0.05 vs. control and sham. Data are shown as mean ± SEM. Reproduced from (Ulrich-Lai et al., 2010).