Intrauterine growth restriction modifies the hedonic response to sweet taste in newborn pups - Role of the accumbal μ-opioid receptors

- IUGR can change the hedonic response to sweet taste.
- IUGR decreases phosphorylation of mu opioid receptor in early life.
- Differences in hedonic response are seen only in early life.

Intrauterine growth restriction (IUGR) is associated with increased preference for palatable foods. The hedonic response to sweet taste, modulated by the nucleus accumbens μ-opioid-receptors, may be involved. We investigated hedonic responses and receptor levels in IUGR and Control animals. From pregnancy day 10, Sprague-Dawley dams received either an ad libitum (Control), or a 50% food restricted (FR) diet. At birth, pups were cross-fostered, and nursed by Adlib fed dams. The hedonic response was evaluated at 1 day after birth and at 90 days of life, by giving sucrose solution or water and analyzing the hedonic facial responses (within 60 s). Control pups exposed either to water or sucrose resolved their hedonic responses after 16 and 18 s, respectively, while FR hedonic responses to sucrose persisted over 20 s. FR pups had deceased phospho-μ-opioid-receptor (p = 0.009) and reduced phosphor:total mu opioid receptor ratio compared to controls pups (p = 0.003). In adults, there was an interaction between group and solution at the end of the evaluation (p = 0.044): Control decreased the response after sucrose solution, FR did not change over time. There were no differences in phosphorylation of μ-opioid-receptor in adults. These results demonstrate IUGR newborn rats exhibit alterations in hedonic response accompanied by a decrease in μ-opioid-receptor phosphorylation, though these alterations do not persist at 3 months of age. Opioid system alterations in early life may contribute to the development of preference for highly palatable foods and contribute to rapid weight gain and obesity in IUGR offspring.