Submitted on September 24, 2006
Accepted on April 3, 2007
PARAVENTRICULAR OPIOIDS ALTER INTAKE OF HIGH-FAT BUT NOT HIGH-SUCROSE DIET DEPENDING ON DIET PREFERENCE IN A "BINGE" MODEL OF FEEDING
Amy M Naleid1, Martha K Grace2, Munya Chimukangara2, Charles Billington3, and Allen S. Levine4*
1 Psychiatry and Behavioral Science, University of Washington, Seattle, Washington, United States
2 Research Service, Minneapolis VA Medical Center, Minneapolis, Minnesota, United States
3 Metabolic Section (111G), Minneapolis VA Medical Center, Minneapolis,, Minnesota, United States
4 Food Science and Nutrition, University of Minnesota, St. Paul, Minnesota, United States
* To whom correspondence should be addressed. E-mail: aslevine{at}umn.edu.
Work from our laboratory indicates that when rats are given a choice between a high-fat and a high-sucrose diet, opioid blockade with naltrexone (NTX) in a reward-related site (central amygdala) inhibits intake of the preferred diet only, whereas NTX injected into a homeostasis-related site, such as the hypothalamic paraventricular nucleus (PVN), inhibits intake of both diets. Other work suggests that opioids increase intake of fat specifically. This study investigates the role of PVN opioids in food choices made by calorically-replete animals. We used a "binge" model with chow-maintained rats given three hours access to a choice of a high-fat or high-sucrose diet three days a week. We hypothesized that intra-PVN injection of the mu-opioid agonist, DAMGO (0, 0.0.025, .25, and 2.5 nmol) would enhance, and NTX (0, 10, 30, and 100 nmol) would inhibit intake of both diets to an equal extent. We found that when animals were divided into groups according to sucrose or fat preference, DAMGO increased fat intake in fat-consuming animals, while having no effect on intake of either diet in sucrose-consuming animals. NTX, however, inhibited fat intake in both groups. Intra-PVN NTX did not inhibit intake of sucrose when presented in the absence of a fat choice, but did so when injected peripherally. Furthermore, intra-PVN and systemic NTX inhibited intake of chow by 24 hour food deprived animals. These results indicate a complex role for PVN opioids in food intake; with preference, nutrient type, and energy state affecting the ability of these compounds to change behavior.
