Changes in the incentive value of food after naltrexone treatment depend on a differential preference for a palatable food in male rats

Abstract

Introduction: Opioid antagonist treatments such as naltrexone (NTX) and naloxone reduce consummatory behavior of palatable food (PF) and other incentives. Meanwhile, a significant increase in alcohol consumption has been observed when it is offered immediately after ending NTX treatment, an effect apparently produced by increased opioidergic activity caused by up-regulation of opioid receptors.

Objective: On this basis we assessed changes in the consumption of PF after opioid antagonist treatment in rats with different preferences for that food.

Methods: The preference of male Wistar rats for a PF was classified as low, medium, or high in a baseline period, after which the animals in each preference level were sub-divided into control and experimental groups that received injections of either NTX (2 mg/kg twice per day/6 days) or a saline solution with a space of 8 hours between doses. At the end of pharmacological treatment (PT), subjects were re-exposed to the PF.

Results: Increased PF intake was found only in the low-preference group, but the increase was observed in both the experimental and control animals. Also, a decrease in chow intake during PT was observed in all preference groups, while recovery after treatment was noted only in the low-preference rats.

Discussion: The increased intake observed in the low-preference rats after treatment phase suggests that the hypothalamic–pituitary–adrenal axis activation during PT could have enhanced the rewarding characteristics of the sweet food and so facilitated and increased its consumption in the re-exposure period.

Keywords:

• Palatable food
• Carbohydrate intake
• Naltrexone
• Opioid system
• Food intake
• Incentive value
• Eating behavior
• Opioid antagonist