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The effect of naloxone on operant behavior for food reinforcers in DBA/2 mice
1The Vollum Institute, Oregon Health & Science University, Portland, OR 97201, USA.
Abstract:
Mice are powerful models to investigate the genetic basis of food reward because many spontaneous obesity mutants exist and the murine genome is accessible to selectively targeted manipulations. Experiments in rats have shown that opioid receptor blockade reduces operant responding to food reinforcers. The present study investigated whether DBA/2J mice would display similar behavior in response to an opioid antagonist. Twelve male DBA/2J mice were trained to lever press for food reinforcers and subsequently randomized in a within subjects design for no injection, saline injection, or 10 mg/kg naloxone injection intraperitoneal (i.p.) 20 min before each daily trial under ad lib or food-deprived conditions. A significant main effect of injection occurred to reduce lever pressing by the mice. However, a greater pharmacological effect of naloxone occurred compared with saline on the operant responding only under the food-deprived conditions. Interestingly, the percentage of dispensed food pellets actually consumed was significantly reduced after naloxone injection compared with saline injection for either chow-based or sucrose pellets under ad lib or deprived feeding conditions. These data suggest that opioids specifically influence consumatory behavior in mice, but our findings on instrumental behavior were confounded by an independent inhibitory effect of an i.p. saline injection.
Insights
Opioid receptor blockade with naloxone reduced food consumption and lever pressing in DBA/2J mice, particularly under food-deprived conditions. Saline injections also affected behavior, confounding instrumental response findings.
Area of Science:
- Neuroscience
- Behavioral Pharmacology
- Genetics
Background:
- Mice are valuable models for studying food reward genetics due to existing obesity mutants and genetic manipulation accessibility.
- Previous rat studies indicate opioid receptor blockade diminishes operant responses to food.
Purpose of the Study:
- To investigate if DBA/2J mice exhibit similar behavioral changes to opioid antagonists as observed in rats.
- To assess the impact of naloxone on operant responding and food consumption in mice.
Main Methods:
- Twelve male DBA/2J mice were trained in lever pressing for food rewards.
- Mice received no injection, saline, or 10 mg/kg naloxone (intraperitoneal) before daily trials.
- Experiments were conducted under both ad libitum and food-deprived conditions.
Main Results:
- Naloxone significantly reduced lever pressing, an effect more pronounced under food-deprived conditions compared to saline.
- Food pellet consumption decreased significantly after naloxone compared to saline, irrespective of diet (chow or sucrose) or feeding condition.
- Saline injections independently inhibited operant responding, confounding the interpretation of instrumental behavior.
Conclusions:
- Opioid signaling specifically influences consummatory behavior in mice.
- The study highlights the complex interplay between opioid antagonists, feeding states, and instrumental behavior in mice.
- Further research is needed to disentangle the effects of naloxone from saline in this model.
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