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Early undernutrition blocks the effect of naltrexone on rat exploratory behavior
Insights
Undernourished rats exhibit altered opioid system function, as evidenced by a lack of response to naltrexone, a drug that typically reduces exploratory behavior in normal rats.
Area of Science:
- Neuroscience
- Developmental Biology
- Nutritional Science
Background:
- Early-life nutrition significantly impacts neurodevelopment.
- The endogenous opioid system plays a role in regulating exploratory behaviors.
Purpose of the Study:
- To investigate the impact of early-life undernutrition on the endogenous opioid system's modulation of exploratory activity in rats.
Main Methods:
- Rats were subjected to maternal dietary protein restriction (8% protein) from birth to weaning, followed by a standard diet.
- Exploratory behavior was assessed using a 2-compartment open-field test.
- The effect of naltrexone, an opioid antagonist, on exploratory activity was evaluated.
Main Results:
- Naltrexone significantly reduced rearing behavior in control rats by approximately 50%.
- Undernourished rats did not show a significant change in exploratory activity after naltrexone administration.
- These findings suggest impaired opioid system function in undernourished rats.
Conclusions:
- Early-life undernutrition alters the endogenous opioid system's involvement in regulating exploratory behavior.
- The opioid system may be a target for interventions aimed at mitigating behavioral deficits associated with malnutrition.
Abstract:
1. Young rats were undernourished by feeding their dams an 8% protein diet (w/w) from birth until weaning (21 days); the dams of control rats were fed a 20% protein diet (w/w) until weaning. All offspring were fed a 20% protein diet from 21 to 120-150 days of age, when they were tested. 2. The involvement of endogenous opioids in the exploratory activity (rearing response and crossing frequency in a 2-compartment open-field test) was evaluated by examining the effects of a single injection of naltrexone (0.75 mg/kg, ip) 6 min prior to testing. 3. Naltrexone decreased exploratory activity (rearing) by approximately 50% in normal rats but had no effect on undernourished rats. 4. These data provide additional evidence for an alteration in the opioid system of undernourished rats.