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Acute opiate withdrawal in rats undernourished during infancy: impact of the undernutrition method
C A Cohen1, J Tonkiss, S B Sparber
1Department of Pharmacology, University of Minnesota, Minneapolis 55455.
Insights
Early life undernutrition in rats affects morphine withdrawal. Different nutritional methods altered responses, with females showing less sensitivity than males, highlighting behavioral measures for assessing opiate dependence.
Area of Science:
- Neuroscience
- Behavioral Pharmacology
- Developmental Neuroscience
Background:
- Early life undernutrition can impact long-term neurodevelopment and behavioral outcomes.
- Opioid dependence and withdrawal are critical areas of study with significant public health implications.
- Understanding how early life experiences influence drug responses is crucial for developing targeted interventions.
Purpose of the Study:
- To investigate the effects of two distinct early postnatal undernutrition methods on acute morphine withdrawal in adult rats.
- To determine if undernutrition influences morphine sensitivity and naloxone-induced withdrawal behaviors.
- To explore potential sex differences in the expression of opiate withdrawal following early life nutritional challenges.
Main Methods:
- Adult male and female rats were subjected to two undernutrition protocols: Large Litter (LL) and Modified Slob (MS).
- Behavioral responses were assessed using an operant conditioning schedule (FR16) followed by morphine administration and naloxone challenge.
- Body temperature changes were monitored as a physiological indicator of opiate and withdrawal effects.
Main Results:
- Rats subjected to the Modified Slob procedure exhibited milder naloxone-induced withdrawal behaviors compared to controls and Large Litter rats.
- Males reared in Large Litters showed minimal behavioral disruption after morphine, suggesting potential insensitivity or rapid tolerance.
- Females generally displayed less sensitivity to both morphine and naloxone-induced withdrawal compared to males, with behavioral measures being more sensitive than body temperature changes.
Conclusions:
- The method of early life undernutrition significantly influences the expression of morphine action and withdrawal.
- Behavioral assessments are more sensitive than body temperature changes in detecting differences in opiate dependence and withdrawal following early nutritional insults.
- Sex differences in opiate withdrawal are evident, with females appearing less sensitive than males, underscoring the importance of considering sex in neurobiological research.
Abstract:
Acute morphine withdrawal was assessed in adult rats following early postnatal undernutrition produced by two different methods (Large Litter procedure-20 pups/litter and Modified Slob procedure-rats cross-fostered on days 2, 4, and 6 to nonlactating dams for 24-hour periods). Response rates were first stabilized on a FR16 operant schedule. A single dose of morphine (20 mg/kg) was then administered, followed 4 h later by a single injection of naloxone (2.5 mg/kg). Males reared in large litters showed little behavioral disruption after morphine, suggesting either insensitivity to the opiate or the rapid development of tolerance. After naloxone. Modified Slob males displayed milder withdrawal than those in the well-nourished control or large litter groups. Thus the method of undernutrition influenced morphine's action and expression of withdrawal. A clear sex difference was also evident, females appearing to be generally less sensitive to the opiate- and naloxone-induced withdrawal than males. Body temperature underwent a characteristic elevation following morphine and a depression following naloxone across all groups, but undernutrition did not affect these responses. Hence, behavior proved to be the more sensitive measure for revealing differences in opiate dependence and withdrawal following early life undernutrition, under the test conditions employed.