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Effects of early life undernutrition in artificially-reared rats. 2. Subsequent behaviour
J Tonkiss1, J L Smart, R F Massey
1Department of Child Health, University of Manchester Medical School.
Insights
Early life undernutrition impacts rat behavior, with artificially-reared undernourished rats showing altered activity and social interactions compared to controls. Mother-reared rats displayed fewer differences, suggesting maternal buffering effects.
Area of Science:
- Neuroscience
- Developmental Biology
- Animal Behavior
Background:
- Early life nutrition significantly influences brain development and subsequent behavior.
- Understanding the long-term effects of undernutrition is crucial for developmental neuroscience.
Purpose of the Study:
- To investigate the behavioral consequences of early life undernutrition in rats.
- To compare the effects of mother-rearing versus artificial-rearing undernourished conditions.
Main Methods:
- Rats were divided into four groups: mother-reared control (MRC), mother-reared undernourished (MRU), artificially-reared control (ARC), and artificially-reared undernourished (ARU).
- Undernutrition was imposed from day 5 to 25 through maternal food restriction or restricted milk infusion.
- Behavioral testing at 18 weeks included open field, social interaction, and operant conditioning (bar-pressing for food).
Main Results:
- Previously undernourished rats exhibited higher response rates on fixed-ratio schedules (FR5) and received fewer rewards on variable-interval schedules (VI 2").
- Undernourished rats displayed increased aggression during social interactions.
- Artificially-reared undernourished rats (ARU) were less active in open field and social tests compared to artificially-reared controls (ARC).
Conclusions:
- Early life undernutrition, particularly when artificially reared, can lead to lasting behavioral changes, including altered activity levels, learning, and social behavior.
- Mother-rearing may offer a protective "buffering" effect against some consequences of undernutrition.
- Findings suggest direct nutritional impacts on brain development influencing adult behavior.
Abstract:
Four groups of rat pups were reared: mother-reared control (well-fed) and undernourished (MRC, MRU) and artificially-reared control and undernourished (ARC, ARU). AR rats were fed expressed rats' milk (days 5-7), mixtures of rats' milk and milk substitute (days 8-16), and milk substitute only (days 17-20) by intermittent infusion via a gastric cannula. Undernutrition, imposed from 5-25 days, was effected initially by underfeeding the mother (MRU) or by infusing restricted quantities of milk (ARU). Weaning was at 21 days and undernutrition from 21-25 days was by restricting the supply of solid food. All rats were fed ad lib from 25 days. From 18 weeks, male rats were subjected to 3 behavioural tests: open field, social behaviour (encounters between rats of like treatment group) and bar-pressing for food (CRF, FR5, VI 1', VI 2' and Extinction). Previously undernourished rats responded at higher rates on FR5, received fewer rewards on VI 2' and displayed more aggression during social interaction. These findings may reflect direct effects of nutrition on brain growth. In the open field and social situations ARU were generally less active than ARC animals, whereas MRU and MRC rats differed little. These results are discussed in terms of MRU pups being maternally "buffered" against the worst effects of undernutrition and ARC rats displaying characteristics of "early stimulated" animals.