Maternal Methyl-Enriched Diet Improves Episodic Memory and Does Not Affect the Conditioned Fear Memory in Offspring of WAG/RIJ Rats

Abstract

The purpose of this study is to find out what effect the maternal methyl-enriched diet (MED) in the perinatal period exerts on cognitive functions in adult offspring of WAG/Rij rats, a genetic model of absence epilepsy with comorbid depression. Cognitive functions (learning and memory) were evaluated in tests of a novel object recognition (NOR) and a conditioning of fear memory (fear conditioning). The experiments were carry out on 6-months old male WAG/Rij rats. The mothers of the experimental group fed MED, and the mothers of the control group fed the control diet. The NOR test was used to assess episodic memory. This test is based on innate exploratory motivation (novelty preference motivation), which is usually reduced in depression. The conditioning of fear memory is the classic Pavlovian defensive conditioned reflex, manifested in the form of freezing reactions in response to negative reinforcement (electrical stimulation of paws). In the NOR test, in rats of the experimental group the recognition index (a measure of episodic memory), as well as the number of entries to the center of the arena (a measure of explorative motivation) were significantly higher compared with corresponding measures in the control group. However, no intergroup differences were found in the manifestation of the conditioned fear memory (% of freezing reactions) to the context and sound signal. The results indicate that the maternal MED improves episodic memory in the NOR test, but does not affect the conditioned fear memory associated with context and sound signal in adult offspring of WAG/Rij rats.