Maternal Methyl-Enriched Diet Improves Episodic Memory but Does Not Affect Conditioned Fear Memory in Offspring of WAG/Rij Rats

Abstract

This study was aimed 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. The cognitive functions (learning and memory) were evaluated in the novel object recognition (NOR) and fear conditioning (for fear memory) tests. The experiments were carried out on 6-month-old male WAG/Rij rats. The mothers of the experimental group fed a MED, while the mothers of the control group fed a control diet. The NOR test was used to assess episodic memory. This test is based on innate exploratory (novelty preference) motivation, which is usually reduced in depression. The conditioning of fear memory is the classical Pavlovian defensive conditioned reflex, manifested as freezing in response to negative reinforcement (electric footshock). In the NOR test, in rats of the experimental group, the novel object recognition index (a measure of episodic memory) and the number of entries to the center of the arena (a measure of exploratory motivation) were significantly higher compared to the corresponding measures in the control group. However, no intergroup differences were revealed in the manifestation of conditioned fear memory (% of freezing responses) to a context and a sound cue. The results indicate that the maternal MED improves episodic memory in the NOR test but does not affect the conditioned fear memory associated with a context and sound cue in the adult offspring of WAG/Rij rats.