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

This study was aimed to find out what effect the maternalmethyl-enriched diet (MED) in the perinatal period exerts on cognitivefunctions in adult offspring of WAG/Rij rats, a genetic model ofabsence 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 experimentswere carried out on 6-month-old male WAG/Rij rats. The mothers ofthe experimental group fed a MED, while the mothers of the controlgroup 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 fearmemory is the classical Pavlovian defensive conditioned reflex,manifested as freezing in response to negative reinforcement (electricfootshock). 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 measureof exploratory motivation) were significantly higher compared tothe corresponding measures in the control group. However, no intergroupdifferences were revealed in the manifestation of conditioned fearmemory (% of freezing responses) to a context and a sound cue. Theresults indicate that the maternal MED improves episodic memoryin the NOR test but does not affect the conditioned fear memoryassociated with a context and sound cue in the adult offspring ofWAG/Rij rats.