The influence of enriched environment on learning and memory in the Morris water maze in rats with acute and chronic pro-inflammatory stress

It is known that housing in an enriched environment (EE) prevents the development of anxiety-depressive disorders and cognitive impairment caused by various stresses. In a very limited number of studies on learning and memory in the Morris water maze, pro-inflammatory stress was elicited before the exposure of animals in the EE. In this study, we, for the first time, examined the inverse sequence of interaction between EE and stress; in the first place was the action of the EE, while on the second place – the influence of stress. 40 rats aged 25 to 45 days were placed in the EE and 40 other rats were kept under standard conditions. Pro-inflammatory stress in rats of both groups was induced by injection of a bacterial toxin, lipopolysaccharide LPS, once (acute stress, 350 μg/kg) and repeatedly (chronic, 200 μg/kg) 1 hour before the start of behavioral experiments and during their performance. Control animals were injected with saline at the same volume. Rats of the EE group found the platform faster and swam a shorter distance to it than rats of the standard group. Improvements in behavioral parameters were observed in animals with acute and chronic LPS stress, and in control rats. It should also be noted that the dynamics of learning and the features of the long-term and working memory in rats with acute and chronic LPS were similar, which points to a similar effect of EE on functional changes in the brain activity of rats, regardless of the nature of the subsequent stress. The results obtained indicate the important role of EE in beneficially influencing the behavior of rats when searching for a safe platform.