Proceedings of The Physiological Society
University of Bristol (2005) J Physiol 567P, PC53
Environmental enrichment decreases the vulnerability to the effects of experimentally induced immune challenge in rats
Jezova, Daniela; Bakos, Jan; Mlynarik, Martin; Makatsori, Aikaterini; Johansson, Barbro;
1. Institute of Experimental Endocrinology, Bratislava, Slovakia.
Environmental enrichment has been shown to induce positive effects on several physiological functions including modulation of neuroendocrine activity (1). Moreover, environmental enrichment is known to induce neural plasticity. Receptors for glutamate, the main excitatory amino acid in the brain, are thought to play an important role in these processes. Presented studies were aimed at verifying the hypothesis that environmental enrichment reduces vulnerability to adverse events such as immune challenge occurring during the prenatal period or in adulthood. The studies were conducted in male and female Wistar rats and the animals were humanely killed by rapid decapitation at the end of experiments. Immune challenge was performed by subchronic (5 days) administration of lipopolysacharide (LPS) to simulate acute infection. For the enriched environment, 10-12 animals were kept together in huge plexiglas boxes (1 m × 0.5 m × 0.5 m). Variety of items (platforms, wood swings, plastic tubes, beams etc.) were added to the cages and changed three times per week. Statistical evaluation of the data was performed using two-way analysis of variance. Male offspring (n=12 per group) of mothers injected with LPS in daily doses of 20, 20, 40, 40 and 80 μg/kg s.c. on days 15-19 of pregnancy were studied. Maternal exposure to LPS resulted in a reduced body weight gain of the offspring, which persisted until adulthood (F=4.536, p<0.05). The differences induced by a prenatal immune challenge were normalized by housing rats in an enriched environment for 8 weeks. In a separate study performed in adult males (n=5 per group) without any prenatal interference, repeated administration of LPS in increasing doses (10, 10, 20, 20, 40 μg/kg i.p.) was performed. LPS treatment induced a rise in corticosterone levels in the adrenals and plasma (1.98 ± 0.8 vs. 11.7 ± 1.6 μg/100 ml; p<0.01) as well as a transient decrease in body weight in controls housed under standard conditions, but not in rats kept in an enriched environment for 5 weeks (corticosterone: 1.0 ± 0.7 vs. 3.1 ± 2.1 μg/100 ml; N.S.). Enriched housing resulted in an increase in adrenal weights and enhanced gene expression of a glutamate receptor subunit in the hippocampus. Thus, vulnerability to some negative effects of repeated immune challenge may be modified by environmental conditions associated with changes in brain plasticity. The finding that differences in housing conditions change responses to external stressors has to be considered in animal physiology.
Where applicable, experiments conform with Society ethical requirements