Enriched Environment Influences Adrenocortical Response to Immune Challenge and Glutamate Receptor Gene Expression in Rat Hippocampus

Abstract

A BSTRACT : Housing of animals in an enriched environment (EE) has many positive effects on brain structure and function and can facilitate recovery from various brain injuries. The purpose of this study was to evaluate whether enriched rearing could alter the stress response induced by repeated immune challenge and to investigate the influence of EE and immune challenge on glutamate receptor gene expression in the hippocampus. Male 2-mo-old Wistar rats were kept under standard conditions (SC) or in an EE for 5 weeks. Immune challenge was performed by Escherichia coli lipopolysaccharide (LPS) injected repeatedly (ip) in increasing doses (10, 20, and 40 µ g/kg/mL) once daily for five consecutive days. The animals were decapitated 2 h after the last injection. Blood samples, adrenals, and hippocampi were collected. LPS induced an increase in plasma and adrenal levels of corticosterone and a transient decrease in body weight of animals kept under SC, but not in an EE. Enriched housing resulted in an increase in adrenal weights and enhanced gene expression of hippocampal AMPA GluR1 receptor subunit. Concerning the LPS treatment, no effects on adrenal and thymus weights and glutamate receptor mRNA levels in the hippocampus were noticed. Thus, vulnerability to some negative effects of repeated immune challenge may be modified by environmental conditions associated with changes in brain plasticity. The fact that differences in housing conditions change stress response has to be considered in biomedical research.

Differential effects of environmental enrichment and isolation housing on the hormonal and neurochemical responses to stress in the prefrontal cortex of the adult rat: relationship to working and emotional memories

“…This result agrees with previous studies examining the effect of EC on the stress-induced increases of plasma corticosterone (Mlynarik et al 2004;Moncek et al 2004;Peña et al 2009;Sztainberg et al 2010). Our results extend these findings to the free levels of corticosterone in the brain, where it acts to modulate the HPA axis activity and behavioral adaptation to stress (Bruce S 2000;Herman et al 2005;Sandi and PineloNava 2007).…”

“…In fact, EC animals show lower anxiety levels (Fernández-Teruel et al 1997;Sztainberg et al 2010), a faster habituation to a novel environment (Zimmermann et al 2001;Schrijver et al 2002;Segovia et al 2008a) and a better recovery from psychosocial stress (Schloesser et al 2010;Lehmann and Herkenham 2011). These behavioral effects of EC are thought to be mediated, at least in part, by a lower release of plasma corticosterone under stress conditions (Mlynarik et al 2004;Moncek et al 2004). In the rat, acute stress leads to the release of corticosterone from the adrenal cortex through the activation of the hypothalamo-pituitary-adrenal (HPA) axis (Antoni 1986).…”

Is exposure to enriched environment beneficial for functional post-lesional recovery in temporal lobe epilepsy?

“…Thus, through increased levels of various neurotrophic factors, environmental enrichment likely decreases the vulnerability of the brain to neurodegeneration following environmental insults and injury. Furthermore, environmental enrichment modulates cholinergic (Rosenzweig and Bennett, 1996;Del Arco et al, 2007;van Praag et al, 2000), serotonin-ergic (Rasmuson et al, 1998), dopaminergic (Bezard et al, 2003;Bowling et al, 1993;Del Arco et al, 2007) and glutamatergic neurotransmission (Foster et al, 1996;Bredy et al, 2004;Naka et al, 2005;Mlynarik et al, 2004). Moreover, adult rats placed in an enriched environment demonstrated increased levels of proteins involved in learning and memory function.…”

Impact of certain immunomodulators on LPS-induced hematotoxicity

“…LPS) Klebsiella pneumonia lipopolysaccharide used in the present study was purchased from Sigma-Aldrich (Steinheim, Germany). It was injected repeatedly (ip) in increasing doses (10, 10, 20, 20 and 40 lg/kg) along 5 consecutive days for inducing repeated immune challenge (Mlynarik et al, 2004).…”