Anxiety- and depression-like behaviors are accompanied by an increase in oxidative stress in a rat model of fetal alcohol spectrum disorders: Protective effects of voluntary physical exercise☆
Highlights
► Perinatal ethanol exposure leads to anxiety and depression-like behaviors in rats. ► Exercise reverses depression-like behaviors in ethanol-exposed adult male rats. ► Perinatal ethanol exposure leads to an increase in oxidative stress in adult rats. ► Exercise restores glutathione levels in ethanol-exposed adult female and male rats. ► Exercise reduces oxidative stress by enhancing glutathione levels.
Introduction
Ethanol acts as a teratogen during development, producing both structural and functional deficits in the developing brain. The range of clinical abnormalities that are associated with prenatal ethanol exposure are grouped under the umbrella term fetal alcohol spectrum disorders (FASD). In humans, the most common manifestation of FASD is a reduction in cognitive abilities (Sampson et al., 1997, Streissguth and O’Malley, 2000); however prenatal ethanol exposure has also been associated with psychiatric illnesses, including depression and anxiety (Caldwell et al., 2008, Famy et al., 1998, O’Connor and Kasari, 2000, O’Connor and Paley, 2006, Roebuck et al., 1999, Streissguth and O’Malley, 2000).
The mechanisms by which ethanol induces neuropathology during fetal development are likely multifaceted and complex. Perinatal ethanol exposure has been shown to cause an increase in oxidative stress in a number of developing organs, including the brain (for review see Brocardo et al., 2011, Chu et al., 2007, Dembele et al., 2006, Heaton et al., 2003, Petkov et al., 1992, Ramachandran et al., 2001, Reyes et al., 1993a). In fact, the brain is particularly vulnerable to the production of reactive oxygen species (ROS) since it metabolizes 20% of the total oxygen in the body and has a limited amount of antioxidant capacity (Floyd, 1999, Floyd and Carney, 1992, Halliwell, 2006). Recently, a number of studies have indicated that oxidative stress also plays a major role in the etiology of depression and anxiety, and that these mood disorders are accompanied by an increase in markers of oxidative stress (Michel et al., 2007, Tsuboi et al., 2006) and a concomitant decrease in the endogenous antioxidant defenses [for review see (Hovatta et al., 2010, Maes et al., 2011)].
Endogenous antioxidant defenses include multiple enzymes and their co-factors that can either inhibit the formation of ROS or promote the removal or scavenging of free radicals and their precursors. The major antioxidant enzymes directly involved in the neutralization of ROS are: superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), and glutathione-S-transferases (GSTs). SOD, the first line of defense against free radicals, catalyzes the dismutation of superoxide anion radical (O2•−) into hydrogen peroxide (H2O2) (McCord and Fridovich, 1988). In turn, H2O2 can be further reduced to water and molecular oxygen by either CAT (Chelikani et al., 2004) or GPx (Flohe, 1971). Besides detoxifying H2O2, GPx can also reduce lipid and non-lipid hydroperoxides at the expense of reduced glutathione (GSH), which is in turn oxidized, forming glutathione disulfide (GSSG) (Flohe, 1971). GSH is arguably the most important non-enzymatic endogenous antioxidant and can be regenerated by GR with the consumption of nicotinamide adenosine dinucleotide phosphate (NADPH) (Krohne-Ehrich et al., 1977). Importantly, GSH is also a co-factor for the redox reactions catalized by GSTs, which play a role in detoxifying a variety of electrophilic xenobiotics, producing less toxic compounds (Jakoby, 1978).
Clinical trials have indicated that physical exercise can have antidepressant and anxiolytic effects (Strawbridge et al., 2002, Strohle, 2009). Similar findings have been observed in animal models of depression- (Bjornebekk et al., 2006, Zheng et al., 2006) and anxiety- (Greenwood et al., 2008) like behaviors. Specifically, voluntary exercise has been shown to reduce anxiety- and depressive-like behaviors and to counteract the cognitive and mood effects of stress (Duman et al., 2008). In addition, moderate physical exercise also reduces oxidative stress (Salim et al., 2010), suggesting that exercise can be an effective and cost-efficient therapeutic alternative for a variety of anxiety and mood-related disorders. Furthermore, voluntary physical exercise has also been shown to be beneficial in rodent models of FASD. Indeed, exercise has been shown to have a positive impact at the biochemical and structural levels in rodent models of FASD by increasing the levels of brain-derived neurotrophic factor (BDNF) (Boehme et al., 2011) and promoting adult hippocampal neurogenesis (Redila et al., 2006, Helfer et al., 2009, Boehme et al., 2011). Moreover, exercise has also been shown to have a functional and behavioral impact, by increasing long-term potentiation (LTP) (Titterness and Christie, 2008) and spatial learning and memory (Christie et al., 2005, Thomas et al., 2008) in these FASD models. Together, these findings indicate that exercise, even during adulthood, has potential as a therapy for FASD.
Considering that prenatal and/or early postnatal ethanol exposure leads to oxidative stress [for review see (Brocardo et al., 2011)] and that increased oxidative stress may be a predisposing factor for anxiety and depression (Bilici et al., 2001, Ozcan et al., 2004), in the present study we evaluated the occurrence of anxiety- and depressive-like behaviors and the levels of oxidative stress in a rat model of FASD. Furthermore, we also evaluated the therapeutic potential of a regime of 12 days of voluntary physical exercise in reversing these behaviors as well as oxidative damage in the brains of rats that were exposed to ethanol during the perinatal period.
Section snippets
Animals
Sixty female virgin Sprague-Dawley rats and 10 proven male breeders (Charles River, Quebec, Canada) were utilized to generate 240 pups (120 females and 120 males) that were used in this study. For each experimental group, a maximum of two subjects from each litter was used. All animal procedures were conducted in accordance with the Canadian Council on Animal Care and the University of Victoria Animal Care Committee.
Prenatal and early postnatal ethanol exposure
The procedures of prenatal and early postnatal ethanol exposure were performed
Body weight, food consumption, BAC and CORT levels
In agreement with our previous studies (Boehme et al., 2011, Gil-Mohapel et al., 2011) a significant decrease in body weight gain was observed in ethanol-exposed (p < 0.001) and pair-fed (p < 0.001) dams when compared with their ad libitum controls [F (2, 48) = 11.13, p < 0.001] (Table 1). Furthermore, both ethanol-exposed (p < 0.001) and pair-fed (p < 0.001) dams consumed significantly less food when compared with their ad libitum controls [F (2, 50) = 97.72, p < 0.001] (Table 1). Analysis of
Discussion
In the present study we used a three-trimester equivalent gavage model of FASD that has been thoroughly characterized by our group (Gil-Mohapel et al., 2011, Boehme et al., 2011). In accordance with our previous studies, a steady increase in BAC across the three trimesters equivalent was also observed in this study. This increase in BAC might be explained by a progressive decrease in the maternal capacity to metabolize and detoxify ethanol as the pregnancy progresses. Indeed, when dams reach GD
Conclusions
In the present study we demonstrate that exposure to ethanol during the perinatal period induces a long-lasting dysregulation of the intracellular redox state in the brain. Ethanol may lead to an increase in the brain metabolic rate, triggering intracellular cascades of oxidative stress during development, which then undergo cycles of self-reinforcement and perpetuation during postnatal life and into adulthood. In this three-trimester model of FASD, oxidative stress in the brain was accompanied
Acknowledgments
The authors would like to thank Erica Giles, Jennifer Graham, and Sarah de Rham for technical support. P.S.B. was supported by a post-doctoral fellowship from the Canadian Bureau for International Education. F.B. received a Masters’ scholarship from the University of Victoria. A.P. is funded by a Graduate Award from the University of Victoria and a Pacific Century Scholarship. A.C. received a Natural Sciences and Engineering Research Council of Canada (NSERC) Undergraduate Student Research
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Paper submitted as part of the Special Issue entitled ‘Anxiety and Depression’, Neuropharmacology 2012 (62/1).