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Behavior in the Elevated Plus Maze Is Differentially Affected by Testing Conditions in Rats Under and Over Three Weeks of Age Sarah H

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Behavior in the Elevated Plus Maze Is Differentially Affected by Testing Conditions in Rats Under and Over Three Weeks of Age Sarah H View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Frontiers - Publisher Connector ORIGINAL RESEARCH ARTICLE published: 17 February 2015 BEHAVIORAL NEUROSCIENCE doi: 10.3389/fnbeh.2015.00031 Behavior in the elevated plus maze is differentially affected by testing conditions in rats under and over three weeks of age Sarah H. Albani , Marina M. Andrawis , Rio Jeane H. Abella , John T. Fulghum , Naghmeh Vafamand and Theodore C. Dumas * Department of Molecular Neuroscience, Krasnow Institute for Advanced Study, George Mason University, Fairfax, VA, USA Edited by: The late postnatal period in rats is marked by numerous changes in perceptual and Gal Richter-Levin, University of cognitive abilities. As such, age-related variation in cognitive test performance might Haifa, Israel result in part from disparate sensitivities to environmental factors. To better understand Reviewed by: Gregg Stanwood, Vanderbilt how testing conditions might interact with age, we assessed anxiety behavior on an University, USA elevated plus maze (EPM) in juvenile rats around 3 weeks of age under diverse testing Mouna Maroun, University of Haifa, conditions. Plasma corticosterone and neuronal activation patterns in the forebrain were Israel examined after maze exposure. We found that anxiety was differentially expressed during Antonio Armario, Universitat Autònoma de Barcelona, Spain different stages of late postnatal development. Bright illumination and morning testing *Correspondence: encouraged greatest open arm exploration on the EPM in younger animals, while older Theodore C. Dumas, Department of rats explored open areas more under dim illumination in the morning compared to bright Molecular Neuroscience, Krasnow illumination in the afternoon/evening. Older rats exhibited higher plasma corticosterone Institute for Advanced Study, levels at baseline compared to younger rats; however, this trend was reversed for George Mason University, 4400 University Drive, MS 2A1, Fairfax, post-testing corticosterone. Additionally, post-testing corticosterone levels were inversely VA 22030, USA related to time of testing. Compared to testing in the morning, EPM exposure in the e-mail: [email protected] afternoon/evening elicited greater neuronal Arc expression in the amygdala. Arc expression in the amygdala after morning testing was greater at P22–24 than P17–19. In layer 2/3 of primary visual cortex, Arc expression was elevated in younger animals and age interacted with time of testing to produce opposing effects at P17–19 and P22–24. These data suggest that age-related differences in anxiety-associated behavior during the late postnatal period are due in part to changes in light sensitivity and emergence of a circadian cycle for corticosterone. The findings illustrate that late postnatal behavioral development in rodents is a complex orchestration of changes in neural systems involved in perception, cognition, affect and homeostatic regulation. Keywords: elevated plus-maze, anxiety, postnatal development, environment, corticosterone, Arc, immediate early-gene, juvenile INTRODUCTION begin to shift in response to light during the third postnatal week Perceptual and cognitive abilities in rats undergo substantial and are not different from adult cycles by the fourth postnatal postnatal modification between the second and fourth weeks week (Reppert et al., 1984; Honma and Honma, 1986; Rosenfeld of life. While being tended for in the nest, the rat pup et al., 1992). The comprehensive alterations in physiological and hormonal stress response to most environmental stimuli is behavioral processes that occur during the late postnatal period blunted (Vázquez, 1998), focusing physiological responses to represent a qualitative change in how the organism interacts interactions between offspring and dam. At around 2 weeks of with its environment and suggest that performance differences in age, rat pups exit this stress hyporesponsive period and are more tasks designed to investigate cognitive maturation near 3 weeks sensitive to environmental stimuli (Sapolsky and Meaney, 1986; of age may be influenced by developmental changes in basic Widmaier, 1990) as they begin to explore outside of the nest. perceptual skills, homeostatic regulation, or affective responses Also during this time, more distal sensory capacities such as to environmental conditions. Therefore, it is important to better vision and audition start to mature and reach adult status in understand how testing conditions impact innate anxiety and the fourth postnatal week (Crowley and Hepp-Reymond, 1966; risk assessment in subjects under and over three postnatal Hyson and Rudy, 1984; Fagiolini et al., 1994; Morishita and weeks of age. Hensch, 2008). In parallel, activity-rest cycles and the circadian Prominently, excitatory synaptic transmission in the rhythm for the major stress hormone, corticosterone (CORT), forebrain continues to mature throughout the first month Frontiers in Behavioral Neuroscience www.frontiersin.org February 2015 | Volume 9 | Article 31 | 1 Albani et al. Age and environmental effects on anxiety behavior after birth (Dumas, 2005; Stoneham et al., 2010; Cooper and lighting, and spatial encoding, respectively. The results indicated Bear, 2012). The major glutamatergic ionotropic receptors, no effect of AMPAR modulation on EPM behavior, plasma a-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid CORT level, or neural activation in select brain regions at receptors (AMPARs), undergo structural and functional either testing age. However, environmental variables differentially modification during late postnatal development (Durand influenced behavioral performance, plasma CORT responses, and Zukin, 1993; Standley et al., 1995; Martin et al., 1998; and neuronal activation according to age. Overall, this study Dingledine et al., 1999 review) along with changes in reveals endocrine and neural regulators of anxiety-like behavior exploratory behavior (Douglas et al., 1973; Dumas, 2004). during an important period of postnatal forebrain and cognitive Direct implication of alterations in AMPAR function in the maturation in rats. developmental emergence of spatial cognition was recently shown via acute delivery of the positive allosteric modulator METHODS of AMPARs, CX614 (Arai and Kessler, 2007), during the same SUBJECTS developmental stage examined in the present study (Blair et al., Long-Evans rats were bred in the Krasnow Institute Animal 2013). Enhanced exploration produced by pharmacological Facility and housed in individually ventilated cages in a modulation of AMPARs could be the result of drug effects temperature- and humidity-controlled vivarium under a 12:12 h on developing sensory systems, affective circuits, or spatial light/dark cycle (lights on at 0700 h). Female breeders were navigation networks. Specific perceptual, affective, and cognitive drawn from the colony while male breeders were imported affects of drug delivery in juvenile rats may be resolved (Charles River Labs, Frederick, MD). Food and water were by testing animals in different mazes under varied testing available ad libitum. Pups were not weaned until completion of conditions. behavior testing. Rats were maintained and handled in accordance The elevated plus maze (EPM) is used to assess innate anxiety with the regulations stated in the Guide for Care and Use of in rodents (Handley and Mithani, 1984; Ohl et al., 2001; Walf Laboratory Animals by the National Research Council. The George and Frye, 2007). While extensively validated (Pellow et al., 1985; Mason University Institutional Animal Care and Use Committee Walf and Frye, 2007), EPM studies often produce inconsistent (IACUC) approved all procedures employed. findings, which may be attributed in part to methodological Rats were pseudorandomly assigned to experimental groups, differences, including age, strain, or sex of the subjects and with each group reflecting an age, time of day (TOD) for behavior housing or testing conditions (Nagy and Glaser, 1970; Rodgers testing, lighting during behavior testing, and CX614 dosage and Dalvi, 1997; File, 2001; Andrade et al., 2003; Walf and Frye, assignment. Litters were evenly divided such that half of the pups 2007). To some extent, subject age has been investigated (Imhof were tested at postnatal day (P) 17–19, while the remaining half et al., 1993; Andrade et al., 2003; Doremus et al., 2006; Lynn were tested at P22–24. Time of day (TOD, AM or PM) and and Brown, 2010), but only one study included a time point lighting conditions (dim or bright) were varied across litters, but under 1 month of age and this group was compared to adults remained consistent within litters. at 2 months (Smith and Morrell, 2007), limiting the resolution of the developmental time course for innate anxiety. Similarly, lighting conditions have been examined in adult animals, but BEHAVIORAL TESTING most studies compare between light and dark cycles, such that Apparatus and setup lighting condition is confounded by circadian period (Andrade The EPM was constructed from pine boards, painted black and et al., 2003), and to our knowledge, only one study has looked sealed with polyurethane. It consisted of two opposing open arms at circadian influences strictly within either the light or dark (length: 40 cm, width: 9 cm) and two opposing wall-enclosed period (Griebel et al., 1993). Without proper parametric analysis arms (wall height: 15 cm) extending off of a center square (9 cm of developmental changes in EPM performance, it is not
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