GABAergic Control of Critical Developmental Periods for Anxiety- and Depression-Related Behavior in Mice Qiuying Shen1,2,4, Thomas Fuchs1,4, Nadia Sahir1,4, Bernhard Luscher1,2,3,4* 1 Department of Biology, Pennsylvania State University, University Park, Pennsylvania, United States of America, 2 Department of Biochemistry & Molecular Biology, Pennsylvania State University, University Park, Pennsylvania, United States of America, 3 Department of Psychiatry, Pennsylvania State University, College of Medicine, Hershey, Pennsylvania, United States of America, 4 Center for Molecular Investigation of Neurological Disorders, Pennsylvania State University, University Park, Pennsylvania, United States of America Abstract Vulnerability for anxiety and depressive disorders is thought to have origins in early life and is increasingly recognized to involve deficits in GABAergic neurotransmission. Mice that were rendered heterozygous for the c2 subunit gene of GABAA receptors (GABAARs) show behavioral, cognitive, neuroendocrine and pharmacologic features expected of a mouse model of melancholic anxious depression, including reduced survival of adult-born hippocampal neurons. Here we embarked on elucidating the developmental substrate underlying this phenotype, focusing on the Elevated Plus Maze and Forced Swim Test as relevant behavioral paradigms. In a first series of experiments using hemizygous tamoxifen-induced genetic inactivation of a floxed c2 genomic locus we show that reducing the gene dosage at postnatal days (P)13/14 but not P27/28 results in altered behavior in both of these tests in adulthood, reminiscent of the anxious-depressive phenotype previously described for global heterozygous mice. However, in contrast to global heterozygous mice, the behavioral changes induced by c2 subunit knockdown at P13/14 occurred without changes in adult hippocampal neurogenesis, indicating that altered neurogenesis is not an absolute prerequisite for anxiety- and depression-related behavior in this model. In a separate series of experiments using a pharmacological approach, acute but transient potentiation of GABAARs with diazepam uncovered distinct developmental vulnerabilities for altered behavior in the Elevated Plus Maze and Forced Swim Test, respectively. Specifically, diazepam given during P10-16 but not during later weeks resulted in increased anxiety-like behavior in adulthood, while diazepam administered during P29-35 but not earlier nor later resulted in increased immobility behavior in adulthood. We conclude that anxiety-like behavior in the Elevated Plus Maze and behavioral despair-like immobility in the Forced Swim Test are controlled by separate postnatal critical periods characterized by distinct developmental sensitivity to manipulation of GABAergic transmission via c2 subunit-containing GABAARs. Citation: Shen Q, Fuchs T, Sahir N, Luscher B (2012) GABAergic Control of Critical Developmental Periods for Anxiety- and Depression-Related Behavior in Mice. PLoS ONE 7(10): e47441. doi:10.1371/journal.pone.0047441 Editor: Uwe Rudolph, McLean Hospital/Harvard Medical School, United States of America Received June 24, 2012; Accepted September 17, 2012; Published October 11, 2012 Copyright: 2012 Shen et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This publication was made possible by grants MH60989 and MH089111 to B.L. from the National Institutes of Mental Health (NIMH) and a grant from the Pennsylvania Department of Health using Tobacco Settlement Funds. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: BXL25@psu.edu Introduction Extensive comorbidity among major depressive disorder (MDD) and anxiety disorders suggests related disease etiologies [1,2]. Reduced brain concentrations of the inhibitory neurotransmitter c-aminobutyric acid (GABA) and altered function or reduced expression of its principal receptors (GABAARs) are increasingly implicated in both types of disorders [3]. GABAARs serve as the principal receptors mediating neural inhibition in the brain. Structurally they are heteropentameric chloride channels com- posed of a1-6, b1-3, c1-3, d, e, p, h, and r1-3 subunits [4]. The c2 subunit-containing subtypes of GABAARs (containing two a1-3 or 5 subunits, two b1-3 subunits and one c2 subunit) are of particular interest as they mediate the behavioral actions of benzodiazepines (BZs) [5,6]. Mice that are heterozygous for the c2 subunit gene (gabrg2, c2+/2) exhibit anxious-depression-related behavior, in- cluding cognitive, cellular, neuroendocrine and pharmacological alterations expected of a mouse model of melancholic major depression [7,8,9]. Behavioral changes reminiscent of those of c2+/ 2 mice have also been described for mice that lack the a2 subunit of GABAARs [10,11]. Clinical and animal experiments together indicate that pre- and/or postsynaptic functional deficits in GABAergic transmission may be causative for anxiety and mood disorders (reviewed in [3,12,13]). Conditional hemizygous inactivation of the c2 gene in the embryonic telencephalon of mice results in an anxious-depressive- like phenotype in adulthood comparable to that of global c2+/2 mice [8,9]. By contrast, forebrain-specific heterozygous inactiva- tion of the c2 gene that is developmentally delayed to approxi- mately the fifth postnatal week is without behavioral consequences [8]. These findings point to an embryonic or postnatal de- velopmental origin of anxiety- and depression-related behavior. Consistent with these preclinical findings there is also significant clinical evidence that the vulnerability for anxiety and major depression is increased during early life [14]. Moreover, the two types of disorders have been proposed to have distinct de- velopmental origins [15,16]. PLOS ONE | www.plosone.org 1 October 2012 | Volume 7 | Issue 10 | e47441