Abstract
BackgroundTo investigate neurobiological correlates of trait anxiety, CD1 mice were selectively bred for extremes in anxiety-related behavior, with high (HAB) and low (LAB) anxiety-related behavior mice additionally differing in behavioral tests reflecting depression-like behavior.Methodology/ Principal FindingsIn this study, microarray analysis, in situ hybridization, quantitative real-time PCR and immunohistochemistry revealed decreased expression of the vasopressin gene (Avp) in the hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei of adult LAB mice compared to HAB, NAB (normal anxiety-related behavior) and HABxLAB F1 intercross controls, without detecting differences in receptor expression or density. By sequencing the regions 2.5 kbp up- and downstream of the Avp gene locus, we could identify several polymorphic loci, differing between the HAB and LAB lines. In the gene promoter, a deletion of twelve bp Δ(−2180–2191) is particularly likely to contribute to the reduced Avp expression detected in LAB animals under basal conditions. Indeed, allele-specific transcription analysis of F1 animals revealed a hypomorphic LAB-specific Avp allele with a reduced transcription rate by 75% compared to the HAB-specific allele, thus explaining line-specific Avp expression profiles and phenotypic features. Accordingly, intra-PVN Avp mRNA levels were found to correlate with anxiety-related and depression-like behaviors. In addition to this correlative evidence, a significant, though moderate, genotype/phenotype association was demonstrated in 258 male mice of a freely-segregating F2 panel, suggesting a causal contribution of the Avp promoter deletion to anxiety-related behavior.DiscussionThus, the identification of polymorphisms in the Avp gene promoter explains gene expression differences in association with the observed phenotype, thus further strengthening the concept of the critical involvement of centrally released AVP in trait anxiety.
Highlights
Despite decades of intensive research, anxiety and depression disorders remain two of the most common and debilitating psychiatric illnesses
In accordance with our breeding strategy, LAB, HAB and NAB male mice showed significant differences in the percent of total test time spent on the open arms of the elevated plus-maze (EPM) (Fig. 1A), with LABs spending most time on the open arms, HABs least time and NAB animals displaying an intermediate phenotype
Gene and protein expression analysis and validation Analysis of genome wide expression revealed a significantly decreased Avp mRNA level in the PVN (p,0.05) and showed a tendency towards the same direction in the SON (p,0.1) of LAB compared to HAB mice
Summary
Despite decades of intensive research, anxiety and depression disorders remain two of the most common and debilitating psychiatric illnesses. Their causes and appropriate medication are still elusive [1], and the number of affected people continues to increase [2,3]. Depression is a highly heritable disorder; epidemiologic studies have shown that about 40–50% of the risk for depression is genetically determined [4,5] and that depression is in 60% of all cases comorbid with anxiety disorders [6,7]. To investigate neurobiological correlates of trait anxiety, CD1 mice were selectively bred for extremes in anxiety-related behavior, with high (HAB) and low (LAB) anxiety-related behavior mice differing in behavioral tests reflecting depression-like behavior
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