Late gestational exposure to dexamethasone and fetal programming of abnormal behavior in Wistar Kyoto rats

Abstract

Introduction Fetal programming was characterized a few decades ago, explaining the correlation of physiological phenotypes of offspring exposed to early‐life stress. High acute or chronic prenatal stress can overwhelm the enzymatic placental barrier, inducing transcriptional changes in the fetus that can result in different adverse behavioral and physiological phenotypes. The current study investigates the impact of exposure to the synthetic glucocorticoid, dexamethasone, during late gestation on behavioral outcomes. Methods Pregnant Wistar Kyoto rats were given daily subcutaneous injections from gestational days 15–21 of either dexamethasone (0.9% NaCl, 4% EtOH, 100 µg kg−1 day−1) or were physically manipulated as naïve controls. Pups were raised normally until 17 weeks of age and underwent the Porsolt swim task and elevated plus maze for depressive and anxiety‐like behaviors, respectively. Neural tissue was preserved for genetic analysis using quantitative real‐time polymerase chain reaction. Results Statistical analyses show significant disruption of behavior and genetic profiles of offspring exposed to dexamethasone in‐utero. Exposed animals spent more time immobile on the swim task and entered open arms of the elevated plus maze more often than their naïve counterparts. In the prefrontal cortex, there was a sex by treatment interaction on gene expression relevant to neural transmission in ryanodine receptor 2, as well as increased gene expression in SNAP25, COMT, and LSAMP in males prenatally exposed to dexamethasone compared with controls. Both dysregulated genes and behavior are linked to decreased anxiety and fear inhibition. Conclusion Our results indicate adult offspring exposed to dexamethasone in‐utero have a tendency toward passive stress‐coping strategies and an inhibition of anxiety on behavioral tasks. Methyltransferase activity, synaptic activity, and cellular processes were disrupted in the prefrontal cortices of these animals. Specifically, genes involved in emotional response pathways were overexpressed, supporting the link between the behavioral and genetic profiles. Combined, we determine that dexamethasone offspring have adaptive predispositions when faced with novel situations, with increased immobility in the swim task and increased exploration on the elevated plus maze.

Gene Dysregulation in the Adult Rat Paraventricular Nucleus and Amygdala by Prenatal Exposure to Dexamethasone

“…Four dams were selected for the exposure group and were subjected to daily subcutaneous injections of Dex (Sigma-Aldrich, Milwaukee, WI, USA; 0.9% sodium chloride, 4% ethanol, and 100 μg per kg body mass Dex), while another dam received vehicle only to produce sham controls. Injections were given during the light cycle, as previously described [ 17 , 18 , 20 ].…”

“…The tissues retrieved from the right amygdala and the paraventricular nucleus of each rat were placed in TRI reagent (Sigma-Aldrich, Oakville, ON, Canada; 1 mL/50 mg of tissue) and subjected to two 2-min cycles at 30 hertz in a TissueLyser (Qiagen, Hilden, Germany) for the mechanical homogenization of the sample. mRNA was then extracted from the samples using a TRIzol extraction method, as previously described [ 18 ].…”

“…Under normal physiological conditions, this placental barrier is effective in shielding the fetus from the deleterious effects of prenatal GC exposure [ 13 ]. However, synthetic GCs and heightened chronic maternal stress have been shown to bypass or overwhelm this barrier [ 6 , 14 , 15 , 16 , 17 , 18 ]. By bypassing the barrier, GCs may interact with fetal tissues relatively unhindered.…”

“…There is also evidence to suggest that behavioral tendencies may be programmed as well. Rats exposed to Dex prenatally have shown increased immobility on the Porsolt swim test (PST), a measure of learned helplessness and despondency, among other behaviors likened to a depressive presentation [ 18 , 33 , 34 ]. Similarly, in humans, elevated maternal GCs have corresponded to the presence of affective issues and internalizing behaviors [ 16 , 23 , 35 ].…”

“…The elevated plus maze (EPM) is a well-validated test whereby anxiety-like behaviors, or the lack of these, can be measured based on the typical rodent’s proclivity for dark, enclosed spaces and locations away from observable heights [ 45 ]. Dex-programmed animals entered the open arms with 4 paws more often than the sham-treated offspring, while entering the enclosed arms with 2 paws less often, reflecting a reversal of expected normal thigmotaxic behaviors [ 18 , 46 ]). In this study, we measured changes in gene expression in the PVN and amygdala of the same Dex-programmed animals from the original study.…”