Generalization of contextual fear is sex-specifically affected by high salt intake

Abstract

A hallmark symptom of many anxiety disorders, and multiple neuropsychiatric disorders more broadly, is generalization of fearful responses to non-fearful stimuli. Anxiety disorders are often comorbid with cardiovascular diseases. One established, and modifiable, risk factor for cardiovascular diseases is salt intake. Yet, investigations into how excess salt consumption affects anxiety-relevant behaviors remains little explored. Moreover, no studies have yet assessed how high salt intake influences generalization of fear. Here, we used adult C57BL/6J mice of both sexes to evaluate the influence of two or six weeks of high salt consumption (4.0% NaCl), compared to controls (0.4% NaCl), on contextual fear acquisition, expression, and generalization. Further, we measured osmotic and physiological stress by quantifying serum osmolality and corticosterone levels, respectively. Consuming excess salt did not influence contextual fear acquisition nor discrimination between the context used for training and a novel, neutral context when training occurred 48 prior to testing. However, when a four week delay between training and testing was employed to induce natural fear generalization processes, we found that high salt intake selectively increases contextual fear generalization in females, but the same diet reduces contextual fear generalization in males. These sex-specific effects were independent of any changes in serum osmolality nor corticosterone levels, suggesting the behavioral shifts are a consequence of more subtle, neurophysiologic changes. This is the first evidence of salt consumption influencing contextual fear generalization, and adds information about sex-specific effects of salt that are largely missing from current literature.

Heterotypic stressors unmask behavioral influences of PMAT deficiency in mice

“…This 2 h timepoint was the focus here because no sex nor genotype differences were detected in PMAT mice when serum corticosterone was measured 30 min following a single acute swim stressor (Supplemental Table S1; Supplemental Fig.S1). All serum corticosterone levels were log-transformed (hereafter referred to as “cort”) to ensure normal distribution, as previously reported [39,41–43].…”

“…Testing for context fear occurred 48 h after training, in Context A. Testing lasted for 10 min; freezing from min 2 through 6 was averaged to assess contextual fear expression [38,39] (Supplemental Figures S2, S3). The full time course of the testing period was evaluated to determine contextual fear expression and extinction.…”

“…Serum corticosterone levels were quantified using corticosterone ELISA kits (ADI-900-097, Enzo Life Sciences, Inc., Farmingdale, NY). Log-transformation of serum corticosterone levels was performed prior to analyses to correct for typical skewness of these data [39,[41][42][43].…”

“…S1). All serum corticosterone levels were log-transformed (hereafter referred to as "cort") to ensure normal distribution, as previously reported [39,[41][42][43].…”

Heterotypic Stressors Unmask Behavioral Influences of PMAT Deficiency in Mice

“…This 2 h time point was the focus here because no sex nor genotype differences were detected in PMAT mice when serum corticosterone was measured 30 min following a single acute swim stressor (Supplemental Table S14 and Supplemental Figure S1). All serum corticosterone levels were log-transformed (hereafter referred to as "cort") to ensure normal distribution, as previously reported [37][38][39][40].…”