Swim stress-induced ultrasonic vocalizations forecast resilience in rats

Individual Vulnerability to Stress Is Associated With Increased Demand for Intravenous Heroin Self-administration in Rats

Opioid use is a widespread epidemic, and traumatic stress exposure is a critical risk factor in opioid use and relapse. There is a significant gap in our understanding of how stress contributes to heroin use, and there are limited studies investigating individual differences underlying stress reactivity and subsequent stress-induced heroin self-administration. We hypothesized that greater individual vulnerability to stress would predict higher demand for heroin self-administration in a within-subjects rodent model of stress and heroin use comorbidity. Male rats were exposed to inescapable intermittent swim stress (ISS) and individual biological (corticosterone) or behavioral [open field, social exploration, and forced swim tests (FSTs)] measures were assessed before and after the stress episode. Individual demand for self-administered heroin (0.05 mg/kg/infusion; 12-h sessions) was assessed using a behavioral economics approach followed by extinction and reinstatement tests triggered by stress re-exposure, non-contingent cue presentations, and yohimbine (0, 1.0, or 2.5 mg/kg). We found that behavioral, biological, and a combination of behavioral and biological markers sampled prior to and after the stress episode that occurred weeks before the access to heroin self-administration predicted the magnitude of individual demand for heroin. Non-contingent presentation of cues, that were previously associated with heroin, reinstated heroin seeking in extinction. For the first time, we show that individual biological response to an ecologically relevant stressor in combination with associated behavioral markers can be used to predict subsequent economic demand for heroin.

Ultrasonic vocalizations during intermittent swim stress forecasts resilience in a subsequent juvenile social exploration test of anxiety

Current behavioral paradigms of stress resilience traditionally employ forms of prior manipulation or subsequent testing. Recent work has reported adult rat ultrasonic vocalizations (USVs) emitted during intermittent swim stress (ISS) may serve as a predictor of resilience. ISS-induced USVs predicted resilience on several endpoints of behavioral depression and may be considered a forecast of innate resilience. However, a potential problem for these previous findings is the lack of generalizability to other contexts, because both the stress induction and post-stress testing occur in water. The current study tests the generalizability of USVs as a predictor of stress resilience in a non-water-based post-test, the juvenile social exploration test of anxiety. The results provide further support that USVs emitted during ISS predict resilience to depression- and anxiety-like behaviors. Extensions of this work to examine the neurobiology of innate resilience associated with ISS-induced USVs are discussed with comparisons to extant models of learned resilience.

The emission of stress-induced 22-kHz calls in female rats is independent of testosterone levels

Although emission of ultrasonic calls in rats induced by stress, referred to as "22-kHz calls," is dependent on circulating testosterone levels in males, it is still unknown whether the same testosterone-based regulation is applicable to female rats. In this study, we investigated the sex difference in the emission of air-puff-induced 22-kHz calls in rats on the basis of the hypothesis that female rats would emit fewer 22-kHz calls, and assessed whether male-like circulating testosterone levels can also influence the emission of 22-kHz calls in females. The experimental results showed that female rats emit significantly fewer 22-kHz calls than male rats. However, male-like circulating testosterone levels have little effect on the emission of 22-kHz calls in females. Hence, it is suggested that there is a sex difference in stress-induced 22-kHz calls in rats and, in contrast to male rats, the emission of 22-kHz calls in female rats may be independent of circulating testosterone levels, as tested in response to air-puff stimulation.

Ultrasonic vocalizations during intermittent swim stress forecasts resilience in subsequent forced swim and spatial learning tests

The examination of stress resilience has substantially increased in recent years. However, current paradigms require multiple behavioral procedures, which themselves may serve as secondary stressors. Therefore, a novel predictor of stress resilience is needed to advance the field. Ultrasonic vocalizations (USVs) have been observed as a behavioral correlate of stress in various rodent species. It was recently reported that rats that emitted ultrasonic vocalizations during intermittent swim stress (ISS) later showed resilience when tested on an instrumental swim escape test. In the current study, we extend this earlier observation on two additional behavioral endpoints. Rats were subjected to ISS, and USVs were recorded. Twenty-four hours later, behavioral performance was evaluated in either the forced swim test or Morris water maze. Rats that emitted ultrasonic vocalizations were resilient to the effects of ISS as indicated by performance similar to controls on both measures. These results extend the original findings that ISS-induced USVs are associated with resilience and are related to subsequent aversively motivated behavior. Such a non-invasive forecast of stress responsivity will allow future work to utilize USVs to examine the neural correlates of initial stress resistance/resilience, thereby eliminating potential confounds of further behavioral testing. Future studies can utilize USVs to target potentially unappreciated neural systems to provide novel pharmacotherapeutic strategies for treatment-resistant depression.

Abnormal stress responsivity in a rodent developmental disruption model of schizophrenia

Although numerous studies have implicated stress in the pathophysiology of schizophrenia, less is known about how the effects of stress interact with genetic, developmental, and/or environmental determinants to promote disease progression. In particular, it has been proposed that in humans, stress exposure in adolescence could combine with a predisposition towards increased stress sensitivity, leading to prodromal symptoms and eventually psychosis. However, the neurobiological substrates for this interaction are not fully characterized. Previous work in our lab has demonstrated that rats born to dams administered with the DNA-methylating agent methylazoxymethanol acetate (MAM) at gestational day 17 exhibit as adults behavioral and anatomical abnormalities consistent with those observed in patients with schizophrenia. Here, we examined behavioral and neuroendocrine responses to stress in the MAM model of schizophrenia. MAM-treated male rats were exposed to acute and repeated footshock stress at prepubertal, peripubteral, and adult ages. Ultrasonic vocalizations (USVs), freezing, and corticosterone responses were quantified. We found that juvenile MAM-treated rats emitted significantly more calls, spent more time vocalizing, emitted calls at a higher rate, and showed more freezing in response to acute footshock stress when compared with their saline (SAL) treated counterparts, and that this difference is not present in older animals. In addition, adolescent MAM-treated animals displayed a blunted HPA axis corticosterone response to acute footshock that did not adapt after 10 days of stress exposure. These data demonstrate abnormal stress responsivity in the MAM model of schizophrenia and suggest that these animals are more sensitive to the effects of stress in youth.

Resilience in shock and swim stress models of depression

Experimental models of depression often entail exposing a rodent to a stressor and subsequently characterizing changes in learning and anhedonia, which may reflect symptoms of human depression. Importantly, not all people, and not all laboratory rats, exposed to stressors develop depressed behavior; these “resilient” individuals are the focus of our review. Herein we describe research from the “learned helplessness” and “intermittent swim stress” (ISS) models of depression in which rats that were allowed to control the offset of the aversive stimulus with a behavioral response, and in a subset of rats that were not allowed to control the stressor that appeared to be behaviorally and neurochemically similar to rats that were either naive to stress or had controllability over the stressor. For example, rats exposed to inescapable tailshock, but do not develop learned helplessness, exhibit altered sensitivity to the behavioral effects of GABA_A receptor antagonists and reduced in vitro benzodiazepine receptor ligand binding. This pattern suggested that resilience might involve activation of an endogenous benzodiazepine-like compound, possibly an allostatic modulator of the GABA_A receptor like allopregnanolone. From the ISS model, we have observed in resilient rats protection from stressor-induced glucocorticoid increases and immune activation. In order to identify the neural mediators of these correlates of resilience, non-invasive measures are needed to predict the resilient or vulnerable phenotype prior to analysis of neural endpoints. To this end, we found that ultrasonic vocalizations (USVs) appear to predict the resilient phenotype in the ISS paradigm. We propose that combining non-invasive predictive measures, such as USVs with biological endpoint measures, will facilitate future research into the neural correlates of resilience.

Vesicular signalling and immune modulation as hedonic fingerprints: proteomic profiling in the chronic mild stress depression model

Extensive preclinical research has focused at unravelling the underlying molecular mechanisms leading to depression and recovery. In this study, we investigated the quantitative changes in protein abundance in the ventral hippocampal granular cell layer. We compared different phenotypes from the chronic mild stress (CMS) model of depression using chronic administration with two selective serotonin reuptake inhibitors (SSRIs), escitalopram and sertraline. We isolated granular cells using Laser-Capture Microdissection (LCM) and we identified their regulated proteins using two-dimensional (2D) differential gel electrophoresis (DIGE) and tandem mass spectrometry (MS/MS). The majority of the proteins we identified were enzymes involved in different metabolic activities. Additional proteins were functionally classified as vesicular proteins and immune system proteins. Rab GDP dissociation inhibitor alpha (GDIA) and syntaxin-binding protein 1 (STXB1) were potential markers for stress reactivity. Dynamin 1 (DYN1), glutathione S-transferase omega-1 (GSTO1) and peroxiredoxin (PRDX6) were associated with treatment response. In addition, an imbalance between different post-translationally modified versions of DYN1 and GSTO1 potentially accounted for SSRI treatment refraction. In the present study, we searched for new markers of stress reactivity and treatment response as well as any underlying molecular mechanisms correlating to the development of anhedonia and antidepressant therapy refraction. Our results pointed towards an essential role of post-translational modifications in both vesicular and immune protein systems.

Candidate hippocampal biomarkers of susceptibility and resilience to stress in a rat model of depression

Susceptibility to stress plays a crucial role in the development of psychiatric disorders such as unipolar depression and post-traumatic stress disorder. In the present study the chronic mild stress rat model of depression was used to reveal stress-susceptible and stress-resilient rats. Large-scale proteomics was used to map hippocampal protein alterations in different stress states. Membrane proteins were successfully captured by two-phase separation and peptide based proteomics. Using iTRAQ labeling coupled with mass spectrometry, more than 2000 proteins were quantified and 73 proteins were found to be differentially expressed. Stress susceptibility was associated with increased expression of a sodium-channel protein (SCN9A) currently investigated as a potential antidepressant target. Differential protein profiling also indicated stress susceptibility to be associated with deficits in synaptic vesicle release involving SNCA, SYN-1, and AP-3. Our results indicate that increased oxidative phosphorylation (COX5A, NDUFB7, NDUFS8, COX5B, and UQCRB) within the hippocampal CA regions is part of a stress-protection mechanism.

Intermittent and continuous swim stress-induced behavioral depression: sensitivity to norepinephrine- and serotonin-selective antidepressants

RATIONALE

Intermittent swim stress (ISS) produces deficits in swim escape learning and increases immobility in the forced swim test (FST). A previous attempt to reverse this immobility with the selective serotonin reuptake inhibitor (SSRI), fluoxetine (FLX), was unsuccessful, but the sensitivity of this immobility to other types of antidepressants is unknown.

OBJECTIVES

In experiment 1, we evaluate the ability of the norepinephrine (NE) selective reuptake inhibitor (NSRI), desipramine (DES), to reverse the ISS-induced immobility in the FST compared to confined controls (CC), while in experiment 2, we test the efficacy of either the SSRI or NSRI to reverse the immobility produced by either ISS or continuous swim (CS)/FST.

METHODS

Rats were exposed to their respective behavioral pretreatment (ISS, CS/FST, or CC) and were then injected with an antidepressant or saline solution 23.5, 5, and 1 h prior to the FST.

RESULTS

In experiment 1, DES reduced immobility and increased the climbing behavior in the ISS group without altering these behaviors in the CC, while in experiment 2, the CS/FST-induced immobility was reduced by both antidepressants (i.e., FLX and DES), while the ISS-induced immobility was only affected by DES.

CONCLUSIONS

These results suggest that the ISS-induced immobility is mediated through the NE system and may represent a model for atypical depression.

Stressor experiences during the juvenile period increase stressor responsivity in adulthood: transmission of stressor experiences

Stressors experienced by rodents during the juvenile period may have repercussions on anxiety and impulsivity that extend into adulthood. In the present investigation we demonstrate that during social interactions stressed adults might transmit their responses to juveniles thereby affecting later behavioral responses in adulthood. In the present investigation adult mice exposed to a stressor, exhibited altered social exploration of a juvenile (26-28 day old) mouse that comprised reduced body contact but elevated anogenital and facial contact. The juvenile mice that encountered the stressed adult, in turn, exhibited greater impulsivity in an elevated plus maze test, as well as elevated corticosterone levels. In a second experiment, adult animals that had experienced a stressor during the juvenile period also exhibited reduced social exploration (of a juvenile), but upon exposure to a further social stressor (social defeat), social exploration was altered further. Furthermore, when tested in an elevated plus maze the juvenile mice that had encountered an adult that had itself been stressed as a juvenile, exhibited increased impulsivity. However, if they encountered an adult that had been stressed both as a juvenile and as an adult, the behavioral profile of the juveniles was altered yet again in that they exhibited greater impulsivity coupled with anxiety. It is suggested that the juvenile period represents one during which stressor sensitivity is high, so that transmission of stressor effects from adults occurs readily. Moreover, stressors experienced during the juvenile period may have persistent effects on social behaviors, thereby affecting conspecifics with which they interact.