D-578, an orally active triple monoamine reuptake inhibitor, displays antidepressant and anti-PTSD like effects in rats.

Significant unmet needs exist for development of better pharmacotherapeutic agents for major depressive disorder (MDD) and post-traumatic stress disorder (PTSD) as the current drugs are inadequate. Our goal in this study is to investigate behavioral pharmacological characterization of a novel triple reuptake inhibitor (TRI) D-578 which exhibits nanomolar potency at all three monoamine transporters (Ki; 16.2. 16.2, 3.23 nM, and 29.6, 20.6, 6.10 nM for the rat brain and cloned human dopamine, serotonin and norepinephrine transporters, respectively) and exhibited little to no affinity for other off-target CNS receptors. In a rat forced swim test, compound D-578 upon oral administration displayed high efficacy and not stimulating in locomotor behavior. The effects of D-578 and paroxetine were next evaluated in a rat model for traumatic stress exposure - the single prolonged stress (SPS) model - which has been shown to have construct, predictive, and behavioral validity in modeling aspects of PTSD. Our results show that SPS had no effect on the acquisition of conditioned fear, but impaired extinction learning and extinction retention of fear behavior compared to sham treatment. D-578, but not paroxetine, attenuated the extinction and extinction-retention deficit induced by SPS. These findings suggest that D-578 has greater efficacy in normalizing traumatic stress-induced extinction-retention learning in a model for PTSD compared to paroxetine. Overall these results suggest that D-578, in addition to producing a robust and efficacious antidepressant effect, may attenuate maladaptive retention of fearful memories and support further testing of this agent for the pharmacotherapy of depression and PTSD.

Single-Prolonged Stress Impairs Prefrontal Cortex Control of Amygdala and Striatum in Rats.

Medial prefrontal cortex (mPFC), amygdala, and striatum neurocircuitry has been shown to play an important role in post-traumatic stress disorder (PTSD) pathology in humans. Clinical studies show hypoactivity in the mPFC and hyperactivity in the amygdala and striatum of PTSD patients, which has been associated with decreased mPFC glutamate levels. The ability to refine neurobiological characteristics of PTSD in an animal model is critical in furthering our mechanistic understanding of the disease. To this end, we exposed male rats to single-prolonged stress (SPS), a validated model of PTSD, and hypothesized that traumatic stress would differentially activate mPFC subregions [prelimbic (PL) and infralimbic (IL) cortices] and increase striatal and amygdalar activity, which would be associated with decreased mPFC glutamate levels. in vivo, neural activity in the subregions of the mPFC, amygdala, and striatum was measured using manganese-enhanced magnetic resonance imaging (MEMRI), and glutamate and N-acetylaspartate (NAA) levels in the mPFC and the dorsal striatum (dSTR) were measured using proton magnetic resonance spectroscopy (1H-MRS) longitudinally, in rats exposed to SPS or control conditions. As hypothesized, SPS decreased MEMRI-based neural activity in the IL, but not PL, cortex concomitantly increasing activity within the basolateral amygdala (BLA) and dorsomedial striatum (dmSTR). 1H-MRS studies in a separate cohort revealed SPS decreased glutamate levels in the mPFC and increased NAA levels in the dSTR. These results confirm previous findings that suggest SPS causes mPFC hypoactivation as well as identifies concurrent hyperactivation in dmSTR and BLA, effects which parallel the clinical neuropathology of PTSD.

Cognitive Flexibility Training Improves Extinction Retention Memory and Enhances Cortical Dopamine With and Without Traumatic Stress Exposure.

Stress exposure can cause lasting changes in cognition, but certain individual traits, such as cognitive flexibility, have been shown to reduce the degree, duration, or severity of cognitive changes following stress. Both stress and cognitive flexibility training affect decision making by modulating monoamine signaling. Here, we test the role cognitive flexibility training, and high vs. low cognitive flexibility at the individual level, in attenuating stress-induced changes in memory and monoamine levels using the single prolonged stress (SPS) rodent model of traumatic stress in male Sprague-Dawley rats. Exposure to SPS can heighten fear responses to conditioned cues (i.e., freezing) after a fear association has been extinguished, referred to as a deficit in extinction retention. This deficit is thought to reflect an impairment in context processing that is characteristic of posttraumatic stress disorder (PTSD). During a cognitive flexibility training we assessed individual variability in cognitive skills and conditioned rats to discriminately use cues in their environment. We found that cognitive flexibility training, alone or followed by SPS exposure, accelerated extinction learning and decreased fear responses over time during extinction retention testing, compared with rats not given cognitive flexibility training. These findings suggest that cognitive flexibility training may improve context processing in individuals with and without traumatic stress exposure. Individual performance during the reversal phase of the cognitive flexibility training predicted subsequent context processing; individuals with high reversal performance exhibited a faster decrease in freezing responses during extinction retention testing. Thus, high reversal performance predicted enhanced retention of extinction learning over time and suggests that cognitive flexibility training may be a strategy to promote context processing. In a brain region vital for maintaining cognitive flexibility and fear suppression, the prelimbic cortex (PLC), cognitive flexibility training also lastingly enhanced dopamine (DA) and norepinephrine (NE) levels, in animals with and without traumatic stress exposure. In contrast, cognitive flexibility training prior to traumatic stress exposure decreased levels of DA and its metabolites in the striatum, a region mediating reflexive decision making. Overall, our results suggest that cognitive flexibility training can provide lasting benefits by enhancing extinction retention, a hallmark cognitive effect of trauma, and prelimbic DA, which can maintain flexibility across changing contexts.

Divergent effects of repeated cocaine and novel environment exposure on locus coeruleus c-fos expression and brain catecholamine concentrations in rats.

INTRODUCTION: Chronic administration of cocaine causes a disinhibited, hyperexploratory response to novel environments. As the norepinephrine (NE) system regulates exploration and is dysregulated following cocaine exposure, we hypothesized that this cocaine-mediated hyperexploratory response is associated with increased locus coeruleus (LC) reactivity. METHODS: To test this hypothesis, we used dual fluorescent in situ hybridization immunofluorescence to analyze novelty-induced c-fos and tyrosine hydroxylase expression in the LC and high-pressure liquid chromatography to measure dopamine (DA) and NE concentrations in key catecholamine projection regions following exposure to cocaine. RESULTS: Repeated cocaine exposure followed by a 14-day drug-free period increased exploration of novel environments, replicating previous findings. Novelty exposure increased LC c-fos expression, increased anterior cingulate NE, and decreased ventral tegmental area DA. Cocaine exposure decreased amygdala (AMY) DA, but had no effect on LC c-fos expression or NE in any tested brain region. No interactions between cocaine and novelty were found. Open arm exploration was positively correlated with LC c-fos expression and NE concentrations in both the anterior cingulate and nucleus accumbens, and negatively correlated with AMY DA concentration. CONCLUSIONS: Our findings confirm that exposure to novel environments increases LC activity and NE in the anterior cingulate cortex, that long-term exposure to cocaine dysregulates AMY DA, and that disinhibited exploration in novel environments correlates with NE and DA in regions that modulate risk-taking and avoidance behavior. Further studies investigating the effects of cocaine on brain catecholamine systems are important in understanding the long-lasting effects of cocaine on brain function.

Single-Prolonged Stress: A Review of Two Decades of Progress in a Rodent Model of Post-traumatic Stress Disorder.

Post-traumatic stress disorder (PTSD) is a common, costly, and often debilitating psychiatric condition. However, the biological mechanisms underlying this disease are still largely unknown or poorly understood. Considerable evidence indicates that PTSD results from dysfunction in highly-conserved brain systems involved in stress, anxiety, fear, and reward. Pre-clinical models of traumatic stress exposure are critical in defining the neurobiological mechanisms of PTSD, which will ultimately aid in the development of new treatments for PTSD. Single prolonged stress (SPS) is a pre-clinical model that displays behavioral, molecular, and physiological alterations that recapitulate many of the same alterations observed in PTSD, illustrating its validity and giving it utility as a model for investigating post-traumatic adaptations and pre-trauma risk and protective factors. In this manuscript, we review the present state of research using the SPS model, with the goals of (1) describing the utility of the SPS model as a tool for investigating post-trauma adaptations, (2) relating findings using the SPS model to findings in patients with PTSD, and (3) indicating research gaps and strategies to address them in order to improve our understanding of the pathophysiology of PTSD.

Binge-pattern cocaine administration causes long-lasting behavioral hyperarousal but does not enhance vulnerability to single prolonged stress in rats.

Cocaine use disorder and post-traumatic stress disorder (PTSD) commonly co-occur. This could be due to vulnerability to post-traumatic symptoms conferred by previous exposure to cocaine. Therefore, we combined chronic binge-pattern cocaine with a model of psychological trauma (single prolonged stress) to determine whether the behavioral effects of psychological trauma are enhanced in cocaine-sensitized individuals. Adult male Sprague Dawley rats received 14 days of cocaine (15mg/kg/injection) or saline in a binge pattern (3 injections per day, 1h apart). Seven days after the last injection animals were exposed to traumatic stress or a control procedure. Seven days after stress, activity and anxiety-like behaviors were measured. Binge-pattern cocaine increased locomotor activity in the open field and elevated plus maze, and both cocaine and SPS exposure increased the rapidity with which rats moved through grooming sequences. Neither binge-pattern cocaine nor SPS increased anxiety-like behaviors, and no interactions were found between binge-pattern cocaine exposure and SPS exposure. A behavioral phenotype categorization approach demonstrated that cocaine-exposed groups expressed a high incidence of hyperactivity-like symptoms. These results suggest that binge-pattern cocaine exposure causes a long-lasting hyper-exploratory phenotype but does not make individuals more vulnerable to a later traumatic stress exposure.

Cocaine-induced locomotor sensitization in rats correlates with nucleus accumbens activity on manganese-enhanced MRI.

A long-standing goal of substance abuse research has been to link drug-induced behavioral outcomes with the activity of specific brain regions to understand the neurobiology of addiction behaviors and to search for drug-able targets. Here, we tested the hypothesis that cocaine produces locomotor (behavioral) sensitization that correlates with increased calcium channel-mediated neuroactivity in brain regions linked with drug addiction, such as the nucleus accumbens (NAC), anterior striatum (AST) and hippocampus, as measured using manganese-enhanced MRI (MEMRI). Rats were treated with cocaine for 5 days, followed by a 2-day drug-free period. The following day, locomotor sensitization was quantified as a metric of cocaine-induced neuroplasticity in the presence of manganese. Immediately following behavioral testing, rats were examined for changes in calcium channel-mediated neuronal activity in the NAC, AST, hippocampus and temporalis muscle, which was associated with behavioral sensitization using MEMRI. Cocaine significantly increased locomotor activity and produced behavioral sensitization compared with saline treatment of control rats. A significant increase in MEMRI signal intensity was determined in the NAC, but not AST or hippocampus, of cocaine-treated rats compared with saline-treated control rats. Cocaine did not increase signal intensity in the temporalis muscle. Notably, in support of our hypothesis, behavior was significantly and positively correlated with MEMRI signal intensity in the NAC. As neuronal uptake of manganese is regulated by calcium channels, these results indicate that MEMRI is a powerful research tool to study neuronal activity in freely behaving animals and to guide new calcium channel-based therapies for the treatment of cocaine abuse and dependence.