Post-traumatic stress disorder: emerging concepts of pharmacotherapy

An evidence-based approach to psychopharmacology for posttraumatic stress disorder (PTSD) - 2022 update

Algorithms for posttraumatic stress disorder were published by this team in 1999 and 2011. Developments since then warrant revision. New studies and review articles from January 2011 to November 2021 were identified via PubMed and analyzed for evidence supporting changes. Following consideration of variations required by special patient populations, treatment of sleep impairments remains as the first recommended step. Nightmares and non-nightmare disturbed awakenings are best addressed with the anti-adrenergic agent prazosin, with doxazosin and clonidine as alternatives. First choices for difficulty initiating sleep include hydroxyzine and trazodone. If significant non-sleep PTSD symptoms remain, an SSRI should be tried, followed by a second SSRI or venlafaxine as a third step. Second generation antipsychotics can be considered, particularly for SSRI augmentation when PTSD-associated psychotic symptoms are present, with the caveat that positive evidence is limited and side effects are considerable. Anti-adrenergic agents can also be considered for general PTSD symptoms if not already tried, though evidence for daytime use lags that available for sleep. Regarding other pharmacological and procedural options, e.g., transcranial magnetic stimulation, cannabinoids, ketamine, psychedelics, and stellate ganglion block, evidence does not yet support firm inclusion in the algorithm. An interactive version of this work can be found at www.psychopharm.mobi.

Ameliorating Impact of Prophylactic Intranasal Oxytocin on Signs of Fear in a Rat Model of Traumatic Stress

Oxytocin treatment reduces signs of long-term emotional stress after exposure to trauma; however, little is known about the potential protective effects of oxytocin treatment on behavioral and physiological changes associated with extreme stress exposure. The objective of this study was to investigate oxytocin treatment as a prophylactic measure against rat signs of fear. Two separate experiments were conducted in which the time of intranasal oxytocin administration differed. Intranasal oxytocin (1.0 μg/kg) was administered 5 min after daily exposure to foot shock in Experiment #1 and 1 h before foot shock in Experiment #2. In Experiment #1, possible massage-evoked oxytocin release (5 min after foot shock) was also investigated. In both experiments, a contextual fear conditioning procedure was employed in which stress was induced via inescapable foot shock (3 days, 40 shocks/day, 8 mA/shock) in a fear conditioning chamber. Male Sprague-Dawley rats (n = 24) were divided into four groups (n = 6, per group) for each experiment. Experiment #1 groups: Control Exp#1 (intranasal saline and no foot shock); Stress Exp#1 (intranasal saline 5 min after foot shock); Massage+Stress Exp#1 (massage-like stroking and intranasal saline 5 min after foot shock); Oxytocin+Stress Exp#1 (intranasal oxytocin 5 min after foot shock). Experiment #2 groups: Control Exp#2 (intranasal saline and no foot shock); Stress Exp#2 (intranasal saline 1 h before foot shock); Oxytocin Exp#2 (intranasal oxytocin and no foot shock); Oxytocin+Stress Exp#2 (intranasal oxytocin 1 h before foot shock). One week after fear conditioning (and other treatments), rats were independently evaluated for behavioral signs of fear. Two weeks after conditioning, physiological signs of fear were also assessed (Experiment #1). Relative to controls, rats treated with intranasal oxytocin 5 min after daily foot shock sessions exhibited significantly less immobility upon re-exposure to the shock chamber and attenuated physiological responses related to fear (e.g., elevated heart rate and blood pressure). Furthermore, intranasal oxytocin treatment given 1 h before daily foot shock sessions significantly decreased immobility and defecation upon re-exposure to the shock chamber, relative to controls. The results of this study suggest that prophylactic intranasal oxytocin, administered contemporaneously with aversive stimuli, mitigates behavioral and physiological responses associated with traumatic stress.

Dynamic Patterns of Threat-Associated Gene Expression in the Amygdala and Blood

Stress and trauma profoundly influence psychiatric biobehavioral outcomes. The identification of treatment and biomarker targets would be accelerated by a broad understanding of the biological responses to these events. The goal of this study was to determine genes responsive to auditory fear conditioning (FC), a well-characterized amygdala-dependent rodent model of threat-exposure, in the presence or absence of prior stress history, providing insight into the physiological processes underlying response to trauma. RNA-sequencing was performed in blood and amygdala from mice that underwent fear conditioning with (Immo+FC) and without (FC) prior immobilization stress, a paradigm that induces HPA axis, and behavioral stress sensitization. In the amygdala, 607 genes were regulated by FC vs. home-cage (HC) controls, and 516 genes differed in stress-sensitized mice (Immo+FC vs. FC). In the former, we observed an enhancement of specific biological processes involved in learning and synaptic transmission, and in the latter processes associated with cell proliferation and the cellular response to drugs. In the blood of stress-sensitized animals, 468 genes were dynamically regulated when compared to FC, and were enriched for the biological pathways of inflammation and cytokine signaling. This study identified genes and pathways that respond to threat in the amygdala and blood of mice with and without a prior stress history and reveals the impact of stress history on subsequent inflammation. Future studies will be needed to examine the role of these dynamically regulated genes may play in human clinical stress and trauma-related disorders.

Different frequency repetitive transcranial magnetic stimulation (rTMS) for posttraumatic stress disorder (PTSD): A systematic review and meta-analysis

Posttraumatic stress disorder (PTSD) is a psychiatric disorder. Repetitive transcranial magnetic stimulation (rTMS) has been found to be effective for treating PTSD, but whether different frequencies have different effects remains controversial. We conducted this systematic review and meta-analysis to address this question. We searched the literature for studies written in English or Chinese in 9 electronic databases from the databases' inception to August 1, 2016. Additional articles were identified from the reference lists of identified studies and from personal reference collections. Eighteen articles were included, and 11 were suitable for the meta-analysis (Combined sample size was 377 (217 in active rTMS groups, 160 in sham-controlled groups)). Low-frequency (LF) rTMS resulted in a significant reduction in the PTSD total score and the depression score (1. PTSD total score: pooled SMD, 0.92; CI, 0.11-1.72; 2. Depression: pooled SMD, 0.54; CI, 0.08-1.00). High-frequency (HF) rTMS showed the following results: 1. PTSD total score: pooled SMD, 3.24; CI, 2.24-4.25; 2. re-experiencing: pooled SMD, -1.77; CI, -2.49-(-1.04); 3. Avoidance: pooled SMD, -1.57; CI, -2.50-(-0.84); 4. hyperarousal: pooled SMD, -1.32; CI, -2.17-(-0.47); 5. depression: pooled SMD, 1.92; CI, 0.80-3.03; and 6. Anxiety: pooled SMD, 2.67; CI, 1.82-3.52. Therefore, both HF and LF rTMS can alleviate PTSD symptoms. Although the evidence is extremely limited, LF rTMS can reduce overall PTSD and depression symptoms. HF rTMS can improve the main and related symptoms of PTSD. However, additional research is needed to substantiate these findings.

D-Cycloserine acts via increasing the GluN1 protein expressions in the frontal cortex and decreases the avoidance and risk assessment behaviors in a rat traumatic stress model

D-cycloserine (DCS), an FDA approved anti-tuberculosis drug has extensively been studied for its cognitive enhancer effects in psychiatric disorders. DCS may enhance the effects of fear extinction trainings in animals during exposure therapy and hence we investigated the effects of DCS on distinct behavioral parameters in a predator odor stress model and tested the optimal duration for repeated daily administrations of the agent. Cat fur odor blocks were used to produce stress and avoidance and risk assessment behavioral parameters were used where DCS or saline were used as treatments in adjunct to extinction trainings. We observed that DCS facilitated extinction training by providing further extinction of avoidance responses, risk assessment behaviors and increased the contact with the cue in a setting where DCS was administered before extinction trainings for 3 days without producing a significant tolerance. In amygdala and hippocampus, GluN1 protein expressions decreased 72h after the fear conditioning in the traumatic stress group suggesting a possible down-regulation of NMDARs. We observed that extinction learning increased GluN1 proteins both in the amygdaloid complex and the dorsal hippocampus of the rats receiving extinction training or extinction training with DCS. Our findings also indicate that DCS with extinction training increased GluN1 protein levels in the frontal cortex. We may suggest that action of DCS relies on enhancement of the consolidation of fear extinction in the frontal cortex.

Patient-reported outcomes in post-traumatic stress disorder. Part II: focus on pharmacological treatment

Post-traumatic stress disorder (PTSD) may be associated with long-lasting psychological suffering, distressing psychosocial disability, markedly reduced health-related quality of life, and increased morbidity and mortality in a subgroup of individuals in the aftermath of serious traumatic events. Both etiopathogenesis and treatment modalities of PTSD are best conceptualized within a biopsychosotial model. Pharmacotherapy may lay claim to a major role in the multimodal treatment approaches. Here we outline two different pharmacotherapeutic trends that aim to modify the encoding, consolidation, and rehearsal of traumatic memory in order to reduce the risk of PTSD immediately after trauma exposure on the one hand, and that endeavor to treat the clinical state of PTSD on the other. The theoretical rationales of both pharmacological strategies are the complex neurobiological underpinnings that characterize traumatic memory organization and clinical PTSD. Meanwhile, promising data from randomized controlled trials have been obtained for both approaches. Empirical evidence may inform clinicians in their clinical efforts for this special group of patients. The efficacy of several classes of drugs that have been investigated within a context of research should be evaluated critically and still have to stand the test of effectiveness in daily clinical practice. From a patient perspective, empirical results may serve as a psychoeducative guideline to what pharmacotherapeutic approaches may realistically achieve, what their risks and benefits are, and what their limits are in contributing to reducing the often major chronic suffering caused by serious traumatic events. Ethical issues have to be considered, particularly in the context of pharmacological strategies projected to prevent PTSD in the aftermath of traumatic exposure.

On the Road to Translation for PTSD Treatment: Theoretical and Practical Considerations of the Use of Human Models of Conditioned Fear for Drug Development

The use of quantitative, laboratory-based measures of threat in humans for proof-of-concept studies and target development for novel drug discovery has grown tremendously in the last 2 decades. In particular, in the field of posttraumatic stress disorder (PTSD), human models of fear conditioning have been critical in shaping our theoretical understanding of fear processes and importantly, validating findings from animal models of the neural substrates and signaling pathways required for these complex processes. Here, we will review the use of laboratory-based measures of fear processes in humans including cued and contextual conditioning, generalization, extinction, reconsolidation, and reinstatement to develop novel drug treatments for PTSD. We will primarily focus on recent advances in using behavioral and physiological measures of fear, discussing their sensitivity as biobehavioral markers of PTSD symptoms, their response to known and novel PTSD treatments, and in the case of d-cycloserine, how well these findings have translated to outcomes in clinical trials. We will highlight some gaps in the literature and needs for future research, discuss benefits and limitations of these outcome measures in designing proof-of-concept trials, and offer practical guidelines on design and interpretation when using these fear models for drug discovery.

Methylphenidate and desipramine combined treatment improves PTSD symptomatology in a rat model

Antidepressant medication constitutes the first line pharmacological treatment for posttraumatic stress disorder (PTSD), however, because many patients display no beneficial drug effects it has been suggested that combinations of antidepressants with additional drugs may be necessary. The defining symptoms of PTSD include re-experiencing, avoidance and hyperarousal. In addition, PTSD patients were shown to become easily distracted and often suffer from poor concentration together with indications of comorbidity with attention-deficit hyperactivity disorder (ADHD). Methylphenidate (MPH) is the most common and effective drug treatment for ADHD, thus we aimed to investigate the effects of MPH treatment, by itself or in combination with the antidepressants fluoxetine (FLU) or desipramine (DES). We modified an animal model of PTSD by exposing rats to chronic stress and evaluating the subsequent development of behavioral PTSD-like symptoms, as well as the effects on proinflammatory cytokines, which were implicated in PTSD. We report that while FLU or DES had a beneficial effect on avoidance and hyperarousal symptoms, MPH improved all three symptoms. Moreover, the combination of MPH with DES produced the most dramatic beneficial effects. Serum levels of interleukin-1β (IL-1β) and IL-6 were elevated in the PTSD-like group compared with the control group, and were decreased by MPH, FLU, DES or the combination drug treatments, with the combination of DES+MPH producing the most complete rescue of the inflammatory response. Considering the versatile symptoms of PTSD, our results suggest a new combined treatment for PTSD comprising the antidepressant DES and the psychostimulant MPH.

Intranasal neuropeptide Y reverses anxiety and depressive-like behavior impaired by single prolonged stress PTSD model

PTSD is a debilitating neuropsychiatric disorder and many patients do not respond sufficiently to current treatments. Neuropeptide Y (NPY) is suggested to provide resilience to the development of PTSD and co-morbid depression. Injections of NPY to the rodent brain are anxiolytic. Recently we showed that intranasal delivery of NPY to rats before or immediately after exposure to single prolonged stress (SPS) animal model of PTSD prevented development of many biochemical and behavioral symptoms of PTSD, indicating its prophylactic potential. Here, we investigated whether intranasal NPY might provide benefits once symptoms have already developed. One week after exposure to SPS stressors, animals were given intranasal NPY or vehicle and tested on elevated plus maze 2h or 2 days later. The NPY treated rats had lower anxiety-like behavior than vehicle treated rats as indicated by more entries into open arms and fewer into closed arms, lower anxiety index, higher risk assessment and unprotected head dips and reduced grooming time. Their anxiety index was similar to that of unstressed controls. On most of these variables there was no effect of time interval and rats displayed similar overall changes 2h or 2 days after the infusion. Moreover, intranasal NPY led to reduced depressive-like behavior, assessed by forced swim test. Thus, intranasal NPY reversed several behavioral impairments triggered by the traumatic stress of SPS and has potential for non-invasive PTSD therapeutic intervention.

Intranasal infusion of melanocortin receptor four (MC4R) antagonist to rats ameliorates development of depression and anxiety related symptoms induced by single prolonged stress

Brain melanocortinergic systems and specifically melanocortin receptor four (MC4R) are implicated in modulation of anxiety- and depressive-like behavior induced by mild or moderate stress. Here we examine whether blockage of central MC4Rs with HS014 before severe traumatic stress may protect against development of anxiety and depression co-morbid with post-traumatic stress disorder (PTSD). Male rats were treated intranasally (IN) with vehicle or varied doses of HS014, 30min prior to single prolonged stress (SPS) animal model of PTSD. IN administration of 100μg HS014 pre-SPS improved despair behavior in forced swim (FS) immediately after immobilization stress part of SPS protocol. During all 4 intervals of 20min FS these rats spent less time immobile than rats given vehicle or 3.5ng HS014. This dose of HS014 also had a long-term beneficial effect manifested as reduction of immobility time in forced swim test performed after SPS. However, both HS014 doses were effective in ameliorating development of anxiety-like behavior after traumatic stress. Thus, rats given IN HS014 prior to SPS exhibited less open arms (OA) visits in elevated plus maze (EPM), spent longer time in OA and less in closed arms, had lower anxiety index, higher risk assessment and more head dips over borders in OA. They also spent longer time in the center of the open field and defecated less. Reduced grooming behavior in EPM was observed with 100μg HS014. This is the first study revealing pronounced resilience effects of HS014 on development of behavioral symptoms co-morbid with PTSD.

Recent progress in understanding the pathophysiology of post-traumatic stress disorder: implications for targeted pharmacological treatment

Post-traumatic stress disorder (PTSD) is a common and chronic anxiety disorder that can result after exposure to a traumatic event. Though our understanding of the aetiology of PTSD is incomplete, several neurobiological systems have been implicated in the pathophysiology and vulnerability towards developing PTSD after trauma exposure. We aimed to provide a concise review of benchmark findings in important neurobiological systems related to the aetiology and maintenance of PTSD symptomology. Specifically, we discuss functional aetiologies in the noradrenergic, serotonergic, endogenous cannabinoid and opioid systems as well as the hypothalamic-pituitary adrenal (HPA) axis. This article provides a succinct framework to appreciate the current understanding of neurobiological mechanisms related to the pathophysiology of PTSD and how these findings may impact the development of future, targeted pharmacological treatments for this debilitating disorder.

Post-traumatic stress disorder as a comorbidity: impact on disease outcomes

Post-traumatic stress disorder (PTSD) is associated with many psychiatric and nonpsychiatric comorbidities. Growing evidence suggests that PTSD as a comorbidity may impair drug adherence, quality of life and sleep quality, as well as increase rehospitalization rates, disease relapses, intensity of symptoms, morbidity and mortality. The aim of this article is to examine the literature regarding the effects of PTSD comorbidity on physical and mental health.

Treadmill exercise during pregnancy ameliorates post‑traumatic stress disorder‑induced anxiety‑like responses in maternal rats

Post‑traumatic stress disorder (PTSD) is an anxiety disorder triggered by life‑threatening events that cause intense fear. Exercise is known to have protective effects on neuropsychiatric diseases. The present study investigated whether treadmill exercise during pregnancy reduced or alleviated symptoms of PTSD in maternal rats. To induce predator stress in pregnant rats, rats were exposed to a hunting dog in an enclosed room. Exposure time was three 10‑min daily sessions separated by 1 h, starting at week 1 of pregnancy until delivery. Pregnant rats in the exercise group were forced to run on a treadmill for 30 min once a day, starting one week following pregnancy until delivery. Rats receiving predator stress during pregnancy exhibited PTSD anxiety‑like behaviors following delivery. Expression of 5‑hydroxytryptamine (5‑HT) and its synthesizing enzyme tryptophan hydroxylase (TPH) in the dorsal raphe was increased compared with unstressed rats. Expression of c‑Fos and neuronal nitric oxide synthases (nNOS) in the hypothalamus and locus coeruleus were higher in the rats receiving stress during pregnancy compared with unstressed rats. By contrast, treadmill exercise during pregnancy ameliorated anxiety‑like behaviors and reduced the expression of 5‑HT, TPH, c‑Fos and nNOS in the PTSD maternal rats. The results of the present study indicate that exercise during pregnancy is suitable for use as a therapeutic strategy to reduce anxiety‑related disorders, including PTSD.

Consolidation of remote fear memories involves Corticotropin-Releasing Hormone (CRH) receptor type 1-mediated enhancement of AMPA receptor GluR1 signaling in the dentate gyrus

Persistent dreadful memories and hyperarousal constitute prominent psychopathological features of posttraumatic stress disorder (PTSD). Here, we used a contextual fear conditioning paradigm to demonstrate that conditional genetic deletion of corticotropin-releasing hormone (CRH) receptor 1 within the limbic forebrain in mice significantly reduced remote, but not recent, associative and non-associative fear memories. Per os treatment with the selective CRHR1 antagonist DMP696 (3 mg/kg) attenuated consolidation of remote fear memories, without affecting their expression and retention. This could be achieved, if DMP696 was administered for 1 week starting as late as 24 h after foot shock. Furthermore, by combining electrophysiological recordings and western blot analyses, we demonstrate a delayed-onset and long-lasting increase in AMPA receptor (AMPAR) GluR1-mediated signaling in the dentate gyrus (DG) of the dorsal hippocampus 1 month after foot shock. These changes were absent from CRHR1-deficient mice and after DMP696 treatment. Inactivation of hippocampal GluR1-containing AMPARs by antisense oligonucleotides or philantotoxin 433 confirmed the behavioral relevance of AMPA-type glutamatergic neurotransmission in maintaining the high levels of remote fear in shocked mice with intact CRHR1 signaling. We conclude that limbic CRHR1 receptors enhance the consolidation of remote fear memories in the first week after foot shock by increasing the expression of Ca(2+)-permeable GluR1-containing AMPARs in the DG. These findings suggest both receptors as rational targets for the prevention and therapy, respectively, of psychopathology associated with exaggerated fear memories, such as PTSD.

The Psychopharmacology Algorithm Project at the Harvard South Shore Program: an update on posttraumatic stress disorder

BACKGROUND

This project aimed to provide an organized, sequential, and evidence-supported approach to the pharmacotherapy of posttraumatic stress disorder (PTSD), following the format of previous efforts of the Psychopharmacology Algorithm Project at the Harvard South Shore Program.

METHOD

A comprehensive literature review was conducted to determine the best pharmacological choices for PTSD patients and to update the last published version (1999) of the algorithm. We focused on optimal pharmacological interventions to address the prominent symptoms of PTSD, with additional attention to the impact that common comorbidities have on treatment choices.

RESULTS

We found that SSRIs and SNRIs are not as effective as previously thought, and that awareness of their long-term side effects has increased. New evidence suggests that addressing fragmented sleep and nightmares can improve symptoms (in addition to insomnia) that are frequently seen with PTSD (e.g., hyperarousal, reexperiencing). Prazosin and trazodone are emphasized at this initial step; if significant PTSD symptoms remain, an antidepressant may be tried. For PTSD-related psychosis, an antipsychotic may be added. In resistant cases, two or three antidepressants may be used in sequence. Following that, or with partial improvement and residual symptomatology, augmentation may be tried; the best options are antipsychotics, clonidine, topiramate, and lamotrigine.

CONCLUSION

This heuristic may be helpful in producing faster symptom resolution, fewer side effects, and increased compliance.

Pharmacological treatment of PTSD - established and new approaches

A large proportion of humans will experience a traumatic event at least once in their lifetime, with up to 10% then going on to developing posttraumatic stress disorder (PTSD). In this review we will discuss established pharmacological interventions for PTSD as well as highlight novel therapeutic strategies undergoing extensive pre-clinical research as well as ongoing clinical research. Such strategies include prophylactic treatments and use of pharmacotherapy as adjunctive treatment with established trauma-focused psychological therapies. These potential treatment approaches include modulation of stress effects on memory consolidation after trauma (e.g., glucocorticoid, corticotropin-releasing factor and norepinephrine signalling modulators), as well as putative cognitive enhancers that target mechanisms of conditioned fear extinction and reconsolidation (e.g., glucocorticoid receptor modulators and modulators of glutamate signalling such as positive allosteric modulators of glutamate receptors, glycine transporter inhibitors, or glycine agonists). We will discuss evidence for and against these potential novel treatment strategies and their limitations. This article is part of a Special Issue entitled 'Post-Traumatic Stress Disorder'.

Hippocampal dysfunction effects on context memory: possible etiology for posttraumatic stress disorder

Hippocampal volume reductions and functional impairments are reliable findings in posttraumatic stress disorder (PTSD) imaging studies. However, it is not clear if and how hippocampal dysfunction contributes to the etiology and maintenance of PTSD. Individuals with PTSD are often described as showing fear responses to trauma reminders outside of contexts in which these cues would reasonably predict danger. Animal studies suggest that the hippocampus is required to form and recall associations between contextual stimuli and aversive events. For example, the hippocampus is critical for encoding memories in which a complex configuration of multiple cues is associated with the aversive event. Conversely, the hippocampus is not required for associations with discrete cues. In animal studies, if configural memory is disrupted, learning strategies using discrete cue associations predominate. These data suggest poor hippocampal function could bias the organism toward forming multiple simple cue associations during trauma, thus increasing the chances of fear responses in multiple environments (or contexts) in which these cues may be present. Here we will examine clinical and preclinical literature to support a theory of hippocampal dysfunction as a primary contributory factor to the etiology of PTSD, and discuss future research required to test these hypotheses. This article is part of a Special Issue entitled 'Post-Traumatic Stress Disorder'.

Environmental enrichment induces behavioral recovery and enhanced hippocampal cell proliferation in an antidepressant-resistant animal model for PTSD

Background

Post traumatic stress disorder (PTSD) can be considered the result of a failure to recover after a traumatic experience. Here we studied possible protective and therapeutic aspects of environmental enrichment (with and without a running wheel) in Sprague Dawley rats exposed to an inescapable foot shock procedure (IFS).

Methodology/Principal Findings

IFS induced long-lasting contextual and non-contextual anxiety, modeling some aspects of PTSD. Even 10 weeks after IFS the rats showed reduced locomotion in an open field. The antidepressants imipramine and escitalopram did not improve anxiogenic behavior following IFS. Also the histone deacetylase (HDAC) inhibitor sodium butyrate did not alleviate the IFS induced immobility. While environmental enrichment (EE) starting two weeks before IFS did not protect the animals from the behavioral effects of the shocks, exposure to EE either immediately after the shock or one week later induced complete recovery three weeks after IFS. In the next set of experiments a running wheel was added to the EE to enable voluntary exercise (EE/VE). This also led to reduced anxiety. Importantly, this behavioral recovery was not due to a loss of memory for the traumatic experience. The behavioral recovery correlated with an increase in cell proliferation in hippocampus, a decrease in the tissue levels of noradrenalin and increased turnover of 5-HT in prefrontal cortex and hippocampus.

Conclusions/Significance

This animal study shows the importance of (physical) exercise in the treatment of psychiatric diseases, including post-traumatic stress disorder and points out the possible role of EE in studying the mechanism of recovery from anxiety disorders.

Central noradrenergic lesion induced by DSP-4 impairs the acquisition of avoidance reactions and prevents molecular changes in the amygdala

The noradrenergic system plays and an important modulatory role in memory consolidation of emotionally arousing tasks. However, the molecular cascades regulated in the brain by norepinephrine and involved in memory formation are still largely unknown. The purpose of the present study was to evaluate the role of the noradrenergic system on the acquisition of a highly emotionally arousing task-two-way active avoidance training-and its molecular and cellular substrates. The selective norepinephrine neurotoxin N-(2-chloroethyl)-N-ethyl-2 bromobenzylamine (DSP-4, 50mg/kg) was used. DSP-4-treated rats were trained in a shuttle box to avoid a footshock signaled by an auditory stimulus. Immunohistochemical mapping of the neuronal plasticity-related molecules c-Fos protein and the activated form of extracellular signal-regulated kinase (phosphorylated ERK [pERK]) was then employed. We found that DSP-4 treatment depleted the expression of the norepinephrine marker dopamine -hydroxylase (DBH) in the locus coeruleus and its projection area, the basolateral nucleus of the amygdala, confirming locus coeruleus noradrenergic lesion in the experimental animals. Furthermore, DSP-4 treatment impaired the acquisition of the avoidance reaction. We also found that acquisition of the active avoidance reaction induced c-Fos expression and ERK activation in the amygdala and piriform cortex. This upregulation was prevented by DSP-4 treatment. Thus, our data suggest that the noradrenergic system is involved in the acquisition of the active avoidance reaction by regulating ERK pathway activity and c-Fos expression in the amygdala and piriform cortex.