Augmentation treatment of psychotherapy for anxiety disorders with D-cycloserine

Neuronal mechanisms underlying development of nicotine dependence: implications for novel smoking-cessation treatments

Tobacco smoking causes high rates of mortality and morbidity throughout the world. Despite the availability of smoking-cessation medications, maintenance of long-term abstinence is difficult, and most individuals who attempt to quit smoking relapse. Although tobacco smoke contains many substances, researchers and policymakers agree that nicotine is a major cause of tobacco dependence. Understanding the neural substrates of nicotine dependence is essential for the development of more effective antismoking medications than those currently available. This article focuses on the neural substrates, especially nicotinic acetylcholine receptors, that mediate the reinforcing effects of nicotine and the development of nicotine dependence. Neuroadaptations in the function of the neurotransmitters dopamine, glutamate, and gamma-aminobutyric acid (GABA), which have been shown to be critically involved in nicotine dependence, are also reviewed. Finally, the article discusses progress in the discovery and development of smoking-cessation medications.

A pilot study of the effectiveness of D-cycloserine during cue-exposure therapy in abstinent alcohol-dependent subjects

RATIONALE

Cue-exposure therapy (CET) has been advocated as a potentially effective treatment of addictive behaviours. Strategies that enhance learning may improve the outcome of CET. D-cycloserine (DCS), a partial N-methyl-D-aspartate receptor agonist, has been shown to facilitate extinction of learned fear in rats and augment exposure-based treatment in some anxiety disorders in man.

OBJECTIVE

This double-blind placebo-controlled pilot study used a cue-exposure paradigm, salient for an individual's alcohol drinking, to see if DCS would reduce cue-reactivity compared with placebo.

METHODS

Sixteen abstinent, alcohol-dependent individuals were randomised to receive either a single-dose (250 mg) DCS or placebo before CET sessions, separated by at least 1 week. Subjective responses were assessed using the Alcohol Urge Questionnaire (AUQ) and visual analogue scales. Cardiovascular responses were assessed using Finapres©.

RESULTS

The cue-exposure paradigm significantly increased craving assessed with the AUQ during the first session. In subsequent sessions, the degree of craving was reduced. However, no significant difference was seen between the DCS and placebo groups in any outcome measure. The variability of responses between individuals was great with more than half the groups reporting no or very small changes in AUQ scores.

CONCLUSION

This is the first human study to our knowledge to assess the efficacy of DCS in facilitating CET in alcohol dependence. The high proportion of subjects with little or no response to cue-exposure would make any effect of DCS very difficult to detect. It is important that future studies carefully consider the criteria for inclusion.

New perspectives in glutamate and anxiety

Anxiety and stress-related disorders, namely posttraumatic stress disorder (PTSD), generalized anxiety disorder (GAD), obsessive-compulsive disorder (ODC), social and specific phobias, and panic disorder, are a major public health issue. A growing body of evidence suggests that glutamatergic neurotransmission may be involved in the biological mechanisms underlying stress response and anxiety-related disorders. The glutamatergic system mediates the acquisition and extinction of fear-conditioning. Thus, new drugs targeting glutamatergic neurotransmission may be promising candidates for new pharmacological treatments. In particular, N-methyl-d-aspartate receptors (NMDAR) antagonists (AP5, AP7, CGP37849, CGP39551, LY235959, NPC17742, and MK-801), NMDAR partial agonists (DCS, ACPC), α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate receptors (AMPARs) antagonists (topiramate), and several allosteric modulators targeting metabotropic glutamate receptors (mGluRs) mGluR1, mGluR2/3, and mGluR5, have shown anxiolytic-like effects in several animal and human studies. Several studies have suggested that polyamines (agmatine, putrescine, spermidine, and spermine) may be involved in the neurobiological mechanisms underlying stress-response and anxiety-related disorders. This could mainly be attributed to their ability to modulate ionotropic glutamate receptors, especially NR2B subunits. The aim of this review is to establish that glutamate neurotransmission and polyaminergic system play a fundamental role in the onset of anxiety-related disorders. This may open the way for new drugs that may help to treat these conditions.

Medial prefrontal cortex activation facilitates re-extinction of fear in rats

It has been suggested that reduced infralimbic (IL) cortical activity contributes to impairments of fear extinction. We therefore explored whether pharmacological activation of the IL would facilitate extinction under conditions it normally fails (i.e., immediate extinction). Rats received auditory fear conditioning 1 h before extinction training. Immediately prior to extinction, rats received microinfusions into the IL of the GABA(A) receptor antagonist, picrotoxin, or the NMDA receptor partial agonist, D-cycloserine. Although neither drug facilitated extinction, they both facilitated the subsequent re-extinction of fear when animals were trained in a drug-free state, suggesting that activating the IL primes behavioral extinction.

Advances in pharmacotherapy for pediatric anxiety disorders

Pediatric anxiety disorders are prevalent, chronic, and often lead to significant impaired functioning that impacts both short- and long-term outcomes for children and adolescents. Treatment options include pharmacotherapy and psychosocial interventions. This presentation will review treatment advances specifically for pharmacotherapy. Current research supports serotonin reuptake inhibitors as the medication class to be the first-line treatment option for pediatric anxiety disorders. Available evidence for the efficacy of other classes of medications will be reviewed, along with the available approaches to manage partial responders and nonresponders. The risks and benefits of pharmacotherapy will also be reviewed. In addition, recent research has shown the potential promise of novel agents that act upon other neural systems implicated in the development of pediatric anxiety disorders. Novel compounds that affect the glutamate system will be discussed.

Cognitive enhancers for anxiety disorders

Cognitive-behavioral therapy is an effective intervention for anxiety disorders. However, a significant number of people do not respond or only show partial response even after an adequate course of the treatment. Recent research has shown that the efficacy of the intervention can be improved by the use of cognitive enhancers that augment the core learning processes of cognitive-behavior therapy. This manuscript provides a review of the current state of cognitive enhancers for the treatment of anxiety disorders.

The Effects of Prior Cognitive Control Task Exposure on Responses to Emotional Tasks in Healthy Participants

Background: Recent advances have been made in the application of cognitive training strategies as interventions for mental disorders. One novel approach, cognitive control training (CCT), uses computer-based exercises to chronically increase prefrontal cortex recruitment. Activation of prefrontal control mechanisms have specifically been identified with attenuation of emotional responses. However, it is unclear whether recruitment of prefrontal resources alone is operative in this regard, or whether prefrontal control is important only in the role of explicit emotion regulation. This study examined whether exposure to cognitive tasks before an emotional challenge attenuated the effects of the emotional challenge. Aims: We investigated whether a single training session could alter participants' reactivity to subsequent emotional stimuli on two computer-based tasks as well as affect ratings made during the study. We hypothesized that individuals performing the Cognitive Control (CC) task as compared to those performing the Peripheral Vision (PV) comparison task would (1) report reduced negative affect following the mood induction and the emotion task, and (2) exhibit reduced reactivity (defined by lower affective ratings) to negative stimuli during both the reactivity and recovery phases of the emotion task and (3) show a reduced bias towards threatening information. Method: Fifty-nine healthy participants were randomized to complete CC tasks or PV, underwent a negative mood induction, and then made valence and arousal ratings for IAPS images, and completed an assessment of attentional bias. Results: Results indicated that a single-session of CC did not consistently alter participants' responses to either task. However, performance on the CC tasks was correlated on subsequent ratings of emotional images. Conclusions: While overall these results do not support the idea that affective responding is altered by making healthy volunteers use their prefrontal cortex before the affective task, they are discussed in the context of study design issues and future research directions.

The COMTval158met polymorphism is associated with symptom relief during exposure-based cognitive-behavioral treatment in panic disorder

BACKGROUND

Cognitive behavioral therapy (CBT) represents a learning process leading to symptom relief and resulting in long-term changes in behavior. CBT for panic disorder is based on exposure and exposure-based processes can be studied in the laboratory as extinction of experimentally acquired fear responses. We have recently demonstrated that the ability to extinguish learned fear responses is associated with a functional genetic polymorphism (COMTval158met) in the COMT gene and this study was aimed at transferring the experimental results on the COMTval158met polymorphism on extinction into a clinical setting.

METHODS

We tested a possible effect of the COMTval158met polymorphism on the efficacy of CBT, in particular exposure-based treatment modules, in a sample of 69 panic disorder patients.

RESULTS

We present evidence that panic patients with the COMTval158met met/met genotype may profit less from (exposure-based) CBT treatment methods as compared to patients carrying at least one val-allele. No association was found with the 5-HTTLPR/rs25531 genotypes which is presented as additional material.

CONCLUSIONS

We were thus able to transfer findings on the effect of the COMTval158met polymorphism from an experimental extinction study obtained using healthy subjects to a clinical setting. Furthermore patients carrying a COMT val-allele tend to report more anxiety and more depression symptoms as compared to those with the met/met genotype. Limitations of the study as well as possible clinical implications are discussed.

TRIAL REGISTRATION

Clinical Trial Registry name: Internet-Versus Group-Administered Cognitive Behavior Therapy for Panic Disorder (IP2). Registration Identification number: NCT00845260, http://www.clinicaltrials.gov/ct2/show/NCT00845260.

Structural determinants of D-cycloserine efficacy at the NR1/NR2C NMDA receptors

We have studied relative efficacies of NR1 agonists glycine and d-cycloserine (DCS), and found efficacy to be dependent on the NR2 subunit. DCS shows partial agonism at NR1/NR2B but has higher relative efficacy than glycine at NR1/NR2C receptor. Molecular dynamics (MD) simulations of the NR1/NR2B and NR1/NR2C agonist binding domain dimer suggest only subtle differences in the interactions of DCS with NR1 binding site residues relative to glycine. The most pronounced differences were observed in the NR1/NR2C simulation between the orientation of helices F and G of the NR1 subunit. Interestingly, Helix F was previously proposed to influence receptor gating and to adopt an orientation depending on agonist efficacy. MD simulations and site-directed mutagenesis further suggest a role for residues at the agonist binding domain dimer interface in regulating DCS efficacy. To relate the structural rearrangements to receptor gating, we recorded single-channel currents from outside-out patches containing a single active NR1/NR2C receptor. DCS increased the mean open time and open probability of NR1/NR2C receptors compared with glycine. Maximum likelihood fitting of a gating model for NR1/NR2C receptor activation to the single-channel data suggests that DCS specifically accelerates the rate constant governing a fast gating step and reduces the closing rate. These changes appear to reflect a decreased activation energy for a pregating step and increased stability of the open states. We suggest that the higher efficacy of DCS at NR1/NR2C receptors involves structural rearrangements at the dimer interface and an effect on NR1/NR2C receptor pregating conformational changes.

Genetic disruptions of Drosophila Pavlovian learning leave extinction learning intact

Individuals who experience traumatic events may develop persistent posttraumatic stress disorder. Patients with this disorder are commonly treated with exposure therapy, which has had limited long-term success. In experimental neurobiology, fear extinction is a model for exposure therapy. In this behavioral paradigm, animals are repeatedly exposed in a safe environment to the fearful stimulus, which leads to greatly reduced fear. Studying animal models of extinction already has lead to better therapeutic strategies and development of new candidate drugs. Lack of a powerful genetic model of extinction, however, has limited progress in identifying underlying molecular and genetic factors. In this study, we established a robust behavioral paradigm to study the short-term effect (acquisition) of extinction in Drosophila melanogaster. We focused on the extinction of olfactory aversive 1-day memory with a task that has been the main workhorse for genetics of memory in flies. Using this paradigm, we show that extinction can inhibit each of two genetically distinct forms of consolidated memory. We then used a series of single-gene mutants with known impact on associative learning to examine the effects on extinction. We find that extinction is intact in each of these mutants, suggesting that extinction learning relies on different molecular mechanisms than does Pavlovian learning.

Pharmacological enhancement of behavioral therapy: focus on posttraumatic stress disorder

Improved efficacy in the treatment of posttraumatic stress disorder (PTSD) and other anxiety disorders is urgently needed. Traditional anxiety treatments of hypnosis and psychodynamic therapy may be of some help, but uncontrolled studies lead to inconclusive results on the efficacy of these treatment techniques. There is a larger literature supporting the efficacy of cognitive-behavioral procedures with PTSD, including prolonged exposure therapy, eye movement desensitization and reprocessing, and anxiety management techniques. The cutting-edge technology of virtual reality-based exposure therapy for PTSD is particularly exciting. To further build on effective psychosocial treatments, current pharmacological augmentation approaches to emotional learning are being combined with psychotherapy. In particular, D-cycloserine, a partial NMDA agonist, has shown to be effective in facilitating the exposure/extinction therapy to improve the efficacy of treating anxiety disorders, and may guide the way for new pharmacological enhancements of behavioral therapy.

Propranolol and D-cycloserine as adjunctive medications in reducing dental fear in sedation practice

Extensive research and clinical experience have demonstrated the usefulness of sedation in helping fearful patients receive dental treatment, particularly when they have urgent treatment needs. In addition, the efficacy of behavioural programmes for managing dental fears is well established. While often these two approaches are seen as oppositional, our work in Seattle, Morgantown and at King's College London Dental Institute demonstrates the complementarity of the two approaches. Using the example of two compounds, one very familiar, propranolol, and one that has recently become of interest, D-cycloserine, we wish to illustrate the manner in which these medications can be used to enhance behavioural approaches to managing dental anxiety.

D-cycloserine into the BLA reverses the impairing effects of exposure to stress on the extinction of contextual fear, but not conditioned taste aversion

We investigated whether the N-methyl-D-aspartate (NMDA) receptor partial agonist D-cycloserine (DCS, 20 microg/side) microinfused into the basolateral amygdala (BLA) would reverse stress-induced impairment of extinction in two aversive learning paradigms: contextual fear conditioning and conditioned taste aversion (CTA). We found that DCS in the BLA show differential involvement in the extinction of these two paradigms and in its modulation of stress-induced impairment of extinction. This may suggest that the dysfunctional extinction of fear and taste aversion following exposure to a stressful experience may be modulated by different mechanisms.

First-line treatment: a critical appraisal of cognitive behavioral therapy developments and alternatives

In this article, the authors assess the successes, remaining challenges, and new developments in cognitive behavioral therapy (CBT) for anxiety disorders. They define CBT, examine treatment components, review treatment efficacy, and discuss the challenges of attrition, long-term follow-up, co-occurring/comorbid disorders, limited treatment comparisons, treatment mediators, and broader implementation. In addition, they present recent developments in cognitive behavioral therapy for anxiety disorders, including linking exposure therapy to basic science, mindfulness and acceptance-based treatments, and unified or transdiagnostic treatment protocols.

Psychotherapy for obsessive-compulsive disorder

Cognitive-behavioral therapy (CBT) with exposure and response prevention is a first-line intervention for adult and childhood obsessive-compulsive disorder. Methodologically rigorous controlled trials have suggested that benefits from CBT exceed those from placebo and attention-control conditions and have similar or greater efficacy than serotonergic monotherapy. This article reviews the nature of CBT and associated outcome data, highlighting recent empiric findings in the treatment literature.

The effects of yohimbine and amphetamine on fear expression and extinction in rats

RATIONALE

Psychostimulants, such as yohimbine and amphetamine, can enhance learning and memory. Extinction of conditioned fear involves new learning, so we asked whether psychostimulants could enhance this learning. Previous work suggests that yohimbine facilitates extinction, using freezing as a fear measure. However, psychostimulant-induced alterations in locomotion can confound freezing measurements. Furthermore, the effects of amphetamine on fear extinction have never been examined.

OBJECTIVE

We evaluated the effectiveness of yohimbine and amphetamine in enhancing fear extinction. In addition to freezing, we measured bar-press suppression, which is less sensitive to changes in locomotion. We asked: Do psychostimulants reduce fear during extinction training when drug is present? Does learning extinction with psychostimulants result in better extinction retention?

MATERIALS AND METHODS

Rats received fear conditioning on day 1 followed by partial extinction training on days 2 and 3. Yohimbine (1.0, 2.0, or 5.0 mg/kg, i.p.), amphetamine (1.0 mg/kg, i.p.), or vehicle were injected prior to extinction on day 2.

RESULTS

Yohimbine dose-dependently reduced freezing during extinction training on day 2, whereas bar-press suppression was reduced at the highest dose only. When tested drug-free, yohimbine-treated rats showed equivalent levels of freezing and suppression to controls. Amphetamine also decreased freezing during extinction, but did not decrease suppression. During the drug-free test, there was no difference between amphetamine-treated rats and controls in either measure.

CONCLUSIONS

Although yohimbine and amphetamine are capable of decreasing freezing, neither drug strengthened retention of fear extinction. Based on these rodent findings, psychostimulants may not be suitable adjuncts to extinction-based therapies for the treatment of anxiety disorders.

Augmenting in vivo exposure with fear antagonistic actions: a preliminary test

The current study investigated the efficacy of an exposure augmentation strategy in which the phobic individual is encouraged to enact actions that are in direct opposition to the fear action tendencies associated with acrophobia. Participants (N=88) meeting DSM-IV criteria for specific phobia (acrophobia) were randomized to (a) exposure with oppositional actions (E+OA), (b) exposure only (EO), (c) a credible placebo consisting of pulsed audio-photic stimulation (APS), or (d) a waitlist control (WLC). Treatment consisted of six, 6-min exposure trials. Participants were assessed with questionnaire, behavioral, and physiologic measures at pre- and posttreatment, and at a 1-month follow-up session. Participants receiving E+OA showed significantly greater improvement on behavioral and questionnaire measures than those in the other 3 conditions at both posttreatment and follow-up. Further, whereas treatment improvement generalized to an untrained context for those receiving E+OA, such was not the case for EO- and APS-treated participants. Findings suggest augmenting exposure with oppositional actions may enhance treatment outcome and thus warrant additional investigation with clinical samples.

The facilitative effects of D-cycloserine on extinction of a cocaine-induced conditioned place preference can be long lasting and resistant to reinstatement

RATIONALE AND OBJECTIVE

The N-methyl-D-aspartate receptor agonist, D-cycloserine (DCS), accelerates extinction of a cocaine-induced conditioned place preference (CPP) when given after daily extinction tests. Here, we studied the effects of DCS in rats given spaced-extinction sessions at 3- or 7-day intervals using two different extinction procedures.

MATERIALS AND METHODS

Rats were trained on a CPP (four cocaine, 10 mg/kg, i.p., and four saline pairings with one of two compartments). Immediately following the CPP test and all extinction tests (days 4, 7, 10, and 24, experiment 1), DCS (15 mg/kg, i.p.) or saline was administered. In experiment 2, extinction was conducted by exposing rats to the drug-paired cues for 2 or 20 min, three times, at 7-day intervals followed immediately by DCS or saline. After extinction, tests for retention and cocaine-induced reinstatement were given.

RESULTS

In experiment 1, rats given DCS lost the cocaine CPP after one extinction trial, an effect that persisted for 2 weeks after the last DCS injection and that was resistant to cocaine-induced reinstatement. In experiment 2, extinction was facilitated by DCS compared to saline when rats received 2-min exposures to the conditioned stimulus. Longer 20-min exposures minus/plus repeated testing led to retention of extinction in both groups regardless of DCS treatment.

CONCLUSIONS

Extinction of appetitive conditioning is facilitated by DCS after 1-3 post-spaced trial injections, and retention is lasting and resistant to reinstatement. The facilitative effects appear early in extinction, but when extinction procedures are intensive, DCS appears to have no additional benefit.

Psychobiology of anxiety disorders and obsessive-compulsive spectrum disorders

Obsessive-compulsive disorder is currently classified as an anxiety disorder. However, there is growing interest in the concept of an obsessive-compulsive spectrum of disorders (OCSDs). The relationship between anxiety disorders and OCSDs has been questioned. The psychobiology of anxiety disorders and OCSDs is briefly reviewed in this article. While there appear to be several distinct contrasts in the underlying psychobiology of these conditions, there is also evidence of overlapping mechanisms. In addition, there are crucial gaps in our current database, confounding nosological decision-making. Conceptualizing various anxiety disorders and putative OCSDs as lying within a broader spectrum of emotional disorders may be useful. However, clinicians must also recognize that individual anxiety and obsessive-compulsive spectrum conditions, including disorders characterized by body-focused repetitive behaviors, have distinct psychobiological underpinnings and require different treatment approaches.

A meta-analysis of D-cycloserine and the facilitation of fear extinction and exposure therapy

BACKGROUND

Translational research suggests that D-cycloserine (DCS), a partial N-methyl-D-aspartate (NMDA) receptor agonist, might facilitate fear extinction and exposure therapy by either enhancing NMDA receptor function during extinction or by reducing NMDA receptor function during fear memory consolidation. This article provides a quantitative review of DCS-augmented fear extinction and exposure therapy literature.

METHODS

English-language journal articles that examined DCS augmented with fear extinction or exposure therapy were identified through public databases from June 1998 through September 2007, through references of originally identified articles and contact with DCS investigators. Data were extracted for study author, title, and year; trial design; type of subject (animal vs. human; clinical vs. nonclinical); sample size, DCS dose, and timing in relation to extinction/exposure procedures; dependent variable; group means and SDs at post-extinction/exposure; and follow-up outcome.

RESULTS

D-cycloserine enhances fear extinction/exposure therapy in both animals and anxiety-disordered humans. Gains generally were maintained at follow-up, although some lessening of efficacy was noted. D-cycloserine was more effective when administered a limited number of times and when given immediately before or after extinction training/exposure therapy.

CONCLUSIONS

This meta-analysis suggests that DCS is a useful target for translational research on augmenting exposure-based treatment via compounds that impact neuroplasticity. D-cycloserine 's major contribution to exposure-based therapy might be to increase its speed or efficiency, because the effects of DCS seem to decrease over repeated sessions. This information might guide translational researchers in discovering more selective and/or effective agents that effectively enhance (or reduce) NMDA receptor function.

Role of L-type Ca2+ channel isoforms in the extinction of conditioned fear

Dihydropyridine (DHP) L-type Ca(2+) channel (LTCC) antagonists, such as nifedipine, have been reported to impair the extinction of conditioned fear without interfering with its acquisition. Identification of the LTCC isoforms mediating this DHP effect is an essential basis to reveal their role as potential drug targets for the treatment of specific anxiety disorders. Ca(V)1.2 and Ca(V)1.3 are the predominant LTCCs in the mammalian brain. However, since no isoform-selective DHP blockers are available, their individual contribution to fear memory extinction is unknown. We used a novel mouse model expressing DHP-insensitive Ca(V)1.2 LTCCs (Ca(V)1.2DHP(-/-) mice) to address this question. In line with previous studies, wild-type (WT) mice treated with systemic nifedipine displayed markedly impaired fear extinction. This DHP effect was completely abolished in Ca(V)1.2DHP(-/-) mice, indicating that it is mediated by Ca(V)1.2, but not by Ca(V)1.3 LTCCs. Supporting this conclusion, Ca(V)1.3-deficient mice (Ca(V)1.3(-/-)) showed extinction identical to the respective WT mice. The inhibition of fear extinction was not observed after intracerebroventricular (i.c.v.) application of different doses of nifedipine, suggesting that this effect is secondary to inhibition of peripheral Ca(V)1.2 channels. The LTCC activator BayK, which lacks neurotoxic effects in Ca(V)1.2DHP(-/-) mice, did not influence the extinction time course. In summary, we demonstrate that LTCC signaling through the Ca(V)1.2 isoform of LTCCs interferes with fear memory extinction, presumably via a peripherally mediated mechanism. Activation of other LTCC isoforms (predominantly Ca(V)1.3) is not sufficient to accelerate extinction of conditioned fear in mice.

Combining and sequencing medication and cognitive-behaviour therapy for childhood anxiety disorders

Despite the absence of data on the efficacy of combination therapy (i.e., psychosocial and medication) for the treatment of anxiety disorders in youths, clinicians in clinical practice often utilize this treatment approach. This paper discusses issues related to sequencing, combining, and integrating cognitive behavioural and pharmacological interventions for anxiety disorders in children and adolescents. We briefly summarize the empirical evidence for mono and combination therapy and raise a variety of issues that should be considered when making treatment decisions. Finally, we present an integrated treatment model to facilitate the delivery of a comprehensive treatment approach across care providers. These suggestions are geared toward optimizing clinical outcomes for anxious youths.

Recent trends in the study of specific phobias

PURPOSE OF REVIEW

Specific phobias are prevalent and often disabling anxiety disorders. The present review examines relevant investigations that have been published during the last 2 years on major aspects of this group of disorders.

RECENT FINDINGS

Recent studies have come mainly from epidemiology, brain imagery and cognitive-behavioral therapy, including virtual reality exposure therapy.

SUMMARY

Studies published in the last 2 years confirm the high prevalence of specific phobias in the general population and provide new insights into the mechanisms underlying the fear reaction after exposure to a phobic stimulus.

Neural mechanisms of extinction learning and retrieval

Emotional learning is necessary for individuals to survive and prosper. Once acquired, however, emotional associations are not always expressed. Indeed, the regulation of emotional expression under varying environmental conditions is essential for mental health. The simplest form of emotional regulation is extinction, in which conditioned responding to a stimulus decreases when the reinforcer is omitted. Two decades of research on the neural mechanisms of fear conditioning have laid the groundwork for understanding extinction. In this review, we summarize recent work on the neural mechanisms of extinction learning. Like other forms of learning, extinction occurs in three phases: acquisition, consolidation, and retrieval, each of which depends on specific structures (amygdala, prefrontal cortex, hippocampus) and molecular mechanisms (receptors and signaling pathways). Pharmacological methods to facilitate consolidation and retrieval of extinction, for both aversive and appetitive conditioning, are setting the stage for novel treatments for anxiety disorders and addictions.

Emerging anxiolytics

Anxiety disorders are the most common of the psychiatric disorders and are also associated with significant economic costs and impaired work productivity. The first-line pharmacotherapy of pharmatherapy for a number of anxiety disorders comprises selective serotonin re-uptake inhibitors (SSRIs) and serotonin and noradrenaline re-uptake inhibitors (SNRIs). Benzodiazepines are still widely used for the treatment of several anxiety disorders. Although these agents are effective, many patients are treatment-refractory and more effective, better tolerated medications are required. This paper discusses the understandings of mechanisms involved in the anxiety disorders and reviews emerging medications. Mechanisms underlying the use of d-cycloserine, second generation antipsychotics and beta-blockers are particularly exciting.

Enhancing exposure-based therapy from a translational research perspective

Combining an effective psychological treatment with conventional anxiolytic medication is typically not more effective than unimodal therapy for treating anxiety disorders. However, recent advances in the neuroscience of fear reduction have led to novel approaches for combining psychological therapy and pharmacological agents. Exposure-based treatments in humans partly rely on extinction to reduce the fear response in anxiety disorders. Animal studies have shown that D-cycloserine (DCS), a partial agonist at the glycine recognition site of the glutamatergic N-methyl-D-aspartate receptor facilitates extinction learning. Similarly, recent human trials have shown that DCS enhances fear reduction during exposure therapy of some anxiety disorders. This article discusses the biological and psychological mechanisms of extinction learning and the therapeutic value of DCS as an augmentation strategy for exposure therapy. Areas of future research will be identified.

Modulation of fear and anxiety by the endogenous cannabinoid system

The last decade has witnessed remarkable progress in the understanding of the mammalian cannabinoid system, from the cloning of the endogenous cannabinoid receptor to the discovery of new pharmacologic compounds acting on this receptor. Current and planned studies in humans include compounds with effects ranging from direct antagonists to inhibitors of reuptake and breakdown. This progress has been accompanied by a much greater understanding of the role of the cannabinoid system in modulating the neural circuitry that mediates anxiety and fear responses. This review focuses on the neural circuitry and pharmacology of the cannabinoid system as it relates to the acquisition, expression, and extinction of conditioned fear as a model of human anxiety. Preclinical studies suggest that these may provide important emerging targets for new treatments of anxiety disorders.