Differential effects of alprazolam on the baseline and fear-potentiated startle reflex in humans: a dose-response study

Pharmacological modulation of conditioned fear in the fear-potentiated startle test: a systematic review and meta-analysis of animal studies

RATIONALE AND OBJECTIVES

Fear conditioning is an important aspect in the pathophysiology of anxiety disorders. The fear-potentiated startle test is based on classical fear conditioning and over the years, a broad range of drugs have been tested in this test. Synthesis of the available data may further our understanding of the neurotransmitter systems that are involved in the expression of conditioned fear.

METHODS

Following a comprehensive search in Medline and Embase, we included 68 research articles that reported on 103 drugs, covering 56 different drug classes. The systematic review was limited to studies using acute, systemic drug administration in naive animals.

RESULTS

Qualitative data synthesis showed that most clinically active anxiolytics, but not serotonin-reuptake inhibitors, reduced cued fear. Anxiogenic drugs increased fear potentiation in 35% of the experiments, reduced fear potentiation in 29% of the experiments, and were without effect in 29% of the experiments. Meta-analyses could be performed for five drug classes and showed that benzodiazepines, buspirone, 5-HT1A agonists, 5-HT1A antagonists, and mGluR2,3 agonists reduced cued conditioned fear. The non-cued baseline startle response, which may reflect contextual anxiety, was only significantly reduced by benzodiazepines and 5-HT1A antagonists. No associations were found between drug effects and methodological characteristics, except for strain.

CONCLUSIONS

The fear-potentiated startle test appears to have moderate to high predictive validity and may serve as a valuable tool for the development of novel anxiolytics. Given the limited available data, the generally low study quality and high heterogeneity additional studies are warranted to corroborate the findings of this review.

Differential effects of the translocator protein 18 kDa (TSPO) ligand etifoxine and the benzodiazepine alprazolam on startle response to predictable threat in a NPU-threat task after acute and short-term treatment

RATIONALE

Benzodiazepines have been extensively investigated in experimental settings especially after single administration, which mostly revealed effects on unpredictable threat (U-threat) rather than predictable threat (P-threat). Given the need for pharmacological alternatives with a preferable side-effect profile and to better represent clinical conditions, research should cover also other anxiolytics and longer application times.

OBJECTIVES

The present study compared the acute and short-term effects of the translocator protein 18 kDa (TSPO) ligand etifoxine and the benzodiazepine alprazolam on P-threat and U-threat while controlling for sedation.

METHODS

Sixty healthy male volunteers, aged between 18 and 55 years, were randomly assigned to receive a daily dose of either 150 mg etifoxine, 1.5 mg alprazolam, or placebo for 5 days. On days 1 and 5 of intake, they performed a NPU-threat task including neutral (N), predictable (P), and unpredictable (U) conditions, while startle responsivity and self-reports were studied. Sedative effects were assessed using a continuous performance test.

RESULTS

Neither alprazolam nor etifoxine affected startle responsivity to U-threat on any of the testing days. While etifoxine reduced the startle response to P-threat on day 1 of treatment for transformed data, a contrary effect of alprazolam was found for raw values. No effects on self-reports and no evidence of sedation could be observed for either drug.

CONCLUSIONS

None of the anxiolytic substances had an impact on startle potentiation to U-threat even after several days of intake. The effects of the anxiolytics on startle responsivity to P-threat as well as implications for future studies are discussed.

Comparison of mouse models reveals a molecular distinction between psychotic illness in PWS and schizophrenia

Prader-Willi Syndrome (PWS) is a neurodevelopmental disorder caused by mutations affecting paternal chromosome 15q11-q13, and characterized by hypotonia, hyperphagia, impaired cognition, and behavioural problems. Psychotic illness is a challenging problem for individuals with PWS and has different rates of prevalence in distinct PWS genotypes. Previously, we demonstrated behavioural and cognitive endophenotypes of relevance to psychiatric illness in a mouse model for one of the associated PWS genotypes, namely PWS-IC, in which deletion of the imprinting centre leads to loss of paternally imprinted gene expression and over-expression of Ube3a. Here we examine the broader gene expression changes that are specific to the psychiatric endophenotypes seen in this model. To do this we compared the brain transcriptomic profile of the PWS-IC mouse to the PWS-cr model that carries a deletion of the PWS minimal critical interval spanning the snoRNA Snord116 and Ipw. Firstly, we examined the same behavioural and cognitive endophenotypes of relevance to psychiatric illness in the PWS-cr mice. Unlike the PWS-IC mice, PWS-cr exhibit no differences in locomotor activity, sensory-motor gating, and attention. RNA-seq analysis of neonatal whole brain tissue revealed a greater number of transcriptional changes between PWS-IC and wild-type littermates than between PWS-cr and wild-type littermates. Moreover, the differentially expressed genes in the PWS-IC brain were enriched for GWAS variants of episodes of psychotic illness but, interestingly, not schizophrenia. These data illustrate the molecular pathways that may underpin psychotic illness in PWS and have implications for potential therapeutic interventions.

Behavioral and Neurophysiological Signatures of Benzodiazepine-Related Driving Impairments

Impaired driving due to drug use is a growing problem worldwide; estimates show that 18-23.5% of fatal accidents, and up to 34% of injury accidents may be caused by drivers under the influence of drugs (Drummer et al., 2003; Walsh et al., 2004; NHTSA, 2010). Furthermore, at any given time, up to 16% of drivers may be using drugs that can impair one's driving abilities (NHTSA, 2009). Currently, drug recognition experts (DREs; law enforcement officers with specialized training to identify drugged driving), have the most difficult time with identifying drivers potentially impaired on central nervous system (CNS) depressants (Smith et al., 2002). The fact that the use of benzodiazepines, a type of CNS depressant, is also associated with the greatest likelihood of causing accidents (Dassanayake et al., 2011), further emphasizes the need to improve research tools in this area which can facilitate the refinement of, or additions to, current assessments of impaired driving. Our laboratories collaborated to evaluate both the behavioral and neurophysiological effects of a benzodiazepine, alprazolam, in a driving simulation (miniSim(TM)). This drive was combined with a neurocognitive assessment utilizing time synched neurophysiology (electroencephalography, ECG). While the behavioral effects of benzodiazepines are well characterized (Rapoport et al., 2009), we hypothesized that, with the addition of real-time neurophysiology and the utilization of simulation and neurocognitive assessment, we could find objective assessments of drug impairment that could improve the detection capabilities of DREs. Our analyses revealed that (1) specific driving conditions were significantly more difficult for benzodiazepine impaired drivers and (2) the neurocognitive tasks' metrics were able to classify "impaired" vs. "unimpaired" with up to 80% accuracy based on lane position deviation and lane departures. While this work requires replication in larger studies, our results not only identified criteria that could potentially improve the identification of benzodiazepine intoxication by DREs, but also demonstrated the promise for future studies using this approach to improve upon current, real-world assessments of impaired driving.

Tracking explicit and implicit long-lasting traces of fearful memories in humans

Recent accounts of Posttraumatic Stress Disorder (PTSD) suggest that the encoding of an episode within a fearful context generates different implicit and explicit memory representations. Whilst implicit memory traces include the associated emotional states, explicit traces include a recoding into an abstract or gist-based structural context of the episode. Theoretically, the long-term preservation of implicit memory traces may facilitate the often untreatable memory intrusions in PTSD. Here, we tracked in two experiments how implicit and explicit memory traces for fearful episodes dissociate and evolve over time. Subjects (N=86) were presented with semantically-related word-lists in a contextual fear paradigm and tested for explicit memories either immediately (i.e., 30 min) or after a delay (i.e., 1 or 2 weeks) with a verbal recognition task. Skin Conductance Response (SCR) was used to assess implicit memory responses. Subjects showed high memory accuracy for words when tested immediately after encoding. At test, SCR was higher during the presentation of verbatim but not gist-based words encoded in a fearful context, and remained unchanged after 2 weeks, despite subjects being unaware of words' encoding context. We found no clear evidence of accurate explicit memory traces for the fearful or neutral contexts of words presented during encoding, either 30 min or 2 weeks afterwards. These findings indicate that the implicit, but not the explicit, memory trace of a fearful context of an episode can be detected at long-term through SCR and is dissociated from the gist-based memory. They may have implicationstowards the understanding of how the processing of fearful memoriescould lead to PTSD.

Advancing the defensive explanation for anxiety disorders: lorazepam effects on human defense are systematically modulated by personality and threat-type

Clinically effective drugs against human anxiety and fear systematically alter the innate defensive behavior of rodents, suggesting that in humans these emotions reflect defensive adaptations. Compelling experimental human evidence for this theory is yet to be obtained. We report the clearest test to date by investigating the effects of 1 and 2 mg of the anti-anxiety drug lorazepam on the intensity of threat-avoidance behavior in 40 healthy adult volunteers (20 females). We found lorazepam modulated the intensity of participants' threat-avoidance behavior in a dose-dependent manner. However, the pattern of effects depended upon two factors: type of threat-avoidance behavior and theoretically relevant measures of personality. In the case of flight behavior (one-way active avoidance), lorazepam increased intensity in low scorers on the Fear Survey Schedule tissue-damage fear but reduced it in high scorers. Conversely, in the case of risk-assessment behavior (two-way active avoidance), lorazepam reduced intensity in low scorers on the Spielberger trait anxiety but increased it in high scorers. Anti-anxiety drugs do not systematically affect rodent flight behavior; therefore, we interpret this new finding as suggesting that lorazepam has a broader effect on defense in humans than in rodents, perhaps by modulating general perceptions of threat intensity. The different patterning of lorazepam effects on the two behaviors implies that human perceptions of threat intensity are nevertheless distributed across two different neural streams, which influence effects observed on one-way or two-way active avoidance demanded by the situation.

An updated overview of animal models in neuropsychiatry

Animal models are vital tools to study the genetic, molecular, cellular, and environmental parameters involved in several neuropsychiatric disorders. Over the years, these models have expanded our understanding of the pathogenesis of many neuropsychiatric disorders and neurodegenerative diseases. Although animal models have been widely used in psychiatry, and despite several years of extensive research with these models, their validity is still being investigated and presents a challenge to both investigators and clinicians as well. In this concise review, we will describe the most common animal models utilized in neuropsychiatry, including animal models of depression, anxiety, and psychosis. In addition, we will also discuss the validity and reliability of these models and current challenges in this domain. Furthermore, this work will discuss the role of gene-environment interaction as an additional contributing factor that modulates neuropsychological outcome and its implication on animal models. This overview will give a succinct summary of animal models in psychiatry which will be useful both to the seasoned researcher, as well as novices in the field.

Effects of anxiolytic treatment on potentiated startle during aversive image anticipation

OBJECTIVE

Heightened anticipation of future events has been characterized as a feature of certain anxiety disorders. In functional magnetic resonance imaging studies, anticipation of fearful/threatening images has been shown to robustly activate the insular cortex and amygdala in healthy subjects, in subjects with high trait anxiety, and in some with anxiety disorders. Blood oxygenation level dependent activation in response to negative image anticipation is also sensitive to anxiolytic treatment, suggesting that image anticipation probes anxiety systems. It is not clear, however, if behavioral responses to image anticipation are also sensitive to anxiolytics. This study tested the hypothesis that anxiety behaviors during anticipation of negative images are sensitive to anxiolytic treatment.

METHOD

This study examined the effects of alprazolam and pregabalin treatment on potentiated startle during affective image anticipation.

RESULTS

There was an effect of anticipation type (negative versus neutral versus positive) on startle reactivity and subjective ratings, suggesting that the task was effective in assaying negative anticipatory arousal. Both treatments significantly reduced overall startle magnitude. However, neither treatment specifically affected potentiated startle during aversive anticipation.

CONCLUSION

These data suggest that potentiated startle in response to anticipation of aversive images is not sensitive to anxiolytic treatments in a healthy population, limiting its use as a predictive model of anxiolytic activity. This article is a US Government work and is in the public domain in the USA.

Phasic and sustained fear are pharmacologically dissociable in rats

Previous findings suggest differences in the neuroanatomical substrates of short- (seconds) vs longer-duration (minutes) fear responses. We now report that phasic and sustained fear can also be differentiated pharmacologically, based on their response to several treatments that either are or are not clinically effective anxiolytics. For these experiments, short- or long-duration clicker stimuli were paired with footshock. Acoustic startle amplitude was later measured in the absence of the clicker, or within seconds (phasic fear) or minutes (sustained fear) of its onset. Before testing, rats received a single injection of vehicle, the benzodiazepine chlordiazepoxide, the 5HT(1A) agonist and dopamine D2 antagonist buspirone, the selective serotonin reuptake inhibitor fluoxetine, or a 3-week treatment with either vehicle or fluoxetine. Chlordiazepoxide blocked sustained, but not phasic startle increases. Acute buspirone, which is not anxiolytic in human beings, did not affect sustained startle increases, but did disrupt phasic increases. Chronic fluoxetine blocked sustained startle increases and unreliably reduced phasic increases; acute fluoxetine affected neither. The results indicate that phasic and sustained fear responses can be pharmacologically dissociated, further validating this distinction, and suggest that sustained startle increases may be especially useful as anxiety models and anxiolytic screens.

Anxiolytic-like effects of the neurokinin 1 receptor antagonist GR-205171 in the elevated plus maze and contextual fear-potentiated startle model of anxiety in gerbils

Gerbils show a neurokinin (NK)1 receptor pharmacological profile, which is similar to that observed in humans, and thus have become a commonly used species to test efficacy of NK1 receptor antagonists. The aim of this study was to determine whether systemic administration of the NK1 receptor antagonist GR-205171 produced anxiolytic-like effects in the elevated plus maze and in a novel contextual conditioned fear test using fear-potentiated startle (FPS). On the elevated plus maze, treatment with GR-205171 at 0, 0.3, 1.0, and 5.0 mg/kg doses, 30 min before testing produced anxiolytic-like effects in an increasing dose-response manner as measured by the percentage of open arm time and percentage of open arm entries. For contextual fear conditioning, gerbils were given 10 unsignaled footshocks (0.6 mA) at a 2-min variable interstimulus interval in a distinctive training context. Twenty-four hours after training, gerbils received treatment of GR-205171 at 0, 0.3, 1.0, and 5.0 mg/kg doses, 30 min before testing in which startle was elicited in the same context in which they were trained. Contextual FPS was defined as an increase in startle over pretraining baseline values. All drug dose levels (0.3, 1.0, and 5.0 mg/kg) significantly attenuated contextual FPS when compared with the vehicle control group. A control group, which received testing in a different context, showed little FPS. These findings support other evidence for anxiolytic activity of NK1 receptor antagonists and provide a novel conditioned fear test that may be an appropriate procedure to test other NK1 antagonists for preclinical anxiolytic activity in gerbils.

Reduction of fear-potentiated startle by benzodiazepines in C57BL/6J mice

RATIONALE

Anxiety disorders affect 18% of the United States adult population annually. Recent surges in the diagnosis of posttraumatic stress disorder (PTSD) from combat-exposed veterans have prompted an urgent need to understand the pathophysiology underlying this debilitating condition.

OBJECTIVES

Anxiety and fear responses are partly modulated by gamma aminobutyric acid type A (GABA(A)) receptor-mediated synaptic inhibition; benzodiazepines potentiate GABAergic inhibition and are effective anxiolytics. Many genetically modified mouse lines are generated and/or maintained on the C57BL/6J background, a strain where manipulation of anxiety-like behavior using benzodiazepines is difficult. Fear-potentiated startle (FPS), a test of conditioned fear, is a useful preclinical tool to study PTSD-like responses but has been difficult to establish in C57BL/6J mice.

METHODS

We modified several FPS experimental parameters and developed a paradigm to assess conditioned fear in C57BL/6J mice. The 6-day protocol consisted of three startle Acclimation days, a Pre-Test day followed by Training and Testing for FPS. Subject responses to the effects of three benzodiazepines were also examined.

RESULTS

C57BL/6J mice had low levels of unconditioned fear assessed during Pre-Test (15-18%) but showed robust FPS (80-120%) during the Test session. Conditioned fear responses extinguished over repeated test sessions. Administration of the benzodiazepines alprazolam (0.5 and 1 mg/kg, i.p.), chlordiazepoxide (5 and 10 mg/kg, i.p.), and diazepam (1, 2, and 4 mg/kg, i.p.) significantly reduced FPS to Pre-Test levels.

CONCLUSIONS

We used a modified and pharmacologically-validated paradigm to assess FPS in mice thereby providing a powerful tool to examine the neurobiology of PTSD in genetic models of anxiety generated on the C57BL/6J background.

Alterations in neonatal neurosteroids affect exploration during adolescence and prepulse inhibition in adulthood

Allopregnanolone (AlloP) is a neurosteroid that plays an important role during neural development. Alterations of endogenous neonatal allopregnanolone levels alter the localisation and function of GABA neurons in the adult brain and affect behaviour in adulthood. We have carried out research into the effects of an increase (AlloP administration) or a decrease (administration of finasteride, inhibitor of the AlloP synthesis) of neonatal AlloP levels during the fifth to ninth postnatal days in male Wistar rats on the novelty exploration (Boissier test) at adolescent ages (40 and 60 days old), and on the prepulse inhibition achievement in adulthood (85 days). We also investigated the role of a GABA(A) modulator (midazolam, 1, 1.75 or 2.5mg/kg body weight) in the long-lasting behavioural changes in adulthood (85 days). Results indicate that neonatal finasteride decreases both novelty-exploration (head-dipping and locomotion) and anxiety-relevant scores (the distance travelled in and the number of entries into the central zone) at adolescent age, along with a reduction in body weight and general locomotion. Also, neonatal AlloP administration decreases prepulse inhibition in adulthood. Prepulse inhibition disruption was only partially reproduced decreasing the neonatal AlloP levels by means of finasteride administration. Although there was no interaction between neonatal neurosteroid manipulation and adult benzodiazepine treatments, the effects of midazolam were dose-dependent: the lowest dose of midazolam increased whereas the highest disrupted the expected progressive reduction of the startle response (and the consequent improvement of the PPI percentage) after the gradual increase in prepulse intensity. Reduced prepulse inhibition of startle provides evidence of deficient sensorimotor gating in several disorders, including schizophrenia. Alterations of AlloP levels during maturation could partly explain the inter-individual differences shown by adult subjects in response to novelty (exploration) and in the sensorimotor gating and prepulse inhibition. Also, abrupt changes in neonatal levels of AlloP could be related to a susceptibility to neurodevelopmental disorders.

Method development studies for repeatedly measuring anxiolytic drug effects in healthy humans

Human experimental models for anxiety may serve as translational tools for translating preclinical psychopharmacological investigations into human studies. For the evaluation of drugs of which pharmacokinetics and pharmacodynamics are unidentified, repeating measurements after drug administration is necessary for characterising the time course of drug effects. In experiment 1, a threat-of-shock paradigm and adaptations of the Trier mental arithmetic test and the Stroop colour naming test were repeated four times within a day to evaluate whether anxiety responses to this test battery remain stable after repeated testing. This procedure was repeated on 4 days in a second experiment to evaluate suitability of the paradigm for a crossover design with multiple sessions. Results indicate no reductions or changes in fear potentiated startle, the main outcome measure for the threat paradigm, over test sessions or days. Skin conductance responses and subjective ratings under threat-of-shock showed significant fluctuations but also no systematic decline over time. Finally, the threat paradigm and Stroop test resulted in small increases in reported state anxiety while mental arithmetic produced larger effects that diminished after the first test day. It is concluded that especially the startle paradigm could be a useful new instrument for screening new anxiolytic drugs.

Behavioral correlates of anxiety

The tripartite model of anxiety includes three response domains: cognitive (most often identified by self report), behavioral, and physiological. Each is suggested to bring a separate element of response characteristics and, in some cases, potentially independent underlying mechanisms to the construct of anxiety. In this chapter, commonly used behavioral correlates of anxiety in human research, including startle reflex, attentional bias, and avoidance tasks, as well as future tasks using virtual reality technology will be discussed. The focus will be in evaluating their translational utility supported by (1) convergent validity with other measures of anxiety traits or anxiety disorders, (2) their use in identifying neural and genetic mechanisms of anxiety, and (3) ability to predict treatment efficacy.

Phasic vs sustained fear in rats and humans: role of the extended amygdala in fear vs anxiety

Data will be reviewed using the acoustic startle reflex in rats and humans based on our attempts to operationally define fear vs anxiety. Although the symptoms of fear and anxiety are very similar, they also differ. Fear is a generally adaptive state of apprehension that begins rapidly and dissipates quickly once the threat is removed (phasic fear). Anxiety is elicited by less specific and less predictable threats, or by those that are physically or psychologically more distant. Thus, anxiety is a more long-lasting state of apprehension (sustained fear). Rodent studies suggest that phasic fear is mediated by the amygdala, which sends outputs to the hypothalamus and brainstem to produce symptoms of fear. Sustained fear is also mediated by the amygdala, which releases corticotropin-releasing factor, a stress hormone that acts on receptors in the bed nucleus of the stria terminalis (BNST), a part of the so-called 'extended amygdala.' The amygdala and BNST send outputs to the same hypothalamic and brainstem targets to produce phasic and sustained fear, respectively. In rats, sustained fear is more sensitive to anxiolytic drugs. In humans, symptoms of clinical anxiety are better detected in sustained rather than phasic fear paradigms.

Recurrence of major depressive disorder is predicted by inhibited startle magnitude while recovered

BACKGROUND

Major depressive disorder, for some, follows a chronic relapsing course. However, no reliable marker has been established that allows the identification of this sub-group of patients. Preliminary findings suggest that baseline startle magnitude may be such a marker. This study evaluated whether differences in baseline startle magnitude during remission could prospectively predict depressive symptomatology and recurrence.

METHODS

A group of previously depressed individuals (n=25), who were in full remission at the time of testing, had their startle reflex measured via surface EMG electrodes on the left orbicularis oculi muscle. These people were then followed-up 2 years later and their depressive symptomatology during the intervening period was assessed using the psychiatric ratings scale of the Longitudinal Interval Follow-up Evaluation (LIFE; [Keller, M.B., Lavori, P.W., Friedman, B., Nielsen, E., Endicott, J., McDonald-Scott, P., et al. (1987). The Longitudinal Interval Follow-up Evaluation. A comprehensive method for assessing outcome in prospective longitudinal studies. Arch. Gen. Psychiatry, 44(6), 540-548]) and incidents of recurrence assessed using the Structured Clinical Interview for DSM-IV (SCID-I/P; [First, M.B., Spitzer, R.L., Gibbon, M., & Williams, J.B.W. (2001). Structured clinical interview for axis 1 DSM-IV disorders. New York: New York State Psychiatric Institute]).

RESULTS

It was found that a relatively attenuated startle response at initial assessment was strongly predictive of both depressive symptomatology and those who would experience relapse.

LIMITATIONS

This study has a relatively small sample size that limits the degree to which a thorough co-variant analysis can be conducted and also makes the analysis of gender-based difference impracticable. Additionally, as no healthy control group is included, we report a relative rather than absolute attenuation of startle to be indicative of symptom severity and recurrence proclivity.

CONCLUSIONS

These preliminary findings suggest that an attenuated startle response may have utility as an endophenotypic marker of risk for recurrence of Major Depression and residual sub-syndromal symptomatology. Such a marker may facilitate the early identification and treatment of those most at risk of recurrent Major Depression.

Validating a human model for anxiety using startle potentiated by cue and context: the effects of alprazolam, pregabalin, and diphenhydramine

BACKGROUND

Fear-potentiated startle has been suggested as a translational model for evaluating efficacy of anxiolytic compounds in humans. Several known anxiolytic compounds have been tested as well as several putative anxiolytics. Because results of these studies have been equivocal, the aim of the present study was to examine another pharmacological permutation of the human potentiated startle model by comparing two anxiolytic agents to a non-anxiolytic sedative and placebo.

METHODS

Twenty healthy volunteers participated in a double-blind, placebo-controlled, cross-over study with four sessions in which they received single doses of the anxiolytics alprazolam (1 mg) and pregabalin (200 mg), as well as diphenhydramine (50 mg) as a non-anxiolytic sedative control and placebo. The design included a cued shock condition that presumably evokes fear and an unpredictable shock context condition presumably evoking anxiety.

RESULTS

None of the treatments reliably reduced either fear- or anxiety-potentiated startle. Alprazolam and diphenhydramine reduced overall baseline startle. Alprazolam was found to only affect contextual anxiety in a statistical significant way after two subjects who failed to show a contextual anxiety effect in the placebo condition were excluded from the analysis. Pregabalin did not significantly affect any of the physiological measures.

DISCUSSION

The negative findings from this study are discussed in terms of methodological differences between designs and in variability of startle both between and within study participants.

CONCLUSION

Even though fear-potentiated startle may be used to translate preclinical evidence to human populations, methodological issues still hamper the application of this model to early screening of putative anxiolytic drugs.

Juvenile stress-induced alteration of maturation of the GABAA receptor alpha subunit in the rat

Profound evidence indicates that GABAA receptors are important in the control of physiological response to stress and anxiety. The alpha subunit type composition contributes significantly to the functional characterization of the GABAA receptors. The alpha2, alpha3, alpha5 subunits are predominately expressed in the brain during embryonic and early postnatal periods of normal rats, whilst alpha1 are most prominent during later developmental stages. In the present study, we examined the long-term effects of juvenile stress on GABA alpha subunit expression in adulthood in the amygdala and hippocampus. We applied the elevated platform stress paradigm at juvenility and used the open-field and startle response tests to assess anxiety level in adulthood. Juvenile stress effects without behavioural tests in adulthood were also examined since previous studies indicated that the mere exposure to these tests might be stressful for rats, enhancing the effects of the juvenile exposure to stress. In adulthood, we quantitatively determined the level of expression of alpha1, alpha2 and alpha3 in the hippocampus and amygdala. Our results indicate that subjecting juvenile stressed rats to additional challenges in adulthood results in an immature-like expression profile of these subunits. To test for potential functional implications of these alterations we examined the effects of the anxiolytic (diazepam) and the sedative (brotizolam) benzodiazepines on juvenile stressed and control rats following additional challenges in adulthood. Juvenile stressed rats were more sensitive to diazepam and less sensitive to brotizolam, suggesting that the alterations in GABA alpha subunit expression in these animals have functional consequences.

Metabotropic glutamate receptor modulation, translational methods, and biomarkers: relationships with anxiety

RATIONALE

The increasing awareness of the need to align clinical and preclinical research to facilitate rapid development of new drug therapies is reflected in the recent introduction of the term "translational medicine". This review examines the implications of translational medicine for psychiatric disorders, focusing on metabotropic glutamate (mGlu) receptor biology in anxiety disorders and on anxiety-related biomarkers.

OBJECTIVES

This review aims to (1) examine recent progress in translational medicine, emphasizing the role that translational research has played in understanding of the potential of mGlu receptor agonists and antagonists as anxiolytics, (2) identify lacunas where animal and human research have yet to be connected, and (3) suggest areas where translational research can be further developed.

RESULTS

Current data show that animal and human mGlu(5) binding can be directly compared in experiments using the PET ligand (11)C-ABP688. Testing of the mGlu(2/3) receptor agonist LY354740 in the fear-potentiated startle paradigm allows direct functional comparisons between animals and humans. LY354740 has been tested in panic models, but in different models in rats and humans, hindering efforts at translation. Other potentially translatable methods, such as stress-induced hyperthermia and HPA-axis measures, either have been underexploited or are associated with technical difficulties. New techniques such as quantitative trait loci (QTL) analysis may be useful for generating novel biomarkers of anxiety.

CONCLUSIONS

Translational medicine approaches can be valuable to the development of anxiolytics, but the amount of cross-fertilization between clinical and pre-clinical departments will need to be expanded to realize the full potential of these approaches.

Models and mechanisms of anxiety: evidence from startle studies

RATIONALE

Preclinical data indicates that threat stimuli elicit two classes of defensive behaviors, those that are associated with imminent danger and are characterized by flight or fight (fear), and those that are associated with temporally uncertain danger and are characterized by sustained apprehension and hypervigilance (anxiety).

OBJECTIVE

The objectives of the study are to (1) review evidence for a distinction between fear and anxiety in animal and human experimental models using the startle reflex as an operational measure of aversive states, (2) describe experimental models of anxiety, as opposed to fear, in humans, (3) examine the relevance of these models to clinical anxiety.

RESULTS

The distinction between phasic fear to imminent threat and sustained anxiety to temporally uncertain danger is suggested by psychopharmacological and behavioral evidence from ethological studies and can be traced back to distinct neuroanatomical systems, the amygdala and the bed nucleus of the stria terminalis. Experimental models of anxiety, not fear, are relevant to non-phobic anxiety disorders.

CONCLUSIONS

Progress in our understanding of normal and abnormal anxiety is critically dependent on our ability to model sustained aversive states to temporally uncertain threat.

Emotion regulation and potentiated startle across affective picture and threat-of-shock paradigms

Past studies beginning with Jackson et al. [Jackson, D.C., Malmstadt, J.R., Larson, C.L., Davidson, R.J., 2000. Suppression and enhancement of emotional responses to unpleasant pictures. Psychophysiology 37 (4), 515-522.] document increases and decreases in emotionally-potentiated startle by way of instructing participants to enhance or suppress their emotional responses to symbolic sources of threat (unpleasant pictures). The present study extends this line of work to a threat-of-shock paradigm to assess whether startle potentiation elicited by threat of actual danger or pain is subject to emotion regulation. Results point to successful volitional modulation for both Affective-Picture and Threat-of-Shock experiments with startle magnitudes from largest to smallest occurring in the enhance, maintain, and suppress conditions. Successful regulation of startle potentiation to the threat of shock found by the current study supports the external validity of the Jackson paradigm for assessment of regulation processes akin to those occurring in the day-to-day context in response to real elicitors of emotion.

Startle potentiation in rapidly alternating conditions of high and low predictability of threat

Effects of predictability of threat on potentiation of the startle reflex were investigated by presenting participants with predictable and unpredictable electric shocks. Shocks were presented either paired with a visual cue (paired condition) or unrelated to the presentation of the visual cues (unpaired condition). In contrast to previous slower-paced studies, conditions alternated at a rapid rate: each context lasted 8.5 s and within these contexts the visual cues had a duration of 1.5 s. Results replicated previous findings: in the predictable condition, startle responses were augmented by a threat-signaling stimulus, and startle responses in the unpredictable condition were larger than in a neutral condition in which no shocks were presented. In all three conditions, visual stimuli that did not carry information about when a shock could be presented augmented startle reactivity. A control experiment showed that the effects of threat on the startle response could not be ascribed to attention and that the effects of the lead stimuli that did not signal threat are likely to be unrelated to the effects of threat. These results show that the fear system is modulated dynamically as a function of rapidly changing information about threat and emphasize the role of predictability of an aversive stimulus in the distinction between cue-specific and contextual fear.

Modelling anxiety in humans for drug development

Animal behavioural profiles are commonly employed to investigate new therapeutic agents to treat anxiety disorders as well as to investigate the mechanism of action of anxiolytic drugs. However, many clinically important symptoms of anxiety can not be modelled directly in animals. Human models of anxiety should bridge between animal models and anxiety disorders. Experimental anxiety states in humans can be induced by either pharmacological means such as CO(2) inhalation or psychological means such as aversive conditioning of skin conductance responses to tones. Investigation of these models may contribute to a better understanding of anxiety disorders, both from a biological and behavioural point of view. In a comprehensive review existing models of human experimental anxiety states are summarized and validity is discussed.

Lorazepam dose-dependently decreases risk-taking related activation in limbic areas

RATIONALE

Several studies have examined the role of different neurotransmitter systems in modulating risk-taking behavior.

OBJECTIVE

This investigation was aimed to determine whether the benzodiazepine lorazepam dose-dependently alters risk-taking behavior and underlying neural substrates.

MATERIALS AND METHODS

Fifteen healthy, nonsmoking, individuals (six women, nine men), aged 18-39 years (mean 27.6 +/- 1.4 years) with 12-18 years of education (mean 15.6 +/- 0.3 years) underwent functional magnetic resonance imaging while performing a risk-taking decision-making task.

RESULTS

Our results show that lorazepam did not affect risky behavior at 0.25 and 1 mg, but dose-dependently attenuated activation in (a) the amygdala and medial prefrontal cortex during the response selection phase, and in (b) the bilateral insular cortex and amygdala during the outcome (i.e., rewarded or punished) phase. Furthermore, a lorazepam-induced increase in insular cortex activation was associated with less risky responses.

CONCLUSIONS

Taken together, our findings support the idea that GABAergic modulation in limbic and paralimbic structures is important during both the response selection and outcome phase of risk-taking decision-making.

The benzodiazepine alprazolam dissociates contextual fear from cued fear in humans as assessed by fear-potentiated startle

BACKGROUND

The startle reflex is potentiated by aversive states. It has been proposed that phasic startle potentiation to a threat cue and sustained startle potentiation to contextual stimuli reflect distinct processes mediated by different brain structures. The present study tested the hypothesis that alprazolam would reduce the sustained startle potentiation to contextual threats but not the startle potentiation to a threat cue.

METHODS

Sixteen healthy subjects received each of four treatments: placebo, .5 mg of alprazolam, 1 mg of alprazolam, and 50 mg of diphenhydramine (Benadryl) in a crossover design. Participants were exposed to three conditions, including one in which predictable aversive shocks were signaled by a cue, a second in which shocks were administered unpredictably, and a third condition in which no shocks were anticipated. Acoustic startle were delivered regularly across conditions.

RESULTS

Phasic startle potentiation to the threat cue in the predictable condition was not affected by alprazolam. In contrast, the sustained increase in startle in the predictable and unpredictable conditions was reduced significantly by the high dose of alprazolam.

CONCLUSIONS

Startle responses to an explicit threat cue and to an aversive context are psychopharmacologically distinct, suggesting that they may represent functionally dissociable aversive states.

Tiermodelle für Angst und Angststörungen

Zusammenfassung. Zahlreiche Tiermodelle haben entscheidend zur Aufklärung der neurobiopsychologischen Grundlagen von Angst und damit auch zum Verständnis von Angststörungen beigetragen. An zwei unterschiedlichen Tiermodellen, dem Elevated Plus-Maze und der potenzierten Schreckreaktion, sollen die verschiedenen Ansätze exemplarisch veranschaulicht werden. Ansätze zur Untersuchung individueller Differenzen habitueller Angstmerkmale ergeben sich bei der Betrachtung natürlich vorkommender Variation innerhalb einer Stammesgeneration, bei selektiven Züchtungen und bei genetisch manipulierten Modellen. Schließlich bestehen auch Möglichkeiten zur Untersuchung kognitiver Prozesse in Tieren. Auch zukünftig werden tierexperimentelle Ansätze wesentlich zu unserem Wissen um die behavioralen und neurobiologischen Grundlagen der Angst im Humanbereich beitragen.

Influence of individual differences in Behavioral Inhibition System on the magnitude and time course of the fear-potentiated startle

Previous research has shown that the startle reflex is potentiated during experimentally induced anxiety (fear-potentiated startle). In the present study, the magnitude and time course of the startle blink reflex were examined among 35 undergraduates scoring one standard deviation above (n = 14) or below (n = 21) the mean in a self-report measure of sensitivity to punishment (SP) in a paradigm involving the anticipation of electric shocks. Contrary to our predictions, SP did not relate to differences in the magnitude or in the time course of fear-potentiated startle. Our data do not support an association between this individual differences variable and the fear-potentiated startle.

A neurophysiological study of the detrimental effects of alprazolam on human action monitoring

In order to adapt their behavior to different unexpected situations, humans need to be able to monitor their performance and detect and correct errors. Benzodiazepines have long been shown to impair performance in humans, but the performance-related neurophysiological processes targeted by these drugs remain largely unknown. In the present article, we assessed the impact of alprazolam administration on relevant aspects of action monitoring, i.e., the monitoring of response conflict and the detection and correction of errors by means of neurophysiological measures. Multichannel event-related brain potentials (ERPs) were recorded to assess the impact of the benzodiazepine alprazolam (0.25 mg and 1.00 mg) on action monitoring and motor preparation in a group of twelve healthy male volunteers who participated in a double-blind cross-over placebo-controlled clinical trial involving a letter flanker task. Error detection was evaluated using the error-related negativity (ERN); response conflict on correct trials was measured by means of the N2 amplitude difference between congruent and incongruent trials; motor preparation was assessed by means of the lateralized readiness potentials (LRPs); and post-error adjustments were assessed by measuring post-error slowing in reaction time. Alprazolam significantly reduced the amplitude of the ERN and the number of corrective responses and increased reaction time and LRP latencies. The drug had no effect on amplitude differences in the N2 component between congruent and incongruent trials or on post-error slowing. Thus, alprazolam was shown to affect brain correlates of error detection (ERN) and motor preparation (LRPs), while it did not disturb conflict monitoring on correct trials (N2) or post-error adjustments of behavior.

Effects of lorazepam on fear-potentiated startle responses in man

Sudden intense sensory stimuli elicit a cascade of involuntary responses, including a short-latency skeletal muscular response ('eyeblink startle response') and longer-latency autonomic responses. These responses are enhanced when subjects anticipate an aversive event compared to periods when subjects are resting ('fear potentiation'). It has been reported previously that the anxiolytic diazepam can suppress fear-potentiation of the eyeblink startle response in human volunteers. The present experiment aimed to confirm and extend these observations by examining the effect of another benzodiazepine, lorazepam, on the eyeblink and skin conductance components of the acoustic startle, and on fear-potentiation of these responses. Eighteen male volunteers participated in three weekly sessions in which they received oral treatment with placebo, lorazepam (1 mg) and lorazepam (2 mg), according to a balanced three-period, crossover, double-blind design. Two hours after ingestion of the treatments, electromyographic responses of the orbicularis oculi muscle and skin conductance responses were evoked by sound pulses during alternating periods in which the threat of an electric shock (electrodes attached to the subject's wrist) was present (THREAT) and absent (SAFE). The THREAT condition was associated with significant increase in the amplitude of the electromyographic (EMG) and skin conductance responses; there were also increases in baseline skin conductance, the number and amplitude of 'spontaneous' skin conductance fluctuations and self-rated anxiety. Lorazepam attenuated the effect of THREAT on self-rated anxiety and on the amplitude of the EMG response, but had no significant effect on fear-potentiation of the skin conductance responses. These results extend previous findings of the effect of diazepam on the fear-potentiated eyeblink startle response to lorazepam, and suggest that fear-potentiation of the later autonomic component of the startle response may be less sensitive to benzodiazepines than the fear-potentiated eyeblink response and self-rated anxiety.

Effects of additional oxazepam in long-term users of oxazepam

Although additional dosages of benzodiazepines in long-term users of benzodiazepines are common, it is unknown whether these additional dosages resort any effect. The effects of an additional 20-mg dosage oxazepam were assessed in a double-blind, balanced-order, crossover randomized study comparing 16 long-term users of oxazepam (patients) with 18 benzodiazepine-naive controls (controls). The effects of 10 and 30 mg oxazepam were assessed at pretest and 2.5 hours after drug administration on: (a) saccadic eye movements as proxy for the sedative effect, (b) acoustic startle response (ASR) as proxy for the anxiolytic effects, (c) memory, (d) reaction time tasks, and (e) subjective measurements. Dose-related effects were found in patients on the peak velocity of saccadic eye movement and on response probability, respectively peak amplitude of the ASR. Comparison with controls, however, suggests that in patients the sedative effects might be mixed up with suppression of sedative withdrawal symptoms, whereas patients were as sensitive as benzodiazepine-naive controls for the effects of an additional dosage on the ASR. Neither 10 nor 30 mg oxazepam challenge affected the reaction time tasks in patients, whereas controls show a dose-related impairment. The memory impairing effects, however, did not differ significantly between patients and controls. In contrast to controls, patients could not discriminate between a 10- and 30-mg dosage as assessed by visual analogue scales and the STAI-DY-1, which might indicate a placebo effect in the 10-mg challenge in patients. We conclude that additional dosages of oxazepam still exert pronounced effects after daily use for more than 10 years.

Pavlovian Conditioning: A Functional Perspective

From a functional perspective, Pavlovian conditioning involves learning about conditioned stimuli (CSs) that have a pre-existing relation to an unconditioned stimulus (US) rather than learning about arbitrary or neutral CSs. In addition, the most important product of learning involves changes in how the organism responds to the US, not in how it responds to the CS, because the US is the more biologically relevant stimulus. These concepts are illustrated using examples from a variety of behavioral and physiological situations including caloric intake and digestion, breast feeding, poison-avoidance learning, eyeblink conditioning, sexual conditioning, fear conditioning, aggression, and drug tolerance and sensitization.

Affective modulation of the startle response in depression: influence of the severity of depression, anhedonia, and anxiety

BACKGROUND

The amplitude of the startle reflex response is known to be influenced by the concomitant presentation of affect-toned material--if it is positive affect-toned, the reflex is inhibited, and if it is negative affect-toned, the reflex is augmented. Abundant evidence demonstrates the utility of the affect-startle paradigm as a significant tool for measuring both positive and negative emotions. We applied this paradigm to study emotional reactivity in depression, particularly in relation to symptoms of depression, anhedonia, and anxiety.

METHODS

Depressed patients (22) and controls (22) were shown a series of film clips, consisting of two clips with positive valence, two with negative valence, and two with relatively neutral valence. The startle response was measured in reaction to the acoustic startle-eliciting stimuli presented three times binaurally during each clip.

RESULTS

Highly depressed and anhedonic patients, relative to controls, showed a reduced mood (self-ratings) and a lack of startle modulation in response to affective film clips whereas patients relatively low on depression/anhedonia displayed a reduced mood only with pleasant clips and a normal pattern of affective startle modulation. Anhedonia and depression were highly positively correlated but neither correlated with anxiety. Anxious patients displayed larger reflexes across all clips and showed a reduced mood modulation with pleasant, but not unpleasant, clips.

LIMITATIONS

The large majority of patients was medicated with antidepressants which may have influenced the results. CONCLUSIONS. Reactivity to pleasant stimuli is diminished in patients suffering from low levels of depression and/or anhedonia, but reactivity even to unpleasant stimuli seems compromised at high levels of depression and/or anhedonia. Anxiety is associated with hyperstartle responding.

Anxious responses to predictable and unpredictable aversive events

Anxiety induced by 2 types of predictable and unpredictable aversive stimuli, an unpleasant shock or a less aversive airblast to the larynx, were investigated in a between-group design. Participants anticipated predictable (signaled) or unpredictable (not signaled) aversive events, or no aversive event. Unpredictable, relative to predictable, contexts potentiated the startle reflex in the shock group but not in the airblast group. These data suggest that unpredictability can lead to a sustained level of anxiety only when the pending stimulus is sufficiently aversive. Because predictable and unpredictable danger may induce different types of aversive responses, the proposed design can serve as a useful tool for studying the neurobiology and psychopharmacology of fear and anxiety.

Clinical pharmacology, clinical efficacy, and behavioral toxicity of alprazolam: a review of the literature

Alprazolam is a benzodiazepine derivative that is currently used in the treatment of generalized anxiety, panic attacks with or without agoraphobia, and depression. Alprazolam has a fast onset of symptom relief (within the first week); it is unlikely to produce dependency or abuse. No tolerance to its therapeutic effect has been reported. At discontinuation of alprazolam treatment, withdrawal and rebound symptoms are common. Hence, alprazolam discontinuation must be tapered. An exhaustive review of the literature showed that alprazolam is significantly superior to placebo, and is at least equally effective in the relief of symptoms as tricyclic antidepressants (TCAs), such as imipramine. However, although alprazolam and imipramine are significantly more effective than placebo in the treatment of panic attacks, Selective Serotonin Reuptake Inhibitors (SSRIs) appear to be superior to either of the two drugs. Therefore, alprazolam is recommended as a second line treatment option, when SSRIs are not effective or well tolerated. In addition to its therapeutic effects, alprazolam produces adverse effects, such as drowsiness and sedation. Since alprazolam is widely used, many clinical studies investigated its cognitive and psychomotor effects. It is evident from these studies that alprazolam may impair performance in a variety of skills in healthy volunteers as well as in patients. Since the majority of alprazolam users are outpatients, this behavioral impairment limits the safe use of alprazolam in patients routinely engaged in potentially dangerous daily activities, such as driving a car.

A review of the modulation of the startle reflex by affective states and its application in psychiatry

OBJECTIVE

To provide an overview of startle reflex methodologies applied to the examination of emotional and motivational states in humans and to review the findings in different forms of psychopathology.

METHODS

Pertinent articles were searched mostly via MEDLINE and PsycINFO.

RESULTS

The startle reflex is a non-invasive translational tool of research that bridges the gap between animal and human investigations. Startle is used to study fear and anxiety, affective disturbances, sensitization, motivational states, and homeostasis.

CONCLUSIONS

The startle reflex is highly sensitive to various factors that are of interest in the studies of emotional disorders and has promoted new areas of investigations in psychiatry. However, research in psychiatry is still in its infancy and most findings await replication. Future progress will benefit from the development of innovative and powerful designs tailored to investigate specific disorders.

SIGNIFICANCE

The startle reflex has utility as a research tool to examine trauma-related disorders, fear learning, drug addiction, and to contrast affective states and emotional processing across diagnostic groups, but its usefulness as a diagnostic tool is limited.

Anxiolytic effects of a novel group II metabotropic glutamate receptor agonist (LY354740) in the fear-potentiated startle paradigm in humans

RATIONALE

LY354740, a structural analogue of glutamate that shows specificity at the mGluR2/3 receptor, has anxiolytic effects in animal models.

OBJECTIVE

This study investigated the anxiolytic effects of LY354740 in humans using the fear-potentiated startle reflex methodology.

METHODS

Subjects were given either placebo (n=16), 20 mg LY354740 (n=15), or 200 mg LY354740 (n=13). The fear-potentiated startle tests examined startle potentiation to shock anticipation and to darkness.

RESULTS

Consistent with previous results, startle was increased by threat of shock and by darkness. LY354740 did not affect baseline startle. Correspondingly, subjects did not report LY354740 to be sedative. LY354740 significantly reduced the increase in startle magnitude during shock anticipation, but not during darkness. Subjective reports of state anxiety and negative affectivity during the fear-potentiated startle tests were also reduced in a dose-dependent manner by LY354740.

CONCLUSIONS

These results suggest that LY354740 has an anxiolytic profile in humans without being sedative.

Clinical biomarkers in drug discovery and development

Biomarkers enable the characterization of patient populations and quantitation of the extent to which new drugs reach intended targets, alter proposed pathophysiological mechanisms and achieve clinical outcomes. In genomics, the biomarker challenge is to identify unique molecular signatures in complex biological mixtures that can be unambiguously correlated to biological events in order to validate novel drug targets and predict drug response. Biomarkers can stratify patient populations or quantify drug benefit in primary prevention or disease-modification studies in poorly served areas such as neurodegeneration and cancer. Clinically useful biomarkers are required to inform regulatory and therapeutic decision making regarding candidate drugs and their indications in order to help bring new medicines to the right patients faster than they are today.

GABA-A receptor subtypes in the brain: a paradigm for CNS drug discovery?

The clinical importance of benzodiazepines, barbiturates and general anesthetics, all of which act through the gamma-aminobutyric acid (GABA)-A neurotransmitter receptor, is testament to its significance as a CNS drug target. These drugs were all developed before there was any understanding of the diversity of this receptor gene family. Recent studies using genetically modified mice and GABA-A receptor-subtype-selective compounds have helped to delineate the function of some of these subtypes, and have revealed that it might be possible to develop a new generation of selective drugs with improved profiles or novel applications.

Pharmacology of human experimental anxiety

This review covers the effect of drugs affecting anxiety using four psychological procedures for inducing experimental anxiety applied to healthy volunteers and patients with anxiety disorders. The first is aversive conditioning of the skin conductance responses to tones. The second is simulated public speaking, which consists of speaking in front of a video camera, with anxiety being measured with psychometric scales. The third is the Stroop Color-Word test, in which words naming colors are painted in the same or in a different shade, the incongruence generating a cognitive conflict. The last test is a human version of a thoroughly studied animal model of anxiety, fear-potentiated startle, in which the eye-blink reflex to a loud noise is recorded. The evidence reviewed led to the conclusion that the aversive conditioning and potentiated startle tests are based on classical conditioning of anticipatory anxiety. Their sensitivity to benzodiazepine anxiolytics suggests that these models generate an emotional state related to generalized anxiety disorder. On the other hand, the increase in anxiety determined by simulated public speaking is resistant to benzodiazepines and sensitive to drugs affecting serotonergic neurotransmission. This pharmacological profile, together with epidemiological evidence indicating its widespread prevalence, suggests that the emotional state generated by public speaking represents a species-specific response that may be related to social phobia and panic disorder. Because of scant pharmacological data, the status of the Stroop Color-Word test remains uncertain. In spite of ethical and economic constraints, human experimental anxiety constitutes a valuable tool for the study of the pathophysiology of anxiety disorders.

Startle reactivity and anxiety disorders: aversive conditioning, context, and neurobiology

The aim of this article is to review studies on human anxiety using the startle reflex methodology and to apply the literature on context conditioning in rats to interpret the results. A distinction is made between cued fear (as in specific phobia), a phasic response to an explicit threat cue, and anxiety, a more sustained and future-oriented response not linked to a specific discrete cue. Experimentally, contextual fear, as opposed to cued fear, may best reflect the feeling of aversive expectation about potential future dangers that characterizes anxiety. Following a brief description of the neurobiology of cued fear and context conditioning, evidence is presented showing that anxious patients are overly sensitive to threatening contexts. It is then argued that the degree to which contextual fear is prompted by threat depends on whether the danger is predictable or unpredictable. Consistent with animal data, unpredictable shocks in humans result in greater context conditioning compared to predictable shocks. Because conditioning promotes predictability, it is proposed to use conditioning procedures to study the development of appropriate and inappropriate aversive expectations. Cued fear learning is seen as an adaptive process by which undifferentiated fear becomes cue-specific. Deficits in cued fear learning lead to the development of nonadaptive aversive expectancies and an attentional bias toward generalized threat. Lacking a cue for threat, the organism cannot identify periods of danger and safety and remains in a chronic state of anxiety. Factors that may affect conditioning are discussed.