NEUROSCIENCE: The Threatened Brain

Panicolytic-like effects of environment enrichment on male mice threatened by Bothrops jararaca lancehead pit vipers

Environment enrichment (EE) is a well-known eustress model showing beneficial effects in different psychiatric diseases, but its positive properties in panic disorders are not yet established. The confrontation between prey and predator in complex arenas has been validated as a putative panic attack model. The principal aim of this work was to investigate the role of the EE on panic-like defensive responses elicited by mice threatened by venomous snakes. After 6 weeks of exposure either to an enriched or standard environments, 36 male mice were habituated in a complex polygonal arena for snakes containing an artificial burrow and elevated platforms for escape. The animals were confronted by Bothrops jararaca for 5 min, and the following antipredatory responses were recorded: defensive attention, stretched attend posture, flat back approach, prey versus predator interaction, oriented escape behavior, time spent in a safe place, and number of crossings. Mice threatened by snakes displayed several antipredatory reactions as compared to the exploratory behavior of those animals submitted to a nonthreatening situation (toy snake) in the same environment. Notably, EE causes anxiolytic- and panicolytic-like effects significantly decreasing the defensive attention and time spent in safe places and significantly increasing both prey versus predator interaction and exploratory behavior. In conclusion, our data demonstrate that EE can alter the processing of fear modulation regarding both anxiety- and panic-like responses in a dangerous condition, significantly modifying the decision-making defensive strategy.

“Landscape of Stress” for Sheep Owners in the Swedish Wolf Region

Farmers who keep livestock in large carnivore areas are exposed to threat of predation directly impacting on finances and workload as well as the associated psychological stress indirectly impacting on farmers well-being. So far, little is known about such stress responses. The concept of “stress” or “stress reaction” is often used as an undifferentiated umbrella concept for the experience of negative emotional episodes. However, the stress reactions could be divided into cognitive, physiological, and behavioural aspects. This study aimed to develop and apply a theory-based approach to identify stress responses among sheep farmers in the Swedish “wolf-region.” A thematic analysis of interviews conducted with sheep farmers showed ample support for stress responses among the informants in relation to large carnivores and their management, although the interviews were conducted with a different focal topic. The findings support the idea that stress responses could be categorised into cognitive, physiological, and behavioural aspects. This distinction would help to identify and fully understand the cumulative impact of stress from the presence of large carnivores on farmers’ well-being.

Behavioral sensitization induced by dorsal periaqueductal gray electrical stimulation is counteracted by NK1 receptor antagonism in the ventral hippocampus and central nucleus of the amygdala

A single threatening experience may change the behavior of an animal in a long-lasting way and elicit generalized behavioral responses to a novel threatening situation that is unrelated to the original aversive experience. Electrical stimulation (ES) of the dorsal periaqueductal gray (dPAG) produces a range of defensive reactions, characterized by freezing, escape, and post-stimulation freezing (PSF). The latter reflects the processing of ascending aversive information to prosencephalic structures, including the central nucleus of the amygdala (CeA), which allows the animal to evaluate the consequences of the aversive situation. This process is modulated by substance P (SP) and its preferred receptor, neurokinin 1 (NK1). The ventral hippocampus (VH) has been associated with the processing of aversive information and expression of emotional reactions with negative valence, but the participation of the VH in the expression of these defensive responses has not been investigated. The VH is rich in NK1 receptor expression and has a high density of SP-containing fibers. The present study examined the role of NK1 receptors in the VH in the expression of defensive responses and behavioral sensitization that were induced by dPAG-ES. Rats were implanted with an electrode in the dPAG for ES, and a cannula was implanted in the VH or CeA for injections of vehicle (phosphate-buffered saline) or the NK1 receptor antagonist spantide (100 pmol/0.2 μL. Spantide reduced the duration of PSF that was evoked by dPAG-ES, without changing the aversive freezing or escape thresholds. One and 7 days later, exploratory behavior was evaluated in independent groups of rats in the elevated plus maze (EPM). dPAG-ES in rats that received vehicle caused higher aversion to the open arms of the EPM compared with rats that did not receive dPAG stimulation at both time intervals. Injections of spantide in the VH or CeA prevented the proaversive effects of dPAG-ES in the EPM only 1 day later. These findings suggest that NK1 receptors are activated in both the VH and CeA during the processing of aversive information that derives from dPAG-ES. As previously shown for the CeA, SP/NK1 receptors in the VH are recruited during PSF that is evoked by dPAG-ES, suggesting that a 24-h time window is susceptible to interventions with NK1 antagonists that block the passage of aversive information from the dPAG to higher brain areas.

Epigenetic and Neural Circuitry Landscape of Psychotherapeutic Interventions

The science behind psychotherapy has garnered considerable interest, as objective measures are being developed to map the patient's subjective change over the course of treatment. Prenatal and early life influences have a lasting impact on how genes are expressed and the manner in which neural circuits are consolidated. Transgenerationally transmitted epigenetic markers as well as templates of enhanced thought flexibility versus evasion can be passed down from parent to child. This influences gene expression/repression (impacting neuroplasticity) and kindling of neurocircuitry which can perpetuate maladaptive cognitive processing seen in a number of psychiatric conditions. Importantly, genetic factors and the compounding effects of early life adversity do not inexorably lead to certain fated outcomes. The concepts of vulnerability and resilience are becoming more integrated into the framework of "differential susceptibility," speaking to how corrective environmental factors may promote epigenetic change and reconfigure neural templates, allowing for symptomatic improvement. Psychotherapy is one such factor, and this review will focus on our current knowledge of its epigenetic and neurocircuitry impact.

Metacognitions Are Associated with Subjective Memory Problems in Individuals on Sick Leave due to Chronic Fatigue

Background: Subjective cognitive impairments are frequent, but poorly understood in patients with chronic fatigue. We hypothesized that maladaptive metacognitive beliefs at baseline were associated with baseline subjective cognitive impairments, that they predict subjective cognitive impairments at treatment termination, and that a reduction in maladaptive metacognitive beliefs was associated with less subjective cognitive impairments at treatment termination, independent of changes in fatigue, pain, insomnia, depression, and anxiety.

Methods: In this non-controlled study, patients (n = 137) on sick leave due to chronic fatigue received a 3.5-week inpatient RTW rehabilitation program. Of these patients 69 (50.4%) was referred with a ICPC-2 diagnosis of chronic fatigue. Patients completed questionnaires about metacognitive beliefs, somatic complaints, psychological complaints, and cognitive impairments before and after treatment. To test the hypotheses we performed paired t-tests of change, as well as seven hierarchical linear regressions.

Results: Results showed that baseline maladaptive metacognitive beliefs were significantly associated with subjective cognitive impairments at baseline, controlling for symptoms. Score on baseline metacognitive beliefs did not predict impairments post-treatment. Testing specific maladaptive beliefs, pre-treatment scores on cognitive confidence were associated with subjective cognitive impairments both pre and post-treatment, controlling for symptoms. Post-treatment metacognitive beliefs and post-treatment cognitive confidence were associated with post-treatment subjective cognitive impairments, controlling for pre-treatment impairments and pre-treatment metacognitive beliefs, as well as pre and post-scores on symptom measures.

Conclusion: This study reports associations between maladaptive metacognitive beliefs and subjective cognitive impairments in patients with chronic fatigue. Targeting metacognitive beliefs could prove an effective therapeutic intervention for subjective cognitive impairments in these patients.

Differences in neurotransmitter systems of ventrolateral periaqueductal gray between the micturition reflex and nociceptive regulation: An in vivo microdialysis study

OBJECTIVES

To elucidate the possible involvement of glutamate and serotonin (5-hydroxytryptamine) neurons in the ventrolateral midbrain periaqueductal gray during noxious stimulation.

METHODS

The study was carried out by evoking a noxious stimulation by acetic acid in an animal model of cystitis. Changes in glutamate and 5-hydroxytryptamine in the periaqueductal gray during the micturition reflex and acetic acid-induced cystitis were determined using in vivo microdialysis combined with cystometry in rats.

RESULTS

Extracellular glutamate levels slightly, but significantly, increased during the micturition reflex induced by saline infusion into the bladder. Intravesical infusion of acetic acid facilitated the micturition reflex characterized by increases in voiding pressure and decreases in the intercontraction interval. Glutamate levels were markedly increased by acetic acid, and this enhancement was sustained for at least 3 h. 5-Hydroxytryptamine levels, which were not altered during the micturition reflex, were increased after intravesical infusion of acetic acid.

CONCLUSION

The results suggest that periaqueductal gray glutamate and 5-hydroxytryptamine neurons differentially participate in the modulation of both nociception and the micturition reflex. Furthermore, periaqueductal gray 5-hydroxytryptamine levels appear to reflect the nociceptive stimuli.

Translational approach to studying panic disorder in rats: hits and misses

Panic disorder (PD) patients are specifically sensitive to 5–7% carbon dioxide. Another startling feature of clinical panic is the counterintuitive lack of increments in ‘stress hormones’. PD is also more frequent in women and highly comorbid with childhood separation anxiety (CSA). On the other hand, increasing evidence suggests that panic is mediated at dorsal periaqueductal grey matter (DPAG). In line with prior studies showing that DPAG-evoked panic-like behaviours are attenuated by clinically-effective treatments with panicolytics, we show here that (i) the DPAG harbors a hypoxia-sensitive alarm system, which is activated by hypoxia and potentiated by hypercapnia, (ii) the DPAG suffocation alarm system is inhibited by clinically-effective treatments with panicolytics, (iii) DPAG stimulations do not increase stress hormones in the absence of physical exertion, (iv) DPAG-evoked panic-like behaviours are facilitated in neonatally-isolated adult rats, a model of CSA, and (v) DPAG-evoked responses are enhanced in the late diestrus of female rats. Data are consistent with the DPAG mediation of both respiratory and non-respiratory types of panic attacks.

Amygdala activation and symptom dimensions in obsessive-compulsive disorder

BACKGROUND

Despite knowledge of amygdala involvement in fear and anxiety, its contribution to the pathophysiology of obsessive-compulsive disorder (OCD) remains controversial. In the context of neuroimaging studies, it seems likely that the heterogeneity of the disorder might have contributed to a lack of consistent findings.

AIMS

To assess the influence of OCD symptom dimensions on amygdala responses to a well-validated emotional face-matching paradigm.

METHOD

Cross-sectional functional magnetic resonance imaging (fMRI) study of 67 patients with OCD and 67 age-, gender- and education-level matched healthy controls.

RESULTS

The severity of aggression/checking and sexual/religious symptom dimensions were significantly associated with heightened amygdala activation in those with OCD when responding to fearful faces, whereas no such correlations were seen for other symptom dimensions.

CONCLUSIONS

Amygdala functional alterations in OCD appear to be specifically modulated by symptom dimensions whose origins may be more closely linked to putative amygdala-centric processes, such as abnormal fear processing.

Fear extinction memory consolidation requires potentiation of pontine-wave activity during REM sleep

Sleep plays an important role in memory consolidation within multiple memory systems including contextual fear extinction memory, but little is known about the mechanisms that underlie this process. Here, we show that fear extinction training in rats, which extinguished conditioned fear, increased both slow-wave sleep and rapid-eye movement (REM) sleep. Surprisingly, 24 h later, during memory testing, only 57% of the fear-extinguished animals retained fear extinction memory. We found that these animals exhibited an increase in phasic pontine-wave (P-wave) activity during post-training REM sleep, which was absent in the 43% of animals that failed to retain fear extinction memory. The results of this study provide evidence that brainstem activation, specifically potentiation of phasic P-wave activity, during post-training REM sleep is critical for consolidation of fear extinction memory. The results of this study also suggest that, contrary to the popular hypothesis of sleep and memory, increased sleep after training alone does not guarantee consolidation and/or retention of fear extinction memory. Rather, the potentiation of specific sleep-dependent physiological events may be a more accurate predictor for successful consolidation of fear extinction memory. Identification of this unique mechanism will significantly improve our present understanding of the cellular and molecular mechanisms that underlie the sleep-dependent regulation of emotional memory. Additionally, this discovery may also initiate development of a new, more targeted treatment method for clinical disorders of fear and anxiety in humans that is more efficacious than existing methods such as exposure therapy that incorporate only fear extinction.

Fear bradycardia and activation of the human periaqueductal grey

Animal models of predator defense distinguish qualitatively different behavioral modes that are activated at increasing levels of predation threat. A defense mode observed at intermediate threat levels is freezing: a cessation of locomotion that is characterized by a parasympathetically dominated autonomic nervous system response that causes heart rate deceleration, or fear bradycardia. Studies in rodents have shown that freezing depends on amygdalar projections to the periaqueductal grey (PAG). In humans, freezing-like behaviors are implicated in development and maintenance of psychopathology, but neural mechanisms underlying freezing or its characteristic autonomic response profile have not been identified. Here, we combined event-related blood oxygenation level-dependent functional MRI (BOLD-fMRI) with autonomic response measures in a picture viewing paradigm to probe activity and interconnectivity within the amygdala-PAG pathway and test for an association with parasympathetic as opposed to sympathetic activation. In response to negatively arousing pictures, we observed parasympathetic (bradycardia) and sympathetic (pupil dilation) autonomic responses, BOLD responses in the amygdala and PAG, and effective connectivity between these regions. Critically, BOLD responses in the PAG to negative pictures correlated on a trial-by-trial basis with bradycardia but not pupil dilation. This correlation with bradycardia remained significant when partialling out pupil dilation. Additionally, activity in regions associated with motor planning and inhibition mirrored the PAG response. Thus, our findings implicate the human PAG in a parasympathetically dominated defense mode that subserves a state of attentive immobility. Mechanistic insight into this qualitatively distinct defense mode may importantly advance translational models of anxiety disorders.

Hypervigilance for fear after basolateral amygdala damage in humans

Recent rodent research has shown that the basolateral amygdala (BLA) inhibits unconditioned, or innate, fear. It is, however, unknown whether the BLA acts in similar ways in humans. In a group of five subjects with a rare genetic syndrome, that is, Urbach-Wiethe disease (UWD), we used a combination of structural and functional neuroimaging, and established focal, bilateral BLA damage, while other amygdala sub-regions are functionally intact. We tested the translational hypothesis that these BLA-damaged UWD-subjects are hypervigilant to facial expressions of fear, which are prototypical innate threat cues in humans. Our data indeed repeatedly confirm fear hypervigilance in these UWD subjects. They show hypervigilant responses to unconsciously presented fearful faces in a modified Stroop task. They attend longer to the eyes of dynamically displayed fearful faces in an eye-tracked emotion recognition task, and in that task recognize facial fear significantly better than control subjects. These findings provide the first direct evidence in humans in support of an inhibitory function of the BLA on the brain's threat vigilance system, which has important implications for the understanding of the amygdala's role in the disorders of fear and anxiety.

Differentially organized top-down modulation of prepulse inhibition of startle

Prepulse inhibition (PPI) of startle is the suppression of the startle reflex when a weaker sensory stimulus (the prepulse) shortly precedes the startling stimulus. PPI can be attentionally enhanced in both humans and laboratory animals. This study investigated whether the following three forebrain structures, which are critical for initial cortical processing of auditory signals, auditory fear conditioning/memories, and spatial attention, respectively, play a role in the top-down modulation of PPI in rats: the primary auditory cortex (A1), lateral nucleus of the amygdala (LA), and posterior parietal cortex (PPC). The results show that, under the noise-masking condition, PPI was enhanced by fear conditioning of the prepulse in a prepulse-specific manner, and the conditioning-induced PPI enhancement was further increased by perceptual separation between the conditioned prepulse and the noise masker. Reversibly blocking glutamate receptors in the A1 with 2 mm kynurenic acid eliminated both the conditioning-induced and perceptual separation-induced PPI enhancements. Blocking the LA eliminated the conditioning-induced but not the perceptual separation-induced PPI enhancement, and blocking the PPC specifically eliminated the perceptual separation-induced PPI enhancement. The two types of PPI enhancements were also eliminated by the extinction manipulation. Thus, the top-down modulation of PPI is differentially organized and depends on operations of various forebrain structures. Due to the fine-tuned modulation by higher-order cognitive processes, functions of PPI can be more flexible to complex environments. The top-down enhancements of PPI in rats are also useful for modeling some mental disorders, such as schizophrenia, attention deficit/hyperactivity disorder, and posttraumatic stress disorder.

Feeling without seeing? Engagement of ventral, but not dorsal, amygdala during unaware exposure to emotional faces

The ability to selectively perceive items in the environment may be modulated by the emotional content of those items. The neural mechanism that underlies the privileged processing of emotionally salient content is poorly understood. Here, using fMRI, we investigated this issue via a binocular rivalry procedure when face stimuli depicting fearful or neutral expressions competed for awareness with a house. Results revealed an interesting dissociation in the amygdala during rivalry condition: Whereas its dorsal component exhibited dominant activation to aware fearful faces, a ventral component was more active during the suppression of fearful faces. Moreover, during rivalry, the dorsal and ventral components of the amygdala were coupled with segregated cortical activations in the brainstem and medial PFC, respectively. In summary, this study points to a differential involvement of two clusters within the amygdala and their connected networks in naturally occurring perceptual biases of emotional content in faces.

A novel coding mechanism for social vocalizations in the lateral amygdala

The amygdala plays a central role in evaluating the significance of acoustic signals and coordinating the appropriate behavioral responses. To understand how amygdalar responses modulate auditory processing and drive emotional expression, we assessed how neurons respond to and encode information that is carried within complex acoustic stimuli. We characterized responses of single neurons in the lateral nucleus of the amygdala to social vocalizations and synthetic acoustic stimuli in awake big brown bats. Neurons typically responded to most of the social vocalizations presented (mean = nine of 11 vocalizations) but differentially modulated both firing rate and response duration. Surprisingly, response duration provided substantially more information about vocalizations than did spike rate. In most neurons, variation in response duration depended, in part, on persistent excitatory discharge that extended beyond stimulus duration. Information in persistent firing duration was significantly greater than in spike rate, and the majority of neurons displayed more information in persistent firing, which was more likely to be observed in response to aggressive vocalizations (64%) than appeasement vocalizations (25%), suggesting that persistent firing may relate to the behavioral context of vocalizations. These findings suggest that the amygdala uses a novel coding strategy for discriminating among vocalizations and underscore the importance of persistent firing in the general functioning of the amygdala.

αCaMKII autophosphorylation controls exploratory activity to threatening novel stimuli

Autophosphorylation of αCaMKII is regarded as a 'molecular memory' for Ca(2+) transients and a crucial mechanism in aversely, but less so in appetitively, motivated learning and memory. While there is a growing body of research implicating αCaMKII in general in behavioral responses to threat or fearful stimuli, little is known about the contribution of the autophosphorylation. The present study asked how αCaMKII autophosphorylation controls anxiety-like behavioral responses toward novel, potentially threatening stimuli. We tested homozygous and heterozygous T286A αCaMKII autophosphorylation deficient mice and wild types in a systematic series of behavioral tests. Homozygous mutants were more active in the open field test and showed reduced anxiety-related behavior in the light/dark test, but these findings were confounded by a hyperlocomotor phenotype. The analysis of elevated plus maze showed significantly reduced anxiety-related behavior in the αCaMKII autophosphorylation-deficient mice which appeared to mediate a hyperlocomotor response. An analysis of home cage behavior, where neither novel nor threatening stimuli were present, showed no differences in locomotor activity between genotypes. Increased locomotion was not observed in the novel object exploration test in the αCaMKII autophosphorylation-deficient mice, implying that hyperactivity does not occur in response to discrete novel stimuli. The present data suggest that the behavior of αCaMKII autophosphorylation-deficient mice cannot simply be described as a low anxiety phenotype. Instead it is suggested that αCaMKII autophosphorylation influences locomotor reactivity to novel environments that are potentially, but not necessarily threatening.

Imaging escape and avoidance behavior in zebrafish larvae

This review provides an overview of the assays that are used for measuring escape and avoidance behavior in zebrafish, with a specific focus on zebrafish larvae during the first week of development. Zebrafish larvae display a startle response when exposed to tactile, acoustic, or visual stimuli and will avoid dark areas, moving objects, conspecifics, and open spaces. Emotional states such as fear and anxiety might be induced when larvae are exposed to stimuli that they would normally escape from or avoid. Although these emotional states probably differ between species and change during development, much can be learned about human fear and anxiety using zebrafish as a model system. The molecular mechanisms of fear and anxiety are highly conserved in vertebrates and are present during early zebrafish development. Larvae during the first week of development display elevated cortisol levels in response to stress and are sensitive to the same anxiolytics that are used for the management of anxiety in humans. Zebrafish larvae are well suited for high-throughput analyses of behavior, and automated systems have been developed for imaging and analyzing the behavior of zebrafish larvae in multiwell plates. These high-throughput analyses will not only provide a wealth of information on the genes and environmental factors that influence escape and avoidance behaviors and the emotional states that might accompany them but will also facilitate the discovery of novel pharmaceuticals that could be used in the management of anxiety disorders in humans.

Different role of the ventral medial prefrontal cortex on modulation of innate and associative learned fear

Reversible inactivation of the ventral portion of medial prefrontal cortex (vMPFC) of the rat brain has been shown to induce anxiolytic-like effects in animal models based on associative learning. The role of this brain region in situations involving innate fear, however, is still poorly understood, with several contradictory results in the literature. The objective of the present work was to verify in male Wistar rats the effects of vMPFC administration of cobalt chloride (CoCl(2)), a selective inhibitor of synaptic activity, in rats submitted to two models based on innate fear, the elevated plus-maze (EPM) and light-dark box (LDB), comparing the results with those obtained in two models involving associative learning, the contextual fear conditioning (CFC) and Vogel conflict (VCT) tests. The results showed that, whereas CoCl(2) induced anxiolytic-like effects in the CFC and VCT tests, it enhanced anxiety in rats submitted to the EPM and LDB. Together these results indicate that the vMPFC plays an important but complex role in the modulation of defensive-related behaviors, which seems to depend on the nature of the anxiety/fear inducing stimuli.

Acids in the brain: a factor in panic?

Several methods to experimentally induce panic cause profound acid-base disturbances. Evidence suggests that CO(2) inhalations, lactate infusions and, to a certain extent, voluntary hyperventilation can conceivably lead to a common scenario of brain acidosis in the face of disparate intravascular pH alterations. The importance of this event is reflected in data that support a model in which experimental panic attacks, as proxy to those occurring spontaneously, constitute a response to acute brain acidosis. Given that central CO(2)/H(+) chemoreception is an important drive for ventilation, and many chemosensitive neurons are related to respiration and arousal, this model can explain much of the connection between panic and respiration. We propose that the shared characteristics of CO(2)/H(+) sensing neurons overlap to a point where threatening disturbances in brain pH homeostasis, such as those produced by CO(2) inhalations, elicit a primal emotion that can range from breathlessness to panic.

Neuroanatomy of anxiety

The evolutionary approach to human anxiety is based on the defensive responses that nonhuman animals show to fear-provoking stimuli. Studies performed mostly on rodents have related areas such as the medial prefrontal cortex, amygdaloid and hypothalamic nuclei, hipoccampal formation, and midbrain central gray to these responses. It is clear, however, that animals show different and sometimes opposite responses according to the threatening stimulus. These responses include immediate reactions such as freezing or flight, behavioral inhibition or avoidance, which are organized by at least partially distinct brain systems. As discussed in this chapter, several pieces of evidence indicate that these brain systems are similar in rodents and primates. In addition, recent neuroimaging studies also suggest dysfunctions in these systems are probably related to anxiety disorders in humans.

Role of homocysteic acid in the guinea pig (Cavia porcellus) anterior cingulate cortex in tonic immobility and the influence of NMDA receptors on the dorsal PAG

Tonic immobility (TI) is an innate defensive behaviour elicited by physical restriction and postural inversion, and is characterised by a profound and temporary state of akinesis. Our previous studies demonstrated that glutamatergic stimulation of the dorsomedial/dorsolateral portion of periaqueductal gray matter (dPAG) decreases the duration of TI in guinea pigs (Cavia porcellus). Furthermore, evidence suggests that the anterior cingulate cortex (ACC) constitutes an important source of glutamate for the dPAG. Hence, in the current study, we investigated the effects of microinjection of the excitatory amino acid (EAA) agonist DL-homocysteic acid (DLH) and the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 into the ACC on the duration of TI in guinea pigs. We also assessed the effect of the NMDA receptor antagonist (MK-801) into the dorsal periaqueductal gray matter (dPAG) prior to DLH microinjection into the ACC on the TI duration in the guinea pig. Our results demonstrated that DLH microinjections into the ACC decreased the duration of TI. This effect was blocked by previous MK-801 microinjections into the ACC or into the dPAG. The MK-801 microinjections alone did not influence TI duration. These results provide the new insight that EAAs in the ACC can decrease the duration of TI. The mechanism seems to be dependent on the NMDA receptors present in the ACC and in the dPAG.

Both predator and prey: emotional arousal in threat and reward

This research examined the psychophysiology of emotional arousal anticipatory to potentially aversive and highly pleasant outcomes. Human brain reactions (event-related potentials) and body reactions (heart rate, skin conductance, the probe startle reflex) were assessed along motivational gradients determined by apparent distance from sites of potential punishment or reward. A predator-prey survival context was simulated using cues that signaled possible money rewards or possible losses; the cues appeared to loom progressively closer to the viewer, until a final step when a rapid key response could ensure reward or avoid a punishing loss. The observed anticipatory response patterns of heightened vigilance and physiological mobilization are consistent with the view that the physiology of emotion is founded on action dispositions that evolved in mammals to facilitate survival by dealing with threats or capturing life-sustaining rewards.

Activity of the medial prefrontal cortex and amygdala underlies one-trial tolerance of rats in the elevated plus-maze

The anxiolytic effects of benzodiazepines are reduced after a single exposure of rats to elevated plus-maze test (EPM). Midazolam showed an anxioselective profile in animals submitted to one session (T1) but did not change the usual exploratory behavior of rats exposed twice (T2) to the EPM. In this study we examined further the one-trial tolerance by performing a factor analysis of the exploratory behavior of rats injected with saline before both trials as well as an immunohistochemistry study for quantification of Fos expression in encephalic structures after these sessions. Factor analysis of all behavioral categories revealed that factor 1 consisted of anxiety-related categories in T1 whereas these same behavioral categories loaded on factor 2 in T2. Risk assessment was also dissociated as it loaded stronger on T2 (factor 3) than on T1 (factor 4). Locomotor activity in T1 loaded on factor 5. Immunohistochemistry analyses showed that Fos expression predominated in limbic structures in T1 group. The medial prefrontal cortex and amygdala were the main areas activated in T2 group. These data suggest that anxiety and risk assessment behaviors change their valence across the EPM sessions. T2 is characterized by the emergence of a fear factor, more powerful risk assessment and medial prefrontal cortex activation. The amygdala functions as a switch between the anxiety-like patterns of T1 to the cognitive control of fear prevalent in T2. The EPM retest session is proposed as a tool for assessing the cognitive activity of rodents in the control of fear.