Functional neuroanatomy of CCK-4-induced panic attacks in healthy volunteers

Neural basis of anxiolytic effects of cannabidiol (CBD) in generalized social anxiety disorder: a preliminary report

Animal and human studies indicate that cannabidiol (CBD), a major constituent of cannabis, has anxiolytic properties. However, no study to date has investigated the effects of this compound on human pathological anxiety and its underlying brain mechanisms. The aim of the present study was to investigate this in patients with generalized social anxiety disorder (SAD) using functional neuroimaging. Regional cerebral blood flow (rCBF) at rest was measured twice using (99m)Tc-ECD SPECT in 10 treatment-naïve patients with SAD. In the first session, subjects were given an oral dose of CBD (400 mg) or placebo, in a double-blind procedure. In the second session, the same procedure was performed using the drug that had not been administered in the previous session. Within-subject between-condition rCBF comparisons were performed using statistical parametric mapping. Relative to placebo, CBD was associated with significantly decreased subjective anxiety (p < 0.001), reduced ECD uptake in the left parahippocampal gyrus, hippocampus, and inferior temporal gyrus (p < 0.001, uncorrected), and increased ECD uptake in the right posterior cingulate gyrus (p < 0.001, uncorrected). These results suggest that CBD reduces anxiety in SAD and that this is related to its effects on activity in limbic and paralimbic brain areas.

CCK-4: Psychophysiological conditioning elicits features of spontaneous panic attacks

INTRODUCTION

Cholecystokinin-tetrapeptide (CCK-4) is an established model to generate subjective panic anxiety. CCK-4 injection also results in consistent and dose-dependent rise of stress hormones. Effects other than upon subjective panic and stress hormone activity have barely been examined. The purpose of the study was to investigate CCK-4 effects on emotional facial expression and especially on fear relevant facial muscles establishing therewith a more objective method to measure subjective panic anxiety.

METHODS

20 healthy male subjects were randomly and double-blindedly assigned in two groups (dose groups), each of which was investigated three times once with placebo and twice with 25 μg or 50 μg CCK-4 respectively. Subjects of each group were randomly assigned in two different balanced orders of investigations: CCK-CCK-Placebo vs. Placebo-CCK-CCK. Facial muscle and hypothalamo-pituitary-adrenocortical (HPA)-axis activity were recorded.

RESULTS

CCK-4 led dose-dependently to an increase of panic anxiety, an activation of fear relevant facial muscles and a rise of stress hormones. Whereas placebo administration before CCK-4 revealed no significant panic and stress response, during placebo following CCK-4 stimulations a psychophysiological conditioning effect could be observed without rise in HPA-axis activity.

DISCUSSION

Our findings indicate the possibility to measure different intensities of panic anxiety and conditioning effects with a facial EMG method. Dissociation of HPA-activity and fear relevant facial muscle activity is in accordance with former results about spontaneous panic attacks.

First episode drug-naïve major depressive disorder with panic disorder: gray matter deficits in limbic and default network structures

This study was designed to investigate the structural differences in the brains of first episode, drug-naïve patients with major depressive disorder and panic disorder versus healthy control subjects. High-resolution brain magnetic resonance images were performed on patients and health control subjects (age, sex and handedness matched). Structural magnetic resonance images of brain were estimated by optimized voxel-based morphometry of FSL (FMRIB Software Library). Patients had deficits of gray matter volumes over right anterior cingulate cortex, right medial frontal gyrus, left posterior cingulate cortex, right parahippocampal gyrus, limbic areas, occipital lingual gyrus and bilateral cerebellums when compared to controls. These results suggested that this group of patients has possible deficits of gray matter volumes over the default-mode network, fronto-cingulate and limbic structures. The decline of gray matter volumes might have started since the first episode.

The neurocircuitry of fear, stress, and anxiety disorders

Anxiety disorders are a significant problem in the community, and recent neuroimaging research has focused on determining the brain circuits that underlie them. Research on the neurocircuitry of anxiety disorders has its roots in the study of fear circuits in animal models and the study of brain responses to emotional stimuli in healthy humans. We review this research, as well as neuroimaging studies of anxiety disorders. In general, these studies have reported relatively heightened amygdala activation in response to disorder-relevant stimuli in post-traumatic stress disorder, social phobia, and specific phobia. Activation in the insular cortex appears to be heightened in many of the anxiety disorders. Unlike other anxiety disorders, post-traumatic stress disorder is associated with diminished responsivity in the rostral anterior cingulate cortex and adjacent ventral medial prefrontal cortex. Additional research will be needed to (1) clarify the exact role of each component of the fear circuitry in the anxiety disorders, (2) determine whether functional abnormalities identified in the anxiety disorders represent acquired signs of the disorders or vulnerability factors that increase the risk of developing them, (3) link the findings of functional neuroimaging studies with those of neurochemistry studies, and (4) use functional neuroimaging to predict treatment response and assess treatment-related changes in brain function.

Neuroimaging in anxiety disorders

Neuroimaging studies have gained increasing importance in validating neurobiological network hypotheses for anxiety disorders. Functional imaging procedures and radioligand binding studies in healthy subjects and in patients with anxiety disorders provide growing evidence of the existence of a complex anxiety network, including limbic, brainstem, temporal, and prefrontal cortical regions. Obviously, "normal anxiety" does not equal "pathological anxiety" although many phenomena are evident in healthy subjects, however to a lower extent. Differential effects of distinct brain regions and lateralization phenomena in different anxiety disorders are mentioned. An overview of neuroimaging investigations in anxiety disorders is given after a brief summary of results from healthy volunteers. Concluding implications for future research are made by the authors.

Unstable prefrontal response to emotional conflict and activation of lower limbic structures and brainstem in remitted panic disorder

Background

The neural mechanisms of panic disorder (PD) are only incompletely understood. Higher sensitivity of patients to unspecific fear cues and similarities to conditioned fear suggest involvement of lower limbic and brainstem structures. We investigated if emotion perception is altered in remitted PD as a trait feature.

Methodology/Principal Findings

We used blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) to study neural and behavioural responses of 18 remitted PD patients and 18 healthy subjects to the emotional conflict paradigm that is based on the presentation of emotionally congruent and incongruent face/word pairs. We observed that patients showed stronger behavioural interference and lower adaptation to interference conflict. Overall performance in patients was slower but not less accurate. In the context of preceding congruence, stronger dorsal anterior cingulate cortex (dACC) activation during conflict detection was found in patients. In the context of preceding incongruence, controls expanded dACC activity and succeeded in reducing behavioural interference. In contrast, patients demonstrated a dropout of dACC and dorsomedial prefrontal cortex (dmPFC) recruitment but activation of the lower limbic areas (including right amygdala) and brainstem.

Conclusions/Significance

This study provides evidence that stimulus order in the presentation of emotional stimuli has a markedly larger influence on the brain's response in remitted PD than in controls, leading to abnormal responses of the dACC/dmPFC and lower limbic structures (including the amygdala) and brainstem. Processing of non-panic related emotional stimuli is disturbed in PD patients despite clinical remission.