Panic results in unique molecular and network changes in the amygdala that facilitate fear responses

Recurrent panic attacks (PAs) are a common feature of panic disorder (PD) and post-traumatic stress disorder (PTSD). Several distinct brain regions are involved in the regulation of panic responses, such as perifornical hypothalamus (PeF), periaqueductal gray, amygdala and frontal cortex. We have previously shown that inhibition of GABA synthesis in the PeF produces panic-vulnerable rats. Here, we investigate the mechanisms by which a panic-vulnerable state could lead to persistent fear. We first show that optogenetic activation of glutamatergic terminals from the PeF to the basolateral amygdala (BLA) enhanced the acquisition, delayed the extinction and induced the persistence of fear responses 3 weeks later, confirming a functional PeF-amygdala pathway involved in fear learning. Similar to optogenetic activation of PeF, panic-prone rats also exhibited delayed extinction. Next, we demonstrate that panic-prone rats had altered inhibitory and enhanced excitatory synaptic transmission of the principal neurons, and reduced protein levels of metabotropic glutamate type 2 receptor (mGluR2) in the BLA. Application of an mGluR2-positive allosteric modulator (PAM) reduced glutamate neurotransmission in the BLA slices from panic-prone rats. Treating panic-prone rats with mGluR2 PAM blocked sodium lactate (NaLac)-induced panic responses and normalized fear extinction deficits. Finally, in a subset of patients with comorbid PD, treatment with mGluR2 PAM resulted in complete remission of panic symptoms. These data demonstrate that a panic-prone state leads to specific reduction in mGluR2 function within the amygdala network and facilitates fear, and mGluR2 PAMs could be a targeted treatment for panic symptoms in PD and PTSD patients.

Respiratory variability in panic disorder

Disordered breathing may play an important role in the pathophysiology of panic disorder. Several studies have now indicated that panic disorder patients have greater respiratory variability than normal controls. In this study, we examine baseline respiratory measures in four diagnostic groups to determine whether greater respiratory variability is specific to panic disorder and whether effective anti-panic treatment alters respiratory variability. Patients with panic disorder, major depression, or premenstrual dysphoric disorder, and normal control subjects underwent two respiratory exposures (5% and 7% CO(2) inhalation), while in a canopy system. Panic disorder patients returned after 12 weeks of either anti-panic medication or cognitive behavioral therapy, and were retested. Normal control subjects were also retested after a period of 12 weeks. Panic disorder patients had significantly greater respiratory variability at baseline than normal control subjects and patients with major depression. The premenstrual dysphoric patients also had greater variability than the normal control group. Panic disorder patients who panicked to 7% CO(2) inhalation had significantly greater baseline variability than panic disorder patients who did not panic. Anti-panic treatment did not significantly alter baseline respiratory variability. Our data suggest that increased respiratory variability may be an important trait feature for some panic disorder patients and may make them more vulnerable to CO(2)-induced panic.

Specificity of panic response to CO(2) inhalation in panic disorder: a comparison with major depression and premenstrual dysphoric disorder

OBJECTIVE

The behavioral response to CO(2) inhalation has been used to differentiate panic disorder patients from normal subjects and other clinical populations. This study extended examination of the diagnostic specificity of CO(2)-induced anxiety by testing panic disorder patients and clinical populations with reported low and high sensitivity to CO(2) inhalation (patients with major depression and patients with premenstrual dysphoric disorder, respectively).

METHOD

The behavioral responses to inhalation of 5% and 7% CO(2), administered by means of a respiratory canopy, were studied in 50 patients with panic disorder, 21 with major depression, and 10 with premenstrual dysphoric disorder and in 34 normal comparison subjects. Occurrence of panic attacks was judged with DSM-IV criteria by a blind rater. Subjects were rated on three behavioral scales at baseline and after each CO(2) inhalation.

RESULTS

Panic disorder patients had a higher rate of CO(2)-induced panic attacks than depressed patients and normal subjects, whose panic rates were not distinguishable. The panic rate for patients with premenstrual dysphoric disorder was similar to that for panic disorder patients and higher than that for normal subjects. Subjects with CO(2)-induced panic attacks had similarly high ratings on the behavioral scales, regardless of diagnosis, including the small number of panicking normal subjects. Seven percent CO(2) was a more robust panicogen than 5%, and response to 7% CO(2 )better distinguished panic disorder patients from normal subjects than response to 5% CO(2).

CONCLUSIONS

Patients with panic disorder and patients with premenstrual dysphoric disorder are highly susceptible to CO(2)-induced panic attacks, and depressed patients appear to be insensitive to CO(2) inhalation. The symptoms of CO(2)-induced panic attacks have a similar intensity regardless of the subject's diagnosis.

Childhood obsessive-compulsive disorder: a review

Obsessive-compulsive disorder (OCD) holds a particular interest for child psychiatrists because of the high proportion of cases with onset in childhood and adolescence. Over the last two decades, substantial progress has been made in describing OCD in children and adolescents and in developing and implementing effective treatments. In addition, research on the phenomenology, neurobiology, and psychopharmacology of OCD has led to its current conceptualization as a developmental neuropsychiatric disorder. In this article, the fourth in a series on OCD, the authors summarize the most recent data on the phenomenology, etiology, neurobiology, and treatment of OCD in children and adolescents.

Neuroanatomical hypothesis of panic disorder, revised

OBJECTIVE

In a 1989 article, the authors provided a hypothesis for the neuroanatomical basis of panic disorder that attempted to explain why both medication and cognitive behavioral psychotherapy are effective treatments. Here they revise that hypothesis to consider developments in the preclinical understanding of the neurobiology of fear and avoidance.

METHOD

The authors review recent literature on the phenomenology, neurobiology, and treatment of panic disorder and impressive developments in documenting the neuroanatomy of conditioned fear in animals.

RESULTS

There appears to be a remarkable similarity between the physiological and behavioral consequences of response to a conditioned fear stimulus and a panic attack. In animals, these responses are mediated by a "fear network" in the brain that is centered in the amygdala and involves its interaction with the hippocampus and medial prefrontal cortex. Projections from the amygdala to hypothalamic and brainstem sites explain many of the observed signs of conditioned fear responses. It is speculated that a similar network is involved in panic disorder. A convergence of evidence suggests that both heritable factors and stressful life events, particularly in early childhood, are responsible for the onset of panic disorder.

CONCLUSIONS

Medications, particularly those that influence the serotonin system, are hypothesized to desensitize the fear network from the level of the amygdala through its projects to the hypothalamus and the brainstem. Effective psychosocial treatments may also reduce contextual fear and cognitive misattributions at the level of the prefrontal cortex and hippocampus. Neuroimaging studies should help clarify whether these hypotheses are correct.

SNaRIs, NaSSAs, and NaRIs: new agents for the treatment of depression

A major goal of antidepressant development is to improve on preceding drug classes with agents with greater specificity (and therefore fewer unwanted side-effects) and with more rapid onset of antidepressant action. To this end, four antidepressants with significantly distinct pharmacological characteristics have been recently introduced: venlafaxine, nefazodone, mirtazapine, and reboxetine. Venlafaxine is the first antidepressant in a new drug class referred to as the serotonin noradrenergic reuptake inhibitors (SNaRIs). Nefazodone is a weaker serotonin and norepinephrine reuptake inhibitor, but a potent serotonin 5-HT2 receptor antagonist. Mirtazapine is a potent antagonist of central 2alpha-adrenergic autoreceptors, and heteroreceptors and is an antagonist of serotonin 5-HT2 and 5-HT3 receptors. The result of these actions is to increase both noradrenergic and specific (5-HT1) serotonergic transmission, and mirtazapine has therefore been termed a noradrenergic and specific serotonergic antidepressant (NaSSA). Reboxetine is the first selective noradrenaline reuptake inhibitor (NaRI) to be introduced since the tricyclics, and lacks immediate serotonergic effects.

The noradrenergic system in pathological anxiety: a focus on panic with relevance to generalized anxiety and phobias

Over the past three decades of psychiatric research, abnormalities in the noradrenergic system have been identified in particular anxiety disorders such as panic disorder. Simultaneously, neuroscience research on fear pathways and the stress response have delineated central functions for the noradrenergic system. This review focuses on the noradrenergic system in anxiety spectrum disorders such as panic disorder, generalized anxiety disorder, and phobias for the purpose of elucidating current conceptualizations of the pathophysiologies. Neuroanatomic pathways that are theoretically relevant in anxiogenesis are discussed and the implications for treatment reviewed.

SSRIs and SNRIs: broad spectrum of efficacy beyond major depression

Originally studied and introduced for the treatment of depression, the selective serotonin reuptake inhibitors (SSRIs) and serotonin/norepinephrine reuptake inhibitors (SNRIs) have proven effective for a broad range of psychiatric illnesses, including several anxiety disorders, bulimia, and dysthymia. These drugs have in common important effects on the serotonergic (5-HT) neurotransmission system, which is involved in mediating a substantial number of important functions, including mood, aggression, sexual behavior, and pain. In addition, some of the new antidepressants, like venlafaxine/venlafaxine XR, also have effects on the noradrenergic neurotransmission system, which also appears important in mood and anxiety disorders. These new drugs, because of their specificity for the serotonin and norepinephrine reuptake proteins, lack most of the adverse side effects of tricyclic antidepressants and monoamine oxidase inhibitors. Consequently, in addition to being the usual first-line treatments for major depression, they are also first-line for panic disorder, obsessive-compulsive disorder, social phobia, posttraumatic stress disorder, and bulimia. They may also be the best medication treatments for dysthymia and generalized anxiety disorder. Further advances in psychopharmacology will be driven by discoveries from brain imaging and molecular biological research.

Clinical utility of the selective serotonin reuptake inhibitors in the spectrum of anxiety

The selective serotonin reuptake inhibitors (SSRIs) are now being employed in the treatment of the full spectrum of anxiety disorders. In comparative trials, the SSRIs are proving to be equal or superior in efficacy to traditional antianxiety medications. Due to their favorable side effect profile, safety, and tolerability, they are rapidly replacing older agents in the treatment of anxiety. Neuroanatomical pathways that may be important in the antianxiety effect of the SSRIs are outline and discussed, followed by a review of the clinical evidence supporting the efficacy of this class of medications in the treatment of anxiety disorders.

Ventilatory effects of tryptophan depletion in panic disorder: a preliminary report

On the basis of preclinical studies, we hypothesized that deficient serotonin neurotransmission may be associated with the respiratory hyperactivity and carbon dioxide sensitivity seen in panic disorder. We used the tryptophan depletion method to investigate the effects of transient reductions in serotonin on respiration in five patients with panic disorder and seven normal control subjects. During room air breathing, the patients showed significantly increased ventilation when tryptophan-depleted, while the normal subjects showed no significant changes in respiration. These preliminary data suggest that serotonergic manipulation may affect ventilatory indices, with panic disorder patients being particularly sensitive to the effect of tryptophan depletion.