Lactate- and isoproterenol-induced panic attacks in panic disorder patients and controls

Interoceptive Anxiety and Body Representation in Anorexia Nervosa

Individuals with anorexia nervosa (AN) typically display anxious traits prior to the onset of food avoidance and weight loss that characterize the disorder. Meal associated anxiety is an especially common clinical feature in these patients, and heightened sensitivity to sympathetically mediated interoceptive sensations has also been observed. However, it remains unclear how heightened interoceptive sensitivity relates to experiences of anxiety before and after meals. To investigate this relationship, we experimentally induced anxiety and panic symptoms with isoproterenol, a peripheral sympathetic agonist similar to adrenaline, across several different conditions: during panic provocation, during anticipation of a 1,000 Calorie meal, and after meal consumption. Fifteen AN and 15 age- and sex-matched healthy comparisons received bolus infusions of isoproterenol and saline in a double-blinded, randomized design. Participants rated anxiety symptoms after each infusion, completed panic rating scales, and traced the location of perceived palpitations on a manikin to index interoceptive "body map" representation. The AN group reported significantly elevated anxiety relative to healthy comparisons during infusions before and after the meal, but surprisingly, not during panic provocation. These symptoms were accompanied by geographical differences in patterns of perceived heartbeat sensations across each condition. In particular, the AN group localized heartbeat sensations disproportionately to the chest during meal related saline infusions, when no cardiorespiratory modulation actually occurred. The AN group also showed a trend toward higher panic attack rates during the meal anticipation period. Correcting for anxiety levels reported during saline infusions abolished group differences in anxiety change across all conditions, suggesting a significant contribution of anxious traits in AN. The observation of meal related "visceral illusions" provides further evidence that AN is associated with abnormal interoceptive representation of the heartbeat and suggests that meal consumption, particularly when anticipated, preferentially alters the processing of interoception related signals in AN.

Panic Anxiety in Humans with Bilateral Amygdala Lesions: Pharmacological Induction via Cardiorespiratory Interoceptive Pathways

We previously demonstrated that carbon dioxide inhalation could induce panic anxiety in a group of rare lesion patients with focal bilateral amygdala damage. To further elucidate the amygdala-independent mechanisms leading to aversive emotional experiences, we retested two of these patients (B.G. and A.M.) to examine whether triggering palpitations and dyspnea via stimulation of non-chemosensory interoceptive channels would be sufficient to elicit panic anxiety. Participants rated their affective and sensory experiences following bolus infusions of either isoproterenol, a rapidly acting peripheral β-adrenergic agonist akin to adrenaline, or saline. Infusions were administered during two separate conditions: a panic induction and an assessment of cardiorespiratory interoception. Isoproterenol infusions induced anxiety in both patients, and full-blown panic in one (patient B.G.). Although both patients demonstrated signs of diminished awareness for cardiac sensation, patient A.M., who did not panic, reported a complete lack of awareness for dyspnea, suggestive of impaired respiratory interoception. These findings indicate that the amygdala may play a role in dynamically detecting changes in cardiorespiratory sensation. The induction of panic anxiety provides further evidence that the amygdala is not required for the conscious experience of fear induced via interoceptive sensory channels.

SIGNIFICANCE STATEMENT

We found that monozygotic twins with focal bilateral amygdala lesions report panic anxiety in response to intravenous infusions of isoproterenol, a β-adrenergic agonist similar to adrenaline. Heightened anxiety was evident in both twins, with one twin experiencing a panic attack. The twin who did not panic displayed signs of impaired cardiorespiratory interoception, including a complete absence of dyspnea sensation. These findings highlight that the amygdala is not strictly required for the experience of panic anxiety, and suggest that neural systems beyond the amygdala are also involved. Determining these additional systems could provide key neural modulation targets for future anxiolytic treatments.

Lifestyle Behaviours Add to the Armoury of Treatment Options for Panic Disorder: An Evidence-Based Reasoning

This article presents an evidence-based reasoning, focusing on evidence of an Occupational Therapy input to lifestyle behaviour influences on panic disorder that also provides potentially broader application across other mental health problems (MHP). The article begins from the premise that we are all different. It then follows through a sequence of questions, examining incrementally how MHPs are experienced and classified. It analyses the impact of individual sensitivity at different levels of analysis, from genetic and epigenetic individuality, through neurotransmitter and body system sensitivity. Examples are given demonstrating the evidence base behind the logical sequence of investigation. The paper considers the evidence of how everyday routine lifestyle behaviour impacts on occupational function at all levels, and how these behaviours link to individual sensitivity to influence the level of exposure required to elicit symptomatic responses. Occupational Therapists can help patients by adequately assessing individual sensitivity, and through promoting understanding and a sense of control over their own symptoms. It concludes that present clinical guidelines should be expanded to incorporate knowledge of individual sensitivities to environmental exposures and lifestyle behaviours at an early stage.

An animal model of panic vulnerability with chronic disinhibition of the dorsomedial/perifornical hypothalamus

Panic disorder (PD) is a severe anxiety disorder characterized by susceptibility to induction of panic attacks by subthreshold interoceptive stimuli such as sodium lactate infusions or hypercapnia induction. Here we review a model of panic vulnerability in rats involving chronic inhibition of GABAergic tone in the dorsomedial/perifornical hypothalamic (DMH/PeF) region that produces enhanced anxiety and freezing responses in fearful situations, as well as a vulnerability to displaying acute panic-like increases in cardioexcitation, respiration activity and "flight" associated behavior following subthreshold interoceptive stimuli that do not elicit panic responses in control rats. This model of panic vulnerability was developed over 15 years ago and has provided an excellent preclinical model with robust face, predictive and construct validity. The model recapitulates many of the phenotypic features of panic attacks associated with human panic disorder (face validity) including greater sensitivity to panicogenic stimuli demonstrated by sudden onset of anxiety and autonomic activation following an administration of a sub-threshold (i.e., do not usually induce panic in healthy subjects) stimulus such as sodium lactate, CO(2), or yohimbine. The construct validity is supported by several key findings; DMH/PeF neurons regulate behavioral and autonomic components of a normal adaptive panic response, as well as being implicated in eliciting panic-like responses in humans. Additionally, patients with PD have deficits in central GABA activity and pharmacological restoration of central GABA activity prevents panic attacks, consistent with this model. The model's predictive validity is demonstrated by not only showing panic responses to several panic-inducing agents that elicit panic in patients with PD, but also by the positive therapeutic responses to clinically used agents such as alprazolam and antidepressants that attenuate panic attacks in patients. More importantly, this model has been utilized to discover novel drugs such as group II metabotropic glutamate agonists and a new class of translocator protein enhancers of GABA, both of which subsequently showed anti-panic properties in clinical trials. All of these data suggest that this preparation provides a strong preclinical model of some forms of human panic disorders.

The age of anxiety: role of animal models of anxiolytic action in drug discovery

Anxiety disorders are common, serious and a growing health problem worldwide. However, the causative factors, aetiology and underlying mechanisms of anxiety disorders, as for most psychiatric disorders, remain relatively poorly understood. Animal models are an important aid in giving insight into the aetiology, neurobiology and, ultimately, the therapy of human anxiety disorders. The approach, however, is challenged with a number of complexities. In particular, the heterogeneous nature of anxiety disorders in humans coupled with the associated multifaceted and descriptive diagnostic criteria, creates challenges in both animal modelling and in clinical research. In this paper, we describe some of the more widely used approaches for assessing the anxiolytic activity of known and potential therapeutic agents. These include ethological, conflict-based, hyponeophagia, vocalization-based, physiological and cognitive-based paradigms. Developments in the characterization of translational models are also summarized, as are the challenges facing researchers in their drug discovery efforts in developing new anxiolytic drugs, not least the ever-shifting clinical conceptualization of anxiety disorders. In conclusion, to date, although animal models of anxiety have relatively good validity, anxiolytic drugs with novel mechanisms have been slow to emerge. It is clear that a better alignment of the interactions between basic and clinical scientists is needed if this is to change.

Changes in central sodium and not osmolarity or lactate induce panic-like responses in a model of panic disorder

Panic disorder is a severe anxiety disorder characterized by recurrent panic attacks that can be consistently provoked with intravenous (i.v.) infusions of hypertonic (0.5 M) sodium lactate (NaLac), yet the mechanism/CNS site by which this stimulus triggers panic attacks is unclear. Chronic inhibition of GABAergic synthesis in the dorsomedial hypothalamus/perifornical region (DMH/PeF) of rats induces a vulnerability to panic-like responses after i.v. infusion of 0.5 M NaLac, providing an animal model of panic disorder. Using this panic model, we previously showed that inhibiting the anterior third ventricle region (A3Vr; containing the organum vasculosum lamina terminalis, the median preoptic nucleus, and anteroventral periventricular nucleus) attenuates cardiorespiratory and behavioral responses elicited by i.v. infusions of NaLac. In this study, we show that i.v. infusions of 0.5 M NaLac or sodium chloride, but not iso-osmolar D-mannitol, increased 'anxiety' (decreased social interaction) behaviors, heart rate, and blood pressure responses. Using whole-cell patch-clamp preparations, we also show that bath applications of NaLac (positive control), but not lactic acid (lactate stimulus) or D-mannitol (osmolar stimulus), increases the firing rates of neurons in the A3Vr, which are retrogradely labeled from the DMH/PeF and which are most likely glutamatergic based on a separate study using retrograde tracing from the DMH/PeF in combination with in situ hybridization for vesicular glutamate transporter 2. These data show that hypertonic sodium, but not hyper-osmolarity or changes in lactate, is the key stimulus that provokes panic attacks in panic disorder, and is consistent with human studies.

Experimental induction of panic-like symptoms in patients with postural tachycardia syndrome

Patients with postural tachycardia syndrome (POTS) might be misdiagnosed with panic disorder due to shared clinical features. The first aim of our study was to investigate the relationship between symptoms of POTS and panic disorder. The second aim was to delineate clinical features distinguishing symptoms of POTS from panic disorder. A total of 11 patients with POTS and 11 control subjects participated in an IRB-approved, prospective, placebo-controlled study. The experimentally induced panic-like symptoms of POTS were systematically studied using the Acute Panic Inventory (API) questionnaire. The participants answered the questionnaire after each placebo infusion and after each of the three provoking stimuli: head-up tilt test (HUT), isoproterenol infusion (ISI), and sodium lactate infusion (SLI). API responses were summed for each subject at each time point of administration. Individual API symptoms and summed responses were analyzed for statistical significance. All patients with POTS developed symptoms of orthostatic intolerance during HUT. Pharmacologically induced symptoms subjectively mimicked spontaneous symptoms in 5 of 11 patients during ISI and in none of 11 patients during SLI. In contrast, API scores in these patients reached panic threshold in 0 of 11 following HUT, in 4 of 11 following ISI and in 4 of 11 following SLI. Individual symptoms analysis revealed that significant increase in scores was limited to the somatic symptoms of palpitations, dyspnea, and twitching or trembling. In conclusion, the symptoms of POTS are phenomenologically different and clinically distinguishable from panic disorder symptoms.

Lactate-induced anxiety after imipramine and diazepam treatment

To examine the effect of treatment on lactate-induced anxiety in a controlled study, we infused 44 panic disorder patients with lactate and placebo before and after eight weeks of double-blind treatment with imipramine, diazepam, or placebo. During treatment, both imipramine and diazepam groups improved more than the placebo group. After treatment, patients in both the imipramine and diazepam groups had significantly less anxiety than the placebo patients when reinfused with lactate. In addition, imipramine decreased posttreatment panic attack frequency and diazepam decreased the perceived severity of posttreatment lactate-induced panic attacks. This study demonstrates that diazepam, like imipramine, is an effective treatment for panic disorder, and that both imipramine and diazepam blunt lactate-induced anxiety in a placebo controlled study.

Intravenous sodium lactate decreases plasma GABA levels in man

Gamma aminobutyric acid (GABA), an inhibitory neurotransmitter, may play an important role in anxiety. We studied changes in plasma GABA levels in nine healthy subjects before and after infusions of sodium lactate and dextrose. Plasma GABA significantly decreased during infusions of sodium lactate (109.3 +/- 4.4 versus 91.6 +/- 5.1 pmol/ml; P = 0.0001) but not during infusions of dextrose.

Differential responses to anxiogenic challenge studies in patients with major depressive disorder and panic disorder

Anxiogenic challenge studies (intravenous lactate infusion and oral fenfluramine challenge) were conducted in 17 patients with panic disorder (PD), 12 patients with major depressive disorder and a history of panic attacks (MDD-PD), 27 patients with major depression and no history of panic (MDD), and 12 normal controls. PD and MDD-PD patients revealed significantly greater anxiogenic responses to lactate infusion and fenfluramine administration than either MDD patients or controls. PD patients revealed the most robust anxiogenic responses to both challenges as well as associated significant prolactin and cortisol responses to fenfluramine. The findings suggest that the predisposition to panic attacks as seen in PD and MDD-PD patients may represent a distinct neurobiological diathesis which may coexist with a major depressive diathesis in some patients. The delineation of subgroups within the more heterogenous groups of patients with MDD and/or PD will lead to greater precision in the development of clinical treatment strategies. Thus, MDD-PD patients (better called panic-depressives) may have a more severe illness than patients with MDD alone which must be accounted for in the course of pharmacotherapy and psychotherapy.

Somatic and psychological symptoms during isoproterenol-induced panic attacks

To determine which symptoms characterized isoproterenol-induced panic attacks, we analyzed the presence of panic attacks in 54 panic disorder patients who panicked, 24 patients who did not panic, and 37 controls who did not panic during isoproterenol infusions. The increases over the baseline of the symptoms shortness of breath and fear of going crazy were highly associated with panicking patients when compared to nonpanicking patients and nonpanicking controls. The increases of the symptoms trembling and shaking, generally nervous, and fear of going crazy were highly associated with patients when compared to controls. The possibility of a cognitive theory of panic attacks is discussed.

Fenfluramine provocation of anxiety in patients with panic disorder

Fenfluramine, and indirect serotonergic agonist, was administered to nine women with panic disorder, nine women with major depressive disorder, and nine women controls. Panic disorder patients revealed significantly greater anxiogenic responses to fenfluramine administration at all 5 hourly measurement points than either depressed patients or control subjects. Prolactin and cortisol responses to fenfluramine were also significantly greater in panic disorder patients than in either depressed patients or control subjects. Placebo administration did not elicit robust or significantly different anxiety or hormonal responses in panic disorder patients or control subjects. These data offer evidence that serotonergic hyperresponsivity must be considered as an important factor in the mechanism of events provoking overt panic attacks.

Lactate infusions in panic disorder patients and normal controls: autonomic measures and subjective anxiety

The anxiety symptoms, heart rate and blood pressure of 61 patients who panicked during lactate infusions were compared with 25 control nonpanickers. There was no significant difference in the increase in heart rate and blood pressure over baseline between patients and controls. There appeared to be no significant correlation between the subjective anxiety ratings and the measures of heart rate and blood pressure during lactate-induced panic. The symptoms of shortness of breath, feeling frightened or afraid, feeling dizzy and fear of losing control were significantly associated with lactate-induced panic. In addition, the cognitive symptoms of fear of losing control and fear of going crazy appear to be important determinants of lactate-induced panic.

Isoproterenol-induced panic attacks

Eighty-six panic disorder patients and 45 nonpsychiatric controls were infused with isoproterenol at a rate of 1 microgram/min for up to 20 min in a placebo-controlled, double-blind study. Sixty-six percent of panic disorder patients experienced panic attacks during isoproterenol infusions, compared to 16% during placebo infusions. Nine percent of control subjects panicked with isoproterenol, but none panicked with placebo. Patients were more sensitive than controls to the anxiogenic effects of isoproterenol, as measured by subject self-ratings on a panic description scale. The frequency of panic attacks induced in patients was related to the dosage of isoproterenol; 79% of the patients who received a mean of 18.5 ng/min/kg of isoproterenol panicked. The panic attacks experienced by patients during isoproterenol infusions were similar to those experienced during placebo infusions.

Phenomenological comparison of dextrose, lactate, and isoproterenol associated panic attacks

To investigate the relationship between naturally occurring and drug-induced panic attacks, we compared the phenomenology of panic attacks in 12 panic disorder patients who panicked during both placebo and lactate infusion and in 9 panic disorder patients who panicked during both placebo and isoproterenol infusions. Panic attacks during lactate and isoproterenol infusions were similar to the panic attacks during placebo infusions.