Panic and fear induced by deep brain stimulation

BACKGROUND

Mood, cognitive, and behavioural changes have been reported with deep brain stimulation (DBS) in the thalamus, globus pallidus interna, and anterior limb of the internal capsule/nucleus accumbens region.

OBJECTIVE

To investigate panic and fear resulting from DBS.

METHODS

Intraoperative DBS in the region of the right and then left anterior limb of the internal capsule and nucleus accumbens region was undertaken to treat a 52 year old man with treatment refractory obsessive-compulsive disorder (OCD). Mood, anxiety, OCD, alertness, heart rate, and subjective feelings were recorded during intraoperative test stimulation and at follow up programming sessions.

RESULTS

DBS at the distal (0) contact (cathode 0-, anode 2+, pulse width 210 ms, rate 135 Hz, at 6 volts) elicited a panic attack (only seen at the (0) contact). The patient felt flushed, hot, fearful, and described himself as having a "panic attack." His heart rate increased from 53 to 111. The effect (present with either device) was witnessed immediately after turning the device on, and abruptly ceased in the off condition

CONCLUSIONS

DBS of the anterior limb of the internal capsule and nucleus accumbens region caused severe "panic." This response may result from activation of limbic and autonomic networks.

Functional and ultrastructural neuroanatomy of interactive intratectal/tectonigral mesencephalic opioid inhibitory links and nigrotectal GABAergic pathways: Involvement of GABAA and μ1-opioid receptors in the modulation of panic-like reactions elicited by electrical stimulation of the dorsal midbrain

In the present study, the functional neuroanatomy of nigrotectal-tectonigral pathways as well as the effects of central administration of opioid antagonists on aversive stimuli-induced responses elicited by electrical stimulation of the midbrain tectum were determined. Central microinjections of naloxonazine, a selective mu(1)-opiod receptor antagonist, in the mesencephalic tectum (MT) caused a significant increase in the escape thresholds elicited by local electrical stimulation. Furthermore, either naltrexone or naloxonazine microinjected in the substantia nigra, pars reticulata (SNpr), caused a significant increase in the defensive thresholds elicited by electrical stimulation of the continuum comprised by dorsolateral aspects of the periaqueductal gray matter (dlPAG) and deep layers of the superior colliculus (dlSC), as compared with controls. These findings suggest an opioid modulation of GABAergic inhibitory inputs controlling the defensive behavior elicited by MT stimulation, in cranial aspects. In fact, iontophoretic microinjections of the neurotracer biodextran into the SNpr, a mesencephalic structure rich in GABA-containing neurons, show outputs to neural substrate of the dlSC/dlPAG involved with the generation and organization of fear- and panic-like reactions. Neurochemical lesion of the nigrotectal pathways increased the sensitivity of the MT to electrical (at alertness, freezing and escape thresholds) and chemical (blockade of GABA(A) receptors) stimulation, suggesting a tonic modulatory effect of the nigrotectal GABAergic outputs on the neural networks of the MT involved with the organization of the defensive behavior and panic-like reactions. Labeled neurons of the midbrain tectum send inputs with varicosities to ipsi and contralateral dlSC/dlPAG and ipsilateral substantia nigra, pars reticulata and compacta, in which the anterograde and retrograde tracing from a single injection indicates that the substantia nigra has reciprocal connections with the dlSC/dlPAG featuring close axo-somatic and axo-dendritic appositions in both locations. In addition, ultrastructural approaches show inhibitory axo-axonic synapses in MT and inhibitory axo-somatic/axo-axonic synapses in the SNpr. These findings, in addition to the psychopharmacological evidence for the interaction between opioid and GABAergic mechanisms in the cranial aspects of the MT as well as in the mesencephalic tegmentum, offer a neuroanatomical basis of a pre-synaptic opioid inhibition of GABAergic nigrotectal neurons modulating fear in defensive behavior-related structures of the cranial mesencephalon, in a short link, and through a major neural circuit, also in GABA-containing perikarya and axons of nigrotectal neurons.

Role of serotonin receptors in panic-like behavior induced by nitric oxide in the rat dorsolateral periaqueductal gray: effects of chronic clomipramine treatment

Local administration of serotonin (5-HT) receptor agonists inhibits panic-like reactions induced by electrical stimulation of the rat dorsolateral periaqueductal grey (dlPAG). This anti-aversive effect is enhanced by chronic treatment with anti-panic drugs such as clomipramine. Since nitric oxide (NO) may mediate panic-like behavior in the dlPAG, we tested the hypothesis that chronic clomipramine treatment would also potentiate the effects of locally injected 5-HT-receptor agonists on panic-like reactions induced by intra-dlPAG injection of an NO-donor (SIN). After 21 days of daily i.p. injections of saline or clomipramine (10 mg/kg) male Wistar rats received local injections of saline, the 5-HT(1A)-receptor agonist 8-OH-DPAT (8 nmol) or the 5-HT2A/2C-receptor agonist DOI (16 nmol) followed by saline or SIN (150 nmol). NO-induced panic-like reactions were inhibited by DOI, but not by 8-OH-DPAT. Chronic clomipramine did not modify these effects but tended to produce anti-aversive effect by itself. In chronically clomipramine treated animals 8-OH-DPAT potentiated NO-induced panic-like reactions. The results indicate that the panic-like effects of NO in the dlPAG may be attenuated by 5-HT2A/2C-, but not by 5-HT1A-receptors. The anti-aversive effect of DOI is not modified by chronic clomipramine treatment.

Electrocortical evidence for an early abnormal processing of panic-related words in panic disorder patients

Panic patients are hypothesized to have particularly elaborated cortical networks for panic-related stimuli, and this characteristic should be associated with an abnormal automatic processing of these stimuli. Panic-related and neutral words were presented to 25 panic patients and 25 matched healthy controls either at individually determined perception thresholds (threshold condition) or for 1000 ms (above threshold condition). Word recognition for words presented at perception threshold (threshold words), and event-related brain potentials (ERPs) triggered by threshold and above threshold words were analyzed. In the threshold condition, both panic patients and control participants correctly recognized more panic-related than neutral words. An additional analysis restricted to participants who used an intuitive strategy for word identification revealed an enhanced frequency of correctly identified panic-related words in panic patients. In the ERPs, only panic patients exhibited enhanced positive potentials during early time windows (200-400 ms after stimulus presentation) triggered by panic-related compared to neutral threshold words. In late (400-600 ms) and very late (600-1000 ms) time windows, both groups showed a greater ERP positivity for panic-related than for neutral words. These data suggest that panic patients are characterized by an early automatic and elaborated processing of disorder-relevant stimuli.

Selective GABAergic treatment for panic? Investigations in experimental panic induction and panic disorder

gamma-Aminobutyric acid (GABA) is the most important inhibitory neurotransmitter in the central nervous system (CNS). It exerts its rapid inhibitory action mostly through GABA(A) receptors, which are targets for benzodiazepines, barbiturates, neuroactive steroids and distinct anticonvulsive agents. There is considerable evidence that dysfunction of GABA(A) receptors or dysregulation of GABA concentrations in the CNS (or both) plays an important role in the pathophysiology of panic disorder. Currently, benzodiazepines are the only drugs directly targeting the GABA(A) receptors that are approved for the treatment of anxiety disorders. Because of their well-known anxiolytic effects, they are widely used in this setting, but side effects limit their use in long-term treatment. The question of whether drugs that selectively increase GABA concentrations in the CNS could improve symptoms of anxiety has been discussed. Recent investigations by our group have demonstrated that enhancement of endogenous GABA (through blockade of GABA transaminase by vigabatrin or through inhibition of GABA transporters by tiagabine) exerts anxiolytic effects on experimentally induced panic. Our studies in healthy volunteers have shown that both compounds lead to a significant reduction in panic symptoms elicited by cholecystokinin-tetrapeptide. Moreover, benzodiazepine-like effects on the activity of the hypothalamic-pituitary-adrenal axis have been observed in association with vigabatrin treatment. Small open studies in patients with panic disorder also showed an improvement in panic and anxiety with both compounds. This review summarizes our recent research on the effects of selective GABAergic treatment in experimentally induced panic and outlines the possible role of compounds targeting the GABA binding site of the GABA(A)-benzodiazepine receptor for the treatment of panic and anxiety.

Panic induction with cholecystokinin-tetrapeptide (CCK-4) Increases plasma concentrations of the neuroactive steroid 3alpha, 5alpha tetrahydrodeoxycorticosterone (3alpha, 5alpha-THDOC) in healthy volunteers

3alpha-reduced neuroactive steroids such as 3alpha, 5alpha-tetrahydroprogesterone (3alpha, 5alpha-THP) and 3alpha, 5alpha-tetrahydrodeoxycorticosterone (3alpha, 5alpha-THDOC) are potent positive allosteric modulators of gamma-aminobutyric acid type A (GABAA) receptors and display pronounced anxiolytic activity in animal models. Experimental panic induction with cholecystokinin-tetrapeptide (CCK-4) and sodium lactate is accompanied by a decrease in 3alpha, 5alpha-THP concentrations in patients with panic disorder, but not in healthy controls. However, no data are available on 3alpha, 5alpha-THDOC concentrations during experimental panic induction. Therefore, we quantified 3alpha, 5alpha-THDOC concentrations in 10 healthy volunteers (nine men, one woman) before and after panic induction with CCK-4 by means of a highly sensitive and specific gas chromatography/mass spectrometry analysis. CCK-4 elicited a strong panic response as assessed by the Acute Panic Inventory. This was accompanied by an increase in 3alpha, 5alpha-THDOC, ACTH and cortisol concentrations. This increase in 3alpha, 5alpha-THDOC might be a consequence of hypothalamic-pituitary-adrenal (HPA) axis activation following CCK-4-induced panic, and might contribute to the termination of the anxiety/stress response following challenge with CCK-4 through enhancement of GABAA receptor function.

Effects of propranolol on symptom and endocrine responses to pentagastrin

Intravenous injections of CCK-B agonists, such as pentagastrin, produce symptoms of panic and potent activation of the human hypothalamic-pituitary-adrenal (HPA) axis. It is unclear whether these psychological and endocrine effects are mediated by similar or independent processes. Independence is supported by prior evidence that beta-adrenergic receptor blockade attenuates cardiovascular and symptom but not vasopressin responses to CCK-4. To further explore associations between somatic, emotional and endocrine responses to CCK-B agents, and potential beta-adrenergic mediating mechanisms, symptom and endocrine responses to pentagastrin were examined after propranolol pre-treatment. Cardiovascular, symptom, and endocrine (ACTH, cortisol, epinephrine) responses to pentagastrin were measured in 16 healthy adult subjects randomly assigned to receive propranolol or placebo pre-treatment. Propranolol significantly blocked the normal cardiac acceleration produced by pentagastrin, but did not reduce panic symptom or anxiety effects. It delayed and perhaps enhanced the cortisol response. No relationship between HPA and symptom responses following pentagastrin could be detected, though pre-pentagastrin cortisol was inversely related to post-injection panic symptom intensity. Endocrine, cardiovascular and symptom responses to pentagastrin appear to be separately mediated, as they did not change in concert in response to propranolol pre-treatment, nor were they correlated with one another. The results are consistent with the presence of inhibitory beta-adrenergic mediation of the HPA axis in humans. They support the hypothesis that the HPA response to pentagastrin is not secondary to the psychological stress of its side effects.

Respiratory symptoms and panic in the National Comorbidity Survey: a test of Klein's suffocation false alarm theory

According to suffocation false alarm theory (Arch. Gen. Psychiatry 50 (1993) 31), respiratory symptoms are the symptoms that best distinguish the panic attacks of individuals with panic disorder (PD) from those of individuals without PD. Using National Comorbidity Survey data from those 609 respondents who had lifetime histories of panic attacks or PD, we tested this prediction. Neither respiratory symptom (smothering; dyspnea) strongly differentiated between respondents with PD and those with only panic attacks. Respiratory symptom endorsement was unrelated to PD when the number of other symptoms endorsed was controlled; furthermore, respiratory symptoms had slight effect sizes and were not included in a multivariate context. In contrast, fear of dying had the largest effect size, an association with PD that persisted after control for other symptom endorsement, and a continuing importance in multivariate analyses. Strikingly, panic attack respondents who reported having had only one panic attack were as likely as PD respondents to report respiratory symptoms during panic. These findings, although based on retrospective self-report and thus subject to recall bias, are inconsistent with the hypothesis that respiratory symptoms during panic have diagnostic significance.

Psychic and occlusal factors in bruxers

BACKGROUND

The aim of this study was to investigate the existence of associations between bruxism and psychic and occlusal factors.

METHODS

Participants in this study (n=85) were recruited from the Section of Odontostomatology, Deparent of Neuroscience, University of Pisa, Italy. They were split into two groups, bruxers (n=34) and non-bruxers (n=51), on the basis of the presence of both clinical and anamnestical indicators of bruxim. All participants were administered two self-reported validated questionnaires to evaluate (MOODS-SR) and panic-agoraphobic (PAS-SR) spetra. A number of occlusal variables (deep-bite: cross-bite, open-bite, mediotrusive and laterotrusive interferences, slide RCP-ICP, laterotrutsive guides, canine and molar classes) were also recorded.

RESULTS

With regards to occlusal factors, the only association was revealed between bruxism mediotrusive interferences (p < 0.05). As for psychiatric investigation, significant differences between bruxers and controls emerged for the presence of both depressive (p < 0.01) and manic symptoms (p < 0.01) in MOODS-SR, and for stress sensitivity (p < 0.01), anxious expectation (p < 0.05), and reassurance sensitivity symptoms (p < 0.05) in PAS-SR. In particular, both mood (p < 0.01) and panic-agoraphobic (p < 0.05) spectra symptoms seem to differentiate bruxers from controls in males, while in females strong differences emerged for stress sensitivity symptoms (p < 0.05).

CONCLUSIONS

It can be confirmed that certain psychic traits are present in bruxers, while occlusal factors are not useful parameters to discern bruxers from non-bruxers.

Context fear conditioning inhibits panic-like behavior elicited by electrical stimulation of dorsal periaqueductal gray

Context fear conditioning has been widely used as an animal model of anxiety whereas electrical stimulation of the dorsal portion of the periaqueductal gray (DPAG) as a model of panic attack. The present study employed these two animal models in order to investigate the influence of anxiety in the occurrence of panic attack. Results indicated that animals exposed to contextual cues that were previously associated with electrical footshocks engaged in robust defensive freezing behavior and were less likely to display flight evoked by electrical stimulation of the DPAG when compared with control animals that were not exposed to the context fear conditioning procedure. These results indicate that activation of the brain mechanisms that underlie anxiety produces an inhibitory effect on panic attack.

The effects of acceptance versus control contexts on avoidance of panic-related symptoms

The present study compared the effects of creating an acceptance versus a control treatment context on the avoidance of aversive interoceptive stimulation. Sixty high anxiety sensitive females were exposed to two 10-min periods of 10% carbon dioxide enriched air, an anxiogenic stimulus. Before each inhalation period, participants underwent a training procedure aimed at encouraging them either to mindfully observe (acceptance context) or to control symptoms via diaphragmatic breathing (control context). A third group was given no particular training or instructions. We hypothesized that an acceptance rather than control context would be more useful in the reduction of anxious avoidance. Compared to control context and no-instruction participants, acceptance context participants were less avoidant behaviorally and reported less intense fear and cognitive symptoms and fewer catastrophic thoughts during the CO(2) inhalations. We discuss the implications of our findings for an acceptance-focused vs. control-focused context when conducting clinical interventions for panic and other anxiety disorders.

Bioterrorism: preparing for the unthinkable

Terrorism is not a new concept but our need to prepare for the effects of bioterrorism has achieved a particular urgency. The use of biological agents provides a new set of challenges to professional caregivers, emergency personnel and Governments. These agents are generally not readily identified through the senses, have delayed effects and have the power to generate fear and panic. They are also intended to demonstrate that Governments and other organisations are not able to protect their citizens and members. What evidence there is suggests bioterrorist incidents have the potential to create higher levels of psychopathology than physical injury. Therefore, the authorities must identify and rehearse suitable methods of psychoprophylaxis and intervention.

Effects of alprazolam on cholecystokinin-tetrapeptide-induced panic and hypothalamic-pituitary-adrenal-axis activity: a placebo-controlled study

Cholecystokinin-tetrapeptide (CCK-4) induces panic attacks both in patients with panic disorder (PD) and healthy volunteers. It has been shown that panic elicited by CCK-4 is improved after treatment with antidepressants. Moreover, a reduction of CCK-4-induced panic has also been demonstrated after treatment with lorazepam in single subjects and after selective GABAergic treatment with vigabatrin. Although benzodiazepines are widely used as anxiolytics, no controlled study on the effects of benzodiazepines on CCK-4-induced panic symptoms is available so far. Therefore, we investigated the effects of alprazolam and placebo on CCK-4-induced panic symptoms in a double-blind, placebo-controlled study. A total of 30 healthy subjects were challenged with 50 microg CCK-4. Out of these 30 subjects, 26 showed a marked panic response to CCK-4. Subjects were rechallenged after a 7-day interval and treated with 1 mg alprazolam or placebo 1 h prior to the second CCK-4 challenge. Panic was assessed using the acute panic inventory (API) and a DSM-IV-derived panic symptom scale (PSS). Moreover, the number of reported symptoms and self-rated anxiety and arousal were recorded. We found a significant reduction of the API and PSS scores and of the number of reported symptoms compared to placebo. Moreover, compared to placebo the CCK-4-induced ACTH and cortisol release were significantly attenuated during the CCK-4 challenge after alprazolam treatment. However, also placebo treatment reduced CCK-4-induced anxiety and HPA-axis activation to a certain extent. In conclusion, our data show that alprazolam reduces CCK-4-induced panic, which supports the hypothesis of a possible interaction between the GABA and the CCK system.

Defensive burying in rodents: ethology, neurobiology and psychopharmacology

Defensive burying refers to the typical rodent behavior of displacing bedding material with vigorous treading-like movements of their forepaws and shoveling movements of their heads directed towards a variety of noxious stimuli that pose a near and immediate threat, such as a wall-mounted electrified shock-prod. Since its introduction 25 years ago by Pinel and Treit [J. Comp. Physiol. Psychol. 92 (1978) 708], defensive (shock-prod) burying has been the focus of a considerable amount of research effort delineating the methodology/ethology, psychopharmacology and neurobiology of this robust and species-specific active avoidance or coping response. The present review gives a summary of this research with special reference to the behavioral (face and construct) and pharmacological (predictive) validity of the shock-prod burying test as an animal model for human anxiety. Emphasis is also placed on some recent modifications of the paradigm that may increase its utility and reliability as to individual differences in expressed emotional coping responses and sensitivity to pharmacological treatments. Overall, the behavioral and physiological responses displayed in the shock-prod paradigm are expressions of normal and functionally adaptive coping patterns and the extremes of either active (i.e., burying) or passive (i.e., freezing) forms of responding in this test cannot simply be regarded as inappropriate, maladaptive or pathological. For this reason, the shock-prod paradigm is not an animal model for anxiety disorder or for any other psychiatric disease, but instead possesses a high degree of face and construct validity for normal and functionally adaptive human fear and anxious apprehension. However, the apparent good pharmacological validation (predictive validity) of this test reinforces the view that normal and pathological anxiety involves, at least partly, common neurobiological substrates. Therefore, this paradigm is not only suitable for screening potential anxiolytic properties of new drugs, but seems to be especially valuable for unraveling the neural circuitry and neurochemical mechanisms underlying the generation of active and passive coping responses as different expressions of anxiety.

[Tachypnea--when breathing induces panic]

Eine gestörte Atmung macht Angst. Zur besseren Charakterisierung sind die Begriffe Tachypnoe, Dyspnoe und Hyperventilation zu differenzieren, welche verschiedene Zustände und Sensationen der Atmung beschreiben. Die wichtigsten pathophysiologischen Mechanismen der Atemnot, wie die Erhöhung der Atemimpedanz, die Störung der Atemmuskulatur, die abnorme Erhöhung der Ventilation und die abnormen Blutgase erklären die verschiedenen Differenzialdiagnosen und leiten über zu den Therapien, welche leider nicht selten symptomatisch bleiben. Möglichkeiten zur Symptomlinderung sind Rehabilitationstraining, Medikamente bzw. das Meiden verschlimmernder Substanzen, Sauerstoff und spezielle Ventilationshilfen. Am wichtigsten ist aber ein möglichst umfassender Therapieansatz mit Einbezug der psychischen und sozialen Patientenressourcen.

A longitudinal investigation of anxiety sensitivity in adolescence

This investigation sought to expand existing knowledge of anxiety sensitivity in a sample of high school students (N = 2,365) assessed over 4 years. The stability of anxiety sensitivity levels across assessment periods was examined, and cluster analyses were used to identify different developmental pathways in levels of anxiety sensitivity. Groups of adolescents with stable low, stable high, and escalating anxiety sensitivity levels were identified. Adolescents with stable high or escalating anxiety sensitivity were significantly more likely to report experiencing a panic attack than individuals with stable low anxiety sensitivity. Results also indicated that Asian and Hispanic adolescents tended to report higher anxiety sensitivity but that their anxiety sensitivity was less strongly associated with panic than that of Caucasian adolescents.

Neuroactive steroid changes in response to challenge with the panicogenic agent pentagastrin

BACKGROUND

Female hormones and female hormone derivatives, including neuroactive steroids (NASs) have been suspected to play a role in the pathophysiology of panic disorder (PD). The panicogenic agent CO(2) has been shown to induce a delayed release of NASs in both brain and plasma of rats. In the present study, we measured NASs plasma levels in response to challenge with another panicogenic agent, pentagastrin, and assessed the effect of ethynil estradiol (EE) pretreatment.

METHODS

A double-blind cross-over placebo-controlled design with randomization of the order of a three day pretreatment of EE (50 microg/day) or placebo was used to assess the effect of a 30 microg iv bolus injection of pentagastrin on the release of allopregnanolone (ALLO) and dehydroepiandrosterone (DHEA) into plasma in 15 male PD patients and 10 male healthy volunteers (HV).

RESULTS

After pentagastrin challenge there was a significant release of DHEA and a trend for the release of ALLO. EE pretreatment did not affect the pentagastrin-induced panic response or NAS release.

CONCLUSIONS

Pentagastrin induced release of NASs into plasma, the purpose of which remains to be determined.

Brain metabolic changes during lactate-induced panic: effects of gabapentin treatment

Six subjects with panic disorder underwent sodium lactate infusions in conjunction with magnetic resonance spectroscopic imaging (MRSI) at study entrance when actively symptomatic and after clinical improvement while under treatment with gabapentin. MRSI was used to serially measure regional brain lactate levels from an axial section at the level of the lateral ventricles at baseline, during lactate infusion and postlactate infusion. Gabapentin treatment appeared to be effective in blocking a lactate-induced panic response but did not alter the magnitude or time course of an abnormal brain lactate response to lactate infusion in all subjects. Additionally, two subjects were reinfused while clinically improved on double-blind placebo and demonstrated a consistent pattern of abnormal brain lactate response.

Prolactin but not ACTH increases during sodium lactate-induced panic attacks

Paradoxically, the pituitary-adrenal axis is not activated during sodium lactate-induced panic. We measured the response of another stress-sensitive hormone, prolactin, to standard lactate and placebo infusion in a double-blind randomised design in eight patients with panic disorder and eight matched normal controls. Prolactin release was significantly elevated (P < 0.05) in panickers compared with non-panickers, whereas ACTH secretion was not activated at all. This differential stress response needs further investigation.

Role of norepinephrine in the dorsomedial hypothalamic panic response: an in vivo microdialysis study

Blockade of gamma-aminobutyric acid-A (GABA(A)) receptors in the dorsomedial hypothalamus (DMH) elicits a panic-like response that includes increases in heart rate (HR), blood pressure (BP), respiration rate (RR), and anxiety. Norepinephrine (NE) has been postulated to be critical in regulating panic and anxiety responses. Therefore, the first study sought to determine changes in extracellular NE levels within the DMH following acute blockade of GABA(A) receptors in the DMH using in vivo microdialysis. Rats were implanted with femoral arterial catheters and microdialysis probes into the DMH. Following recovery, the DMH of conscious rats were perfused with 100, 150, or 200 microM solutions of the GABA(A) receptor antagonist bicuculline methiodide (BMI) via the microdialysis probe. HR and BP responses were recorded and the changes in extracellular levels of NE in the dialysate samples from the DMH were determined by HPLC. Rats receiving BMI injections showed dose-dependent increases in both the extracellular NE levels in the DMH as well as HR and BP. The second study was conducted to test the functional importance of NE in the DMH to the BMI-induced physiological responses. The effects of BMI microinjection into the DMH were measured at baseline and 10 days after local injection of either vehicle or two doses of 6-hydroxydopamine (6-OHDA), a neurotoxin known to lesion NE terminals. There was a significant loss of tissue NE levels as well as BMI-induced HR, BP and RR responses in the 6-OHDA-treated but not vehicle-treated rats. Thus, blockade of GABA(A) receptors in the DMH results in NE release and the presence of NE appears to be necessary for eliciting the physiological components of the panic-like responses in this region.

Correlation between the fighting rates of REM sleep-deprived rats and susceptibility to the 'wild running' of audiogenic seizures

Sleep-deprived rats exhibit defensive fighting as well as explosive flights very similar to the wild-running of audiogenic seizures. In order to determine why sleep deprivation is a common factor that facilitates both panic and convulsive manifestations, the present study was undertaken to investigate whether rats that display sleep deprivation-induced fighting (SDIF) are the same as those that are susceptible to audiogenic wild-running (WR). Twenty-eight male adult Wistar rats were divided into two groups assigned to two experimental schemes. In the first, 18 subjects were submitted to REM-sleep deprivation for 5 days and had their SDIF evaluated in social grouping. After 1 week for recovery, their susceptibility to WR was tested in an acoustic stimulation trial (104 dB, 200 Hz, 60 s). Rats that did not present WR received a lactate infusion and were tested again by acoustic stimulation 40 min later. In the second experimental scheme, 10 subjects were initially evaluated for WR susceptibility and the number of SDIF was recorded in social grouping after 1 week. Three categories of WR-susceptibility were determined: WR-sensitive rats, intermediate WR-sensitive rats and WR-insensitive rats. The number of SDIF in each category was significantly different and there was a high positive correlation (r=0.89; Spearman test) between the number of SDIF and the level of WR-susceptibility. We conclude that the reasons why sleep deprivation exerts facilitatory effects on both panic and convulsive manifestations are due to overlappings of neural pathways responsible for both behavioral patterns and for the property of sleep deprivation to increase neuronal excitability.

Hyperventilation challenge test in panic disorder and depression with panic attacks

Our aim was to determine whether panic disorder (PD) patients, major depressive patients without panic attacks (MD) and major depressive patients with panic attacks (MDP) respond similarly to hyperventilation challenge tests. We randomly selected 35 PD patients, 33 MDP patients, 27 MD patients and 30 normal volunteers with no family history of anxiety or mood disorder. The patients had not been treated with psychotropic drugs for at least 1 week. They were induced to hyperventilate (30 breaths/min) for 4 min, and anxiety was assessed before and after the test. A total of 16 (45.7%) PD patients, 12 (36.4%) MDP patients, four (11.1%) MD patients, and two (6.7%) normal volunteers had a panic attack after hyperventilating. The PD and MDP patients were significantly more responsive to hyperventilation than the MD patients and the normal volunteers. The MD patients had a significantly lower heart-rate response to the test than all the other groups. There is growing evidence that PD patients are more sensitive to the vasoconstrictive effects on basilar arterial blood flow caused by hyperventilation-induced hypocapnia than are comparison subjects. Our data suggest that there is an association between panic attacks and hyperreactivity to an acute hyperventilation challenge test.

Human defensive behaviors to threat scenarios show parallels to fear- and anxiety-related defense patterns of non-human mammals

Defense patterns of rats and mice have been characterized in terms of the relationships between the type of defensive behavior (e.g. flight, freezing, hiding, defensive threat/attack, and risk assessment) and particular features of the eliciting (threat) stimulus and the situation in which it is encountered. Because the defense systems of rodents serve as major models for investigating and understanding both the physiology and the behavioral expression of emotional response to aversive stimuli, it is essential to evaluate whether these systems show strong parallels in human responsivity to threat. One hundred and sixty male and female undergraduate students read a set of 12 scenarios involving a present or potential threatening conspecific, and chose a primary defensive response to each. These scenarios were designed to vary features known to influence defensive responding in rodents: magnitude of threat; escapability of the situation; ambiguity of the threat stimulus; distance between the threat and the subject; presence of a hiding place. Male and female responses to the various scenarios were highly correlated, except for yell, scream, or call for help which was frequent for females, rare for males. However, a combination of this response category with 'attack' showed a highly positive (+0.96) male-female correlation, across scenarios.Correlations between manipulated (and rated) features of the threat stimulus and situation, and type of defensive behavior chosen, strongly supported a view that the patterning of defensive behavior is similar for humans and non-human mammals. Significant correlations were obtained relevant to eight specific hypotheses derived from the animal literature, with some support for two additional hypotheses (non-significant correlations averaging 0.4 or more in expected direction). While three predicted correlations were not supported in these findings, only a single significant correlation was obtained that had not been predicted on the basis of the animal literature. Although the scenario approach, and this application, have specific limitations, these results provide substantial suggestion of congruence between human and non-human mammal defense systems.

Slow recovery from voluntary hyperventilation in panic disorder

OBJECTIVE

Because hyperventilation has figured prominently in theories of panic disorder (PD) but not of social phobia (SP), we compared predictions regarding diagnosis-specific differences in psychological and physiological measures before, during, and after voluntary hyperventilation.

METHOD

Physiological responses were recorded in 14 patients with PD, 24 patients with SP, and 24 controls during six cycles of 1-minute of fast breathing alternating with 1 minute of recovery, followed by 3 minutes of fast breathing and 10 minutes of recovery. Speed of fast breathing was paced by a tone modulated at 18 cycles/minute, and depth by feedback aimed at achieving an end-tidal pCO2 of 20 mm Hg. These values were reached equally by all groups.

RESULTS

During fast breathing, PD and SP patients reported more anxiety than controls, and their feelings of dyspnea and suffocation increased more from baseline. Skin conductance declined more slowly in PD over the six 1-minute fast breathing periods. At the end of the final 10-minute recovery, PD patients reported more awareness of breathing, dyspnea, and fear of being short of breath, and their pCO2s, heart rates, and skin conductance levels had returned less toward normal levels than in other groups. Their lower pCO2s were associated with a higher frequency of sigh breaths.

CONCLUSIONS

PD and SP patients report more distress than controls to equal amounts of hypocapnia, but PD differ from SP patients and controls in having slower symptomatic and physiological recovery. This finding was not specifically predicted by hyperventilation, cognitive-behavioral, or suffocation alarm theories of PD.