Can anti-panic drugs antagonise the anxiety produced in the rat by drugs acting at the GABA-benzodiazepine receptor complex?

The beta-carboline FG 7142 and pentylenetetrazole, believed to act at different sites on the GABA-benzodiazepine receptor complex, have anxiogenic activity in the social interaction test in the rat. Two compounds that have anti-panic activity in man, the tricyclic antidepressant imipramine and the alpha 2-adrenoceptor agonist clonidine, were used to try to antagonise the anxiogenic effects of the 2 drugs. Imipramine (5 and 15 mg/kg) was tested after 0 or 15 days pretreatment. In neither case was it able to reverse the anxiogenic effect of pentylenetetrazole (15 mg/kg). However, after chronic treatment the effects of FG 7142 were reversed. Imipramine itself had an anxiogenic action that was significant after acute treatment, and its effects were not additive with those of FG 7142 or pentylenetetrazole, suggestive of some mutual antagonism between acute imipramine and the 2 drugs. Similar mutual antagonism was obtained after acute treatment with clonidine (0.01 and 0.025 mg/kg).     

The effect of long-term imipramine treatment on carbon dioxide-induced anxiety in panic disorder patients

The authors examined whether long-term treatment with imipramine would decrease CO2-induced anxiety in 10 patients with panic disorder. The patients underwent CO2 testing after single-blind placebo testing and again after imipramine treatment. Scores on self-rated visual analog mood scales and panic attack symptom scales showed that the anxiogenic effects of CO2 were significantly reduced during long-term imipramine treatment. These results suggest that the mechanisms underlying CO2-induced anxiety may be similar to those involved in the pathophysiology of panic disorder.     

Can drug effects on anxiety and convulsions be separated?

The effects of benzodiazepines, barbiturates, a series of novel putative anxiolytic compounds and anxiogenic compounds are reviewed in animal tests of anxiety and on experimentally-induced seizures. It is clear from the data that drug effects on anxiety and convulsions are not always in the same direction; certain compounds are apparently both anxiolytic and proconvulsant, others are anxiogenic and anticonvulsant, others have varied effects depending on the test situation. It is suggested that this work necessitates considerable revision of our traditional concepts of an "anticonvulsant." The extent to which drug-induced anxiety is correlated with weak epileptiform activity in the brain is discussed. Finally, the Discussion considers a number of possible mechanisms that could underlie the separation of drug effects on anxiety and convulsions that is observed.     

Effect of a pharmacological stressor on glutamate efflux in the prefrontal cortex

The anxiogenic β-carboline, FG 7142 (20 mg/kg) significantly increased glutamate efflux in the prefrontal cortex of conscious rats as assessed by microdialysis. Pretreatment with the benzodiazepine receptor agonist, diazepam (5 mg/kg), abolished this effect. These findings indicate that anxiogenic compounds produce an effect similar to physical stressors on the outflow of glutamate, and implicate the GABA/benzodiazepine receptor complex in the stress-induced activation of glutamate systems in the prefrontal cortex.     

Pharmacological modulation of anxiety-related behaviors in the murine Suok test

We have recently introduced a new model of anxiety--the Suok test and its light-dark modification--for behavioral characterization in mice and rats, including simultaneous assessment of their anxiety, activity, and neurological phenotypes. In the present study, testing different inbred (129S1, BALB/c) and hybrid (C57-129S1) mouse strains in both Suok test modifications, we examined the effects on anxiety-related behaviours produced by traditional anxiogenic and anxiolytic drugs. Here we show dose-dependent increases in anxiety-related behaviors produced by anxiogenic drug pentylenetetrazole (10 and 20 mg/kg). In contrast, anxiolytic drugs ethanol (0.75 and 1.5 g/kg) and diazepam (0.5 mg/kg) reduced anxiety and increased mouse exploration in this test. Hyperemotional anxious BALB/c mice were particularly sensitive to pharmacogenic anxiety in Suok test, also showing robust light-dark shifts in the light-dark version of this test. Overall, the results of this study confirm the potential utility of both murine Suok tests, especially when used in selected "sensitive" mouse strains, for high-throughput screening of potential anxiotropic drugs.     

Neuropharmacological and physiological validation of a computer-controlled two-compartment black and white box for the assessment of anxiety

1. 1. The two-compartment black and white box first described by Crawley and Goodwin (1980) has been used to study anti-anxiety properties of drugs but has not been validated.

2. 2. An automated test system and validation of the protocol for the evaluation of compounds with anxiolytic or anxiogenic potential is described.

3. 3. The box is partitioned into black and white sections with an interconnecting opening and is equipped with micro-switch photoelectric controls (light source and photorecciver) and an interface connected to the menudriven computer during anxiety testing.

4. 4. Plasma corticosterone levels in naive mice maintained on a reversed L:D cycle was significantly reduced following restricted exposure to the brightly lit white section but not in the red-illuminated black section.

5. 5. The optimal structural configuration in different test situations was found to be a square rather than a round box.

6. 6. Under normal conditions, mice spend about 60% of the time in the dark compartment so that the exploratory activities and time spent in the white section are taken as a measure of anxiety.

7. 7. Compounds examined included the reference anxiolytic diazepam, nicotine, naloxone, MDL 72222, ICS 205 930 and buspirone, all of which increased mouse exploratory activities in the white section. PTZ, β-CCP, morphine and amphetamine increased exploration in the black compartment and reduced exploration in the white area.

8. 8. Fluphenazine and imipramine had no specific effects on anxiety responding, although the cataleptogenic effect of fluphenarinc was apparent.

9. 9. Daily repeated testing was possible with a maximum of up to four trials a week using naive animals during the 5-min test session.

10. 10. The results suggest that the rapid and automated test system for the assessment of changes in measures of anxiety is not only valid for large scale evaluation of compounds but could be used to elucidate mechanisms of drug action and the CNS pathways linked with anxiolysis and/or anxiogenesis.

Pharmacological analysis of zebrafish (Danio rerio) scototaxis

The scototaxis test has been introduced recently to assess anxiety-like phenotypes in fish, including zebrafish. Parametric analyses suggest that scototaxis represents an approach-avoidance conflict, which hints at anxiety. In this model, white avoidance represents anxiety-like behavior, while the number of shuttling events represents activity. Acute or chronic fluoxetine, buspirone, benzodiazepines, ethanol, caffeine and dizocilpine were assessed using the light-dark box (scototaxis) test in zebrafish. Acute fluoxetine treatment did not alter white avoidance, but altered locomotion in the higher dose; chronic treatment (2 weeks), on the other hand, produced an anxiolytic effect with no locomotor outcomes. The benzodiazepines produced a hormetic (inverted U-shaped) dose-response profile, with intermediate doses producing anxiolysis and no effect at higher doses; clonazepam, a high-potency benzodiazepine agonist, produced a locomotor impairment at the highest dose. Buspirone produced an anxiolytic profile, without locomotor impairments. Moclobemide did not produce behavioral effects. Ethanol also produced a hormetic profile in white avoidance, with locomotor activation in 0.5% concentration. Caffeine produced an anxiogenic profile, without locomotor effects. These results suggest that the light-dark box is sensitive to anxiolytic and anxiogenic drugs in zebrafish.     

The discriminative stimulus effects of pentylenetetrazol as a model of anxiety: recent developments

Pentylenetetrazol (PTZ), a GABA(A) receptor antagonist and prototypical anxiogenic drug, has been extensively utilized in animal models of anxiety. PTZ produces a reliable discriminative stimulus which is largely mediated by the GABA(A) receptor. Several classes of compounds can modulate the PTZ discriminative stimulus including 5-HT(1A), 5-HT(3), NMDA, glycine, and L-type calcium channel ligands. Spontaneous PTZ-lever responding is seen in trained rats during withdrawal from GABA(A) receptor compounds such as chlordiazepoxide and diazepam, and also ethanol, morphine, nicotine, cocaine, haloperidol, and phencyclidine. This effect is largely mediated by the GABA(A) receptor, which suggests that anxiety may be part of a generalized withdrawal syndrome mediated by the GABA(A) receptor. There are also important hormonal influences on PTZ. Corticosterone plays some role in mediation of its anxiogenic effects. There is a marked sex difference in response to the discriminative stimulus effects of PTZ, and estrogens appear to protect against its anxiogenic effects. Further work with the PTZ drug discrimination is warranted for characterization of anxiety during withdrawal, and the hormonal mechanisms of anxiety.     

Treatment effects of alprazolam and imipramine: physiological versus subjective changes in patients with generalized anxiety disorder

The correspondence between changes in physiological activity and somatic symptom reports was assessed in generalized anxiety disorder patients treated with alprazolam or imipramine. After 6 weeks, the two medications produced comparable reductions in self-reported somatic symptoms. However, patients taking alprazolam showed decreases in systolic blood pressure, epinephrine, and norepinephrine, and patients taking imipramine showed increases in heart rate, blood pressure, electromyographic activity, and norepinephrine. Thus, though the physiological changes associated with alprazolam treatment were consistent with changes in symptom reports, treatment with imipramine produced a desynchrony: patients reported significant decreases in cardiovascular symptoms and muscle tension in spite of the fact that heart rate, blood pressure, and electromyographic activity increased. Possible explanations for this counterintuitive phenomenon are discussed.     

Sequential combination of imipramine and self-directed exposure in the treatment of panic disorder with agoraphobia

Thirty-eight patients who had panic disorder with agoraphobia completed 8 weeks of treatment with imipramine followed by 8 weeks of treatment with imipramine combined with behavior therapy consisting of self-directed exposure. Sixty-three percent (24) of the patients responded markedly to this cost-effective combined pharmacologic and behavioral approach. Results also revealed that most of the improvement in panic occurred during the first 8 weeks of treatment when imipramine treatment alone was used, whereas improvement in severity, anxiety, depression, and phobias, in particular, continued to be significant between midtreatment and end of study. Further analysis revealed that improvement in phobic anxiety and avoidance in the first 8 weeks of treatment, rather than improvement in panic, predicted final outcome. Implications of these findings on the complex issue of differential antipanic and antiphobic effects of imipramine are briefly discussed.     

Rat behavior in two models of anxiety and brain [3H]muscimol binding: pharmacological, correlation, and multifactor analysis

The contribution of GABAergic mechanisms to rat emotional behavior in two animal models of anxiety (open field test of neophobia and aversively conditioned freezing reaction), was confirmed by pharmacological analysis, using anxiolytic (midazolam) and anxiogenic (picrotoxin) compounds. Both substances are known to modulate GABA(A) receptors' activity in a positive or negative manner, respectively. It seemed, therefore, worthwhile to check whether the behavioral parameters measured in these animal models of anxiety correlate with [3H]muscimol binding (a highly selective GABA(A) receptor ligand) in different brain structures of nai;ve rats, with a view to establish the role of genetically determined expression of local GABA(A) receptors in the organization of rat emotional and motor behavior. Correlation analysis revealed no links between individually determined expression of GABA(A) receptors (quantitative receptor autoradiography) in the brain structures, and the emotional behavior of nai;ve, drug-free animals, in both tests. Factor analysis confirmed that animal behavior in both tests was under control of different central processes. Moreover, none of the behavioral and ligand binding parameters loaded on the same factor, confirming the negative results of the correlation study. The present results indicate that the origin of emotions is a complex phenomenon, probably involving the interaction between GABA-ergic innervation of many brain structures.     

Effects of beta-carbolines in animal models of anxiety

Animal models of anxiety can be classified into three main groups: those based on conflict or conditioned fear; those exploiting the anxiety produced by novelty; those in which anxiety or aversion is chemically induced. This review briefly describes the existing tests and, where available, the results obtained with beta-carbolines. Many of the beta-carbolines are anxiogenic in the tests, however ZK 91296 and ZK 93423 appear to have anxiolytic properties, and ZK 93426 has a similar profile to that of the benzodiazepine receptor antagonist RO 15-1788. By the results across the spectrum of tests, the reliability and sensitivity of the tests is assessed. The evidence that the anxiogenic and anxiolytic actions of the beta-carbolines are mediated by the BDZ binding sites is also discussed.     

Fluoxetine in panic disorder: pharmacologic and tritiated platelet imipramine and paroxetine binding study.

Serotonergic implication in panic disorder has been demonstrated by the efficacy of serotonin reuptake blockers in treatment. Fluoxetine, a potent 5-HT reuptake blocker, has been suggested to have anti-panic efficacy. This open study examines 30 patients (eight males and 22 females) with an average age of 36.9 years, ranging from 18 to 62, who were treated for eight weeks with fluoxetine (mean dose 20 mg per day). All patients fulfilled DSM-III-R criteria of panic disorder with agoraphobia as determined in a SCID interview schedule. Out of 28 patients who started medication, 64% of the patients completed the clinical trial and 36% of the patients dropped out of treatment because of increased anxiety or a lack of efficacy. Thirty-two percent of the patients had zero panic attacks by week 3. By the end of eight weeks of treatment, 48% of the patients had zero panic attacks. There was a significant reduction in anxiety and phobic avoidance and panic attacks. Tritiated platelet imipramine and paroxetine bindings revealed significantly lower maximal binding for patients with panic disorder in comparison with controls. Paroxetine Bmax showed a trend to increase in the direction of control values by the end of the trial.     

Interactions of corticotropin-releasing factor with antidepressant and anxiolytic drugs: behavioral studies with pigeons

A number of studies have shown significant interactions between neuronal systems involved with corticotropin-releasing factor (CRF) and either the clinical manifestations of depression and anxiety or the effects of antidepressant or anxiolytic drugs. In the present study, effects of CRF were studied alone and in combination with imipramine and with the sedative-hypnotic/anxiolytic drugs pentobarbital and chlordiazepoxide. Interactions of CRF with the novel, atypical anxiolytic buspirone were also examined. Interactions were evaluated through the use of schedule-controlled responding, responding suppressed by punishment, and drug discrimination procedures using the conditioned key-pecking response of pigeons. Effects of CRF were significantly enhanced when given in combination with imipramine with low noneffective imipramine doses potentiating the rate-reducing effects of CRF. Similarly, in pigeons trained to discriminate imipramine from saline, noneffective doses of CRF shifted the imipramine dose-response curve more than twofold to the left. Low doses of imipramine that produced saline key responding, produced imipramine-key responding when coadministered with CRF. The CRF antagonist alpha-helical CRF9-41 did not alter the rate-decreasing effects of imipramine. Effects of CRF on schedule-controlled responding were, however, antagonized by the administration of chlordiazepoxide and pentobarbital but not by buspirone, suggesting that CRF interacts with the GABA/benzodiazepine receptor mechanism complex but not with those systems involved in mediating the effects of buspirone. These results suggest that CRF interacts in significant ways with specific neurotransmitter systems subserving depression and anxiety.     

Contrasting effects of acute and chronic treatment with imipramine and fluoxetine on inhibitory avoidance and escape responses in mice exposed to the elevated T-maze

The elevated T-maze (ETM) is an animal model of anxiety-like behavior that assesses two different defensive behavioral tasks in the same animal—acquisition of inhibitory avoidance and latency to escape from an open and elevated arm. In rats, cute and chronic treatments with anxiolytic-like drugs impair avoidance acquisition while only chronic administration of panicolytic-like drugs impairs open arm withdrawal. To date, only the acute effects of anxiolytic/anxiogenic or panicolytic/panicogenic drugs have been tested in the mouse ETM and the results have partially corroborated those found in the rat ETM. This study investigated the effects of acute (a single intraperitoneal injection 30 min before testing) and chronic (daily i.p. injections for 15 consecutive days) treatment with imipramine or fluoxetine, non-selective and selective serotonin reuptake inhibitors, respectively, on inhibitory avoidance and escape tasks in the mouse ETM. Neither acute nor chronic treatment with imipramine (0, 1, 5 or 10 mg/kg, i.p.) significantly changed the behavioral profile of mice in the two ETM tasks. Interestingly, while acute fluoxetine (0, 5, 10, 20 or 40 mg/kg, i.p.) facilitated inhibitory avoidance and impaired escape latency, chronic treatment (0, 5, 20 or 40 mg/kg, i.p.) with this selective serotonin reuptake inhibitor (SSRI) produced an opposite effect, i.e., it impaired inhibitory avoidance acquisition and facilitated open arm withdrawal. Importantly, acute or chronic treatment with imipramine (except at the highest dose that increased locomotion when given acutely) or fluoxetine failed to alter general locomotor activity in mice as assessed in an ETM in which all arms were enclosed by lateral walls (eETM). These results suggest that inhibitory avoidance acquisition is a useful task for the evaluation of acute and chronic effects of SSRI treatment on anxiety in mice. However, as open arm latency was actually increased and reduced by acute and chronic fluoxetine, respectively, this does not seem to be a useful measure of escape from a proximal threat in this species.     

Treatment of panic and agoraphobia. An integrative review

There is now agreement about the clinical features of panic disorder and agoraphobia but less agreement about treatment because of controversy over whether the disorder is primarily biological or psychological. The authors were requested to produce an impartial review for continuing education and peer review. We chose to do this by using a quantitative review procedure, by providing a bibliography of studies, and by a literature review. We found that symptoms of panic and phobia did not change significantly while on wait-list control or while receiving placebo. The evidence for the efficacy of the low-potency benzodiazepines or of monoamine oxidase inhibitors was limited. It was also clear that only limited improvement can be expected from behavior therapies that do not involve exposure to the symptoms of panic or to the feared situation. Symptoms of panic, as well as the frequency of spontaneous panic, were shown to be substantially improved following imipramine, high-potency benzodiazepines such as alprazolam, exposure in vivo (especially if a cognitive anxiety management procedure was used), and the combination of imipramine and exposure in vivo. The effects on panic produced by the exposure therapies (with or without imipramine) were maintained over long follow-up periods. Imipramine, alprazolam, exposure therapy, and imipramine plus exposure each produced significant improvements in phobias. In the short term and in the long term, the larger improvements in phobias were associated with exposure therapy, particularly if used in combination with imipramine. We conclude that it would be unwise to theorize about the etiology of this disorder on the basis of response to a specific treatment because, both at the meta-analytic level and from the review of individual studies, it is clear that both drug and nondrug therapies can produce substantial and long-lasting changes in panic and in phobias.     

Anxiolytic and anxiogenic effects of kindling--role of baseline anxiety and anatomical location of the kindling electrode in response to kindling of the right and left basolateral amygdala

Effects of kindling of right and left basolateral amygdala (BLA) on plus maze anxiety was studied. Using a validated retest paradigm, it was possible to retest rats in the plus maze without increasing anxiety on retest. This permitted determining prekindling baseline levels of plus maze anxiety. Right BLA kindling of high baseline anxiety rats was anxiolytic one week after kindling. Right BLA kindling of low baseline anxiety rats was anxiogenic. In addition, left BLA kindling was either anxiogenic or without effect on plus maze anxiety, depending on baseline anxiety. Effects in left BLA differ from previous work showing anxiolytic effects of left BLA kindling. The discrepancy could be explained in part by prekindling baseline anxiety. These findings require modification of the previous conclusion that left hemisphere (left BLA) kindling is anxiolytic and right BLA kindling is anxiogenic in the plus maze. Rather the hemisphere difference may be due to an interaction between baseline anxiety level and kindling. If true, anxious disposition in rodents may interact with amygdala kindling to change amygdala function differently. Kindling and baseline anxiety effects on other behaviors (such as risk assessment and resistance to capture) are also described. Present data in the light of past studies suggest both premorbid anxiety state and location of the kindling electrode contribute to the effects of kindling on behavior.     

Ro 15-1788, CGS 8216, picrotoxin, and pentylenetetrazol: do they antagonize anxiolytic drug effects through an anxiogenic action?

Recent evidence suggests that agents that inhibit GABAergic function, particularly at sites on the GABA/benzodiazepine receptor complex, have intrinsic anxiogenic properties. The present experiments further characterize the behavioral effects of these receptor complex inhibitors, using the "defensive burying" test, which is reasonably selective for anxiolytics. Putative blockers of the GABA-receptor coupled chloride channel, picrotoxin and pentylenetetrazol, and the benzodiazepine receptor antagonists Ro 15-1788 and CGS 8216 each blocked the anxiolytic effect of chlordiazepoxide. However, these compounds failed to exert significant anxiogenic effects in the burying test. These findings suggest that different animal models of anxiolytic drug effects are not equally sensitive to the possible anxiogenic effects of drugs that act at the GABA/benzodiazepine receptor complex.     

Changes in [3H]5-HT uptake and [3H]imipramine binding in platelets after chlorimipramine in healthy volunteers. Comparison with maprotiline and amineptine

In the platelets of normal healthy volunteers (n = 8) taking chlorimipramine (50 mg/day) for 1 week, the saturable uptake of [3H]5-hydroxytryptamine (5-HT) was fully inhibited at the end of the week, but returned to control values after 2 weeks washout. The Bmax of [3H]imipramine binding was decreased by 63% at the end of the treatment and remained significantly decreased below control values after 1 week washout, whereas the Kd values were increased at the end of the treatment, but had returned to baseline values after 1 week washout. The time course of recovery following the administration of chlorimipramine showed some variation between subjects, but it was necessary to wait up to 4 weeks of washout before the Bmax of [3H]imipramine returned to baseline levels. In contrast, neither 1-week treatment with maprotiline (50 mg/day) nor with amineptine (100 mg/day) changed the parameters of [3H]5-HT uptake or [3H]imipramine binding in platelets from healthy volunteers. These results support the following conclusions. (1) [3H]Imipramine binding in platelets can be down-regulated by relatively low, subtherapeutic doses of chlorimipramine. (2) It is possible to dissociate [3H]imipramine binding parameters from [3H]5-HT uptake because the time course of recovery was clearly different, indicating that [3H]imipramine labels a site linked with, but different from, the 5-HT recognition site in the transporter complex. (3) A washout of antidepressants of 4 weeks may be needed when studying the parameters of [3H]imipramine binding in platelets from depressed patients if the previous medication involved chlorimipramine. For antidepressants like maprotiline or amineptine, that act through mechanisms other than inhibition of 5-HT uptake, the time of washout appears to be less critical, although it is not possible to rule out the existence of some secondary modifications influencing the 5-HT transporter complex.