Clinical pharmacology of anxiolytics and antidepressants: a psychopharmacological perspective

Unconventional anxiety pharmacology in zebrafish: Drugs beyond traditional anxiogenic and anxiolytic spectra

Anxiety is the most prevalent brain disorder and a common cause of human disability. Animal models are critical for understanding anxiety pathogenesis and its pharmacotherapy. The zebrafish (Danio rerio) is increasingly utilized as a powerful model organism in anxiety research and anxiolytic drug screening. High similarity between human, rodent and zebrafish molecular targets implies shared signaling pathways involved in anxiety pathogenesis. However, mounting evidence shows that zebrafish behavior can be modulated by drugs beyond conventional anxiolytics or anxiogenics. Furthermore, these effects may differ from human and/or rodent responses, as such 'unconventional' drugs may affect zebrafish behavior despite having no such profiles (or exerting opposite effects) in humans or rodents. Here, we discuss the effects of several putative unconventional anxiotropic drugs (aspirin, lysergic acid diethylamide (LSD), nicotine, naloxone and naltrexone) and their potential mechanisms of action in zebrafish. Emphasizing the growing utility of zebrafish models in CNS drug discovery, such unconventional anxiety pharmacology may provide important, evolutionarily relevant insights into complex regulation of anxiety in biological systems. Albeit seemingly complicating direct translation from zebrafish into clinical phenotypes, this knowledge may instead foster the development of novel CNS drugs, eventually facilitating innovative treatment of patients based on novel 'unconventional' targets identified in fish models.

Emotional Roles of Mono-Aminergic Neurotransmitters in Major Depressive Disorder and Anxiety Disorders

A growing body of researches support a role for dysfunction of serotoninergic, noradrenergic, and dopaminergic systems in the neurobiological processes involved in major depression disorder (MDD) and anxiety disorders (ADs). The physiological changes underlying abnormal signaling of 5-HT, NE, and DA may be due to either reduced presynaptic release of these neurotransmitters or aberrant signal transductions, and thus contributing to the alterations in regulation or function of receptors and/or impaired intracellular signal processing. Animal models demonstrate crucial responsiveness to disturbance of 5-HT, NE, and DA neurotransmissions. Postmortem and biochemical studies have shown altered concentrations of 5-HT, NE, and DA metabolites in brain regions that contribute importantly to regulation of mood and motivation in patients with MDD or ADs. Neuroimaging studies have found abnormal 5-HT, NE, and DA receptors binding and regulation in regard to receptor numbers. Medications that act on 5-HT, NE, and DA neurons or receptors, such as SSRIs and SNRIs, show efficacy in both MDD and ADs. The overlapping treatment response presumably suggests a common mechanism underlying the interaction of these disorders. In this paper, we reviewed studies from multiple disciplines to interpret the role of altered 5-HT, NE and DA mono-amine neurotransmitter functions in both MDD and ADs.

Angiotensin AT1 receptors modulate the anxiogenic effects of angiotensin (5-8) injected into the rat ventrolateral periaqueductal gray

Losartan and PD 123,319 are non-peptide angiotensin (Ang) receptor antagonists for the AT1 and AT2 subtypes of Ang II receptors, respectively. The tetrapeptide Ang (5-8) is the smallest Ang-peptide that elicits anxiogenic effects on unconditioned and conditioned experimental models upon injection into the ventrolateral column of the periaqueductal gray (vlPAG), and Ang (5-8) can be synthesized (from Ang II or Ang III) and inactivated in this mesencephalic structure. The vlPAG is also known to play a central role in mechanisms of fear and anxiety. We therefore utilized male Wistar rats to examine the effects of losartan and PD 123,319 injections, selective antagonists of the AT1 and AT2 receptors, respectively, into the vlPAG in the elevated plus-maze, a classic rat model of anxiety, and against the anxiogenic effect of Ang (5-8) (0.4 nmol/0.25μL) upon injection into the same region. The anxiolytic profile was dependent on the dose of intra-vlPAG losartan, whereas no effects on experimental anxiety were observed in the plus-maze following PD 123,319 injection. The anxiogenic effect of Ang (5-8) injection into the vlPAG remained unchanged in the PD 123,319-pretreated rats, but the effect did not occur in losartan-pretreated rats. The results led us to suggest that the anxiogenic effect of Ang (5-8) injection into the vlPAG may depend on the local activation of AT1, but not AT2 receptors. Activation of AT1 receptors in structures nearby vlPAG may be tonically involved in fear and experimental anxiety.

[Psychopharmacology of anxiety and depression: Historical aspects, current treatments and perspectives]

Pharmacological treatment of acute anxiety still relies on benzodiazepines, while chronic anxiety disorders and depression are treated with different antidepressants, according to specific indications. The monoaminergic axis is represented by two families which are being developed: (i) serotonin-norepinephrine-dopamine reuptake inhibitors (SNDRI), also called triple reuptake inhibitors (TRI), for the treatment of depression (amitifadine), (ii) multimodal antidepressants for depression and anxiety disorders (generalized anxiety disorder mainly) (tedatioxetine, vortioxetine and vilazodone). Third-generation antipsychotics (aripiprazole, lurasidone, brexpiprazole, cariprazine) appear relevant in the treatment of resistant depression and some anxiety disorders. Among the modulators of the glutamatergic axis, promising compounds include: (i) ionotropic regulators of NMDA receptors: esketamine, AVP-923 and AVP-786, CERC-301, rapastinel (Glyx-13), NRX-1074 developed for depression, rapastinel and bitopertine developed for obsessive compulsive disorder, (ii) metabotropic glutamate receptors modulators: decoglurant and basimglurant developed for depression and mavoglurant developed for obsessive compulsive disorder.

Prodynorphin gene deletion increased anxiety-like behaviours, impaired the anxiolytic effect of bromazepam and altered GABAA receptor subunits gene expression in the amygdala

This study evaluated the role of prodynorphin gene in the regulation of anxiety and associated molecular mechanisms. Emotional responses were assessed using the light-dark test, elevated plus maze and social interaction tests in prodynorphin knockout and wild-type mice. Corticotrophin releasing factor and proopiomelanocortin gene expressions in the hypothalamus were evaluated after restraint stress using in situ hybridization. The anxiolytic efficacy of bromazepam and GABA(A) receptor subunits gene expression in the amygdala were also assessed in both genotypes. The deletion of prodynorphin increased anxiety-like behaviours and proopiomelanocortin gene expression in the arcuate nucleus (two-fold). Moreover, the anxiolytic action of bromazepam was significantly attenuated in the mutant mice. Decreased GABA(A)γ(2) and increased GABA(A)β(2) gene expression receptor subunits were found in the amygdala of prodynorphin knockout mice. These results indicate that deletion of prodynorphin gene is associated with increased anxiety-like behaviours, enhanced sensibility response to stress stimuli, reduced anxiolytic efficacy of bromazepam and altered expression of the GABA(A) receptor subunits.

Acute and chronic treatment with serotonin reuptake inhibitors exert opposite effects on respiration in rats: possible implications for panic disorder

Prompted by the suggested importance of respiration for the pathophysiology of panic disorder, we studied the influence of serotonin reuptake inhibitors (SRIs) as well as other serotonin-modulating compounds on respiration in freely moving rats. The effect on respiration after acute administration of compounds enhancing synaptic levels of serotonin, that is, the serotonin reuptake inhibitors paroxetine and fluoxetine, the serotonin-releasing agents m-chlorophenylpiperazine and d-fenfluramine, and the selective 5-HT1A antagonist WAY-100635, were investigated. All serotonin-releasing substances decreased respiratory rate in unrestrained, awake animals, suggesting the influence of serotonin on respiratory rate under these conditions to be mainly inhibitory. In line with a previous study, rats administered fluoxetine for 23 days or more, on the other hand, displayed an enhanced respiratory rate. The results reinforce the assumption that the effect of subchronic administration of a serotonin reuptake inhibitor on certain serotonin-regulated parameters may be opposite to that obtained after acute administration. We suggest that our observations may be of relevance for the fact that acute administration of SRIs, d-fenfluramine, or m-chlorophenylpiperazine often is anxiogenic in panic disorder patients, and that weeks of administration of an SRI leads to a very effective prevention of panic.

Can Drug Treatments Enhance Learning in Subjects with Intellectual Disability?

Recent research has identified specific molecular mechanisms that might account for impaired learning in particular intellectual disability syndromes. These and other findings raise the possibility that targeted drug treatments might be developed to enhance learning in subjects with intellectual disability. This review considers strategies for developing treatments, and identifies critical issues that will need to be considered in such programmes.

Anxiety-like behaviors produced by acute fluoxetine administration in male Fischer 344 rats are prevented by prior exercise

RATIONALE

Although selective 5-HT reuptake inhibitors (SSRIs) can reduce anxiety after chronic treatment, acute SSRI administration is associated with an increase in anxiety consistent with an acute increase in 5-HT neurotransmission. Exercise is anxiolytic in humans, and wheel running prevents anxiety-like behavioral consequences of uncontrollable stress in rats, but the effects of exercise on acute fluoxetine-induced anxiety-like behaviors are unknown.

OBJECTIVES

The current studies tested the hypothesis that acute administration of the SSRI fluoxetine would produce behaviors in rats resembling those produced by uncontrollable stress and that these behaviors would be blocked by prior wheel running.

RESULTS

Adult, male Fisher 344 rats administered moderate (10 mg/kg) or high (20 mg/kg) doses of fluoxetine demonstrated exaggerated shock-elicited freezing and an interference with shuttle box escape compared to rats given either saline or low-dose fluoxetine (2.5 mg/kg). Fluoxetine-induced behaviors were similar to, but smaller in magnitude than, those produced by uncontrollable stress and were blocked by pretreatment with the 5-HT(2C) receptor antagonist SB 242084 (1 mg/kg). Rats allowed access to running wheels for 6 weeks were protected against the anxiety-like behaviors produced by a single injection of fluoxetine (10 mg/kg).

CONCLUSIONS

Behavioral effects of acute fluoxetine administration resemble those produced by uncontrollable stress. Results are consistent with the idea that exercise can produce resistance against the anxiogenic effects of acute increases in 5-HT and suggest that acute behavioral effects of antidepressants can depend on history of physical activity.

Efficacy of the MCHR1 Antagonist N-[3-(1-{[4-(3,4-Difluorophenoxy)phenyl]methyl}(4-piperidyl))-4-methylphenyl]-2-methylpropanamide (SNAP 94847) in Mouse Models of Anxiety and Depression following Acute and Chronic Administration Is Independent of Hippocampal Neurogenesis

Melanin-concentrating hormone (MCH) is a hypothalamic neuropeptide that plays a role in the modulation of food intake and mood. In rodents, the actions of MCH are mediated via the MCHR1 receptor. The goal of this study was to investigate the effects of acute (1 h) and chronic (28 days) p.o. dosing of a novel MCHR1 antagonist, N-[3-(1-{[4-(3,4-difluorophenoxy)-phenyl]methyl}(4-piperidyl))-4-methylphenyl]-2-methylpropanamide (SNAP 94847), in three mouse models predictive of antidepressant/anxiolytic-like activity: novelty suppressed feeding (NSF) in 129S6/SvEvTac mice and light/dark paradigm (L/D) and forced swim test (FST) in BALB/cJ mice. A significant increase in the time spent in the light compartment of the L/D box was observed in response to acute and chronic treatment with SNAP 94847. An anxiolytic/antidepressant-like effect was found in the NSF test after acute and chronic treatment, whereas no effect was observed in the FST. Because neurogenesis in the dentate gyrus has been shown to be a requirement for the effects of antidepressants in the NSF test, we investigated whether neurogenesis was required for the effect of SNAP 94847. We showed that chronic treatment with SNAP 94847 stimulated proliferation of progenitors in the dentate gyrus. The efficacy of SNAP 94847 in the NSF test, however, was unaltered in mice in which neurogenesis was suppressed by X-irradiation. These results indicate that SNAP 94847 has a unique anxiolytic-like profile after both acute and chronic administration and that its mechanism of action is distinct from that of selective serotonin reuptake inhibitors and tricyclic antidepressants.

Anxiety but not arousal increases 5-hydroxytryptamine release in the rat ventral hippocampus in vivo

Central serotonin [5-hydroxytryptamine (5-HT)] is involved in the aetiology of numerous disease states, including depression and anxiety disorders. Studies have shown that exposure of rats to animal tests of anxiety increases extracellular 5-HT in the cortex or hippocampus determined by in vivo microdialysis. To discriminate whether this increase is caused by the aversive conditions of an animal test for anxiety or by an unconditioned stressor evoking mainly arousal, the present study investigates the effects of an unconditioned acoustic stimulus and exposure to the elevated plus maze (X-maze), respectively, on the release of 5-HT in the ventral hippocampus compared with hippocampal 5-HT release in the home cage and in a non-aversive unfamiliar environment in freely moving rats. Our results showed a distinct pattern of 5-HT release in the ventral hippocampus depending on the stimulus used. Exposure to the X-maze for 20 min was accompanied by an 'anxious' behaviour in the rats and increased extracellular 5-HT to 165% of basal release, whereas exposure to a less aversive 'deactivated' plus maze (115+/-6%) or to white noise for 20 min in the familiar surroundings of the home cage (98+/-6%) did not change hippocampal 5-HT release significantly, despite similar behavioural activation indicated by increased locomotor activity. While both the X-maze and white noise may model anxiety and stress to a certain extent, it seems that the X-maze is more aversive. The results suggest a close relationship between anxiety-related behaviour, but not arousal/non-specific behavioural activation, and 5-HT release in the ventral hippocampus.

Failure of ethanol and acetaldehyde to alter in vivo norepinephrine release in the striatum and hippocampus of rats

The effect of ethanol (EtOH) and acetaldehyde (AcH) on norepinephrine (NE) release was examined in the striatum and hippocampus of freely moving rats by means of in vivo microdialysis coupled with high-performance liquid chromatography and an electrochemical detector. Rats were treated intraperitoneally with EtOH (1 g/kg) or cyanamide (CY, 50 mg/kg, a potent aldehyde dehydrogenase inhibitor) plus EtOH (1 g/kg). No significant difference in NE levels in the dialysates was observed in the striatum and hippocampus in either the EtOH or CY+EtOH groups. NE levels in the hippocampal dialysates were about fivefolds higher than those in the striatum. The concentration of EtOH and AcH in the striatal dialysate reached a peak at 30 min after EtOH dosing and then gradually decreased in the CY+EtOH group. In the EtOH group the striatal concentration of EtOH also reached a peak at 30 min after EtOH dosing, and then gradually decreased while AcH was not detected. The present study suggests that there is no in vivo effect of brain EtOH or AcH on NE release in the striatum and hippocampus of awake rats.

The role of serotonin in panic: evidence from tryptophan depletion studies

There has been growing interest in the role of serotonin (5-hydroxytryptamine, 5-HT) in anxiety, including pathological states such as panic disorder. The technique of tryptophan depletion (TD), which causes an acute, temporary and reversible reduction in brain 5-HT levels, is a useful minimally invasive paradigm to aid the research of the role of 5-HT in various disorders. This review discusses the evidence supporting the hypothesis that 5-HT function is of importance in the neurobiology of panic disorder and considers in more detail how our understanding has been influenced by work using the technique of TD. Possible avenues for future research are also discussed.

Does the brain noradrenaline network mediate the effects of the CO2 challenge?

The inhalation of carbon dioxide (CO2) is commonly used in patients and volunteers as a means of producing anxiety or panic. It is generally believed that patients with panic disorder are more vulnerable to the effects of CO2 than patients with other anxiety disorders or healthy volunteers and there is speculation and debate as to the mechanism for this apparent sensitivity. Recent work from our group has shown that a single inhalation of 35% CO2 activates the hypothalamic-pituitary-adrenocortical (HPA) axis, increases blood pressure (BP) and increases subjective fear responses in healthy volunteers. Correlation analyses reveal a relationship between the changes in BP and the cortisol increase. These findings led us to postulate that a common mechanism may mediate these and the subjective responses to inhalation of CO2. We propose that the noradrenergic system, particularly the locus coeruleus (LC), but including the A1 and A2 cell groups, may be a key mediator of these responses. This article examines the evidence and discusses the results of studies from our laboratory in relation to a neuroanatomical model centring on the LC.

Simultaneous determination of norepinephrine, serotonin, and 5-hydroxyindole-3-acetic acid in microdialysis samples from rat brain by microbore column liquid chromatography with fluorescence detection following derivatization with benzylamine

A microbore column liquid chromatographic method for the simultaneous determination of norepinephrine (NE), serotonin (5-HT), and 5-hydroxyindole-3-acetic acid (5HIAA) in microdialysis samples from rat brain is described. The method is based on precolumn derivatization of NE, 5HT, and 5HIAA with benzylamine in the presence of potassium hexacyanoferrate(III) resulting in the corresponding highly fluorescent and stable benzoxazole derivatives. A 15-microl sample was mixed with 15 microl derivatization reagent solution containing 0.3M 3-cyclohexylaminopropanesulfonic acid buffer (pH 12.0), 0.5M benzylamine, 10mM potassium hexacyanoferrate(III), and methanol (1/1/1/12, v/v/v/v). The derivatization was carried out at 50 degrees C for 20 min. The benzylamine derivatives of NE, 5HT, and 5HIAA were separated on a reversed-phase column (100 x 1.0mm i.d., packed with C18 silica, 5 microm) within 30 min. The mobile phase consisted of 15 mM acetate buffer (pH 5.0) and acetonitrile (31%, v/v); the flow rate was 50 microl/min. The detection limits (signal-to-noise ratio of 3) for NE, 5HT, and 5HIAA in the injection volume of 20 microl were 90, 210, and 260 amol, respectively. Microdialysis samples were collected in 7.5-min intervals from the probes implanted in the hippocampus and prefrontal cortex of awake rats. The basal levels of NE, 5HT, and 5HIAA in the dialysates from the hippocampus were 4.2+/-0.5, 4.9+/-0.6, and 934.1 +/- 63.4 fmol/20 microl, and those from the prefrontal cortex were 6.0+/-1.2,5.51.3, and 669.1 +/- 96.0 fmol/20 microl (mean +/- SE, n=25), respectively. The NE and 5HT levels were altered by perfusion of high-potassium or low-calcium solution and following antidepressant drugs imipramine and desipramine. It is concluded that the new fluorescence derivatization method in combination with microbore column liquid chromatography allows the simultaneous determination of NE, 5HT, and 5HIAA in the microdialysis samples at higher sensitivity, providing easier maintenance in routine use than that achieved by high-performance liquid chromatographic methods with electrochemical detection.

Rapid desensitization of 5-HT(1A) receptors in Fawn-Hooded rats after chronic fluoxetine treatment

Anxiety, platelet serotonin (5-HT) content and functions of the 5-HT(1A) receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) were measured in Sprague--Dawley (SD) and Fawn-Hooded (FH) rats, a strain with genetically impaired 5-HT storage and reuptake system and a putative model of depression and anxiety. In addition, the effects of 7 and 16 days treatment with the selective serotonin reuptake inhibitor (SSRI) fluoxetine on 8-OH-DPAT-induced responses were studied. FH rats showed significantly higher anxiety in the social interaction test, and much lower platelet 5-HT content compared to SD rats. The efficacy of 8-OH-DPAT (15-120 microg/kg, i.v.) to induce lower lip retraction (an effect mediated by median raphe receptors) was increased in FH rats. In most FH but only a few SD rats a special neurological syndrome, clonic movement of the masseters and in-and-out movement of the eyeballs, was induced by 8-OH-DPAT, and this behaviour like other effects of 8-OH-DPAT, was completely blocked by pretreatment with the 5-HT(1A) receptor antagonist WAY-100635. In SD rats fluoxetine (10 mg/kg/day, i.p.) caused a moderate inhibition of 8-OH-DPAT-induced hypothermia, an effect mediated most likely by hypothalamic 5-HT(1A) receptors, (-19% and -40% after 7 and 16 days of fluoxetine, 24 h after the last injection, respectively). In FH rats fluoxetine caused a rapid and complete reduction in the 8-OH-DPAT-induced hypothermia (-65% and -91% after 7 and 16 days of fluoxetine, respectively). Fluoxetine caused no change in lower lip retraction but a reduction in the masseter-eyeball syndrome in both SD and FH rats. Our data provide evidence that in FH rats, median raphe 5-HT(1A) receptors are hypersensitive, and the hypothalamic 5-HT(1A) receptor desensitization, caused by SSRI antidepressants, is faster and more complete. These data support the notion that chronic treatment with SSRIs induces a desensitization of some 5-HT(1A) receptor populations, and impaired 5-HT storage and reuptake may accelerate this process.

The psychobiology of anxiolytic drugs. Part 1: Basic neurobiology

The authors provide an overview of the current state of knowledge with regards to the neurobiological mechanisms involved in normal and pathological anxiety. A brief review of the classification and cognitive psychology of anxiety is followed by a more in-depth look at the neuroanatomical and neurochemical processes and their relevance to our understanding of the modes of action of anxiolytic drugs. The serotonergic, noradrenergic, and gamma-aminobutyric acidergic systems are reviewed. The numerous physiological and pharmacological methods of anxiety provocation and the increasing importance of functional neuroimaging are also examined. The review provides an overview of the biology and basic pharmacology of anxiolytic drugs, and compliments the more clinically oriented companion review.

Stress-induced C-fos expression in the rat locus coeruleus is dependent on neurokinin 1 receptor activation

These experiments examined the role of substance P-selective neurokinin 1 receptors in the restraint-induced activation of the rat locus coeruleus. Immunohistochemistry revealed high levels of neurokinin 1 receptor expression in the plasma membrane of tyrosine hydroxylase-positive locus coeruleus neurons. The selective neurokinin 1 receptor antagonists, RP 67580 (5 nmol) and L-760,735 (3.4 nmol), were administered intracerebroventricularly prior to restraint stress, and c-fos protein was measured as an index of locus coeruleus activation. Both antagonists attenuated the restraint-induced increase in locus coeruleus c-fos expression, whereas their inactive enantiomers were ineffective. These results suggest that neurokinin 1 receptors may mediate activation of locus coeruleus neurons during stress. Neurokinin 1 receptor antagonists may prove to be novel therapeutic compounds in the treatment of anxiety and depression.

Determination of norepinephrine in microdialysis samples by microbore column liquid chromatography with fluorescence detection following derivatization with benzylamine

A microbore column liquid chromatographic method is described for the determination of norepinephrine (NE) in microdialysis samples from rat brain. The method is based on precolumn derivatization of NE with benzylamine in the presence of potassium hexacyanoferrate(III) resulting in a highly fluorescent and stable benzoxazole derivative. Typically, a 10-microl sample was mixed with 10 microl derivatization reagent containing 0.45 M Caps buffer (pH 12.0), 0.2 M benzylamine, 10 mM potassium hexacyanoferrate(III), and N,N-dimethylformamide (1:1:1:15, v/v). The derivatization was carried out at 50 degrees C for 20 min. Under these conditions only NE and epinephrine produced high fluorescence yields at excitation and emission wavelengths of 345 and 480 nm, respectively, while fluorescence of other catechols and 5-hydroxyindoles was quenched by 10-100 times. The NE derivative was separated on a reversed-phase column (100 x 1.0 mm i.d., packed with C18 silica, 5 microm) within 10 min with no late eluting peaks. The mobile phase consisted of 40 mM Britton-Robinson buffer (pH 7.5) containing 1 mM didodecyldimethylammonium bromide and acetonitrile (34%, v/v), the flow rate was 40 microl/min. The limit of detection (signal-to-noise ratio of 3) for NE was 90 amol in 10 microl sample injected. Microdialysis samples were collected in 5-min intervals from the probes implanted in the hippocampus, frontal cortex, or hypothalamus of awake rats. The basal extracellular NE levels in the respective areas were 4.7 +/- 0.9, 1.8 +/- 0.3, and 0.8 +/- 0.2 fmol/10 microl (mean +/- SE, n = 7). Perfusion with a Ringer solution containing 100 mM K+ increased hippocampal NE levels by 700%, while NE uptake inhibitors maprotiline and amitriptyline administered orally or subcutaneously increased extracellular NE in the frontal cortex by about 300%. On the other hand, reserpine (5 mg/kg) reduced cortical NE levels by 40% 3 h after the administration. This new fluorescence derivatization method provides better selectivity, sensitivity, and speed for NE determination than the electrochemical detection since no late-eluting compounds such as dopamine, serotonin, and their metabolites are detectable in the chromatograms of the microdialysis samples.

Effects of chronic antidepressants in an operant conflict procedure of anxiety in the rat

The effects of chronic antidepressants were investigated in an animal procedure for the study of anxiety and anxiolytics, the conditioned suppression of operant behavior in rats. In daily 18-min sessions, three periods of nonpunished lever pressing for food alternated with two 4-min periods signaled by a light-on conditioned stimulus during which 50% of the responses were randomly punished by electric foot shocks. Antidepressants were administered once daily for 7-8 weeks to trained, food-restricted rats. Desipramine (dose regimen increase from 4 to 16 mg/kg/day) induced a gradual (4-5-week latency) release of response suppression during punished periods over the course of several weeks of testing. This anxiolytic-like effect was still present 3 weeks following drug discontinuation. In contrast, chronic imipramine (dose regimen increase from 4 to 16 mg/kg/day), maprotiline (4 to 16 mg/kg/day), phenelzine (2 to 4 mg/kg/day), and fluoxetine (1 or 8 mg/kg/day; constant dose), resulted in no change in punished responding, suggesting that no anxiolytic-like effect developed in the course of chronic treatment with these compounds. The largest dose of all antidepressants studied (except fluoxetine) induced a moderate to marked reduction of nonpunished performance that disappeared within 1 week after the last injection. A transient release of conditioned response suppression emerged during the week that followed discontinuation of imipramine, maprotiline, and fluoxetine (8 mg/kg/day). This apparent anxiolytic-like activity might be due to a reduction of some adverse effect induced by the high doses used, and/or might have resulted from a new dynamic equilibrium between monoamine release, reuptake processes, and sensitivity of postsynaptic receptors. In conclusion, operant conflict procedures in rats seem not particularly able to model human anxiety sensitive to chronic antidepressant treatments.

Anxiogenic effect of central CCK administration is attenuated by chronic fluoxetine or ipsapirone treatment

The effect of chronic fluoxetine and ipsapirone treatment on the anxiogenic effect of centrally administered cholecystokinin (CCK) was studied in the social interaction test in male Sprague-Dawley rats. Intracerebroventricular injection of unsulfated CCK-8 significantly decreased total interaction time and locomotor activity and caused some increase in selfgrooming and a reduction in rearing behaviour in a familiar arena in low light conditions. The selective serotonin reuptake inhibitor antidepressant fluoxetine alone (5 mg/kg, i.p.) also had clear acute anxiogenic actions (decrease in total interaction time, locomotor activity, rearing, increase in selfgrooming) after single dosing, but all these effects were omitted after chronic (3 weeks) treatment. In contrast, a single injection of the 5-HT1A receptor partial agonist ipsapirone (5 mg/kg, i.p.) alone had only motor effects (decrease in selfgrooming and rearing), and these effects were preserved after chronic treatment. Chronic fluoxetine treatment (5 mg/kg per day, 3 weeks) abolished the effects of CCK-8 (1 nmol/rat, i.c.v.). Chronic treatment with ipsapirone (5 mg/kg per day, 3 weeks) partially attenuated the effects of CCK-8 (1 nmol/rat, i.c.v.). Our studies provide further evidence for a 5-HT/CCK interaction in the regulation of anxiety.

Behavioural effects in mice of subchronic chlordiazepoxide, maprotiline and fluvoxamine. II. The elevated plus-maze

In view of apparent commonalities in the aetiology, symptomatology, and pharmacotherapy of anxiety and depressive disorders, the present study compares the effects of the benzodiazepine, chlordiazepoxide (1.0-8.0 mg/kg), the selective noradrenaline (NA) reuptake inhibitor, maprotiline (0.5-10.0 mg/kg), and the serotonin (5-HT)-selective reuptake inhibitor, fluvoxamine (2.0-8.0 mg/kg), on the behaviour of mice in the elevated plus-maze test of anxiety. To more accurately reflect the clinical situation, subjects were treated daily for 21 days prior to testing, and comprehensive behavioural profiles were obtained through the application of an ethological scoring technique. Results show that subchronic treatment with chlordiazepoxide produced clear anxiolytic-like effects at the highest dose tested, coupled with an inhibition of risk assessment over the entire dose range. With the exception of risk assessment measures, anxiolytic-like effects were also seen with a low dose (0.5 mg/kg) of maprotiline: these effects were lost at higher doses. In contrast to these data, fluvoxamine produced minimal behavioural change under present test conditions. Findings are discussed in relation to the relative efficacy of selective monoamine. reuptake inhibitors in the treatment of anxiety disorders, and the nature of anxiety evoked in mice by exposure to the elevated plus-maze.

Electrophysiological, behavioural and biochemical evidence for activation of brain noradrenergic systems following neurokinin NK3 receptor stimulation

The objective of the present in vitro and in vivo experiments was to examine the involvement of neurokinin NK3 receptors in the regulation of the noradrenergic function in gerbils and guinea-pigs. Application of senktide, a peptide NK3 receptor agonist, on guinea-pig locus coeruleus slices increased the firing rate of presumed noradrenergic neurons (EC50 = 26 nM) in a concentration-dependent manner. Given i.c.v., senktide (0.5-2 micrograms) and (MePhe7)neurokinin B (1-10 micrograms), another NK3 receptor agonist, reduced exploratory behaviour in gerbils in a dose-dependent manner (2 micrograms of senktide producing a 50% reduction of locomotor activity and rearing). In vivo microdialysis experiments in urethane-anaesthetized guinea-pigs showed that senktide (2-8 micrograms i.c.v.) induced a dose-dependent increase in norepinephrine release in the medial prefrontal cortex. The electrophysiological, behavioural and biochemical changes elicited by senktide were concentration- or dose-dependently reduce by SR 142801, the selective non-peptide NK3 receptor antagonist. In the locus coeruleus slice preparation, complete antagonism of senktide (30 nM) was observed with 50 nM of SR 142801, while injected i.p. (0.1-1 mg/kg) it abolished the senktide-induced norepinephrine release in guinea-pigs. In gerbils, SR 142801 (1-10 mg/kg i.p.) reversed the reduction of exploratory behaviour induced by senktide (1 microgram). By contrast, the 100-fold less active enantiomer, SR 142806, did not exert any antagonism in these models. Finally, the reduction of exploratory behaviour in gerbils was found to be reversed by prazosin (0.25-2.56 micrograms/kg i.p.) and to some extent by clonidine, drugs known to depress noradrenergic function. All these experiments strongly support the hypothesis that brain noradrenergic neurons can be activated by stimulation of neurokinin NK3 receptors.

The antidepressant drug phenelzine produces antianxiety effects in the plus-maze and increases in rat brain GABA

Research on the effects of antidepressant/ antipanic drugs in animal models of anxiety has yielded equivocal results, even after chronic drug regimens. In contrast, we found that the antidepressant/antipanic drug phenelzine, given acutely, produced a clear anxiolytic effect in the elevated plus-maze, a widely-used animal model of "anxiety" that is primarily sensitive to benzodiazepine-type anxiolytics (e.g., diazepam). Furthermore, the effective dose of phenelzine (15 mg/kg) administered to rats was associated with more than a 2- fold increase in whole brain levels of gamma-aminobutyric acid (GABA), whereas an ineffective dose of phenelzine (5.1 mg/kg) did not significantly change GABA levels. The N-acetylated metabolite of phenelzine, N2-acetylphenelzine, produced neither an anxiolytic effect in the elevated plus-maze nor a significant change in whole-brain levels of GABA. However, both phenelzine and N2-acetylphenelzine potently inhibited monoamine oxidase, a mechanism commonly thought to be involved in the therapeutic effects of monoamine oxidase inhibitors such as phenelzine in the treatment of depression in humans. These results suggest that the mechanism whereby phenelzine produces anxiolytic effects in the plus-maze model is unique to a facilitatory action on brain levels of GABA, in contrast to classical benzodiazepines, which produce anxiolytic effects by enhancing the affinity of the GABAA-receptor for GABA.

Serotonin reuptake inhibitors reduce conditioned fear stress-induced freezing behavior in rats

Conditioned fear stress (CFS)-induced freezing behavior has been proposed as an animal model of anxiety. In the present study, freezing was used to determine the anxiolytic activity of selective serotonin reuptake inhibitors (SSRIs), which are reported to be clinically effective in anxiety disorders. The duration of freezing behavior was reduced by acute treatment with the SSRIs citalopram (1-10 mg/kg) and fluvoxamine (3-30 mg/kg). Acute treatment with the serotonin (5-HT)/noradrenaline (NA) mixed reuptake inhibitor milnacipran (3-30 mg/kg) also attenuated CFS-induced freezing, while acute treatment with the NA reuptake inhibitors maprotiline and ORG4428, and the dopamine (DA) reuptake inhibitor GBR12909 failed to alter CFS-induced freezing. These results indicate that facilitation of 5-HT availability in the brain produced by 5-HT reuptake inhibition reduces CFS-induced freezing behavior. CFS may be a useful model for detecting the anxiolytic potential of 5-HT reuptake inhibitors.

Stress-induced hyperthermia as a putative anxiety model

In group-housed mice (ten per cage), mice removed last from their home cage always have higher rectal temperatures than mice removed first from this cage. Stress-induced hyperthermia is calculated as the difference (delta T) between the basal temperature (mouse number 1) and the end temperature (mouse number 10) when the temperature of the ten mice is sequentially measured using a 1-min interval between rectal measurements. Using this protocol, various drugs, belonging to different pharmacological classes, were tested in order to investigate their putative anxiolytic effect, measured as a decrease in delta T. Benzodiazepines (diazepam, alprazolam), alcohol, and some (flesinoxan, buspirone), but not all (ipsapirone) 5-HT1A receptor agonists had anxiolytic properties with this protocol. Clonidine (alpha 2-adrenoceptor agonist) and prazosine (alpha 1-adrenoceptor antagonist) had, but at high doses, some anxiolytic actions. Antidepressants (desipramine, fluvoxamine, nomifensine, tianeptine, amitriptyline, clomipramine, imipramine), serotonergic ligands (ondansetron, ketanserin, 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI), fenfluramine, metachlorophenylpiperazine (mCPP), eltoprazine) and various other drugs (phenobarbital, pentetrazol, haloperidol, apomorphine, amphetamine, (+)-N-[1-methyl-2-oxo-5-phenyl-2,3-dihydro-1H-1,4-benzodiazepin-3( R)-yl]- N'-(3-methylphenyl)urea (MSD 365260), dizocilpine and acetyl salicylic acid) had no anxiolytic activity. The stress-induced hyperthermia protocol used was unable to detect anxiogenic properties of drugs, probably due to a (physiological) ceiling in the maximal end temperature. The stress-induced hyperthermia protocol with mice can be used to measure anxiolytic properties of drugs and is a fast and robust model which does not need extensive training of animals.

Ethological comparison of the effects of diazepam and acute/chronic imipramine on the behaviour of mice in the elevated plus-maze

Recent clinical evidence suggests that the tricyclic antidepressant imipramine is effective against not only panic disorder but also generalized anxiety disorder. Although most animal models of anxiety appear to be insensitive to this agent, such work has almost invariably employed an acute treatment regimen. In the present study, ethological methods have been used to assess in detail the effects of acute and chronic imipramine treatment on the behaviour of male DBA/2 mice in the elevated plus-maze test. In contrast to acutely administered diazepam (1 mg/kg), which produced a significant anxiolytic profile on standard and ethological measures, neither acute nor chronic (daily, 15 days) treatment with imipramine (0-20 mg/kg) was associated with anxiety reduction. Data are discussed in relation to test sensitivity factors and the nonspecific mechanism of action of imipramine.

Clinical recovery from panic disorder is associated with evidence of changes in cardiovascular regulation

Cardiovascular measures (spectral derivatives of heart rate variability, the blood pressure response to standing and plasma noradrenaline levels) have been shown to change as clinical recovery follows the treatment of panic disorder patients with either imipramine or cognitive therapy. These findings can be interpreted as evidence of changes in baroreflex modulation, an important feature of the cardiovascular expression of arousal. This offers further evidence of a dysregulation of arousal in this disorder.

Increased dopamine and norepinephrine release in medial prefrontal cortex induced by acute and chronic stress: effects of diazepam

We have examined the effects of diazepam on the stress-induced increase in extracellular dopamine and norepinephrine in the medial prefrontal cortex using in vivo microdialysis. In naive rats, acute tail pressure (30 min) elicited an increase in the concentrations of dopamine and norepinephrine in extracellular fluid of medial prefrontal cortex (+54 and +50%, respectively). Diazepam (2.5 mg/kg, i.p.) decreased the basal concentration of extracellular dopamine and norepinephrine. Diazepam also attenuated the stress-evoked increase in the absolute concentrations of extracellular dopamine (+17%), but did not alter the stress-induced increase in norepinephrine (+41%). However, when the drug-induced decrease in basal dopamine and norepinephrine concentration was taken into account, the stress-induced net increase in dopamine above the new baseline was equivalent to that obtained in vehicle pretreated rats, whereas the net increase in norepinephrine was almost twice that obtained in control subjects. In rats previously exposed to chronic cold (three to four weeks at 5 degrees C), tail pressure again produced an increase in the concentrations of dopamine and norepinephrine in the medial prefrontal cortex (+42% and +92%, respectively). However, in these chronically stressed rats, diazepam no longer decreased basal dopamine or norepinephrine in extracellular fluid, nor did it affect the stress-induced increase in the concentrations of these catecholamines. These data indicate that diazepam has complex effects on the extracellular concentrations of dopamine and norepinephrine which vary depending upon whether the rat is undisturbed or stressed during the period of drug exposure as well as the rat's prior history of exposure to stress. Moreover, these data raise questions regarding the role of catecholamines in the mechanism by which diazepam exerts its anxiolytic properties.

Effects of two stressors on behaviour in the elevated X-maze: preliminary investigation of their interaction with 8-OH-DPAT

Effects of water deprivation and restraint were compared in the rat elevated X-maze. Water deprivation for 12-48 h increased corticosterone and had a duration-dependent "anxiolytic" effect in the elevated X-maze, increasing the ratio of open/total arm entries (OTR) and the proportion of time spent on the open arms (% time) without affecting total entries. Brain 5HIAA/5HT was increased only after 24 or 48 h deprivation. Restraint for 15 min also increased plasma corticosterone and brain 5HIAA/5HT but had no effect on behaviour in the elevated X-maze when rats were tested immediately afterwards. However, 1 h restraint was "anxiogenic" in the elevated X-maze immediately after release, reducing OTR and % time, but with a less consistent reduction in total entries; reductions in OTR and % time were still present 24 h later. The 5HT1A agonist 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) (0.1-0.2 mg/kg), administered 10 min before testing in the elevated X-maze, had "anxiogenic" actions in non-stressed rats. The effect of 0.1 mg/kg 8-OH-DPAT was not significantly altered by 24 or 48 h water deprivation but was abolished by restraint for 1 h immediately beforehand, despite the "anxiogenic" effect of restraint alone. Similar mutual antagonism of 8-OH-DPAT and restraint occurred when the dose of 8-OH-DPAT was increased to 0.2 mg/kg. Twenty-four hours after restraint, restrained rats which had received 8-OH-DPAT (0.1-0.2 mg/kg) still did not show any significant "anxiogenic effect" compared with non-restrained vehicle treated controls. Restraint-induced deficits in elevated X-maze exploration may prove a useful model with which to study the pharmacology of depression-related anxiety. However, the effects of the stressors examined, and their interaction with 8-OH-DPAT in the elevated X-maze, appear to depend on the nature of the stressor.

Guidelines for the rational use of benzodiazepines. When and what to use

The main actions of benzodiazepines (hypnotic, anxiolytic, anticonvulsant, myorelaxant and amnesic) confer a therapeutic value in a wide range of conditions. Rational use requires consideration of the large differences in potency and elimination rates between different benzodiazepines, as well as the requirements of individual patients. As hypnotics, benzodiazepines are mainly indicated for transient or short term insomnia, for which prescriptions should if possible be limited to a few days, occasional or intermittent use, or courses not exceeding 2 weeks. Temazepam, loprazolam and lormetazepam, which have a medium duration of action are suitable. Diazepam is also effective in single or intermittent dosage. Potent, short-acting benzodiazepines such as triazolam appear to carry greater risks of adverse effects. As anxiolytics, benzodiazepines should generally be used in conjunction with other measures (psychological treatments, antidepressants, other drugs) although such measures have a slower onset of action. Indications for benzodiazepines include acute stress reactions, episodic anxiety, fluctuations in generalised anxiety, and as initial treatment for severe panic and agoraphobia. Diazepam is usually the drug of choice, given in single doses, very short (1 to 7 days) or short (2 to 4 weeks) courses, and only rarely for longer term treatment. Alprazolam has been widely used, particularly in the US, but is not recommended in the UK, especially for long term use. Benzodiazepines also have uses in epilepsy (diazepam, clonazepam, clobazam), anaesthesia (midazolam), some motor disorders and occasionally in acute psychoses. The major clinical advantages of benzodiazepines are high efficacy, rapid onset of action and low toxicity. Adverse effects include psychomotor impairment, especially in the elderly, and occasionally paradoxical excitement. With long term use, tolerance, dependence and withdrawal effects can become major disadvantages. Unwanted effects can largely be prevented by keeping dosages minimal and courses short (ideally 4 weeks maximum), and by careful patient selection. Long term prescription is occasionally required for certain patients.

A comparison of cognitive therapy, applied relaxation and imipramine in the treatment of panic disorder

Recent studies have shown that cognitive therapy is an effective treatment for panic disorder. However, little is known about how cognitive therapy compares with other psychological and pharmacological treatments. To investigate this question 64 panic disorder patients were initially assigned to cognitive therapy, applied relaxation, imipramine (mean 233 mg/day), or a 3-month wait followed by allocation to treatment. During treatment patients had up to 12 sessions in the first 3 months and up to three booster sessions in the next 3 months. Imipramine was gradually withdrawn after 6 months. Each treatment included self-exposure homework assignments. Cognitive therapy and applied relaxation sessions lasted one hour. Imipramine sessions lasted 25 minutes. Assessments were before treatment/wait and at 3, 6, and 15 months. Comparisons with waiting-list showed all three treatments were effective. Comparisons between treatments showed that at 3 months cognitive therapy was superior to both applied relaxation and imipramine on most measures. At 6 months cognitive therapy did not differ from imipramine and both were superior to applied relaxation on several measures. Between 6 and 15 months a number of imipramine patients relapsed. At 15 months cognitive therapy was again superior to both applied relaxation and imipramine but on fewer measures than at 3 months. Cognitive measures taken at the end of treatment were significant predictors of outcome at follow-up.

Multiple serotonin mechanisms in animal models of anxiety: environmental, emotional and cognitive factors

Responses to serotonergic drugs in animal models of 'anxiety' are reviewed with emphasis on the elevated X-maze. Evidence for the 'classic' hypothesis, that decreasing serotonergic function is anxiolytic and increasing it anxiogenic, is most consistent in models of behavioural inhibition where the stimulus inhibits an approach response (conflict models). However, paradoxical drug effects are also frequent, especially where the aversive stimulus evokes an active response. Both types of drug effect are equally frequent in the elevated X-maze. 'Anxiety' models may detect multiple sites and mechanisms of action of the same drug; this may indicate multiple anxiety-related neurological mechanisms in the brain. However, not all drug effects in 'anxiety' models are necessarily related to anxiety itself. It is possible that cognitive factors may affect stimulus evaluation, and response inhibition by an aversive stimulus may be a special case of a wider role for serotonin in behavioural control. Clinical implications of these observations are considered.

An assessment of the elevated X-maze for studying anxiety and anxiety-modulating drugs

The elevated X-maze has strong claims to validity as an animal model of anxiety, both in theoretical basis and drug responses. The model is sensitive to actual and putative anxiolytics, but because insufficient time has elapsed since its discovery, no agent first predicted to be anxiolytic in the elevated X-maze has been brought into general use yet. It has an advantage in detecting anxiolytic and anxiogenic agents under the same operating conditions. The design and execution of experiments with the model is discussed and it is shown that baseline arm preference and the size or direction of drug effects differ in the procedural factors affecting them. Because it presents features of both passive and active avoidance and approach/avoidance conflict, it may prove able to detect drug effects in different forms of human anxiety and aid in understanding their neurobiology.

5HT drugs in animal models of anxiety

It has been widely accepted that 5HT neurones promote anxiety, in humans as well as in animal models. This could be termed the "classic" hypothesis and it has led to a determined search for drugs which reduce 5HT function, especially agents which have selective actions at 5HT receptor subtypes. However, these novel agents tend to have weak and/or variable effects in animal models and more detailed examination of their actions suggests that not all findings are accounted for by the classic hypothesis. There appear to be circumstances in which increased 5HT activity can reduce anxious behaviour. There is increasing evidence for multiple anxiety mechanisms, which may be able to explain differential patterns of drug effects within and between models. Animal models of anxiety may also detect non-anxiety factors: effects on cognition or on impulsivity could be reflected in some models. This could be important in the light of recent evidence that 5HT-selective reuptake inhibitors are effective in impulsivity disorders. The classic hypothesis of 5HT function in anxiety may be only one part of an increasingly complex story. Unravelling the rest of this story is likely to lead to new insights in our understanding of anxiety and related disorders.

The Galway Study of Panic Disorder. II: Changes in some peripheral markers of noradrenergic and serotonergic function in DSM III-R panic disorder

Sixty six patients with panic disorders, fulfilling the DSM III criteria for panic attack, together with a group of age and sex matched controls, were studied for changes in their peripheral noradrenergic and serotonergic status before treatment and during six months treatment with either clomipramine or lofepramine. The results of this study suggest that, despite clinical improvement, the peripheral markers of both adrenergic (platelet aggregation to noradrenaline, platelet alpha 2 receptor density and lymphocyte beta receptor density) and serotonergic (platelet aggregation to serotonin, 3H-ketanserin binding to platelet 5HT2 receptors and 3H-5HT uptake into platelets) function largely remained abnormal. It is concluded that such abnormalities are trait markers of biogenic amine function in patients with panic attack. Further studies are needed to determine whether or not these parameters eventually normalize in those patients showing prolonged remission of symptoms.

Panic attacks. A neurochemical overview of models and mechanisms

The delineation of panic disorder as a distinct diagnostic entity has provided renewed impetus for research into panic. This review describes and examines the range of neurobiological theories of panic attacks. It illustrates the diversity of mechanisms that have been invoked to explain the production of panic attacks, and which have influenced much of the current thinking about the neurochemistry of anxiety.

The neuroanatomical basis of anxiety

This review details the neural systems that are important in anxiety-related behaviours. In particular, the role of the amygdaloid complex, Papez circuit, septohippocampal formation and raphe nuclei are described and discussed. Evidence is gathered from a variety of experimental approaches. These include behavioural assessment of anxiety in animals after intracerebral injection of pharmacological agents and following lesions of discrete brain nuclei and selective neurotransmitter pathways. Further evidence is provided by functional brain mapping studies applied to animals and humans. It is proposed that the neural systems recruited in different experimental conditions of anxiety may differ, supporting the notion that clinical anxiety exists in several forms. This has implications for the identification of new anxiolytic treatments. In particular, the findings suggest that approaches aimed at identifying new anxiolytic agents must take into account both the distribution of receptors for the drug and the neuronal systems activated by the experimental protocol.

Effects of 5-HT uptake inhibitors, agonists and antagonists on the burying of harmless objects by mice; a putative test for anxiolytic agents

1. The effects of 5-hydroxytryptamine (5-HT) uptake inhibitors, agonists and antagonists have been evaluated on mouse marble-burying behaviour, a putative test for anxiolytic agents. The high levels of locomotor activity occurring on first exposure to a circular runway (runway were used as a separate test of non-specific drug effects. 2. Fluvoxamine, zimeldine, indalpine and citalopram dose-dependently inhibited burying without affecting runway activity. 5-Hydroxytryptophan (5-HTP, with carbidopa), 5-methoxy-N,N-dimethyltryptamine, 8-hydroxy-2-(di-n-propylamino) tetralin (8-OHDPAT), buspirione, gepirone and ipsapirone reduced burying only at doses reducing runway activity. RU 24969 increased runway activity at all effective doses. 1-(2,5-Dimethoxy-4-iodophenyl)-2-aminopropane (DOI), 1,-(3-trifluoromethylphenyl) piperazine (TFMPP) and 1-(3-chlorophenyl)-piperazine (mCPP) potently and differentially reduced burying at doses below those affecting runway activity. 3. 5-HT antagonists only reduced burying at high doses which also reduced runway activity. Burying inhibition by DOI was antagonized by ritanserin, ICI 169,369 and cyproheptadine but not by pindolol or a low (0.25 mg kg-1) dose of metergoline. Burying inhibition by mCPP was not altered by any of these agents except that it was potentiated by pindolol 5 mg kg-1. 4. Zimeldine burying inhibition was potentiated by ritanserine, ICI 169,369, ICS 205-930, cyproheptadine and pindolol. Runway activity was not affected by these drug combinations. 5. Zimeldine was administered in drinking water at a dose of 10 mg kg-1 daily for 21 days. Burying inhibition had disappeared by day 14 and did not recur 24 or 48h after withdrawal at which times responses to DOI were at control levels.6. Selective inhibition of marble burying was not found to be a property of 5-HT-related putative and actual anxiolytics such as buspirone, gepirone, ipsapirone, ritanserin and ondansetron. Nevertheless it was a general property of both 5-HT uptake inhibitors and 5-HT releasing agents; this generality suggests that elevated synaptic 5-HT could be responsible for the effects of these latter agents. The action of DOI may be attributable to effects at the 5-HT2 receptor but those of the 5-HT agonist and releasing agent mCPP, and the uptake inhibitor zimeldine, could not be attributed to effects at any one 5-HT receptor subtype. This, together with the potentiating effect of several 5-HT antagonists on the response to zimeldine, raises the possibility of multiple interactions between 5-HT receptor subtypes.

Imipramine in panic disorder. 2. Effects on α2-adrenoceptor function

Untreated patients with panic disorder have been shown to have altered α(2)-adrenoceptor sensitivity, as assessed by clonidine challenge testing. We investigated clonidine-induced biochemical, physiological, hor monal and psychological responses in six panic patients, before and after treatment with imipramine. Comparison of the clonidine-induced fall in plasma MHPG pre- and post-treatment showed it to be sig nificantly reduced after imipramine. Significantly smaller clonidine-induced falls in diastolic blood pressure and heart rate occurred after imipramine treatment. However, growth hormone and sedation responses were not altered. These data suggest that reduced sensitivity of some central α(2)-adrenoceptors occurs during treatment of panic disorder with imipramine. However, these changes do not fully explain the therapeutic actions of antidepressants in this condition.

Imipramine in panic disorder. 1. Clinical response and pharmacological changes

Clinical and biochemical variables were monitored in 18 patients with panic disorder before and during treatment with imipramine over 16 weeks. Imipramine dosage was slowly increased from a starting dose of 10 mg daily, to prevent early treatment drop-outs. All patients were effectively treated for at least 6 weeks, and only two patients dropped out before the end of the study. There were substantial reductions in panic attack frequency, ratings of depression and avoidance behaviour, but only small reductions in ratings of state and general anxiety. Plasma levels of the noradrenaline metabolite 3-methoxy-4-hydroxyphenyl- ethylene glycol initially fell after starting imipramine, but returned to pre-treatment levels by week 8 of treatment. Plasma imipramine and/or desipramine concentrations were very variable and did not correlate with either psychological or biochemical changes during treatment.

Psychology and pharmacology in the treatment of anxiety disorders: co-operation or confrontation

5-HT(3) and cholecystokinin receptor antagonists with anxiolytic properties threaten a further round of the 'tranquilizers or treatment' debate. Tricyclic antidepressants have been shown to enhance the effect of exposure therapy upon agoraphobic patients, and it can be argued that the therapeutic success of cognitive therapy in the treatment of anxiety disorders depends upon guided exposure to threatening situations. A consideration of the effects of agents already in use for the treatment of anxiety, and experimental and neuroanatomical findings, suggests that pathological anxiety might well include relatively independent abnormalities of autonomic regulation and psychological reactivity. Proper evaluation of these new compounds is therefore going to require careful evaluation of their cognitive and behavioural effects, as well as their physiology. This work should, therefore, draw the contributions of clinical pharmacology and clinical psychology closer together rather than drive them further apart.

Cardiovascular dystonia in recovered panic patients

Resting heart rate, heart rate variability and blood pressure; the heart rate and blood pressure response to standing; and the heart rate response to Valsalva's manoeuvre, have been measured in a group of 12 patients with panic disorder and a group of 12 age- and sex-matched normal subjects. The patients had undergone treatment for their panic attacks with cognitive therapy; all had responded and all had been panic-free for a minimum of 4 months (mean 7.6 months). Mood ratings (BDI, BAI and SSAI) were comparable with established norms. The patients nevertheless had a raised resting systolic blood pressure, a reduced resting heart rate and an abnormal orthostatic response.

Interactions of anxiolytic and antidepressant drugs with hormones of the hypothalamic-pituitary-adrenal axis

Changes in hormones of the hypothalamic-pituitary-adrenal (HPA) axis in patients suffering from anxiety and depressive disorders are reviewed, and the changes that occur when animals are exposed to test situations used preclinically to model anxiety or depression. The effects of exogenous administration of HPA hormones both clinically and in animal tests is discussed and the effects of clinically used anxiolytics and antidepressants on hormones of the HPA axis. The final section discusses stress-induced changes in the CNS.

The pharmacology of human anxiety

The human pharmacology of anxiety disorders, including panic disorder, is detailed. The major theories center around the role of benzodiazepine receptor, noradrenergic and serotonergic dysfunction. The contribution that challenge tests with lactate, hyper- and hypocapnia, beta- and alpha-2-adrenoceptor agonists, peptides, pentylenetetrazol, and caffeine make to our understanding of the biological basis of anxiety and these major theories are described and discussed.

The neurochemistry of anxiety: an update

1. Recent neurochemical investigations have enhanced our understanding of the anxiety disorders. Emphasis has been placed on dysfunction in central benzodiazepine, serotonergic and noradrenergic systems. 2. Changes in activity of endogenous ligands for the benzodiazepine receptor or in benzodiazepine receptor sensitivity appear to modulate anxiety. 3. There is evidence of serotonergic involvement in anxiety, in that serotonin agonists may increase anxiety, whilst drugs that reduce serotonin function are anxiolytic. 4. Noradrenergic dysfunction, especially that of alpha-2-adrenoceptors, provides the strongest etiological evidence in the development of anxiety. 5. A number of testable hypotheses can be generated from our present knowledge. As a result, new and more specific treatments may become apparent for the anxiety disorders.

Monoamine oxidase inhibitors: rehabilitation from recent research?

For a long time, monoamine oxidase inhibitors (MAOIs) have been the Cinderella drugs of psycho-pharmacy. Although they were introduced just before the tricyclic antidepressants (TCAs), they rapidly became second-line treatments. Several factors contributed to this, in particular the dietary restrictions, the scattered reports of death from overdose and/or toxic interactions, and the unfavourable reports on the efficacy of phenelzine in depression from, among others, the Medical Research Council trial (1965). For a number of years afterwards, prescription of these drugs was limited to a few enthusiasts. More recently, however, their popularity has increased owing firstly to a re-evaluation of their effectiveness in tricyclic-resistant depression and in anxiety disorders, and secondly to growing awareness of the exaggerated claims made about their dangerousness (Pare, 1985).