5-HT and mechanisms of defence

Effects of novel anxiolytic 4-butyl-alpha-agarofuran on levels of monoamine neurotransmitters in rats

4-butyl-alpha-agarofuran (AF-5) is a new compound derived from alpha-agarofuran, a constituent extracted from Aquillaria agallocha Roxb. Our previous research has shown that AF-5 has significant antianxiety activity in several animal models. In this study, an antianxiety effect was observed in a social interaction test after acute treatment with AF-5 (0.5-4.0 mg/kg, i.p.) in rats. Using high-performance liquid chromatography (HPLC)-electrochemical detection (ECD), we further investigated the effects of AF-5 on monoamine neurotransmitters both in rat brain tissues and in striatum dialysates. After acute administration of AF-5 (5.0 mg/kg, i.p.), serotonin (5-hydroxytryptamine, 5-HT) tissue levels significantly decreased by 26.3%, 30.4%, and 17.4% of the vehicle-control levels, in the striatum, cortex, and midbrain, respectively. The dopamine level decreased by 34.7% in the striatum and 19.0% in the midbrain, while in the hypothalamus, it increased to 156.6%. The epinephrine level decreased by 34.6% in the cortex. In cerebral microdialysis perfusates from rat striatum, the extracellular dopamine level declined stepwise after treatment with AF-5 (10.0 mg/kg, i.p.). By 200 min postinjection, the dopamine level reached a minimum, about 40% of the baseline value. At the same time, the extracellular levels of 5-hydroxyindolacetic acid, 3-4-dihydroxyphenylacetic acid, and homovanillic acid increased significantly, the maximum values were 150%, 145%, and 175% above baseline, respectively. This study suggests that AF-5 is a potent anxiolytic agent, and that its beneficial action may be related to its effects on central monoamine neurotransmitters.

Regulation of corticosteroid receptors in the rat brain: the role of serotonin and stress

It has been suggested that physiological resistance to repeated stress is associated with increased 5-hydroxytryptamine (5-HT) release in the dorsal hippocampus and that dysregulation of this neuroadaptation may be implicated in the psychopathology of depression. This study used 5,7-dihydroxytryptamine lesions to investigate the role of 5-HT projections to the hippocampus in physiological responses to repeated stress and putative changes in corticosteroid receptor immunoreactivity in the brain. Repeated exposure to elevated open platform stress (1 h/day) caused regionally selective changes in glucocorticoid and mineralocorticoid receptor immunoreactivity in the dorsal hippocampus that were not observed in ventral hippocampus, frontal cortex, hypothalamus or parietal cortex. Glucocorticoid receptor immunoreactivity in the dorsal hippocampus was decreased after 5 days but increased after 20 days of stress. Mineralocorticoid receptor immunoreactivity was increased after 5 or 10 days of stress. The increases in glucocorticoid and mineralocorticoid receptor immunoreactivity, evoked by repeated stress, were abolished by lesions of the principal 5-HT projections to the hippocampus. The lesions abolished the increased defecation observed in stressed animals, but had no effects on the plasma corticosterone response to the stressor or the habituation of this response observed following repeated stress. The experiments have revealed a dissociation in the regulation of corticosteroid receptor expression in the dorsal and ventral hippocampus by repeated stress and 5-HT. The data suggest that adaptation to inescapable stress is associated with regionally selective changes in corticosteroid receptor expression in dorsal hippocampus that are largely 5-HT-dependent, although these changes do not mediate habituation of the pituitary adrenocortical response to the stressor.

Anxiety and salivary cortisol in symptomatic and nonsymptomatic panic patients and healthy volunteers performing simulated public speaking

Anxiety and salivary cortisol were measured in subjects performing simulated public speaking (SPS), a procedure that has been neurobiologically related to panic disorder. The subjects were divided into three groups: 18 symptomatic panic patients, 16 nonsymptomatic, drug-treated panic patients, and 17 healthy controls. In the experimental session, subjective anxiety (Visual Analogue Mood Scale) and the total score of the Bodily Symptom Scale (BSS) were higher in symptomatic patients than in controls, with nonsymptomatic patients in between. Measures of cortisol taken at home showed that the level was higher at 9:00 h than at 23:00 h in every group, indicating a normal circadian regulation of the hypothalamic-pituitary-adrenal (HPA) axis in panic patients. Also in every group, the level of cortisol was high at the beginning of the experimental session and decreased after 70 min. This fall parallels the decrease in anxiety and BSS ratings, and appears to reflect habituation of initial, anticipatory anxiety. Preparation and performance of speech raised anxiety and BSS scores to the initial levels, but failed to increase cortisol measured over 60 min, starting at the end of the speech. Therefore, SPS does not seem to activate the HPA axis, as reported in panic attacks.

The role of 5ht2c receptors in affective disorders

5-HT(2C) receptors are predominantly localised in the brain and their dysregulation may contribute to particular symptoms of anxiety and depression. The marked affinity of several clinically established psychotropic agents sites (e.g., tricyclic antidepressants, clozapine, fluoxetine) for 5-HT(2C) receptor has generated interest in the therapeutic potential of selective, high affinity 5-HT(2C) receptor ligands. Like the selective serotonin re-uptake inhibitor (SSRI) fluoxetine, high affinity selective agonists such as Ro 60-0175 and Ro 60-0332 have potent in vivo activity in animal models suggestive of therapeutic action against depression, obsessive-compulsive disorder (OCD) and panic disorders. In contrast, 5-HT(2C) receptor antagonists such as SB-200646A or SB-221284 show signs of anxiolytic-like activity in tests for conditioned and phobic-like anxiety in rodents whereas they are inactive in tests indicative of antidepressant, antiOCD and antipanic activity. These results are consistent with an important hypothesis proposing that 5-HT has a complex, dual action on the neural mechanism of anxiety by either facilitating or inhibiting different kinds of anxiety in different brain regions. They also suggest that 5-HT(2C) receptor subtypes play an important role in the therapeutic properties of SSRIs. Certain 5-HT(2C) receptor antagonists may possess negative efficacy at 5-HT(2C) receptors and, as inverse agonists, may control constitutive receptor activity possibly characterising some psychopathological states. Receptor variants exist in the human population and indicate possible associations between somatic mutations in the 5-HT(2C) receptor and psychopathology or response to drug treatment. Selective 5-HT(2C) receptor ligands may offer innovative and improved therapeutic opportunities for the biological treatment of specific aspects of psychiatric syndromes.

Effect of acute tryptophan depletion on the response to controllable and uncontrollable noise stress

BACKGROUND

Previous research provides evidence linking serotonin (5-hydroxytryptamine, 5-HT) with stress and depression. The controllable/uncontrollable (C/UC) stress paradigm aims to generate a state/condition, namely a feeling of lack of control in the context of a stressor, which might be an important factor in precipitating a negative mood state. Acute tryptophan depletion (ATD) is a technique that produces a decrease in central 5-HT levels in vivo. This study investigated the role of 5-HT in the behavioral response to a C/UC stress paradigm with ATD.

METHODS

Healthy adult volunteers were randomly assigned to receive either a TRP-supplemented (n = 15) or TRP-deficient (n = 13) amino acid drink. At 5 hours postdrink, volunteers were subjected to sessions of controllable and uncontrollable noise stress (100-dB white noise). Subjective ratings of mood were obtained before and after the interventions.

RESULTS

Participants who received the tryptophan-depleting drink had greater self-report ratings of negative mood on visual analogue scales and the Profile of Mood States after the uncontrollable stress than did participants who received the balanced drink.

CONCLUSIONS

The results suggest that 5-HT might play a role in providing resilience to uncontrollable stress. Additional studies with specific 5-HT pharmacologic probes will further clarify the results.

Association between serotonin-related genetic polymorphisms and CCK-4-induced panic attacks with or without 5-hydroxytryptophan pretreatment in healthy volunteers

Genetic regulation of the function of serotonin (5-HT) may be important for the neurobiology of panic disorder. In order to evaluate the influence of 5-HT-related gene variants on the vulnerability to panic attacks, we genotyped 32 healthy volunteers who participated in the study of the effect of 5-hydroxytryptophan on panic attacks induced with cholecystokinin tetrapeptide (CCK-4). The polymorphisms of interest included those of 5-HT transporter (5-HTTLPR) and monoamine oxidase A (MAO-A promoter region) genes. The results showed significant associations between certain genotypes and panic rate in females but not in male volunteers. Specifically, there was a significantly lower rate of CCK-4-induced panic attacks in female subjects who had MAO-A longer alleles or 5-HTTLPR short allele gene variants. These data suggest that functional genetic polymorphisms of the 5-HT system may influence the vulnerability to panic attacks and add to the growing evidence of inhibitory function of 5-HT in the neuronal circuitry of panic.

Role of nitric oxide in brain regions related to defensive reactions

Nitric oxide synthase (NOS) positive neurons are located in most brain areas related to defensive reactions, including the dorsolateral periaqueductal grey (dlPAG). NOS inhibitors injected into this structure induce anxiolytic-like responses whereas NO donors promote flight reactions. Intra-dlPAG administration of carboxy-PTIO, a NO scavenger, or ODQ, a soluble guanylate cyclase inhibitor, produced anxiolytic-like effects on rats exposed to the elevated plus-maze (EPM). A double-staining experiment using NADPHd histochemistry and c-Fos immunohistochemistry in rats exposed to a cat or to the EPM showed increased activation of NO producing neurons in the dlPAG, paraventricular and lateral nuclei of hypothalamus and dorsal raphe nucleus. Cat exposure also increased activation of NOS neurons in the medial amygdala, dorsal pre-mammillary nucleus and bed nucleus of stria terminalis. Local infusion into the dlPAG of a glutamate NMDA-receptor antagonist (AP7) or a benzodiazepine agonist (midazolam) completely prevented the flight reactions induced by intra-dlPAG administration of SIN-1, a NO donor. The responses were also inhibited by the 5-HT2A/C agonist DOI but not by a 5-HT1A agonist. These results suggest a modulatory role for NO on brain areas related to defensive reactions, probably by interacting with glutamate, serotonin and/or GABA-mediated neurotransmission.

SPECT imaging of serotonin transporter binding in patients with generalized anxiety disorder

The purpose of this study was to characterize the binding properties of serotonin transporter (5-HTT) in the brain of the patients with generalized anxiety disorder (GAD) in comparison to healthy subjects using single photon emission computer tomography (SPECT) with the radioligand [123I]nor-beta-CIT. The subjects were 7 patients with GAD and 7 matched healthy volunteers. The regions of interest (ROI) were the midbrain and the thalamus. The comparison of the volumes of distribution did not show significant differences between the patients and controls in the binding of nor-beta-CIT to 5-HTT in the ROI. Binding of 5-HTT in the midbrain of patients was significantly and negatively correlated with their anxiety levels measured by the visual analogue scale immediately before the first scan (r=-0.79, p=0.035). This study failed to demonstrate an altered functional activity of 5-HTT in patients with GAD when compared with controls.

Effects of sibutramine on anxiety-related behaviours in rats

Sibutramine is an anorexiant drug that inhibits the reuptake of noradrenaline and serotonin, a pharmacological property shared with drugs clinically effective in treating anxiety pathologies. However, the effects of this compound on experimental and clinical anxiety have not been assessed yet. In this study, we evaluated the effects of sibutramine on anxiety-related behaviours which have been related to specific anxiety disorders. Acute injection of sibutramine (5, 10 or 20 mg kg(-1); intraperitoneally) in male Wistar rats impaired inhibitory avoidance in the elevated T-maze (ETM) and in the light/dark transition test, indicative of an anxiolytic effect. The drug also inhibited one-way escape in the ETM. Sibutramine, however, was ineffective in changing rat performance in the elevated plus-maze. Therefore, sibutramine decreased the expression of defensive behaviours that have been associated with generalized anxiety disorder (inhibitory avoidance) and with panic disorder (one-way escape). Yet, in contrast to what has been reported with drugs such as the tricyclic anti-depressants that also inhibit monoamine reuptake, the anxiolytic effects of sibutramine were revealed after a single administration.

Benzodiazepine receptor and serotonin 2A receptor modulate the aversive-like effects of nitric oxide in the dorsolateral periaqueductal gray of rats

RATIONALE

Escape reactions induced by electrical stimulation of the dorsolateral periaqueductal gray (dlPAG) are inhibited by local administration of benzodiazepine (BZ) or serotonin (5-HT) receptor agonists. Nitric oxide (NO) is a gas messenger that may mediate aversive behaviors. NO donors injected into the dlPAG induce escape reactions.

OBJECTIVES

To test the hypothesis that the escape reactions induced by a NO donor in the dlPAG would be attenuated by pre-treatment with BZ-receptor or 5-HT-receptor agonists.

METHODS

Male Wistar rats with cannulae aimed at the dlPAG received microinjections of vehicle (0.2 microl), the BZ midazolam maleate (80 nmol), the 5-HT(1A)-receptor agonist 8-OH-DPAT (8 nmol or 16 nmol) or the 5-HT(2A/2C)-receptor agonist DOI (16 nmol) 10 min before the administration of the NO donor SIN-1 (150 nmol). Behavioral observation took place immediately after the last injection in an open arena over a 10-min period.

RESULTS

SIN-1 induced escape reactions characterized by running and jumps. Pre-treatment with DOI, but not 8-OH-DPAT, partially inhibited the effects of SIN-1. Pre-treatment with midazolam maleate, however, completely prevented the effects of the NO donor.

CONCLUSION

The results suggest that the aversive-like effects of NO donor in the dlPAG may be modulated by the BZ and 5-HT(2A/2C) receptors.

Effects of acute and chronic fluoxetine and diazepam on freezing behavior induced by electrical stimulation of dorsolateral and lateral columns of the periaqueductal gray matter

The defensive responses induced by electrical stimulation of the dorsal periaqueductal gray matter (dPAG) of the rat have been proposed as a model of panic attacks in humans. In the present study we investigated the acute and chronic effects of fluoxetine and diazepam on freezing and escape reactions elicited by electrical stimulation of the dorsolateral (dlPAG) and lateral (lPAG) columns of the periaqueductal gray matter (PAG). The frequencies of crossing, rearing, bouts of micturition and fecal boli were also recorded. Electrodes were unilaterally implanted in the brainstem aimed at the PAG. Drug treatments were given daily for 2 weeks with fluoxetine (5, 10 and 20 mg/kg ip), a selective inhibitor of serotonin reuptake, diazepam (1, 2 and 4 mg/kg ip), or saline. Drug effects were assessed acutely (15 min after the first injection) and chronically (15 min after the 14th injection). Chronic, but not acute, administration of fluoxetine caused a significant increase in the threshold of freezing without affecting the escape response elicited by dlPAG/lPAG stimulation. This characteristic pattern of effects could not be attributed to motor deficit, since this drug did not change the number of crossings and rearings. In contrast, no significant threshold changes were observed following acute and chronic treatment with diazepam. These data give further evidence for (a) an antiaversive effect of chronic treatment with fluoxetine, which caused a selective reduction in freezing behavior and neurovegetative responses associated with fearlike reaction elicited by dlPAG/lPAG electrical stimulation; (b) the involvement of the dlPAG and lPAG in the generation and organization of defensive responses and that freezing may probably be associated with panic attacks; and (c) the lack of effect of diazepam in this model is in line with its inefficacy as a panicolytic drug. The study of the unconditioned freezing behavior evoked by dlPAG/lPAG stimulation may constitute a new and interesting model for the study of panic disorder.

Growth hormone, cortisol and prolactin responses to physical exercise: higher prolactin response in depressed patients

This study was designed to compare growth hormone, cortisol and prolactin responses to physical exercise in depressed patients and healthy comparison subjects. Patients fulfilled the DSM-IV diagnostic criteria for current major depressive disorder; subjective depressive symptoms were rated with Montgomery-Asberg Depression Rating Scale (MADRS) immediately before the experiment. Growth hormone, cortisol and prolactin were measured before and immediately after physiologically stressful bicycle cardiopulmonary exercise test. After exercise, there were three additional hormone measurements, with 30-min intervals. No significant difference was found in baseline growth hormone, cortisol or prolactin levels between patients and the control group. Plasma growth hormone and cortisol levels increased significantly during physical exercise in both patients and controls and returned to baseline in 90 min. There was no significant difference in growth hormone or cortisol responses to physical exercise between the two groups. However, prolactin levels increased only in the depressed patients group during the exercise. We hypothesize that acute exercise may have a stronger effect on serotonin (5-HT) release in depressed patients, which is reflected in increased plasma prolactin concentration.

The cognitive paradox in posttraumatic stress disorder: a hypothesis

Posttraumatic stress disorder (PTSD) is characterized by a peculiar cognitive state. The traumatic event(s) are partly hypermemorized, partly blurred, whereas the ability to store and retrieve new information is impaired. The question is raised as to what the biological systems might be that 'carry' this cognitive paradox. Four possible candidate systems are discussed. It is concluded that understimulation of the corticosteroid receptors, particularly the glucocorticoid receptors (GRs), overactivity of the noradrenaline (NA) and vasopressin (VA) systems, and deficits in the 5-Hydroxytryptamine (5-HT) system, particularly the 5-HT(1A) system, could generate a cognitive syndrome similar to the one observed in PTSD. A dual hypothesis is launched holding that (a) in PTSD, downregulation of the 5-HT(1A) receptor system is the primary lesion, while the other dysfunctions mentioned are subsidiaries and that (b) underdevelopment of or damage to the 5-HT(1A) receptor system will make a person PTSD-prone.

Neuroanatomia do transtorno de pânico

OBJETIVOS: O Transtorno de Pânico (TP) é um transtorno de ansiedade que permite um estudo comparativo de modelos animais visando à elucidação dos circuitos cerebrais envolvidos na sua gênese, embora estes ainda tenham sido pouco discutidos. MÉTODOS: Os autores realizam uma revisão da literatura sobre neurobiologia e neuroanatomia do TP. RESULTADOS: Uma revisão de dados demonstra a existência de uma "rede de medo", que tem como ponto principal o núcleo central da amígdala e compreende o hipotálamo, o tálamo, o hipocampo, a substância cinzenta periaquedutal, o locus ceruleus e outras estruturas do tronco cerebral. Sua presença é evidenciada em estudos de modelos animais de estados emocionais e comportamentais, e sua presença e importância podem ser extrapoladas para o TP em humanos. CONCLUSÃO: Esta rede de medo pode permitir que novos avanços e estudos utilizando técnicas de neuroimagem e/ou psicofármacos possam auxiliar na maior elucidação da circuitos cerebrais do TP.

The effect of 5-hydroxytryptophan on cholecystokinin-4-induced panic attacks in healthy volunteers

Previous studies suggest a modulatory role of serotonin (5-HT) in experimentally-induced panic attacks. In the current study, we investigated the acute effects of 5-HT precursor l-5-hydroxytryptophan (5-HTP) on the response to panicogenic challenge with cholecystokinin-tetrapeptide (CCK-4) in healthy volunteers. Thirty-two subjects were randomized to receive either 200 mg of 5-HTP or placebo with the CCK-4 challenge following in 90 min in a double-blind, parallel-group design. The results showed a nonsignificant difference between the groups in panic rate (19% after 5-HTP and 44% after placebo, p = 0.13) with a trend for lower intensity of symptoms after 5-HTP (p = 0.08). Further analysis by gender revealed that females in the 5-HTP group had a significantly lower panic rate and intensity of cognitive symptoms whereas, in males, the effect of 5-HTP was limited to lowering the intensity of somatic panic symptoms. Thus, an increased availability of 5-HT may have a gender-dependent protective effect in CCK-4-induced panic.

Serotonin 5-HT2 and 5-HT1A receptors in the periaqueductal gray matter differentially modulate tonic immobility in guinea pig

Tonic immobility (TI) is an inborn defensive behavior characterized by a temporary state of profound and reversible motor inhibition elicited by some forms of physical restraint. We have previously reported that cholinergic stimulation of the dorsal periaqueductal gray matter (PAG) decreases the duration of TI episodes, while stimulation of the ventrolateral region increases it. The ventrolateral PAG modulates this behavior via a similar neural circuit proposed to be involved in the antinociceptive system. Some studies have indicated that alterations in the levels of cerebral 5-hydroxytryptamine (5-HT) mediate or modulate the analgesic effect of PAG stimulation. Thus, in this study we investigated the possibility that the serotoninergic system is involved in the modulation of TI by this neural substrate. Our results showed that the effect of serotonin into the ventrolateral and dorsal PAG seems to be biphasic and dose dependent. The microinjection of low doses (0.1 microg) of 5-HT into the PAG increased the duration of TI, while high doses (1, 3 and 6 microg) decreased this behavior. Our results also showed that microinjection of a 5-HT(1A) agonist (0.003, 0.01 and 0.1 microg of 8-hydroxy-dipropylaminotretalin (8-OH-DPAT)) into the PAG increased the duration of TI episodes. However, the microinjection of 5-HT(2) agonist (0.01 and 0.1 microg of alpha-methyl-5-HT) into the PAG decreased the duration of TI and this effect could be reversed by pretreatment with an ineffective dose (0.01 microg) of ketanserin. In contrast, ketanserin (0.03 and 0.16 microg) increased this behavior in a dose-dependent manner. These results suggest that the PAG 5-HT(1A) and 5-HT(2) receptors have different roles in the modulation of TI in guinea pigs, since the 5-HT(1A) and 5-HT(2) agonists, respectively, increased and decreased the duration of TI.

A two-dimensional neuropsychology of defense: fear/anxiety and defensive distance

We present in this paper a picture of the neural systems controlling defense that updates and simplifies Gray's "Neuropsychology of Anxiety". It is based on two behavioural dimensions: 'defensive distance' as defined by the Blanchards and 'defensive direction'. Defensive direction is a categorical dimension with avoidance of threat corresponding to fear and approach to threat corresponding to anxiety. These two psychological dimensions are mapped to underlying neural dimensions. Defensive distance is mapped to neural level, with the shortest defensive distances involving the lowest neural level (periaqueductal grey) and the largest defensive distances the highest neural level (prefrontal cortex). Defensive direction is mapped to separate parallel streams that run across these levels. A significant departure from prior models is the proposal that both fear and anxiety are represented at all levels. The theory is presented in a simplified form that does not incorporate the interactions that must occur between non-adjacent levels of the system. It also requires expansion to include the dimension of escapability of threat. Our current development and these proposed future extensions do not change the core concepts originally proposed by Gray and, we argue, demonstrate their enduring value.

Serotonin, the periaqueductal gray and panic

This article reviews experimental evidence and theoretical constructs that implicate serotonin (5-HT) modulation of defensive behavior within the midbrain periaqueductal gray in panic disorder (PD). Evidence with conflict tests in experimental animals indicates that 5-HT enhances anxiety, whereas results with aversive stimulation of the dorsal periaqueductal gray point to an anxiolytic role of 5-HT. To solve this contradiction, it has been suggested that the emotional states determined by the two types of animal model are different. Conflict tests would generate conditioned anxiety, whereas periaqueductal gray stimulation would produce unconditioned fear, as evoked by proximal threat. Clinically, the former would be related to generalized anxiety while the latter to PD. Thus, 5-HT is supposed to facilitate anxiety, but to inhibit panic. This hypothesis has been tested in the animal model of anxiety and panic named the elevated T-maze, in two procedures of human experimental anxiety applied to healthy volunteers or panic patients, and in CO2-induced panic attacks. Overall, the obtained results have shown that drugs that enhance 5-HT function increase different indexes of anxiety, but decrease indexes of panic. Drugs that impair 5-HT function have the opposite effects. Thus, so far the predictions derived from the above hypothesis have been fulfilled.

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.

Reproducibility of negative mood induction: a self-referent plus musical mood induction procedure and a controllable/uncontrollable stress paradigm

Mood induction procedures (MIPs) have been used extensively as a means of inducing a variety of mood states in laboratory settings. Recently, MIPs have been employed in a repeated measures design in combination with such techniques as functional imaging and psychopharmacological investigations. This study attempted to assess the repeatability of two paradigms designed to induce a depressed/negative affect, a self-referent plus musical MIP and a controllable/uncontrollable stress paradigm, to assess the viability of using such procedures in a repeated design. Healthy volunteers were enrolled in to one of two studies. Study 1 administered a self-referent plus musical MIP on three separate occasions: neutral and depressive mood induction (MI) in a balanced order, followed by a further depressive MI. In study 2, volunteers were subjected to sessions of controllable and uncontrollable noise stress in a balanced order on two different occasions. Subjective ratings of mood were obtained prior to and following the interventions. Depressive MI successfully increased ratings of negative affect, although this effect tended to be greater on the first occasion than on the second. Correlation between mood change on the first and second occasions were low, both for the MIP and stress paradigm. As such, caution should be exercised in using these procedures in a repeated measures design. However, the results may vary depending on the type of MIP employed.

Effects of cannabidiol (CBD) on regional cerebral blood flow

Animal and human studies have suggested that cannabidiol (CBD) may possess anxiolytic properties, but how these effects are mediated centrally is unknown. The aim of the present study was to investigate this using functional neuroimaging. Regional cerebral blood flow (rCBF) was measured at rest using (99m)Tc-ECD SPECT in 10 healthy male volunteers, randomly divided into two groups of five subjects. Each subject was studied on two occasions, 1 week apart. In the first session, subjects were given an oral dose of CBD (400 mg) or placebo, in a double-blind procedure. SPECT images were acquired 90 min after drug ingestion. The Visual Analogue Mood Scale was applied to assess subjective states. In the second session, the same procedure was performed using the drug that had not been administered in the previous session. Within-subject between-condition rCBF comparisons were performed using statistical parametric mapping (SPM). CBD significantly decreased subjective anxiety and increased mental sedation, while placebo did not induce significant changes. Assessment of brain regions where anxiolytic effects of CBD were predicted a priori revealed two voxel clusters of significantly decreased ECD uptake in the CBD relative to the placebo condition (p<0.001, uncorrected for multiple comparisons). These included a medial temporal cluster encompassing the left amygdala-hippocampal complex, extending into the hypothalamus, and a second cluster in the left posterior cingulate gyrus. There was also a cluster of greater activity with CBD than placebo in the left parahippocampal gyrus (p<0.001). These results suggest that CBD has anxiolytic properties, and that these effects are mediated by an action on limbic and paralimbic brain areas.

The neurobiology of social anxiety disorder: the relevance of fear and anxiety

OBJECTIVE

Social anxiety disorder (SAD) is a ubiquitous anxiety disorder. Despite being the third most common psychiatric disorder, little is known about the interaction between genetic predisposition and environmental factors in the development of SAD. The available literature on SAD has been compared with data on the genetics and environmental impact on the phenotypic expression of fear and anxiety, and its implicated neurobiology, in order to explore the neurobiology of SAD as understood through the neurochemical dysregulation expressed in fear and anxiety.

METHOD

A systematic review of the literature was employed for the years from 1966 to 2001.

RESULTS

SAD does indeed have much overlap with fear and anxiety. This is best demonstrated by the interactions of the noradrenergic and serotonergic systems with each other and the hypothalamic-pituitary-adrenal axis.

CONCLUSION

SAD may well be understood as one potential outcome for predisposed individuals who are exposed to the proverbial 'second hit', or environmental insult, in childhood. Behavioral inhibition may be an early expression of this predisposition, with natural progression to SAD occurring via a disruption of neurochemical homeostasis. Through animal and human data it has become evident that fear and anxiety have shared, as well as distinct, neurochemical and neuroanatomical pathways. These similarities are expressed as symptoms and objective signs that are common to many individuals with social anxiety disorder.

Stress control and human nutrition

Stress is a pervasive factor in everyday life that critically affects development and functioning. Severe and prolonged stress exposure impairs homeostatic mechanisms, particularly associated with the onset of depressive illness. Brain food is aimed at preventing as well as treating a growing number of stress-related mental disorders. Some topics on the association of stress and nutrition is reviewed. (1) An increased activity of serotonergic neurons in the brain is an established consequence of stress. An increase in brain tryptophan levels on the order of that produced by eating a carbohydrate-rich/protein-poor meal causes parallel increases in the amounts of serotonin released into synapses. (2) Eating is thought to be suppressed during stress, due to anorectic effects of corticotrophin releasing hormone, and increased during recovery from stress, due to appetite stimulating effects of residual cortisol. (3) A strong inverse association between coffee intake and risk of suicide. (4) Night eating syndrome has been found to occur during periods of stress and is associated with poor results at attempts to lose weight and disturbances in the hypothalamic-pituitary-adrenal axis. (5) Dietary antioxidants present in fruits and vegetables may improve cognitive function. Therefore, it is concluded that the establishment of functional foods that correctly regulate stress response must be firmly based upon scientific knowledge and legal regulation.

Why do some individuals develop social phobia? A review with emphasis on the neurobiological influences

Social phobia, or social anxiety disorder, is now considered the most common anxiety disorder. Still, the etiology of the disorder is to an essential degree unknown. This paper presents an overview of various pathways to be considered in relation to the development of social phobia. The literature concerning genetics and family aggregation, behavioral inhibition, various forms of the learning account, and neurobiological influences was examined. The reviewed studies suggest that social phobia has a neuroanatomical basis in a highly sensitive fear network centered in the amygdaloid-hippocampal region, i.e. "the alarm system" of the brain, and encompassing the prefrontal cortex. This pattern is congruent with genetic studies proposing that the genetic component comprises a general vulnerability to fearfulness rather than to social phobia itself. Further, both family and twin studies support a hereditary contribution to social phobia resulting from genetic and environmental factors, which most likely operate in an interactive way rather than acting in isolation.

Serotonina, matéria cinzenta periaquedutal e transtorno do pânico

Este artigo é uma revisão de evidências experimentais e construtos teóricos que implicam a modulação do comportamento de defesa pela serotonina (5-HT), atuando na matéria cinzenta periaquedutal do mesencéfalo (MCP) no transtorno do pânico. Resultados obtidos com testes de conflito em animais de laboratório indicam que a 5-HT aumenta a ansiedade, enquanto que a estimulação aversiva da MCP aponta para um papel ansiolítico. Para resolver esta contradição, sugeriu-se que os estados emocionais determinados pelos dois paradigmas são diferentes. Testes de conflito gerariam ansiedade antecipatória, enquanto que a estimulação da MCP produziria medo de perigo iminente. Clinicamente, o primeiro estado estaria relacionado com o transtorno de ansiedade generalizada e o segundo, com o transtorno do pânico. Assim sendo, supõe-se que a 5-HT facilita a ansiedade, porém inibe o pânico. Esta hipótese tem sido testada por meio de um modelo animal de ansiedade e pânico, denominado labirinto em T-elevado, e de dois procedimentos experimentais que geram ansiedade, aplicados tanto em voluntários sadios como em pacientes de pânico. Em geral, os resultados obtidos até agora mostram que drogas que aumentam a ação da 5-HT elevam diferentes índices de ansiedade, enquanto reduzem índices de pânico. Portanto, as predições baseadas na hipótese em questão têm se cumprido. As principais implicações clínicas são as de que um déficit de 5-HT na MCP possa participar da fisiopatogenia do transtorno de pânico e que a intensificação da 5-HT na mesma região medeie a ação antipânico dos medicamentos antidepressivos.

Transmissão pelo glutamato como alvo molecular na ansiedade

O glutamato (GLU) é o principal neurotransmissor excitatório do cérebro de mamíferos. Os receptores do GLU são classificados em ionotrópicos ou metabotrópicos. A interferência do GLU no desenvolvimento neural, na plasticidade sináptica, no aprendizado e na memória, na epilepsia, na isquemia neural, na tolerância e na dependência a drogas, na dor neuropática, na ansiedade e na depressão tem limitado o uso de compostos que agem nos receptores de GLU, quando existe a necessidade de ações mais seletivas dessas drogas. Dados pré-clínicos em roedores e humanos têm mostrado que compostos que reduzem a ativação do GLU, pelo bloqueio dos seus receptores ou através da redução da sua liberação dos terminais, produzem um perfil ansiolítico em modelos de ansiedade. A aplicação desses compostos em áreas específicas do cérebro, envolvidas na mediação do comportamento defensivo, tal como a substância cinzenta periaquedutal dorsal, também reproduzem o mesmo perfil ansiolítico de ação. O conhecimento crescente acerca da neurotransmissão pelo GLU e o desenvolvimento de compostos mais seletivos atuantes nesta neurotransmissão, renovaram a atenção para esse sistema neurotransmissor como alvo molecular possível para uma nova classe de drogas no tratamento de condições neuropsiquiátricas. Embora incompleta, esta revisão tenta atrair a atenção para a importância de estudos colaborativos entre clínicos e pesquisadores de ciências básicas na geração de idéias para alvos potenciais no desenvolvimento de novos compostos ansiolíticos. e desta maneira contribuir para a compreensão das bases biológicas da ansiedade.

Antipanic-like effect of serotonin reuptake inhibitors in the elevated T-maze

There has been an increasing interest in the development of animal models that address different types of anxiety disorders. The elevated T-maze (ETM) was developed based on the assumption that inhibitory avoidance and one-way escape are respectively related to generalized anxiety (GAD) and panic disorder (PD). Although anxiolytic effects on the inhibitory avoidance task have been shown for drugs used in clinical settings to treat GAD, positive effects of antipanic drugs in one-way escape have been described only for imipramine. The study extends the pharmacological validation of the ETM to other serotonin reuptake inhibitors that have antipanic properties. To this end, we investigated the effects of acute and chronic (21 days) IP administration of clomipramine (3, 10 and 30 mg/kg) and fluoxetine (5, 10 and 15 mg/kg). Buspirone (0.3, 1 and 3 mg/kg) was used as a negative control since the drug is effective in GAD but not PD. Chronically, both clomipramine and fluoxetine impaired one-escape, an antipanic-like effect, not altering avoidance latencies. Clomipramine, but not fluoxetine, also affected locomotion. Acute injection of buspirone impaired avoidance, an anxiolytic-like effect. Neither acute nor chronic buspirone altered one-escape. These results corroborate the suggestion that one-way escape is related to PD.

Estresse, depressão e hipocampo

A exposição a fatores estressantes tem papel importante no desenvolvimento de transtornos depressivos. Os mecanismos envolvidos nesta relação, no entanto, ainda são pouco conhecidos, mas algumas evidências sugerem a participação da formação hipocampal: 1. o estresse pode causar alterações plásticas no hipocampo, que incluem remodelação dendrítica e inibição de neurogênese. Drogas antidepressivas impendem estes efeitos, possivelmente por aumentarem a expressão de fatores neurotróficos; 2. a facilitação da neurotransmissão serotoninérgica no hipocampo atenua conseqüências comportamentais do estresse e produz efeitos antidepressivos em modelos animais; 3. o antagonismo do principal neurotransmissor excitatório no hipocampo, o glutamato, produz efeitos semelhantes; 4. o hipocampo parece estar "hiperativo" em animais mais sensíveis em modelos de depressão e em humanos resistentes à antidepressivos; 5. o hipocampo, em conjunto com o complexo amigdalar, parece ter papel fundamental na consolidação e evocação de memórias aversivas. Não obstante estas evidências, o desafio futuro será o de tentar integrar os resultados destes diferentes campos (farmacológico, molecular, eletrofisiológico, clínico) em uma teoria unificadora sobre o papel do hipocampo na regulação do humor e seus transtornos bem como nos efeitos de tratamentos antidepressivos.

The effects of acute tryptophan depletion on neuropsychological function

Serotonin (5-HT, 5-hydroxytryptamine) may have an important role in the maintenance of normal neuropsychological functioning. The method of acute tryptophan depletion (ATD) provides a pharmacological challenge by which central 5-HT levels can be temporarily decreased and effects on learning, memory and mood examined. Twenty healthy male volunteers were recruited to take part in this within-subject, double-blind, crossover study. Neuropsychological function was evaluated 4-6 h after ingestion of a control or 52 g tryptophan (TRP) depleting amino-acid drink. ATD significantly lowered levels of plasma total and free TRP (p < 0.001), but this did not affect mood or performance on tests of verbal and visuo-spatial learning and memory, attention or executive function. These results contradict previous findings; however, the degree of disruption of central 5-HT levels resulting from the use of the 52 g amino-acid protocol may be an important factor in explaining the lack of effect. By utilizing more specific probes of individual 5-HT receptor subtypes, future studies can fully explore the role of 5-HT in neuropsychological functioning and may elucidate the factors determining vulnerability to the effects of serotonergic dysfunction.

Depression and antisocial personality disorder: two contrasting disorders of 5HT function

Impaired 5HT functioning has been implicated in two very different psychiatric syndromes: antisocial personality disorder and depression. In both, reduced csf concentration of 5HIAA and blunted circulating hormone responses to 5HT drug challenge have been described. The paradox can be resolved by the theory that the two main ascending 5HT pathways mediate adaptive responses to future and current adversity. Projections of the anterior group of raphe 5HT cells (dorsal raphe nucleus) oppose the action of dopamine and mediate avoidance of threats. Impaired function sensitises the dopamine system resulting in impulsivity and drug addiction. Posterior 5HT cells (median raphe nucleus) innervate hippocampus and cingulate gyrus and suppress memory and awareness of current and past adversity. Impaired function results in low mood, low self-esteem, hopelessness and pessimism. Modern imaging methods are providing startling corroboration of these ideas.

Bringing natural behaviors into the laboratory: a tribute to Paul MacLean

Paul MacLean's work has exemplified and encouraged an approach in which natural behaviors are elicited and investigated in laboratory settings. Our own experiences with bringing natural behaviors into the laboratory indicate that this is best achieved by providing the social and environmental stimuli necessary to support these behaviors and by an initial process of ethological/observational analysis of them. Examples discussed in support of these suggestions include the development of more natural habitats, including visible burrow systems (VBS), for fossorial rodents such as rats and mice; analysis of aggressive and defensive behaviors among social groups in such habitats and to introduced predators; and the development of defense test batteries in which individual defensive behaviors may be elicited through manipulations of threat and environmental stimuli. These situations have proved useful in analysis of the effects of drugs active against anxiety-related psychopathologies. However, an equally important use for them is in the analysis of normal defensive and aggressive behaviors. Detailed analysis of natural behaviors in socially and environmentally adequate situations provides an important link between molecular findings and both normal and pathological behavior patterns. Investigation of natural behaviors in adequate stimulus contexts does not represent an antiexperimental stance but one that supplements and enhances the generalizability of more conventional experimental laboratory approaches.

Effects of Hypericum perforatum and paroxetine on rat performance in the elevated T-maze

Hypericum perforatum extract exhibits an antidepressant effect and since several antidepressant drugs are also effective on generalised anxiety disorder (GAD) and panic disorders (PD), H. perforatum may possess some anxiolytic/antipanic effect. Thus, the aim of the present study was to evaluate the putative antipanic/anxiolytic effect of standardised H. perforatum extract (LI 160) on rats tested in the elevated T-maze, an animal model of innate (panic) and learned (generalised) anxiety, at doses that exhibit antidepressant-like activity. H. perforatum (150, 300 and 500 mg/kg, administered orally 24, 18 and 1h before the test) decreased the immobility time in the forced swim test. Rats were treated orally with H. perforatum (150 or 300 mg/kg) or paroxetine (5mg/kg) 24, 18, and 1h before being tested in the elevated T-maze (subacute treatment). Immediately after this test, the animals were submitted to the open field to evaluate locomotor activity. Paroxetine was used as a positive control, since it was clinically effective in GAD and PD. Other groups of animals were submitted to the same drug treatment for 7 days (subchronic treatment). Paroxetine (5mg/kg) impaired inhibitory avoidance after subacute treatment, while subchronic administration increased one-way escape latency. Subacute treatment with H. perforatum (300 mg/kg) exerts a partial anxiolytic-like effect in the inhibitory avoidance task. Repeated administration of H. perforatum (300 mg/kg) induced an anxiolytic effect (decreased inhibitory avoidance) and an antipanic effect (increased one-way escape). No effect on locomotor activity was found with any treatment. Thus, the results suggest that H. perforatum extract could exert an anxiolytic and antipanic effect.

Serotonin in the dorsal periaqueductal gray modulates inhibitory avoidance and one-way escape behaviors in the elevated T-maze

The dorsal periaqueductal gray has been implicated in the modulation of escape behavior, a defensive behavior that has been related to panic disorder. Intra-dorsal periaqueductal gray injection of serotonin or drugs that mimic its effects inhibits escape induced by electrical or chemical stimulation of this brainstem area. In this study, we investigate whether intra-dorsal periaqueductal gray injection of 5-HT receptor agonists attenuates escape generated by an ethologically based model of anxiety, the elevated T-maze. This test also allows the measurement of inhibitory avoidance, which has been related to generalized anxiety disorder. The effects of the 5-HT receptor agonists were compared in animals with or without a previous exposure to the open arms of the elevated T-maze. In these two test conditions, intra-dorsal periaqueductal gray injection of the endogenous agonist serotonin or the 5-HT(2B/2C) receptor agonist m-chlorophenylpiperazine (mCPP) enhanced inhibitory avoidance, suggesting an anxiogenic effect. The 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) impaired this response, suggesting an anxiolytic effect, and the preferential 5-HT2A receptor agonist 2,5-dimethoxy-4-iodoamphetamine (DOI) was ineffective. All these agonists inhibited escape behavior. Apart from mCPP, the effect on escape was detected only in animals pre-exposed to the open arm. None of the drugs tested affected locomotion in the open-field test. Taken altogether, our findings suggest that 5-HT1A and 5-HT2c receptors in the dorsal periaqueductal gray exert opposed control on inhibitory avoidance, implicating these receptors in anxiety conditioning. As previously observed in tests employing the aversive stimulation of the dorsal periaqueductal gray, 5-HT1A and 5-HT2A receptors in this brain area are involved in escape inhibition. Therefore, in different animal models, the activation of these two subtypes of receptors in the dorsal periaqueductal gray consistently attenuates the expression of a panic-related behavior.

Activation of post-synaptic 5-HT(1A) receptors in the dorsal hippocampus prevents learned helplessness development

Activation of post-synaptic 5-HT(1A) receptors in the dorsal hippocampus is proposed to mediate stress adaptation. Chronic social stress and high corticosteroid levels would impair this coping mechanism, predisposing animals to learned helplessness. To test the hypothesis that increasing serotonin levels in the dorsal hippocampus would attenuate the development of learned helplessness, rats received inescapable foot-shock (pre-test session) and were tested in a shuttle box 24-h later. Pre-stressed animals showed impairment of escape responses. This effect was prevented by chronic (21 days) treatment with imipramine (15 mg/kg). Similar results were obtained when the animals received bilateral intra-hippocampal injections, immediately after pre-test, of zimelidine (100 nmol/0.5 microl), a serotonin reuptake blocker, or 8-OH-DPAT (10 nmol), a 5-HT(1A) receptor agonist. The zimelidine effect was prevented by pre-treatment with WAY-100635 (30 nmol), a 5-HT(1A) receptor antagonist. These data suggest that facilitation of serotonergic neurotransmission in the dorsal hippocampus mediates adaptation to severe inescapable stress, probably through the activation of post-synaptic 5-HT(1A) receptors.

Decreased left temporal lobe volume of panic patients measured by magnetic resonance imaging

Reported neuroimaging studies have shown functional and morphological changes of temporal lobe structures in panic patients, but only one used a volumetric method. The aim of the present study was to determine the volume of temporal lobe structures in patients with panic disorder, measured by magnetic resonance imaging. Eleven panic patients and eleven controls matched for age, sex, handedness, socioeconomic status and years of education participated in the study. The mean volume of the left temporal lobe of panic patients was 9% smaller than that of controls (t21 = 2.37, P = 0.028). In addition, there was a trend (P values between 0.05 and 0.10) to smaller volumes of the right temporal lobe (7%, t21 = 1.99, P = 0.06), right amygdala (8%, t21 = 1.83, P = 0.08), left amygdala (5%, t21 = 1.78, P = 0.09) and left hippocampus (9%, t21 = 1.93, P = 0.07) in panic patients compared to controls. There was a positive correlation between left hippocampal volume and duration of panic disorder (r = 0.67, P = 0.025), with recent cases showing more reduction than older cases. The present results show that panic patients have a decreased volume of the left temporal lobe and indicate the presence of volumetric abnormalities of temporal lobe structures.

The dorsal raphe nucleus exerts opposed control on generalized anxiety and panic-related defensive responses in rats

It has been proposed that the ascending dorsal raphe (DR)-serotonergic (5-HT) pathway facilitates conditioned avoidance responses to potential or distal threat, while the DR-periventricular 5-HT pathway inhibits unconditioned flight reactions to proximal danger. Dysfunction on these pathways would be, respectively, related to generalized anxiety (GAD) and panic disorder (PD). To investigate this hypothesis, we microinjected into the rat DR the benzodiazepine inverse receptor agonist FG 7142, the 5-HT(1A) receptor agonist 8-OH-DPAT or the GABA(A) receptor agonist muscimol. Animals were evaluated in the elevated T-maze (ETM) and light/dark transition test. These models generate defensive responses that have been related to GAD and PD. Experiments were also conducted in the ETM 14 days after the selective lesion of DR serotonergic neurons by 5,7-dihydroxytriptamine (DHT). In all cases, rats were pre-exposed to one of the open arms of the ETM 1 day before testing. The results showed that FG 7142 facilitated inhibitory avoidance, an anxiogenic effect, while impairing one-way escape, an anxiolytic effect. 8-OH-DPAT, muscimol, and 5,7-DHT-induced lesions acted in the opposite direction, impairing inhibitory avoidance while facilitating one-way escape from the open arm. In the light/dark transition, 8-OH-DPAT and muscimol increased the time spent in the lighted compartment, an anxiolytic effect. The data supports the view that distinct DR-5-HT pathways regulate neural mechanisms underlying GAD and PD.

The neurobiology and control of anxious states

Fear is an adaptive component of the acute "stress" response to potentially-dangerous (external and internal) stimuli which threaten to perturb homeostasis. However, when disproportional in intensity, chronic and/or irreversible, or not associated with any genuine risk, it may be symptomatic of a debilitating anxious state: for example, social phobia, panic attacks or generalized anxiety disorder. In view of the importance of guaranteeing an appropriate emotional response to aversive events, it is not surprising that a diversity of mechanisms are involved in the induction and inhibition of anxious states. Apart from conventional neurotransmitters, such as monoamines, gamma-amino-butyric acid (GABA) and glutamate, many other modulators have been implicated, including: adenosine, cannabinoids, numerous neuropeptides, hormones, neurotrophins, cytokines and several cellular mediators. Accordingly, though benzodiazepines (which reinforce transmission at GABA(A) receptors), serotonin (5-HT)(1A) receptor agonists and 5-HT reuptake inhibitors are currently the principle drugs employed in the management of anxiety disorders, there is considerable scope for the development of alternative therapies. In addition to cellular, anatomical and neurochemical strategies, behavioral models are indispensable for the characterization of anxious states and their modulation. Amongst diverse paradigms, conflict procedures--in which subjects experience opposing impulses of desire and fear--are of especial conceptual and therapeutic pertinence. For example, in the Vogel Conflict Test (VCT), the ability of drugs to release punishment-suppressed drinking behavior is evaluated. In reviewing the neurobiology of anxious states, the present article focuses in particular upon: the multifarious and complex roles of individual modulators, often as a function of the specific receptor type and neuronal substrate involved in their actions; novel targets for the management of anxiety disorders; the influence of neurotransmitters and other agents upon performance in the VCT; data acquired from complementary pharmacological and genetic strategies and, finally, several open questions likely to orientate future experimental- and clinical-research. In view of the recent proliferation of mechanisms implicated in the pathogenesis, modulation and, potentially, treatment of anxiety disorders, this is an opportune moment to survey their functional and pathophysiological significance, and to assess their influence upon performance in the VCT and other models of potential anxiolytic properties.

Pharmacology of human experimental anxiety

This review covers the effect of drugs affecting anxiety using four psychological procedures for inducing experimental anxiety applied to healthy volunteers and patients with anxiety disorders. The first is aversive conditioning of the skin conductance responses to tones. The second is simulated public speaking, which consists of speaking in front of a video camera, with anxiety being measured with psychometric scales. The third is the Stroop Color-Word test, in which words naming colors are painted in the same or in a different shade, the incongruence generating a cognitive conflict. The last test is a human version of a thoroughly studied animal model of anxiety, fear-potentiated startle, in which the eye-blink reflex to a loud noise is recorded. The evidence reviewed led to the conclusion that the aversive conditioning and potentiated startle tests are based on classical conditioning of anticipatory anxiety. Their sensitivity to benzodiazepine anxiolytics suggests that these models generate an emotional state related to generalized anxiety disorder. On the other hand, the increase in anxiety determined by simulated public speaking is resistant to benzodiazepines and sensitive to drugs affecting serotonergic neurotransmission. This pharmacological profile, together with epidemiological evidence indicating its widespread prevalence, suggests that the emotional state generated by public speaking represents a species-specific response that may be related to social phobia and panic disorder. Because of scant pharmacological data, the status of the Stroop Color-Word test remains uncertain. In spite of ethical and economic constraints, human experimental anxiety constitutes a valuable tool for the study of the pathophysiology of anxiety disorders.

5-HT mechanisms of median raphe nucleus in the conditioned freezing caused by light/foot-shock association

We have shown that 5-HT mechanisms of the median raphe nucleus (MRN) are involved in contextual fear-conditioning processes as electrolytic or neurotoxic lesions with N-methyl-D-aspartate (NMDA) or injections of 8-hydroxy-2-(di-n-propilamino)-tetralin (8-OH-DPAT) into this structure inhibit freezing behavior in a contextual fear paradigm. In this work, we extend these studies by analyzing the behavioral responses in a classical fear-conditioning paradigm (light or tone/foot-shock association) in rats with either neurochemical lesion with NMDA or injected with 8-OH-DPAT into the MRN. The animals received NMDA or 8-OH-DPAT or saline microinjections into the MRN and were submitted to conditioning trials in an experimental chamber, where they received 10 foot-shocks (0.6 mA, 1 s, variable interval between 10 and 50 s) paired with tone or light (CS). On the next day, they were tested in a different experimental chamber, with or without CS presentation, where the duration of freezing and the number of rearing episodes were recorded. Light or tone alone caused a significant amount of freezing. NMDA lesions or 8-OH-DPAT injections into the MRN clearly inhibited freezing behavior in rats conditioned to light/foot-shock association, but not in the conditioning sessions with tones. Besides the proposed role in contextual fear conditioning, these results clearly show that MRN is involved in the fear conditioning with light as conditioned stimuli. Distinct neural substrates seem to subserve conditioning fear with acoustic stimuli.

Effects of Hypericum perforatum and paroxetine in the mouse defense test battery

Since (a) Hypericum perforatum shows anxiolytic-like effect in some animal models, (b) antidepressant drugs (AD) have been used as the main drug treatment for panic disorder (PD), (c) AD are also effective in generalized anxiety disorder (GAD), and (d) H. perforatum exhibits antidepressant activity, it was hypothesized that H. perforatum might possess an antipanic-like and/or anxiolytic-like effect. Previous studies with the mouse defense test battery (MDTB) have suggested that this model may be useful for the investigation of anxiolytic-like and antipanic-like compounds. Thus, the aim of the present study was to evaluate the effect of H. perforatum extract in the MDTB. The effect of acute, subchronic (7 days), and chronic (21 days) H. perforatum (150 and 300 mg/kg) extract administration was evaluated in mice submitted to the MDTB. Paroxetine (5 mg/kg), a selective serotonin re-uptake inhibitor with anxiolytic and antipanic effect, was used as a positive control. The results showed that 21 days of repeated administration of H. perforatum 300 mg/kg and paroxetine 5 mg/kg reduced flight reactions (number of avoidances, avoidance distance, and overall flight speed) to the presence of the predator. While the effect of paroxetine confirms that MDTB is useful for the detection of antipanic-like drugs, the effect of H. perforatum suggests a putative antipanic-like effect for this extract. Moreover, after 21 days of repeated administration, paroxetine increased the number of approaches/withdrawals and reduced the number of upright postures, suggesting a partial anxiolytic-like effect, while H. perforatum only reduced the number of upright postures. The present results suggest anxiolytic-like and antipanic-like effects of H. perforatum extract. However, it should be emphasized that the risk assessment (the main index of anxiety) was not affected by the extract, while the attack reactions were only weakly modified.

The Mouse Defense Test Battery: pharmacological and behavioral assays for anxiety and panic

The Mouse Defense Test Battery was developed from tests of defensive behaviors in rats, reflecting earlier studies of both acute and chronic responses of laboratory and wild rodents to threatening stimuli and situations. It measures flight, freezing, defensive threat and attack, and risk assessment in response to an unconditioned predator stimulus, as well as pretest activity and postthreat (conditioned) defensiveness to the test context. Factor analyses of these indicate four factors relating to cognitive and emotional aspects of defense, flight, and defensiveness to the test context. In the Mouse Defense Test Battery, GABA(A)-benzodiazepine anxiolytics produce consistent reductions in defensive threat/attack and risk assessment, while panicolytic and panicogenic drugs selectively reduce and enhance, respectively, flight. Effects of GABA(A)-benzodiazepine, serotonin, and neuropeptide ligands in the Mouse Defense Test Battery are reviewed. This review suggests that the Mouse Defense Test Battery is a sensitive and appropriate tool for preclinical evaluation of drugs potentially effective against defense-related disorders such as anxiety and panic.

The Vogel conflict test: procedural aspects, gamma-aminobutyric acid, glutamate and monoamines

A multitude of mechanisms are involved in the control of emotion and in the response to stress. These incorporate mediators/targets as diverse as gamma-aminobutyric acid (GABA), excitatory amino acids, monoamines, hormones, neurotrophins and various neuropeptides. Behavioural models are indispensable for characterization of the neuronal substrates underlying their implication in the etiology of anxiety, and of their potential therapeutic pertinence to its management. Of considerable significance in this regard are conflict paradigms in which the influence of drugs upon conditioned (trained) behaviours is examined. For example, the Vogel conflict test, which was introduced some 30 years ago, measures the ability of drugs to release the drinking behaviour of water-deprived rats exposed to a mild aversive stimulus ("punishment"). This model, of which numerous procedural variants are discussed herein, has been widely used in the evaluation of potential anxiolytic agents. In particular, it has been exploited in the characterization of drugs interacting with GABAergic, glutamatergic and monoaminergic networks, the actions of which in the Vogel conflict test are summarized in this article. More recently, the effects of drugs acting at neuropeptide receptors have been examined with this model. It is concluded that the Vogel conflict test is of considerable utility for rapid exploration of the actions of anxiolytic (and anxiogenic) drugs. Indeed, in view of its clinical relevance, broader exploitation of the Vogel conflict test in the identification of novel classes of anxiolytic agents, and in the determination of their mechanisms of action, would prove instructive.

Interferon, tryptophan and depression

Depression is a frequent comorbid disorder of many inflammatory diseases and it is suggested that brain inflammatory processes have a pathogenic role in mood dysregulation. Several immunocompromised patients have been treated with cytokines and long-term treatments have resulted in a variety of neuropsychiatric side-effects. The objective of the study was to present evidence for an association between the induction of neuropsychiatric side-effects during treatment with interferon-α (IFN-α) and changes in serotonergic and immunological parameters. Moreover, the use of IFN-α-induced depression as a paradigm for research into the pathophysiology of depressive disorders in general will be discussed. This literature review focused on the relationships between tryptophan, serotonin, cytokines and depression associated with interferon treatment. Immunotherapy with IFN-α influences several immunological and serotonergic parameters, and induces in most patients neurovegetative, somatic and depressive symptoms. Literature findings indicate that the development of depressive symptoms in patients undergoing cytokine therapy are secondary to cytokine induction and could be mediated by a reduced availability of tryptophan to the brain, resulting ultimately in decreased serotonergic activity. Changes in the metabolism of tryptophan and consequently of serotonin may play a role in the pathophysiology of interferon-induced depression. Studies on interferon-induced neuropsychiatric side-effects may be a promising research paradigm and shed light on the role of immunological and serotonergic factors in the pathogenesis of depressive disorders in general. However, first the appropriate symptomatology of the interferon-induced depressive states has to be documented.

Tryptophan depletion alters the decision-making of healthy volunteers through altered processing of reward cues

While accumulating evidence suggests that effective real-life decision-making depends upon the functioning of the orbitofrontal cortex, much less is known about the involvement of the monoamine neurotransmitter systems and, in particular, serotonin. In the present study, we explored the impact of depleting the serotonin precursor, tryptophan, on human decision-making. Eighteen healthy volunteers consumed an amino-acid drink containing tryptophan and 18 healthy volunteers consumed an amino-acid drink without tryptophan, before choosing between simultaneously presented gambles, differing in the magnitude of expected gains (ie reward), the magnitude of expected losses (ie punishment), and the probabilities with which these outcomes were delivered. Volunteers also chose between gambles probing identified non-nomative biases in human decision-making, namely, risk-aversion when choosing between gains and risk-seeking when choosing between losses. Tryptophan-depleted volunteers showed reduced discrimination between magnitudes of expected gains associated with different choices. There was little evidence that tryptophan depletion was associated with altered discrimination between the magnitudes of expected losses, or altered discrimination between the relative probabilities with which these positive or negative outcomes were delivered. Risk-averse and risk-seeking biases were also unchanged. These results suggest that serotonin mediates decision-making in healthy volunteers by modulating the processing of reward cues, perhaps represented within the orbitofrontal cortex. It is possible that such a change in the cognition mediating human choice is one mechanism associated with the onset and maintenance of anhedonia and lowered mood in psychiatric illness.

Acute L-5-hydroxytryptophan administration inhibits carbon dioxide-induced panic in panic disorder patients

Previous research showed that lowering the availability of serotonin to the brain by tryptophan depletion increases the vulnerability of panic disorder patients for an experimental 35% CO(2) panic challenge. The results also suggested that increased availability of serotonin inhibits the response to such a challenge. In the present study, this latter possibility is examined. The reaction of 24 panic disorder patients and 24 healthy volunteers to a 35% CO(2) panic challenge was assessed following administration of 200-mg L-5-hydroxytryptophan (the immediate precursor of serotonin) or placebo. L-5-Hydroxytryptophan significantly reduced the reaction to the panic challenge in panic disorder patients, regarding subjective anxiety, panic symptom score and number of panic attacks, as opposed to placebo. No such effect was observed in the healthy volunteers. L-5-Hydroxytryptophan acts to inhibit panic, which supports a modulatory role of serotonin in panic disorder.

Pharmacotherapy of anxious disorders

The present paper is a review of the treatment of anxious disorders by the current pharmaceutical medications; a short epidemiological survey is given for anxious disorders including: general anxiety disorder, panic disorder, obsessive compulsive disorder, social anxiety and post-traumatic stress disorder. For all these disorders there are proposals of treatment built on literature data mainly on meta-analysis as well on personal experience.

Elevated dietary intake of L-tryptophan counteracts the stress-induced elevation of plasma cortisol in rainbow trout (Oncorhynchus mykiss)

Juvenile rainbow trout were isolated in individual compartments and allowed to acclimate for 1 week, during which they were fed commercial trout pellets. The feed was then replaced by pelleted feed supplemented with L-tryptophan(TRP) at two, four or eight times the concentration in the commercial feed. Fish were fed these supplemented feeds daily to satiety for 1 week, after which half of the fish were stressed, by lowering the water level for 2 h,while the remaining fish were left undisturbed. In undisturbed fish,supplementary dietary TRP resulted in slightly elevated plasma cortisol levels. In response to the stress, fish that had been fed control feed showed elevated plasma cortisol levels, but fish fed the TRP-supplemented feed displayed a significant reduction in this stress-induced elevation of plasma cortisol levels. Plasma and brain TRP levels were elevated in fish fed TRP-supplemented feed. TRP is the precursor of the monoamine neurotransmitter serotonin. Brain serotonergic activity was elevated by stress and also tended to be increased by elevated dietary TRP intake. The central serotonergic system is involved in the control of the hypothalamic—pituitary—interrenal axis, the action of serotonin being to stimulate or inhibit this neuroendocrine axis through different projections.

Envolvimento dos receptores 5-HT2 da amígdala nos níveis de ansiedade induzidos pela exposição de ratos ao labirinto em cruz elevado

O efeito de microinjeções intra-amigdalóides do antagonista 5-HT2A/2C de receptores serotoninérgicos RP 62203 (1,0; 2,5; 5,0 mg) foi investigado em medidas tradicionais e etológicas (esquadrinhar, espreitar e explorações da extremidade) de ansiedade de ratos no labirinto em cruz elevado. A dose de 5,0 mg aumentou as porcentagens de entrada e de tempo nos braços abertos, sem alterar no número de entradas nos braços fechados. As categorias esquadrinhar, espreitar e explorações da extremidade também foram alteradas pela droga. As doses de 2,5 e 5,0 mg aumentaram o tempo gasto em esquadrinhar e diminuíram o tempo gasto em espreitar. O número de explorações da extremidade também foi aumentado pela injeção da droga na dose de 5,0 mg. Este padrão comportamental sugere um efeito ansiolítico do RP 62203. A participação dos receptores 5-HT2A/2C da amígdala na regulação desse efeito é discutida.

Cortisol modulation of 5-HT-mediated growth hormone release in recovered depressed patients

BACKGROUND

Recent formulations of the pathophysiology of major depression suggest that stress-induced cortisol secretion may lower brain serotonin (5-HT) function, thereby precipitating depressive symptomatology. This implies that people who develop depression after stressful life events may be particularly vulnerable to the effect of cortisol on brain 5-HT activity. We therefore assessed the effect of a single dose of hydrocortisone on 5-HT-mediated growth hormone (GH) release in healthy volunteers and euthymic subjects recovered from at least two episodes of major depression.

METHODS

Eleven recovered depressed patients and 20 healthy controls received intravenous tryptophan (TRP) 10.5 h after placebo and hydrocortisone (50 mg orally) in a double-blind, cross-over design. Plasma GH levels were sampled for 90 min after TRP infusion.

RESULTS

The GH response to TRP was significantly lower in the recovered depressed patients than controls after hydrocortisone.

LIMITATIONS

The number of recovered depressed subjects studied was small and the effect of hydrocortisone on TRP-induced GH release was different to that observed in a previous study.

CONCLUSIONS

These findings are consistent with other evidence suggesting abnormal regulation of 5-HT neurotransmission in people vulnerable to recurrent depression.