The Role of Life Events and HPA Axis in Anxiety Disorders: A Review

Transcription

1 Current Pharmaceutical Design, 2012, 18, The Role of Life Events and HPA Axis in Anxiety Disorders: A Review Carlo Faravelli* 1, Carolina Lo Sauro 1, Lorenzo Lelli 2, Francesco Pietrini 2, Lisa Lazzeretti 2, Lucia Godini 2, Laura Benni 2, Giulia Fioravanti 1, Gabriela Alina Talamba 2, Giovanni Castellini 2 and Valdo Ricca 2 1 Department of Psychology, University of Florence, Italy; 2 Psychiatric Unit, Department of Neuroscience, Florence University School of Medicine, Italy Abstract: Stressful life events and dysfunctional Hypothalamic Pituitary Adrenal (HPA) axis have been implicated in the pathogenesis of psychiatric disorders, including anxiety disorders. This paper attempts to review the existing literature on childhood traumata, recent life events, HPA axis functioning and their relationship in Post-Traumatic Stress Disorder, Panic Disorder, Generalized Anxiety Disorder, Obsessive Compulsive Disorder and Social Phobia. Preclinical and clinical models will be analyzed. Stressful life events seem to have a role in the onset and in the course of these disorders and HPA axis abnormalities have been reported in almost all anxiety disorders. The hypothesis that early stressful life events may provoke alterations of the stress response and thus of the HPA axis, that can endure during adulthood, predisposing individuals to develop psychopathology, will be evaluated. Keywords: Animal models, anxiety disorders, childhood traumata, cortisol, Hypothalamic Pituitary Adrenal axis, life events, stress response, vulnerability. INTRODUCTION According to Robert and Caroline Blanchard [1], anxiety is the emotion evoked in situations when the danger is uncertain (potential threat), either because the context is novel or because the danger stimulus (e.g., a predator) had been present in the past but is no longer in the environment. Furthermore, psychosocial stress is a common condition in human life: a state of challenge or threat to which the organism, in order to preserve its internal equilibrium, reacts with an array of adaptive responses mediated by neural and neuroendocrine cascades, involving either the autonomic nervous system and the activation of the limbic-hypothalamic-pituitary adrenal system [2-5]. Stressful Life Events and Anxiety Exposure to stressors (like childhood traumata) and sensitivity to stress have been strongly implicated in the manifestation or exacerbation of psychiatric disorders, including anxiety disorders [6-17]. For instance, elevated rates of childhood abuse were observed among patients with anxiety disorders, providing conflicting data on its specificity to any anxiety diagnoses. In fact, while Stein et al. [18] found higher rates of childhood abuse in women with panic disorder than in women with others anxiety disorders, Mancini et al. [19] found no difference in the incidence of childhood sexual and physical abuse in patients with different anxiety disorder diagnoses. Moreover, Safren et al. [16] found that patients with panic disorder had significantly higher rates of childhood physical or sexual abuse than patients with social phobia, while patients with generalized anxiety disorder appeared to have intermediate rates, not significantly different from those of the two other diagnoses addressed in that study. Stress System The particular features of stress response depend on the characteristics of the stressor itself, such as intensity and duration, and on *Address correspondence to this author at the Studio Dea, Via P.F. Calvi 10, 50100, Florence, Italy: Tel: ; Fax: ; carlo.faravelli@unifi.it the individual psychological resources, which may determine its particular appraisal and the resulting coping strategies [20]. Usually, the stress system involves initially the nuclei of the amygdala, which, once activated, convey their message to the hypothalamic neurons through different pathways, activating the Hypothalamus-Pituitary-Adrenal (HPA) axis, through the secretion of the Corticotropic Releasing Hormone (CRH) into the portal circulation of the pituitary gland by the hypothalamic paraventricular nucleus. In the anterior pituitary, CRH stimulates the release of adrenocorticotropin (ACTH) into the blood stream, which acts on the adrenal cortex promoting cortisol release into the blood vessels [3]. In addition to the HPA axis, acute stress also activates the sympathetic division of the neurovegetative nervous system as part of the fight/flight reaction, or emergency response [2]. As a result, noradrenaline is released from peripheral sympathetic nerve fibers in different tissues and adrenaline (also some noradrenaline) from the adrenal medulla into the blood stream. Stress Response and Anxiety Corticotrophin Releasing Factor (CRF) systems (like hypothalamus, amygdala, neocortex) mediate the neuroendocrine responses to psychological stressors and are involved in the cognitive and emotional processing that accounts for many of the symptoms of depression and anxiety [6,15, 21-23]. In acute anxiety, the activation of the HPA axis is adaptive, since cortisol seems to reduce perceived fear by impairing the memory retrieval of emotionally arousing information [24]. Conversely, in chronic anxiety, the gradual development of a disconnection between the stressor and its behavioral consequences is the main coping mechanism [25] which allows the person to function normally, despite the presence of annoying events that cannot be escaped or avoided. When this mechanism fails, the HPA axis persists activated and may become harmful, since corticoids decrease the hippocampal serotonin receptors, impairing coping mechanisms and inducing resilience and low tolerance to the chronic stress [26]. Therefore chronic stress, such as that observed during the prolonged exposure to various stressful life events, along with the inadequacy to cope with them or the perceived loss of controllability, may lead to the persistent activation of the HPA system [27] which /12 $ Bentham Science Publishers

2 2 Current Pharmaceutical Design, 2012, Vol. 18, No. 00 Faravelli et al. results in a sustained increase of cortisol levels. Accordingly, Carpenter et al. [8] reported that emotional neglect and physical abuse were the only significant predictors of the blunted cortisol response in healthy adults, while childhood sexual abuse was a significant predictor of higher cortisol curves in adulthood. Based on these data, the hypothesis that severe stress early in life (like childhood abuse, or adverse parenting experiences) is associated with persistent sensitization of the pituitary-adrenal and autonomic stress response, which, in turn, is likely to mediate the increased risk for the development of affective and anxiety disorders in adulthood, has been explored in different studies [6,9,10,17,23,28-36 ]. Breier et al. [35] observed 90 subjects exposed to early parental loss in childhood and found higher plasma cortisol and ACTH concentrations in subjects who were diagnosed with a lifetime psychiatric disorder, than in those who did not receive a psychiatric diagnosis. More recently, some Authors observed that children who experienced permanent or long-term separations from parents, or parental death, show a hyperactive HPA axis, with increased basal salivary cortisol concentrations [32,33,35] and cortisol non-suppression after the Dexamethasone (Dex) Suppression Test (DST) [37], as well as after the combined Dex/CRH test [38]. Pfeffer et al. [32] reported that bereaved children (suffering parent death from September 11, 2001 terror attacks), but not nonbereaved children, had significantly increased rates of anxiety disorders and significantly and persistently higher morning and 4:00 pm baseline cortisol, after September 11, 2001, compared with the retrospective assessments before September 11, Animal Models of the Relationship Between Stress and Psychiatric Disorders A large body of work on rodents and non-human primates has shown that stressful life events influence the behavior and biology of a living organism [39,40]. The main behavioral stress models are the Learned Helplessness model [41], the Behavioral Despair model [42], the Neonatal Maternal Separation model [43] and the Chronic Intermittent Stress model [44]. In particular, works on early maternal separation have demonstrated changes in brain circuitry regulating the stress reactivity, mood and behavior, with an associated exaggeration or attenuation of the HPA axis activity [33,36,45]. For instance, studies on rodents have shown that early social isolation is able to provoke abnormalities in behavior similar to human depression and anxiety disorders, while environmental enrichment shows an antidepressive and anxiolytic like effect in animal models of depression and anxiety [45,46]. Moreover an increase in plasmatic ACTH and cortisol levels has been reported during behavioral despair [47,48]. Moreover, as CRF mediates the autonomic and behavioral stress responses, when it is administered directly into the Central Nervous System (CNS) of laboratory animals, it produces effects that are reminiscent of stress, depression, and anxiety [21,49], through actions on specific brain regions [12,50]. HPA Axis Dysregulation and Anxiety Disorders Stress-system dysregulation and the resulting hypercortisolism have been widely reported in psychiatric disorders, including depression and anxiety disorders [5,22,51-56]. Either higher basal cortisol levels or normal concentrations have been reported in the different diagnostic subgroups of anxiety disorders [57-63]. For instance, Vreeburg et al. [5] showed a modest but significantly higher 1-hour cortisol awakening response among current anxiety disordered patients, especially in those with panic disorder with agoraphobia and those with comorbid depression. No associations were observed for the anxiety status and evening cortisol level or cortisol suppression after dexamethasone administration [5]. Summary Animal models, as well as clinical studies, seem to underline that stressful life events, especially early life events, may provoke dysfunctions in CNS and an alteration of the stress response that endures during adulthood [8,10,17,23,28-31,34,36]. However, neither the abnormalities of the HPA axis, nor the excess of traumatic stressful events during childhood seem to be specific to any diagnostic group [10,12,16] and data about the role of the HPA axis in the relationship between stressful life events and anxiety disorders are scarce and sometimes discordant [6,10,12]. Aim The present paper is aimed at reviewing data on the relationship between early and recent life events and the HPA axis functioning in all anxiety disorders, except for simple phobias, as to our knowledge literature on this topic is still poor. METHODS PubMed ( ) and PsycINFO (1984-March 2011) databases were used with the combinations of the following terms: HPA axis, cortisol, ACTH, stressful life events, childhood traumata, anxiety disorders, panic disorder, generalized anxiety disorder, obsessive-compulsive disorder, post-traumatic stress disorder, social phobia, simple phobia, animal models, CRH, vulnerability. RESULTS Stressful Life Events, Post-Traumatic Stress Disorder (PTSD) and the HPA Axis Post-Traumatic Stress Disorder (PTSD) is a chronic psychiatric condition that may develop in subjects who have been exposed to or have witnessed a traumatic event of an extreme nature [64]. It is well known that a history of prior trauma increases a person s risk of developing PTSD [12,17,29-31], mainly in response to subsequent traumata, but the biological phenomenon underlying the onset of psychopathology has not yet been identified [9,10,12,23]. Carpenter et al. [8] hypothesized that a chronic stressor, like an emotional abuse in childhood, may contribute to an enhanced vulnerability to stress-induced diseases, as it can induce difficulties with attachment and interpersonal interaction that perpetuate a pattern of chronic stress in the subsequent relationships across the life span. However, not only the kind of event, but also the perception of it, the social context within which it happens, the emotions elicited by the stress, the controllability of the stress, and the individual response to the situation, seem to influence the consequences of trauma [8,65]. Accordingly, animal models of PTSD revealed that animals behavior is not uniformly disturbed, but rather demonstrates a broad range of variation in the severity of anxiety-like behaviors. After an inescapable electric (foot) shock [66], social confrontations [67], underwater trauma [68], and exposure of a rodent to a predator [39,69-71], some rats were minimally affected and others were highly affected [39]. The variation in the behavioral response among a genetically uniform group of rats suggests that early individualized environmental factors are relevant in this response. The clinical syndrome of PTSD, however, clearly affects only a proportion of the exposed [72] and revolves around differential degrees of responses [39], probably reflecting the differential vulnerability or resilience. From a biological point of view, the relationship between childhood traumata and PTSD seems to be mediated by persistent changes of the stress responses, i.e. corticotrophin releasing factor [e.g. 14,28]. Accordingly, preclinical evidences have showed a long-term sensitization of the stress response after early life stress

3 Life Events, HPA Axis and Anxiety Disorders Current Pharmaceutical Design, 2012, Vol. 18, No and recent studies have provided evidence for sustained increases in the CRF activation in the cerebrospinal fluid (CSF) of PTSD patients [73]. Furthermore, several Authors reported increased urinary cortisol levels in subjects who experienced a sexual abuse or maltreatment in childhood and who have a current PTSD diagnosis [74,75], compared to healthy controls. These data are confirmed also after a stressful cognitive challenge or after a CRF-ACTH administration, since afterwards PTSD patients with a childhood abuse showed higher mean cortisol levels compared to healthy subjects [76,77] and greater than usual ACTH response [28]. On the other hand, a smaller cortisol response after ACTH stimulation test has been observed in childhood abused women with PTSD [28] and an hypersuppression of cortisol after a low dose of dexamethasone (0.5 mg) have been reported in a similar group of patients, compared to control [52,78-80]. Moreover, other studies found no differences between women with PTSD and healthy subjects both in terms of circadian and baseline cortisol and ACTH levels [77,81,82] and of cortisol levels after dexamethasone suppression test (DST) [82] or after a stressful cognitive challenge [83]. A recent study underlined the importance of the age of the index trauma: data showed that PTSD subjects had a less strong ACTH response in comparison to controls, regardless of the age of the index trauma, but persistently higher and post-task cortisol levels when the trauma occurred in childhood, compared to subjects with adult trauma and controls [84]. As far as adult trauma is concerned, lower cortisol levels have been reported in PTSD patients, compared to other psychiatric patients [85] and to controls [86,87]. Accordingly, patients with chronic combat [85,88] or holocaust-related [89] PTSD showed decreased 24h urine and plasma cortisol levels [90], and an attenuated ACTH and cortisol response to CRH challenges [91], compared to healthy controls. Moreover, enhanced cortisol suppression after a low-dose DST (0.5 mg or even 0.25 mg) has been observed in PTSD patients [52,87,92,93]. Furthermore, higher elevations in ACTH levels following metyrapone (an inhibitor of cortisol synthesis) were observed in combat veterans with PTSD, than in those without PTSD and the nonexposed group [94]. Conversely, increased 24h urine cortisol [95] and high CSF CRH levels were reported in PTSD related to combat or to adult trauma [96,97]. More recently, increased plasma cortisol levels were showed in eleven exposed Oklahoma City bombing survivors [98] and in twenty-three spouses bereaved from September 11, 2001 terror attacks [99]. Less afternoon postdexamethasone cortisol suppression was observed in bereaved subjects than in nonbereaved ones [99]. Further investigations revealed increased plasma cortisol levels in response to a non-pharmacological stressful test in PTSD veterans compared to controls [100]. Furthermore, higher elevations in ACTH levels following CRF [101] and a lower ACTH response after metyrapone were observed in Gulf War veterans with PTSD [102], than in those without PTSD and the non-exposed group. On the other hand, other findings reported no systematic difference in basal cortisol levels, or in the HPA axis reactivity to CRH challenges, regardless of the type of assessment used (salivary, plasma/serum, urinary), in subjects with chronic PTSD and controls [86, ]. After dexamethasone-corticotrophin releasing hormone (DEX-CRH) test, ACTH and cortisol responses were similar in male veterans exposed to similar traumatic events with and without PTSD, differentiating only by a lower ACTH response in patients with comorbid major depression disorder [106]. Moreover, even after a person develops PTSD, biology underlying constant symptomology changes over time [103,107]. In fact, Aardal-Eriksson, Eriksson & Thorell [108] examine HPA abnormalities in subjects exposed to an accident, five days after the event, 2 and 9 month later. Subjects from the high distressed group reported significantly lower morning and higher evening cortisol levels compared with the low-impact group, at the first time points. Within 9 months, the posttraumatic distress of the high-impact group was reduced, accompanied by an increase in morning and a decrease in evening cortisol levels. These data were confirmed by Shalev et al. [109] who observed that plasma cortisol levels decreased with time in survivors with and without PTSD. Furthermore, it seems that the parental response to trauma induces physiological consequences on the child: Nugent et al. [110] observed that it may interact with the child acute physiological responses, to predict the persistent child s posttraumatic stress symptoms. Yehuda [111] has demonstrated that the adult children of holocaust survivors had lower levels of cortisol, indicating that a predisposition to PTSD can be passed on from parent to child, and they were three times more likely to develop PTSD if traumatized. Lower salivary cortisol levels were also observed in infants of mothers who developed PTSD versus those who did not develop PTSD after exposure to the World Trade Center collapse on September 11, 2001, while pregnant, particularly if exposed during the third trimester [32]. No differences in offspring cortisol levels have been reported in those who had 1 versus 2 parents with PTSD, but low cortisol levels seemed to be more strongly associated with the maternal-only than with the paternal-only PTSD [111]. The mechanism involved in this phenomenon is likely not the inheritance of lower levels of cortisol per se, but rather a transmission via early glucocorticoid programming in the fetus as a result of changes in the hormonal milieu of the mother [111]. The reduced cortisol levels during trauma exposure permit an extended psychophysical distress response that facilitates the development of PTSD, since the cortisol release inhibits other stress induced biological responses [111]. Several Authors tried to explain these data. Yehuda [72] hypothesized that high cortisol levels might reflect the persistent intrusive nature of the memories and the continued sense of threat experienced by these individuals. After an initial sensitization, with the hypotalamic CRF hypersecretion due to the early life stress, a blunted responses follows, reflecting a down-regulation of pituitary CRF receptors [12,28] and a physiological adaptation of the HPA axis to chronic stress [72,103]. This data is confirmed by neuroimaging studies, which reported reduced hippocampal volumes in adult patients with PTSD [e.g. 97,112], as if the long-term overexposure to glucocorticoids would lead to cell atrophy, loss, or decreased neurogenesis [113]. On the other hand, the decreased cortisol production due to the enhanced negative feedback inhibition can be related to the higher availability of glucocorticoid receptors on pituitary cells [92,114], or to the insufficient pituitary and/or adrenal response to CRF or ACTH stimulation [114], or the reduced sensitivity to low cortisol levels [114], or to an excess of bioavailability of dexamethasone [114] or an inadequate vasopressin reaction [114]. Furthermore, the possibility of a different corticolimbic activation after a psychosocial, rather than a chemical, stressor, can explain an overcoming negative feedback inhibition which causes a blunted ACTH/cortisol response [12]. Among the possible factors that can be involved in the altered stress regulation in PTSD, hormone binding proteins (e.g., CRH binding protein and corticosteroid binding globulin), immune factors, samples differences (e.g. age, gender, inclusion and exclusion

4 4 Current Pharmaceutical Design, 2012, Vol. 18, No. 00 Faravelli et al. criteria, the presence of comorbidity like a major depression disorder, medication use), the diurnal rhythm and pulsatile secretion of adrenal hormones, the time passed since the traumatic event, the experienced stress during the assessment, the subjectivity of the perception of stressors, alterations in the activity of the central nervous system and/or in hormone bioavailability and/or in hormone receptor function [114], must be taken into account. Stressful Life Events, Panic Disorder (PD) and the HPA Axis Findings on HPA axis abnormalities in patients suffering from Panic Disorder (PD) are conflicting and inconsistent [55], as anxiety and panic seem to be qualitatively different. Referring to animal models, rodents immediate defensive reactions connected to the flight or fight system and the escape behaviors seem to be related to panic disorder [115,116] and the same neurobiological processes that organize proximal defense are involved in panic disorder, as well [25]. These behaviors, as equivalent of panic attacks, have been tested in the mouse defensive test battery (MDTB) [116], the unstable elevated exposed plusmaze (UEEPM) [117], and the elevated T-maze [118]. Recently, Lim et al. [119] showed an increased in plasma level of corticosterone in rats after the induction of an escape or paniclike response, suggesting that the panic attack or escape response activates the HPA axis. In humans, if anxiety is an emotional state related to a potential threat mostly activating the HPA and the sympathoadrenal axes, panic is an emotion evoked by the perception of an actual danger that causes major sympathetic activation with possibly small effects on the HPA axis [26]. Several studies investigated the different HPA axis responses to real life panic attacks and to artificially induced panic attacks. Higher salivary cortisol levels have been reported only at the beginning of the panic attack [58,120], while normal salivary or plasma cortisol levels have been reported during the panic attack [26,121]. These results can be explained if we consider that anticipatory anxiety can arouse the HPA axis, that afterwards normalizes due to a successful habituation to the repeated experiences of panic [122]. Graeff et al. [26] showed that only non-selective panicogenic agents (e.g., agonists of the cholecystokinin receptor B) induce the release of stress hormones, regardless of the occurrence of the panic attack, while real life panic attacks and selective panicogens stimuli (e.g., sodium lactate and carbon dioxide) do not activate the HPA axis. Conversely, van Duinen et al. [123] reported an increase in cortisol and ACTH levels following 35% CO2 inhalation in both panic disorder patients and controls, thus independently of the specific panicogenic properties of CO2. Similarly, while yohimbine, mccp and Fenfluramine increase anticipatory anxiety and the release of stress hormones, without inducing a true panic attack, Flumazenil and benzodiazepine receptors antagonists seem not to activate the HPA axis nor to induce panic attacks [26]. Several authors suggested a hypersensitivity to CO2 in PD patients [ ]. Such an over sensitiveness could be explained by a disturbed warning system involved in suffocation fear. In fact, models of panic using pharmacological agents, such as sodium lactate, 5% CO2 or doxapram (a respiratory analeptic), induce false suffocation alarms as well, similar to those found in panic attack in terms of physiological specificity and pharmacological reactivity [55,124, ]. Dealing with PD, during the resting state, both normal [129,130] and elevated plasma and salivary cortisol levels have been described [57,131,132]. Vreeburg et al. [5] reported a significantly higher 1-hour cortisol awakening response mainly in PD patients with agoraphobia and in those with comorbid depressive disorder. Moreover, some DST abnormalities have been observed in PD subjects [51,133,134], even if a clear escape or hypersuppression after dexamethasone administration has not been demonstrated [131,135]. However, an hyperresponsivity of the HPA axis to the Dex-CRH test [51,54] and a normal response to CRH [59] have been registered by other studies. The discordancy in data concerning the HPA axis can be due to several factors that can modulate the system, as the novelty exposure, the social separation or support, or the perceived control over a challenge [55]. However, further studies are needed, as Petrowski et al. [136] showed a lack of cortisol responsivity to an acute uncontrollable stress in PD patients. HPA abnormalities can be associated with anatomical findings, as pituitary volume of PD patients seems to be smaller than that of healthy people and is believed to reflect the functional status of the gland and the inadequate hormonal response [137]. Authors speculated that the decrease in the pituitary volume might be related to the potential degenerative and progressive process of PD [137]. Moreover, this reduction seems to be more pronounced in patients with agoraphobia and it is related to the severity of symptoms and the illness duration [137]. As far as stressful life events are concerned, early traumata are known to be contributing factors to the onset of PD [7]. Safren et al. [16] found higher rates of childhood physical or sexual abuse among women with PD, than among subjects with other anxiety disorders. Moreover, childhood abuse [18] and events that lead to separation from the parents, such as death or major hospitalization of the father during childhood, being brought up by persons other than the natural parents, or long-standing illness of the child, were associated with panic disorder [7]. Furthermore, Moitra et al. [138] showed that panic symptoms worsened progressively after a stressful life event. However, traumatic life events may have a triggering function, but they are not a condicio sine qua non that supports the development of panic disorder. In fact, childhood-adolescence seems to be a sensitive period to the action of the events which contribute to modify the susceptibility to panic-related trait [139]. Thus both cumulative and specific life events ( such as threat, interpersonal and health-related events in adulthood, and abuse or loss/separation experiences in childhood) weigh upon the pathogenesis of panic disorder [140]. However, almost two thirds of PD subjects did not experience a traumatic life event and rate of life events in PD patients do not differ very much from that of other anxiety disorders [7,19]. Thus, genetic vulnerability factors, personality and behavioral characteristics, such as anxiety sensitivity, neuroticism, hypersensitivity to novelty cues and cognitive appraisal, might moderate the influence of life events on the development of panic disorder [55,140]. Stressful life events, Generalized Anxiety Disorder (GAD) and the HPA Axis Generalized anxiety disorder (GAD) is a psychiatric disorder characterized by excessive anxiety and uncontrollable worry about various life problems and circumstances that occur on the majority of days for at least 6 months [64] Environmental factors are supposed to be implicated in the onset and maintenance of this disorder and the documented first ones are negative life events, either in childhood or in adulthood. Among the identified environmental factors are natural disasters [141,142], childhood physical or sexual abuse [16], familial problems, separation or role inversion during childhood, lack of social interactions, poor life satisfaction, and modeling of a relative having an anxiety disorder [143]. Researchers noted that the occurrence of one or more negative life events, being significant and appearing in an unexpected way, was associated with an increased risk of developing GAD [143].

5 Life Events, HPA Axis and Anxiety Disorders Current Pharmaceutical Design, 2012, Vol. 18, No This finding appears to be related to anticipatory anxiety and, in fact, the same neurobiological processes that regulate anticipatory anxiety are involved in generalized anxiety disorder [25]. Moreover, referring to animal models, rodents anticipatory defensive behaviors, such as the risk assessment, seem to be related to generalized anxiety disorder [115]. However, other psychological dimensions seem to be relevant. High scores in the loss and danger dimensions of stressful life events seem to predict the onset of pure generalized anxiety syndrome [144]. Nordahl et al. [145] indicate that specific psychosocial dimensions like overprotection, parental pressures and acute life events are related to childhood GAD. Although these GAD features suggest that affected subjects perceive high levels of stress which over time could lead to an altered cortisol secretory pattern, little research to date has examined the neuroendocrine changes underlying GAD. The first analysis of the HPA axis functioning in GAD involved the use of the dexamethasone suppression test, with nonsuppression rates of 27-37%, indicating a reduced negative feedback sensitivity of the HPA axis [146,147]. More recently, Mantella et al. [61] demonstrated a 40-50% increase in basal cortisol levels of elderly individuals with GAD, compared to controls, particularly during early morning hours with higher peak cortisol levels and larger areas under the curve. Furthermore, the elevated diurnal cortisol profile is associated with greater worry and more severe GAD symptoms [61,148]. Increased levels of basal cortisol in saliva and in plasma were reported also in other studies [ ] and, in order to demonstrate that this pattern reflects a state rather than a trait of anxiety, treatment trials have been conducted. GAD patients showed reductions in anxiety symptoms and in cortisol levels after 24 weeks of cognitive behavioral therapy [150], after a successful nondrug behavioral treatment [147], following an acute and chronic diazepam treatment [149,151], and after a SSRI treatment [152]. In fact, Tafet et al. [150] reported that the cognitive therapy (CT) is effective not only in improving the distressful clinical symptoms of GAD, but also in recovering the psychoneuroendocrinological functions of these subjects: after a maximum of 24 sessions of CT, a significant decrease in the Hamilton Anxiety Rating Scale (HAM-A) and a significant decrease in the previously increased levels of circulating cortisol were observed. Moreover, Pomara et al. [149] reported reduced plasma cortisol levels, following an acute and chronic diazepam treatment, even if Klein et al. [153] did not show a significant reduction in cortisol levels after an alprazolam treatment in GAD subjects. Conversely, a number of studies have failed to show an aberrant adrenocortical activity in GAD. Rosenbaum et al. [154] found no differences between the 24-h urinary cortisol levels of GAD patients and those of a healthy control group. Similarly, no differences in plasma cortisol levels between GAD patients and healthy controls were reported later [60,62,155]. Steudte et al. [156] reported no group differences in the diurnal profiles of salivary cortisol, but lower hair cortisol levels, which provide a retrospective reflection of the cortisol secretion for a period of up to six months, were observed in GAD subjects compared to controls. Steudte hypothesized that the hypocortisolism can be due to a chronic compensatory mechanism related to an initial hypercortisolism in GAD or, vice versa, the hypocortisolism might lead to heightened anxiety awareness and enhanced elicitation of worry chains, thus promoting the development of GAD [156]. Lastly, Vreeburg et al. [5] observed that GAD patients did not show a significantly greater cortisol awakening response than controls, when comorbid depressive disorder was absent. Despite some discrepancies in the literature, most evidences suggest that GAD is associated with hypercortisolism. A conceivable explanation of this finding is that chronic stress, such as that observed during the prolonged exposure to various stressful life events, along with the inadequacy to cope with them or the perceived loss of controllability, may lead to the persistent activation of the HPA system which results in a sustained increase of cortisol levels [27]. The unremitting activation of the HPA axis is supposed to be mediated by changes in CRH or in the sensitivity or number of the CRH and/or glucocorticoid receptors at the level of the hippocampus, limbic system, and cortical levels (brain areas associated with anxiety disorders). Other factors related to the hypercortisolism can be the impaired corticosteroid receptor functioning, or the persistency of anxiety problems which induces a persistent activation of the HPA axis. Thus, it is possible that there are differences in the autoregulatory feedback of GAD and comparison subjects, due to the corticosteroid receptor performance [61]. Stressful life events, Obsessive Compulsive Disorder (OCD) and the HPA Axis A large number of studies reported that the onset of Obsessive Compulsive Disorder (OCD) is often preceded by stressful events, like increased responsibility (e.g., job promotion, birth of a child), losses (e.g., death of a family member, dismissal from employment) and traumata, such as abuse or combat [157]. Moreover, it is well documented that OCD symptoms increase under stressful situations and that patients with OCD suffer from daily life stress more than healthy controls [158]. Thus, stress and HPA axis seem to have a role in the onset and course of this disorder. However, data about the relationship between stress, HPA axis functioning and OCD are scarce and discordant [157]. Moreover, animal models for OCD (ethological models and laboratory-based genetic, pharmacological and neurobehavioral models) do not add many information as they may be used to investigate several features of OCD, but none of them provide a good model for obsessions, as opposed to compulsive behaviors [159]. Few studies examined the role of life events in OCD, but several Authors [160,161] reported that they are significantly more frequent in OCD patients. On the other hand, Grabe et al. [162] and Maina et al [163] observed no significant association of traumatic events and PTSD with OCD subjects, compared with controls. However, OCD related to stressful life events displays specific features: at first, the severity of OC symptoms seems to be directly proportional to the number of stressful life events experienced in the last six months prior to their onset [161]; second, OC symptoms are more frequently obsessions/checking and symmetry/ordering [160]. Similarly, Real et al. [164] observed that OCD associated with stressful life events is different from that unrelated to stressful life events: the former has a later onset, it is strongly associated to a history of complicated birth and to contamination/cleaning symptoms, while a family history of OCD is less frequent. As far as HPA axis is concerned, Kluge et al. [157] reported elevated nocturnal plasma cortisol and ACTH levels in OCD patients, compared to healthy controls. Monteleone et al. [165] observed a preserved but at higher level circadian rhythm of cortisol in OCD patients, significantly related to the severity of the obsessive-compulsive symptoms. Furthermore, CRH and arginine vasopressin (AVP) levels have been found significantly elevated in the cerebrospinal fluid and plasma of these patients, compared to healthy controls [166]. Data on DST are discordant, as Catapano et al. [167] observed that OCD males patients may escape the DST, while Coryell et al.[168] reported a normal suppression after 1mg Dex. Moreover, the intracerebroventricular administration of ACTH or CRH in rats prolongs the maintenance of the conditioned behaviors acquired during a period of stress (i.e., the induction of aversive stimuli, like shock and loud noises), and promotes grooming, which is considered a behavioral model for OCD [157]. In humans, the intranasal administration of vasopressin seems to narrow the focus of attention and to influence the cognitive processes, similarly to the focused-

6 6 Current Pharmaceutical Design, 2012, Vol. 18, No. 00 Faravelli et al. obsessive thoughts and the compulsive rituals of obsessivecompulsive patients [166]. Moreover, as Maina et al. [163] reported that OCD females are more likely than normal females to report postpartum events, a subsequent study [169] observed that postpartum women with OCD had a marginally greater cortisol stress response to a psychosocial task compared to healthy post-partum women, associated with a distinct brain activation pattern involving the orbitofrontal and temporal cortices. Accordingly, structural neuroimaging studies on OCD patients observed dysfunctions in the anterior cingulated gyrus, which is known to be involved in the regulation of the HPA axis [170]. Stressful Life Events, Social Phobia (SP) and the HPA Axis According to the hypothesis that Social Phobia (SP) (together with other anxiety disorders) may represent a stress-related condition, hyperactivity of the HPA axis has been considered the linkage between stressful events and the onset and the development of this disorder [10,12]. Several data reported a normal basal HPA axis functioning in adult social phobics [63,171,172]. Nonetheless, a recent study reported that mean basal morning plasma cortisol levels were significantly lower in patients with SP than in healthy control subjects, and observed a significant correlation between cortisol plasma levels and trait but not state anxiety scores [173]. Concerning the reactivity of the HPA axis to stress in SP, a recent investigation by Roelofs et al. [174] provided the first evidence for a direct link between the increased cortisol stressresponsiveness and social avoidance behavior in SP patients. During a social approach-avoidance task (the Trier Social Stress Test), social phobics showed enhanced cortisol responses compared to healthy participants and PTSD patients. Moreover, an elicited social stress increased the avoidance tendencies toward the social threat stimuli in SP patients and this behavior was predicted by cortisol responses [174]. The hyper-responsiveness of the adrenal cortex during the psychosocial stressor and the similar basal levels of cortisol with respects to controls were confirmed also by Condren et al. [53]. Nonetheless, overall research on the HPA axis hyperactivity after a stress test produced conflicting results. Levin et al. [175] found decreased plasma cortisol levels in response to a public speaking task, both in adult patients with SP and normal controls. Furlan et al. [176] reported that SP patients display a bimodal salivary cortisol response and a larger increase in salivary cortisol levels following a speech task, but found no difference between patients and normal subjects under physical stress or in basal conditions. Studying SP in children and adolescents can help in clarifying findings on the possible role of a HPA axis dysfunction [ ]. Martel et al. [177] observed similar salivary cortisol levels in social phobic adolescent girls and controls, in response to a modified Trier Social Stress Test (TSST), even if cortisol levels appeared to be a sensitive measure of anticipatory anxiety prior to the performance task in both groups. These findings were partly confirmed by a recent study by Krämer et al. [179], in which a group of forty-one 12-year-old children with SP showed heightened reactivity to a modified TSST on subjective anxiety compared to controls, but not a heightened salivary cortisol response. On the opposite, van West et al. [178] reported that prepubertal subjects with social anxiety show elevated salivary cortisol response to a psychosocial stressor. Stating that shyness, separation anxiety disorder (SAD) and behavioral inhibition (BI) have been postulated to be the precursors of SP [181], high cortisol levels have been reported in shy children and adults [38,182], in children suffering from SAD [183], and in children with BI [180,184]. Some Authors hypothesized that the increased CRH and cortisol levels of these children can exacerbate their fearfulness and can predispose them to develop social phobia [182]. Moreover, cortisol responses predicted the increase in social avoidance tendencies during stress and these findings are consistent with those derived from animal models of avoidance and behavioral inhibition in social situations [185,186]. Russ et al. [180] reported an HPA axis disrupted activity in response to a universal social stressor (starting school) in two groups of female children: one with social phobia and one with no history of anxiety. Child behavioral inhibition at 14 months was also assessed in order to explore the influence of early temperament on the later stress responses. All children provided salivary cortisol samples at three times surrounding the school start. Both children suffering from SP and healthy controls displayed an elevation from baseline in morning and afternoon cortisol, during the first week at school, which remained elevated until the end of the first term. However, SP children also displayed an equivalent elevation in bedtime cortisol, which was not observed for comparison children. Moreover, SP children classified as inhibited at 14 months displayed significantly higher afternoon cortisol levels overall. Several studies suggested that negative social events may be a particularly prevalent environmental stress component implicated in the onset of social phobia [13,16,28, ]. In particular, sexual and/or physical abuse represent important risk factors for the development of this disorder [12,13,190]. In fact, Elzinga et al. [191] reported a significant association between the history of childhood abuse and a greatly enhanced cortisol reactivity to a psychosocial stress task in patients with SP, even if any differences in baseline cortisol levels were reported between SP patients, PTSD patients and healthy controls. However, other stressful life events, like separation from parents, parents marital discord, sexual/physical/emotional abuse, familial violence, childhood illnesses, bullying, as well as dysfunctional parental rearing practices (i.e. overprotection, overcontrol, rejection, neglect) and behavioral patterns (as those facilitated by a family history of psychiatric disorders, especially of anxiety disorders, depression and suicidality), are believed to play a role in the onset of SP and to increase the severity of social phobic symptoms [13,16,28,189,190,192]. These data are in line with the existing diatheses-stress and maintenance models for social anxiety disorder [11,192,193]. These models include biological, psychological and environmental factors, where a predisposition to a disorder (diathesis) and the environmental disturbances (stress) may lead to a clinical social anxiety disorder. The predisposition seems to be related to genetic and temperament factors, cognitive aspects, parent-child interactions and adverse early environments, together with societal and cultural influences [192]. DISCUSSION A large body of studies reports that men and women recently or chronically exposed to high levels of stress are at higher risk of experiencing mental health problems [11,12,14,15,34,60]. The exposure to stressors was found to be associated to a common pattern of up-regulated diurnal cortisol secretion in persons with anxiety disorders, suggesting a stable trait across disorders [5,60]. Animal models seem to confirm that stressful life events, especially early life events, may provoke dysfunctions in the CNS [36] and an alteration of the stress response that endures during adulthood [45]. Data concerning the relationship between childhood and adulthood life events, HPA axis and anxiety disorders have been reviewed. Patients with PTSD show high baseline CRH levels and low plasma cortisol levels, maybe due to a physiological adaptation of the HPA axis to chronic stress [72] (after an initial hypersecretion of CRH due to the early life stress [12,28] and to the persistent

7 Life Events, HPA Axis and Anxiety Disorders Current Pharmaceutical Design, 2012, Vol. 18, No intrusive nature of the memories and the continued sense of threat [72]). Other hypotheses about the enhanced cortisol suppression in PTSD have been illustrated: activation of different corticolimbic pathways under a psychosocial, rather than a chemical stressor [12]; higher availability of glucocorticoid receptors on pituitary cells [92,114]; an insufficient pituitary and/or adrenal response to central stimulation, or a reduced sensitivity in response to low cortisol levels [114]; an enhanced bioavailability of dexamethasone or an inadequate vasopressin reaction to a low dose dexamethasone administration [114]. Literature on the HPA axis functioning in PD subjects is inconclusive, as well, even if several Authors reported increased HPA axis activity in these patients [5,57,58,120,123,129,131,132]. In order to explain these findings, it could be hypothesized that HPA axis abnormalities of PD patients might all be due to an arousal in reaction to novelty cues and to anticipatory anxiety, that afterwards normalizes because of a successful habituation to the repeated experiences of panic [55,122]. Moreover, traumatic life events are known to be contributing factors to PD onset [7,16,18,138], but other factors, such as genetic vulnerability factors, personality and behavioral characteristics, such as anxiety sensitivity, neuroticism, and cognitive appraisal, and recent life events might moderate the influence of childhood and adult life events on the development of panic [55,140]. Different studies suggest that GAD is associated with hypercortisolism, maybe due to the chronic stress, related to the inadequacy to cope with it or the perceived loss of controllability [27]. The lack of downregulation of the system may be related to the changes in the sensitivity or in the number of CRH and/or glucocorticoid receptors of the hippocampus, limbic system, and cortical levels (which are brain areas associated with anxiety disorders) [61]. Moreover, both early childhood trauma and recent life events seem to be implicated in the onset and maintenance of GAD [ ]. Obsessive-compulsive disordered subjects show an hyperactivity of the HPA axis, but the increased hormonal levels might be a consequence of stress [15], or vice versa they might be involved in the pathophysiology of OCD, sustaining clinical features like perseverative or grooming behaviors [157]. Discordant data have been reported on the association between life events and OCD [ ], but stress-related OCD display more severe symptoms [158,161] and usually they are obsessions/checking and symmetry/ordering [160]. Social phobia patients show both an hyper-responsiveness of the adrenal cortex [174,176,178] and an higher frequency of childhood traumata and environmental stress [12,13,16,28, ]. Moreover, a link between childhood traumata and HPA axis reactivity in social phobics [191] seems to exist and it sustains the hypothesis of SP as a stress-related condition, where HPA axis hyperactivity links stressful events to the development of SP [5,10]. To our knowledge, specific literature on the relationship between the HPA axis functioning and simple phobias is poor. In fact, Risbrough and Stein [22] investigated simple phobias only with other phobic disorders (i.e., social phobia, agoraphobia). Thus, this disorder has not been analyzed in the present manuscript. In summary, feeling highly and persistently stressed, anxious subjects show a state of chronically stress-induced adrenal hyperreactivity and persistently elevated cortisol concentrations. This may induce an habituation phenomena, with a downregulation of the HPA axis responsiveness to stress, reflecting the resilience rather than the risk of psychopathology [8,33]. Conversely, the long-term exposure to elevated cortisol levels could result in damage to the hippocampal glucocorticoid receptors or even loss of hippocampal neurons [112], reducing the negative feedback of CRH secretion and resulting in higher CRH and cortisol concentrations [148]. CONCLUSION The large existing literature on the relationships between HPA axis activity and anxiety disorders is inconclusive, as some studies have found higher basal cortisol levels whereas others have found normal concentrations, in the different diagnostic subgroups [57-63]. Several hypothesis attempt to explain these findings: 1) Comorbidity with depression induces alterations of the HPA axis, which otherwise would be not relevant. In fact, Vreeburg et al. [5] observed that a modest but significantly higher 1- hour cortisol awakening response among anxiety patients was driven mainly by those with comorbid depression. Similar data were reported by de Kloet et al. [106] and Young and Breslau [105]. On the other hand, Catapano et al. [167] observed that OCD male patients may escape the DST independently from the coexistence of depressive features. 2) HPA axis dysregulation represents a state rather than a trait effect. Vreeburg et al. [5] reported that remitted anxiety disorder patients showed only borderline significant cortisol levels, while current anxious subjects had higher cortisol levels, as well as a trend toward a higher increase within the hour after awakening. This difference can indicate that the HPA axis dysregulation may be state dependent in anxiety disorder. Moreover, several Authors observed a normalization of the HPA axis of panic patients after treatment [55] and a cognitive/emotional modulation of the HPA axis abnormalities, thus suggesting a state, rather than a trait, condition. On the other hand, Chaudieu et al. [60] and Lanzenberger et al. [173] observed altered cortisol secretion in anxiety subjects, regardless of diagnostic subtype, suggesting a stable trait. 3) HPA axis dysregulation is not specific to any of the anxiety disorders, but rather it is a general feature. For instance, Vreeburg et al. [5] found that independently of the presence of comorbid depression especially panic disorder with agoraphobia was associated with an increased cortisol awakening response, while PD, GAD, and social phobia were not as much associated. Graeff [4] reported that while anticipatory anxiety and generalized anxiety disorder activate both the HPA and the sympathoadrenal axes, panic attack causes major sympathetic activation, but has little effect on the HPA axis. Chaudieu et al. [60] observed a common pattern of up-regulated diurnal cortisol secretion in anxious subjects with lifetime and current anxiety disorder irrespective of sub-type (generalized anxiety, phobias), and a common "core" across disorders. Pfeffer et al. [32] reported that bereaved children with PTSD had significantly lower 4:00 pm baseline cortisol and significantly greater 4:00 pm cortisol suppression; while those with generalized anxiety disorder had significantly less morning cortisol suppression, compared with bereaved children without psychopathology. 4) Exacerbation of affective or anxiety symptoms in adulthood may depend on additive factors, including genetic vulnerability, temperament and recent life stress [10]. In summary, stress exposure during a crucial developmental time period, being not specific of any psychiatric disorder, may induce a biological vulnerability, in particular an HPA axis dysregulation, that in addition with other factors (comorbidity, recent life events, temperament, genetic vulnerability factors, personality and behavioral characteristics, such as anxiety sensitivity, neuroticism, and cognitive appraisal) might moderate the influence of new life events on the development of symptoms of depression and anxiety [8,10,16,23,33,34,38,73,111,139,140]. The neuroendocrine alterations can result in a biological wound that increases the individual s vulnerability to stressors later in life, predisposing an individual to develop mood or anxiety disorders, that are known to develop or worsen in relation to acute or chronic life stress [6,10,12,16,189]. In fact, once HPA axis is