Behavioral control, the medial prefrontal cortex, and resilience

Identification of chronic stress-activated regions reveals a potential recruited circuit in rat brain

Chronic stress induces presynaptic and postsynaptic modifications in the paraventricular nucleus of the hypothalamus that are consistent with enhanced excitatory hypothalamo-pituitary-adrenocortical (HPA) axis drive. The brain regions mediating these molecular modifications are not known. We hypothesized that chronic variable stress (CVS) tonically activates stress-excitatory regions that interact with the paraventricular nucleus of the hypothalamus, culminating in stress facilitation. In order to identify chronically activated brain regions, ΔFosB, a documented marker of tonic neuronal activation, was assessed in known stress regulatory limbic and brainstem sites. Four experimental groups were included: CVS, repeated restraint (RR) (control for HPA habituation), animals weight-matched (WM) to CVS animals (control for changes in circulating metabolic factors due to reduced weight gain), and non-handled controls. CVS, (but not RR or WM) induced adrenal hypertrophy, indicating that sustained HPA axis drive only occurred in the CVS group. CVS (but not RR or WM) selectively increased the number of FosB/ΔFosB nuclei in the nucleus of the solitary tract, posterior hypothalamic nucleus, and both the infralimbic and prelimbic divisions of the medial prefrontal cortex, indicating an involvement of these regions in chronic drive of the HPA axis. Increases in FosB/ΔFosB-immunoreactive cells were observed following both RR and CVS in the other regions (e.g. the dorsomedial hypothalamus), suggesting activation by both habituating and non-habituating stress conditions. The data suggest that unpredictable stress uniquely activates interconnected cortical, hypothalamic, and brainstem nuclei, potentially revealing the existence of a recruited circuitry mediating chronic drive of brain stress effector systems.

Short- and long-term consequences of stressor controllability in adolescent rats

Adolescence is a developmental period in which brain structures involved with stress responses, such as the medial pre-frontal cortex (mPFC), mature. Therefore, exposure to a stressor at this time may have effects that endure the lifespan. The goal of the present study was to determine whether behavioral control over an adolescent stressor mitigates the behavioral and neurochemical consequences of the stressor as occurs in adult rats. Adolescent rats (post natal day 35) were exposed to either inescapable (IS) or escapable tailshocks (ES). As in adults we observed a "stressor controllability effect"; IS reduced social exploration and activated the serotonergic dorsal raphé nucleus while ES did not. Excitotoxic lesions of the medial prefrontal cortex prevented the stressor controllability effect. We also demonstrate that a controllable adolescent stress prevents the behavioral and neurochemical consequences of IS in adulthood. Thus, the controllability of a stressor during adolescence is an important psychological factor.

A meta-analysis of heart rate variability and neuroimaging studies: implications for heart rate variability as a marker of stress and health

The intimate connection between the brain and the heart was enunciated by Claude Bernard over 150 years ago. In our neurovisceral integration model we have tried to build on this pioneering work. In the present paper we further elaborate our model and update it with recent results. Specifically, we performed a meta-analysis of recent neuroimaging studies on the relationship between heart rate variability and regional cerebral blood flow. We identified a number of regions, including the amygdala and ventromedial prefrontal cortex, in which significant associations across studies were found. We further propose that the default response to uncertainty is the threat response and may be related to the well known negativity bias. Heart rate variability may provide an index of how strongly 'top-down' appraisals, mediated by cortical-subcortical pathways, shape brainstem activity and autonomic responses in the body. If the default response to uncertainty is the threat response, as we propose here, contextual information represented in 'appraisal' systems may be necessary to overcome this bias during daily life. Thus, HRV may serve as a proxy for 'vertical integration' of the brain mechanisms that guide flexible control over behavior with peripheral physiology, and as such provides an important window into understanding stress and health.

Beyond Depression: Towards a Process-Based Approach to Research, Diagnosis, and Treatment

Despite decades of research on the etiology and treatment of depression, a significant proportion of the population is affected by the disorder, fails to respond to treatment and is plagued by relapse. Six prominent scientists, Aaron Beck, Richard Davidson, Fritz Henn, Steven Maier, Helen Mayberg, and Martin Seligman, gathered to discuss the current state of scientific knowledge on depression, and in particular on the basic neurobiological and psychopathological processes at play in the disorder. These general themes were addressed: 1) the relevance of learned helplessness as a basic process involved in the development of depression; 2) the limitations of our current taxonomy of psychological disorders; 3) the need to work towards a psychobiological process-based taxonomy; and 4) the clinical implications of implementing such a process-based taxonomy.

Glutamatergic input is selectively increased in dorsal raphe subfield 5-HT neurons: role of morphology, topography and selective innervation

Characterization of glutamatergic input to dorsal raphe (DR) serotonin (5-HT) neurons is crucial for understanding how the glutamate and 5-HT systems interact in psychiatric disorders. Markers of glutamatergic terminals, vGlut1, 2 and 3, reflect inputs from specific forebrain and midbrain regions. Punctate staining of vGlut2 was homogeneous throughout the mouse DR whereas vGlut1 and vGlut3 puncta were less dense in the lateral wing (lwDR) compared with the ventromedial (vmDR) subregion. The distribution of glutamate terminals was consistent with the lower miniature excitatory postsynaptic current frequency found in the lwDR; however, it was not predictive of glutamatergic synaptic input with local activity intact, as spontaneous excitatory postsynaptic current (sEPSC) frequency was higher in the lwDR. We examined the morphology of recorded cells to determine if variations in dendrite structure contributed to differences in synaptic input. Although lwDR neurons had longer, more complex dendrites than vmDR neurons, glutamatergic input was not correlated with dendrite length in the lwDR, suggesting that dendrite length did not contribute to subregional differences in sEPSC frequency. Overall, glutamatergic input in the DR was the result of selective innervation of subpopulations of 5-HT neurons and was rooted in the topography of DR neurons and the activity of glutamate neurons located within the midbrain slice. Increased glutamatergic input to lwDR cells potentially synergizes with previously reported increased intrinsic excitability of lwDR cells to increase 5-HT output in lwDR target regions. Because the vmDR and lwDR are involved in unique circuits, subregional differences in glutamate modulation may result in diverse effects on 5-HT output in stress-related psychopathology.

NMDA receptor blockade alters stress-induced dendritic remodeling in medial prefrontal cortex

The development and relapse of many psychopathologies can be linked to both stress and prefrontal cortex dysfunction. Glucocorticoid stress hormones target medial prefrontal cortex (mPFC) and either chronic stress or chronic administration of glucocorticoids produces dendritic remodeling in prefrontal pyramidal neurons. Exposure to stress also causes an increase in the release of the excitatory amino acid glutamate, which binds to N-methyl-D-aspartate (NMDA) receptors, which are plentiful in mPFC. NMDA receptor activation is crucial for producing hippocampal dendritic remodeling due to stress and for dendritic reorganization in frontal cortex after cholinergic deafferentation. Thus, NMDA receptors could mediate stress-induced dendritic retraction in mPFC. To test this hypothesis, dendritic morphology of pyramidal cells in mPFC was assessed after blocking NMDA receptors with the competitive NMDA antagonist ±3-(2-carboxypiperazin-4yl)propyl-1-phosphonic acid (CPP) during restraint stress. Administration of CPP prevented stress-induced dendritic atrophy. Instead, CPP-injected stressed rats showed hypertrophy of apical dendrites compared with controls. These results suggest that NMDA activation is crucial for stress-induced dendritic atrophy in mPFC. Furthermore, NMDA receptor blockade uncovers a new pattern of stress-induced dendritic changes, suggesting that other neurohormonal changes in concert with NMDA receptor activation underlie the net dendritic retraction seen after chronic stress.

Recovery after chronic stress within spatial reference and working memory domains: correspondence with hippocampal morphology

Chronic stress results in reversible spatial learning impairments in the Morris water maze that correspond with hippocampal CA3 dendritic retraction in male rats. Whether chronic stress impacts different types of memory domains, and whether these can similarly recover, is unknown. This study assessed the effects of chronic stress with and without a post-stress delay to evaluate learning and memory deficits within two memory domains, reference and working memory, in the radial arm water maze (RAWM). Three groups of 5-month-old male Sprague-Dawley rats were either not stressed [control (CON)], or restrained (6 h/day for 21 days) and then tested on the RAWM either on the next day [stress immediate (STR-IMM)] or following a 21-day delay [stress delay (STR-DEL)]. Although the groups learned the RAWM task similarly, groups differed in their 24-h retention trial assessment. Specifically, the STR-IMM group made more errors within both the spatial reference and working memory domains, and these deficits corresponded with a reduction in apical branch points and length of hippocampal CA3 dendrites. In contrast, the STR-DEL group showed significantly fewer errors in both the reference and working memory domains than the STR-IMM group. Moreover, the STR-DEL group showed better RAWM performance in the reference memory domain than did the CON group, and this corresponded with restored CA3 dendritic complexity, revealing long-term enhancing actions of chronic stress. These results indicate that chronic stress-induced spatial working and reference memory impairments, and CA3 dendritic retraction, are reversible, with chronic stress having lasting effects that can benefit spatial reference memory, but with these lasting beneficial effects being independent of CA3 dendritic complexity.

Effects of stress across the lifespan

Stress is a known precipitant for metabolic and neurological diseases, with sensitive periods identified across the developmental continuum from conception to old age. However, the effects of stress may vary depending on the point or points along the developmental trajectory when adversity strikes. Past research has emphasized the consequences of stress on fully developed physiological systems in the brain and periphery, but more recent studies have explored the impact of stress on systems at different stages of maturation, with differential effects being revealed. This review provides an overview of the diverse effects of stress at critical developmental stages and the potential outcomes that may be associated with experiencing environmental adversity during ontogeny.

Distinct behavioral consequences of stress models of depression in the elevated T-maze

Animals exposed to inescapable stress develop behavioral consequences that are similar to symptoms of depression. Therefore, most of the animal models of depression are based on animal exposure to such stressors. The stress-induced behavioral consequences induced by pre-exposure to shock in the learned helplessness model of depression have been proposed to be a consequence of excessive activation of fear/anxiety related structures which would lead to inhibitory avoidance and impaired escape performance. However, this hypothesis has not yet been investigated in a test that is able to generate these different defense strategies in a same rat, such as the elevated T-maze (ETM). Therefore, the objective of the present study was to test the effects of footshock pre-exposure (inescapable-IS or escapable-ES) on both inhibitory avoidance and escape responses of rats submitted to the ETM 24 h later. Moreover, since it is not known whether these effects would be a common feature to other inescapable stressors used as animal models of depression, we have also investigated the behavior of rats previously exposed to forced swimming or restraint. All stressed groups displayed anxiogenic-like behavior when compared to control groups (non-stressed), evidenced by facilitated acquisition of inhibitory avoidance in the ETM. However, only rats exposed to IS showed impaired escape performance. These results support the hypothesis that the facilitated inhibitory avoidance is a common behavioral consequence of distinct stressful stimuli. However, the impaired escape response is likely to be particularly involved in the mediation of the helpless behavior observed in rats pre-exposed to IS. The neurobiological mechanisms involved in these responses are discussed in the manuscript.

Cannabinoids and emotionality: a neuroanatomical perspective

The endocannabinoid system has recently emerged as a promising therapeutic target for the treatment of stress-related emotional disorders. A growing literature base has collectively demonstrated that facilitation of endocannabinoid signaling promotes antidepressant- and anxiolytic-like responses in preclinical animal models, while disruption of this system profoundly affects emotion, cognition, and neuroendocrine functioning. Although these findings are encouraging, the role of endocannabinoid signaling within discrete corticolimbic brain structures is considerably complex. Consequently, researchers have recently shifted focus to examining the effects of local cannabinoid manipulations on emotion from a neuroanatomical standpoint. This review provides an overview of the site-specific effects of cannabinergic compounds in preclinical tests of emotionality, as well as the alterations in endocannabinoid signaling observed in animal models of depression. Broadly speaking, these studies indicate that CB(1) receptors in the medial prefrontal cortex and ventral hippocampus appear to be responsible for the antidepressant- and anxiolytic-like phenotype elicited by systemic CB(1) receptor agonists, which parallels biochemical studies showing that endocannabinoids are downregulated in these two regions following exposure to chronic stress. Conversely, CB(1) receptor activation within distinct amygdalar nuclei yields opposing effects on emotional behavior, such that local stimulation of CB(1) receptors in the basolateral amygdala and central amygdala promoting anxiogenesis and anxiolysis, respectively. Moreover, a series of elegant studies has revealed that cannabinoid transmission in the basolateral amygdala strongly modulates the acquisition and processing of associative fear memory via interactions with the medial prefrontal cortex. Given the crucial role of this corticolimbic network in regulating emotional behavior, it is palpable that alterations in endocannabinoid signaling within any of these structures could have profound implications for the pathophysiological development of affective illnesses. Accordingly, local pharmacological augmentation of endocannabinoid signaling within discrete corticolimbic subregions may serve as a promising therapeutic strategy for the treatment of these debilitating disorders.

Collateralized dorsal raphe nucleus projections: a mechanism for the integration of diverse functions during stress

The midbrain dorsal raphe nucleus (DR) is the origin of the central serotonin (5-HT) system, a key neurotransmitter system that has been implicated in the expression of normal behaviors and in diverse psychiatric disorders, particularly affective disorders such as depression and anxiety. One link between the DR-5-HT system and affective disorders is exposure to stressors. Stress is a major risk factor for affective disorders, and stressors alter activity of DR neurons in an anatomically specific manner. Stress-induced changes in DR neuronal activity are transmitted to targets of the DR via ascending serotonergic projections, many of which collateralize to innervate multiple brain regions. Indeed, the collateralization of DR efferents allows for the coordination of diverse components of the stress response. This review will summarize our current understanding of the organization of the ascending DR system and its collateral projections. Using the neuropeptide corticotropin-releasing factor (CRF) system as an example of a stress-related initiator of DR activity, we will discuss how topographic specificity of afferent regulation of ascending DR circuits serves to coordinate activity in functionally diverse target regions under appropriate conditions.

Genetic, pharmacological and lesion analyses reveal a selective role for corticohippocampal GLUN2B in a novel repeated swim stress paradigm

Glutamate and N-methyl-d-aspartate receptor (NMDAR) dysfunction is strongly implicated in the pathophysiology of mood and anxiety disorders. Treatment with NMDAR antagonists has antidepressant efficacy in treatment-resistant depressives. In preclinical rodent models, NMDAR antagonist administration reduces anxiety- and stress-related behaviors in concert with increases in prefrontal cortical (PFC) dendritic spinogenesis and synaptic proteins. While these effects have been attributed to actions at the NMDAR GluN2B subunit, the precise role of cortical GluN2B in mediating emotional behaviors and stress-responsivity is not fully understood. Here, we employed a novel mutant model in which the GluN2B subunit is postnatally deleted in principal neurons in the cortex and the dorsal CA1 subregion of the hippocampus. GluN2BKO mice were phenotyped on a battery of tests for anxiety-related (light/dark exploration, stress-induced hyperthermia) and antidepressant-sensitive (sucrose preference, novelty-induced hypophagia, single-trial forced swim) behaviors. A novel repeated inescapable forced swim paradigm (riFS) was developed to assess behavioral responses to repeated stress in the GluN2BKO mice. For comparison, non-mutant C57BL/6J mice were tested for single-trial forced swim behavior after systemic Ro 25-6981 treatment and for riFS behavior after lesions of the ventromedial prefrontal cortex. riFS-induced alterations in corticolimbic GluN2B expression were also examined in C57BL/6J mice. We found that GluN2BKO mice reduced "despair-like" behavior in the riFS procedure, as compared to GluN2BFLOX controls. By contrast, GluN2BKO mice showed minimal alterations on anxiety-like or antidepressant-sensitive assays, including the single-trial forced swim test. In C57BL/6J mice, induction of "despair-like" responses in the riFS test was attenuated by vmPFC lesions, and was associated with changes in limbic GluN2B expression. Collectively, these data suggest that cortical GluN2B plays a major role in modulating adaptive responses to stress. Current findings provide further support for GluN2B as a key mechanism underlying stress responsivity, and a novel pharmacotherapeutic target for stress-related neuropsychiatric disorders.

The importance of serotonin for orbitofrontal function

The orbitofrontal cortex (OFC) receives a dense serotonin (5-hydroxytryptamine, or 5-HT) innervation from the dorsal raphe nucleus, with a smaller contribution from the median raphe nucleus. The reciprocal innervation from the OFC enables the OFC to regulate not only its own 5-HT input but the 5-HT input to the rest of the forebrain. This article reviews the evidence from studies in rodents and primates that implicate 5-HT in the OFC in the ability of animals to adapt their responding to changes in reward contingencies in the environment. A consensus is emerging that reductions in orbitofrontal 5-HT, whether the result of localized infusions of 5,7-dihydroxytryptamine (5,7-DHT), peripheral treatment with parachloroamphetamine (PCA) or para-chlorophenylalanine (PCPA), or chronic cold stress impairs this ability. Genetic variation in the 5-HT transporter can also affect this ability. An explanation regarding insensitivity to reward loss is ruled out by the finding that marmosets with 5-HT reductions in the OFC display a decline of responding as rapid as that of control animals when reward is withheld during extinction of a two-pattern discrimination task. The failure of these same animals to explore alternative stimuli during extinction, along with the recent electrophysiological evidence that dorsal raphe nucleus neurons encode future motivational outcomes, implicates orbitofrontal 5-HT in the process by which animals either exploit current resources or explore alternative resources based on current reward expectations.

Effects of stressor predictability and controllability on sleep, temperature, and fear behavior in mice

STUDY OBJECTIVES

Predictability and controllability are important factors in the persisting effects of stress. We trained mice with signaled, escapable shock (SES) and with signaled, inescapable shock (SIS) to determine whether shock predictability can be a significant factor in the effects of stress on sleep.

DESIGN

Male BALB/cJ mice were implanted with transmitters for recording EEG, activity, and temperature via telemetry. After recovery from surgery, baseline sleep recordings were obtained for 2 days. The mice were then randomly assigned to SES (n = 9) and yoked SIS (n = 9) conditions. The mice were presented cues (90 dB, 2 kHz tones) that started 5.0 sec prior to and co-terminated with footshocks (0.5 mA; 5.0 sec maximum duration). SES mice always received shock but could terminate it by moving to the non-occupied chamber in a shuttlebox. SIS mice received identical tones and shocks, but could not alter shock duration. Twenty cue-shock pairings (1.0-min interstimulus intervals) were presented on 2 days (ST1 and ST2). Seven days after ST2, SES and SIS mice, in their home cages, were presented with cues identical to those presented during ST1 and ST2.

SETTING

NA.

PATIENTS OR PARTICIPANTS

NA.

INTERVENTIONS

NA.

MEASUREMENTS AND RESULTS

On each training and test day, EEG, activity and temperature were recorded for 20 hours. Freezing was scored in response to the cue alone. Compared to SIS mice, SES mice showed significantly increased REM after ST1 and ST2. Compared to SES mice, SIS mice showed significantly increased NREM after ST1 and ST2. Both groups showed reduced REM in response to cue presentation alone. Both groups showed similar stress-induced increases in temperature and freezing in response to the cue alone.

CONCLUSIONS

These findings indicate that predictability (modeled by signaled shock) can play a significant role in the effects of stress on sleep.

Alterations in corticolimbic dendritic morphology and emotional behavior in cannabinoid CB1 receptor-deficient mice parallel the effects of chronic stress

Many changes produced by chronic stress are similar to those seen in cannabinoid CB(1) receptor-deficient mice. In the current study, we examined both anxiety-like behavior and dendritic complexity within the prefrontal cortex and basolateral amygdala (BLA) in wild-type and CB(1) receptor-deficient mice, under basal conditions and following exposure to 21 days of protracted restraint stress. CB(1) receptor-deficient mice exhibited increased indices of anxiety in the elevated plus maze under basal conditions that were similar in magnitude to changes seen in wild-type mice exposed to chronic stress. Chronic stress or deletion of the CB(1) receptor also produced a reduction in both apical dendritic length and branch points of neurons within layer II/III of the prelimbic region of the prefrontal cortex. Pyramidal neurons in the (BLA) of CB(1) receptor-deficient mice were found to have increased dendritic length compared with wild type. Chronic stress increased dendritic length of these amygdalar neurons in both wild-type and CB(1) receptor-deficient mice. Collectively, these data demonstrate that loss of cannabinoid CB(1) receptor signaling produces a chronic stress-like phenotype under basal conditions and provide a putative neural substrate that may subserve the changes in emotional behavior seen following disruption of CB(1) receptor signaling.

Born to choose: the origins and value of the need for control

Belief in one's ability to exert control over the environment and to produce desired results is essential for an individual's wellbeing. It has repeatedly been argued that perception of control is not only desirable, but is also probably a psychological and biological necessity. In this article, we review the literature supporting this claim and present evidence of a biological basis for the need for control and for choice-that is, the means by which we exercise control over the environment. Converging evidence from animal research, clinical studies and neuroimaging suggests that the need for control is a biological imperative for survival, and a corticostriatal network is implicated as the neural substrate of this adaptive behavior.

Activation of the infralimbic cortex in a fear context enhances extinction learning

Activation of the infralimbic region (IL) of the medial prefrontal cortex (mPFC) reduces conditioned fear in a variety of situations, and the IL is thought to play an important role in the extinction of conditioned fear. Here we report a series of experiments using contextual fear conditioning in which the IL is activated with the GABAa antagonist picrotoxin (Ptx) during a single extinction session in the fear context. We investigate the impact of this manipulation on subsequent extinction sessions in which Ptx is no longer present. First, we demonstrate that a single treatment with intra-IL Ptx administered in a conditioned fear context greatly accelerates the rate of extinction on the following days. Importantly, IL-Ptx also enhances extinction to a different fear context than the one in which IL-Ptx was administered. Thus, IL-Ptx primes extinction learning regardless of the fear context in which the IL was initially activated. Second, activation of the IL must occur in conjunction with a fear context in order to enhance extinction; the extinction enhancing effect is not observable if IL-Ptx is administered in a neutral context. Finally, this extinction enhancing effect is specific to the IL for it does not occur if Ptx is injected into the prelimbic region (PL) of the mPFC. The results indicate a novel persisting control of fear induced by activation of the IL and suggest that IL activation induces changes in extinction-related circuitry that prime extinction learning.

Born to choose: the origins and value of the need for control

Belief in one's ability to exert control over the environment and to produce desired results is essential for an individual's wellbeing. It has repeatedly been argued that perception of control is not only desirable, but is also probably a psychological and biological necessity. In this article, we review the literature supporting this claim and present evidence of a biological basis for the need for control and for choice-that is, the means by which we exercise control over the environment. Converging evidence from animal research, clinical studies and neuroimaging suggests that the need for control is a biological imperative for survival, and a corticostriatal network is implicated as the neural substrate of this adaptive behavior.

Susceptibility to stress in transgenic mice overexpressing TrkC, a model of panic disorder

Stressful life events increase the susceptibility for subsequent onset of psychiatric disorders in humans. Previous research has implicated neurotrophins in the onset of some stress-related diseases, such as major depression disorder, post-traumatic stress disorder or panic disorder. We have tested the hypothesis that the neurotrophin-3 (NT-3)/TrkC system is a genetic interface mediating the deleterious effects of stress on the initiation of panic disorder and other pathologies. To this aim, we have analyzed the functionality of HPA axis and the behavioral consequences of different types of stressful conditions in a mouse model of panic disorder, which overexpresses TrkC, the high affinity-receptor for NT-3 (TgNTRK3). Our results reveal that TgNTRK3 mice exhibit an altered circadian corticosterone rhythm that is reversed by clonidine treatment, but normal expression of genes involved in the control of the hypothalamus-pituitary-adrenal (HPA) axis (CRH, GR) and normal corticosterone response to acute and chronic stressors. In contrast, they exhibit an altered pattern of activation of stress-related brain areas and showed enhanced anxiety-related behavior and more passive strategies than wild types under some chronic stress conditions. We conclude that TgNTRK3 mice present differences in their response to stress characterized by subtle changes in the HPA axis, marked changes in acute stress-induced brain activation and altered coping strategies, suggesting a key role of TrkC receptor in the stress neural circuitry and in the behavioral consequences of chronic stress.

Medial prefrontal cortex damage affects physiological and psychological stress responses differently in men and women

The ability to produce appropriate physiological and psychological responses to stressful situations depends on accurate recognition and appraisal of such situations. Such ability is also important for proper emotion regulation. A number of studies have suggested that the medial prefrontal cortex (mPFC) plays a significant role in emotion regulation, as well as in the control of physiological endpoints of emotion regulation such as the hypothalamic-pituitary-adrenal (HPA) axis and autonomic nervous system (ANS). Further, recent work has suggested that men and women may differ in these mechanisms of neural control of emotion regulation. Here, we examined the role of the human mPFC in self-report, ANS, and HPA stress reactivity by testing a group of participants with damage to this region (9 women and 9 men), a brain damaged comparison group (6 women and 6 men), and healthy comparison participants (27 women and 27 men) on an orthostatic challenge and the Trier Social Stress Test (TSST). The mPFC participants showed heightened self-reported stress in response to the TSST. In women, mPFC damage led to an increased cortisol response to the TSST. By contrast, in men, greater volume of mPFC damage was correlated with a decreased cortisol response. Finally, men with mPFC damage showed altered autonomic control of the heart (higher heart rate and lower high frequency heart rate variability) during an orthostatic challenge. These findings support the idea that the mPFC is involved in the regulation of physiological and psychological responses to stress and that this regulation may differ between men and women.

The mechanism of life-threatening water imbalance in schizophrenia and its relationship to the underlying psychiatric illness

Impaired water excretion was noted to coincide with psychotic exacerbations in the first decades of the past century. In the ensuing decades, life-threatening water intoxication and elevated plasma levels of the antidiuretic hormone, arginine vasopressin (AVP) were reported in a subset of persons with schizophrenia. Subsequent studies demonstrated that the osmotic set point for AVP secretion was transiently reset in these patients by an unknown process and that this was further exacerbated by acute psychosis. More recent studies indicate that the AVP dysfunction is a manifestation of a hippocampal-mediated impairment in the regulation of both AVP and HPA axis responses to psychological, but not other types of, stimuli. Of potential significance, is that schizophrenic patients without water imbalance exhibit the opposite pattern of responses. Preliminary data indicate those with water imbalance also demonstrate a closely linked deficit in central oxytocin activity which may account for their diminished social function. These latter behavioral deficits are perhaps the most disabling and treatment resistant features of schizophrenia, which recent studies suggest, may respond to oxytocin agonists. Together these findings support the view that schizophrenia is a heterogeneous disorder, and provide novel biomarkers and approaches for exploring the pathophysiology and treatment of severe mental illness.

Psychobiology and molecular genetics of resilience

Every individual experiences stressful life events. In some cases acute or chronic stress leads to depression and other psychiatric disorders, but most people are resilient to such effects. Recent research has begun to identify the environmental, genetic, epigenetic and neural mechanisms that underlie resilience, and has shown that resilience is mediated by adaptive changes in several neural circuits involving numerous neurotransmitter and molecular pathways. These changes shape the functioning of the neural circuits that regulate reward, fear, emotion reactivity and social behaviour, which together are thought to mediate successful coping with stress.

The effects of the selective 5-HT(2C) receptor antagonist SB 242084 on learned helplessness in male Fischer 344 rats

RATIONALE

Rats exposed to an uncontrollable stressor demonstrate a constellation of behaviors such as exaggerated freezing and deficits in shuttle box escape learning. These behaviors in rats have been called learned helplessness and have been argued to model human stress-related mood disorders. Learned helplessness is thought to be caused by hyperactivation of serotonin (5-HT) neurons in the dorsal raphe nucleus (DRN) and a subsequent exaggerated release of 5-HT in DRN projection sites. Blocking 5-HT(2C) receptors in the face of an increase in serotonin can alleviate anxiety behaviors in some animal models. However, specific 5-HT receptor subtypes involved in learned helplessness remain unknown.

OBJECTIVES

The current experiments tested the hypothesis that 5-HT(2C) receptor activation is necessary and sufficient for the expression of learned helplessness.

RESULTS

The selective 5-HT(2C) receptor antagonist SB 242084 (1.0 mg/kg) administered i.p. to adult male Fischer 344 rats prior to shuttle box behavioral testing, but not before stress, blocked stress-induced deficits in escape learning but had no effect on the exaggerated shock-elicited freezing. The selective 5-HT(2C) receptor agonist CP-809101 was sufficient to produce learned helplessness-like behaviors in the absence of prior stress and these effects were blocked by pretreatment with SB 242084.

CONCLUSIONS

Results implicate the 5-HT(2C) receptor subtype in mediating the shuttle box escape deficits produced by exposure to uncontrollable stress and suggest that different postsynaptic 5-HT receptor subtypes underlie the different learned helplessness behaviors.

Region specific gene expression profile in mouse brain after chronic corticotropin releasing factor receptor 1 activation: the novel role for diazepam binding inhibitor in contextual fear conditioning

We have previously reported that repeated central administration of sub-anxiogenic doses of the corticotropin releasing factor 1 (CRF(1)) agonist Cortagine, termed "priming," elicits a phenotype of increased anxiety-like behaviors in the elevated plus maze (EPM) and open-field test, and enhanced retention of contextual conditioned fear in C57BL/6J mice. Observed behavioral changes were functionally coupled to CRF(1)-mediated elevated central cholecystokinin (CCK) tone in discrete brain regions. However, the changes in gene expression that mediated "priming"-induced behavioral and concurrent molecular changes in specific brain regions remained unknown. In the present study, a complementary DNA microarray analysis was used to investigate gene expression profiles in the hippocampus and prefrontal cortex (PFC) of C57BL/6J mice following the "priming" procedure. Here, we report that chronic stimulation of CRF(1), by i.c.v. administration of 10 ng Cortagine for five days, brought about alterations in the expression of a wide range of hippocampal (31 genes) and PFC (18 genes) genes, implicated in anxiety and aversive memory formation. These expression changes involved genes associated with signal transduction, neurotransmitter secretion, synaptic transmission, myelination, and others involved in the transport, biosynthesis, and binding of proteins. In particular, several genes of the protein kinase A (PKA) and protein kinase C (PKC) signaling cascades, known to be involved in synaptic plasticity, such as neurogranin, calmodulin 3, and the PKA regulatory subunit 1 b were found to be upregulated in the PFC and hippocampus of CRF(1) agonist "primed" mice. Moreover, we show pharmacologically that one of the newly implicated memory regulatory elements, diazepam-binding inhibitor (DBI) is functionally involved in hippocampus-dependent enhancement of contextual fear, a cardinal phenotypic feature of the "primed" mice. Finally, an interaction network mapping of the altered genes and their known interacting partners identified additional molecular candidates responsible for CRF(1)-mediated hypersensitive fear circuitry.

Stressor controllability and Fos expression in stress regulatory regions in mice

Controllability is an important determinant of the effects of stress on behavior. We trained mice with escapable (ES) and inescapable (IS) shock and examined behavioral freezing and Fos expression in brain regions involved in stress to determine whether stressor controllability produced differential activation of these regions. Mice (C57BL/6J) were trained to escape footshock by moving to a safe chamber in a shuttlebox. This terminated shock for both ES mice (n=5) and yoked-control mice receiving IS (n=5). Handling control (HC) mice (n=5) experienced the shuttlebox, but never received footshock. Training took place on three days (20 trials per day, 0.2 mA, 5.0 s maximum duration, 1.0 min interstimulus interval). On day 3, the animals were killed 2 h after training and the brains were processed for Fos expression in the amygdala, hypothalamic paraventricular nucleus (PVN), laterodorsal tegmental nucleus, locus coeruleus and dorsal raphe nucleus. Fos expression after IS was greater than after ES and HC in all regions (p<.05). Fos expression after ES was greater than HC only in PVN (p<.05). Freezing in ES mice was equal to or greater than in IS mice whereas HC mice showed minimal freezing. Differential activation of brain regions implicated in stress may, in part, account for differences in behavior in the aftermath of uncontrollable and controllable stress.

Prospective and retrospective temporal difference learning

A striking recent finding is that monkeys behave maladaptively in a class of tasks in which they know that reward is going to be systematically delayed. This may be explained by a malign Pavlovian influence arising from states with low predicted values. However, by very carefully analyzing behavioral data from such tasks, La Camera and Richmond (2008) observed the additional important characteristic that subjects perform differently on states in the task that are at equal distances from the future reward, depending on what has happened in the recent past. The authors pointed out that this violates the definition of state value in the standard reinforcement learning models that are ubiquitous as accounts of operant and classical conditioned behavior; they suggested and analyzed an alternative temporal difference (TD) model in which past and future are melded. Here, we show that, in fact, a standard TD model can actually exhibit the same behavior, and that this avoids deleterious consequences for choice. At the heart of the model is the average reward per step, which acts as a baseline for measuring immediate rewards. Relatively subtle changes to this baseline occasioned by the past can markedly influence predictions and thus behavior.

Stress and the neuroendocrinology of anxiety disorders

Stress is a risk factor for depressive and anxiety disorders. Changes in lifestyle patterns that are associated with increased stress therefore place a greater burden on mental health. Stress challenges the organism's homeostatic mechanisms, triggering a cascade of events that should, normally, maintain or allow a return to equilibrium. Stressful events are perceived by sensory systems in the brain, facilitating evaluation and comparison of the existing and previous stimuli as well as the activation of hormones responsible for energy mobilization. The limbic system coordinates the release of corticosteroids, the primary stress hormones, by modulating activation of the hypothalamic paraventricular nucleus (PVN). The amygdala, a limbic structure related to emotional behavior, has a putative role in the evaluation of emotional events and formation of fearful memories; it is also a target of the neurochemical and hormonal mediators of stress. Clinical and experimental data have correlated changes in the structure/function of the amygdala with emotional disorders such as anxiety. In this chapter we review the neuroendocrinology of the stress response, focusing on the role of the limbic system in its establishment and supplementing that information with new experimental data that demonstrates the relationship between stress and anxiety disorders; we also discuss the structural changes that occur in the amygdala after stress.

Stress-induced prefrontal reorganization and executive dysfunction in rodents

The prefrontal cortex (PFC) mediates a range of higher order 'executive functions' that subserve the selection and processing of information in such a way that behavior can be planned, controlled and directed according to shifting environmental demands. Impairment of executive functions typifies many forms of psychopathology, including schizophrenia, mood and anxiety disorders and addiction, that are often associated with a history of trauma and stress. Recent research in animal models demonstrates that exposure to even brief periods of intense stress is sufficient to cause significant structural remodeling of the principle projection neurons within the rodent PFC. In parallel, there is growing evidence that stress-induced alterations in PFC neuronal morphology are associated with deficits in rodent executive functions such as working memory, attentional set-shifting and cognitive flexibility, as well as emotional dysregulation in the form of impaired fear extinction. Although the molecular basis of stress-induced changes in PFC morphology and function are only now being elucidated, an understanding of these mechanisms could provide important insight into the pathophysiology of executive dysfunction in neuropsychiatric disease and foster improved strategies for treatment.

The ventro-medial prefrontal cortex: a major link between the autonomic nervous system, regulation of emotion, and stress reactivity?

Recent progress in neuroscience revealed diverse regions of the CNS which moderate autonomic and affective responses. The ventro-medial prefrontal cortex (vmPFC) plays a key role in these regulations. There is evidence that vmPFC activity is associated with cardiovascular changes during a motor task that are mediated by parasympathetic activity. Moreover, vmPFC activity makes important contributions to regulations of affective and stressful situations.This review selectively summarizes literature in which vmPFC activation was studied in healthy subjects as well as in patients with affective disorders. The reviewed literature suggests that vmPFC activity plays a pivotal role in biopsychosocial processes of disease. Activity in the vmPFC might link affective disorders, stressful environmental conditions, and immune function.

Genetic variation in cortico-amygdala serotonin function and risk for stress-related disease

The serotonin system is strongly implicated in the pathophysiology and therapeutic alleviation of stress-related disorders such as anxiety and depression. Serotonergic modulation of the acute response to stress and the adaptation to chronic stress is mediated by a myriad of molecules controlling serotonin neuron development (Pet-1), synthesis (tryptophan hydroxylase 1 and 2 isozymes), packaging (vesicular monoamine transporter 2), actions at presynaptic and postsynaptic receptors (5-HT1A, 5-HT1B, 5-HT2A, 5-HT2C, 5-HT3A, 5-HT4, 5-HT5A, 5-HT6, 5-HT7), reuptake (serotonin transporter), and degradation (monoamine oxidase A). A growing body of evidence from preclinical rodents models, and especially genetically modified mice and inbred mouse strains, has provided significant insight into how genetic variation in these molecules can affect the development and function of a key neural circuit between the dorsal raphe nucleus, medial prefrontal cortex and amygdala. By extension, such variation is hypothesized to have a major influence on individual differences in the stress response and risk for stress-related disease in humans. The current article provides an update on this rapidly evolving field of research.

Spirituality and autonomic cardiac control

BACKGROUND

Spirituality has been suggested to be associated with positive health, but potential biological mediators have not been well characterized.

PURPOSE AND METHODS

The present study examined, in a population-based sample of middle-aged and older adults, the potential relationship between spirituality and patterns of cardiac autonomic control, which may have health significance. Measures of parasympathetic (high-frequency heart rate variability) and sympathetic (pre-ejection period) cardiac control were obtained from a representative sample of 229 participants. Participants completed questionnaires to assess spirituality (closeness to and satisfactory relationship with God). Personality, demographic, anthropometric, health behavior, and health status information was also obtained. A series of hierarchical regression models was used to examine the relations between spirituality, the autonomic measures, and two derived indexes--cardiac autonomic balance (CAB, reflecting parasympathetic to sympathetic balance) and cardiac autonomic regulation (CAR, reflecting total autonomic control).

RESULTS

Spirituality, net of demographics, or other variables were found to be associated with enhanced parasympathetic as well as sympathetic cardiac control (yielding a higher CAR) but was not associated with CAB. Although the number of cases was small (N = 11), both spirituality and CAR were significant negative predictors of the prior occurrence of a myocardial infarction.

CONCLUSIONS

In a population-based sample, spirituality appears to be associated with a specific pattern of CAR, characterized by a high level of cardiac autonomic control, irrespective of the relative contribution of the two autonomic branches. This pattern of autonomic control may have health significance.

Exercise, learned helplessness, and the stress-resistant brain

Exercise can prevent the development of stress-related mood disorders, such as depression and anxiety. The underlying neurobiological mechanisms of this effect, however, remain unknown. Recently, researchers have used animal models to begin to elucidate the potential mechanisms underlying the protective effects of physical activity. Using the behavioral consequences of uncontrollable stress or "learned helplessness" as an animal analog of depression- and anxiety-like behaviors in rats, we are investigating factors that could be important for the antidepressant and anxiolytic properties of exercise (i.e., wheel running). The current review focuses on the following: (1) the effect of exercise on the behavioral consequences of uncontrollable stress and the implications of these effects on the specificity of the "learned helplessness" animal model; (2) the neurocircuitry of learned helplessness and the role of serotonin; and (3) exercise-associated neural adaptations and neural plasticity that may contribute to the stress-resistant brain. Identifying the mechanisms by which exercise prevents learned helplessness could shed light on the complex neurobiology of depression and anxiety and potentially lead to novel strategies for the prevention of stress-related mood disorders.

More appraisal please: a commentary on Pfaff et al. (2007) "Relations between mechanisms of CNS arousal and mechanisms of stress"

This article provides a brief commentary on Pfaff et al's timely review of the relations between mechanisms of CNS arousal and mechanisms of stress. Pfaff and colleagues use the review as a platform to propose the existence of a coherent stress-arousal state. We suggest that this proposal is, on a number of grounds, flawed. In turn, we counter that the while the states of stress and arousal are related they are as entities fundamentally separate. Moreover, we propose that any productive attempt to unite the two states must acknowledge the importance of and therefore centrally include higher order integrative phenomena, such as, appraisal.

Glucocorticoid hyper- and hypofunction: stress effects on cognition and aggression

It is now well documented that both increased and decreased stress responses can profoundly affect cognition and behavior. This mini review presents possible neural mechanisms subserving stress effects on memory and aggression, particularly focusing on glucocorticoid (GC) hyper- and hypofunction. First, uncontrollable stress impedes hippocampal memory and long-term potentiation (LTP). Because the hippocampus is important for the stability of long-term memory and because LTP has qualities desirable of an information storage mechanism, it has been hypothesized that stress-induced alterations in LTP contribute to memory impairments. Recent evidence suggests a neural-endocrine network comprising amygdala, prefrontal cortex (PFC), and glucocorticoids may be involved in regulating stress effects on hippocampal mnemonic functioning. Second, antisocial aggressiveness correlates with chronically decreased glucocorticoid production, and this condition leads in rats to behavioral-autonomic deficits reminiscent of the human disorder. Glucocorticoid deficiency-induced antisocial aggressiveness results from functional changes in the PFC, medial and central amygdala, and altered serotonin and substance P neurotransmissions. Accordingly, a neurobiological understanding of how stress and glucocorticoid deficiency alter brain, cognition, and behavior is an important challenge facing modern neuroscience with broad implications for individual and social well-being.

Emotion-induced retrograde amnesia varies as a function of noradrenergic-glucocorticoid activity

RATIONALE

Privileged episodic encoding of an aversive event often comes at a cost of neutral events flanking the aversive event, resulting in decreased episodic memory for these neutral events. This peri-emotional amnesia is amygdala-dependent and varies as a function of norepinephrine activity. However, less is known about the amnesiogenic potential of cortisol.

OBJECTIVE

We used a strategy of pharmacologically potentiating cortisol and norepinephrine activity to probe the putative neurochemical substrates of peri-emotional amnesia.

MATERIALS AND METHODS

Fifty-four healthy individuals participated in a randomized double-blind placebo-controlled study. Within the experimental context of an established peri-emotional amnesia paradigm, we tested the amnesiogenic potential of hydrocortisone (30 mg p.o.) in the presence or absence of the norepinephrine-reuptake inhibitor reboxetine (4 mg p.o.).

RESULTS

Under dual challenge conditions, we observed a linear dose-response relationship in the magnitude and duration of emotion-induced retrograde amnesia.

CONCLUSIONS

Our results are consistent with a phenotypic expression of retrograde amnesia varying as a function of norepinephrine and cortisol coactivation during episodic encoding of aversive events. Our study demonstrates that the adverse cognitive and behavioral sequelae of aversive emotion can be experimentally modeled by a pharmacological manipulation of its putative neurochemical substrates.

Stress inoculation-induced indications of resilience in monkeys

The negative consequences of stress are well-recognized in mental health research. Exposure to early life stressors, for example, increases the risk for the development of mood, anger, anxiety, and substance abuse disorders. Interestingly, however, early life stressors have also been linked to the subsequent development of resilience. Variously described as inoculating, immunizing, steeling, toughening, or thriving, the hypothesis that early life stressors provide a challenge that, when overcome, induces adaptations that enhance emotional processing, cognitive control, curiosity, and neuroendocrine regulation is examined in this review of squirrel monkey research.