Early exposure to chronic variable stress facilitates the occurrence of anhedonia and enhanced emotional reactions to novel stressors: reversal by naltrexone pretreatment

Maternal probiotic Lactocaseibacillus rhamnosus HN001 treatment alters postpartum anxiety, cortical monoamines, and the gut microbiome

Peripartum mood and anxiety disorders (PMADs) affect 15-20% of peripartum women and are well known to disrupt infant caregiving. A recent study in humans reported that anxiety and depressive symptoms were alleviated by peripartum treatment with the probiotic, Lactocaseibacillus rhamnosus HN001. The current study determined the effects of chronic Lactocaseibacillus rhamnosus HN001 (HN001) treatment on postpartum affective and caregiving behaviors in a laboratory rodent model. Female rats were given probiotic overnight in their drinking water, or untreated water, from the first day of pregnancy through postpartum day 10. To determine whether the HN001 effects were influenced by a background of stress, half the females underwent chronic variable pregnancy stress and the other half remained undisturbed. The results revealed that, even without pregnancy stress, HN001 reduced postpartum anxiety-related behavior, increased variability in behavioral fragmentation when dams interacted with pups, increased time away from pups, and decreased prefrontal cortex norepinephrine (NE), dopamine (DA) and serotonin (5-HT). Probiotic plus stress consistently reduced the latency to float in the forced swim test, increased DA and 5-HT turnovers in the prefrontal cortex, increased hippocampal NE, and reduced hypothalamic DA. Fecal microbe alpha and beta diversities were lower postpartum than prepartum, which was prevented by the probiotic treatment and/or stress. Across the entire sample lower postpartum anxiety behavior was associated with lower fecal Bacteroides dorei. This study reveals novel information about how L. rhamnosus HN001 influences postpartum behavior and microbiota-gut-brain physiology in female laboratory rats, with implications for probiotic supplement use by pregnant and postpartum women.

Stress to inflammation and anhedonia: Mechanistic insights from preclinical and clinical models

Anhedonia, as evidenced by impaired pleasurable response to reward, reduced reward motivation, and/or deficits in reward-related learning, is a common feature of depression. Such deficits in reward processing are also an important clinical target as a risk factor for depression onset. Unfortunately, reward-related deficits remain difficult to treat. To address this gap and inform the development of effective prevention and treatment strategies, it is critical to understand the mechanisms that drive impairments in reward function. Stress-induced inflammation is a plausible mechanism of reward deficits. The purpose of this paper is to review evidence for two components of this psychobiological pathway: 1) the effects of stress on reward function; and 2) the effects of inflammation on reward function. Within these two areas, we draw upon preclinical and clinical models, distinguish between acute and chronic effects of stress and inflammation, and address specific domains of reward dysregulation. By addressing these contextual factors, the review reveals a nuanced literature which might be targeted for additional scientific inquiry to inform the development of precise interventions.

High-Fat Diet and Short-Term Unpredictable Stress Increase Long-Chain Ceramides Without Enhancing Behavioral Despair

Clinical and preclinical studies suggest that increases in long-chain ceramides in blood may contribute to the development of depressive-like behavior. However, which factors contribute to these increases and whether the increases are sufficient to induce depressive-like behaviors is unclear. To begin to address this issue, we examined the effects of high fat diet (HFD) and short-term unpredictable (STU) stress on long-chain ceramides in the serum of male and female rats. We found that brief exposure to HFD or unpredictable stress was sufficient to induce selective increases in the serum concentrations of long-chain ceramides, associated with depression in people. Furthermore, combined exposure to HFD and unpredictable stress caused a synergistic increase in C16:0, C16:1, and C18:0 ceramides in both sexes and C18:1 and C24:1 in males. However, the increased peripheral long-chain ceramides were not associated with increases in depressive-like behaviors suggesting that increases in serum long-chain ceramides may not be associated with the development of depressive-like behaviors in rodents.

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

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

Antidepressant-like effects of paeoniflorin on post-stroke depression in a rat model

BACKGROUND

Post-stroke depression (PSD) is one of the most prevalent emotional disorders after stroke and often results in poor outcomes. However, the underlying physiopathologic mechanism and effective treatment of PSD remain poorly elucidated.

OBJECTIVE

To investigate whether paeoniflorin has antidepressant-like activity in a rat model of PSD.

METHODS

Rats were randomly divided into four groups: sham-operated control (Sham), PSD, paeoniflorin (with PSD) and fluoxetine group(with PSD). PSD was developed by the right middle cerebral artery occlusion followed 21 days chronic unpredictable mild stress combined (CUMS) with raised alone. Tests of sucrose preference and open field were used to assess the depression-like behavior. Neurological function was evaluated by neurological deficit score and beam balance test. Expression of phosphorylated CREB (p-CREB) and brain-derived neurotrophic factor (BDNF) in the CA1 region of the hippocampal complex was evaluated by western blot and immunofluorescence.

RESULTS

Te depressive-like behaviors markedly improved after paeoniflorin and fluoxetine treatment. Furthermore, paeoniflorin treatment significantly increased BDNF and p-CREB expression in the CA1 region.

CONCLUSIONS

Observed results suggested that paeoniflorin could ameliorate the symptoms and improve the functional capability of PSD rats, similar to the effect of fluoxetine.

ABBREVIATIONS

PSD: post-stroke depression; CUMS: chronic unpredictable mild stress stimulation; MCAO: middle cerebral artery occlusion; OFT: open field test; SPT: sucrose preference test, NDS: neurological deficit score, BBT: beam balance test; BDNF: brain-derived neurotrophic factor protein; p-CREB: phosphorylated Cyclic-AMP responsive element binding protein.

Chronic stress dysregulates amygdalar output to the prefrontal cortex

Chronic stress contributes to the neuropathology of mental health disorders, including those associated with anxiety. The basolateral amygdala (BLA) coordinates emotional behavioral responses through glutamatergic outputs to downstream regions such as the prefrontal cortex (PFC), nucleus accumbens core (NAcc) and bed nucleus of the stria terminalis (BNST). We explored the effects of chronic stress on BLA outputs to the PFC, NAcc and BNST using slice electrophysiology combined with optogenetics in two inbred mouse strains with distinct stress-induced anxiety responses. We found that ten consecutive days of chronic restraint stress enhanced pre-synaptic glutamate release at BLA-to-PFC synapses in C57BL/6J mice, but reduced pre-synaptic glutamate release at these synapses in DBA/2J mice. To assess the behavioral relevance of enhanced glutamate output at BLA-to-PFC synapses, we approximated the effects of chronic stress on the BLA-PFC circuit using optogenetics. We found that photostimulation of the BLA-PFC circuit in unstressed C57BL/6J mice produced persistent (i.e., post-stimulation) increased anxiety-like behavior and hyperactivity in the elevated plus-maze - a profile consistent with prototypical behavioral responses of stressed C57BL/6J mice. These data demonstrate that chronic stress dysregulates the BLA-PFC circuit by altering pre-synaptic glutamate release from BLA outputs, and provide a mechanism by which chronic stress can lead to increased anxiety.

Effects of oregano essential oil on brain TLR4 and TLR2 gene expression and depressive-like behavior in a rat model

The aim of the present study was to evaluate the effects of oregano essential oil (OEO) on the hippocampus and prefrontal cortex TLR 2/4 gene expression and depressive like behavior induced by chronic unpredictable stress (CUS). Sucrose preference and forced swim tests were adopted to examine the antidepressant effect. Control (CON), OEO, CUS, and CUS + OEO groups were used. The OEO and CUS + OEO groups received OEO (0.2 mL/kg, i.p.), CON and CUS received saline (0.2 mL/kg, i.p.), and the positive drug groups of CUS rats received fluoxetine (10 mg/kg) and diazepam (3 mg/kg) once daily for 14 days. The expression of TLR 2/4 was determined using real time quantitative polymerase chain reaction with the SYBR green reporter dye. The compositions of the OEO were determined by gas chromatography-mass spectroscopy. The main constituents were thymol (20.72%), gamma-terpinene (8.83%), borneol (8.72%), cymene (6.83%), carvacrol (6.274%), alfa-terpinene (5.26%), and sabinene (4.92%). Administration of OEO significantly alleviated the depressive symptoms of CUS. A higher level of TLR2/4 mRNA was seen in the brain of CUS group (P < 0.05). The CUS-induced increases in the TLR2/4 levels were not reversed by OEO. According to the present study OEO may have the antidepressant-like activity but have no effect on the stress-induced TLR-2/4 upregulation.

Exogenous daytime melatonin modulates response of adolescent mice in a repeated unpredictable stress paradigm

The immediate and short-term behavioural and physiological implications of exposure to stressful scenarios in the adolescent period are largely unknown; however, increases in occurrence of stress-related physiological and psychological disorders during puberty highlight the need to study substances that may modulate stress reactivity during a crucial stage of maturation. Seven groups of mice (12-15 g each) were administered distilled water (DW) (non-stressed and stressed controls), sertraline (10 mg/kg), diazepam (2 mg/kg) or one of three doses of melatonin (5, 10 and 15 mg/kg). Mice were exposed to 30 min of chronic mild stress (25 min of cage shaking, cage tilting, handling and 5 min of forced swimming in tepid warm water at 25 °C, in a random order) after administration of DW or drugs, daily for 21 days. Behavioural assessments were conducted on day 1 and day 21 (after which mice were sacrificed, blood taken for estimation of corticosterone levels and brain homogenates used for estimation of antioxidant activities). Administration of melatonin resulted in an increase in horizontal locomotion and self-grooming, while rearing showed a time-dependent increase, compared to non-stress and stress controls. Working memory improved with increasing doses of melatonin (compared to controls and diazepam); in comparison to setraline however, working memory decreased. A dose-related anxiolytic effect is seen when melatonin is compared to non-stressed and stressed controls. Melatonin administration reduced the systemic/oxidant response to repeated stress. Administration of melatonin in repeatedly stressed adolescent mice was associated with improved central excitation, enhancement of working memory, anxiolysis and reduced systemic response to stress.

Astrocyte plasticity induced by emotional stress: A new partner in psychiatric physiopathology?

A growing body of evidence has demonstrated that astrocytes play a pivotal role in the normal functioning of the nervous system. This new conceptual framework has set the groundwork to be able to hypothesize that astrocytes could underlie signs and symptoms of mental diseases. Stress is a major risk factor in the etiology of several psychiatric diseases, such as anxiety disorders and depression. Hence, understanding the effects of stress on astrocytes and how these changes contribute to the development of psychiatric endophenotypes is crucial for both a better comprehension of mental illness and for potential targeted treatment of stress-related mental disorders. Here, we describe the currently used approaches and recent evidence showing astrocyte alterations induced by chronic and acute stress in animals. In addition, the relevance of these changes in stress-induced behavioral sequelae and human data linking astrocytes with neuropsychiatric disorders related to stress are also discussed. All together, the data indicate that astrocytes are also an important target of stress, with both chronic and acute stressors being able to alter the morphology or the expression of several astrocyte specific proteins in brain areas that are known to play a critical role in emotional processing, such as the prefrontal cortex, hippocampus and amygdala. Furthermore, different lines of evidences suggest that these changes may contribute, at less in part, to the behavioral consequences of stress.

Naltrexone alters the processing of social and emotional stimuli in healthy adults

Endogenous opioids have complex social effects that may depend on specific receptor actions and vary depending on the "stage" of social behavior (e.g., seeking vs. responding to social stimuli). We tested the effects of a nonspecific opioid antagonist, naltrexone (NTX), on social processing in humans. NTX is used to treat alcohol and opiate dependence, and may affect both mu and kappa-opioid systems. We assessed attention ("seeking"), and subjective and psychophysiological responses ("responding") to positive and negative social stimuli. Based on literature suggesting mu-opioid blockade impairs positive social responses, we hypothesized that NTX would decrease responses to positive social stimuli. We also tested responses to negative stimuli, which might be either increased by NTX's mu-opioid effects or decreased by its kappa-opioid effects. Thirty-four healthy volunteers received placebo, 25 mg, or 50 mg NTX across three sessions under double-blind conditions. At each session, participants completed measures of attention, identification, and emotional responses for emotional faces and scenes. NTX increased attention to emotional expressions, slowed identification of sadness and fear, and decreased ratings of arousal for social and nonsocial emotional scenes. These findings are more consistent with anxiolytic kappa-antagonist than mu-blocking effects, suggesting effects on kappa receptors may contribute to the clinical effects of NTX.

A Possible Role of Anhedonia as Common Substrate for Depression and Anxiety

Depression and anxiety are often comorbid, in up to 70% of cases, and the level of one or the other may fluctuate, leading now to a diagnosis of depression, now to a diagnosis of anxiety. For these reasons, and for the presence of many other common factors, it has been suggested that both are part of the same continuum of problems and that they have a common substrate. This paper proposes the possibility that anhedonia may be an important component of this possible common substrate, and it tries to identify the mechanism with which anhedonia could contribute to causing both depression and anxiety. It also proposes an explanation why an intense pleasure could improve both depression and anxiety.

The long-term impact of early life pain on adult responses to anxiety and stress: Historical perspectives and empirical evidence

Approximately 1 in 6 infants are born prematurely each year. Typically, these infants spend 25 days in the Neonatal Intensive Care Unit (NICU) where they experience 10-18 painful and inflammatory procedures each day. Remarkably, pre-emptive analgesics and/or anesthesia are administered less than 25% of the time. Unalleviated pain during the perinatal period is associated with permanent decreases in pain sensitivity, blunted cortisol responses and high rates of neuropsychiatric disorders. To date, the mechanism(s) by which these long-term changes in stress and pain behavior occur, and whether such alterations can be prevented by appropriate analgesia at the time of insult, remains unclear. Work in our lab using a rodent model of early life pain suggests that inflammatory pain experienced on the day of birth blunts adult responses to stress- and pain-provoking stimuli, and dysregulates the hypothalamic pituitary adrenal (HPA) axis in part through a permanent upregulation in central endogenous opioid tone. This review focuses on the long-term impact of neonatal inflammatory pain on adult anxiety- and stress-related responses, and underlying neuroanatomical changes in the context of endogenous pain control and the HPA axis. These two systems are in a state of exaggerated developmental plasticity early in postnatal life, and work in concert to respond to noxious or aversive stimuli. We present empirical evidence from animal and clinical studies, and discuss historical perspectives underlying the lack of analgesia/anesthetic use for early life pain in the modern NICU.

Interaction of metabolic stress with chronic mild stress in altering brain cytokines and sucrose preference

There is growing evidence that metabolic stressors increase an organism's risk of depression. Chronic mild stress is a popular animal model of depression and several serendipitous findings have suggested that food deprivation prior to sucrose testing in this model is necessary to observe anhedonic behaviors. Here, we directly tested this hypothesis by exposing animals to chronic mild stress and used an overnight 2-bottle sucrose test (food ad libitum) on Day 5 and 10, then food and water deprive animals overnight and tested their sucrose consumption and preference in a 1-hr sucrose test the following morning. Approximately 65% of stressed animals consumed sucrose and showed a sucrose preference similar to nonstressed controls in an overnight sucrose test, and 35% showed a decrease in sucrose intake and preference. Following overnight food and water deprivation the previously "resilient" animals showed a significant decrease in sucrose preference and greatly reduced sucrose intake. In addition, we evaluated whether the onset of anhedonia following food and water deprivation corresponds to alterations in corticosterone, epinephrine, circulating glucose, or interleukin-1 beta (IL-1β) expression in limbic brain areas. Although all stressed animals showed adrenal hypertrophy and elevated circulating epinephrine, only stressed animals that were food deprived were hypoglycemic compared with food-deprived controls. Additionally, food and water deprivation significantly increased hippocampus IL-1β while food and water deprivation only increased hypothalamus IL-1β in stress-susceptible animals. These data demonstrate that metabolic stress of food and water deprivation interacts with chronic stressor exposure to induce physiological and anhedonic responses.

Neurochemical and behavioral effects of chronic unpredictable stress

Chronic stress can influence behaviors associated with medial prefrontal cortex (mPFC) function, such as cognition and emotion regulation. Dopamine in the mPFC is responsive to stress and modulates its behavioral effects. The current study tested whether exposure to 10 days of chronic unpredictable stress (CUS) altered the effects of acute elevation stress on dopamine release in the mPFC and on spatial recognition memory. Male rats previously exposed to CUS or nonstressed controls were tested behaviorally, underwent microdialysis to assess mPFC dopamine levels or underwent blood sampling for corticosterone analysis. Dopamine in the mPFC significantly increased in both groups during acute elevation stress compared with baseline levels, but the level was attenuated in CUS rats compared with controls. Control rats exposed to elevation stress immediately before the T-maze test showed impaired performance, whereas CUS rats did not. No group differences were observed in general motor activity or plasma corticosterone levels following elevation stress. The present results indicate that prior exposure to this CUS procedure reduced dopamine release in the mPFC during acute elevation stress and prevented the impairment of performance on a spatial recognition test following an acute stressor. These findings may contribute to an understanding of the complex behavioral consequences of stress.

Depression, stress, and anhedonia: toward a synthesis and integrated model

Depression is a significant public health problem, but its etiology and pathophysiology remain poorly understood. Such incomplete understanding likely arises from the fact that depression encompasses a heterogeneous set of disorders. To overcome these limitations, renewed interest in intermediate phenotypes (endophenotypes) has resurfaced, and anhedonia has emerged as one of the most promising endophenotypes of depression. Here, a heuristic model is presented postulating that anhedonia arises from dysfunctional interactions between stress and brain reward systems. To this end, we review and integrate three bodies of independent literature investigating the role of (a) anhedonia, (b) dopamine, and (c) stress in depression. In a fourth section, we summarize animal data indicating that stress negatively affects mesocorticolimbic dopaminergic pathways critically implicated in incentive motivation and reinforcement learning. In the last section, we provide a synthesis of these four literatures, present initial evidence consistent with our model, and discuss directions for future research.

Housing conditions affect rat responses to two types of ambiguity in a reward-reward discrimination cognitive bias task

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We investigated how an unpredictable housing treatment (UHT) influenced measures of rat affect.

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Control rats showed more anxiety-like behaviour in open-field and elevated plus maze tests than UHT rats.

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Controls also made more ‘pessimistic’ decisions in an automated cognitive bias task.

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Our go/go reward–reward task was learnt faster than previous automated go/go tasks.

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We developed a new ambiguity test that may probe biases in attentional processes.

Decision-making under ambiguity in cognitive bias tasks is a promising new indicator of affective valence in animals. Rat studies support the hypothesis that animals in a negative affective state evaluate ambiguous cues negatively. Prior automated operant go/go judgement bias tasks have involved training rats that an auditory cue of one frequency predicts a Reward and a cue of a different frequency predicts a Punisher (RP task), and then measuring whether ambiguous cues of intermediate frequency are judged as predicting reward (‘optimism’) or punishment (‘pessimism’). We investigated whether an automated Reward–Reward (RR) task yielded similar results to, and was faster to train than, RP tasks. We also introduced a new ambiguity test (simultaneous presentation of the two training cues) alongside the standard single ambiguous cue test. Half of the rats experienced an unpredictable housing treatment (UHT) designed to induce a negative state. Control rats were relatively ‘pessimistic’, whilst UHT rats were quicker, but no less accurate, in their responses in the RR test, and showed less anxiety-like behaviour in independent tests. A possible reason for these findings is that rats adapted to and were stimulated by UHT, whilst control rats in a predictable environment were more sensitive to novelty and change. Responses in the new ambiguity test correlated positively with those in single ambiguous cue tests, and may provide a measure of attention bias. The RR task was quicker to train than previous automated RP tasks. Together, they could be used to disentangle how reward and punishment processes underpin affect-induced cognitive biases.

Unpredictable neonatal stress enhances adult anxiety and alters amygdala gene expression related to serotonin and GABA

Anxiety-related disorders are among the most common psychiatric illnesses, thought to have both genetic and environmental causes. Early-life trauma, such as abuse from a caregiver, can be predictable or unpredictable, each resulting in increased prevalence and severity of a unique set of disorders. In this study, we examined the influence of early unpredictable trauma on both the behavioral expression of adult anxiety and gene expression within the amygdala. Neonatal rats were exposed to unpaired odor-shock conditioning for 5 days, which produces deficits in adult behavior and amygdala dysfunction. In adulthood, we used the Light/Dark box test to measure anxiety-related behaviors, measuring the latency to enter the lit area and quantified urination and defecation. The amygdala was then dissected and a microarray analysis was performed to examine changes in gene expression. Animals that had received early unpredictable trauma displayed significantly longer latencies to enter the lit area and more defecation and urination. The microarray analysis revealed over-represented genes related to learning and memory, synaptic transmission and trans-membrane transport. Gene ontology and pathway analysis identified highly represented disease states related to anxiety phenotypes, including social anxiety, obsessive-compulsive disorders, post-traumatic stress disorder and bipolar disorder. Addiction-related genes were also overrepresented in this analysis. Unpredictable shock during early development increased anxiety-like behaviors in adulthood with concomitant changes in genes related to neurotransmission, resulting in gene expression patterns similar to anxiety-related psychiatric disorders.

Long-term changes in cognitive bias and coping response as a result of chronic unpredictable stress during adolescence

Animals that experience adverse events in early life often have life-long changes to their physiology and behavior. Long-term effects of stress during early life have been studied extensively, but less attention has been given to the consequences of negative experiences solely during the adolescent phase. Adolescence is a particularly sensitive period of life when regulation of the glucocorticoid “stress” hormone response matures and specific regions in the brain undergo considerable change. Aversive experiences during this time might, therefore, be expected to generate long-term consequences for the adult phenotype. Here we investigated the long-term effects of exposure to chronic unpredictable stress during adolescence on adult decision-making, coping response, cognitive bias, and exploratory behavior in rats. Rats exposed to chronic unpredictable stress (e.g., isolation, crowding, cage tilt) were compared to control animals that were maintained in standard, predictable conditions throughout development. Unpredictable stress during adolescence resulted in a suite of long-term behavioral and cognitive changes including a negative cognitive bias [F_{(1, 12)} = 5.000, P < 0.05], altered coping response [T_{(1, 14)} = 2.216, P = 0.04], and accelerated decision-making [T_{(1, 14)} = 3.245, P = 0.01]. Exposure to chronic stress during adolescence also caused a short-term increase in boldness behaviors; in a novel object test 15 days after the last stressor, animals exposed to chronic unpredictable stress had decreased latencies to leave a familiar shelter and approach a novel object [T_{(1, 14)} = 2.240, P = 0.04; T_{(1, 14)} = 2.419, P = 0.03, respectively]. The results showed that stress during adolescence has long-term impacts on behavior and cognition that affect the interpretation of ambiguous stimuli, behavioral response to adverse events, and how animals make decisions.

Protective effects of curcumin and sertraline on the behavioral changes in chronic variable stress-induced rats

Behavioral characteristics of the animal models and humans are impaired in chronic stress. The present study aimed to evaluate and compare the protective effects of sertraline and curcumin on stress-induced learning and memory impairment, anxiety and anhedonia in rats. Male rats were divided into seven groups: stress+water, stress+olive oil, stress+curcumin (100 mg/kg/day), stress+sertraline (10 mg/kg/day), curcumin, sertraline, and control groups. The rats were exposed to chronic variable stress for 56 days. At the end of 40 days and while the previous treatments were continued, the rats were tested in the eight radial maze, elevated plus maze, and sucrose consumption for learning and memory, anxiety, and anhedonia, respectively. In comparison to the non-stressed group, stress+water and stress+olive oil groups revealed a significantly lower percent of correct choices and higher reference and working memory errors during learning and retention phases (p<0.001). In addition these stress groups showed a significant lower percent of the open arms time and open arms entries in the elevated plus maze and consuming less sucrose solution. In addition, the stress+curcumin and stress+sertraline groups showed a better performance in the evaluated parameters of the radial arm maze, elevated plus maze, and sucrose consumption tests. It appears that curcumin and sertraline have the similar effectiveness on behavioral changes in chronic variable stress-induced rats.

Animal models of post-traumatic stress disorder: face validity

Post-traumatic stress disorder (PTSD) is a debilitating condition that develops in a proportion of individuals following a traumatic event. Despite recent advances, ethical limitations associated with human research impede progress in understanding PTSD. Fortunately, much effort has focused on developing animal models to help study the pathophysiology of PTSD. Here, we provide an overview of animal PTSD models where a variety of stressors (physical, psychosocial, or psychogenic) are used to examine the long-term effects of severe trauma. We emphasize models involving predator threat because they reproduce human individual differences in susceptibility to, and in the long-term consequences of, psychological trauma.

Role of NPY Y1 receptor on acquisition, consolidation and extinction on contextual fear conditioning: dissociation between anxiety, locomotion and non-emotional memory behavior

Neuropeptide Y (NPY) is the most abundant peptide in the central nervous system (CNS) and is densely localized in the brain regions involved in stress, memory, fear and anxiety. Although previous research supports a role for NPY in the mediation of rodent and human emotional behavior, there is currently a lack of information on the effects of low doses of NPY that could have a potential therapeutic advantage, minimizing side-effects such as cognition impairment or sedation. Herein, we assessed the effects of intracerebroventricular (i.c.v.) administration of low doses of NPY, and of the Y1-agonist Leu31Pro34-NPY (LP-NPY) on contextual fear conditioning (CFC), as they have no effect on unconditioned anxiety-like, locomotor activity and non-emotional memory. NPY (3 pmol) and LP-NPY (1 pmol) inhibited freezing behavior when administered in the acquisition or consolidation stages, indicating a reduction of fear. When injected in the extinction phase, only NPY inhibited freezing behavior on CFC. Pre-treatment with the Y1-antagonist BIBO3304 before NPY and LP-NPY was able to prevent the inhibition of fear responses induced by both NPY agonists. Taken together, our results demonstrate robust fear-inhibiting effects of i.c.v. injection of NPY on contextual fear conditioning in rats, a response that is mediated, at least in part, by the Y1 receptor. Moreover, these treatments were unable to change locomotor activity or to show an anxiolytic-like effect, as evaluated in an open-field and an elevated plus-maze. This specific fear reduction effect may underlie resilience systems in the CNS and has potential therapeutic relevance in PTSD.

Antidepressant-like effects of tea polyphenols on mouse model of chronic unpredictable mild stress

Tea polyphenols (TPs), which are the natural compounds extracted from tea leaves, possess a number of beneficial properties, such as reducing the risks of cancer and heart diseases, alleviating cognitive impairments and showing antidepressant-like activity in the forced swim test (FST) and tail suspension test (TST). The present study was designed to investigate the protective effect of TPs on the chronic unpredictable mild stress (CUMS)-induced depression model in mice and to elucidate the related underlying mechanisms. With the daily exposure to stressor for 5 consecutive weeks, TPs were administered in mice at a daily dose of 25 mg/kg or 50 mg/kg by gavage for 3 consecutive weeks from the 3rd week. Our results showed that CUMS significantly decreased the levels of serum serotonin (5-HT) and norepinephrine (NE) in the hippocampus, the prefrontal cortex and serum, and the activities of superoxide dismutase (SOD) and catalase (CAT), with an increase in lipid peroxidation level as well as a reduction in glutathione (GSH) level and an elevation in the production of malondialdehyde (MDA) in the hippocampus and the prefrontal cortex. CUMS also reduced open-field activity, sucrose consumption, as well as increased immobility duration in FST and TST. TPs administration could effectively reverse the alterations in the concentrations of 5-HT and NE, elevate the activities of SOD and CAT as well as the level of GSH, reduce the MDA level and inhibit lipid peroxidation. Moreover, TPs could effectively reverse alterations in immobility duration, sucrose consumption and open-field activity. In conclusion, TPs administration has exhibited significant antidepressant-like effects in mice with CUMS-induced depression. The antidepressant activity of TPs might be related to the alteration of monoaminergic responses and antioxidant defenses.

Central, but not basolateral, amygdala involvement in the anxiolytic-like effects of midazolam in rats in the elevated plus maze

The role of the amygdala in the mediation of fear and anxiety has been extensively investigated. However, how the amygdala functions during the organization of the anxiety-like behaviors generated in the elevated plus maze (EPM) is still under investigation. The basolateral (BLA) and the central (CeA) nuclei are the main input and output stations of the amygdala. In the present study, we ethopharmacologically analyzed the behavior of rats subjected to the EPM and the tissue content of the monoamines dopamine (DA) and serotonin (5-HT) and their metabolites in the nucleus accumbens (NAc), dorsal hippocampus (DH), and dorsal striatum (DS) of animals injected with saline or midazolam (20 and 30 nmol/0.2 µL) into the BLA or CeA. Injections of midazolam into the CeA, but not BLA, caused clear anxiolytic-like effects in the EPM. These treatments did not cause significant changes in 5-HT or DA contents in the NAc, DH, or DS of animals tested in the EPM. The data suggest that the anxiolytic-like effects of midazolam in the EPM also appear to rely on GABA-benzodiazepine mechanisms in the CeA, but not BLA, and do not appear to depend on 5-HT and DA mechanisms prevalent in limbic structures.

Hyperthermia protects mice against chronic unpredictable stress-induced anxiety-like behaviour and hippocampal CA3 cell apoptosis

PURPOSE

It is widely accepted that chronic stress can induce anxiety; however, the cellular and molecular mechanisms of stress-induced anxiety are far from being elucidated. Hyperthermia has been shown to induce expression of heat shock proteins (HSPs) to provide protection against a variety of stresses. To our knowledge, the effect of hyperthermia on the development of chronic unpredictable stress (CUS)-induced anxiety has not been studied. This study was to determine the relationship between hyperthermia induced Hsp72 and CUS related anxiety.

MATERIALS AND METHODS

Heat shock factor 1 knockout (hsf1(-/-)) and wild-type (hsf1(+/+)) mice were subjected to CUS with or without hyperthermia treatment. Anxiety-like behaviours were evaluated by elevated plus maze and open field tests. Apoptosis in the hippocampal CA3 area was detected by TUNEL staining. Hsp72 protein level in the hippocampus was measured by Western blot.

RESULTS

CUS caused significant apoptosis in hippocampal CA3 cells in both hsf1(-/-) and hsf1(+/+) mice, which significantly correlated with anxiety-like behaviours. Hyperthermia induced Hsp72 expression in hsf1(+/+) mice, but not in hsf1(-/-) mice. Importantly, hyperthermia protected hsf1(+/+) mice against developing CUS-related anxiety-like behaviours and reduced CUS-induced apoptosis in hippocampal CA3 cells. In contrast, hyperthermia exhibited no protective role in hsf1(-/-) mice.

CONCLUSIONS

Apoptosis of hippocampal CA3 cells is involved in the development of anxiety-like behaviours underlying CUS. Hsp72 protein is a crucial player in the protective effect of hyperthermia against CUS-induced apoptosis and development of anxiety-like behaviours. Our study suggests hyperthermia is an effective treatment for CUS-induced mood disorders.

Effects of stress on alcohol drinking: a review of animal studies

RATIONALE

While stress is often proposed to play a significant role in influencing alcohol consumption, the relationship between stress and alcohol is complex and poorly understood. Over several decades, stress effects on alcohol drinking have been studied using a variety of animal models and experimental procedures, yet this large body of literature has generally produced equivocal results.

OBJECTIVES

This paper reviews results from animal studies in which alcohol consumption is evaluated under conditions of acute/sub-chronic stress exposure or models of chronic stress exposure. Evidence also is presented indicating that chronic intermittent alcohol exposure serves as a stressor that consequently influences drinking.

RESULTS

The effects of various acute/sub-chronic stress procedures on alcohol consumption have generally been mixed, but most study outcomes suggest either no effect or decreased alcohol consumption. In contrast, most studies indicate that chronic stress, especially when administered early in development, results in elevated drinking later in adulthood. Chronic alcohol exposure constitutes a potent stressor itself, and models of chronic intermittent alcohol exposure reliably produce escalation of voluntary alcohol consumption.

CONCLUSIONS

A complex and dynamic interplay among a wide array of genetic, biological, and environmental factors govern stress responses, regulation of alcohol drinking, and the circumstances in which stress modulates alcohol consumption. Suggestions for future directions and new approaches are presented that may aid in developing more sensitive and valid animal models that not only better mimic the clinical situation, but also provide greater understanding of mechanisms that underlie the complexity of stress effects on alcohol drinking.

Might the inability to feel pleasure (anhedonia) explain the symptoms of major depression and schizophrenia, including unmotivated anxiety, delusions and hallucinations?

Inability to enjoy normally pleasurable experiences (anhedonia) is a symptom common both to major depression and schizophrenia. It also regularly accompanies and follows stress, and its presence in the two mental illnesses could depend on the fact that both are facilitated and often preceded by stressful events. Anhedonia might possibly accompany stress because the loss of the pleasure of aiming for a goal and achieving it (including defending oneself and escaping from a danger) could lead to immobility, and immobility (playing dead) offers the extreme chance of safety when an animal is facing the worst possible stressful situation--being seized by a predator--as in this case any movement can further stimulate the predator's aggressiveness. Perceiving and connecting sensory information also gives pleasure, and this appears to enhance the clarity of sensations and is an important factor in learning. We propose that anhedonia, by reducing or eliminating the pleasure, might jeopardize the usual appearance of the environment, which must not only be clearly perceived but also continuously interpreted (for instance a foreshortening, or something far off seen as small, must not be seen as a real deformation; the same holds for words, where the meaning has to be grasped from the single letters, and so on). Consequently, anhedonia could in some cases make the environment's image strange, distorted and frightening, and this could cause anxiety, confusion, and give problems in contacts with people and things. As correct information about images and sounds can inhibit visual and auditory hallucinations (considering them, like delusions, as attempts to reconstruct and make sense again of a world that is becoming confused and alien), we propose that anhedonia, interfering with the correct perceiving and processing of sensations, may facilitate them.

Chronic social isolation and chronic variable stress during early development induce later elevated ethanol intake in adult C57BL/6J mice

Experience with stress situations during early development can have long-lasting effects on stress- and anxiety-related behaviors. Importantly, this can also favor drug self-administration. These studies examined the effects of chronic social isolation and/or variable stress experiences during early development on subsequent voluntary ethanol intake in adult male and female C57BL/6J mice. The experiments were conducted to evaluate the effect of chronic isolation between weaning and adulthood (Experiment 1), chronic isolation during adulthood (Experiment 2), and chronic variable stress (CVS) alone or in combination with chronic social isolation between weaning and adulthood (Experiment 3) on subsequent voluntary ethanol intake. Mice were born in our facility and were separated into two housing conditions: isolate housed (one mouse/cage) or group housed (four mice/cage) according to sex. Separate groups were isolated for 40 days starting either at time of weaning postnatal day 21 (PD 21) (early isolation, Experiments 1 and 3) or at adulthood (PD 60: late isolation, Experiment 2). The effects of housing condition on subsequent ethanol intake were assessed starting at around PD 65 in Experiments 1 and 3 or PD 105 days in Experiment 2. In Experiment 3, starting at PD 32, isolate-housed and group-housed mice were either subjected to CVS or left undisturbed. CVS groups experienced random presentations of mild stressors for 14 days, including exposure to an unfamiliar open field, restraint, physical shaking, and forced swim, among others. All mice were tested for ethanol intake for 14 days using a two-bottle choice (ethanol 15% vol/vol vs. water) for a 2-h limited access procedure. Early social isolation resulted in greater ethanol intake compared with the corresponding group-housed mice (Experiment 1). In contrast, social isolation during adulthood (late isolation) did not increase subsequent ethanol intake compared with the corresponding group-housed mice (Experiment 2). For mice that did not experience CVS, early social isolation resulted in greater ethanol intake compared with group-housed mice (Experiment 3). CVS subsequently resulted in a significant increase in ethanol intake in group-housed mice, but CVS failed to further increase ethanol intake in mice that experienced chronic social isolation early in life (Experiment 3). Overall, female mice consumed more ethanol than males, whether isolated (early or late) or group housed. These results indicate that early but not late social isolation can subsequently influence ethanol consumption in C57BL/6J mice. Thus, the developmental timing of chronic social isolation appears to be an important factor in defining later effects on ethanol self-administration behavior. In addition, experience with CVS early in life results in elevated ethanol intake later in adulthood. Taken together, these results emphasize the important role of early stress experiences that modulate later voluntary ethanol intake during adulthood.

Kinin B1 receptors mediate depression-like behavior response in stressed mice treated with systemic E. coli lipopolysaccharide

BACKGROUND

Kinin B1 receptors are inducible molecules up-regulated after inflammatory stimuli. This study evaluated the relevance of kinin B1 receptors in a mouse depression behavior model.

METHODS

Mice were exposed to a 5-min swimming session, and 30 min later they were injected with E. coli lipopolysaccharide (LPS). Depression-like behavior was assessed by determining immobility time in a tail suspension test. Different brain structures were collected for molecular and immunohistochemical studies. Anhedonia was assessed by means of a sucrose intake test.

RESULTS

Our protocol elicited an increase in depression-like behavior in CF1 mice, as assessed by the tail-suspension test, at 24 h. This behavior was significantly reduced by treatment with the selective B1 receptor antagonists R-715 and SSR240612. Administration of SSR240612 also prevented an increase in number of activated microglial cells in mouse hippocampus, but did not affect a reduction in expression of mRNA for brain-derived neurotrophic factor. The increased immobility time following LPS treatment was preceded by an enhancement of hippocampal and cortical B1 receptor mRNA expression (which were maximal at 1 h), and a marked production of TNFα in serum, brain and cerebrospinal fluid (between 1 and 6 h). The depression-like behavior was virtually abolished in TNFα p55 receptor-knockout mice, and increased B1 receptor mRNA expression was completely absent in this mouse strain. Furthermore, treatment with SSR240612 was also effective in preventing anhedonia in LPS-treated mice, as assessed using a sucrose preference test.

CONCLUSION

Our data show, for the first time, involvement of kinin B1 receptors in depressive behavioral responses, in a process likely associated with microglial activation and TNFα production. Thus, selective and orally active B1 receptor antagonists might well represent promising pharmacological tools for depression therapy.

Comparative Fear-Related Behaviors to Predator Odors (TMT and Natural Fox Feces) before and after Intranasal ZnSO(4) Treatment in Mice

The possibility that synthetic 2,4,5-trimethylthiazoline (TMT), frequently used to induce unconditioned fear in rodents, could be more a pungent odor activating intranasal trigeminal nerve fibers rather than a predator odor index is currently discussed. In order to explore this question, the present study compared fear-related behaviors to predator odors (synthetic 10% TMT and natural fox feces) and toluene (as an irritant compound without ecological significance) before and after intranasal ZnSO₄ perfusion which is known to provoke transient anosmia. Results show that natural fox feces could be consider as a pure olfactory (CN I) nerve stimulant while 10% TMT appeared to be a mixed olfactory (CN I) and trigeminal (CN V) nerves stimulant with a great olfactory power and a low trigeminal power. These findings suggest that behavioral neuroscience studies should use concentrations lower than 10% TMT to obtain fear-related behaviors similar to those obtained with natural fox feces odor.

Regulation of histone acetylation in the hippocampus of chronically stressed rats: a potential role of sirtuins

The hippocampus is a brain region that is particularly susceptible to structural and functional changes in response to chronic stress. Recent literature has focused on changes in gene transcription mediated by post-translational modifications of histones in response to stressful stimuli. Chronic variable stress (CVS) is a rodent model that mimics certain symptoms of depression in humans. Given that stress exhibits distinct effects on the cells of the sub-regions of the hippocampus, we investigated changes in histone acetylation in the CA1, CA3, and dentate gyrus (DG) of the hippocampus in response to CVS. Western blotting revealed a significant decrease in acetylation of histone 4 (H4) at Lys12 in CA3 and DG of CVS animals compared to control animals. Furthermore, phospho-acetyl H3 (Lys9/Ser10) was also decreased in the CA3 and DG regions of the hippocampus of CVS animals. In addition, since histone deacetylases (HDACs) contribute to the acetylation state of histones, we investigated the effects of two HDAC inhibitors, sodium butyrate, a class I and II global HDAC inhibitor, and sirtinol, a class III sirtuin inhibitor, on acetylation of histone 3 (H3) and H4. Application of HDAC inhibitors to hippocampus slices from control and CVS animals revealed increased histone acetylation in CVS animals, suggesting that levels of histone deacetylation by HDACs were higher in the CVS animals compared to control animals. Interestingly, histone acetylation in response to sirtinol was selectively increased in the slices from the CVS animals, with very little effect of sirtuin inhibitors in slices from control animals. In addition, sirtuin activity was increased specifically in CA3 and DG of CVS animals. These results suggest a complex and regionally-specific pattern of changes in histone acetylation within the hippocampus which may contribute to stress-induced pathology.

Therapeutic utility of non-peptidic CRF1 receptor antagonists in anxiety, depression, and stress-related disorders: evidence from animal models

Adaptive responding to threatening stressors is of fundamental importance for survival. Dysfunctional hyperactivation of corticotropin releasing factor type-1 (CRF(1)) receptors in stress response system pathways is linked to stress-related psychopathology and CRF(1) receptor antagonists (CRAs) have been proposed as novel therapeutic agents. CRA effects in diverse animal models of stress that detect anxiolytics and/or antidepressants are reviewed, with the goal of evaluating their potential therapeutic utility in depression, anxiety, and other stress-related disorders. CRAs have a distinct phenotype in animals that has similarities to, and differences from, those of classic antidepressants and anxiolytics. CRAs are generally behaviorally silent, indicating that CRF(1) receptors are normally in a state of low basal activation. CRAs reduce stressor-induced HPA axis activation by blocking pituitary and possibly brain CRF(1) receptors which may ameliorate chronic stress-induced pathology. In animal models sensitive to anxiolytics and/or antidepressants, CRAs are generally more active in those with high stress levels, conditions which may maximize CRF(1) receptor hyperactivation. Clinically, CRAs have demonstrated good tolerability and safety, but have thus far lacked compelling efficacy in major depressive disorder, generalized anxiety disorder, or irritable bowel syndrome. CRAs may be best suited for disorders in which stressors clearly contribute to the underlying pathology (e.g. posttraumatic stress disorder, early life trauma, withdrawal/abstinence from addictive substances), though much work is needed to explore these possibilities. An evolving literature exploring the genetic, developmental and environmental factors linking CRF(1) receptor dysfunction to stress-related psychopathology is discussed in the context of improving the translational value of current animal models.

Brain-derived neurotrophic factor and hypothalamic-pituitary-adrenal axis adaptation processes in a depressive-like state induced by chronic restraint stress

Depression is potentially life-threatening. The most important neuroendocrine abnormality in this disorder is hypothalamo-pituitary-adrenocortical (HPA) axis hyperactivity. Recent findings suggest that all depression treatments may boost the neurotrophin production especially brain-derived neurotrophic factor (BDNF). Moreover, BDNF is highly involved in the regulation of HPA axis activity. The aim of this study was to determine the impact of chronic stress (restraint 3h/day for 3 weeks) on animal behavior and HPA axis activity in parallel with hippocampus, hypothalamus and pituitary BDNF levels. Chronic stress induced changes in anxiety (light/dark box test) and anhedonic states (sucrose preference test) and in depressive-like behavior (forced swimming test); general locomotor activity and body temperature were modified and animal body weight gain was reduced by 17%. HPA axis activity was highly modified by chronic stress, since basal levels of mRNA and peptide hypothalamic contents in CRH and AVP and plasma concentrations in ACTH and corticosterone were significantly increased. The HPA axis response to novel acute stress was also modified in chronically stressed rats, suggesting adaptive mechanisms. Basal BDNF contents were increased in the hippocampus, hypothalamus and pituitary in chronically stressed rats and the BDNF response to novel acute stress was also modified. This multiparametric study showed that chronic restraint stress induced a depressive-like state that was sustained by mechanisms associated with BDNF regulation.

Analysis of licking microstructure provides no evidence for a reduction in reward value following acute or sub-chronic phencyclidine administration

RATIONALE

The N-methyl D-aspartate antagonist phencyclidine (PCP) is purported to mimic the negative, cognitive and positive symptoms of schizophrenia. Thus, acute and sub-chronic PCP treatment in rodents might produce anhedonia, a decrease in the pleasure produced by rewards.

OBJECTIVES

Experiment 1 investigated whether acute PCP treatment changes the value of sucrose. A comparison was made to (+)MK-801, a drug often used interchangeably with PCP in preclinical studies. Experiment 2 assessed the effects of withdrawal from sub-chronic PCP treatment on the value of sucrose.

METHODS

Experiment 1 examined the dose-response effects of PCP and (+)MK-801 on licking microstructure during sucrose consumption. Experiment 2 assessed the effects of withdrawal from sub-chronic PCP treatment (5 mg/kg twice daily for 7 days), on licking microstructure during sucrose consumption. Locomotor activity testing was carried out in experiment 2 to confirm the sensitisation effect of the PCP regimen on amphetamine-induced hyperlocomotion.

RESULTS

Low to moderate acute doses of PCP and (+)MK-801 increased the amount of sucrose consumed. Higher doses decreased consumption and the number of licks per cluster (cluster size) but also increased the average inter-lick interval, which may indicate motor impairment. There was no evidence that withdrawal from sub-chronic PCP treatment produced decreases in consumption or lick cluster size.

CONCLUSIONS

Following acute PCP treatment, we found no evidence of reduced reward value without the presence of confounding motor deficits. Sub-chronic PCP withdrawal also produced no decrease in reward value. Therefore, the current results indicate that neither acute PCP treatment nor sub-chronic PCP withdrawal produce consummatory anhedonia.

Mutant mouse models: genotype-phenotype relationships to negative symptoms in schizophrenia

Negative symptoms encompass diminution in emotional expression and motivation, some of which relate to human attributes that may not be accessible readily in animals. Additionally, their refractoriness to treatment precludes therapeutic validation of putative models. This review considers critically the application of mutant mouse models to the study of the pathobiology of negative symptoms. It focuses on 4 main approaches: genes related to the pathobiology of schizophrenia, genes associated with risk for schizophrenia, neurodevelopmental-synaptic genes, and variant approaches from other areas of neurobiology. Despite rapid advances over the past several years, it is clear that we continue to face substantive challenges in applying mutant models to better understand the pathobiology of negative symptoms: the majority of evidence relates to impairments in social behavior, with only limited data relating to anhedonia and negligible data concerning avolition and other features; even for the most widely examined feature, social behavior, studies have used diverse assessments thereof; modelling must proceed in cognizance of increasing evidence that genes and pathobiologies implicated in schizophrenia overlap with other psychotic disorders, particularly bipolar disorder. Despite the caveats and challenges, several mutant lines evidence a phenotype for at least one index of social behavior. Though this may suggest superficially some shared relationship to negative symptoms, it is not yet possible to specify either the scope or the pathobiology of that relationship for any given gene. The breadth and depth of ongoing studies in mutants hold the prospect of addressing these shortcomings.

Effect of Bupleurum falcatum on the stress-induced impairment of spatial working memory in rats

Many studies have shown that Bupleurum falcatum (BF), which is widely used in the treatment of various psychosomatic diseases in traditional Oriental medicine, is an effective therapeutic intervention for memory impairment. The purpose of this study was to examine the effect of BF on stress-induced alterations in learning and memory in rats using the Morris water maze (MWM) and elevated plus maze (EPM) behavioral tests. In addition, we examined the effects of BF treatment on the cholinergic system, as indicated by changes in neuronal choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) immunoreactivity in the hippocampus. BF (150, 300, or 600 mg/kg) was administered orally 30 min before exposure to repeated immobilization (IMO) stress (4 h/d for 14 d). The BF treatment produced a significant improvement in escape latency (time required to find the platform) in the MWM, and it also produced an anxiolytic-like effect in the EPM. Consistent with the behavioral data, BF treatment significantly attenuated the IMO stress-induced loss of cholinergic immunoreactivity in the hippocampus. These findings indicate that BF has a protective effect against repeated IMO stress-induced neuronal and cognitive impairments, and they suggest that BF may be useful in the treatment of stress-induced memory impairment.

Effect of subchronic phencyclidine administration on sucrose preference and hippocampal parvalbumin immunoreactivity in the rat

Persistent blockade of NMDA receptor function by repeated phencyclidine dosing produces pathophysiological changes that model deficits observed in schizophrenia. The present study investigates the effects of subchronic phencyclidine administration (PCP; 2 or 5mg/kg bi-daily for 7 days followed by a drug-free period) on sucrose choice, a measure of anhedonia. Sucrose preference in a two-bottle sucrose-water choice test was assessed 1 and 2 weeks after PCP. Results showed no differences in sucrose intake between PCP rats and controls, nor a difference in water intake or total volume of liquid consumed at either time-point. Six weeks post-PCP, analysis of brains showed a reduction in expression of parvalbumin immunoreactive neurons in the hippocampus with significant reductions localised to the CA1 and CA2/3 regions. These results demonstrate that while subchronic PCP may not be a valid model for the negative symptom of anhedonia observed in schizophrenia, it induces pathology in the brain in hippocampal subregions that are reminiscent of changes observed in schizophrenia.

Desipramine prevents stress-induced changes in depressive-like behavior and hippocampal markers of neuroprotection

Extracellular signal-regulated kinases (ERKs) are widely implicated in multiple physiological processes. Although ERK1/2 has been proposed as a common mediator of antidepressant action in naive rodents, it remains to be determined whether the ERK1/2 pathway plays a role in depressive disorder. Here, we investigated whether chronic restraint stress (14 days) and antidepressant treatment [desipramine (DMI), 10 mg/kg intraperitoneally] induce changes in animal behavior and hippocampal levels of phospho-ERK1/2 and its substrate phospho-cAMP response element-binding protein (CREB). The results indicated that stress-induced depressive-like behaviors were correlated with an increase in P-ERK1/2 and P-CREB in the hippocampus evaluated by immunoblot analysis. As an indication of CREB activity, we evaluated changes in mRNA levels of its target genes. Brain-derived neurotrophic factor (BDNF) mRNA was reduced by stress, an effect prevented by DMI only in the CA3 area of hippocampus. Bcl-2 mRNA was reduced in all hippocampal regions by stress, an effect independent of DMI treatment. However, immunoblot from hippocampal extracts revealed that stress increased BCL-2 levels, an effect prevented by chronic DMI. These results suggest that ERKs and BDNF may be altered in depressive disorder, modifications that are sensitive to DMI action. In contrast, the stress-induced increase in BCL-2 may correspond to a neuroprotective response.

Gender-specific impact of brain-derived neurotrophic factor signaling on stress-induced depression-like behavior

BACKGROUND

Major depressive disorder is a leading debilitating disease known to occur at a two-fold higher rate in women than in men. The neurotrophic hypothesis of depression suggests that loss of brain-derived neurotrophic factor (BDNF) may increase susceptibility for depression-like behavior, although direct evidence is lacking.

METHODS

Using the chronic unpredictable stress (CUS) paradigm, we investigated whether male and female mice with inducible BDNF deletion in the forebrain were more susceptible to depression-related behavior.

RESULTS

We demonstrate that in certain behavioral measures the loss of BDNF lowers the threshold for female mice studied at random throughout estrus to display anxiogenic and anhedonic behaviors after chronic stress compared with wild-type female mice. However, the loss of BDNF in forebrain does not increase the susceptibility to depression-like behavior in male mice.

CONCLUSIONS

These gender differences suggest a role for BDNF in mediating some aspects of depression-related behavior in females.

The effect of antidepressant drugs on the HPA axis activity, glucocorticoid receptor level and FKBP51 concentration in prenatally stressed rats

Dysregulation of hypothalamic-pituitary-adrenal (HPA) axis activity is thought to be an important factor in pathogenesis of depression. In animals, stress or glucocorticoids given in prenatal period lead to long-lasting behavioral and neuroendocrine changes similar to those observed in depressed patients. However, molecular basis for HPA disturbances in animals exposed to prenatal stress - a model of depression - have been only partially recognized. Therefore, in the present study we investigated the effect of prenatal stress on behavioral changes, blood corticosterone level, concentrations of glucocorticoid receptor (GR) and its cochaperone, FKBP51, in the hippocampus and frontal cortex in adult rats. It has been found that prenatally stressed rats display high level of immobility in the Porsolt test and anxiety-like behavior. The HPA axis hyperactivity in theses animals was evidenced by corticosterone hypersecretion at the end of the light phase and 1h following acute stress. Western blot study revealed that GR level was significantly elevated in the hippocampus but not in the frontal cortex of prenatally stressed rats, whereas concentration of FKBP51 was decreased only in the former brain structure. Chronic treatment with imipramine, fluoxetine, mirtazapine and tianeptine have diminished both behavioral and biochemical alterations observed in this animal model of depression. These data indicate that the increase in hippocampal GR level and low concentration of FKBP51 in the frontal cortex may be responsible for enhanced glucocorticoid action in depression.

Antidepressant-like effects of curcumin on serotonergic receptor-coupled AC-cAMP pathway in chronic unpredictable mild stress of rats

Serotonergic receptors take their physiologic effects by affecting adenylyl cyclase (AC) catalytic activity and cyclic adenosine monophosphate (cAMP) concentration. AC-cAMP second messenger pathway has been recently suggested to play an important role in depression. Therefore, the compound that regulates the signal pathway may have potential as antidepressant. Curcumin is the main component of Curcuma longa L, a well-known indigenous herb with comprehensive bioactivities. In the present study, we investigated the effects of chronic unpredictable mild stress (CUMS) and curcumin on behaviours and serotonergic receptor-coupled AC-cAMP signal pathway in rats. Curcumin produced beneficial effects on the stressed rats by effectively improving CUMS-induced low sucrose consumption and reducing serum corticosterone levels in rats. Moreover, curcumin enhanced AC activity and cAMP levels in platelet and various brain regions, and up-regulated mRNA expressions of AC subtypes AC 2, AC 8 and cAMP response element binding protein (CREB) in the hippocampus, cortex and hypothalamus of the CUMS rats. Curcumin also attenuated CUMS-induced reductions of 5-hydroxytryptamine (5-HT) levels and high expressions of central 5-HT(1A/1B/7) receptors in rats. These results suggested that the potent antidepressant property of curcumin might be attributed to its improvement of AC-cAMP pathway as well as CREB via suppressing central 5-HT(1A/1B/7) receptors in the CUMS rats. Our findings provided a basis for examining the interaction of serotonergic receptors and AC-cAMP pathway in depression and curcumin treatment.

Effects of acupuncture on chronic corticosterone-induced depression-like behavior and expression of neuropeptide Y in the rats

Repeated injection of corticosterone (CORT) induces dysregulation in the HPA axis, resulting in depression and anxiety. Many studies have shown that acupuncture, which is widely used for the treatment of stress and mental illness, in East Asian countries, is an effective therapeutic intervention for psychosomatic disorders. We investigated the influence of acupuncture therapy on chronic CORT-induced behavioral responses to the forced swimming test (FST) and elevated plus maze (EPM) and expression of neuropeptide Y (NPY) in the rat brain using immunohistochemistry. Male Sprague-Dawley rats were injected with CORT (40 mg/kg, i.p.) once daily for 19 consecutive days. The dysregulation of HPA axis by external injection of CORT was confirmed by measuring the CORT concentration in plasma and the expression level of CRF in hypothalamus. Acupuncture was performed at the PC6 acupoint for 5 min before CORT injection. Acupuncture significantly reduced depression- and anxiety-like behavior and increased NPY expression in the hypothalamus. These results demonstrated that stimulation of the PC6 acupoint suppresses the symptopathology of the hypoactivated HPA axis in chronic CORT-induced rat model of depression.

Effect of chronic psychosocial stress-induced by subordinate colony (CSC) housing on brain neuronal activity patterns in mice

Chronic subordinate colony (CSC) housing has been recently validated as a murine model of chronic psychosocial stress which induces alterations of stress-related parameters including decreased body-weight gain and an increased level of anxiety in comparison with single housed control (SHC) mice. By using immunohistochemical immediate early gene (IEG) mapping we investigated whether CSC housing causes alterations in neuronal activation patterns in limbic areas including the amygdala, hippocampus, septum and the periaqueductal gray (PAG) and hypothalamic paraventricular nucleus (PVN). While CSC housing increased basal Zif-268 expression in the nucleus accumbens shell compared to SHC, IEG responses to subsequent open arm (OA) exposure were attenuated in the ventral and intermediate sub-regions of the lateral septum, parvocellular PVN and the dorsal CA3 region of the hippocampus of CSC compared with SHC mice. In contrast, a potentiated c-Fos response in CSC mice was observed in the dorsomedial PAG after OA exposure. Confirming previous findings obtained on the elevated plus-maze, an enhanced anxiety-related behavior in CSC compared with SHC mice was also observed during OA exposure. In order to investigate the appropriate control conditions for CSC housing, group housed control (GHC) mice were additionally included in the behavioral testing. Interestingly, GHC as well as CSC mice showed significantly less risk assessment/exploratory behavior during OA exposure compared with SHC mice indicating that group housing itself is stressful for mice and not an adequate control for the CSC paradigm. Overall, CSC housing is an ethologically relevant chronic psychosocial stressor which results in an elevated sensitivity to a subsequent novel, aversive challenge. However, the CSC-induced increase in anxiety-related behavior was accompanied by differences in neuronal activation, compared with SHC, in defined sub-regions of brain areas known to be involved in the processing of emotionality and stress responses.

Attenuation of high sweet solution preference by mood stabilizers: a possible mouse model for the increased reward-seeking domain of mania

The lack of appropriate animal models for bipolar disorder (BPD) is a major factor hindering the research of its pathophysiology and the development of new drug treatments. In line with the notion that BPD might represent a heterogeneous group of disorders, it was suggested that models for specific domains of BPD should be developed and then integrated. The present study tested sweet solution preference as a rodent model for increased reward seeking, a central component of manic behavior and a possible endophenotype of the disorder. The study identified that Black Swiss mice show high baseline saccharin preference compared with C57bl/6, CBA/J and A/J strains. Sweet solution preference in Black Swiss mice was therefore evaluated across a number of saccharin concentrations, with or without treatment with the mood stabilizers lithium and valproate and the antidepressant imipramine. Results indicated that the structurally dissimilar mood stabilizers lithium and valproate, but not the antidepressant imipramine, reduce sweet solution preference. However, different dosing schedules were needed for the two drugs to induce this effect. These findings support the face and the predictive validity of the sweet solution preference test as an animal model for the elevated reward-seeking domain of mania. As such, this test might be well integrated into a battery of models for different domains of BPD. Such a battery can be effectively utilized to screen new treatments, to distinguish between specific effects of different drugs, and to explore the mechanisms underlying BPD.

Antidepressant-like effect of liquiritin from Glycyrrhiza uralensis in chronic variable stress induced depression model rats

Many flavonoids extracted from nature plants have been reported to exert antidepressant-like effect in animal studies. The present study was designed to observe the effects of liquiritin, a flavone compound derived from Glycyrrhiza uralensis, on the behaviors of chronic variable stress induced depression model rats and to explore the possible association between its antidepressant-like effect and antioxidative activity by measuring erythrocyte superoxide dismutase (SOD) activity and plasma malondialdehyde (MDA) level of the experimental animals. With the exposure to stressor once daily for consecutive 5 weeks, liquiritin and a positive control drug fluoxetine were administered via gastric intubation to rats once daily for consecutive 3 weeks from the 3rd week. The results showed that CVS reduced open-field activity and sucrose consumption significantly, but increased immobility time in forced swimming test. Treatment of liquiritin could effectively reverse alteration in immobility time and sucrose consumption but did not show significant effect on open-field activity. Moreover, liquiritin could increase SOD activity, inhibit lipid peroxidation, and lessen production of MDA, while fluoxetine did not. In conclusion, the present study demonstrated a potential antidepressant-like effect of liquiritin treatment on chronic variable stress induced depression model rats, which might be related to defense of liquiritin against oxidative stress.

Behavioral processes mediating phencyclidine-induced decreases in voluntary sucrose consumption

Prior exposure to phencyclidine (PCP) has been shown to decrease voluntary sucrose consumption in rats, which may indicate reduced reward function. To further characterize the effects of PCP on sucrose consumption, we examined the dose-response relationship between PCP and sucrose consumption, the longevity of the effect, the effects of repeated injections of PCP, variation of the PCP effect across sucrose concentrations, and the effects of PCP on gustatory hedonic responses. A single injection of PCP (2.5-20 mg/kg) dose-dependently suppressed sucrose consumption 20 h post-injection, with significant decreases after 15 and 20 mg/kg PCP. These decreases were sustained three days following withdrawal from PCP. Repeated injections of PCP (7.5 mg/kg bid for 7 days) decreased sucrose consumption 20 h after withdrawal, which returned to baseline on the second day. A single injection of PCP (15 mg/kg) suppressed 0.15 M sucrose more than 1 M sucrose consumption, with no effect on 0.3 M sucrose, suggesting that PCP suppressed intake of moderately rewarding taste stimuli. Finally, a single injection of PCP (15 mg/kg) suppressed brief access (20 s) licking for the majority of concentrations of sucrose solutions offered (0.031 M, 0.062 M, 0.125 M, 0.25 M, 0.5 M, and 1.0 M), while it had no effect on licking for 0.016 M sucrose, water, or for bitter quinine hydrochloride solutions (range: 0.94 mM-30 mM), suggesting that the PCP effect is specific to palatable taste stimuli without disruption of sensitivity to taste quality or intensity. We conclude that PCP produces moderate anhedonia as reflected through a specific decrease in the sustained consumption of moderately palatable sucrose solutions.