Depression: The predisposing influence of stress

Maternal profiling of corticotropin-releasing factor receptor 2 deficient mice in association with restraint stress

Mice deficient in corticotropin-releasing factor receptor 2 (CRF2) (C57BL/6J:129Sv background) exhibit impaired maternal defense (protection of offspring) and are more reactive to stressors than wild-type mice. To further understand CRF2's role in maternal behavior, we crossed the knockout mice with a line bred for high maternal defense that also has elevated maternal care relative to inbred lines. Maternal care was normal in knockout mice (relative to wild-type). Maternal defense was impaired as previously observed. Exposure to a mild stressor (15 min restraint) did not trigger deficits in maternal defense in either genotype as determined by a two-way repeated measures ANOVA analysis. However, when examining difference scores between unrestrained and restrained conditions, knockout mice exhibited significant decreases in maternal defense with stress, suggesting knockouts are more susceptible to a mild stressor's effects. To gain possible insights into brain activity differences between WT and KO mice, we examined c-Fos expression in association with stress. Unrestrained KO mice exhibited significantly lower c-Fos levels relative to unrestrained WT mice in 9 regions, including lateral septum and periaqueductal gray. For WT mice, restraint stress triggered c-Fos activity increases in 3 regions while for KO mice, restraint stress triggered c-Fos increases in 16 regions. Taken together, our results suggest both altered behavioral and c-Fos responses to stress in lactating CRF2 KO mice.

A new short self-rating questionnaire to assess stress in children

We constructed a test to assess stress in children and compared it with established measures of depression, anxiety, angel; disruptive behavior, and negative self-perception. A total of 181 children aged between 9 and 12 years were enrolled at various stages of the construction of a new short questionnaire; Stress in Children (SiC). Baseline data, completed questionnaires, salivary cortisol (SC)five times during (1 day), and 24-h urinary catecholamines were collected during an ordinary school week. The SiC was validated using the Beck Youth Inventories of Emotional andnt (BYI). Associations with self-reported psychosomatic symptoms for urinary catecholamines and cortisol concentrations were assessed. Cronbach's 6 used in this study for the entire SiC questionnaire is 0.86. Statistically significant associations were found between the SiC Global Mean Score (GMS) and all of the five BYI subscales. Spearman's rho coefficient for the association of SiC GMS with the first SC sample is 0.30 (p = 0.01). When stratified by sex, the magnitude of the association between SC and SiC was higher in girls, while there was no significant association among boys. No significant associations with catecholamine levels were observed for self-rating scores from the SiC or BYI. This study demonstrated that the SiC questionnaire has satisfactory reliability and its ratings are associated with those generated by the BYI. The SiC GMS was associated with higher morning saliva cortisol in girls. Our results demonstrate that it is possible to screen for stress in schoolchildren using an easily administered self-rating instrument.

The role of corticotropin-releasing factor in the pathophysiology of affective and anxiety disorders: laboratory and clinical studies

The unique distribution of corticotropin-releasing factor (CRF) and its receptors within the central nervous system, its pre-eminent role in mediating the endocrine, behavioural, autonomic and immunological effects of stress and its potent effects after direct administration into the CNS all support the hypothesis that alterations in CRF neuronal systems contribute to the pathophysiology of depression and certain anxiety disorders. This report summarizes a series of preclinical and clinical investigations which have sought to test the hypothesis that CRF-containing neurons show alterations in depression and anxiety, and that drugs used to treat these disorders alter CRF neuronal circuits. Direct injection of CRF into the locus ceruleus or nearby parabrachial nucleus evokes an anxiogenic response. Stress increases CRF concentrations in the locus ceruleus, whereas alprazolam, a benzodiazepine anxiolytic, decreases the concentration of the peptide in the same area. Clinical studies reveal that drug-free depressed patients show: (1) hyperactivity of the hypothalamo-pituitary-adrenal axis; (2) increased CRF concentrations in the cerebrospinal fluid; (3) a blunted release of ACTH in response to CRF; (4) a reduced density of CRF receptors in the frontal cortex; (5) pituitary and adrenal gland hypertrophy. These findings are all concordant with hypersecretion of CRF from hypothalamic and extrahypothalamic CRF neurons in depression.

Glucocorticoids plus opioids up-regulate genes that influence neuronal function

(1) This study investigated the functional genomics of glucocorticoid and opioid receptor stimulation in cellular adaptations using a cultured neuronal cell model. (2) Human SH-SY5Y neuroblastoma cells grown in hormone-depleted serum were treated for 2-days with the glucocorticoid receptor-II agonist dexamethasone (30 nM); the mu-opioid receptor agonist [D-Ala2, N-Me-Phe4, Gly5-ol]-Enkephalin acetate (DAMGO; 1 nM); or dexamethasone (30 nM) plus DAMGO (1 nM). RNA was extracted; purified, reverse transcribed, and labeled cDNA was hybridized to a 10,000-oliogonucleotide-array human gene chip. Gene expression changes that were significantly different between treatment groups and were of interest due to biological function were verified by real-time reverse transcription polymerase chain reaction (RT-PCR). Five relevant genes were identified for which the combination of dexamethasone plus DAMGO, but neither one alone, significantly up-regulated gene expression (ANOVA, P < 0.05). (3) Proteins coded by the identified genes: FRS2 (fibroblast growth factor receptor substrate-2; CTNNB1 (beta1-catenin); PRCP (prolyl-carboxypeptidase); MPHOSPH9 (M-phase phosphoprotein 9); and ZFP95 (zinc finger protein 95) serve important neuronal functions in signal transduction, synapse formation, neuronal growth and development, or transcription regulation. Neither opioid, glucocorticoid nor combined treatments significantly altered the cell growth rate determined by cell counts and protein. (4) We conclude that sustained mu-opioid receptor stimulation accompanied by glucocorticoids can synergistically regulate genes that influence neuronal function. Future studies are warranted to determine if combined influences of glucocorticoid fluctuations and opioid receptor stimulation in vivo can orchestrate exagerated neuroadaptation to reinforcing drugs under chronic mild stress conditions.

Experimental animal models for the simulation of depression and anxiety

An impressive number of animal models to assess depression and anxiety are available today. However, the relationship between these models and the clinical syndromes of depression and anxiety is not always clear. Since human anxiety disorders represent a multifactorial phenomenon frequently comorbid with major depression and/or other psychiatric problems, the chance of creating animal models which consistently reflect the human situation is quite poor. When using experimental models to understand homologies between animal and human behavior, we have to consider the context in which an animal is investigated, and both the functional significance and relevance of the behavioral parameters that are quantified. Moreover, gender and interindividual and interspecies variabilities in behavioral responses to the test situation and in the sensitivity to pharmacological treatments are potential sources for confounding results. In the past, these aspects have been often neglected in preclinical approaches to behavioral pharmacology and psychopharmacology. A pragmatic approach of combined preclinical and clinical efforts is necessary to imitate one or more aspects relevant to pathological anxiety disorders and depression. The resulting models may identify central nervous processes regulating defined behavioral output, with the potential to develop more effective treatments.

Antidepressant-like effect of saponins extracted from Chaihu-jia-longgu-muli-tang and its possible mechanism

In this study, we investigated the antidepressant-like effect of saponins (SCLM) extracted from a traditional Chinese medicine, Chaihu-jia-longgu-muli-tang (CLM), in mice and rats using the tail suspension test (TST) and forced swimming test (FST). Subchronic administration of 100 and 200 mg/kg (p.o.) SCLM for 7 days reduced immobility time in the TST and FST in mice and also decreased immobility time at 70 and 140 mg/kg (p.o.) in the FST in rats. The results also showed that the anti-immobility activity of SCLM in these two tests is dose-dependent, without accompanying significant effects on locomotor activity. In addition, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) and lactic dehydrogenase (LDH) assays showed that 25, 50 and 100 microg/ml SCLM or 10 microM fluoxetine (FLU), protected PC12 cells from the lesion induced by 10 microM corticosterone (Cort) treatment for 48 h. In the fura-2/AM (acetoxymethyl ester) labeling assay, 50 and 100 microg/ml SCLM, 10 microM FLU attenuated the intracellular Ca2+ overloading induced by 200 microM Cort treatment for 48 h in PC12 cells. Using RT-PCR, the mRNA level of nerve growth factor (NGF) was also detected. Treatment with SCLM (50, 100 microg/ml) for 48 h elevated the NGF mRNA expression in PC12 cells. In summary, these results suggest that SCLM possesses an antidepressant-like activity in behavioral models that might be mediated via the cytoprotective action shown in PC12 cells.

Antidepressant Effect of Extracts from Ginkgo biloba Leaves in Behavioral Models

Extracts of Ginkgo biloba (EGB) are a complex product prepared from green leaves of the Ginkgo biloba tree. In the present study, the antidepressant effect of EGB was examined using two behavioral models, the forced swimming test (FST) in rats and tail suspension test (TST) in mice. EGB significantly reduced immobility time in the FST at a dosage of 10 and 50 mg/kg body weight after repeated oral treatment for 14 d, although no change of motor dysfunction was observed with the same dosage in the open field test. These results indicate that EGB might possess an antidepressant activity. In addition, EGB markedly shortened immobility time in the TST after acute inter-peritoneal treatment at a dosage of 50 and 100 mg/kg body weight. The present study clearly demonstrated that EGB exerts an antidepressant effect in these two behavioral models.

Cognitive activation theory of stress (CATS): from fish brains to the Olympics

The Cognitive Activation Theory of Stress (CATS) offers formal and systematic definitions of the terms and concepts used in stress research. The stress response depends on acquired expectancies to the outcome of the stimulus and the available responses. The stress response itself is an alarm, an increase in arousal necessary for performance and adequate reactions to challenges. The response is healthy and necessary for survival. Only when sustained over time may potential health risks occur. The basic rules for when stress occurs are the same across cultures and species, from fish to Olympic performance in humans. The important dimensions for health are positive expectancies of outcome (coping), control, and safety, for all individuals in all species.

Immobility in the swim test and observations of maternal behavior in lactating flinders sensitive line rats

In order to elucidate the relationship between maternal behavior and depression, the Flinders sensitive line (FSL) model of depression was studied and compared to Sprague-Dawley (SD) controls. Immobility in the swim test was measured, as an index for depressive-like behavior, and frequencies of maternal and non-maternal behaviors were recorded using short un-intrusive observations in the home cage. Lactating FSL rats displayed higher levels of immobility in the swim test compared to controls, indicating depressive-like behavior. In addition, compared to SD rats, FSL dams showed less frequent pup licking and non-nutritive contact with pups during the first and third weeks of lactation. In the third postpartum week, FSL dams showed less frequent nursing postures and more frequent self-directed behaviors. Thus, lactating FSL dams exhibit both depressed-like behavior and some abnormalities in maternal behavior.

Stress, depression, and anhedonia: caveats concerning animal models

Numerous animal models of depression have been advanced, each having multiple attributes and some limitations. This review provides caveats concerning etiologically valid animal models of depression, focusing on characteristics of the depressive subtype being examined (e.g. typical vs atypical major depression, dysthymia, melancholia), and factors that contribute to the interindividual behavioral variability frequently evident in stressor-related behavioral paradigms. These include the stressor type (processive vs systemic stressors), and characteristics of the stressor (controllability, predictability, ambiguity, chronicity, intermittence), as well as organismic variables (genetic, age, sex), experiential variables (stressor history, early life events) and psychosocial and personality factors that moderate stressor reactivity. Finally, a model of depression is reviewed that evaluates the effects of stressors on hedonic processes, reflected by responding for rewarding brain stimulation. Anhedonia is a fundamental feature of depression, and assessment of stressor-related reductions in the rewarding value of brain stimulation, especially when coupled with other potential symptoms of depression, provides considerable face, construct and predictive validity. Stressful events markedly impact rewarding brain stimulation, and this effect varies across strains of mice differentially reactive to stressors, is modifiable by antidepressant treatments, and allows for analyses of the contribution of different brain regions to anhedonic processes. The paradigm is sensitive to several factors known to acts as moderators of stress responses, but analyses remain to be conducted with regard to several such variables.

Social stress in tree shrews as an animal model of depression: an example of a behavioral model of a CNS disorder

Animal models are invaluable in preclinical research on human psychopathology. Valid animal models to study the pathophysiology of depression and specific biological and behavioral responses to antidepressant drug treatments are of prime interest. In order to improve our knowledge of the causal mechanisms of stress-related disorders such as depression, we need animal models that mirror the situation seen in patients. One promising model is the chronic psychosocial stress paradigm in male tree shrews. Coexistence of two males in visual and olfactory contact leads to a stable dominant/subordinate relationship, with the subordinates showing obvious changes in behavioral, neuroendocrine, and central nervous activity that are similar to the signs and symptoms observed during episodes of depression in patients. To discover whether this model, besides its "face validity" for depression, also has "predictive validity," we treated subordinate animals with the tricyclic antidepressant clomipramine and found a time-dependent recovery of both endocrine function and normal behavior. In contrast, the anxiolytic diazepam was ineffective. Chronic psychosocial stress in male tree shrews significantly decreased hippocampal volume and the proliferation rate of the granule precursor cells in the dentate gyrus. These stress-induced changes can be prevented by treating the animals with clomipramine, tianeptine, or the selective neurokinin receptor antagonist L-760,735. In addition to its apparent face and predictive validity, the tree shrew model also has a "molecular validity" due to the degradation routes of psychotropic compounds and gene sequences of receptors are very similar to those in humans. Although further research is required to validate this model fully, it provides an adequate and interesting non-rodent experimental paradigm for preclinical research on depression.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Social environment determines the long-term effects of social defeat

A single social defeat by a dominant conspecific induces long-term changes in several physiological and behavioral parameters in rats. These changes may represent an increased vulnerability to subsequent stress and stress-related pathology. Environmental factors, in particular possibilities for social interactions, could modulate these effects. Therefore, we assessed the influence of social environment on susceptibility for the long-term effects of social defeat. Socially housed males of an unselected strain of wild-type rats were equipped with radio-telemetry transmitters that recorded heart rate, temperature and activity. They were individually subjected to defeat and subsequently either housed alone or returned to their group. Behavioral and physiological responses to various novelty stressors were determined during a three-week period after the social defeat. Furthermore, changes in baseline behavior and physiology following defeat were studied in the rat's homecage. The results show a complex interaction between defeat and housing conditions. Depending on the parameters measured, effects were caused by both isolation alone, defeat alone or a combination of both defeat and isolation. Individual housing alone caused a characteristic hyperactive response to novelty stress. Though defeat did not affect behavioral responses, it amplified the physiological response to novelty and social housing did not attenuate this effect. However, social housing did reduce the effects of defeat on heart rate, temperature and activity in the home cage and completely prevented defeat-induced weight loss. Together these results indicate that social housing may indeed positively affect the animal's capacity to cope with stressors.

Long-term effects of social stress on brain and behavior: a focus on hippocampal functioning

In order to study mechanisms involved in the etiology of human affective disorders, there is an abundant use of various animal models. Next to genetic factors that predispose for psychopathologies, environmental stress is playing an important role in the etiology of these mental diseases. Since the majority of stress stimuli in humans that lead to psychopathology are of social nature, the study of consequences of social stress in experimental animal models is very valuable. The present review focuses on one of these models that uses the resident-intruder paradigm. In particular the long-lasting effects of social defeat in rats will be evaluated. Data from our laboratory on the consequences of social defeat on emotional behavior, stress responsivity and serotonergic functionality are presented. Furthermore, we will go into detail on hippocampal functioning in socially stressed rats. Very recent results show that there is a differential effect of a brief double social defeat and repetitive social defeat stress on dendritic remodeling in hippocampal CA3 neurons and that this has repercussions on hippocampal LTP and LTD. Both the structural and electrophysiological changes of principal neurons in the hippocampal formation after defeat are discussed as to their relationship with the maintenance in cognitive performance that was observed in socially stressed rats. The results are indicative of a large dynamic range in the adaptive plasticity of the brain, allowing the animals to adapt behaviorally to the previously occurred stressful situation with the progression of time.

Pavlovian autoshaping procedures increase plasma corticosterone and levels of norepinephrine and serotonin in prefrontal cortex in rats

Pavlovian autoshaping procedures provide for pairings of a small object conditioned stimulus (CS) with a rewarding substance unconditioned stimulus (US), resulting in the acquisition of complex sequences of CS-directed skeletal-motor responses or autoshaping conditioned responses (CRs). Autoshaping procedures induce higher post-session levels of corticosterone than in controls receiving CS and US randomly, and the enhanced post-session corticosterone levels have been attributed to the appetitive or arousal-inducing effects of autoshaping procedures. Enhanced corticosterone release can be induced by aversive stimulation or stressful situations, where it is often accompanied by higher levels of norepinephrine (NE) and serotonin (5-HT) in prefrontal cortex (PFC) but not in striatum (ST). Effects of autoshaping procedures on post-session corticosterone levels, NE contents in PFC, and 5-HT contents in PFC and ST were investigated in male Long-Evans rats. Post-session blood samples revealed higher corticosterone levels in the CS-US Paired group (n = 46) than in the CS-US Random control group (n = 21), and brain samples revealed higher levels of PFC NE and 5-HT in CS-US Paired group. Striatal 5-HT levels were unaltered by the autoshaping procedures. Autoshaping procedures provide for appetitive stimulation and induce an arousal-like state, as well as simultaneous stress-like changes in plasma corticosterone and monoamine levels in PFC. Autoshaping, therefore, may be useful for the study of endocrine and central processes associated with appetitive conditions.

Effect of glucocorticoïd receptor ligands on myosin heavy chains expression in rat skeletal muscles during controllable stress

The influence of agonist (dexamethasone) and antagonist (mifepristone) of glucocorticoïd receptor during controllable painless stress was evaluated on myosin heavy chains expression in three masticatory and two nape rat muscles: anterior digastric (AD), anterior temporalis (AT), masseter superficialis (MS), longissimus capitis (L) and rectus capitis dorsalis major (R). The relative amounts of myosin heavy chain (MHC) protein isoform contained were significantly affected in four muscles studied by dexamethasone and in three muscles studied under mifepristone, versus control during the stress procedure, after only 1 week of treatment. The control group AT muscles contained respectively 18.2% of MHC 2A, 34.5% of MHC 2X and 47.4% of MHC 2B. The effects of dexamethasone and mifepristone were opposite in this muscle: under dexamethasone, the relative proportions of the three isoforms were 14.2, 31.0 and 54.8%: consequently, MHC 2A and 2X decreased with the profit of 2B. Under mifepristone, the relative proportions were 21.1, 36.6 and 42.3% (MHC 2A and 2X increased to the detriment of 2B). The L muscle was not affected by the two treatments and MS muscle was only affected by dexamethasone. Dexamethasone increased MHC 2B to the detriment of MHC 2A in MS, AD and R. Mifepristone and dexamethasone induced the same changes in AD. The mifepristone treatment decreased the MHC 2X profile in R. Under dexamethasone, four muscles exhibited a significantly higher proportion of the more rapid isoforms than under mifepristone. A previous work showed that controllable stress induced a marked increase in the relative expression of MHC 2B in the same skeletal muscles (Martrette et al. , 1998). Our results confirm then a significant participation of glucocorticoïd in MHC isoform expression during controllable stress.

Chronic Stress Conditions Do Explain Posttraumatic Brain Injury Depression

Psychosocial and biologic mechanisms are implicated in depression after traumatic brain injury (TBI). Using McEwen's stress theory of allostasis as a guidepost, this study examined whether pre- and postinjury chronic stress conditions could explain post-TBI depressive symptoms. Seventy-five community-dwelling persons who sustained a mild-to-moderate TBI and were within 2 years of the injury participated in this cross-sectional study. The participants completed measures of chronic stress and depression, measured with the Neurobehavioral Functioning Inventory. Data were collected also on brain injury severity. Using multiple regression analysis, the frequency of childhood adversities and postinjury stress explained post-TBI depression. When time-since-injury was in the regression model, the frequency of preinjury stressors and postinjury stress significantly explained post-TBI depressive symptoms while the combined effect of childhood adversity with postinjury stress was not significant in explaining depressive symptoms. Pre- and postinjury chronic stress explained post-TBI depressive symptoms. These findings support stress-diathesis theory within the psychiatric literature and a linkage between chronic stress, an indicator of allostatic load, and post-TBI depression. These findings are important for nurse specialists working with persons who sustained brain injury, for chronic stress can be buffered by efficient and effective support systems.

Stress, stress response, and health

Components of stress and the stress response differ between men and women. The tend-and-befriend response, mediated by oxytocin and endogenous opioids, may be more applicable to women than the fight-or-flight response, which was based largely on studies of men. Even within the flight-or-flight response pattern there are sex-based differences. The HPA axis interacts with reproductive function, such as menstruation. For immune function there are sex differences as well as differences within the menstrual phase. Inclusion of men and women in stress response studies is critical. Further study is needed to clarify the influence of ovarian hormones on the stress and immune responses during the reproductive stages in women's lives, including menarche. pregnancy, and perimenopause.

The promises and pitfalls of reboxetine

The antidepressant compound, morpholine, 2-[(2-ethoxyphenoxy)phenylmethyl]-,methanesulfonate, or reboxetine, is a selective noradrenergic reuptake inhibitor that acts by binding to the norepinephrine (NE) transporter and blocking reuptake of extracellular NE back into terminals. This compound has low affinity for other transporters and receptors. The development of reboxetine as a potential antidepressant stems from the prior demonstration that blockade of the NE transporter imparts antidepressant activity. Desipramine, lofepramine, and nortryptiline are examples of tricyclic antidepressant (TCA) compounds from the first generation of antidepressants that exert their effects by blockade of NE reuptake. Maprotiline, a non-tricyclic compound, is also a NE selective reuptake inhibitor. Unfortunately, these antidepressants are also associated with interactions with muscarinic, histaminergic, and adrenergic receptors, which are known to contribute to a variety of untoward side effects. Despite the positive pharmacological profile of reboxetine, i.e., selectivity and specificity, with relatively fewer side effects, its use as an antidepressant is currently limited to Europe. Reboxetine is marketed as Edronax in the UK, Norebox in Italy, and as Irenor in Spain. It is registered in Germany, Sweden, Denmark, Ireland, Austria and Finland. Based on studies conducted primarily outside the US, the FDA granted a preliminary letter of approval in 1999. However, more recent clinical studies conducted in the US and Canada, prompted by the FDA, resulted in a letter of non-approval. To date, it is unclear why the further development of reboxetine as an antidepressant in the US has been halted. Despite this setback, reboxetine has been a valuable pharmacological tool to assess the role of the noradrenergic system in preclinical studies of depressive disorder.

Strain and gender specific effects in the forced swim test: effects of previous stress exposure

The chronic mild stress (CMS) procedure was developed in rodents to target anhedonia, the core symptom of depressive melancholia. Stress exposure has been shown to induce a variety of physiological, biochemical and behavioral alterations associated with depression, although its anhedonic consequences as indexed by either sucrose intake and preference or thresholds for brain stimulation reward are less reliably observed. In the present study, we assessed the effects of six weeks of CMS on the latter measure in two strains of male and female rats subsequently challenged with an acute psychophysical stressor, forced swimming; their behavior in the swimming cylinder was evaluated on two consecutive days. While brain stimulation reward thresholds and response rates were unchanged by CMS exposure, significant differences in forced swim behaviors were observed between male control and CMS groups. In particular, male Long Evans rats with a history of CMS showed the largest decrease in the duration of active behaviors on the second test day, a pattern less evident in the Sprague-Dawley strain of rats, or in any of the female groups. The results suggest that the effects of depressogenic manipulations are strain and gender dependent, with male Long Evans rats most susceptible, as demonstrated by the selective reduction of struggling behaviors. Inclusion of multiple measures, including the forced swim test, would provide a better understanding of the psychopathological profile engendered by chronic exposure to mild stressors and its genetic specificity.

Evaluation of the effects of chronic mild stressors on hedonic and physiological responses: sex and strain compared

The chronic mild stress (CMS) paradigm was developed in order to simulate in animals the symptom of anhedonia, a major feature of depression. Typically, changes in hedonic status are interpreted from a decrease in either intake or preference for a mild sucrose solution. Although the incidence of clinical depression is significantly higher in women than in men, the study of this disorder in most animal models of depression has been based on the responses of male rodents. The purpose of this study was to compare the effects of 6 weeks of CMS administration among male and female rats of two rat strains, Sprague-Dawley (SD) and Long Evans (LE), with respect to physiological (body, adrenal gland, and spleen weight) and biochemical (plasma corticosterone levels) indices of stress as well as evaluations of 1 and 24 h sucrose intake and preference. Estrous cycle was tracked throughout the study. Overall, our results indicate a slower rate of weight gain in animals, greater in males, exposed to the chronic stressor regime. Furthermore, CMS is shown to disrupt estrous cycling, predominantly in the Long Evans strain of rats. The main behavioral finding was a significant reduction in 24 h sucrose intake in female treated groups, which was not accompanied by alterations in preference. Corticosterone levels were elevated in CMS-treated animals relative to the singly housed control groups, but exposure to a subsequent stressor was not influenced by the stress history. Taken together, the effects of chronic stressor exposure are evident, based on physiological and biochemical indices, although none of the measures distinguished any striking gender specific reactions. The usefulness of sucrose intake or preference as behavioral indices of CMS-induced anhedonia in males and females is modest at best.

Saiko-ka-ryukotsu-borei-to, a herbal medicine, ameliorates chronic stress-induced depressive state in rotarod performance

Exposure to chronic stress is thought to play an important role in the etiology of depression. This disorder has been shown to involve disruption of the hypothalamo-pituitary-adrenal (HPA) system and dysfunction of the prefrontal cortex (PFC). We have demonstrated that chronic stress in rats induces similar HPA disruption or a depressive state caused by a reduction of dopaminergic and serotonergic transmission in the PFC. We have also shown that saiko-ka-ryukotsu-borei-to, a herbal medicine, prevents such chronic stress-induced HPA disruption. However, the behavioral and neurochemical bases of this drug remain unclear. Here we examined the effects of saiko-ka-ryukotsu-borei-to on the depressive behavioral state and the reduction of transmission resulting from chronic stress. The chronic stress was induced by water immersion and restraint (2 h/day) for 4 weeks followed by recovery for 10 days. The treatment with saiko-ka-ryukotsu-borei-to (100, 300, or 1000 mg/kg p.o.) ameliorated the stress-induced depressive state in a dose-dependent manner, evaluated by a rotarod test. A microdialysis study indicated that the drug treatment significantly prevented the chronic stress-induced decreases in extracellular concentrations of dopamine and serotonin in the PFC. These results suggest that saiko-ka-ryukotsu-borei-to ameliorates the chronic stress-induced depressive state based on the prevention of PFC dysfunction. These findings provide important information for treatment of depression.

The neurobiology of depression: perspectives from animal and human sleep studies

This article reviews human and animal studies in the neurobiology of depression. The etiology of the illness, associated neurotransmitter dysregulation, sex steroids, the role of stress, and sleep regulation are discussed. It is suggested that the genesis of depression is related to homeostatic maladaptation that is sexually dimorphic. The authors propose that depressed females are hyperresponsive to stress, whereas depressed males are hyporesponsive to stress. This divergence reflects the exaggeration of naturally occurring differences between males and females, which are most obvious under challenge conditions. The authors conclude that future work in this area should fully evaluate sexual dimorphism, neural plasticity, critical periods, and individual differences in vulnerability.

Exposure to chronic mild stress alters thresholds for lateral hypothalamic stimulation reward and subsequent responsiveness to amphetamine

Chronic mild stress in rodents has been proposed to model some of the environmental factors that contribute to the induction of depressive disorders in humans. This model is based on the hypothesis that chronic mild stress induces a change in brain reward function that resembles the symptomatology of major depression, namely, a decrease in responsiveness to rewarding stimuli. The purpose of the first experiment was to investigate whether chronic mild stress affects brain reward function as measured by alterations in lateral hypothalamic self-stimulation behavior in rats. Exposure to chronic mild stress induces a reduction in body weight which might affect brain reward function on its own. Therefore, the potential contribution of a reduction in body weight to the chronic mild stress-induced alterations in brain reward function was examined in a separate group of food-restricted rats. Thresholds for lateral hypothalamic self-stimulation were slightly but significantly lowered in animals exposed to chronic mild stress, indicating an enhancement of stimulation reward efficacy. Food restriction had no effect on brain reward function. The second experiment examined the interaction between prior exposure to chronic mild stress or food restriction and responsiveness to a pharmacological challenge, amphetamine, that enhances brain reward function. Acute administration of amphetamine produced a greater enhancement of lateral hypothalamic self-stimulation reward in animals exposed to chronic stress relative to non-stressed and food-restricted animals. Taken together, the present findings indicate that chronic mild stress sensitizes the neural substrates that mediate both lateral hypothalamic stimulation and psychostimulant drug reward. These findings support the hypothesis that prior exposure to stress affects the vulnerability for drug-taking behavior by increasing the positive reinforcing properties of drug of abuse.

Sleep deprivation in depression: An integrative approach

The question as to whether the beneficial effect of sleep deprivation in depression is related to the increased wakefulness or to the sleep suppression by itself, is made moot by the search activity concept. According to this concept, rapid eye movement (REM) sleep is functionally deficient in depression and increases feelings of helplessness and hopelessness instead of restoring mood and search activity. Thus, REM sleep deprivation, either selective or not, is beneficial by breaking a vicious circle: depression in wakefulness…giving up (helplessness) in dream scenario…increased depression in the subsequent wakefulness. In addition, sleep deprivation is an important challenge for the depressed patient. The ability to confront this challenge and maintain wakefulness has a positive outcome on depression, especially when wakefulness is accompanied by active behavior.

Effects of partial locus coeruleus denervation and chronic mild stress on behaviour and monoamine neurochemistry in the rat

It has been proposed that lesions of the ascending noradrenergic projections render animals more vulnerable to stress. In this study, the effects of partial denervation of the locus coeruleus (LC) by DSP-4 (10 mg/kg) treatment, chronic mild stress (CMS) and their combination were examined. DSP-4 was administered to rats 1 week before the onset of CMS, which was applied for 5 weeks. In the forced swimming test, the immobility time was decreased by both DSP-4 and CMS. In the open field test, the number of defecations was increased after DSP-4 treatment plus CMS. Partial LC denervation decreased the levels of noradrenaline (NA) by 34%, increased NA turnover, and decreased the density of beta-adrenoceptors in the cerebral cortex. CMS decreased the binding affinity of beta-adrenoceptors, an effect not observed in the DSP-4 treated animals. In conclusion, 6 weeks after partial LC denervation NA turnover is increased in the cortex, and the effect of CMS on emotionality is enhanced.

Biological mechanisms in the relationship between depression and heart disease

Psychological depression is shown to be associated with several aspects of coronary artery disease (CAD), including arrhythmias, myocardial infarction, heart failure and sudden death. The physiological mechanisms accounting for this association are unclear. Hypothalamic-pituitary-adrenal dysregulation, diminished heart rate variability, altered blood platelet function and noncompliance with medial treatments have been proposed as mechanisms underlying depression and cardiovascular disease. Recent evidence also suggests that reduced baroreflex sensitivity, impaired immune function, chronic fatigue and the co-morbidity of depression and anxiety may be involved in the relationship between depression and cardiovascular dysregulation. An experimental strategy using animal models for investigating underlying physiological abnormalities in depression is presented. A key to understanding the bidirectional association between depression and heart disease is to determine whether there are common changes in brain systems that are associated with these conditions. Such approaches may hold promise for advancing our understanding of the interaction between this mood disorder and CAD.

The effects of chronic mild stress on male Sprague-Dawley and Long Evans rats: I. Biochemical and physiological analyses

The chronic unpredictable mild stress (CMS) is a paradigm developed in animals to model the relatively minor and unanticipated irritants that lead to a state of anhedonia in some individuals. However, the effectiveness of CMS is sometimes difficult to establish, for which unique strain sensitivities has been attributed as one contributing factor. These considerations led us to design the present study, which was an investigation of the corticosterone response to CMS in two outbred rat strains--Sprague-Dawley and Long Evans. Animals were exposed to one of two conditions--control or CMS--for 3 weeks during which body weight and fecal count were regularly monitored. At the end of this period, blood was sampled at a variety of time intervals following induction of a brief restraint stressor. First, a significant effect of CMS on corticosterone levels was evident at time 0 (prior to the application of the acute restraint stressor) in both strains. Second, the typical quadratic pattern of stressor-elicited fluctuations in this measure was similar in both Sprague-Dawley and Long Evans rats, with consistently elevated levels for the first hour following exposure to the acute stressor; near baseline values were observed at 2 h. However, only in the Long Evans strain were CMS related values much less than that observed in the control group after restraint stress. Third, both strains showed a reduced weight gain in the CMS groups relative to control groups. Fourth, spleen and adrenal weights were similar across all groups. Fifth, fecal counts remained stable across weeks of treatment in all groups with the exception of the Long Evans rats exposed to CMS; in this group, average counts were systematically reduced over the treatment period. We conclude that a history of chronic stress significantly blunts corticosterone levels in Long Evans but not Sprague-Dawley rats following exposure to an acute stressor. Physiological indices however are less influenced by this experience, at least when the exposure is limited to 3 weeks.

A comparison of female and male rats' ETOH-induced ataxia and exploration following restraint or swim stress

Animal models of stress reactivity are often employed in developing treatments for humans. Many studies use shock stress, and most use male rats. These experiments compare female and male rats exposed to either restraint stress (RS) or ambient-temperature swim stress (SS), using two durations of each stressor and naive controls. The ataxic effects of a 0.6 g/kg i.p. dose of ethanol (ETOH) were measured. Females exhibited less ataxia than males following ETOH administration. There were no significant effects of stress on ETOH-induced ataxia. Exploration was also measured in an open-field test (OFT) both pre- and poststress. In the prestress OFT, females were more active than males. For the no-stress groups and the shorter-duration stress groups, exploration decreased between the first and second OFTs. However, the groups exposed to the longer-duration stress did not show this expected decrease in exploration. A key finding of this research is that while sex differences may be present at baseline, the sexes may react similarly to stress. These data extend knowledge on sex differences in stress, alcohol reactivity and exploratory behavior.

Chronic stress impairs rotarod performance in rats: implications for depressive state

Exposure to chronic stress is thought to precipitate or exacerbate several neuropsychiatric disorders such as depression. Here, we examined the effects of chronic stress administered by water immersion and restraint (2 h/day) for 4 weeks followed by a 10-day recovery period on rotarod performance. The time course study revealed that the riding time on a rotating rod was not affected at Day 1 or Week 1 of the stress period, but was significantly decreased at Week 4 and after the 10-day recovery period. However, traction performance and locomotor activity were not changed by chronic stress. We next examined the involvement of a serotonergic mechanism in the impairment of rotarod performance. The post-stress administration of a serotonergic antidepressant, trazodone (10 mg/kg, daily for 10 days) significantly ameliorated the impairment of rotarod performance. A microdialysis study also revealed a decrease in the extracellular concentration of serotonin in the prefrontal cortex. These results indicate that chronic stress impairs the rotarod performance in a manner that is not due to muscle relaxation or motor dysfunction, and this impairment may imply a behaviorally depressive state mediated by a serotonergic mechanism. These findings provide insight into the underlying mechanisms of stress-induced neuropsychiatric disorders.

Pre- and postsynaptic responses to 1-(1-naphthylpiperazine) following adaptation to stress in rats

In view of a role of pre- and postsynaptic serotonin (5-hydroxytryptamine; 5-HT) receptors in adaptation to stress, effects of 1-(1-naphthylpiperazine) (1-NP) were compared in unrestrained and repeatedly restrained adapted rats. In the first part of the study, effects of various doses (1.0-15 mg/kg ip) of 1-NP were monitored on brain 5-HT metabolism (presynaptic response) and on the activity (postsynaptic response) of rats in an activity cage to which the rats were habituated before the drug administration. The drug injected at doses of 2.5-15.0 mg/kg increased motor activity and decreased brain 5-hydroxyindoleacetic acid (5-HIAA) concentration in a dose-dependent manner. In the second part of the study, rats were restrained on wire grids 2 h/day for 5 days. First-day episode of 2-h restraint decreased 24-h cumulative food intake, water intake and growth rate. The decreases attenuated following second-, third- and fourth-day episodes of 2-h restraint were not observed following fifth-day episode of 2-h restraint stress, suggesting adaptation to the stress schedule has occurred. Serotonergic and motor responses to 1-NP in unrestrained and repeatedly restrained adapted rats were compared by injecting the drug at a dose of 5 mg/kg, a dose that above results suggested would not produce maximal effects on 5-HT metabolism or motor activity. Administration of 1-NP at a dose of 5 mg/kg increased motor activity and decreased brain 5-HIAA concentration in unrestrained and repeatedly restrained adapted rats. Increases of motor activity were much greater in repeatedly restrained adapted than unrestrained rats. Decreases of 5-HIAA concentration were comparable in the two groups. The results are discussed in the context of an increase in the effectiveness of postsynaptic 5-HT-1A and 5-HT-1B receptors and a decrease in the effectiveness of presynaptic 5-HT-1A (somatodendritic) and 5-HT-1B (terminal) receptors following adaptation to stress. It is suggested that these changes of receptor responsiveness might help coping with stress demand to produce adaptation to stress.

Acute stress-induced increases in thalamic CRH mRNA are blocked by repeated stress exposure

Corticotropin-releasing hormone (CRH) coordinates multiple aspects of the stress response. Recently, CRH mRNA has been identified in two regions of the thalamus: the posterior nuclear group (Po), and a region located at the interface of the central medial and ventral posteromedial nucleus (parvicellular part) (CM-VPMpc). Previous studies demonstrated that in both regions CRH mRNA increases following 1 h of restraint stress, suggesting involvement of thalamic CRH in processing somatosensory and visceral information related to stress. The current study was proposed to further understand the effects of repeated and acute restraint stress on levels of thalamic CRH mRNA. Adult male rats were assigned to one of four groups in a 2 (repeated stress, no repeated) x2 (acute, no acute) design. Brain sections were processed for CRH mRNA in situ hybridization. ANOVA revealed no main effects of acute or repeated stress in either thalamic region. However, significant interactions between acute and repeated stress for levels of CRH mRNA were found for both regions of the thalamus. Compared to the no stress condition, acute restraint significantly increased CRH mRNA in the Po (39%) and the CM-VPMpc (32%). Repeated restraint did not alter baseline CRH mRNA levels, but blocked the acute restraint-induced effects. Thus, while acute stress increases levels of thalamic CRH mRNA, repeated exposure to the same stressor is without effect and prevents the acute response. These findings add to data establishing a role for thalamic CRH in the stress response and suggest a mechanism that may underlie habituation to repeated stress exposure.

Antidepressant-like action of AGN 2979, a tryptophan hydroxylase activation inhibitor, in a chronic mild stress model of depression in rats

Chronic mild stress (CMS) procedure was used to study an antidepressant-like activity of AGN 2979, a selective inhibitor of tryptophan hydroxylase (TH) activation. At the dose of 4 mg/kg, AGN 2979 fully reversed the CMS-induced reduction in the consumption of 1% sucrose solution. This effect was maintained for at least 1 week after cessation of treatment and no signs of withdrawal were observed in either stressed or control animals receiving AGN 2979. The lower (1 mg/kg) and higher (16 mg/kg) doses were ineffective. The magnitude of action of AGN 2979 in the CMS model was comparable to that of imipramine (10 mg/kg) but its onset of action appears to be faster since the inhibition of sucrose intake in stressed animals was already reversed after the 1st week of AGN 2979 administration while imipramine required 3 weeks of treatment to cause similar effect. These results provide support for the hypothesis that inhibition of TH activation may result in a potent antidepressant activity.

Chronic variable stress and partial 5-HT denervation by parachloroamphetamine treatment in the rat: effects on behavior and monoamine neurochemistry

Chronic variable stress (CVS) and manipulations of 5-HT-ergic neurotransmission are increasingly used as animal models of depression. In the present study, CVS for 2 weeks and a partial lesion of 5-HT projections by a small dose of parachloroamphetamine (PCA, 2 mg/kg) were applied independently or in combination. CVS reduced significantly the gain in body weight and increased the number of defecations in the open field test. PCA reduced body weight only within the first 24 h after its administration. Consumption of sucrose solution and its preference to water in non-deprived rats were significantly higher in PCA-pretreated rats 2 weeks after CVS compared to control animals. In the forced swimming test, both PCA and CVS treatments reduced immobility on the first but not the second session. Both treatments reduced significantly the time rats spent in social interaction. CVS also elicited an increase in the weight of the right adrenal, but this effect was not present in the PCA-pretreated group. PCA reduced 5-HT and 5-HIAA levels in the frontal cortex, hippocampus, and septum by approximately 20%. CVS increased HVA levels in the frontal cortex. Applied together, PCA pretreatment and CVS increased dopamine turnover in the frontal cortex. Conclusively, this study has provided evidence that chronic variable stress, which elicited expected physiological and neurochemical changes, does not reduce sucrose intake or preference in non-deprived animals, but, instead, may increase it after partial 5-HT-ergic denervation; and that partial 5-HT-ergic denervation by a low dose PCA treatment has a long-lasting effect on forced swimming and social behavior similar to chronic stress.

Behavioral, neurochemical and endocrinological characterization of the early social isolation syndrome

Rearing rats in isolation has been shown to be a relevant paradigm for studying early life stress and understanding the genesis of depression and related affective disorders. Recent studies from our laboratory point to the relevance of studying the social isolation syndrome as a function of home caging conditions. Accordingly, the present series of experiments assessed the contribution of each condition to the expression of the prepulse inhibition of the acoustic startle, food hoarding and spontaneous locomotor activity. In addition, ex vivo neurochemical changes in the brains of isolated and grouped rats reared either in sawdust-lined or in grid-floor cages were determined by measuring dopamine and serotonin as well as their major metabolites in a "psychosis circuit" that includes mainly the hippocampus and selected hippocampal efferent pathways projecting towards the anterior cingulate and infralimbic cortices, nucleus accumbens, dorsolateral caudate nucleus, amygdala and entorhinal cortex. The results of the present study demonstrate that rearing rats in isolation (i) produces a syndrome of generalized locomotor hyperactivity; (ii) increases the startle response; (iii) impairs prepulse inhibition; (iv) tends to increase food hoarding behavior; (v) increases basal dopamine turnover in the amygdaloid complex; (vi) decreases basal dopamine turnover in the infralimbic part of the medial prefrontal cortex; and (vii) decreases basal turnover of serotonin in the nucleus accumbens. In the entorhinal cortex, dopamine neurotransmission seemed to be more sensitive to the caging conditions since a decreased basal turnover of dopamine was observed in grid-reared animals. Plasma corticosterone levels were also increased in grid-reared animals compared with rats reared in sawdust cages. Finally, isolates reared on grids showed a significant positive correlation between plasma corticosterone levels and dopamine in the left nucleus accumbens.Altogether, these results support the contention that there is a link between social isolation, attention deficit, spontaneous locomotor hyperactivity and reduced dopamine turnover in the medial prefrontal cortex. Furthermore, our data demonstrate that rearing rats in grid-floor cages represents a form of chronic mild stress associated with increased corticosterone levels, decreased basal turnover of entorhinal dopamine and increased dopamine activity in the left nucleus accumbens. Finally, a significant and selective decrease in the basal turnover of serotonin in the nucleus accumbens of isolated rats may be linked to the isolation-induced locomotor hyperactivity.

How valuable are animal models in defining antidepressant activity?

Animal models of depression have been utilised to screen novel compounds with antidepressant potential although uncertainty lingers concerning their clinical relevance. In order for a model to be considered of any value, it must possess predictive validity (does drug action in the model correspond to that in the clinic?), face validity (are there phenomenological similarities between the model and the clinic?) and construct validity (does the model possess a strong theoretical rationale?). On the one hand, there are models based on stress such as the learned helplessness model, the forced swimming test and the chronic mild stress model and, on the other hand, models based on neuronal deficits such as the olfactory bulbectomy model. To date, among models more frequently used in depression, none of them meet all these criteria. Moreover, improvements to tests are often poorly validated and estimating time of onset of action of antidepressants remains a major challenge in animal model research. Finally, reproducing the tests outside the laboratory of origin continues to be problematic and leads to variability in results. Although animal models of depression fail to be unequivocally valid, they represent the best tool to define potential antidepressant activity of drugs, to investigate their mechanism of action and, to a greater extent, explore this complex heterogeneous illness. Copyright 2001 John Wiley & Sons, Ltd.

Investigatory behavior of a novel conspecific by Wistar Kyoto, Wistar and Sprague-Dawley rats

The assumption was made that investigatory behaviors (i.e., ano-genital and general body sniffing) of a female conspecific by a mature male rat, has positive hedonic characteristics. Because reduced interest in pleasurable events (i.e., anhedonia) is diagnostically related to depressive behavior, the hypothesis was advanced that less investigatory behavior would be observed in an animal model of depression, namely the Wistar Kyoto (WKY) rat strain. In Experiment 1, WKY, Wistar and Sprague-Dawley male rats were subjected, in the first test series, to three consecutive 2-min exposures to one intruder stimulus female, followed later by another three consecutive 2-min exposures to a second stimulus intruder female. On the second test series, 24 h later, the male rats were exposed to one female for 2 min, followed 6 min later to another 2-min exposure to another stimulus female. Half the male subjects were subjected to tail shock stress 2 h before the first test series. All males demonstrated a habituation of the investigatory response to the same stimulus female, but a dishabituation when subsequently exposed to a new stimulus female. Only WKY rats, exposed to prior stress, revealed a significant reduction in investigatory behavior. In Experiment 2, using only WKY and Wistar rats, a factorial design was used to observe any differences between two stressors, namely tail shock and water restraint, and also to observe possible differences in investigatory behavior towards male vs. female intruder rats. Restraint stress and shock stress elicited significant reductions in investigatory behavior for WKY rats, but not Wistar rats, when confronted with female intruder rats. Male intruders elicited more freezing behavior, as well as aggressive defensive fighting behavior from resident male rats. The results are interpreted to suggest that the significant decrease in investigatory behavior towards a female intruder, which was observed primarily in stressed WKY males, reflects the presence of anhedonia in stressed WKY rats, and reinforces our assertion that the WKY rat strain represents a useful animal model of depressive behavior.

The ultimate resignation: suicide and search activity

This paper presents an integrative approach to suicidal behavior in terms of search activity concept. Search activity concept displays a broad and holistic approach to behavior, adaptation to environment, body resistance, brain amine metabolism, and REM-sleep functions. Search activity is defined as activity that is oriented to change the situation (or at least the subject's attitude to it) in the absence of a precise prediction of the outcome of such activity, but taking into consideration outcomes at all previous stages of activity. According to the proposed hypothesis, renunciation of search (a state opposed to search activity) leads to a feeling of helplessness, problem-solution deficits, inefficient coping, dreams that represent renunciation of search, and a drop in the activity of amines. All these factors further exacerbate the state of renunciation of search and elevate suicidal risk. In addition, the remnants of search activity are misdirected to self-defeating behaviors that increase mental pain and contribute to renunciation of search. This hypothesis integrates findings from a number of fields of study of suicidal behavior, resolves some paradoxes, suggests new lines of research, and raises suggestions for assessment and treatment of suicidal behavior.

Psychosomatic medicine: state of the art

Contemporary psychosomatic medicine must take into consideration developments in psychobiology. The difficulty in accepting dualistic concepts is a serious challenge to positions distinguishing between psychological and 'real' causes of disease. There is more emphasis on life style factors for disease and on the impact of psychosocial factors on illness rather than on disease. The neurophysiological concept of activation or arousal has been important in the development of rational pathophysiological models that describe how sustained arousal may be a pathophysiological factor. For illness, sensitization may be an acceptable psychobiological mechanism underlying very frequently occurring and expensive medical conditions that require medical and economical assistance. One possible alternative to old dynamic concepts is the development of a cognitive arousal theory of stress.

Serotonin, stress and corticoids

There is evidence for stressor- and brain region-specific selectivity in serotonergic transmission responses to aversive stimuli. The aim of the present review is to provide an overview of the effects of different acute and repeated/chronic stressors on serotonin (5-HT) release and reuptake, extracellular 5-HT levels, and 5-HT pre- and postsynaptic receptors in areas tightly linked to the control of fear and anxiety, namely the dorsal and median raphe nuclei, the frontal cortex, the amygdala and the hippocampus. In addition, our knowledge of the impacts of corticoids on serotonergic systems in these brain areas is also briefly provided to examine whether the hypothalamo-pituitary-adrenal axis may play a role in stress-induced alterations in 5-HT neurotransmission. Taken together, the data presented reinforce the hypothesis that stress affects such a transmission, partly through the actions of corticoids. However, we are still left with unanswered, albeit crucial questions. First, the question of the specificity of the serotonergic responses to stress, with regard to the site of action and the nature of the stressor still remains open due to the heterogeneity of the results obtained so far. This could indicate that environmental factors, other than the stressor itself, may have enduring consequences on 5-HT sensitivity to stress. Second, the question regarding the role of stress-elicited changes in 5-HT transmission within coping processes finds in most cases no clearcut answer. In keeping with human symptomatology, the need to consider the environment (including the early one) and the genetic status when assessing the effects of stress on 5-HT neurotransmission is underlined. Such a consideration could help to answer the questions raised.

Behavioral effects Of 8-OH-DPAT in chronically stressed male and female rats

The present study tested the hypothesis that chronic stress desensitizes serotonergic 5-HT(1A) receptors and alters behavioral changes following 5-HT(1A) agonist administration. Eating, acoustic startle response (ASR), and locomotor activity were measured in stressed and nonstressed male and female rats after 8-OH-DPAT administration. Stressed rats were paired and stressed by around-the-clock intermittent foot shock. Controllable stress (CS) rats could avoid/terminate shock for themselves and their yoked partners by pulling a ceiling chain, whereas their partners, the uncontrollable stress (UCS) rats, could not. Rats earned their entire daily ration of food by pressing a lever. In previous experiments, this paradigm was stressful, but not debilitating and rats continued to eat, groom, sleep, and avoid/escape greater than 99% of shock trials. Locomotor activity and ASR were measured in the present study after saline and 8-OH-DPAT administration (0.25 mg/kg, IP) before, 24 h, and 72 h after shock onset. 8-OH-DPAT only decreased food intake significantly in male and female rats after the first administration. Stress decreased food intake in both the CS and UCS rats, with UCS rats eating the least. However, the effects of stress and 8-OH-DPAT were not additive. 8-OH-DPAT significantly increased peak startle amplitude at 100 and 120 dB, and decreased latency to peak startle amplitude at 100 dB in male and female rats. In contrast, 8-OH-DPAT did not alter percent prepulse inhibition (%PPI) at 100 dB, but significantly decreased %PPI in males but not females at 120 dB. Stress did not have a consistent effect on ASR, but reduced %PPI in males, but not females. Neither stress nor 8-OH-DPAT significantly altered locomotor activity. Although the results do not show an increased sensitivity to 8-OH-DPAT in stressed rats, the unexpectedly weak effects of 8-OH-DPAT alone on the behavioral measures chosen limits the conclusions that can be drawn.

Plasma noradrenaline response to a cognitive stressor in subtypes of depressive illness

Noradrenergic function has been shown to be disrupted in depressive illness. The plasma noradrenaline response to a cognitive stressor (the Stroop test) was used to investigate noradenergic activity in subtypes of depressive illness. A Stroop test was carried out, under standardised conditions, on patients with melancholic or psychotic depression, non-melancholic depression, general anxiety disorder and normal controls. Blood samples were taken during testing for measurement of plasma noradrenaline. Although there was a trend for the plasma noradrenergic response to be reduced in the melancholic/psychotic depressed patients compared to all other groups, this did not reach statistical significance. No other inter-group comparisons were statistically significant. The plasma noradrenaline response to a cognitive stressor does not discriminate subtypes of depressive illness from normal controls. Copyright 2000 John Wiley & Sons, Ltd.

The interaction between cytokines and neurotransmitters in depression and stress: possible mechanism of antidepressant treatments

No Abstract