Stress revisited: a critical evaluation of the stress concept

With the steadily increasing number of publications in the field of stress research it has become evident that the conventional usage of the stress concept bears considerable problems. The use of the term 'stress' to conditions ranging from even the mildest challenging stimulation to severely aversive conditions, is in our view inappropriate. Review of the literature reveals that the physiological 'stress' response to appetitive, rewarding stimuli that are often not considered to be stressors can be as large as the response to negative stimuli. Analysis of the physiological response during exercise supports the view that the magnitude of the neuroendocrine response reflects the metabolic and physiological demands required for behavioural activity. We propose that the term 'stress' should be restricted to conditions where an environmental demand exceeds the natural regulatory capacity of an organism, in particular situations that include unpredictability and uncontrollability. Physiologically, stress seems to be characterized by either the absence of an anticipatory response (unpredictable) or a reduced recovery (uncontrollable) of the neuroendocrine reaction. The consequences of this restricted definition for stress research and the interpretation of results in terms of the adaptive and/or maladaptive nature of the response are discussed.

Granins as disease-biomarkers: translational potential for psychiatric and neurological disorders

The identification of biomarkers represents a fundamental medical advance that can lead to an improved understanding of disease pathogenesis, and holds the potential to define surrogate diagnostic and prognostic endpoints. Because of the inherent difficulties in assessing brain function in patients and objectively identifying neurological and cognitive/emotional symptoms, future application of biomarkers to neurological and psychiatric disorders is extremely desirable. This article discusses the biomarker potential of the granin family, a group of acidic proteins present in the secretory granules of a wide variety of endocrine, neuronal and neuroendocrine cells: chromogranin A (CgA), CgB, Secretogranin II (SgII), SgIII, HISL-19 antigen, 7B2, NESP55, VGF and ProSAAS. Their relative abundance, functional significance, and secretion into the cerebrospinal fluid (CSF), saliva, and the general circulation have made granins tractable targets as biomarkers for many diseases of neuronal and endocrine origin, recently impacting diagnosis of a number of neurological and psychiatric disorders including amyotrophic lateral sclerosis (ALS), Alzheimer's disease, frontotemporal dementia, and schizophrenia. Although research has not yet validated the clinical utility of granins as surrogate endpoints for the progression or treatment of neurological or psychiatric disease, a growing body of experimental evidence indicates that the use of granins as biomarkers might be of great potential clinical interest. Advances that further elucidate the mechanism(s) of action of granins, coupled with improvements in biomarker technology and direct clinical application, should increase the translational effectiveness of this family of proteins in disease diagnosis and drug discovery.

Pathophysiological role of TLQP-21: gastrointestinal and metabolic functions

The present review summarizes recent findings on the metabolic and gastroenteric role of the VGF gene and a peptide derived by post-translational cleavage of the VGF pro-hormone, i.e. TLQP-21. The vgf gene is widely expressed through the central nervous system as well as in the peripheral nervous system, in myenteric plexus ganglia and also in the glandular portion of the stomach. A few VGF derived peptide have been shown to possess biological activity, among them TLQP-21 attracted particular interest following its identification within rat nervous system. In particular, recent studies from our and other groups implicated TLQP-21 in both the modulation of energy homeostasis, body weight regulation and neuroendocrine functions as well as in the central control of gut functions. Overall, findings available point to a role for TLQP-21 in negatively affecting the body energy balance.

Interaction with stressed mothers affects corticosterone levels in pups after reunion and impairs the response to dexamethasone in adult mice

BACKGROUND

Early adverse experiences are preeminent factors for the development of affective disorders. In the present study, we analyzed the effects of different postnatal manipulations applied either on the mother or on the offspring in mice. Maternal behavior and adrenocortical activity of both mothers and offspring at the end of postnatal stress and at adulthood were considered.

METHODS

From postnatal day (PND) 1 to 14 mice underwent 15min of: (a) brief (15min) pups' exposure to clean bedding (CB: clean bedding), (b) mothers' exposure to the odor of a novel male (SM: stressed mother) or (c) mothers' exposure to a clean cage (CSM: control stressed mother), and (d) standard rearing (N-H: non-handled). The behavior of mouse dams during and after stress sessions was analyzed. Serum corticosterone of mothers and pups at the end of the stress session and 30min after reunion was assessed on PND 14. Moreover, anxiety levels and HPA-axis inhibitory feedback in response to dexamethasone administration were evaluated in adult male offspring.

RESULTS

Overall, during the 14 days of treatment CB mothers when reunited with their pups showed higher maternal behavior than other dams. After the last stress (PND 14) SM and CSM maternal corticosterone levels increased as well as those of CB pups. While 30min of mother-infant interaction restored baseline corticosterone levels in SM and CSM mothers and in CB pups, SM and CSM offspring showed a decrease of corticosterone under baseline levels. At adulthood, SM and CSM males did not show the suppressive hormonal response to dexamethasone treatment. Moreover, adult CB and SM male mice displayed decreased anxiety in the open field.

CONCLUSIONS

Maternal psychosocial stress during lactation seems to permanently affect the offspring's HPA functioning. These effects may be dissociated from the behavioral response as suggested by the decrease of anxiety in SM and CB adult mice.

Chronic intracerebroventricular TLQP-21 delivery does not modulate the GH/IGF-1-axis and muscle strength in mice

OBJECTIVE

Biallelic ablation of VGF determines a dwarf phenotype. VGF precursor protein encodes for different biologically active peptides none of which has been related to growth or muscular abnormalities. Here we present the first attempt to fill this gap. We tested the hypothesis that a recently identified VGF-derived peptide, TLQP-21, shown to centrally modulate metabolic functions, could also modulate growth hormone (GH)-axis and muscle strength.

DESIGN

Adult male mice were chronically icv injected with TLQP-21 (15 microg/day for 14 days). Physiological, molecular and behavioral parameters related to the GH/IGF-1-axis were investigated.

RESULTS

Except for a reduction in the soleus weight, TLQP-21 did not affect GH/IGF-1-axis mediators, muscle strength and muscle weight.

CONCLUSIONS

Results collected exclude a role for TLQP-21 in modulating the GH/IGF1-axis and muscle functions. VGF-derived peptides involved in the dwarf phenotype of VGF-/- mice have to be identified yet.

TLQP-21, a VGF-derived peptide, increases energy expenditure and prevents the early phase of diet-induced obesity

The vgf gene has been identified as an energy homeostasis regulator. Vgf encodes a 617-aa precursor protein that is processed to yield an incompletely characterized panel of neuropeptides. Until now, it was an unproved assumption that VGF-derived peptides could regulate metabolism. Here, a VGF peptide designated TLQP-21 was identified in rat brain extracts by means of immunoprecipitation, microcapillary liquid chromatography-tandem MS, and database searching algorithms. Chronic intracerebroventricular (i.c.v.) injection of TLQP-21 (15 mug/day for 14 days) increased resting energy expenditure (EE) and rectal temperature in mice. These effects were paralleled by increased epinephrine and up-regulation of brown adipose tissue beta2-AR (beta2 adrenergic receptor) and white adipose tissue (WAT) PPAR-delta (peroxisome proliferator-activated receptor delta), beta3-AR, and UCP1 (uncoupling protein 1) mRNAs and were independent of locomotor activity and thyroid hormones. Hypothalamic gene expression of orexigenic and anorexigenic neuropeptides was unchanged. Furthermore, in mice that were fed a high-fat diet for 14 days, TLQP-21 prevented the increase in body and WAT weight as well as hormonal changes that are associated with a high-fat regimen. Biochemical and molecular analyses suggest that TLQP-21 exerts its effects by stimulating autonomic activation of adrenal medulla and adipose tissues. In conclusion, we present here the identification in the CNS of a previously uncharacterized VGF-derived peptide and prove that its chronic i.c.v. infusion effected an increase in EE and limited the early phase of diet-induced obesity.

Chronic administration of olanzapine induces metabolic and food intake alterations: a mouse model of the atypical antipsychotic-associated adverse effects

RATIONALE

Most of atypical antipsychotics (AAPs) are highly related to a major risk of metabolic drawbacks leading to dyslipidemia and obesity.

OBJECTIVE

To set up a mouse model of the AAP-associated weight gain in mice under the influence of chronic olanzapine regimen.

MATERIALS AND METHODS

Female mice were housed in pairs and habituated to spontaneous feeding with a high-palatable diet (10% sucrose wet mash). Firstly, we orally administered olanzapine (0.75, 1.5 and 3 mg/kg), evaluating body weight and periuterine fat mass, as well as insulin, non-esterified fatty acids, triglycerides, and glucose levels. In a second experiment, we assessed the effect of olanzapine on energy expenditure through indirect calorimetry (IC). A third experiment was conducted to investigate the effects of olanzapine on a high fat-high sweet palatable diet (10% sucrose + 30% fat, HF-HS) in mice implanted with subcutaneous osmotic mini-pumps. Locomotor activity was also assessed.

RESULTS

In experiment 1, the highest dose of chronically administered olanzapine (3 mg/kg) induced significant weight gain accompanied by augmentation of periuterine fat depots, with no changes in locomotor activity. In experiment 2, chronic administration did not alter energy expenditure, whereas, decreased respiratory quotient (RQ). In experiment 3, subcutaneously infused olanzapine evidenced a dose and time-dependent increase of body weight and HF-HS diet consumed. Notably, serum analyses revealed a hyperinsulinemia together with increased levels of triglycerides and glucose.

CONCLUSIONS

In this study, we describe in female mice metabolic alterations matching the metabolic syndrome, thus resembling the clinical situation of schizophrenic patients taking AAPs.

Psychosocial stress affects energy balance in mice: modulation by social status

Stress has been associated with changes in eating behaviour and food preferences. Moreover, psychosocial and socio-economical challenges have been related with neuroendocrine-autonomic dysregulation followed by visceral obesity and associated risk factors for disease. In the current study, we provide a model of body weight development, food intake, energy expenditure of subordinate and dominant mice under psychosocial stress either in the presence of a standard diet or of a high palatable diet. When only standard chow was available stressed animals consumed more food in comparison to the control counterpart. Moreover, subordinate mice, at the end of the stress period were heavier in comparison to dominant animals. This last result was due to a decrease in the caloric efficiency of dominant animals in comparison to subordinates. Confirming this, the results of the experiment 2 showed that dominant mice significantly increase their energy expenditure at the end of the chronic psychosocial stress procedure in comparison to subordinate mice, as measured by indirect calorimetry. When a palatable high fat diet was available subordinate animals became heavier in comparison with both dominant and control animals. No differences in the caloric intake were found between groups. Subordinate mice ingested more calories from fat than controls, while dominant animals ingested more calories from carbohydrates. These results suggest that psychosocial stress can be a risk factor for overeating and weight gain in mice. However, social status influences the extent to which an individual keeps up with adverse environment, influencing the vulnerability toward stress related disorders.

Cross fostering in mice: behavioral and physiological carry-over effects in adulthood

Cross fostering is a widely used laboratory practice. However, relatively few studies have directly investigated the carry-over effects of this procedure in adult animals. The aim of the present study is to investigate the late effects of cross fostering (CF) at birth (in litters composed of no siblings) on adult mice. When adults, cross-fostered male and female mice were examined for intrasex aggression, and levels of emotionality, exploration and anxiety. In addition, body weight was monitored, several internal organs were weighed and plasma corticosterone levels were measured. When compared to controls, body weight of CF male and female mice was increased, at least after early puberty. CF males showed smaller preputial glands, while basal corticosterone level was not affected by cross fostering. In the free-exploratory test, CF males, but not females, showed a behavioral profile suggestive of lower anxiety. These effects in adulthood cannot be ascribed to differences in the maternal care received, which was not affected by cross fostering. In conclusion, cross fostering at birth induced a number of behavioral and physiological alterations in mice, particularly in males. These findings should be carefully evaluated when applying cross fostering procedure to laboratory animals.

Individual housing induces altered immuno-endocrine responses to psychological stress in male mice

Social isolation and lack of social support have deleterious effects on health, thus being regarded as one of the most relevant causes of diseases in human and other mammalian species. However, only few are the studies aimed at evaluating the psychoneuroimmunological functions of individually housed subjects. The present study was designed to understand how the behavior and the physiology of male house mice might be affected by individual housing. We first analyzed whether individual housing of different duration (1-42 days) would result in immuno-endocrine dysfunction (experiment 1). Then we investigated whether housing conditions would affect the reaction to an acute mild psychological stress (experiments 2 and 3). There were three main findings: first, individually housing mice for increasing time periods did not induce any major immuno-endocrine effects compared to a stable sibling group housing. Therefore, prolonged isolation does not seem to dramatically impair mice immuno-endocrine functions. Second, when exposed to a mild acute stress, i.e. forced exposure to a novel environment, isolated mice showed higher basal corticosterone and lower type 1 (IL-2) and type 2 (IL-4) cytokines as well as splenocytes proliferation compared to group housed male mice. Finally, when faced with a free choice between a novel environment and their home cage, individually housed mice showed reduced neophobic responses resulting in increased exploration of the novel environment, thus suggesting a low anxiety profile. Altogether, our findings suggest that individual housing in itself does not change immunocompetence and corticosterone level, but does affect reactivity to a stressor. In fact, individually housed mice showed high behavioral arousal, as well as altered immuno-endocrine parameters, when challenged with mild psychological novelty-stress.

How tree shrews (Tupaia belangeri) perform in a searching task: evidence for strategy use

This study investigated how male tree shrews (Tupaia belangen) performed in a searching task while in their home cages and assessed whether different food distributions affected their performance. The animals were faced with a holeboard containing 9 food sources arranged in a 3 x 3 matrix or in 3 clusters, each containing 3 sources. Animals tended to start and end the trials from preferred locations, thereafter solving the task by strategically organizing the reward collection according to a minimum-distance principle. In the cluster configuration, they visited the sources hierarchically. Food distribution did not affect the performance. Comparison with data from mice and capuchin monkeys revealed that tree shrews and capuchins solved the task in a similar strategic way, whereas mice did not. These findings attract particular attention because of the phylogenetic position of tree shrews, which are regarded as closely related to primates.

Stress-induced changes in cerebral metabolites, hippocampal volume, and cell proliferation are prevented by antidepressant treatment with tianeptine

Stress-induced structural remodeling in the adult hippocampus, involving debranching and shortening of dendrites and suppression of neurogenesis, provides a cellular basis for understanding the impairment of neural plasticity in the human hippocampus in depressive illness. Accordingly, reversal of structural remodeling may be a desirable goal for antidepressant therapy. The present study investigated the effect of tianeptine, a modified tricyclic antidepressant, in the chronic psychosocial stress model of adult male tree shrews (Tupaia belangeri), a model with high validity for research on the pathophysiology of major depression. Animals were subjected to a 7-day period of psychosocial stress to elicit stress-induced endocrine and central nervous alterations before the onset of daily oral administration of tianeptine (50 mg/kg). The psychosocial stress continued throughout the treatment period of 28 days. Brain metabolite concentrations were determined in vivo by proton magnetic resonance spectroscopy, cell proliferation in the dentate gyrus was quantified by using BrdUrd immunohistochemistry, and hippocampal volume was measured post mortem. Chronic psychosocial stress significantly decreased in vivo concentrations of N-acetyl-aspartate (-13%), creatine and phosphocreatine (-15%), and choline-containing compounds (-13%). The proliferation rate of the granule precursor cells in the dentate gyrus was reduced (-33%). These stress effects were prevented by the simultaneous administration of tianeptine yielding normal values. In stressed animals treated with tianeptine, hippocampal volume increased above the small decrease produced by stress alone. These findings provide a cellular and neurochemical basis for evaluating antidepressant treatments with regard to possible reversal of structural changes in brain that have been reported in depressive disorders.

Social status in mice: behavioral, endocrine and immune changes are context dependent

The aim of the present study was to investigate the effect of social status on the endocrine, immune and behavior response of male mice. We found that in mice reared in a group of siblings since weaning, no difference exists between dominants and subordinates in basal corticosterone level, in behavior in the open-field test (OFT) and in a series of immune parameters. These results suggest that living with siblings is not a stressful condition for either dominant or subordinate mice. Therefore, group-housed siblings can be regarded as a valid control group in social stress studies. When mice were subjected to chronic psychosocial stress for 21 days, four types of social outcome occurred: residents becoming dominants, intruders becoming subordinates, residents becoming subordinates and intruders becoming dominants. Interestingly, the behavioral profile in the OFT revealed a status-dependent effect, with resident dominants (RD) and intruder dominants (InD) showing the highest locomotor and exploratory activity, whereas the corticosterone level was higher than control for all four categories. In addition, a context-dependent effect emerged at the immune level: resident subordinates (RS) had a reduced splenocyte proliferation and IL-4 and IL-10 production. Mice in all the other three social ranks showed no immune alterations. Therefore, the loss of an individual's social rank position seems a promising field of study to investigate the psychological impact of stressful events.

Learning to cope with two different food distributions: the performance of house mice (Mus musculus domesticus)

Search abilities of mice (Mus musculus domesticus) were evaluated using an arena closed by a ceiling in which 9 food sources (which mice could reach standing on their hind legs) could be arranged according to 2 configurations: a 3 x 3 square matrix and 3 clusters each containing 3 food sources. Testing conditions prevented olfactory and visual cues from being left after visits to food sources, and mice were able to choose alternative routes between food sources. Results showed that mice were more efficient with the matrix than with the cluster configuration. Sex differences were observed: Females improved their performance with both configurations, whereas males improved only with the matrix one. Mice did not develop evident search strategies that would minimize task complexity. Comparison with data published on capuchin monkeys revealed differences, with monkeys performing better with the cluster configuration than with the matrix and applying searching strategies.