Sladjana Dronjak

Immobilization and cold stress affect sympatho–adrenomedullary system and pituitary–adrenocortical axis of rats exposed to long-term isolation and crowding

Changes in plasma levels of noradrenaline (NA), adrenaline (A), adrenocorticotropic hormone (ACTH) and corticosterone (CORT), as well as in cytosol glucocorticoid receptor (GR) and heat shock protein 70 (Hsp 70) in hippocampus of adult rat males exposed to two long-term types of psychosocial stress, both under basal conditions and in response to immobilization and cold as heterotypic additional stressor were studied. Long-term isolation produced a significant elevation of basal plasma ACTH and CORT levels, but did not affect that of NA and A, while long-term crowding conditions did not elevate the basal plasma levels of these hormones. Long-term isolation of rats exposed to 2 h of immobilization or cold led to a significant elevation of plasma NA, A and CORT in comparison with the controls. Long-term crowding conditions and exposure of animals to immobilization or cold also resulted in an increased plasma NA, A and CORT levels, but to a lesser extent in comparison with the long-term isolation. At the same time, plasma ACTH was significantly more elevated in long-term crowded than in long-term isolated rats. Both kinds of long-term psychosocial stresses (isolation and crowding) had similar but less pronounced effects on cytosol GR and Hsp 70 concentrations in hippocampus comparing to acute immobilization and cold stress. It seems that long-term psychosocial stresses attenuate the effects of an additional stress on hippocampal GR and Hsp 70 concentrations. These data suggest that individual housing of rats appear to act as a stronger stressor than crowding conditions. When the animals suffering a long-term isolation were exposed to either acute immobilization or cold, a stronger activation of the sympatho-adrenomedullary system (SAS) was recorded in comparison with that found in the long-term crowded group subjected to short-term immobilization or cold. No significant differences in the activity of hypotalamo-pituitary-adrenal (HPA) axis were observed between long-term isolated and long-term crowded rats.

Brain glucocorticoid receptor and heat shock protein 70 levels in rats exposed to acute, chronic or combined stress

The pattern and intensity of glucocorticoid receptor (GR) and heat shock 70 protein (Hsp 70) changes in the hippocampus and brain cortex of adult Wistar rat males exposed to acute (immobilization, cold) and chronic (social isolation, crowding, daily swimming) stress or their combinations were followed by Western immunoblotting. Plasma ACTH and CORT were measured by chemiluminescent method and RIA. A significant decrease in cytosol GR and Hsp 70 was observed after acute stress, while chronic stresses led to negligible changes in both these proteins and caused a reduced responsiveness to a novel acute stress. This was valid irrespective of the type of chronic or acute stress combinations for both hippocampal and cortical GR and Hsp 70. The results support the hypothesis that chronic stress-induced deregulation of the LHPA axis may be caused, at least in part, by partial disruption of intracelullar negative feedback control in the higher centers of the brain.

Different Effects of Novel Stressors on Sympathoadrenal System Activation in Rats Exposed to Long‐Term Immobilization

Abstract: Activation of the sympathoadrenal system, evaluated by plasma levels of epinephrine (E) and norepinephrine (NE) after exposure of rats to various stressors, is well documented. However, response of rats exposed long‐term to a homotypic stressor and then exposed once to a heterotypic novel stressor is poorly understood. In the present study, we examined changes in plasma levels of catecholamines (CA) and corticosterone (COR) of rats after a single (2‐h) or long‐term repeated immobilization (41 times, 2 h daily) and in rats adapted to long‐term immobilization exposed once to the novel stress of cold exposure or insulin or 2‐deoxy‐D‐glucose (2DG) administration. Long‐term immobilization produced a significant elevation of basal plasma COR but not NE and E levels. Long‐term immobilized rats exposed to insulin or 2DG showed significant elevation of plasma CA and COR levels in comparison to the administration to control rats. Exposure of long‐term immobilized and control rats to cold stress increased plasma NE and COR, whereas plasma E was not significantly changed. The exposure of long‐term immobilized rats to a further single immobilization (2 h) increased plasma CA levels, but, in naive control rats, the single immobilization produced more pronounced increases. These data suggest that rats exposed to homotypic long‐term immobilization are able to respond to heterotypic stressors by higher activation of the sympathoadrenal system as compared with the control, previously unstressed rats. Reduced plasma CA levels in long‐term immobilized rats exposed to homotypic stressor are most probably due to an adaptation at the level of brain regulatory centers.

Do RCAN1 proteins link chronic stress with neurodegeneration

It has long been suspected that chronic stress can exacerbate, or even cause, disease. We now propose that the RCAN1 gene, which can generate several RCAN1 protein isoforms, may be at least partially responsible for this phenomenon. We review data showing that RCAN1 proteins can be induced by multiple stresses, and present new data also implicating psychosocial/emotional stress in RCAN1 induction. We further show that transgenic mice overexpressing the RCAN1‐1L protein exhibit accumulation of hyperphosphorylated tau protein (AT8 antibody), an early precursor to the formation of neurofibrillary tangles and neurodegeneration of the kind seen in Alzheimer disease. We propose that, although transient induction of the RCAN1 gene might protect cells against acute stress, persistent stress may cause chronic RCAN1 overexpression, resulting in serious side effects. Chronically elevated levels of RCAN1 proteins may promote or exacerbate various diseases, including tauopathies such as Alzheimer disease. We propose that the mechanism by which stress can lead to these diseases involves the inhibition of calcineurin and the induction of GSK‐3β by RCAN1 proteins. Both inhibition of calcineurin and induction of GSK‐3β contribute to accumulation of phosphorylated tau, formation of neurofibrillary tangles, and eventual neurodegeneration.—Ermak, G., Pritchard, M. A., Dronjak, S., Niu, B., Davies, K. J. A. Do RCAN1 proteins link chronic stress with neurodegeneration? FASEB J. 25, 3306–3311 (2011). www.fasebj.org

Chronic Individual Housing-Induced Stress Decreased Expression of Catecholamine Biosynthetic Enzyme Genes and Proteins in Spleen of Adult Rats

Objective: Social isolation is regarded as one of the most relevant causes of diseases in mammalian species. The activation of the sympathoneural system represents one of the key components of the stress response. The sympathetic nervous system is one of the major pathways involved in immune-neuroendocrine interactions. The aim of the present study was to determine plasma epinephrine and norepinephrine in individually housed rats, as well as to find out whether splenic gene expression of catecholamine synthesizing enzymes and their protein levels are affected by chronic psychosocial stress. Methods: Tyrosine hydroxylase (TH), dopamine-β-hydroxylase (DBH) and phenylethanolamine N-methyltransferase (PNMT) mRNA levels were quantified by quantitative real-time RT-PCR. The TH, DBH and PNMT immunoproteins were assayed by Western blot. Results: Chronic social isolation of adult male rats produced a significant increase in plasma catecholamine levels and a decrease in splenic TH mRNA, DBH mRNA and PNMT mRNA. Protein levels of TH, DBH and PNMT were also reduced. Conclusion: These results suggest that increased plasma catecholamines and decreased gene expression and protein levels of catecholamine biosynthetic enzymes in the spleen of chronically individually housed animals might reduce catecholamine synthesis, thus leaving the immunocompetent tissues depleted of catecholamines and consequently leading to an impairment of immune response.

The Effect of Repeated Physical Exercise on Hippocampus and Brain Cortex in Stressed Rats

Abstract:  Sensitivity of target cells to glucocorticoids is regulated by the expression of intracellular glucocorticoid receptor (GR), which mediates the effects of glucocorticoids. The level of GR and of its nuclear transporter protein 70 (Hsp70) were followed in hippocampus and brain cortex of adult Wistar rat males exposed to acute (immobilization, cold) and chronic (social isolation, isolation, and 15 min daily swimming) stress or their combinations. Changes in plasma levels of adenocorticotropic hormone and corticosterone were also studied. A significant decrease in cytosol GR and Hsp70 was observed after acute stress. Opposite to that, chronic stress led to negligible changes in both cytosol GR and Hsp70 levels. Isolation, as chronic psychosocial stressor, caused reduced responsiveness to novel acute stressors, judged by the cytosol GR and Hsp70 levels. This was not observed if chronic isolation was combined with 15 min daily swimming prior to acute exposure to immobilization. The data suggest that repeated physical exercise may, at least in some cases, diminish detrimental effects of chronic social isolation on limbic‐hypothalamic‐pituitary‐adrenocortical axis, as judged by the levels of GR and Hsp70 in the Wistar rat brain.

Effects of repeated maprotiline and fluoxetine treatment on gene expression of catecholamine synthesizing enzymes in adrenal medulla of unstressed and stressed rats.

1 Repeated maprotiline (a noradrenaline reuptake inhibitor) and fluoxetine (a serotonin reuptake inhibitor) treatment on gene expression of catecholamine biosynthetic enzymes were examined in adrenal medulla of unstressed control and chronic unpredictable mild stressed rats. 2 Maprotiline did not change gene expression of catecholamine biosynthetic enzymes in control and stressed rats. 3 Fluoxetine increased gene expression of tyrosine hydroxylase (TH) and dopamine-β-hydroxylase (DBH), but did not phenylethanolamine N-methyltransferase in both unstressed and chronic unpredictable mild stressed animals. 4 In conclusion, we have demonstrated that repeated administration of fluoxetine enhanced gene transcription of TH and DBH and subsequently stimulates noradrenaline synthesis in adrenal medulla of control and stressed rats.

Psychosocial stress-related changes in gene expression of norepinephrine biosynthetic enzymes in stellate ganglia of adult rats

In this study we investigated the changes in norepinephrine biosynthetic enzymes tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DBH) and phenylethanolamine N-methyltransferase (PNMT) gene expression in the stellate ganglia of naive controls and long-term socially isolated (12 weeks) adult rats and the response of these animals to additional immobilization stress. Psychosocial stress produced a significant increase of both TH mRNA and DBH mRNA levels in stellate ganglia. Additional immobilization of long-term psychosocially stressed rats expressed no effect on gene expression of these enzymes. The results presented here suggest that psychosocial stress-induced increase in gene expression of norepinephrine biosynthetic enzymes in stellate ganglia may be connected to the increased risk of cardiovascular disease.

Novel stressors affected catecholamine stores in socially isolated normotensive and spontaneously hypertensive rats

Catecholamines in some central (hypothalamus and hippocampus) and peripheral tissues (adrenal glands and heart auricles) of long-term socially isolated normotensive and spontaneously hypertensive rats exposed to novel immobilization stress were determined by a simultaneous single isotope radioenzymatic assay. Long-term isolation (21 days) produced depletion of hypothalamic norepinephrine (NE) stores and hippocampal dopamine (DA) stores in both normotensive and spontaneously hypertensive rats. Acute immobilization stress (2 h) significantly decreased NE and DA stores in hypothalamus and hippocampus of naive normotensive and spontaneously hypertensive rats controls. However, novel immobilization stress applied to normotensive rats previously subjected to long-term isolation produced no changes in catecholamine levels in hypothalamus, while resulting in somewhat higher depletion of NE stores in hypothalamus of spontaneously hypertensive rats treated in the same way. Novel immobilization stress decreased NE and DA stores in hippocampus of normotensive but was without effect on NE and DA stores of spontaneously hypertensive rats. Social isolation did not affect catecholamine stores in peripheral tissues but novel immobilization stress produced a significant decrease in catecholamine content. The results suggest that some central and peripherals tissues of spontaneously hypertensive rats and normotensive rats differ with regard to catecholamine content and that there are certain differences in their responsiveness to stress.

Treadmill exercise does not change gene expression of adrenal catecholamine biosynthetic enzymes in chronically stressed rats

Chronic isolation of adult animals represents a form of psychological stress that produces sympatho-adrenomedullar activation. Exercise training acts as an important modulator of sympatho-adrenomedullary system. This study aimed to investigate physical exercise-related changes in gene expression of catecholamine biosynthetic enzymes (tyrosine hydroxylase, dopamine-ß-hydroxylase and phenylethanolamine N-methyltransferase) and cyclic adenosine monophosphate response element-binding (CREB) in the adrenal medulla, concentrations of catecholamines and corticosterone (CORT) in the plasma and the weight of adrenal glands of chronically psychosocially stressed adult rats exposed daily to 20 min treadmill running for 12 weeks. Also, we examined how additional acute immobilization stress changes the mentioned parameters. Treadmill running did not result in modulation of gene expression of catecholamine synthesizing enzymes and it decreased the level of CREB mRNA in the adrenal medulla of chronically psychosocially stressed adult rats. The potentially negative physiological adaptations after treadmill running were recorded as increased concentrations of catecholamines and decreased morning CORT concentration in the plasma, as well as the adrenal gland hypertrophy of chronically psychosocially stressed rats. The additional acute immobilization stress increases gene expression of catecholamine biosynthetic enzymes in the adrenal medulla, as well as catecholamines and CORT levels in the plasma. Treadmill exercise does not change the activity of sympatho-adrenomedullary system of chronically psychosocially stressed rats.