Subsequent stress increases gene expression of catecholamine synthetic enzymes in cardiac ventricles of chronic-stressed rats

Antioxidant defense system in the prefrontal cortex of chronically stressed rats treated with lithium

Background

This study aimed to investigate the effects of lithium treatment on gene expression and activity of the prefrontal antioxidant enzymes: copper, zinc superoxide dismutase (SOD1), manganes superoxide dismutase (SOD2), catalase (CAT), and glutathione peroxidase (GPx) in animals exposed to chronic restraint stress (CRS).

Methods

The investigated parameters were quantified using real-time RT-PCR, Western blot analyses, and assays of enzyme activities.

Results

We found that lithium treatment decreased gene expression of SOD2, as well as the activities of SOD1 and SOD2 in chronically stressed rats to the levels found in unstressed animals. However, lithium treatment in animals exposed to CRS increased prefrontal GPx activity to the levels found in unstressed animals.

Conclusions

These findings confirm that treatment with lithium induced the modulation of prefrontal antioxidant status in chronically stressed rats. Our results may be very important in biomedical research for understanding the role of lithium in maintaining the stability of prefrontal antioxidant defense system in neuropsychiatric disorders caused by chronic stress.

Modulation of Hippocampal Antioxidant Defense System in Chronically Stressed Rats by Lithium

This study examined the effects of lithium on gene expression and activity of the antioxidant enzymes copper zinc superoxide dismutase (SOD1), manganese superoxide dismutase (SOD2), catalase (CAT), glutathione peroxidase (GPx), and glutathione reductase (GR) in the hippocampus of chronically stressed rats. In addition, we examined the effects of lithium on anxiety behaviors, hippocampal concentrations of dopamine (DA) and malondialdehyde (MDA), protein levels of brain-derived neurotrophic factor (BDNF), tyrosine hydroxylase (TH), dopamine transporter (DAT), and catechol-O-methyltransferase (COMT), as well as activity of monoamine oxidase (MAO) in chronically stressed rats. The investigated parameters were quantified by real-time RT-PCR, Western blot analyses, and assays of enzyme activities. We found that lithium did not change gene expression of SOD1, CAT, GPx, and GR but decreased gene expression of SOD2 in chronically stressed rats. A very important result in this study was that lithium treatment decreased the enzyme activities of SOD1 and SOD2 but increased the enzyme activities of GPx and GR in stress condition, which indicates the control of redox balance. The reduced concentration of MDA confirms this. In addition, we found that lithium treatment decreased high protein levels of BDNF and DAT in chronically stressed rats to the level found in unstressed animals. Also, lithium treatment increased the expression of TH but decreased the enzyme activity of MAO B, which contributed to the increase of hippocampal concentration of DA in chronically stressed rats to the level of unstressed animals. Finally, lithium treatment in animals exposed to chronic stress increased the time spent in open arms. Lithium-induced modulation of hippocampal antioxidant status and attenuation of oxidative stress stabilized behavior in animals with high anxiety index. In addition, reduced oxidative stress was followed by the changes of both turnover of DA and levels of BDNF protein in chronically stressed rats treated with lithium. These findings may be important in preclinical research of the effects of lithium on oxidative stress level in pathological conditions.

Does the Stress of Laboratory Life and Experimentation on Animals Adversely Affect Research Data? A Critical Review

Recurrent acute and/or chronic stress can affect all vertebrate species, and can have serious consequences. It is increasingly and widely appreciated that laboratory animals experience significant and repeated stress, which is unavoidable and is caused by many aspects of laboratory life, such as captivity, transport, noise, handling, restraint and other procedures, as well as the experimental procedures applied to them. Such stress is difficult to mitigate, and lack of significant desensitisation/habituation can result in considerable psychological and physiological welfare problems, which are mediated by the activation of various neuroendocrine networks that have numerous and pervasive effects. Psychological damage can be reflected in stereotypical behaviours, including repetitive pacing and circling, and even self-harm. Physical consequences include adverse effects on immune function, inflammatory responses, metabolism, and disease susceptibility and progression. Further, some of these effects are epigenetic, and are therefore potentially transgenerational: the biology of animals whose parents/grandparents were wild-caught and/or have experienced chronic stress in laboratories could be altered, as compared to free-living individuals. It is argued that these effects must have consequences for the reliability of experimental data and their extrapolation to humans, and this may not be recognised sufficiently among those who use animals in experiments.

Cardiac phenylethanolamine N-methyltransferase: localization and regulation of gene expression in the spontaneously hypertensive rat

Phenylethanolamine N-methyltransferase (PNMT) is the terminal enzyme in the catecholamine biosynthetic pathway responsible for adrenaline biosynthesis. Adrenaline is involved in the sympathetic control of blood pressure; it augments cardiac function by increasing stroke volume and cardiac output. Genetic mapping studies have linked the PNMT gene to hypertension. This study examined the expression of cardiac PNMT and changes in its transcriptional regulators in the spontaneously hypertensive (SHR) and wild type Wistar-Kyoto (WKY) rats. SHR exhibit elevated levels of corticosterone, and lower levels of the cytokine IL-1β, revealing systemic differences between SHR and WKY. PNMT mRNA was significantly increased in all chambers of the heart in the SHR, with the greatest increase in the right atrium. Transcriptional regulators of the PNMT promoter show elevated expression of Egr-1, Sp1, AP-2, and GR mRNA in all chambers of the SHR heart, while protein levels of Sp1, Egr-1, and GR were elevated only in the right atrium. Interestingly, only AP-2 protein-DNA binding was increased, suggesting it may be a key regulator of cardiac PNMT in SHR. This study provides the first insights into the molecular mechanisms involved in the dysregulation of cardiac PNMT in a genetic model of hypertension.

Chronic social stress induces cardiomyocyte contractile dysfunction and intracellular Ca2+ derangement in rats

Chronic psychosocial stress triggers cardiovascular diseases although underlying mechanisms are still elusive. This study examined the effect of social stress on cardiomyocyte contractile function and pathological changes in myocardium using the visible burrow system (VBS) model. Chronic social stress was induced using a mixed-sex VBS housing in adult Sprague-Dawley (SD) rats. Contractile and intracellular Ca(2+) properties were evaluated in isolated cardiomyocytes including peak shortening (PS), time-to-PS (TPS), time-to-90% relengthening (TR(90)), maximal velocity of shortening/relengthening (± dL/dt), Fura-2 fluorescence intensity, and intracellular Ca(2+) decay. Myocardial histology was evaluated using Masson trichrome staining. Social stress led to depressed PS, ± dL/dt, shortened TPS and prolonged TR(90) compared with the unstressed controls. Baseline and electrically-stimulated rise in Ca(2+) were reduced whereas intracellular Ca(2+) decay was delayed in stressed rats. Histological analyses exhibited overt interstitial fibrosis and cardiomyocyte hypertrophy in stressed rats. The GSH/GSSG ratio (indicative of oxidative stress status) was reduced whereas oxidative protein carbonyl formation was elevated in stressed rats. Western blot analysis showed unchanged expression of superoxide dismutase 1 (SOD1), β(1)-adrenoceptor (β(1)-AR) levels, reduced sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA2a) levels, and elevated phosphorylation of the stress signaling protein kinase JNK but not ERK in myocardium from stressed rats. Short-term in vitro treatment of cardiomyocytes with the stress inducer phenylephrine mimicked cell damage and intracellular Ca(2+) mishandling, the effects of which were mitigated by antioxidant, JNK inhibition, carvedilol and SERCA2a adenovirus. These findings indicate that chronic social stress is detrimental to cardiac structure and function possibly via mechanisms associated with oxidative injury and intracellular Ca(2+) mishandling.

Regulation of catecholamine-synthesising enzymes and beta-adrenoceptors gene expression in ventricles of stressed rats

Stress exposure activates the sympathoneural system, resulting in catecholamine release. Chronic stress is associated with development of numerous disorders, including cardiovascular diseases. Here we investigated the expression of mRNAs for catecholamine biosynthetic enzymes tyrosine-hydroxylase, dopamine-beta-hydroxylase and phenylethanolamine N-methyl-transferase, and for beta(1)- and beta(2)-adrenoceptors in the right and left ventricles of rats exposed to chronic unpredictable mild stress. The tyrosine-hydroxylase and dopamine-beta-hydroxylase mRNA levels were not affected by stress, whereas the phenylethanolamine N-methyltransferase mRNA levels significantly increased in both right and left ventricles. No changes in beta(1)-adrenoceptor mRNA levels in either right or left ventricles were observed. At the same time, stress produced a significant increase of beta(2)-adrenoceptor mRNA levels in left ventricles. These results suggest that elevated expression of phenylethanolamine N-methyltransferase in both ventricules and beta(2)-adrenoceptor genes in left ventricles could provide a molecular mechanism that leads to altered physiological response, which is important for the organism coping with stress.

L-NAME treatment enhances exercise-induced content of myocardial heat shock protein 72 (Hsp72) in rats

BACKGROUND/AIM

Nitric oxide (NO) modulates the expression of the chaperone Hsp72 in the heart, and exercise stimulates both NO production and myocardial Hsp72 expression. The main purpose of the study was to investigate whether NO interferes with an exercise-induced myocardial Hsp72 expression.

METHODS

Male Wistar rats (70-100 days) were divided into control (C, n=12), L-NAME-treated (L, n=12), exercise (E, n=13) and exercise plus L-NAME-treated (EL, n=20) groups. L-NAME was given in drinking water (700 mg·L(-1)) and the exercise was performed on a treadmill (15-25 m·min(-1), 40-60 min.day(-1)) for seven days. Left ventricle (LV) protein Hsp content, NOS and phosphorylated-NOS (p-NOS) isoforms were measured using Western blotting. The activity of NOS was assayed in LV homogenates by the conversion of [(3)H]L-arginine to [(3)H]L-citrulline.

RESULTS

Hsp72 content was increased significantly (223%; p < 0.05) in the E group compared to the C group, but exercise alone did not alter the NOS content, p-NOS isoforms or NOS activity. Contrary to our expectation, L-NAME enhanced (p < 0.05) the exercise-induced Hsp72 content (EL vs. C, L and E groups = 1019%, 548% and 457%, respectively). Although the EL group had increased stimulatory p-eNOS(Ser1177) (over 200%) and decreased inhibitory p-nNOS(Ser852) (ñ50%) compared to both the E and L groups (p < 0.05), NOS activity was similar in all groups.

CONCLUSIONS

Our results suggest that exercise-induced cardiac Hsp72 expression does not depend on NO. Conversely, the in vivo L-NAME treatment enhances exercise-induced Hsp72 production. This effect may be due to an increase in cardiac stress.