Effects of stress on catecholamine stores in central and peripheral tissues of long-term socially isolated rats

Both the peripheral sympatho-adrenomedullary and central catecholaminergic systems are activated by various psycho-social and physical stressors. Catecholamine stores in the hypothalamus, hippocampus, adrenal glands, and heart auricles of long-term socially isolated (21 days) and control 3-month-old male Wistar rats, as well as their response to immobilization of all 4 limbs and head fixed for 2 h and cold stress (4 degrees C, 2 h), were studied. A simultaneous single isotope radioenzymatic assay based on the conversion of catecholamines to the corresponding O-methylated derivatives by catechol-O-methyltransferase in the presence of S-adenosyl-1-(H-3-methyl)-methionine was used. The O-methylated derivatives were oxidized to H-3-vanilline and the radioactivity measured. Social isolation produced depletion of hypothalamic norepinephrine (about 18%) and hippocampal dopamine (about 20%) stores and no changes in peripheral tissues. Immobilization decreased catecholamine stores (approximately 39%) in central and peripheral tissues of control animals. However, in socially isolated rats, these reductions were observed only in the hippocampus and peripheral tissues. Cold did not affect hypothalamic catecholamine stores but reduced hippocampal. dopamine (about 20%) as well as norepinephrine stores in peripheral tissues both in control and socially isolated rats, while epinephrine levels were unchanged. Thus, immobilization was more efficient in reducing catecholamine stores in control and chronically isolated rats compared to cold stress. The differences in rearing conditions appear to influence the response of adult animals to additional stress. In addition, the influence of previous exposure to a stressor on catecholaminergic activity in the brainstem depends on both the particular catecholaminergic area studied and the properties of additional acute stress. Therefore, the sensitivity of the catecholaminergic system to habituation appears to be tissue-specific

Different behavioral effects of maprotiline and fluxilan in rats

Serotonin and noradrenaline are involved in the mechanisms of action of most antidepressant drugs. We examined the effects of chronic treatment with maprotiline, a selective inhibitor of noradrenaline reuptake, and fluxilan, a selective inhibitor of serotonin reuptake, on the behavior of unstressed controls and chronic unpredictable mild stress (CUMS) model rats in the forced swim test (FST) and elevated plus maze test. Both selective reuptake inhibitors resulted in a significant reduction of time spent in immobility. Climbing was significantly increased in maprotiline- and swimming was exclusively elicited in the fluxilan-treated unstressed control and CUMS rats. Maprotiline-treated animals displayed decreased anxiety and fluxilan-treated rats enhanced anxiety. The obtained results suggest that central noradrenergic and serotonergic systems might be affected differently during FST. The results also demonstrate that the anxiogenic effects of chronic fluxilan treatment are similar to those reported by many other studies. These differences observed for the effects of fluxilan in relation to those reported for maprotiline and probably due to the different pharmacological profiles of these drugs

Maprotiline treatment differentially influences cardiac beta-adrenoreceptors expression under normal and stress conditions

Alterations in cardiac function were observed in antidepressants treated patients and published in several clinical reports. These detected changes could be either a consequence of the treatment or of depression itself, which has already been proved to be a risk factor in heart diseases. In order to determine a possible influence of chronic treatment with norepinephrinergic reuptake inhibitor, maprotiline, on the heart, we investigated gene expression of cardiac beta-adrenoceptors both in controls and in animals with signs of depression. The rats were divided into two groups, unstressed controls and those exposed to chronic unpredictable mild stress (CUMS). The groups were further divided into two subgroups, one receiving daily intraperitoneal injections of vehicle (sterile water) and another one maprotiline (10 mg/kg) for four weeks. Tissue samples were collected after the last application. Gene expression of cardiac beta(1)- and beta(2)-adrenoceptor was determined using Real-time RT-PCR analysis. Our results show that in control animals expression of both adrenoreceptors was decreased in the right atria after 4 weeks of maprotiline application. Contrary, the same treatment led to a significant increase in expression of cardiac beta(1)-adrenoceptor in the stressed rats, with no change in the characteristics of beta(2)-adrenoceptor. Our findings might reflect the that molecular mechanisms are underlying factors involved in the development of cardiovascular diseases linked with antidepressant treatment

Differential regulation of catecholamine synthesis and transport in rat adrenal medulla by fluoxetine treatment

We have recently shown that chronic fluoxetine treatment acted significantly increasing plasma norepinephrine and epinephrine concentrations both in control and chronically stressed adult male rats. However, possible effects of fluoxetine on catecholamine synthesis and re-uptake in adrenal medulla have been largely unknown. In the present study the effects of chronic fluoxetine treatment on tyrosine hydroxylase, a rate-limiting enzyme in catecholamine synthesis, as well as a norepinephrine transporter and vesicular monoamine transporter 2 gene expressions in adrenal medulla of animals exposed to chronic unpredictable mild stress (CUMS) for 4 weeks, were investigated. Gene expression analyses were performed using a real-time quantitative reverse transcription-PCR. Chronically stressed animals had increased tyrosine hydroxylase mRNA levels and decreased expression of both transporters. Fluoxetine increased tyrosine hydroxylase and decreased norepinephrine transporter gene expression in both unstressed and CUMS rats. These findings suggest that chronic fluoxetine treatment increased plasma catecholamine levels by affecting opposing changes in catecholamine synthesis and uptake

Dysregulation of BDNF and PI3K/Akt signaling in the brain of female Wistar-Kyoto rats exposed to chronic mild stress

Background: The neurobiology underlying depression has not yet been fully identified, but is thought to result from molecular and cellular abnormalities that interact with genetic and environmental factors. Depression is twice as prevalent in women as in men, however, females remain underrepresented in preclinical research. In addition to the neurotransmission theory of depression, the inflammatory processes and the disrupted signaling pathways also play a crucial role in the pathophysiology of depression. The WKY rat strain has long been established as a model of depression. These rats demonstrate an exaggerated response to stress compared to other strains. WKY strain fail to respond to chronic antidepressant treatment after exposure to chronic mild stress (CMS) and considered to be nonresponsive to antidepressant drugs. The hippocampus and the medial prefrontal cortex (mPFC) are thought to be an important regions for depression. Brain-derived neurotrophic factor (BDNF) play a vital role in the pathophysiology of depression. BDNF-stimulated signaling cascades, including the phosphatidylinositol 3-kinase (PI3K)–/serine threonine kinase (Akt), also implicated in depression and treatment respons. In the present study, we have examined the effects of CMS on behavior and BDNF and PI3K/Akt signaling in the hippocampus and mPFC of female WKY rats. Method: In the experiment, we used three months old Wistar (WI) and WKY female rats. Animals were divided in two groups: control and animals exposed to CMS for 6 weeks. On the last day of stress procedure, animals were tested in elevated plus maze to determine the levels of anxiety. Animals were then sacrificed and hippocampus and mPFC were isolated. Levels of BDNF and pAkt were determined by Western blot method. Data were analyzed using the two way ANOVA and Tuckey’s post-hoc test. Results: WKY rats showed significantly decreased number of rearings (by 70%, p<0.01),decreased number of total arm entries (by 21%, p<0.05) and the time spent in the open arms (by 73%, p<0.001) of the elevated plus-maze compared to WI control group. WKY females had a significantly lower level of BDNF in the hippocampus (by 12%, p<0.05) and mPFC (by 16%, p<0.05) and pAkt (by 14%, p<0.01) only in mPFC as compared to the WI female rats. Exposure of WKY females to CMS enhanced an anxiety-like behavior and hypolomotion (decrease in number of rearings by 31%, p<0.05, number of total arm entries by 89%, p<0.001, and timevspent in the open arms by 92%, p<0.001), further down-expression of BDNF in both brain areas (in PFC: by 15%, p<0.001; in hippocampus: by 7%, p<0.05) and Akt phosphorylation in the mPFC (by 17%, p<0.05) as well as a decreased pAkt in the hippocampus (by 36%, p<0.001). Conclusions: The difference in the balance of BDNF and PI3K/Akt signaling pathways may be relevant to the resistance of WKY rats to antidepressant drug treatment and may be useful for developing new targets for depression treatment, especially in females.Abstracts of the 36th ECNP Congress 202

Melatonin modulates catecholamine biosynthesis and re-uptake in adrenal medulla of rats exposed to chronic unpredictable mild stress

Introduction: Stress is considered a determinant in the etiology of depression. The adrenal medulla plays a key role in response to stress by releasing catecholamines, which are important to maintain homeostasis. Many studies have assessed the antidepressant-like activity of the melatonin, a neurohormone synthesized in the pineal gland. Thus, in the present study, we examined the effect of chronic melatonin treatment on mRNA levels and protein content of catecholamines biosynthetic enzymes (TH, DBH and PNMT) and transporters (NET, VMAT2) in adrenal medulla of rats exposed to chronic unpredictable mild stress (CUMS). Material and Methods: CUMS was used as an animal model of depression. Exposure of rats to CUMS and placebo or melatonin (10 mg/kg body weight, i.p.) administration started on the same day and was continued for 4 weeks. For quantifying TH, DBH, PNMT, NET and VMAT2 mRNA and protein levels we used realtime PCR and Western blot analysis. Results: We observed that CUMS induced increased mRNA levels of catecholamine biosynthetic enzymes (TH, DBH, and PNMT), and noradrenaline transporter NET, while treatment with melatonin decreased these biosynthetic enzymes and transporter. Conversely, CUMS induced a decrease in protein content of TH and NET, while chronic melatonin treatment increased NET protein levels in both control and stressed rats. CUMS and melatonin treatment has no effect on mRNA levels and protein content of VMAT2. Conclusion: This study suggests that the observed decrease of catecholamine biosynthesis and enhanced re-uptake in adrenal medulla of rats exposed to CUMS are connected to the beneficial effects of chronic melatonin treatment

Effects of chronic diazepam treatments on behavior on individually housed rats

The present study analyzed the effects of chronic treatment with low doses of diazepam on body weight, defecations and urinations, vertical rears, the elevated platform test; and self-grooming in male rats exposed for 21 days to social isolation. The rats were treated for 21 days with diazepam (0.2 mg/kg, i.p) or its vehicle. Social isolation led to decreased body weight and vertical rears, more defecations and urinations, increased reluctance to step down from the test platform, shorter duration of grooming, and longer reluctance to start grooming. Chronic diazepam in individually housed rats produced increase in body weight and vertical rears, decrease in the number of defecations and urinations, and shortening of the time of reluctance to step down from the platform. The number of grooming bouts, their duration, and reluctance to start grooming were not altered by diazepam, but it decreased the percentage of incorrect transitions. The obtained data indicate that chronic diazepam treatment of socially isolated rats changes non-grooming behavior and some grooming, behavior parameters

Effects of acute stress on gene expression of splenic catecholamine biosynthetic enzymes in chronically stressed rats

The aim of this study was to examine how acute immobilization stress affects the concentrations of catecholamines in the plasma and the expression of the splenic catecholamine biosynthetic enzymes tyrosine hydroxylase (TH), dopamine-Я-hydroxylase (DBH) and phenylethanolamine N-methyltransferase (PNMT) in chronically socially isolated rats. We found that acute immobilization increases the plasma catecholamine levels and splenic PNMT protein levels in chronically socially isolated rats. These results show that acute stress of chronically stressed animals activates the sympatho-adrenomedullary system and increases synthesis of splenic PNMT by 37%, both of which can modulate the immune function. [Projekat Ministarstva nauke Republike Srbije, br. III 41027, br. III 41022 and br. ON 173044

Melatonin modulate the expression of α1- and β2-adrenoceptors in the hippocampus of rats subjected to unpredictable chronic mild stress

OBJECTIVE: This study investigated the effects of chronic melatonin treatment on gene expression of α1-, α2-, β1- and β2-adrenoceptors in the hippocampus of rats subjected to chronic unpredictable mild stress (CUMS). BACKGROUND: Preclinical studies have also shown that melatonin prevented short- and long-term memory impairments and exhibited antidepressant-like actions. METHODS: For this study, we used 24 animals, which were divided into four groups, and the experiment lasted 4 weeks. We quantifi ed the changes in mRNA and protein levels of α1-, α2-, β1- and β2-adrenoceptors in the hippocampus after melatonin treatment. RESULTS: Our results demonstrated a decreased gene expression of α1-, α2- and β2-adrenoceptors in the hippocampus of rats subjected to unpredictable chronic mild stress, while there was no change in gene expression of β1-adrenoceptors. Melatonin treatment in the CUMS rats prevented the stress-induced decrease in mRNA and protein levels of α1-and β2-adrenoceptors, whereas did not affect either on mRNA or protein level of β1-and α2-adrenoceptors. CONCLUSION: Our data suggest that melatonin, by increasing reduced levels of α1- and β2-adrenoceptors mRNA and protein in the hippocampus of chronic stressed rats, may be benefi cial in conditions such as chronic stress and provides an experimental opportunity to probe into further molecular mechanisms underlying the regulation of these receptor subtype

Uticaj hroničnog blagog stresa na ponašanje Wistar-Kyoto soja pacova kao animalnog modela rezistentne depresije

Brojni dokazi ukazuju da socijalna izolacija može imati dugoročne efekte na ponašanje i u odgovoru na stres. Wistar-Kyoto (WK) soj pacova se smatra dobrim animalnim modelom rezistentne depresije jer su, za razliku od Wistar (W) soja, nakon izlaganja stresu neosetljivi na terapiju antidepresivima. U ovoj studiji smo izlagali ženke WK i W soja pacova hroničnom blagom stresu (CMS) u trajanju od 6 nedelja. Kontrolne životinje su bile u grupi po 3 jedinke, dok je CMS grupa pacova bila izolovana 3 nedelje pre početka CMS procedure do kraja eksperimenta. Znaci anhedonije su tokom 6 nedelja bili procenjivani testom unosa saharoze, dok je stepen anksioznosti utvrđen testom izdignutog plus lavirinta na kraju eksperimenta. Kontrolna WK grupa je pokazivala od prve do poslednje nedelje eksperimenta smanjen unos saharoze, hipolokomociju i smanjen broj ulaza u otvorene krake u odnosu na kontrolnu W grupu, što potvrđuje da ovaj soj i u odsustvu stresa pokazuje simptome depresije i anksioznosti. Izlaganje CMS je dovelo do dodatnih razlika između sojeva u unosu saharoze. Izolacija u trajanju od 3 nedelje pre CMS dovela je kod oba soja do povećanja unosa saharoze, što može ukazati na povećanu potrebu za zadovoljstvima. Hronični blagi stres je samo kod W soja doveo do znakova anhedonije, dok su ženke WK soja i nakon 6 nedelja CMS imale povećan unos saharoze. Ovi rezultati su relevantni za razumevanje načina na koji socijalna izolacija doprinosi osetljivosti pojedinca na poremećaje povezane sa stresom tokom života.Treći kongres biologa Srbije; Septembar 21-25, Zlatibor, 2022