Ivabradine reduces baseline and stress-induced increase of heart rate and blood pressure and modulates neuroendocrine stress response in rats depending on stressor intensity.

Ivabradine, a selective inhibitor of the sinoatrial pacemaker, is used in clinical practice to reduce heart rate. However, its potential effect on the neuroendocrine stress response has not been investigated. Therefore, we determined the effect of administering ivabradine to rats on cardiovascular parameters and plasma levels of epinephrine, norepinephrine, and corticosterone. Ivabradine was administered intraperitoneally 30 min before exposing animals to either handling, restraint, or immobilization stress. Heart rate and blood pressure were monitored telemetrically. Blood samples were collected before, during, and after stressor exposure to determine the extent of the neuroendocrine stress response as reflected by plasma epinephrine, norepinephrine, and corticosterone levels. In animals pretreated with ivabradine, significantly lower values of heart rate and blood pressure were found during both the baseline period and during exposure to stressors, as well as during the rest period following stressor exposure. Ivabradine also significantly reduced handling-induced epinephrine and norepinephrine release into the bloodstream. However, ivabradine significantly potentiated restraint- and immobilization-induced increases of plasma epinephrine levels, whereas stress-induced changes in plasma norepinephrine and corticosterone levels were ambiguous. Our data shows that ivabradine significantly reduces blood pressure in rats during both baseline and stressful conditions, and also affects the neuroendocrine stress response. These findings show that viscerosensory signaling from the cardiovascular system may significantly modulate the neuroendocrine stress response.

The vagus nerve role in antidepressants action: Efferent vagal pathways participate in peripheral anti-inflammatory effect of fluoxetine.

The mechanisms responsible for the anti-inflammatory effects of antidepressants are only partially understood. Published data indicate that the vagal anti-inflammatory pathway could be involved in mediating this effect. Therefore, we investigated the influence of subdiaphragmatic vagotomy on the anti-inflammatory effect of fluoxetine in rats injected with lipopolysaccharide (LPS) to induce an inflammatory response. The extent of this response was determined by measurement of TNF-α, IL-1ß, and IL-6 plasma levels, along with gene expression of TNF-α, IL-1ß, and IL-6 in the spleen and selected structures of the brain. To evaluate possible central mechanisms, c-fos mRNA levels were determined in the nucleus of the solitary tract, dorsal motor nucleus of the vagus, paraventricular hypothalamic nucleus, basolateral amygdala, central nucleus of the amygdala, hippocampus, and frontal cortex. We found that pretreatment with fluoxetine substantially prevented LPS-induced increases of pro-inflammatory cytokines in plasma and gene expression in the spleen and brain in animals with an intact vagus nerve. However, in vagotomized animals, fluoxetine pretreatment only partially attenuated the LPS-induced increase in these markers of peripheral inflammation. Our data has shown that fluoxetine exerts potent anti-inflammatory effects in both the periphery and brain. Moreover, we found that the peripheral anti-inflammatory action of fluoxetine is mediated, at least partially, by activation of a vagal anti-inflammatory pathway. The role of the vagus nerve in mediating the anti-inflammatory effects of antidepressants has been marginally explored and our findings highlight its potential contribution to this mechanism of action of antidepressants.

Brain region-specific effects of immobilization stress on cholinesterases in mice.

Brain acetylcholinesterase (AChE) variant AChER expression increases with acute stress, and this persists for an extended period, although the timing, strain and laterality differences, have not been explored previously. Acute stress transiently increases acetylcholine release, which in turn may increase activity of cholinesterases. Also the AChE gene contains a glucocorticoid response element (GRE), and stress-inducible AChE transcription and activity changes are linked to increased glucocorticoid levels. Corticotropin-releasing hormone knockout (CRH-KO) mice have basal glucocorticoid levels similar to wild type (WT) mice, but much lower levels during stress. Hence we hypothesized that CRH is important for the cholinesterase stress responses, including butyrylcholinesterase (BChE). We used immobilization stress, acute (30 or 120 min) and repeated (120 min daily × 7) in 48 male mice (24 WT and 24 CRH-KO) and determined AChER, AChE and BChE mRNA expression and AChE and BChE activities in left and right brain areas (as cholinergic signaling shows laterality). Immobilization decreased BChE mRNA expression (right amygdala, to 0.5, 0.3 and 0.4, × control respectively) and AChER mRNA expression (to 0.5, 0.4 and 0.4, × control respectively). AChE mRNA expression increased (1.3, 1.4 and 1.8-fold, respectively) in the left striatum (Str). The AChE activity increased in left Str (after 30 min, 1.2-fold), decreased in right parietal cortex with repeated stress (to 0.5 × control). BChE activity decreased after 30 min in the right CA3 region (to 0.4 × control) but increased (3.8-fold) after 120 min in the left CA3 region. The pattern of changes in CRH-KO differed from that in WT mice.

Exaggerated phosphorylation of brain tau protein in CRH KO mice exposed to repeated immobilization stress.

Neuroendocrine and behavioral stress responses are orchestrated by corticotropin-releasing hormone (CRH) and norepinephrine (NE) synthesizing neurons. Recent findings indicate that stress may promote development of neurofibrillary pathology in Alzheimer's disease. Therefore, we investigated relationships among stress, tau protein phosphorylation, and brain NE using wild-type (WT) and CRH-knockout (CRH KO) mice. We assessed expression of phosphorylated tau (p-tau) at the PHF-1 epitope and NE concentrations in the locus coeruleus (LC), A1/C1 and A2/C2 catecholaminergic cell groups, hippocampus, amygdala, nucleus basalis magnocellularis, and frontal cortex of unstressed, singly stressed or repeatedly stressed mice. Moreover, gene expression and protein levels of tyrosine hydroxylase (TH) and CRH receptor mRNA were determined in the LC. Plasma corticosterone levels were also measured. Exposure to a single stress increases tau phosphorylation throughout the brain in WT mice when compared to singly stressed CRH KO animals. In contrast, repeatedly stressed CRH KO mice showed exaggerated tau phosphorylation relative to WT controls. We also observed differences in extent of tau phosphorylation between investigated structures, e.g. the LC and hippocampus. Moreover, CRH deficiency leads to different responses to stress in gene expression of TH, NE concentrations, CRH receptor mRNA, and plasma corticosterone levels. Our data indicate that CRH effects on tau phosphorylation are dependent on whether stress is single or repeated, and differs between brain regions. Our findings indicate that CRH attenuates mechanisms responsible for development of stress-induced tau neuropathology, particularly in conditions of chronic stress. However, the involvement of central catecholaminergic neurons in these mechanisms remains unclear and is in need of further investigation.

Tauopathy in transgenic (SHR72) rats impairs function of central noradrenergic system and promotes neuroinflammation.

BACKGROUND: Brain norepinephrine (NE) plays an important role in the modulation of stress response and neuroinflammation. Recent studies indicate that in Alzheimer's disease (AD), the tau neuropathology begins in the locus coeruleus (LC) which is the main source of brain NE. Therefore, we investigated the changes in brain NE system and also the immune status under basal and stress conditions in transgenic rats over-expressing the human truncated tau protein. METHODS: Brainstem catecholaminergic cell groups (LC, A1, and A2) and forebrain subcortical (nucleus basalis of Meynert), hippocampal (cornu ammonis, dentate gyrus), and neocortical areas (frontal and temporal association cortices) were analyzed for NE and interleukin 6 (IL-6) mRNA levels in unstressed rats and also in rats exposed to single or repeated immobilization. Moreover, gene expression of NE-biosynthetic enzyme, tyrosine hydroxylase (TH), and several pro- and anti-inflammatory mediators were determined in the LC. RESULTS: It was found that tauopathy reduced basal NE levels in forebrain areas, while the gene expression of IL-6 was increased in all selected areas at the same time. The differences between wild-type and transgenic rats in brain NE and IL-6 mRNA levels were observed in stressed animals as well. Tauopathy increased also the gene expression of TH in the LC. In addition, the LC exhibited exaggerated expression of pro- and anti-inflammatory mediators (IL-6, TNFα, inducible nitric oxide synthases 2 (iNOS2), and interleukin 10 (IL-10)) in transgenic rats suggesting that tauopathy affects also the immune background in LC. Positive correlation between NE and IL-6 mRNA levels in cornu ammonis in stressed transgenic animals indicated the reduction of anti-inflammatory effect of NE. CONCLUSIONS: Our data thus showed that tauopathy alters the functions of LC further leading to the reduction of NE levels and exaggeration of neuroinflammation in forebrain. These findings support the assumption that tau-related dysfunction of LC activates the vicious circle perpetuating neurodegeneration leading to the development of AD.

Subdiaphragmatic vagotomy enhances stress-induced epinephrine release in rats.

Neuroendocrine stress response is regulated by several feedback loops. Since it has been suggested that afferent vagal pathways contribute to these feedback loops, we examined the effect of surgical subdiaphragmatic vagotomy on both baseline and stress-induced increases in plasma epinephrine, norepinephrine, and corticosterone levels in vagotomized and sham-operated Sprague Dawley rats. On either the 3rd or 14th day following vagotomy, the animals were exposed to acute immobilization stress and blood from the jugular vein was collected both before and during stress exposure. We found that vagotomy significantly enhanced immobilization-induced increases of plasma epinephrine, norepinephrine, and corticosterone levels on the 3rd day following surgery. However, on the 14th day following surgery, vagotomy enhanced only increase of plasma epinephrine levels in stressed rats. Our data indicate that afferent pathways of the vagus nerve are involved in negative feedback regulation of epinephrine secretion from the adrenal medulla during stressful conditions. We hypothesize that this feedback mechanism might be mediated by the binding of circulating epinephrine on ß2-adrenergic receptors localized on sensory endings of the vagus nerve.

Ambiguous effect of signals transmitted by the vagus nerve on fibrosarcoma incidence and survival of tumor-bearing rats.

While the parasympathetic nervous system appears to be involved in the regulation of tumor progression, its exact role is still unclear. Therefore, using a rat BP6-TU2 fibrosarcoma tumor model, we investigated the effect of (1) reduction of vagal activity produced by subdiaphragmatic vagotomy; and (2) enhancement of vagal activity produced by continuous delivery of electric impulses to the cervical part of the vagus nerve on tumor development and survival of tumor-bearing rats. We also evaluated the expression of cholinergic receptors within in vitro cultivated BP6-TU2 cells. Interestingly, we found that both, vagal stimulation and subdiaphragmatic vagotomy slightly reduced tumor incidence. However, survival of tumor-bearing rats was not affected by any of the experimental approaches. Additionally, we detected mRNA expression of the α1, α2, α5, α7, and α10 subunits of nicotinic receptors and the M1, M3, M4, and M5 subtypes of muscarinic receptors within in vitro cultivated BP6-TU2 cells. Our data indicate that the role of the vagus nerve in modulation of fibrosarcoma development is ambiguous and uncertain and requires further investigation.

Stress-induced activation of the sympathoadrenal system is determined by genetic background in rat models of tauopathy.

Stress may accelerate onset of neurodegenerative diseases in vulnerable subjects and, vice versa, neurodegeneration affects the responsiveness to stressors. We investigated the neuroendocrine response to immobilization stress in normotensive Wistar-Kyoto rats (WKY), spontaneously hypertensive rats (SHR), and transgenic rats of respective WKY and SHR strains overexpressing human truncated tau protein. Plasma levels of epinephrine, norepinephrine, and corticosterone were determined. An immobilization-induced elevation of epinephrine and norepinephrine was significantly reduced in WKY transgenic rats compared to WKY wild-type rats, while no differences were seen between SHR transgenic and SHR wild-type animals. Our data have shown that sympathoadrenal system response to stress strongly depends on both tau protein-induced neurodegeneration and genetic background of experimental animals.

Complete regression of glioblastoma by mesenchymal stem cells mediated prodrug gene therapy simulating clinical therapeutic scenario.

Suicide gene therapy mediated by mesenchymal stem cells with their ability to engraft into tumors makes these therapeutic stem cells an attractive tool to activate prodrugs directly within the tumor mass. In this study, we evaluated the therapeutic efficacy of human mesenchymal stem cells derived from bone marrow and from adipose tissue, engineered to express the suicide gene cytosine deaminase::uracil phosphoribosyltransferase to treat intracerebral rat C6 glioblastoma in a simulated clinical therapeutic scenario. Intracerebrally grown glioblastoma was treated by resection and subsequently with single or repeated intracerebral inoculations of therapeutic stem cells followed by a continuous intracerebroventricular delivery of 5-fluorocytosine using an osmotic pump. Kaplan-Meier survival curves revealed that surgical resection of the tumor increased the survival time of the resected animals depending on the extent of surgical intervention. However, direct injections of therapeutic stem cells into the brain tissue surrounding the postoperative resection cavity led to a curative outcome in a significant number of treated animals. Moreover, the continuous supply of therapeutic stem cells into the brain with growing glioblastoma by osmotic pumps together with continuous prodrug delivery also proved to be therapeutically efficient. We assume that observed curative therapy of glioblastoma by stem cell-mediated prodrug gene therapy might be caused by the destruction of both tumor cells and the niche where glioblastoma initiating cells reside.

Increased ubiquinone concentration after intracerebroventricularly-administered ubiquinol to selected rat brain regions.

Brain coenzyme Q10 (CoQ10) concentration can influence the activity of several brain regions, including those which participate in the regulation of cardiovascular circadian rhythms, food intake, neuroendocrine stress response, activity and sleep regulation. However, the effect of supplemented ubiquinol (reduced CoQ) into brain regions is not known. This study determined baseline levels of ubiquinone (oxidized CoQ) in various rat brain regions and proved the bioavailability of the liposomal ubiquinol to selected brain regions after its administration into right brain ventricle. Our data indicate that administration of ubiquinol may create the basis for modulation of neuronal activities in specific brain regions.

Tau protein phosphorylation in diverse brain areas of normal and CRH deficient mice: up-regulation by stress.

Tau protein misfolding is a pathological mechanism, which plays a critical role in the etiopathogenesis of neurodegeneration. However, it is not entirely known what kind of stimuli can induce the misfolding. It is believed that physical and emotional stresses belong to such risk factors. Although the influence of stress on the onset and progression of Alzheimer's disease (AD) has already been proposed, the molecular links between stresses and AD are still unknown. We have therefore focused our attention on determination of the influence of acute immobilization stress (IMO) in normal mice and mice deficient in corticotropin-releasing hormone (CRH). Specifically, we have analyzed levels of hyperphosphorylated tau proteins, bearing the AD-specific phospho-epitopes (AT-8, pT181, and PHF-1), which are implicated in the pathogenesis of AD. We found that IMO induces transient hyperphosphorylation of tau proteins regardless of continuation of the stimulus. Concerning tau modifications, detailed analysis of the mouse brain revealed that neurons in different brain regions including frontal cortex, temporal cortex, hippocampal C1 and CA3 regions, dentate gyrus as well as nucleus basalis Meynert, and several brainstem nuclei such as locus coeruleus but also raphe nucleus and substantia nigra respond similarly to IMO. The strongest tau protein phosphorylation was observed after 30 min of IMO stress. Stress lasting for 120 min led either to the disappearance of tau hyperphosphorylation or to the induction of a second wave of hyperphosphorylation. Noteworthy is the magnitude of pathological phosphorylation of tau protein in CRH and glucocorticoids deficient mice, being much lower in comparison to that observed in wild-type animals, which suggests a critical role of CRH in the pathogenesis of AD. Thus, our results indicate that hyperphosphorylation of tau protein induced by stress may represent the pathogenic event upstream of tau protein misfolding, which leads to progression or eventually initiation of neurodegeneration. The data show that CRH plays an important role in stress induced hyperphosphorylation of tau protein, which might be either a direct effect of CRH innervations in the brain or an effect mediated via the hypothalamo-pituitary-adrenal axis.

Human adipose tissue-derived mesenchymal stem cells expressing yeast cytosinedeaminase::uracil phosphoribosyltransferase inhibit intracerebral rat glioblastoma.

Prodrug cancer gene therapy by mesenchymal stem cells (MSCs) targeted to tumors represents an attractive tool to activate prodrugs directly within the tumor mass, thus avoiding systemic toxicity. In this study, we tested the feasibility and efficacy of human adipose tissue-derived MSCs, engineered to express the suicide gene cytosine deaminase::uracil phosphoribosyltransferase to treat intracranial rat C6 glioblastoma. Experiments were designed to simulate conditions of future clinical application for high-grade glioblastoma therapy by direct injections of therapeutic stem cells into tumor. We demonstrated that genetically modified therapeutic stem cells still have the tumor tropism when injected to a distant intracranial site and effectively inhibited glioblastoma growth after 5-fluorocytosine (5-FC) therapy. Coadministration of C6 cells and therapeutic stem cells with delayed 5-FC therapy improved the survival in a therapeutic stem cell dose-dependent manner and induced complete tumor regression in a significant number of animals. Continuous intracerebroventricular delivery of 5-FC using osmotic pump reduced the dose of prodrug required for the same therapeutic effect, and along with repeated administration of therapeutic stem cells increased the survival time. Intracerebral injection of therapeutic stem cells and treatment with 5-FC did not show any detectable adverse effects. Results support the arguments to begin clinical studies for treatment of high-grade brain tumors.

The role of the vagus nerve in depression.

The etiopathogenesis of depression is a highly complex process characterized by several neurobiological alterations including decreased monoamine neurotransmission in the brain, dysregulated hypothalamic-pituitary-adrenal axis activity, decreased neuronal plasticity, and chronic inflammation in the brain and peripheral tissues. Experimental and clinical studies indicate that the vagus nerve may influence these processes. The importance of the vagus nerve in the etiopathogenesis of depression is further supported by its involvement in the induction of sickness behavior, as well as by clinical studies confirming a beneficial effect of vagus nerve stimulation in depressed patients. The aim of this article is to describe current knowledge of afferent and efferent vagal pathways role in the development and progression of depression.

Role of nervous system in cancer aetiopathogenesis.

There have been several reports on tumour tissue innervation, the effect of neurotransmitters on tumour growth, the development of metastases, and the effect of altered nervous-system activity on tumour cell proliferation. In this personal view, we summarise recent findings related to the interactions between the nervous system and tumour cells and suggest further research into the role of the nervous system in the aetiopathogenesis of cancer. Data showing the transmission of signals between the brain and tumour tissue create a complex view of the nervous system in the aetiopathogenesis of cancer. This neurobiological view of cancer aetiopathogenesis suggests that humoral and nervous pathways convey signals from tumour cells to the brain, and that the brain might consequently modulate the neuroendocrine-immune system to regulate tumour growth in peripheral tissues.

Neurobiological principles in the etiopathogenesis of disease: when diseases have a head.

There is no doubt that the nervous system is involved in the etiopathogenesis of various pathological states and diseases. Interactions between the nervous, endocrine, and immune systems might represent the anatomical and functional basis for understanding the pathways and mechanisms that enable the brain to modulate the progression of disease. The aim of this article is to encourage us to shift our current opinion of the etiopathogenesis of disease to one of highly complex interactions between peripheral tissues and the brain and in this way introduce new diagnostic and therapeutic approaches.