Effect of chronic unpredictable mild stress on the expression profile of serotonin receptors in rats and mice: a meta-analysis.

Chronic-stress-induced depression is recognized as a widespread public health concern. Selective serotonin reuptake inhibitors (SSRIs) have been the most common treatment for this illness. However, the role of 5-hydroxytryptamine (5-HT) receptor subtypes in stress-induced depression remains unclear. Evidence from Animal studies has reported a variety of results regarding the effects of chronic unpredictable mild stress (CUMS) on serotonin signaling pathways and 5-HT receptor subtypes. This divergence may rely on differences in protocols, methods, and studied pathways. Thus, the aim of this systematic review was to weigh the currently available findings regarding serotonin receptor changes in animal models of CUMS. Overall, our meta-analysis results showed the association of altered expression of 5-HT1A receptors in the frontal cortex and 5-HT2A receptors both in the whole cortex and the hypothalamus of rats following CUMS. Moreover, by using a qualitative-structured analysis and the application of risk-of-bias tools, we identified possible sources of data variation between the studied literature, which should be taken into account in future animal studies of chronic-stress induced depression.

Congenital Zika syndrome is associated with maternal protein malnutrition.

Zika virus (ZIKV) infection during pregnancy is associated with a spectrum of developmental impairments known as congenital Zika syndrome (CZS). The prevalence of this syndrome varies across ZIKV endemic regions, suggesting that its occurrence could depend on cofactors. Here, we evaluate the relevance of protein malnutrition for the emergence of CZS. Epidemiological data from the ZIKV outbreak in the Americas suggest a relationship between undernutrition and cases of microcephaly. To experimentally examine this relationship, we use immunocompetent pregnant mice, which were subjected to protein malnutrition and infected with a Brazilian ZIKV strain. We found that the combination of protein restriction and ZIKV infection leads to severe alterations of placental structure and embryonic body growth, with offspring displaying a reduction in neurogenesis and postnatal brain size. RNA-seq analysis reveals gene expression deregulation required for brain development in infected low-protein progeny. These results suggest that maternal protein malnutrition increases susceptibility to CZS.

Variations in maternal adenylate cyclase genes are associated with congenital Zika syndrome in a cohort from Northeast, Brazil.

BACKGROUND: Vertical transmission of Zika virus (ZIKV) is associated with congenital malformations but the mechanism of pathogenesis remains unclear. Although host genetics appear to play a role, no genetic association study has yet been performed to evaluate this question. In order to investigate if maternal genetic variation is associated with Congenital Zika Syndrome (CZS), we conducted a case-control study in a cohort of Brazilian women infected with ZIKV during pregnancy. METHODS: A total of 100 women who reported symptoms of zika during pregnancy were enrolled and tested for ZIKV. Among 52 women positive for ZIKV infection, 28 were classified as cases and 24 as controls based on the presence or absence of CZS in their infants. Variations in the coding region of 205 candidate genes involved in cAMP signaling or immune response were assessed by high throughput sequencing and tested for association with development of CZS. RESULTS: From the 817 single nucleotide variations (SNVs) included in association analyses, 22 SNVs in 17 genes were associated with CZS under an additive model (alpha = 0.05). Variations c.319T>C (rs11676272) and c.1297G>A, located at ADCY3 and ADCY7 genes showed the most prominent effect. The association of ADCY3 and ADCY7 genes was confirmed using a Sequence Kernel Association Test to assess the joint effect of common and rare variations, and results were statistically significant after adjustment for multiple comparisons (P < 0.002). CONCLUSION: These results suggest that maternal ADCY genes contribute to ZIKV pathogenicity and influence the outcome of CZS, being promising candidates for further replication studies and functional analysis.

Inorganic mercury modifies Ca2+ signals, triggers apoptosis and potentiates NMDA toxicity in cerebellar granule neurons.

Hg2+ (0.1 microM-0.5 microM) modified the Ca2+ signals elicited by either KCl or the glutamate-receptor agonist, N-methyl-D-aspartate (NMDA), in cerebellar granule cells (CGCs). Hg2+ enhanced the intracellular Ca2+ transient elicited by high K+ and prevented a complete recovery of the resting intracellular Ca2+ concentration ([Ca2+]i) after either KCl or NMDA stimulation. Higher Hg2+ concentrations (up to 1 microM) increased [Ca2+]i directly. Following the short-term exposure to Hg2+, CGCs underwent apoptosis, which was identified by the cleavage of DNA into large (700-50 kbp) and oligonucleosomal DNA fragments, and by the appearance of typical apoptotic nuclei. Combined treatment with 0.1-0.3 microM Hg2+ and a sublethal NMDA concentration (50 microM) potentiated DNA fragmentation and apoptotic cell death. When the exposure to Hg2+ was carried out in Ca2+-free media or in the presence of Ca2+ channel blockers (L-type or NMDA-R antagonists), the effects on signalling and apoptosis were prevented. Our results suggest that very low Hg2+ concentrations can trigger apoptosis in CGCs by facilitating Ca2+ entry through membrane channels.

Prenatal exposure to methylmercury alters locomotor activity of male but not female rats.

In the present study the neurotoxic effects of a low dosage (0.5 mg/kg per day) of methylmercury (MeHg) on the developing nervous system were investigated. Pregnant rats were treated with MeHg from day 7 of pregnancy to day 7 of lactation. Locomotor activity (locomotion, rearing, and motility) and spatial learning ability were tested in the offspring at 6 months of age. The expression of tyrosine hydroxylase (TH) was examined by immunohistochemistry and in situ hybridization. A significant decrease in spontaneous motility and rearing was observed only in the MeHg-treated male rats. After administration of a low dose of d-amphetamine (0.5 mg/kg) no differences could be observed between control and MeHg-treated male rats, suggesting that changes in dopaminergic transmission were involved. However, no change in TH messenger RNA expression was observed. No changes in spatial learning acquisition or memory were shown in MeHg-treated rats. Taken together, these findings show that during development a very low dosage of MeHg exerts neurotoxic effects detectable in adulthood, and that susceptibility is gender-dependent.

BCL-2 delay apoptosis and PARP cleavage induced by NO donors in GT1-7 cells.

BCL-2 is a negative regulator of cell death in several systems. Here we report that bcl-2 expression protects against apoptosis induced by nitric oxide (NO) donors in GT1-7 hypothalamic cells. BCL-2 significantly inhibited neuronal death caused by 200 microM S-nitroso-cysteine (SNOC), 200 microM S-nitroso-N-acetyl-penicillamine (SNAP), or 1 mM 3-morpholinosydnonimine (SIN-1). To explore further the protective mechanism(s) elicited by bcl-2 expression, we investigated whether BCL-2 could prevent NO-induced cleavage of poly-ADP-ribose-polymerase (PARP), which is a substrate for interleukin-1 beta converting enzyme (ICE)-like proteases in apoptosis. Formation of 85 and 25 kDa PARP fragments elicited by NO donors was inhibited in cells over-expressing bcl-2.

Triethyltin interferes with Ca2+ signaling and potentiates norepinephrine release in PC12 cells.

We have investigated the effects of triethyltin (TET) on agonist-stimulated Ca2+ signaling and neurosecretion in PC12 cells. Treatment of PC12 cells with 10 microM TET elicited a slow increase of the resting cytosolic free Ca2+ concentration due to Ca2+ release from intracellular stores. Furthermore, TET modified the Ca2+ responses elicited by bradykinin (Bk), adenosine triphosphate (ATP), or high K+. TET potentiated the peak Ca2+ response stimulated by Bk in both the presence and the absence of extracellular Ca2+, and prolonged the recovery phase after ATP stimulation. In contrast, the Ca2+ transient elicited by bathing cells in high K+ was markedly reduced, suggesting that TET can differentially affect several targets on Ca2+-signaling pathways. Neurotransmitter depletion follows in vivo exposure to TET. Since neurotransmitter secretion is strictly dependent on intracellular Ca2+ signals we also investigated whether treatment with TET modified norepinephrine release from PC12 cells. TET did not elicit norepinephrine release, but it enhanced the release of norepinephrine induced by Bk or ATP. The increased release of norepinephrine elicited in combination with Bk was independent from extracellular Ca2+. Our results suggest that possible neurotoxic effects of TET can derive from its ability to modulate Ca2+ signaling and eventually neurosecretion.

Mechanisms of neurotoxicity: applications to human biomonitoring.

Interactions of chemicals with cerebral neurotransmitters, receptors, and second messenger systems are often accompanied by similar changes involving components in non-neural tissues. On this basis, indirect strategies have been developed to investigate neural cell function parameters by methods using accessible cells such as platelets or peripheral blood lymphocytes. The validity of certain surrogate markers of biochemical events occurring in the nervous system has been documented by recent studies in both laboratory animals and humans. Although experience with neurotoxicants is still limited, advantages and limitations of methods using peripheral blood cells as indicators of chemically-induced nervous system changes have been documented by a number of studies in psychopharmacology and biological psychiatry. Applicability of this approach in conventional population studies of environmental chemicals remains to be demonstrated. However, recent data regarding the action of low doses of mercury and organophosphates on receptors and signal transduction pathways in peripheral lymphocytes suggest useful applications of certain surrogate markers in mechanistic studies of neurotoxicity in vivo and, possibly, in assessing early biochemical effects of neurotoxicants in humans.

[Toxicity of chemical elements]. / Aspetti della tossicità da elementi chimici.

A survey is presented of the most important facets of toxicity due to chemical elements as well as of the mechanisms through which it may be triggered. In particular, a detailed discussion is made on the characteristics shown by arsenic, cadmium, chromium, lead, mercury, barium and beryllium, with specific reference to the influence exerted by physiological, environmental and life-style factors.

Organotin compounds induce calcium overload and apoptosis in PC12 cells.

We examined the effects of four tri-substituted organotin compounds on intracellular Ca2+ and survival in PC12 cells. Treatment with micromolar concentrations of tributyltin and triphenyltin caused a rapid increase in the cytosolic free Ca2+ concentration ([Ca2+]i). This was due to enhanced Ca2+ influx and release from intracellular stores. When the [Ca2+]i elevation was maintained for over 30 min, internucleosomal DNA cleavage typical of apoptotic cell death followed. In contrast, when the increase in [Ca2+]i was transient, cells did not show internucleosomal DNA cleavage and retained their viability. Triethyltin modified [Ca2+]i only slightly, whereas trimethyltin had no effect. The latter two agents did not modify cell viability. Our data suggest that the toxicity of organotins in PC12 cells is linked to their ability to promote intracellular Ca2+ overload, which triggers apoptosis.

Nuclear Ca2+: physiological regulation and role in apoptosis.

The last decade has seen the rapid development of research investigating the molecular mechanisms whereby hormones, peptide growth factors and cytokines regulate cell metabolism, differentiation and proliferation. One general signalling mechanism used to transfer the information delivered by agonists into appropriate intracellular compartments involves the rapid Ca2+ redistribution throughout the cell, which results in transient elevations of the cytosolic free Ca2+ concentration. Ca2+ signals are required for a number of cellular processes including the activation of nuclear processes such as gene transcription and cell cycle events. The latter require that appropriate Ca2+ signals elicited in response to agonists be transduced across the nuclear envelope. It has generally been assumed that small molecules, metabolites and ions could freely diffuse across the nuclear envelope. Nevertheless several findings during the past few years have suggested that nuclear pore permeability can be regulated and that ion transport systems and ion-selective channels may exist on the nuclear membranes and regulate intranuclear processes. Intranuclear Ca2+ fluctuations can affect chromatin organization, induce gene expression and also activate cleavage of nuclear DNA by nucleases during programmed cell death or apoptosis. The possible mechanisms involved in nuclear Ca2+ transport and the control of nuclear Ca(2+)-dependent enzymes in apoptosis is discussed below.

Modifications of Ca2+ signaling by inorganic mercury in PC12 cells.

The effects of different levels of inorganic mercury (Hg2+) on depolarization- or agonist-stimulated Ca2+ signals were studied in PC12 cells. Exposure to 50-300 nM Hg2+ did not alter the resting cytosolic free Ca2+ concentration ([Ca2+]i), but enhanced the Ca2+ response to KCL-induced depolarization. Patch-clamp experiments revealed that these Hg2+ concentrations increased the voltage-dependent Ca2+ current through L-type channels. Also, Hg2+ treatment amplified the intracellular [Ca2+]i transients elicited by extracellular ATP. In contrast, the Ca2+ increase stimulated by bradykinin was unaffected. At slightly higher concentrations (1 to 2 microM), Hg2+ caused a sustained rise of the resting [Ca2+]i. This increase did not occur in Ca(2+)-free medium and was prevented by pretreatment with NiCl2 or with the L-type Ca2+ channel blockers, verapamil and nifedipine. Hg2+ did not mobilize Ca2+ from intracellular stores sensitive to thapsigargin, 2,5-di-(tert-butyl)-benzohydroquinone, or caffeine. At 2 microM, Hg2+ inhibited the [Ca2+]i transients elicited by bradykinin, ATP, or KCl-induced depolarization. The loss of the intracellular Ca2+ response to bradykinin was independent from the Ca2+ overload elicit by Hg2+; instead, it was associated with inhibition of polyphosphoinositide generation. Exposure to the lower Hg2+ concentrations (0.3-0.5 microM) greatly potentiated NGF-induced PC12 cell differentiation. Conversely, treatment with 2 microM Hg2+ caused cell death. Our results show that inorganic mercury has selective and different effects on Ca2+ signaling in PC12 cells depending on the concentration, within a narrow range.

Thiol modification and cell signalling in chemical toxicity.

Exposure of cells to thiol oxidizing agents can result in the modification of key proteins involved in cell signalling. Such changes have been shown to affect agonist-stimulated phosphoinositide metabolism, activation of protein kinases and intracellular Ca2+ signals, which result in abnormalities in cell metabolisms and growth. Here, we show that moderate levels of oxidants potentiate growth signals and either enhance cell proliferation or facilitate cell differentiation, whereas inhibition of growth signals by higher oxidant concentrations can block cell proliferation and activate programmed cell death (PCD). Finally, a general alteration of multiple signalling pathways associated with increased catabolic reactions results in cell death by necrosis. Our data suggest that oxidant interaction with cell signalling systems may exert opposite effects, depending on the dose, and that oxidative reactions may either mimic growth factor stimulation and stimulate cell proliferation or inhibit growth signals and activate PCD, in the same cell systems.