Parallel changes of the spontaneous and stimulus-evoked cortical activity elicited by acute treatment with inorganic mercury in rats

Mercury is known to affect the activity of the nervous system of animals and humans, as indicated by the multitude of neurological signs following e.g. occupational exposure. In animal experiments, heavy metals cause a variety of alterations in the central and peripheral nervous system activity but an explanation as to mechanism of action is missing in a number of cases. The aim of the work presented was to find correlation between the changes of spontaneous cortical activity (electrocorticogram, ECoG) and cortical sensory evoked potentials (EPs) recorded from rats acutely treated with mercuric chloride. Adult male Wistar rats were anesthesized with urethane. Silver recording electrodes were placed on the exposed left somatosensory projection area of the whiskers and of the tail. The corresponding peripheral sites were stimulated by electric pulses. During tail stimulation, compound action potentials of the tail nerve were also recorded. After at least 4 control records, mercury (HgCl2, 7 mg/kg) was administered via a peritoneal cannula and the recording was continued for further ca. 2 hours. In the spontaneous activity, increased activity of the low and decreased activity of the high frequency bands was seen Simultaneously, the amplitude of the EPs increased. On the tail nerve potential, Hg caused an amplitude decrease and a latency increase. Latency increase of the cortical EP and the decrease of nerve conduction velocity evolved simultaneously. The alterations are likely due to some specific, and not to a general toxic, effect of Hg

Effect of acute administration of certain heavy metals and their combinations on the spontaneous and evoked cortical activity in rats

The aim of this study was to see the effect of acutely administered inorganic lead, mercury, manganese, and their combinations, on the electrical activity in the somatosensory system of rats. Male Wistar rats were anaesthetised with urethane, the head was fixed in a stereotaxic frame and the left hemisphere was exposed. Weak electric shocks to the whiskers and the tail served as stimuli. Spontaneous and stimulus-evoked activity was recorded from the primary projection area of the whiskers and the tail. After an hour of control recording, one of the following was given to the rat i.p.: 1000 mg/kg Pb2+, 7 mg/kg Hg2+, 50 mg/kg Mn2+, 500 mg/kg Pb2+ + 25 mg/kg Mn2+, or 500 mg/kg Pb2+ + 3.5 mg/kg Hg2+. Lead caused a massive increase in the cortical response amplitude, starting immediately after administration and developing in the next 40-50 min. Latency showed a minimal increase. The spontaneous activity was moderately shifted to lower frequencies. The effect of Hg2+ on the response amplitude and on the ECoG was similar but stronger than that of Pb 2+. The effect of Mn2+ on the evoked activity was marked but less strong than with Pb2+. The ECoG shift was moderate. With Hg2+ and Mn2+, the response amplitude showed first a decrease than an increase. The effect of the Pb2+ + Mn2+ combination on the activities was not additive but the correlation between the alteration of the ECoG and the evoked potential was stronger than with any of the metals alone. With Pb2+ + Hg2+, the effect of Pb 2+ dominated on the evoked and that of Hg2+ on the spontaneous activity. In the peripheral nerve, action potential amplitude and conduction velocity were decreased. These alterations of the spontaneous and stimulus-evoked cortical activity probably reflected a specific action of the heavy metals on the nervous activity. Š 2004 Elsevier B.V. All rights reserved

Molecular surgery concept from bench to bedside: a focus on TRPV1+ pain-sensing neurons

“Molecular neurosurgery” is emerging as a new medical concept, and is the combination of two partners: (i) a molecular neurosurgery agent, and (ii) the cognate receptor whose activation results in the selective elimination of a specific subset of neurons in which this receptor is endogenously expressed. In general, a molecular surgery agent is a selective and potent ligand, and the target is a specific cell type whose elimination is desired through the molecular surgery procedure. These target cells have the highest innate sensitivity to the molecular surgery agent usually due to the highest receptor density being in their plasma membrane. The interaction between the ligand and its receptor evokes an overactivity of the receptor. If the receptor is a ligand-activated non-selective cation channel, the overactivity of receptor leads to excess Ca2+ and Na+ influx into the cell and finally cell death. One of the best known examples of such an interaction is the effect of ultrapotent vanilloids on TRPV1- expressing pain-sensing neurons. One intrathecal resiniferatoxin (RTX) dose allows for the receptor-mediated removal of TRPV1+ neurons from the peripheral nervous system. The TRPV1 receptor-mediated ion influx induces necrotic processes, but only in pain-sensing neurons, and usually within an hour. Besides that, target-specific apoptotic processes are also induced. Thus, as a nano-surgery scalpel, RTX removes the neurons responsible for generating pain and inflammation from the peripheral nervous system providing an option in clinical management for the treatment of morphine-insensitive pain conditions. In the future, the molecular surgery concept can also be exploited in cancer research for selectively targeting the specific tumor cell

Routes of Ca²⁺ shuttling during Ca²⁺ oscillations FOCUS ON THE ROLE OF MITOCHONDRIAL Ca²⁺ HANDLING AND CYTOSOLIC Ca²⁺ BUFFERS

In some cell types, Ca²⁺ oscillations are strictly dependent on Ca²⁺ influx across the plasma membrane, whereas in others, oscillations also persist in the absence of Ca²⁺ influx. We observed that, in primary mesothelial cells, the plasmalemmal Ca²⁺ influx played a pivotal role. However, when the Ca²⁺ transport across the plasma membrane by the “lanthanum insulation method” was blocked prior to the induction of the serum-induced Ca²⁺ oscillations, mitochondrial Ca²⁺ transport was found to be able to substitute for the plasmalemmal Ca²⁺ exchange function, thus rendering the oscillations independent of extracellular Ca²⁺. However, in a physiological situation, the Ca²⁺-buffering capacity of mitochondria was found not to be essential for Ca²⁺ oscillations. Moreover, brief spontaneous Ca²⁺ changes were observed in the mitochondrial Ca²⁺ concentration without apparent changes in the cytosolic Ca²⁺ concentration, indicating the presence of a mitochondrial autonomous Ca²⁺ signaling mechanism. In the presence of calretinin, a Ca²⁺-buffering protein, the amplitude of cytosolic spikes during oscillations was decreased, and the amount of Ca²⁺ ions taken up by mitochondria was reduced. Thus, the increased calretinin expression observed in mesothelioma cells and in certain colon cancer might be correlated to the increased resistance of these tumor cells to proapoptotic/pronecrotic signals. We identified and characterized (experimentally and by modeling) three Ca²⁺ shuttling pathways in primary mesothelial cells during Ca²⁺ oscillations: Ca²⁺ shuttled between (i) the endoplasmic reticulum (ER) and mitochondria, (ii) the ER and the extracellular space, and (iii) the ER and cytoplasmic Ca²⁺ buffers

Acute effects of lead, mercury and manganese on the central and peripheral nervous system in rats in combination with alcohol exposure

Heavy metals, due to their numerous applications in industrial processes, agrochemicals and household articles, have caused a widespread pollution and can be found in different foods. One of their target organs is the central nervous system. The toxic effects of heavy metals can be modified by lifestyle-originated factors such as consumption of alcohol. The aim of this study was to investigate the changes in spontaneous cortical activity (ECoG), cortical sensory evoked potentials (EPs) and peripheral nerve action potentials, recorded in rats pre-treated with alcohol and acutely treated with lead, mercury and manganese by intraperitoneal injection. In the ECoG, Hg2+ caused a massive shift to lower frequencies while the effect of Mn2+ and Pb2+ was slight, and alcohol pre-treatment altered the effect of the metals minimally. The amplitude of EPs increased upon the application of heavy metals, and the peak latency lengthened. The effect of Hg2+ was the strongest and that of Pb2+ the weakest, and these effects were potentiated by alcohol. Exposure to heavy metals, together with alcohol consumption, can aggravate the known neurotoxic effects

Central neurotoxic effects elicited with three organophosphorus compounds: comparison of acute and subchronic effects

The neurotoxic effects of organophosphorous compounds had been amply investigated. There are, however, only a limited number of relevant data concerning neurotoxic effects of these substances exerted on central electrophysiological processes. The aim of the present study was to find out whether the effects of acute and subchronic administration of three organophosphorous compounds (dimethoate, parathion-methyl and dichlorvos) on the spontaneous and evoked cortical activity are comparable. In the acute experiments, male Wistar rats were treated with 1/1 or 1/5 LD50 per os (parathion-methyl: 22.5 and 4.5 mg/kg; dimethoate: 700 and 140 mg/kg; dichlorvos: 98 and 19.6 mg/kg) and the changes of the cortical activity were recorded for at least 2.5 or 4.0 hours. In the subchronic administration, the animals were given 1/25 or 1/100 LD50 (parathion-methyl 0.9 and 0.225 mg/kg; dimethoate 28.0 and 7.0 mg/kg; dichlorvos 3.92 and 0.98 mg/kg) for 4, 8 or 12 weeks after which the animals were prepared and recording was done. In acute experiments, dimethoate was the substance causing the strongest decrease of the ECoG whereas parathion-methyl induced the least changes. The duration of the evoked potentials was the most affected by dimethoate. After 12 weeks of administration, parathion-methyl caused the largest alteration in the spontaneous and stimulus-evoked activity of the somatosensory and auditory focus while in the visual focus dichlorvos was the most effective. The results of the study showed that the changes caused by the subchronic administration of the substances were sometimes equal to or larger than those caused by the acute large doses

Simultaneous changes of the spontaneous and stimulus-evoked cortical activity in rats acutely treated with mercuric chloride

In earlier studies of our laboratory and in several other reports, alterations in the electrical activity of the cortex of experimental animals on subchronic mercury (Hg) administration were described. In the present work, simultaneous changes in the spontaneous and stimulus-evoked cortical activity elicited by acute administration of inorganic Hg were evaluated with the aim of finding any correlation of the two, possibly giving insight into the mechanism of the alterations. In young adult male Wistar rats, spontaneous cortical, as well as stimulus-evoked cortical and peripheral nervous activity was recorded, before and after acute administration of 3.5 and 7.0 mg/kg Hg2+ ip. The effects of Hg2+ appeared within 10 min and most became significant over 3 h. On the cortex, slowed spontaneous activity, as well as increased amplitude and latency of the evoked potentials (EPs) was seen, and in the periphery, decreased nerve conduction velocity. These alterations seemed to be consistent with a separate cortical and peripheral axonal effect of Hg. Š 2003 Elsevier Inc. All rights reserved

Overexpression or absence of calretinin in mouse primary mesothelial cells inversely affects proliferation and cell migration

The Ca2+-binding protein calretinin is currently used as a positive marker for identifying epithelioid malignant mesothelioma (MM) and reactive mesothelium, but calretinin’s likely role in mesotheliomagenesis remains unclear. Calretinin protects immortalized mesothelial cells in vitro from asbestos-induced cytotoxicity and thus might be implicated in mesothelioma formation. To further investigate calretinin’s putative role in the early steps of MM generation, primary mesothelial cells from calretinin knockout (CR−/−) and wildtype (WT) mice were compared. Primary mouse mesothelial cells from WT and CR−/− mice were investigated with respect to morphology, marker proteins, proliferation, cell cycle parameters and mobility in vitro. Overexpression of calretinin or a nuclear-targeted variant was achieved by a lentiviral expression system. CR−/− mice have a normal mesothelium and no striking morphological abnormalities compared to WT animals were noted. Primary mouse mesothelial cells from both genotypes show a typical “cobblestone-like” morphology and express mesothelial markers including mesothelin. In cells from CR−/− mice in vitro, we observed more giant cells and a significantly decreased proliferation rate. Up-regulation of calretinin in mesothelial cells of both genotypes increases the proliferation rate and induces a cobblestone-like epithelial morphology. The length of the S/G2/M phase is unchanged, however the G1 phase is clearly prolonged in CR−/− cells. They are also much slower to close a scratch in a confluent cell layer (2D-wound assay). In addition to a change in cell morphology, an increase in proliferation and mobility is observed, if calretinin overexpression is targeted to the nucleus. Thus, both calretinin and nuclear-targeted calretinin increase mesothelial cell proliferation and consequently, speed up the scratch-closure time. The increased rate of scratch closure in WT cells is the result of two processes: an increased proliferation rate and augmented cell mobility of the border cells migrating towards the empty space. We hypothesize that the differences in proliferation and mobility between WT and CR−/− mesothelial cells are the likely result from differences in their developmental trajectories. The mechanistic understanding of the function of calretinin and its putative implication in signaling pathways in normal mesothelial cells may help understanding its role during the processes that lead to mesothelioma formation and could possibly open new avenues for mesothelioma therapy, either by directly targeting calretinin expression or indirectly by targeting calretinin-mediated downstream signaling