Published by Elsevier
Print ISSN: 0161-813X
The sensitivity of unconditioned reflex and conditioned avoidance tests in evaluating behavioral toxicity was compared. Male rats were exposed by inhalation up to four hours to 0, 200, 400, 800 or 1600 ppm carbon monoxide (CO); 0, 1500, 3000, 6000 or 12,000 ppm 1,1,1-trichloroethane; 0, 800, 1600, 3200, or 6400 ppm toluene; or 0, 4000, 8000, 16,000 or 32,000 ppm ethanol. Animals were tested for behavioral changes at one-half, one, two and four hours during exposure and eighteen hours after exposure ended. In unconditioned reflex testing the presence or absence of specific unconditioned reflexes (such as corneal, placing, grasping and righting reflexes) and simple behavior patterns including locomotor activity and coordination were observed. The conditioned reflex task consisted of shock avoidance by lever press following simultaneous light and sound stimuli. Rats began to fail unconditioned reflex tests at 800 ppm CO, 3000 ppm trichloroethane, 800 ppm toluene and 8000 ppm ethanol. Decrements in conditioned avoidance were observed at 800 ppm CO, 6000 ppm trichloroethane, 3200 ppm toluene and 8000 ppm ethanol. Neither test was consistently more sensitive than the other in detecting behavioral changes. For both methods, the concentrations at which changes were detected in rats were two to tenfold higher than those reported for human effects.
Most laboratory animal studies of the behavioral or neurophysiological effects of repeated exposures to volatile organic solvents find little evidence for substantial tolerance. This study examined the development of tolerance to the effects of 1,1,1-trichloroethane (1,1,1-TCE) on fixed-ratio responding in four mice. The subjects were exposed to 6000 ppm solvent vapor for 20 min of the daily 45-min operant sessions. Once a week, a series of four concentrations (1000-8000 ppm) were substituted for the daily exposure in order to obtain a cumulative concentration-effect curve. This proved to be a rapid and reliable method with which to ascertain the effects of 1,1,1-TCE over a range of concentrations. During the 15 days of 20-min exposure, the subjects showed a slight but significant increase in both response rates during exposure and in the rate of recovery following exposure. Maximal changes in these measures were evident in the first 7 days, with no further decreased sensitivity over the final 8 days of exposure. The concentration-effect curves determined during and after the daily exposures showed no significant shifts in either direction from the initial curve. Thus, while some alteration in the daily acute effects was noted, this tolerance was not of large magnitude and could not be detected as a change in the concentration-effect curve.
3-monochloro-1,2-propanediol (3-MCPD) is a contaminant of acid-hydrolyzed vegetable protein. Several reports have suggested that chronic exposure to 3-MCPD could produce neurotoxicity in vitro or neurobehavioral effects in experimental animals. The present study further explored the in vitro neurotoxic effects of 0.1-100 microM 3-MCPD on PC12 and N18D3 cell lines. In addition, to investigate the effects of repeated ingestion of 3-MCPD on neurobehavioral impairments parameters in rats, motor activity, landing foot splay, and grip strength tests were performed, following treatment with 3-MCPD at dose levels of 10, 20, and 30 mg/kg per day for 11 weeks. We demonstrated that no significant neurotoxic effects were present in 3-MCPD-treated rats compared to saline-treated control rats, whereas, acrylamide, used as a positive control, induced significant deficits in all neurobehavioral parameters in both male and female rats. On the other hand, body weight gain was significantly decreased in high dose 3-MCPD-treated male rats as well as in acrylamide-treated rats. Taken together, these results suggest that 3-MCPD, at the dose levels used for this study, does not produce in vitro neurotoxicity or neuromotor deficits in vivo.
Acrolein, an unsaturated aldehydic product of lipid peroxidation, has been implicated in the pathogenesis of various neurodegenerative disorders including Parkinson's disease. However, protection against acrolein toxicity in neuronal cells via chemical upregulation of cellular aldehyde-detoxification factors has not been investigated. In this study, we have investigated the induction of glutathione (GSH), GSH S-transferase (GST), and aldose reductase (AR) by the unique nutraceutical compound 3H-1,2-dithiole-3-thione (D3T); and the protective effects of the D3T-mediated cellular defenses on acrolein-mediated toxicity in human neuroblastoma SH-SY5Y cells. Incubation of SH-SY5Y cells with D3T (10-100 microM) resulted in a marked concentration- and time-dependent induction of GSH, but not GST or AR. D3T treatment also led to increased mRNA expression of gamma-glutamylcysteine ligase (GCL), the key enzyme in GSH biosynthesis. Incubation of SH-SY5Y cells with 40 microM acrolein for 0.5 or 1 h resulted in a significant depletion of cellular GSH, which preceded the decrease of cell viability, suggesting critical involvement of GSH in acrolein-induced cytotoxicity. Pretreatment of SH-SY5Y cells with 100 microM D3T afforded a dramatic protection against acrolein-induced cytotoxicity, as assessed by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium (MTT) reduction, lactate dehydrogenase release, as well as morphological changes. To further demonstrate the involvement of GSH in protection against acrolein-induced cytotoxicity, buthionine sulfoximine (BSO) was used to inhibit cellular GSH biosynthesis. Depletion of cellular GSH by 25 microM BSO dramatically potentiated acrolein-induced cytotoxicity. Cotreatment of SH-SY5Y cells with BSO and D3T was found to prevent the D3T-mediated GSH induction and completely reverse the cytoprotective effects of D3T on acrolein-induced toxicity. Taken together, this study demonstrates that upregulation of GSH is a predominant mechanism underlying D3T-mediated protection against acrolein-induced neurocytotoxicity.
1,2-diethylbenzene (1,2-DEB) is used in the manufacture of some plastics. Exposure to 1,2-DEB has been shown to induce peripheral neuropathy in rats. This neurotoxicity is thought to be caused by a metabolite, 1,2-diacetylbenzene (1,2-DAB), a γ-diketone-like compound. 1,2-DEB was previously shown to be extensively and rapidly taken up by the nasal mucosa in male rats. In the present study, the nasal mucosa in rats exposed to 1,2-DEB and 1,2-DAB were examined histologically. Results were compared to sections from rats exposed to two other DEB isomers-1,3-diethylbenzene (1,3-DEB) and 1,4-diethylbenzene (1,4-DEB)-and to two other neurotoxic compounds-n-hexane and its γ-diketone metabolite, 2,5-hexanedione (2,5-HD). A single intraperitoneal dose of 1,2-DEB (200mg/kg) induced time-dependent necrosis in the olfactory epithelium and Bowman's glands, with lesions appearing from the earliest observation time (4hours) in the dorsomedial olfactory mucosa. Lesions spread through the lateral and ventral parts of the ethmoturbinates over the following days. The dorsal and medial zones of the nasal cavity started to regenerate from 72hours after treatment, with the new epithelium showing metaplasia. One month after treatment, most of the olfactory epithelium had returned to normal. 1,2-DAB (40mg/kg) caused the same lesions as those observed after treatment with 1,2-DEB. Treatment with 2,5-HD (1g/kg) also caused lesions of the olfactory epithelium, mainly at level IV. However, these were comparatively less severe than those observed after exposure to 1,2-DEB. In contrast, intraperitoneal injection of 1,3-DEB (800mg/kg), 1,4-DEB (800mg/kg) and n-hexane (2g/kg) did not affect the nasal mucosa. Pretreatment of rats with 5-phenyl-1-pentyne, an inhibitor of CYP2F2 and CYP2E1 completely inhibited the olfactory toxicity caused by 1,2-DEB. These results suggest that metabolic activation of 1,2-DEB may be responsible for the toxicity observed.
Endogenous MPTP-like neurotoxins such as 1-benzyl-1,2,3,4-tetrahydroisoquinoline (1BnTIQ) have been suspected in the etiology of Parkinson's disease (PD). 1BnTIQ was found in a concentration three times higher in cerebrospinal fluid of PD brains than control subjects [J. Neurochem. 65 (6) (1995) 2633]. In the present study, we have evaluated the mechanisms of 1BnTIQ toxicity in human dopaminergic SH-SY5Y cells and tested the neuroprotective action of SKF-38393, a dopamine receptor (D(1)) agonist. 1BnTIQ dose dependently decreased cell viability in dopaminergic SH-SY5Y cells and the extent of cell death was more pronounced when compared to MPP(+). Similar to MPP(+), 1BnTIQ significantly decreased [3H]dopamine uptake. 1BnTIQ significantly increased lipid peroxidation, Bax expression, and active caspase-3 formation. Furthermore, it decreased the expression of Bcl-xL, an anti-apoptotic protein, in these cells. SKF-38393, a dopamine receptor (D(1)) agonist (1 and 10 microM) completely prevented the cell death and significantly increased cell viability. These results strongly suggest that 1BnTIQ induces dopaminergic cell death by apoptosis and dopamine receptor agonists may be useful neuroprotective agents against 1BnTIQ toxicity.
The neurotoxin MPTP induces in human and in some laboratory animals parkinsonism-like neurological disorder, biochemically characterized by selective and irreversible decrease of dopamine content in striatum. The terminal step in the mechanism of neurotoxic action of MPTP is the inhibition of mitochondrial respiratory chain by pyridinium metabolite (MPP+) resulting in energy depletion and nervous cells death. Earlier it was shown that some chemical compounds, in particular diethyldithiocarbamate (DTC), can potentiate MPTP neurotoxicity. In the present work we have studied the influence of DTC derivatives on MPTP neurotoxic effect in vivo and on MPP+ inhibition of mitochondrial respiration (both on intact mitochondria and on submitochondrial particles) in vitro. It was revealed that DTC alone change mitochondrial membrane state by respiratory chain uncoupling and inhibition. DTC and MPP+ mutually potentiate inhibition of electron transport as well. The combined effect of DTC plus MPP+ action on mitochondria respiration reflects the sum of reciprocally leveling and potentiating factors and can explain the order of efficacy of MPTP-neurotoxicity potentiation in vivo in series of close DTC derivatives.
Parkinson's disease (PD) is primarily thought of as a disease of aging. However, recent evidence points to the potential for exposure to xenobiotics during development to increase risk of PD. Here, we report that developmental exposure to the organochlorine pesticide heptachlor alters the dopamine system and increases neurotoxicity in an animal model of PD. Exposure of pregnant mice to heptachlor led to increased levels of the dopamine transporter (DAT) and vesicular monoamine transporter 2 (VMAT2) levels at both the protein and mRNA level in their offspring. Increased DAT and VMAT2 levels were accompanied by alterations of mRNA levels of nuclear transcription factors that control dopamine neuron development and regulate DAT and VMAT2 levels in adulthood. At 12 weeks of age, control and heptachlor-exposed offspring were administered a moderate dose (2 x 10mg/kg) of the parkinsonism-inducing agent MPTP. Greater neurotoxicity as evidenced by a greater loss of striatal dopamine and potentiation of increased levels of glial fibrillary acidic protein and alpha-synuclein was observed in heptachlor-exposed offspring. The neurotoxicity observed was greater in the male offspring than the female offspring, suggesting that males are more susceptible to the long-term effects of developmental heptachlor exposure. These data suggest that developmental heptachlor exposure causes long-term alterations of the dopamine system thereby rendering it more susceptible to dopaminergic damage in adulthood.
In animal models of Parkinson's disease (PD), the toxicity of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is mediated by oxidative stress, especially by nitric oxide (NO). Inhibition of NO synthase (NOS) activity in the brain produces a neuroprotective effect against PD induced by MPTP Green tea containing high levels of (-)-epigallocatechin 3-gallate (EGCG) was administered to test whether EGCG attenuates MPTP-induced PD in mice through the inhibition of NOS expression. Both tea and the oral administration of EGCG prevented the loss of tyrosine hydroxylase (TH)-positive cells in the substantia nigra (SN) and of TH activity in the striatum. These treatments also preserved striatal levels of dopamine and its metabolites, 3,4-dihydroxyphenylacetic acid and homovanillic acid (HVA). Both tea and EGCG decreased expressions of nNOS in the substantia nigra. Also tea plus MPTP and EGCG plus MPTP treatments decreased expressions of neuronal NO synthase (nNOS) at the similar levels of EGCG treatment group. Therefore, the preventive effects of tea and EGCG may be explained by the inhibition of nNOS in the substantia nigra.
The N-oxide of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is the major metabolite found in vivo and excreted in urine after the parenteral administration of the neurotoxicant, MPTP. In mice (C57BL/6), stereotaxic injection of MPTP N-oxide (15 micrograms) into the neostriatum produced dopamine (DA) depletion similar to that caused by MPTP. The DA depleting effect of MPTP N-oxide was a direct action, whereas the action of MPTP was mediated by the generation of oxidative metabolites. In the mouse striatal synaptosomal preparation, MPTP, MPP+ and MPTP N-oxide all competed with [3H]DA at its uptake site. In addition, MPP+ and MPTP N-oxide promoted [3H]DA release. In contrast to MPTP and MPDP+, MPTP N-oxide did not alter the electrophysiologically recorded field potential in nigro-striatal slices. These observations suggest that MPTP N-oxide can directly cause the chemical depletion of striatal DA without modifying the characteristics of cortico-striate synaptic transmission.
This comparative evaluation of neurotoxicants previously identified as models of chemicalinduced mitochondrial dysfunction and energy deprivation demonstrated that subtoxic concentrations of 1,3-dinitrobenzene (1,3-DNB), 3-nitropropionic acid (3-NPA), and 3-chloropropanediol (3-CPD) each led to concentration-dependent loss of the mitochondrial membrane potential (ΔΨm) associated with similar patterns of protein carbonylation. Subtoxic concentrations of each neurotoxicant were determined by measuring DI TNC1 cell viability using the MTS cell proliferation assay. Although exposure 1μM, 10μM, and100μM concentrations of each toxicant did not result in loss of cell viability after 48hours, exposure to each toxicant at these concentrations led to concentration-dependent loss of tetramethyl rhodamine methyl ester (TMRM) fluorescence over the same exposure period. Preincubation with the antioxidant, deferoxamine, was effective in preventing loss of TMRM flurorescence. Through the combined use of two-dimensional polyacrylamide gel electrophoresis (2D PAGE) and Oxyblot analysis, this study demonstrated that exposure to each toxicant resulted in the formation of distinctly similar patterns of protein carbonylation comprised of specific proteins identified with tandem MS/MS. Our results provide insight as to how exposure to different neurotoxicants that enhance oxidative stress may, in fact, lead to mitochondrial injury and subsequent toxicity through selective, yet shared, pathways of protein modification by oxidative carbonylation.
To determine whether neuronal activity plays a role in the localisation of brain stem lesions in 1,3-dinitrobenzene intoxication we produced asymmetrical changes in auditory input by rupturing the left tympanic membrane in Fischer rats. This raised the auditory threshold on that side from 57-63 dB to 104-122 dB. It also decreased glucose utilisation in the ipsilateral cochlear nucleus and significantly increased utilisation in the contralateral nucleus, resulting in a relative deficit of 72 +/- 6%. Similarly, tympanic membrane rupture led to decreased glucose utilisation in the contralateral and increased utilisation in the ipsilateral inferior colliculus. Additional exposure to "white noise" prevented the decrease in glucose utilisation in the contralateral inferior colliculus. Dosing with dinitrobenzene (10 mg/kg in 4 doses over 48 hr) to otherwise normal rats produces symmetrical vasculonecrotic lesions in these regions, but in animals with left tympanic membrane rupture the severity of morphological changes in the ipsilateral cochlear nucleus and the contralateral inferior colliculus were substantially reduced. Additional exposure to "white noise" increased the degree of damage in the ipsilateral cochlear nucleus and contralateral inferior colliculus. These findings indicate that altered auditory function in rats, with its associated metabolic consequences exercises a significant role in the development of brain stem damage in auditory pathways following dinitrobenzene intoxication.
1,3-Dinitrobenzene (DNB) produces edematous, glio-vascular lesions in brainstem nuclei with high energy demands. Astrocytes in vulnerable brainstem nuclei appear to be an early and selective target of DNB and other nitroaromatic compounds, though the molecular basis of this susceptibility is poorly understood. It has been postulated that mitochondria are a principal target of DNB in sensitive cell types [Neuropathol. Appl. Neurobiol. 13 (5) (1987) 371], where redox-cycling of DNB increases levels of reactive oxygen species and disrupts cellular energy metabolism. The present study investigates the role of regional differences in activation of the mitochondrial permeability transition pore (mtPTP) by DNB in brainstem and cortical astrocytes and examines the expression of Bcl-2 proteins as potential regulators of mtPTP function. Neonatal rat astrocytes were cultured from both DNB-sensitive (brainstem) and insensitive (cortex) brain regions and evaluated for DNB-induced alterations in cell morphology and mitochondrial function. Exposure to DNB resulted in rapid changes in the morphology of brainstem astrocytes consistent with loss of ion homeostasis and initiation of necrotic cell death. These changes were not observed in cortical astrocytes at corresponding concentrations of DNB and were prevented in brainstem astrocytes by the mtPTP inhibitor, bongkrekic acid, suggesting that mitochondrial dysfunction is involved in DNB-induced morphological changes in brainstem astrocytes. Mitochondrial depolarization in brainstem astrocytes was observed at DNB concentrations as low as 10 microM, whereas no loss of mitochondrial membrane potential (DeltaPsi(mt)) occurred in cortical astrocytes at less than 100 microM DNB. DNB-induced loss of DeltaPsi(mt) followed apparent first-order kinetics, with EC(50)-values for half-maximal rates of mitochondrial depolarization of approximately 23 and approximately 290 microM in brainstem cortical astrocytes, respectively. DNB-induced mitochondrial depolarization was prevented by pretreatment with bongkrekic acid, indicating that loss of DeltaPsi(mt) was mediated by activation of the mtPTP. Inhibition of succinate dehydrogenase (SDH) activity occurred in astrocytes from both brain regions exposed to DNB and was blocked in brainstem, but not cortical, astrocytes by bongkrekic acid. Constitutive expression of Bcl-X(L) was high in cortical tissue and astrocytes, whereas Bax expression was low. However, Bax was highly expressed in brainstem tissue and astrocytes and Bcl-X(L) expression was markedly lower. The expression of Bcl-2 was similar in both brain regions. These data suggest that the selective vulnerability of brainstem astrocytes to DNB is due to a lower threshold for activation of the mtPTP that is be mediated, in part, by distinct expression patterns of Bcl-2 proteins rather than by intrinsic differences in susceptibility of the electron transport chain.
This study demonstrated that 1,3-dinitrobenzene-induced (1,3-DNB) oxidative stress led to the oxidative carbonlyation of specific protein targets in DI TNC1 cells. 1,3-DNB-induced mitochondrial dysfunction, as indicated by loss of tetramethyl rhodamine methyl ester (TMRM) fluorescence, was initially observed at 5h and coincided with peak reactive oxygen species (ROS) production. ROS production was inhibited in cells pre-treated with the mitochondrial permeability transition (MPT) inhibitor, bonkrekic acid (BkA). Pre-incubation with the antioxidant deferoxamine inhibited loss of TMRM fluorescence until 24h after initial exposure to 1,3-DNB. Two-dimensional polyacrylamide gel electrophoresis (2D PAGE) and subsequent Oxyblot analysis were used to determine if 1,3-DNB exposure led to the formation of protein carbonyls. Exposing DI TNC1 cells to 1,3-DNB led to marked protein carbonylation 45 min following initial exposure. Pre-treatment with deferoxamine or Trolox reduced the intensity of protein carbonylation in DI TNC1 cells exposed to 1mM 1,3-DNB. Tandem MS/MS performed on protein samples isolated from 1,3-DNB-treated cells revealed that specific proteins within the mitochondria, endoplasmic reticulum (ER), and cytosol are targets of protein carbonylation. The results presented in this study are the first to suggest that the molecular mechanism of 1,3-DNB neurotoxicity may occur through selective carbonylation of protein targets found within specific intracellular compartments of susceptible cells.
1,3-Dinitrobenzene (DNB) produces edematous, glio-vascular lesions that are initially confined to brainstem nuclei with high energy requirements in rats and mice. Perturbation of energy producing processes in the cell is known to induce formation of the mitochondrial permeability transition pore (mtPTP) complex. Selective vulnerability of brainstem astrocytes to DNB is mediated by a 10-fold lower threshold for opening of the cyclosporin A-inhibitable mitochondrial permeability transition (MPT) pore than their cortical counterparts. Other nitrocompounds, such as 3-nitropropionic acid, selectively interfere with regional energy metabolism, including mitochondrial succinate dehydrogenase activity. However, the link between DNB-induced onset of the MPT and disruption of energy producing processes in the astrocyte remains unclear. The effects of DNB on succinate dehydrogenase activity were evaluated in cultured neonatal rat and mouse brainstem and cortical astrocytes. Both histochemical and spectrophotometric assays confirmed significant temporal inhibition of SDH activity in brainstem and cortical astrocytes 0.5, 2 and 5h following exposure to 100 microM DNB in vitro. Although DNB-induced inhibition of SDH was significantly decreased by CsA pretreatment in brainstem astrocytes after 0.5 and 2h and with a second pore inhibitor, bongkrekic acid (BKA) after 5h, both inhibitors failed to reduce inhibition of SDH activity in cortical astrocytes. These data suggest that DNB-induced inhibition of SDH may be independent of differential regional activation of the mtPTP complex in astrocytes and that an unidentified cyclosporin A-inhibitable factor mediates DNB-induced loss of SDH function.
The selective vulnerability of brainstem astrocytes to 1,3-dinitrobenzene is mediated by a 10-fold lower threshold for opening of the cyclosporin A-inhibitable mitochondrial permeability transition pore (mtPTP). BCL-XL, BAX and BCL-2 are members of the BCL-2 protein family known to regulate both apoptotic and necrotic cell death signaling at the mtPTP. The levels at which these proteins are expressed relative to one another, where in the cell they are located and whether they are post-translational modified contributes greatly to the balance in active agonistic to active antagonistic BCL-2 proteins, and this critical balance has been hypothesized to dictate regional astrocytic susceptibility to DNB. The effects of DNB on the balance in expression of the BCL-2 family proteins have been evaluated in F344 rat DNB-sensitive (brainstem) and non-sensitive (cortical) tissue homogenates and primary astrocytes. No significant treatment-related alterations in BCL-XL, BAX or BCL-2 protein expression are observed in rat tissue homogenates or primary astrocytes. However, moderate increases in BCL-XL are observed only in DNB-treated rat cortical astrocytes, and these increases may be sufficient to shift the constitutive balance in expression of antagonistic to agonistic BCL-2 proteins from a ratio which favors BAX to one in which BAX and BCL-XL are comparably expressed. Rat primary brainstem and cortical astrocytes are also transiently transfected with bcl-xl to evaluate whether or not moderate enhancement of BCL-XL protein expression levels are sufficient to alter regional sensitivity to DNB in vitro. BCL-XL overexpression minimizes DNB-induced inhibition of succinate dehydrogenase (complex II) activity and increases significantly the concentration of DNB required to induce MPT onset in primary brainstem and cortical astrocytes. Results from the current investigation suggest that modest region-specific alterations in the balance in expression of antagonistic to agonistic BCL-2 proteins may adequately explain differential regional sensitivity to DNB-induced mitochondrial dysfunction.
In a previous in vitro study, we demonstrated the protective effects of a new drug, 2-cyclopropylimino-3-methyl-1,3-thiazoline hydrochloride (KHG26377), against glutamate-induced excitotoxicity in cultured glial cells. In this study, we explored the possible mechanisms underlying the neuroprotective and anti-inflammatory effects of this compound against glutamate-induced excitotoxicity in rat brain. Our results showed that pretreatment with KHG26377 significantly attenuated glutamate-induced elevation of lipid peroxidation, TNF-α, IFN-γ, nitric oxide, reactive oxygen species, NADPH oxidase, and Ca(2+) levels, as well as the expression of caspase-3, neuronal nitric oxide synthase, and pERK. Furthermore, KHG26377 pretreatment attenuated key antioxidant parameters such as levels of superoxide dismutase, catalase, glutathione, glutathione peroxidase, and glutathione reductase, and also mitigated suppression of mitochondrial transmembrane potential by glutamate toxicity. Thus, through its antioxidant and anti-inflammatory activities in rat brain, KHG26377 may help protect against glutamate-induced neuronal damage.
1,3-Dinitrobenzene (DNB) has previously been shown to be neuropathic, causing gliovascular lesioning in the rat brainstem, with the nuclei of the auditory pathway being particularly affected. Lesion severity was shown to be dependent on functional activity, which could be markedly decreased within one pathway by monaurally reducing sensory input. The aim of this study was to characterise the changes in electrophysiological and vascular function associated with this asymmetric lesioning. Depth electrodes located in the inferior colliculi were used to measure wave II and IV of the auditory evoked response (AER) and collicular blood flow. These were measured up to eight days after DNB exposure in rats, in which preexisting reduction in sensory input in one ear was achieved by tympanic membrane rupture. Significant increases of between 14-27 dB were seen in the mean stimulus level required to generate a 50% isoamplitude response for wave IV in the intact (ie vulnerable) pathway over days 1-8 post DNB. No significant changes in this response for the other AER waves were seen over the same recording period. Significant increases in blood flow were seen in the inferior colliculi up to 24 hours after the final dose of DNB. Differences in increased flow between the colliculi were also highly significant, with peak increases of 200% and 80% seen in the intact and protected sides respectively. This difference shows that DNB enhanced blood flow appears to reflect the severity of the DNB induced functional deficit. In both cases, disturbance to normal glial function in maintaining K+ homeostasis, may underlie the neurophysiological deficit and the increase in blood flow seen at the level of the inferior colliculi. These asymmetric functional changes were also parallelled by the differential lesion severity between the protected and unprotected pathways. Hence, protection against DNB glial lesion severity by reduction in sensory input, and consequently metabolic demand, is paralleled by the early vascular response and functional neuronal deficit seen over the eight day post DNB recording period.
beta-1,4-Galactosyltransferase-I (beta-1,4-GalT-I) is one of the best studied glycosyltransferases. Previous studies demonstrated that beta-1,4-GalT-I was a major galactosyltransferase responsible for selectin-ligand biosynthesis and that inflammatory responses of beta-1,4-GalT-I deficient mice were impaired. Our previous study suggest that beta-1,4-GalT-I may play an important role in regulating immune cell migration into the inflammatory site. In this study, we investigate beta-1,4-GalT-I may play an important role in mediating microgliosis. The results of this study demonstrated that beta-1,4-GalT-I was strongly induced in the ventral midbrain by intranigral injection of LPS. Most galactose-containing glycans and beta-1,4-GalT-I were expressed in microglia. Moreover, an Ab against beta-1,4-GalT-I attenuated both LPS-induced microglial activation and phagocytosis. We therefore suggest that beta-1,4-GalT-I may play an important role in regulating immune cell migration into the inflammatory site and mediating microgliosis.
Pyrethroid insecticides disrupt nerve function by modifying the gating kinetics of transitions between the conducting and nonconducting states of voltage-gated sodium channels. Pyrethroids modify rat Na(v)1.6+β1+β2 channels expressed in Xenopus oocytes in both the resting state and in one or more states that require channel activation by repeated depolarization. The state dependence of modification depends on the pyrethroid examined: deltamethrin modification requires repeated channel activation, tefluthrin modification is significantly enhanced by repeated channel activation, and S-bioallethrin modification is unaffected by repeated activation. Use-dependent modification by deltamethrin and tefluthrin implies that these compounds bind preferentially to open channels. We constructed the rat Na(v)1.6Q3 cDNA, which contained the IFM/QQQ mutation in the inactivation gate domain that prevents fast inactivation and results in a persistently open channel. We expressed Na(v)1.6Q3+β1+β2 sodium channels in Xenopus oocytes and assessed the modification of open channels by pyrethroids by determining the effect of depolarizing pulse length on the normalized conductance of the pyrethroid-induced sodium tail current. Deltamethrin caused little modification of Na(v)1.6Q3 following short (10ms) depolarizations, but prolonged depolarizations (up to 150ms) caused a progressive increase in channel modification measured as an increase in the conductance of the pyrethroid-induced sodium tail current. Modification by tefluthrin was clearly detectable following short depolarizations and was increased by long depolarizations. By contrast modification by S-bioallethrin following short depolarizations was not altered by prolonged depolarization. These studies provide direct evidence for the preferential binding of deltamethrin and tefluthrin (but not S-bioallethrin) to Na(v)1.6Q3 channels in the open state and imply that the pyrethroid receptor of resting and open channels occupies different conformations that exhibit distinct structure-activity relationships.
The Seychelles Child Development Study was designed to test the hypothesis that prenatal exposure to MeHg from maternal consumption of a diet high in fish is detrimental to child neurodevelopment. To date, no consistent pattern of adverse associations between prenatal exposure and children's development has appeared. In a comprehensive review of developmental studies involving MeHg, a panel of experts recommended a more consistent use of the same endpoints across studies to facilitate comparisons. Both the SCDS and the Faeroe Islands studies administered the Bender Visual Motor Gestalt Test. However, the method of test administration and scoring used was different. We repeated the test on the SCDS Main Study children (mean age 10.7 years) using the same testing and scoring procedure reported by the Faeroe studies to obtain Copying Task and Reproduction Task scores. We found no association between prenatal MeHg exposure and Copying Task scores which was reported from the Faeroese study. However, our analysis did show a significant adverse association between MeHg and Reproduction Task scores with all the data (p=0.04), but not when the single outlier was removed (p=0.07). In a population whose exposure to MeHg is from fish consumption, we continue to find no consistent adverse association between MeHg and visual motor coordination.
The aim of this study was to analyze if differences exist between two available contrast sensitivity tests that use similar stimuli, specifically, the CSV-1000 (VectorVision, Greenville, OH)) and the VCTS-6500 (Vistech, Dayton, OH). Contrast sensitivity was measured on 105 healthy patients with ages ranged from 19 to 26 years with visual acuity of 20/25 or better. The tests were performed in the same room and contrast sensitivity was measured with the VCTS-6500 system and CSV-1000. For both tests, the spatial frequencies of 3, 6, 12 and 18 cycles per degree were recorded. Contrast sensitivity values were generally higher for the Vistech VCTS-6500 test being the difference statistically significant (p<0.001) for all the spatial frequencies. This difference was more significant for 3cpd spatial frequency and the two tests showed a better agreement for the 6cpd spatial frequency. Our results showed that there were significant differences between the VCTS-6500 and the CSV-1000 tests. Developments of some general recommendations or regulations in relation to clinical measurement of contrast sensitivity are necessary.
Glutamate induced excitotoxic injury through over-activation of N-methyl-D-aspartate receptors (NMDARs) plays a critical role in the development of many neurodegenerative diseases. The present study was undertaken to evaluate the role of CGX-1007 (Conantokin G) as a neuroprotective agent against NMDA-induced excitotoxicity. Conantokin G, a cone snail peptide isolated from Conus geographus is reported to selectively inhibit NR2B containing NMDARs with high specificity and is shown to have potent anticonvulsant and antinociceptive effects. CGX-1007 significantly reduced the excitotoxic cell death induced by NMDA in organotypic hippocampal brain slice cultures in a concentration-dependent manner. In contrast, ifenprodil, another NR2B specific antagonist failed to offer neuroprotection against NMDA-induced excitotoxicity. We further determined that the neuroprotection observed is likely due to the action of CGX-1007 at multiple NMDA receptor subtypes. In a series of electrophysiology experiments, CGX-1007 inhibited NMDA-gated currents in human embryonic kidney (HEK) 293 cells expressing NMDA receptors containing either NR1a/NR2B or NR1a/NR2A subunit combinations. CGX-1007 produced a weak inhibition at NR1a/NR2C receptors, whereas it had no effect on NR1a/NR2D receptors. Further, the inhibition of NMDA receptors by CGX-1007 was voltage-dependent with greater inhibition seen at hyperpolarized membrane potentials. The voltage-dependence of CGX-1007 activity was also observed in recordings of NMDA-gated currents evoked in native receptors expressed in cortical neurons in culture. Based on our results, we conclude that CGX-1007 is a potent neuroprotective agent that acts as an antagonist at both NR2A and NR2B containing receptors.
The nitroimidazole radiosensitizer CI-1010 ((R)-alpha-[[(2-bromoethyl)-amino]methyl]-2-nitro-1H-imidazole-1-ethanol monohydrobromide) causes selective, irreversible, retinal photoreceptor apoptosis in vivo. The mouse 661 W photoreceptor cell line was used as a neuronotypic model of CI-1010-mediated retinal degeneration. Exposure to CI-1010 for 24 h induced apoptosis in 661 W cells, as determined by ultrastructural analysis, agarose electrophoresis and analysis of TUNEL-positive nuclei. CI-1010 caused a loss of viability in 661 W cells, as measured by the reduction of MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide). A clear link was established between the onset of apoptosis and activity of caspase-3 and caspase-8, prior to poly[ADP-ribose]polymerase (PARP) cleavage. Pretreatment with caspase inhibitors, ZVAD.fmk or DEVD-CHO, prevented morphological changes in most CI-1010-treated cells. Evaluation of mitochondrial inner membrane potential (Deltapsi(m)) in live 661 W cells using the fluorescent dye, tetramethylrhodamine methyl ester revealed retention of (Deltapsi(m)) until after caspase activation. Absence of cytochrome c in the cytoplasm in treated cells further supports the hypothesis of a mitochondrial-independent mechanism of cell death. Significant increase in DNA crosslinks observed in 661 W cells correlates with induction and phosphorylation of p53 at multiple serine sites. Cell cycle analysis of 661 W cells reveals a G(2) arrest in response to CI-1010-induced DNA damage and neuronal cell death. Increased protein expression of Bax, Fas, and FasL, concomitant to the loss of Bcl-xL in treated 661 W cells may be modulated by p53. This study evaluates in vitro mechanisms of CI-1010-induced cell death in photoreceptors and provides evidence in support of a p53-linked activation of caspase-3 in response to DNA damage caused by CI-1010.
NMDA antagonists of glutamate have psychotomimetic side effects and structural side effects which have been shown to be lethal to CNS neurons in the cingulate and retrosplenial cortex of rodents, yet these compounds may reduce focal ischemic brain damage. This investigation used 38 Wistar rats to determine whether the structural toxicologic profile of a newly developed halogenated quinoxalinedione derivative, a pharmacologic antagonist of the glycine site on the NMDA receptor complex, is identical to that seen with MK-801. In the cingulate and retrosplenial cortex, examination of glutaraldehyde perfusion-fixed, plastic-embedded tissue 4 to 6 hours after intravenous administration of 10 mg/kg of the glycine antagonist 5-nitro-6,7-dichloroquinoxalinedione (ACEA-1021), no changes were seen by light or electron microscopy. At a dose of 30 mg/kg, neurons were seen containing 1 to 2 microns granules in perikarya and axons. Vacuolated neurons, as described in NMDA-antagonist neurotoxicity, were exceedingly rare, comprising only 4 in the entire study. Electron microscopy of the granulated profiles showed intracytoplasmic areas containing grouped mitochondria and lysosomes, located in neuronal perikarya, and rarely in myelinated axons. Neuronal necrosis was evaluated in formaldehyde perfusion-fixed, paraffin-embedded tissue at one week survival, and was absent. MK-801 5 mg/kg, in contrast, caused irreversible (necrotizing) neuronal changes. The results demonstrate that this glycine antagonist is devoid of lethal neurotoxicity, but causes a reversible alteration in a small proportion of cingulate and retrosplenial cortical neurons. Since previous studies have shown anti-ischemic efficacy of this compound in focal, but not global ischemia, it appears that the therapeutic profile of this antagonist of the strychnine-insensitive glycine site is similar, but the toxicologic structural profile is different, from NMDA receptor antagonists.
Because alcohol has an adverse effect on zinc homeostasis, this study was designed to study if zinc content of the diet modifies the severity of fetal alcohol syndrome in a mouse model. The effect of varying zinc intake on the progeny of pregnant mice fed a liquid diet containing 15% of the calories as ethanol was studied. Prenatal mortality was higher when the mothers consumed alcohol with inadequate zinc intake. Because of the adverse effect of alcohol on zinc homeostasis and because zinc deficiency has been shown to potentiate alcohol embryopathy, one group was given zinc supplementation to four times the Recommended Dietary Allowance. Supplemental zinc above the Recommended Dietary Allowance was not protective and appeared to have an adverse effect on fetal weight and prenatal mortality. These results suggest that zinc intake should be optimized during pregnancy but that zinc supplementation above the Recommended Dietary Allowance does not reduce the incidence or severity of fetal alcohol syndrome.
Recent experiments with primates have demonstrated that treatment with atropine/pralidoxime/diazepam, even if administered immediately after organophosphate exposure, does not totally prevent neuronal brain damage. Using primates, we have studied, for the first time, the ability of GK-11 (gacyclidine), an antiglutamatergic drug in the process of agreement for human use, given as an additional therapy, to counteract the neuropathology due to organophosphate exposure that persists after classical treatment with oxime/atropine/benzodiazepine. We have also examined the recovery of the organophosphate-intoxicated primates. Male Cynomolgus monkeys were pretreated 1 hour before poisoning with pyridostigmine, then intoxicated with 8 LD50 of soman and immediately treated with the combination pralidoxime/atropine/diazepam. Some of the animals also received GK-11 at 0.01; 0.03 or 0.1 mg/kg (i.v.) 10 minutes after soman challenge. Recovery of the primates (reflexes, movements, feeding) and the neuropathological changes that occurred three weeks after intoxication (histological examinations and neuronal cell density measurement) were compared in GK-11-treated and control animals. At all doses tested, GK-11 prevented the neuronal rarefaction of the frontoparietal cortex that was observed in soman-intoxicated animals that received only oxime/atropine/diazepam. Moreover, the 0.01 mg/kg dose of GK-11 improved the early recovery of intoxicated primates from 1 day after intoxication. In the view of the most effective management of organophosphate intoxication that is currently available, GK-11 thus appears to be a promising additional neuroprotective therapy. This drug is presently being evaluated in a human clinical trial for a different neuroprotective indication.
Today, organophosphorus nerve agents are still considered as potential threats in both military or terrorism situations. These agents act as potent irreversible inhibitors of acetylcholinesterase in both central and peripheral nervous systems. Conventional treatment of organophosphate poisoning includes the combined administration of a cholinesterase reactivator (an oxime), a muscarinic cholinergic receptor antagonist (atropine) and a benzodiazepine anticonvulsant (diazepam). However, numerous studies have demonstrated that the excitatory amino acid glutamate also plays a prominent role in the maintenance of organophosphate-induced seizures and in the subsequent neuropathology especially through an overactivation of the N-methyl-D-aspartate (NMDA) receptor subtype. Contrary to other non-competitive NMDA antagonists successfully tested in rodents exposed to organophosphate, gacyclidine is a novel antiNMDA compound which is in the process of approval for human use in France for neurotraumatology. This review summarizes the therapeutic value of gacyclidine as a complement to the available emergency treatment against severe organophosphate poisoning. Previous data obtained from experiments on primates in several scenarios mimicking military or terrorist attacks, using soman as the nerve agent, were used. Primates pretreated with pyridostigmine and receiving conventional emergency therapy at the first signs of poisoning survive. However, only gacyclidine is able to ensure complete management of nerve agent poisoning for rapid normalization of EEG activity, clinical recovery and neuroprotection. Gacyclidine also ensures optimal management of severe nerve agent poisoning in animals neither pretreated nor receiving emergency therapy likewise during an unexpected exposure. However, this beneficial effect is obtained provided that medical intervention is conducted rapidly after intoxication. Globally, the current lack of any other NMDA receptor antagonist suitable for human use reinforces the therapeutic value of gacyclidine as a central nervous system protective agent for the treatment of OP poisoning.
Neonatal ketamine (KET) or phencyclidine (PCP) treatment can trigger apoptotic neurodegeneration in rodents. Previously, we described KET- and PCP-induced altered body weight and home cage, slant board and forelimb hang behaviors in preweaning rats (Boctor et al., 2008). In that study, L-carnitine (LC) attenuated the KET-induced behavioral alterations and body weight decrements. The four subcutaneous (sc) treatment groups were: (1) saline; (2) 10 mg/kg PCP on PNDs 7, 9 and 11; (3) 20 mg/kg KET (6 injections; one every 2h on PND 7); or (4) a regimen of KET and 250 mg/kg LC (KLC) both administered on PND 7, with additional 250 mg/kg doses of LC on PNDs 8-11. A portion of each treatment group was evaluated for postweaning behaviors which included grip strength and motor coordination (postnatal days (PNDs) 22 or 71), locomotor sensitization (PND 42), spatial alternation (PNDs 22-70) and residential running wheel activity (PNDs 72-77). On PND 42 or 78, whole and regional brain weights were measured. Grip strength and motor coordination were unaffected at either age by neonatal treatment. On PND 42, neonatally treated KET- or KLC-treated rats responded to a challenge of 5mg/kg KET with activity similar to controls that received the same challenge. Neonatal PCP treatment, however, induced significant sensitization to a challenge of 3mg/kg PCP on PND 42 relative to controls that received the same challenge, causing increased activity which was especially profound in females. Performance on a continuous spatial alternation task requiring a "win-shift, lose-stay" strategy appeared unaffected by neonatal KET or KLC treatment. PCP treatment, however, caused significantly increased random responding and shorter choice latencies. In addition, neonatal PCP treatment elevated light and dark period running wheel activity and reduced PND 42 and 78 body and whole brain weights. These findings provide further evidence that PCP treatment on PNDs 7, 9, and 11 causes subtle cognitive deficits and long-term alterations in activity that are unrelated to deficits in grip strength or motor coordination. Further, repeated KET treatment on PND 7 does not appear to result in severe behavioral modifications.
To contrast subjective and objective measures of neuropsychological health in F-111 aircraft Deseal/Reseal maintenance personnel, against two appropriate comparison groups. Exposed and comparison participants completed a postal questionnaire which included a validated memory questionnaire and additional questions relating to possible cognitive symptoms. They also underwent a comprehensive neuropsychological assessment and screening for a past or current disturbance of mood. Multiple linear or logistic regression was conducted for each outcome using exposure group and potential confounders as explanatory variables. There was a strong and consistent excess of self-reported cognitive problems among the exposed group relative to the comparison groups including a 2.8-4.3-fold increase in self-reported symptoms of forgetfulness, loss of concentration and difficulty finding the right word. On detailed neuropsychological testing, the exposed group performed significantly worse than comparisons on tests of psychomotor speed, executive functioning, and new learning/memory. These findings could not be accounted for by disturbances of mood or other potential confounders. There was a strong and consistent increase in self-reported cognitive problems among the exposed, and small but significant exposure-specific differences on objective tests of cognitive functioning. The findings are consistent with the development of adverse neuropsychiatric changes related to occupational exposure to solvents.
N1E-115 mouse neuroblastoma cells have been reported to possess two types of voltage-sensitive calcium channels: Low voltage activated, rapidly inactivating T-type (type I) and high voltage activated, slowly inactivating L-type (type II). We studied the effects of acute in vitro exposure to inorganic lead on these calcium channels, using the whole-cell variant of patch clamping. Using salines with a high lead-buffering capacity, we found that both T-type and L-type channels are reversibly inhibited in a dose-dependent manner at free Pb2+ concentrations ranging from 20 nM to 14 microM. L-type channels are somewhat more sensitive to Pb2+ than T-type channels are (L-type: IC50 approx. 0.7 microM; T-type: IC50 approx. 1.3 microM). Both channels show small but significant inhibition (approx. 10%) at 20 nM free Pb2+. Pb2+ affects neither activation nor inactivation of T-type channels, but enhances inactivation of L-type channels at holding potentials around -60 to -40 mV. A peculiar phenomenon was observed in cells exposed to 2.3 microM free Pb2+. T-type channels were inhibited in all 20 cells studied. In 15 cells, L-type channels were also inhibited, but in the remaining 5 cells, current flow through L-type channels was enhanced by Pb2+ exposure.
Methylmercury (MeHg) is an environmental toxin that causes severe neurological complications in humans and experimental animals. In addition to neurons, glia in the central nervous system are very susceptible to MeHg toxicity. Pretreatment of glia with the prostaglandin derivative, 15-deoxy-delta-12,14-prostaglandin J(2) (15d-PGJ(2)), caused a significant protection against MeHg cytotoxicity. Results with the C6 glioma cells demonstrated that the protection was dependent on the duration of pretreatment, suggesting that time was required for the up-regulation of cellular defenses. Subsequent experiments indicated that 15d-PGJ(2) prevented MeHg induced mitochondrial depolarization. Similar protection against MeHg cytotoxicity was observed in primary cultures of mouse glia. Analysis of cellular glutathione (GSH) levels indicated that 15d-PGJ(2) caused an up-regulation of GSH and prevented MeHg-induced GSH depletion. Buthionine sulfoximine (BSO), a GSH synthesis inhibitor, completely inhibited the GSH induction by 15d-PGJ(2). However, BSO did not prevent the stabilization of mitochondrial potential and only partially prevented the protection caused by 15d-PGJ(2). While induction of heme oxygenase-1 was implicated in the cytoprotection by 15d-PGJ(2) under some experimental conditions, additional experiments indicated that this enzyme was not involved in the cytoprotection observed in this system. Together, these results suggested that while up-regulation of GSH by 15d-PGJ(2) might help cells to defend against MeHg toxicity, there may be other yet unidentified mechanism(s) initiated by 15d-PGJ(2) treatment that contributed to its protection against MeHg cytotoxicity.
A device using four infra-red light photocells per cage which monitor simultaneously the motility of 120 individual rodents, was developed at our institute. The measuring interval can be chosen freely, the starting time may be set freely and the test may last several weeks. The motility of the offspring (day 35-39) of dams exposed to the neuroleptic haloperidol during lactation was investigated, because of the important stage of the brain development in the neonatal age and of the relatively high concentration of haloperidol in the milk. Mice dams were treated sc. with a single dose (1.5 mg/kg) of haloperidol postnatally on day 3 to 6. Compared to the controls the body weight gain of treated (via milk) pups was reduced (controls = 72%, haloperidol = 30%) and the mortality was higher (controls = 10%, haloperidol = 77%) during the treatment period. The quantitative and qualitative analysis of the locomotor activity from day 35 to day 39 shows a distinct shift in the kind of motility: the locomotor activity of haloperidol offspring is significantly reduced while the number of activity phases is increased. It appears that there is a persistent alteration in the central nervous system that leads to a higher frequency but a lower efficacy of activity.
Among the most persistent and bio-accumulative environmental pollutants are the polybrominated diphenyl ethers (PBDEs), a class of chemicals widely used as flame retardants in plastics and textile coating, and the polychlorinated biphenyls (PCBs), previously used as coolants and lubricants in electrical equipment. Monitoring programs revealed high levels of both these classes of compounds in human breast milk, raising concerns for their potential noxious effects on infants. The aim of the present study was to investigate the neurotoxic effects of 2,2',4,4',5-penta BDE (BDE 99: 18mg/kg/day) or Aroclor 1254 (A1254, a PCB mixture: 10mg/kg/day) administration, from gestational day (GD) 6 to postnatal day (PND) 21, on neurobehavioral development in the CD-1 Swiss mouse. In addition, we investigated whether the administration route affects the emergence or the magnitude of the toxic effects of BDE 99 or A1254. In particular, we compared self-administration, consisting in letting the mouse drink spontaneously the compound dissolved in oil from a syringe, with gavage, consisting in force-feeding a substance by a tube inserted in the mouth and then into the stomach, a procedure reported to be stress-inducing. Both compounds induced hyperactivity, though BDE 99 affected activity profile only during adolescence and A1254 mainly at adulthood. Levels of total circulating thyroxine were decreased by both BDE 99 and A1254 administration, though only in the latter group the decrease was statistically significant. These findings suggest a different neurotoxic action exerted by PBDEs and PCBs. An effect of the administration route, independent from the compound administered, was found on thigmotactic behavior and gavage administration affected pup body weight gain only in the A1254 group, suggesting that the stress induced by gavage procedure may either affect results per se or modulate the detrimental action of selected compounds.
Aroclor 1254 is a mixture of polychlorinated biphenyls (PCBs), a class of environmental toxins which cause a wide spectrum of neurotoxic effects. Learning and memory deficits are the profound effects of PCBs which may be related to hippocampal dysfunction. To get insight into the underlying neurochemical mechanisms, we employed the microdialysis technique to investigate the effect of repeated exposure of adult male Wistar rats to Aroclor 1254 (10mg/kg b.w., daily, ig., for 14days), on the neurochemical parameters of NMDA receptor-mediated glutamatergic signaling in the hippocampus in vivo assessed using the microdialysis technique. The results demonstrated that exposure to Aroclor 1254, which was associated with substantial neuronal damage and loss in the hippocampus, markedly decreased the NMDA-induced extracellular accumulation of newly loaded (45)CaCl(2), cGMP and glutamate, and reduced the basal content of the NO precursor, arginine, indicating inhibition of the NMDA/NO/cGMP pathway. Aroclor 1254 exposure also decreased the basal microdialysate content of glutamate and glutamine, which may cause inadequate supply of the neurotransmitter glutamate, while the level of two other neuroactive amino acids, aspartate or taurine was not affected by the exposure. The results underscore neuronal lesion and inhibition of NMDA receptor-mediated glutamatergic signaling in hippocampus as a potential major contributor to the cognitive deficits associated with exposure to PCB.
Rat pheochromocytoma [PC12] cells were used as models of a dopaminergic system to examine the effects of subchronic exposure to Aroclor 1254 on levels of cellular dopamine in undifferentiated and nerve growth factor (NGF)-stimulated differentiating cells. Either in the absence, or simultaneously in the presence of NGF, exposure to Aroclor 1254 resulted in dose-dependent decreases in levels of cellular dopamine, which with increasing time of exposure, up to 3 days, became increasingly sensitive to lower concentrations of PCBs as evidenced by shifts of the dose-response curves to the left. Pretreatment of PC12 cells with NGF for 7 or 14 days prior to exposure to Aroclor 1254 afforded partial protection from the PCB-mediated decreases in cellular dopamine, consistent with the hypothesis that the cells have different sensitivities to the dopamine decreasing effects of PCBs, depending on the state of differentiation that they are in when exposure to PCBs occurs. Exposure to Aroclor 1254 did not block the morphological aspects of NGF-induced neuronal differentiation, but rather enhanced the NGF-stimulated elongation of neurites in a dose-dependent manner. These results suggest that Aroclor 1254 reduces the levels of cellular dopamine, in both undifferentiated and differentiating PC12 cells, and that pretreatment with NGF may partially prevent PCB-mediated decreases in cellular dopamine. These results also suggest that Aroclor 1254 may enhance neurite elongation.
PCBs are one of the environmental toxicants and neurotoxic compounds which induce the production of free radicals leading to oxidative stress. Oxidative stress is a contributing factor to alteration caused in neurodegenerative processes. The ability of Vitamin C to retard oxidative processes has been recognized for many years. Therefore, the present experiment was carried out to determine the antioxidant role of ascorbate on Aroclor 1254 induced oxidative stress in brain regions of albino rats. One group of rats received corn oil as vehicle for 30 days as control. The other group of rats were administered Aroclor 1254 at a dose of 2 mg/kg bw/day intraperitoneally for 30 days. One group of rats received Vitamin C (100 mg/kg bw/day) orally simultaneously with Aroclor 1254 for 30 days. The brain was dissected to cerebral cortex (Cc), cerebellum (C) and hippocampus (H). Enzymatic and non-enzymatic antioxidants such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione-S-transferase (GST), reduced glutathione (GSH) and Vitamin C were estimated. Hydrogen peroxide (H(2)O(2)), lipid peroxidation (LPO) and acetylcholine esterase activity (AchE) were determined. Activities of SOD, CAT, GPx, GST, AchE and the concentration of GSH, Vitamin C were decreased while an increase in H(2)O(2) and LPO were observed in brain regions of PCB treated animals. Vitamin C administration retrieved all the parameters except GST, significantly. These results suggest that PCB induces oxidative stress in rat brain by decreasing the activities of antioxidant enzymes, which can be protected by Vitamin C treatment.
Oxidative stress (OS) is thought to participate in the pathogenesis of neurodegenerative disorders, including Parkinson's disease (PD). Excessive reactive oxygen species (ROS) production can occur during the normal aging process or following exposure to environmental toxicants. Dopamine neurons, which degenerate during PD, are particularly sensitive to oxidative stress. Polychlorinated biphenyls (PCBs), persistent and widespread pollutants, have been shown to adversely impact dopaminergic (DAergic) pathways, but the role ROS play in neurotoxicity remains unclear. To test the hypothesis that PCB exposure compromises dopamine neurons by stimulating ROS production, the direct toxicity and oxidative stress response following PCB exposure was examined both in MN9D dopamine cells and primary mesencephalic cultures. PCBs induced a time- and concentration-dependent increase in ROS production, which preceded cytotoxicity. Whereas intracellular GSH depletion exacerbated PCB effects, antioxidant pretreatment attenuated ROS production and cell death. Coincident alterations in antioxidant defense enzymes also accompanied ROS production, including decreased MnSOD and increased CuZnSOD protein levels. The robust elevation in heme oxygenase-1 levels further support the activation of oxidative stress mechanisms following PCB exposure. Furthermore, PCBs produced concentration-dependent reductions in intracellular dopamine levels and elevated dopamine turnover. Although the intracellular source of ROS remains unknown, these results suggest that sublethal PCB concentrations activate an oxidative stress-related pathway, which potentially disrupts dopamine neuron function.
Pheochromocytoma (PC-12) cells synthesize, store, release and metabolize dopamine (DA) and norepinephrine (NE) in a manner analogous to that observed in the mammalian central nervous system. These cells were used to develop and validate an alternate method to animal testing to assess the effects of a complex environmental mixture of polychlorinated biphenyls (Aroclor 1254) on cellular catecholamine function. Aroclor 1254, at concentrations of 1 to 100 ppm, significantly decreased cellular catecholamine concentrations after 6 hrs. Exposure at 100 ppm for periods of less than an hr increased cellular catecholamine concentrations while longer exposure times (i.e., 1 to 24 hr) decreased cellular catecholamine concentrations. This in vitro depletion of catecholamines is similar to that seen in vivo. Thus, PC-12 cells may be useful for neurochemical evaluation of neurotoxicants with particular reference to effects on catecholaminergic systems.
Laboratory rats were exposed to chow adulterated with either 500 or 1000 ppm Aroclor 1254 for 30 days. Analysis of biogenic amines and their metabolites in the dorsal frontal cortex, lateral olfactory tract, striatum, basal hypothalamus, hippocampus and brainstem revealed significant decreases in dopamine concentrations and metabolism in only the striatum and lateral olfactory tract. Concentrations of individual PCB congeners in the striatum, lateral olfactory tract and hippocampus were measured by gas chromatography with electron capture detection. Neither total concentration nor variations in concentrations of individual congeners between regions could explain this regional specificity. The susceptibility of the striatum and lateral olfactory tract to insult by PCBs may be due to their innervation by midbrain dopaminergic neurons which have been shown to be particularly sensitive to insult from environmental, infectious and pharmacologic agents.
Enhanced neuronal NADPH-d activity in the SON in response to acute hyperosmotic stimulation is representative of upregulated NOS activity. Early adult male Sprague-Dawley rats were subjected to either normosmotic (0.9 g% NaCl; Norm) or hyperosmotic (3.5 M NaCl, Hyper) injection (0.6 ml/100 g b.w; i.p.). Rats were sacrificed 3–4 h later by transcardial perfusion under deep anesthesia. Brains were processed for NADPH-d staining in the presence or absence of the NOS blocker, N G -nitro- L -arginine ( L -NNA; 10 m M). Images show representative stained SON sections obtained from normosmotic (NORM) and hyperosmotic rats (HYPER). Calibration Bar = 100 m m. 
Lack of effect of adult exposure to Aroclor 1254 on activity-dependent NOS activity within the SON. Bars represent pooled values of mean NADPH-d staining 
In utero exposure to Aroclor 1254 disrupts basal NOS activity in the SON during postnatal development. Rat pups were exposed to Aroclor 1254 in utero (30 mg/kg/day; GD 10–19) and were sacrificed at PD10. TOP: Representative photomicrographs showing NADPH-d activity in paraformaldehyde-fixed coronal sections (40 m m) from the SON of juvenile rats born from pregnant dams fed corn oil (A; Control) or dams exposed to Aroclor 1254 (C; A1254). B and D: magnification of the SON area of A and C, respectively. Calibration Bar = 50 m m for A and C; 25 m m for B and D. BOTTOM: Bars represent average NADPH-d staining densities in SON sections from control and A1254 rats. * Indicates a significant decrease in staining intensity in the SON of Aroclor-exposed compared to control rat pups ( n = 14; p < 0.01). 
Prenatal exposure to Aroclor 1254 compromises physiological activation of NOS activity in the SON of early adult rats. NADPH-d staining density was measured in the SON of male adult (3–5 months) PCB-na  ̈ve and PCB-treated rats (Aroclor 1254; 30 mg/kg/day; GD 10–19) injected with either physiological saline (Normal Control) or hyperosmotic saline (3.5 M NaCl; 0.6 ml/100 g b.w., Hyper Control). # Indicates a statistically significant increase over normal control values ( p < 0.05). * Indicates a statistically significant decrease in hyperosmotic Aroclor 1254-exposed rats compared to hyperosmotic control animals (Hyper PCB, p < 0.05). The number of rats comprising each group is (from left to right): 15, 35, 10 and 12. 
Persistent long-term effects of prenatal exposure to Aroclor 1254 on activity-dependent NOS activity within the SON. Representative micrographs show NADPH-d staining density in the SON of late adult (14–16 month) male rats injected with either physiological saline (Normosmotic, A,C), or hyperosmotic saline (B,D; 3.5 M NaCl; 0.6 ml/100 g b.w.), or hyperosmotic saline with L -NAME (50 mg/kg, E). Aroclor-treated rats are shown in Panels C and D. Calibration Bar = 100 m m. 
Stimulated vasopressin (VP) release from magnocellular neuroendocrine cells in the supraoptic nucleus (SON) of hyperosmotic rats is inhibited by treatment with the industrial polychlorinated biphenyl (PCB) mixture, Aroclor 1254. Because VP responses to hyperosmotic stimulation are regulated by nitric oxide (NO) signaling, we studied NO synthase (NOS) activity in the SON of hyperosmotic rats as potential target of PCB-induced disruption of neuroendocrine processes necessary for osmoregulation. To examine PCB-induced changes in NOS activity under normosmotic and hyperosmotic conditions, male Sprague-Dawley rats were exposed to Aroclor 1254 (30mg/kg/day) in utero and NADPH-diaphorase (NADPH-d) activity assessed in SON sections at 3 ages: postnatal day 10, early adult (3-5 months) or late adult (14-16 months). Hyperosmotic treatment increased mean NADPH-d staining density of oil hyperosmotic controls by 19.9% in early adults and 58% in late adulthood vs normosmotic controls. In utero exposure to PCBs reduced hyperosmotic-induced upregulation of NADPH-d activity to control levels in early adults and by 28% in late adults. Basal NADPH-d was reduced in postnatal rats. Rats receiving PCB exposure as early adults orally for 14 days displayed normal responses. Our findings show that developmental but not adult exposure to PCBs significantly reduces NOS responses to hyperosmolality in neuroendocrine cells. Moreover, reduced NADPH-d activity produced by in utero exposure persisted in stimulated late adult rats concomitant with reduced osmoregulatory capacity vs oil controls (375.0±9 vs 348.6±8 mOsm/L). These findings suggest that developmental PCBs permanently compromise NOS signaling in the activated neuroendocrine hypothalamus with potential osmoregulatory consequences. Copyright © 2014 Elsevier Inc. All rights reserved.
Striatal slices from adult male Wistar-derived rats were exposed to a 1:1 mixture of Aroclor 1254:1260 at concentrations in media of 10, 20, 40, 60 or 100 ppm for 6 hr. Following exposure, slices and media were analyzed by high-performance liquid chromatography for dopamine (DA) and its metabolites. PCBs caused a significant dose-dependent decrease in slice DA content at concentrations greater than 20 ppm. Media concentrations of DA and its metabolites were significantly increased by PCB exposure greater than 60 ppm, indicating that, in addition to their suggested role in inhibiting DA synthesis, PCBs may interfere with either vesicular storage or release of DA. These data suggest that in addition to the recognized action of PCBs in inhibiting tyrosine hydroxylase, PCBs may also interfere with the vesicular monoamine transporter, and thereby suggest an additional mechanism by which DA concentrations and metabolism may be altered by PCB exposure.
Male Atlantic croaker (Micropogonias undulatus) were exposed to Aroclor 1254 (a PCB mixture) in the diet (0.1 mg/100 g body wt./day) for 30 days during gonadal recrudescence to investigate the effects of the PCB mixture on reproductive neuroendocrine function. The concentrations of biogenic amines (epinephrine [E], norepinephrine [NE], dopamine [DA], and 5-HT) and their major metabolites (3,4-dihydroxyphenylacetic acid [DOPAC], 3-methoxytyramine [3-MT], homovanillic acid [HVA], and 5-hydroxyindolacetic acid [5-HIAA]) were measured in the preoptic-anterior hypothalamus (POAH) and medial and posterior hypothalamus (MPH) using HPLC with electrochemical detection. There was a significant decline in 5-HT and DA concentrations and an increase in their metabolite to parent amine ratios in both the POAH and MPH of Aroclor 1254-exposed fish. In addition, Aroclor 1254 exposure resulted in the loss of the in vitro pituitary gonadotropic response to stimulation by a luteinizing hormone-releasing hormone analog (LHRHa). We have previously shown that 5-HT modulates the gonadotropin release in response to LHRHa in Atlantic croaker. Therefore, the reduced availability of neuronal 5-HT may be at least partially responsible for the loss of the gonadotropic response to stimulation by LHRHa.
An equal amount (per weight) of 127m tellurium (Te) was injected IP into weanling and adult rats, some intoxicated with a diet containing Te, others not. The young intoxicated rats presented a segmental demyelination of the sciatic nerve and paralysis of the hind limbs; the adult intoxicated rats did not. Quantitation of 127m Te in nervous and other tissues was done with a gamma counter. Correlative morphological examination of the nervous tissues was done with light and electron microscopy. This study shows that Te crosses the vascular wall without injuring endothelial cells and invades the surrounding sciatic nerve parenchyma following administration of 127m Te to a weanling or adult rat. However, Te damages the endothelium, crosses the vascular wall of endo and perineurial vessels in weanling rats, causes a perivascular oedema, cytoplasmic anomalies in the Schwann cells, destruction of myelin and apparently invades axones--according to autoradiographic studies--following the administration of 127m Te plus the Te-diet. It is concluded that Te penetrates more quickly and in larger amounts the walls of blood vessels in the sciatic nerve of weanling rats intoxicated with Te, than the same nerve in the other weanling and adults rats. Te in the amounts indicated here penetrates the parenchyma of the CNS but apparently does not cause injury.
The realization that the neurotoxicity of chemicals results from interactions between genetic inheritance and exposure to toxicants is relatively novel. The dramatic advances in research, particularly as they relate to the understanding of how external exposures interact with the genetic milieu of individuals that result in central nervous system (CNS) dysfunction, have gained great momentum in the last decade. The five-day 12(th) biennial meeting of the International Neurotoxicology Association (INA) focused on this issue, namely Gene-Environment Interactions in Neurotoxicology. The conference related basic research in the neurosciences and toxicology to major issues confronting our understanding of neurodevelopmental disorders, neurodegeneration and the impact of environmental exposures on human disease processes. The symposia featured many of the world's leading scientists in neurotoxicology and related disciplines who conduct research on the mechanisms of gene-environment interactions that result in injury to the developing and mature nervous system. The INA-12 Meeting provided a collegial setting to develop working relationships among scientists from different countries. This meeting successfully addressed major issues in human environmental health and helped uncover basic mechanisms and methodologies that will ultimately help develop strategies to mitigate human disease. Thus, INA-12 served as an essential component of the "core" meetings that have shaped the neurotoxicology researchers into an interactive, international and dynamic research community.
Descriptive statistics and genotype distributions of the case-control study population
Odds ratios for smoking stratified by gender and genotype a
We tested for gender-specific interactions between smoking and genetic polymorphisms of monoamine oxidase B (MAO-B) intron 13 (G or A allele), monoamine oxidase A (MAO-A) EcoRV (Yor N allele), and dopamine D2 recepor (DRD2) Taq1B (B1 or B2 allele) in a case-control study of 186 incident idiopathic Parkinson's disease (PD) cases and 296 age- and gender-matched controls. The odds ratios (ORs) for PD risk for ever smokers versus never smokers were 0.27 (95% CI: 0.13-0.58) for men of genotype G, and 1.26 (0.60-2.63) for men of genotype A (interaction chi2 = 8.14, P = 0.004). In contrast, for women, the OR for ever smokers versus never smokers were 0.62 (95% CI: 0.25-1.34) and 0.64 (95% CI: 0.18-2.21) for women of genotype GG/GA and AA, respectively (interaction chi2 = 0.001, P = 0.975). No interactions were detected between smoking and either MAO-A EcoRV or DRD2 Taq1B genotypes. These results suggest that a strong gender difference exists with respect to the modifying effect of MAO-B genotype on the smoking association with PD.
Organophosphates, such as the nerve gas soman, cause inhibition of acetylcholine esterase, accumulation of acetylcholine in synaptic clefts, and excessive activation of cholinergic receptors, causing central nervous symptoms such as tremor and seizures. Soman-poisoned animals have low brain levels of ATP, indicating that energy demand is greater than energy supply. We investigated whether soman poisoning is accompanied by an increased brain metabolism of glucose, as can be inferred from the accumulation of radiolabeled 2-deoxyglucose found in previous studies, or whether soman poisoning entails impairment of cerebral energy metabolism. We performed 13C nuclear magnetic resonance spectroscopy on brain extracts from soman-poisoned mice (160 microg/kg; 1 LD50) that had been dosed with 13C-labeled glucose or pyruvate intravenously. Formation of 13C-labeled glutamate, GABA and glutamine from [1-(13)C]glucose was reduced by approximately 30% in awake, soman-intoxicated animals, but formation of these amino acids from [3-(13)C]pyruvate was not different in soman-intoxicated animals and controls. These results suggest that soman intoxication entails inhibition of glycolysis, but not of tricarboxylic acid cycle activity in the brain. However, when brain metabolism was depressed by a sedative dose of diazepam (5 mg/kg) soman intoxication caused increased metabolism of 13C-labeled glucose. The latter finding shows that the soman-poisoned brain has a high energy requirement even during anticonvulsant therapy. We conclude that metabolic inhibition, as seen in awake, soman-intoxicated animals, may lower seizure threshold and contribute to soman-related neurodegeneration and lethality.
Synthetic stimulants commonly sold as "bath salts" are an emerging abuse problem in the U.S. Users have shown paranoia, delusions, and self-injury. Previously published in vivo research has been limited to only two components of bath salts (mephedrone and methylone). The purpose of the present study was to evaluate in vivo effects of several synthetic cathinones found in bath salts and to compare them to those of cocaine (COC) and methamphetamine (METH). Acute effects of methylenedioxyphyrovalerone (MDPV), mephedrone, methylone, methedrone, 3-fluoromethcathinone (3-FMC), 4-fluoromethcathinone (4-FMC), COC, and METH were examined in male ICR mice on locomotor activity, rotorod, and a functional observational battery (FOB). All drugs increased locomotor activity, with different compounds showing different potencies and time courses in locomotor activity. 3-FMC and methylone decreased performance on the rotorod. The FOB showed that in addition to typical stimulant induced effects, some synthetic cathinones produced ataxia, convulsions, and increased exploration. These results suggest that individual synthetic cathinones differ in their profile of effects, and differ from known stimulants of abuse. Effects of 3-FMC, 4-FMC, and methedrone indicate these synthetic cathinones share major pharmacological properties with the ones that have been banned (mephedrone, MDPV, methylone), suggesting that they may be just as harmful.
Top-cited authors
Gary J Myers
  • University of Rochester
Christopher Cox
  • Johns Hopkins Bloomberg School of Public Health
Philip W Davidson
  • University of Rochester
Conrad Shamlaye
  • Health Services, Seychelles
Donna Mergler
  • Université du Québec à Montréal