Selective loss of Purkinje cells from the rat cerebellum caused by acrylamide and the responses of beta-glucuronidase and beta-galactosidase

Mitochondrial dysfunction promotes the necroptosis of Purkinje cells in the cerebellum of acrylamide-exposed rats

Acrylamide (ACR) is a common neurotoxicant that can induce central-peripheral neuropathy in human beings. ACR from occupational setting and foods poses a potential threat to people's health. Purkinje cells are the only efferent source of cerebellum, and their output is responsible for coordinating motor activity. Recent studies have reported that Purkinje cell injury is one of the earliest neurotoxicity at any dose rate of ACR. However, the mechanism underlying ACR-mediated damage to Purkinje cells remains unclear. This research aimed to investigate whether necroptosis is involved in ACR-induced Purkinje cell death and its regulatory mechanism. In this study, rats were treated with ACR (40 mg/kg/every other day) for 6 weeks to establish an animal model of ACR neuropathy. Furthermore, an intervention experiment was achieved by rapamycin (RAPA), which is commonly used to activate mitophagy and maintain mitochondrial homeostasis. The results demonstrated ACR exposure caused necroptosis of Purkinje cells, mitochondrial dysfunction, and inflammatory response. By contrast, RAPA alleviated mitochondrial dysfunction and inhibited activation of necroptosis signaling pathway following ACR. In conclusion, our findings suggest that mitochondrial dysfunction and activation of necroptotic signaling are associated with the loss of Purkinje cells in ACR poisoning, which can be a potential therapeutic target for ACR neurotoxicity.

Effect of long-term exposure to acrylamide on endoplasmic reticulum stress and autophagy in rat cerebellum

Acrylamide (ACR) is a widely used chemical compound that has neurotoxicity in human, but whether ACR could impair the cerebellum and the related mechanism were still unknown. This study aimed to observe the changes in behavioral performance and cerebellar morphology caused by chronic ACR exposure, and to evaluate its influence on apoptosis, endoplasmic reticulum stress (ERS) and autophagy. Rats were treated with 0, 0.5 and 5 mg/kg ACR by drinking water for 12 months. Results showed that 5 mg/kg ACR treatment damaged the gait, balance ability, hindlimb muscle strength and motor coordination ability of rats. The results of hematoxylin and eosin and Nissl staining indicated that ACR impaired the structures of all three layers of the cerebellum, especially the Purkinje cell layer, showing abnormal morphology with nucleus condensation and pyknosis. Accumulation of autophagosomes, dilated endoplasmic reticulum and swollen mitochondria were observed in neurons under transmission electron microscopy. The enhanced apoptotic rates and the increased Bax expression indicated the elevated level of apoptosis. The results of Western blot showed that ACR treatment elevated protein levels of Beclin1, LC3-II/LC3-I, p-PERK/t-PERK, ATF4 and CHOP, indicating the initiation of autophagy, the activation of PERK pathway in ERS. This work helps to demonstrate the ACR neurotoxicity on cerebellum under chronic treatment and its underlying mechanism.

Acrylamide Induced Toxicity and the Propensity of Phytochemicals in Amelioration: A Review

Acrylamide is widely found in baked and fried foods, produced in large amount in industries and is a prime component in toxicity. This review highlights various toxicities that are induced due to acrylamide, its proposed mode of action including oxidative stress cascades and ameliorative mechanisms using phytochemicals. Acrylamide formation, the mechanism of toxicity and the studies on the role of oxidative stress and mitochondrial dysfunctions are elaborated in this paper. The various types of toxicities caused by Acrylamide and the modulation studies using phytochemicals that are carried out on various type of toxicity like neurotoxicity, hepatotoxicity, cardiotoxicity, immune system, and skeletal system, as well as embryos have been explored. Lacunae of studies include the need to explore methods for reducing the formation of acrylamide in food while cooking and also better modulators for alleviating the toxicity and associated dysfunctions along with identifying its molecular mechanisms.

Animal models of peripheral neuropathy due to environmental toxicants

Despite the progress in our understanding of pathogeneses and the identification of etiologies of peripheral neuropathy, idiopathic neuropathy remains common. Typically, attention to peripheral neuropathies resulting from exposure to environmental agents is limited relative to more commonly diagnosed causes of peripheral neuropathy (diabetes and chemotherapeutic agents). Given that there are more than 80,000 chemicals in commerce registered with the Environmental Protection Agency and that at least 1000 chemicals are known to have neurotoxic potential, very few chemicals have been established to affect the peripheral nervous system (mainly after occupational exposures). A wide spectrum of exposures, including pesticides, metals, solvents, nutritional sources, and pharmaceutical agents, has been related, both historically and recently, to environmental toxicant-induced peripheral neuropathy. A review of the literature shows that the toxicity and pathogeneses of chemicals adversely affecting the peripheral nervous system have been studied using animal models. This article includes an overview of five prototypical environmental agents known to cause peripheral neuropathy--namely, organophosphates, carbon disulfide, pyridoxine (Vitamin B6), acrylamide, and hexacarbons (mainly n-hexane, 2,5-hexanedione, methyl n-butyl ketone). Also included is a brief introduction to the structural components of the peripheral nervous system and pointers on common methodologies for histopathologic evaluation of the peripheral nerves.

Effects of rutin on acrylamide-induced neurotoxicity

Background

Rutin is an important flavonoid that is consumed in the daily diet. The cytoprotective effects of rutin, including antioxidative, and neuroprotective have been shown in several studies. Neurotoxic effects of acrylamide (ACR) have been established in humans and animals. In this study, the protective effects of rutin in prevention and treatment of neural toxicity of ACR were studied.

Results

Rutin significantly reduced cell death induced by ACR (5.46 mM) in time- and dose-dependent manners. Rutin treatment decreased the ACR-induced cytotoxicity significantly in comparison to control (P <0.01, P < 0.001). Rutin (100 and 200 mg/kg) could prevent decrease of body weight in rats. In combination treatments with rutin (50, 100 and 200 mg/kg), vitamin E (200 mg/kg) and ACR, gait abnormalities significantly decreased in a dose-dependent manner (P < 0.01 and P < 0.001). The level of malondialdehyde significantly decreased in the brain tissue of rats in both preventive and therapeutic groups that received rutin (100 and 200 mg/kg).

Conclusion

It seems that rutin could be effective in reducing neurotoxicity and the neuroprotective effect of it might be mediated via antioxidant activity.

Acrylamide: review of toxicity data and dose-response analyses for cancer and noncancer effects

Acrylamide (ACR) is used in the manufacture of polyacrylamides and has recently been shown to form when foods, typically containing certain nutrients, are cooked at normal cooking temperatures (e.g., frying, grilling or baking). The toxicity of ACR has been extensively investigated. The major findings of these studies indicate that ACR is neurotoxic in animals and humans, and it has been shown to be a reproductive toxicant in animal models and a rodent carcinogen. Several reviews of ACR toxicity have been conducted and ACR has been categorized as to its potential to be a human carcinogen in these reviews. Allowable levels based on the toxicity data concurrently available had been developed by the U.S. EPA. New data have been published since the U.S. EPA review in 1991. The purpose of this investigation was to review the toxicity data, identify any new relevant data, and select those data to be used in dose-response modeling. Proposed revised cancer and noncancer toxicity values were estimated using the newest U.S. EPA guidelines for cancer risk assessment and noncancer hazard assessment. Assessment of noncancer endpoints using benchmark models resulted in a reference dose (RfD) of 0.83 microg/kg/day based on reproductive effects, and 1.2 microg/kg/day based on neurotoxicity. Thyroid tumors in male and female rats were the only endpoint relevant to human health and were selected to estimate the point of departure (POD) using the multistage model. Because the mode of action of acrylamide in thyroid tumor formation is not known with certainty, both linear and nonlinear low-dose extrapolations were conducted under the assumption that glycidamide or ACR, respectively, were the active agent. Under the U.S. EPA guidelines (2005), when a chemical produces rodent tumors by a nonlinear or threshold mode of action, an RfD is calculated using the most relevant POD and application of uncertainty factors. The RfD was estimated to be 1.5 microg/kg/day based on the use of the area under the curve (AUC) for ACR hemoglobin adducts under the assumption that the parent, ACR, is the proximate carcinogen in rodents by a nonlinear mode of action. When the mode of action in assumed to be linear in the low-dose region, a risk-specific dose corresponding to a specified level of risk (e.g., 1 x 10-5) is estimated, and, in the case of ACR, was 9.5 x 10-2 microg ACR/kg/day based on the use of the AUC for glycidamide adduct data. However, it should be noted that although this review was intended to be comprehensive, it is not exhaustive, as new data are being published continuously.

The Changing View of Acrylamide Neurotoxicity

Acrylamide (ACR) is a water-soluble, vinyl monomer that has multiple chemical and industrial applications: e.g., waste water management, ore processing. In addition, ACR is used extensively in molecular laboratories for gel chromatography and is present in certain foods that have been prepared at very high temperatures. Extensive studies in rodents and other laboratory animals have provided evidence that exposure to monomeric ACR causes cellular damage in both the nervous and reproductive systems, and produces tumors in certain hormonally responsive tissues. Whereas human epidemiological studies have demonstrated a significantly elevated incidence of neurotoxicity in occupationally exposed populations, such research has not, to date, revealed a corresponding increase in cancer risk. Since the announcement by a Swedish research group in April 2002 [J. Ag. Food Chem. 50 (2002) 4998] regarding the presence of ACR in potato and grain-based foods, there has been a renewed interest in the toxic actions of this chemical. Therefore, in this review, we consider the different toxic effects of ACR. The neurotoxic actions of ACR will be the focal point since neurotoxicity is a consequence of both human and laboratory animal exposure and since this area of investigation has received considerable attention over the past 30 years. As will be discussed, a growing body of evidence now indicates that the nerve terminal is a primary site of ACR action and that inhibition of corresponding membrane-fusion processes impairs neurotransmitter release and promotes eventual degeneration. The electrophilic nature of ACR suggests that this neurotoxicant adducts nucleophilic sulfhydryl groups on certain proteins that are critically involved in membrane fusion. Adduction of thiol groups also might be common to the reproductive and carcinogenic effects of ACR. A final goal of this review is to identify data gaps that retard a comprehensive understanding of ACR pathophysiological processes.

Patterned Purkinje cell death in the cerebellum

The object of this review is to assemble much of the literature concerning Purkinje cell death in cerebellar pathology and to relate this to what is now known about the complex topography of the cerebellar cortex. A brief introduction to Purkinje cells, and their regionalization is provided, and then the data on Purkinje cell death in mouse models and, where appropriate, their human counterparts, have been arranged according to several broad categories--naturally-occurring and targeted mutations leading to Purkinje cell death, Purkinje cell death due to toxins, Purkinje cell death in ischemia, Purkinje cell death in infection and in inherited disorders, etc. The data reveal that cerebellar Purkinje cell death is much more topographically complex than is usually appreciated.

Acrylamide axonopathy revisited

Distal swelling and eventual degeneration of axons in the CNS and PNS have been considered to be the characteristic neuropathological features of acrylamide (ACR) neuropathy. These axonopathic changes have been the basis for classifying ACR neuropathy as a central-peripheral distal axonopathy and, accordingly, research over the past 30 years has focused on the primacy of axon damage and on deciphering underlying mechanisms. However, based on accumulating evidence, we have hypothesized that nerve terminals, and not axons, are the primary site of ACR action and that compromise of corresponding function is responsible for the autonomic, sensory, and motor defects that accompany ACR intoxication (NeuroToxicology 23 (2002) 43). In this paper, we provide a review of data from a recently completed comprehensive, longitudinal silver stain study of brain and spinal cord from rats intoxicated with ACR at two different daily dosing rates, i.e., 50 mg/kg/day, ip or 21 mg/kg/day, po. Results show that, regardless of dose-rate, ACR intoxication was associated with early, progressive nerve terminal degeneration in all CNS regions and with Purkinje cell injury in cerebellum. At the lower dose-rate, initial nerve terminal argyrophilia was followed by abundant retrograde axon degeneration in white matter tracts of spinal cord, brain stem, and cerebellum. The results support and extend our nerve terminal hypothesis and suggest that Purkinje cell damage also plays a role in ACR neurotoxicity. Substantial evidence now indicates that axon degeneration is a secondary effect and is, therefore, not pathophysiologically significant. These findings have important implications for future mechanistic research, classification schemes, and assessment of neurotoxicity risk.

Acrylamide neuropathy. III. Spatiotemporal characteristics of nerve cell damage in forebrain

Previous studies of acrylamide (ACR) neuropathy in rat PNS [Toxicol. Appl. Pharmacol. (1998) 151:211-221] and in spinal cord, brainstem and cerebellum [NeuroToxicology (2002a) 23:397-414; NeuroToxicology (2002b) 23:415-429] have suggested that axon degeneration was not a primary effect and was, therefore, of unclear neurotoxicological significance. To conclude our studies of neurodegeneration in rat CNS during ACR neurotoxicity, a cupric silver stain method was used to define spatiotemporal characteristics of nerve cell body, dendrite, axon and terminal argyrophilia in forebrain regions and nuclei. Rats were exposed to ACR at a dose-rate of either 50 mg/kg per day (i.p.) or 21 mg/kg per day (p.o.) and at selected times brains were removed and processed for silver staining. Results show that intoxication at either ACR dose-rate produced a terminalopathy, i.e. nerve terminal degeneration and swelling were present in the absence of significant argyrophilic changes in neuronal cell bodies, dendrites or axons. Exposure to the higher ACR dose-rate caused early onset (day 5), widespread nerve terminal degeneration in most of the major forebrain areas, e.g. cerebral cortex, thalamus, hypothalamus and basal ganglia. At the lower dose-rate, nerve terminal degeneration in the forebrain developed early (day 7) but exhibited a relatively limited spatial distribution, i.e. anteroventral thalamic nucleus and the pars reticulata of the substantia nigra. Several hippocampal regions were affected at a later time point (day 28), i.e. CA1 field and subicular complex. At both dose-rates, argyrophilic changes in forebrain nerve terminals developed prior to the onset of significant gait abnormalities. Thus, in forebrain, ACR intoxication produced a pure terminalopathy that developed prior to the onset of significant neurological changes and progressed as a function of exposure. Neither dose-rate used in this study was associated with axon degeneration in any forebrain region. Our findings indicate that nerve terminals were selectively affected in forebrain areas and, therefore, might be primary sites of ACR action.

Acrylamide neuropathy. I. Spatiotemporal characteristics of nerve cell damage in rat cerebellum

Based on evidence from morphometric studies of PNS, we suggested that acrylamide (ACR)-induced distal axon degeneration was a secondary effect related to duration of exposure [Toxicol. Appl. Pharmacol. 151 (1998) 211]. To test this hypothesis in CNS, the cupric-silver stain method of de Olmos was used to define spatiotemporal characteristics of nerve somal, dendritic, axonal and terminal degeneration in rat cerebellum. Rats were exposed to ACR at either 50 mg/kg per day (i.p.) or 21 mg/kg per day (p.o.) and at selected times (i.p. = 5, 8 and 11 days; p.o. = 7, 14, 21, 28 and 38 days) brains were removed and processed for silver staining. Results demonstrate that intoxication at the higher ACR dose-rate produced early (day 5) and progressive degeneration of Purkinje cell dendrites in cerebellar cortex. Nerve terminal degeneration occurred concurrently with somatodendritic argyrophilia in cerebellar and brainstem nuclei that receive afferent input from Purkinje neurons. Relatively delayed (day 8), abundant axon degeneration was present in cerebellar white matter but not in cortical layers or in tracts carrying afferent fibers (cerebellar peduncles) from other brain nuclei. Axon argyrophilia coincided with the appearance of perikaryal degeneration, which was selective for Purkinje cells since silver impregnation of other cerebellar neurons was not evident in the different cortical layers or cerebellar nuclei. Intoxication at the lower ACR dose-rate produced simultaneous (day 14) dendrite, axon and nerve terminal argyrophilia and no somatic Purkinje cell degeneration. The spatiotemporal pattern of dendrite, axon and nerve terminal loss induced by both ACR dose-rates is consistent with Purkinje cell injury. Injured neurons are likely to be incapable of maintaining distal processes and, therefore, axon degeneration in the cerebellum is a component of a "dying-back" process of neuronal injury. Because cerebellar coordination of somatomotor activity is mediated solely through efferent projections of the Purkinje cell, injury to this neuron might contribute significantly to gait abnormalities that characterize ACR neurotoxicity.

Nerve terminals as the primary site of acrylamide action: a hypothesis

Acrylamide (ACR) is considered to be prototypical among chemicals that cause a central-peripheral distal axonopathy. Multifocal neurofilamentous swellings and eventual degeneration of distal axon regions in the CNS and PNS have been traditionally considered the hallmark morphological features of this axonopathy. However, ACR has also been shown to produce early nerve terminal degeneration of somatosensory, somatomotor and autonomic nerve fibers under a variety of dosing conditions. Recent research from our laboratory has demonstrated that terminal degeneration precedes axonopathy during low-dose subchronic induction of neurotoxicity and occurs in the absence of axonopathy during higher-dose subacute intoxication. This relationship suggests that nerve terminal degeneration, and not axonopathy, is the primary or most important pathophysiologic lesion produced by ACR. In this hypothesis paper, we review evidence suggesting that nerve terminal degeneration is the hallmark lesion of ACR neurotoxicity, and we propose that this effect is mediated by the direct actions of ACR at nerve terminal sites. ACR is an electrophile and, therefore, sulfhydryl groups on presynaptic proteins represent rational molecular targets. Several presynaptic thiol-containing proteins (e.g. SNAP-25, NSF) are critically involved in formation of SNARE (soluble N-ethylmaleimide (NEM)-sensitive fusion protein receptor) complexes that mediate membrane fusion processes such as exocytosis and turnover of plasmalemmal proteins and other constituents. We hypothesize that ACR adduction of SNARE proteins disrupts assembly of fusion core complexes and thereby interferes with neurotransmission and presynaptic membrane turnover. General retardation of membrane turnover and accumulation of unincorporated materials could result in nerve terminal swelling and degeneration. A similar mechanism involving the long-term consequences of defective SNARE-based turnover of Na+/K(+)-ATPase and other axolemmal constituents might explain subchronic induction of axon degeneration. The ACR literature occupies a prominent position in neurotoxicology and has significantly influenced development of mechanistic hypotheses and classification schemes for neurotoxicants. Our proposal suggests a reevaluation of current classification schemes and mechanistic hypotheses that regard ACR axonopathy as a primary lesion.

Detecting necrotic neurons with fluoro-jade stain

Fluoro-jade, a novel stain for detection of neuropathic lesions by fluorescence microscopy, was validated on the models of toxic neuropathy induced with 3-acetylpyridine (3-AP) or with acrylamide (ACR). Groups of male and female albino rats of Wistar strain were either exposed to a single administration of 80 mg/kg i.p. 3-AP followed 5 hours later by 300 mg/kg of nicotinamide i.p. and examined at days 3 and 15, or to 15 daily doses of 30 mg/kg p.o. ACR and examined at day 15. Following in-life behavioral observations and measurements, the rats were fixed by perfusion with formalin. Additional animals treated with same dose of 3-AP and nicotinamide were submitted to purposeful autolysis for 4 or 16 hours before immersion fixation with formalin on test day 3. In-life observations showed in 3-AP-treated animals signs of severe general toxicity, sensorimotor dysfunction and decreased motor activity starting shortly after the treatment and persisting throughout the observation period. ACR-treated rats started to develop abnormal gait on test day 8 and by day 15 developed reduced grip strength, increased landing footsplay and decreased motor activity. Fluoro-jade, applied to paraffin sections of the nervous system, detected selectively and sensitively the necrotic neurons in the brain, especially those in the inferior olivary nucleus of animals treated with 3-AP, at test day 3, as well as the necrotic Purkinje cells in the cerebellum of ACR-treated animals at test day 15. Chromatolytic neurons in the dorsal root ganglia of ACR-treated animals did not stain positively, indicating that this kind of reversible neuronal remodeling is not detectable using fluoro-jade. Necrotic neurons were still stained by fluoro-jade after 4 hour autolysis, but following 16 hour autolysis the results became false negative. There was no false positive fluorescence in fresh or autolytic tissues, except that emitted by red blood cells in unperfused specimens. The study confirmed the validity of fluoro-jade as a stain suitable for detecting necrotic neurons in toxicological safety studies.

A behavioral study of the development of hereditary cerebellar ataxia in the shaker rat mutant

shaker Mutant rats were first identified by their abnormal motor behaviors and degeneration of cerebellar Purkinje cells and brainstem inferior olivary neurons. After 6 generations of inbreeding 77% of shaker rat mutants are mildly ataxic (identified as mild shaker mutants) and 23% are ataxic and exhibit a whole body tremor (strong shaker mutants) by 3 months of age. This study of shaker mutants from birth to 3 months of age was designed to: (1) compare the somatic and motor development of shaker mutants with age matched normal rats; (2) identify the temporal onset of motor deficits; and (3) correlate qualitative differences in Purkinje cell degeneration between 3-month-old mild and strong shaker rat mutants. Shaker mutant rats consistently weighed less than age-matched control animals. Analysis of motor-development using the hindlimb splay test demonstrated the distance between hindpaws was significantly greater in shaker mutant rats than in controls starting at 42 postnatal days (PND) of age. Hindlimb stride width was greater for shaker than control rats at 42 PNDs. However, after 42 PNDS shaker mutant average hindlimb width was narrower than controls. Forelimb stride width was consistently narrower in shaker mutants than in normal rats. Hindlimb placement was impaired in shaker rat mutants after 15 PND. Forelimb placement, cliff avoidance and surface righting were only transiently impaired in shaker mutants. Mid-air righting, performance of a geotaxic response, and climbing and jumping postural reactions were similar in shaker and normal rats. The spatial extent of Purkinje cell survival/degeneration correlated with differences in abnormal motor activity seen in 3-month-old mild and strong shaker mutants. In mild shaker rat mutants, Purkinje cells appeared to have degenerated randomly throughout the cortex. In strong shaker mutants most Purkinje cells in the anterior lobe had degenerated. In the posterior lobe Purkinje cell degeneration appeared to be numerically significant, but many surviving cells were present. Although Purkinje cell loss was not numerically quantified in this study, a strong association between the extent and type of spatial loss of Purkinje cells, and the severity of clinical signs, appears to exist.

Modulation of acrylamide-induced neurochemical and behavioral deficits by cerebellar transplants in rats

Acrylamide (30 mg/kg body wt.) administered intraperitoneally daily to young adult male rats, five times a week for 3 consecutive weeks, affected the cerebellar functions, as exhibited by a significant reduction in rotarod performance, spontaneous locomotor activity, glutathione-S-transferase activity, and 3H-flunitrazepam binding in cerebellum. Transplantation of dissociated fetal cerebellar cells (E14) to cerebellum resulted in a significant recovery in behavioral and neurochemical parameters evaluated 9 weeks after transplantation. Light- and electron-microscopic studies confirmed the viability and specificity of cerebellar grafts.

The volume of Purkinje cells decreases in the cerebellum of acrylamide-intoxicated rats, but no cells are lost

The effects of acrylamide intoxication on the numbers of granule and Purkinje cells and the volume of Purkinje cell perikarya have been evaluated with stereological methods. The analysis was carried out in the cerebella of rats that had received a dose of 33.3 mg/kg acrylamide, twice a week, for 7.5 weeks. The total numbers of cerebellar granule and Purkinje cells were estimated using the optical fractionator and the mean volume of the Purkinje cell perikarya was estimated with the vertical rotator technique. The volumes of the molecular layer, the granular cell layer and the white matter were estimated using the Cavalieri principle. The mean weight of the cerebellum of the intoxicated rats was 7% lower than that of the control rats (2P = 0.001). The numbers of the Purkinje cells and granule cells were the same in both groups, but the mean volume of the perikarya of the Purkinje cells in the intoxicated rats was 10.5% less than that of the control group (2P = 0.004). The volume of the granular cell layer was reduced by 15% (2P = 0.006) but there were no differences in the volumes of the molecular layer and the white matter in the intoxicated and control animals.

Effects of acrylamide and acrylic acid on creatine kinase activity in the rat brain

In vitro, both acrylamide and acrylic acid inhibited creatine kinase (CK) activity in rat brain homogenates, and acrylic acid was more potent than acrylamide. In vivo, however, when given i.p. 50 mg/kg per day for 8 days to rats, only acrylamide inhibited CK activity in the brain and caused apparent neurological signs. 14C in the brain 24h after the injection of 14C-labelled chemicals was more than 7 times greater with acrylamide than with acrylic acid. The inhibition of CK activity by acrylamide varied in eight regions of the brain; from 54% in hypothalamus to 27% in cerebellar vermis. The regional difference of CK inhibition, however, did not agree well with either 14C distribution or with the distribution in regions which appear clinically or pathologically vulnerable to acrylamide.

Acrylamide induces immediate-early gene expression in rat brain

Northern blot analysis was used to study the effects of acrylamide, a potent neurotoxin, on the induction of c-fos and c-jun mRNA in rat brain. Male Sprague-Dawley rats (10-12 weeks old) treated with acrylamide as a single dose (100 mg/kg, i.p.) or via drinking water (0.03% w/v) for 4 weeks, were used to study acute and chronic effects on immediate-early gene expression, respectively. Acute administration of acrylamide caused a statistically significant increase in the expression of c-fos (approx. 37%) and c-jun (approx. 17%) mRNA in rat brain. By contrast, the level of c-fos mRNA in chronic acrylamide treatment was not altered significantly, but the expression of c-jun mRNA was increased almost 100% as compared to control. These data show that the neurotoxin acrylamide induces immediate-early gene expression in the brain. The effects appear to be related to the route of administration, dose and duration of acrylamide treatment.

Effect of acrylamide on the distribution of microtubule-associated proteins (MAP1 and MAP2) in selected regions of rat brain

The effect of acrylamide treatment on the immunocytochemical localization of microtubule-associated proteins (MAP1 and MAP2) was studied in different brain regions (cerebellum, cerebral cortex, and hippocampus) of adult rats. Animals were treated with acrylamide (estimated mean dose: 15 mg/kg/d) orally for 2 wk when they showed slight hindlimb weakness. Immunoreactivity for MAP1 and MAP2 was detected in tissue sections with monoclonal antibodies according to the Sternberger's peroxidase-antiperoxidase technique. Intense MAP1 immunoreactivity was observed in neuronal perikarya and dendrites, with faint staining in axons. By contrast, MAP2 immunostaining was selectively observed in dendrites and neuronal perikarya. Treatment of animals with acrylamide reduced immunoreactivity for both MAP1 and MAP2 in hippocampus and cerebellum, with relatively little change in cerebral cortex. Loss of MAPs immunoreactivity in affected brain areas likely proceeded from dendrite to perikaryon. The results of this study indicate that hippocampal compromise is part of the neurotoxic picture associated with rodent exposure to acrylamide.

Acrylamide-induced depletion of microtubule-associated proteins (MAP1 and MAP2) in the rat extrapyramidal system

Acrylamide, an occupational neurotoxicant, reduced MAP1 and MAP2 distribution in different regions of rat brain. Different components of the extrapyramidal system (caudate-putamen, globus pallidus, substantia nigra and red nucleus) revealed differential distribution of MAP1 and MAP2 in acrylamide-treated animals. Rats were treated with acrylamide (estimated mean dose: 15 mg/kg/day) for 2 weeks and MAP1 and MAP2 were localized according to Sternberger's peroxidase-anti-peroxidase technique. MAP1 labelled neuronal perikarya and dendrites almost with a similar intensity, but MAP2 immunostaining was more intense in dendrites than neuronal perikarya. Acrylamide caused a near-total loss of MAP1 and MAP2 immunoreactivity in caudate-putamen. Other components of the extrapyramidal system were relatively less affected by acrylamide. These results indicate that caudate-putamen is more susceptible to the action of acrylamide than other components of the extrapyramidal system studied. The depletion of MAP1 and MAP2 immunoreactivity by acrylamide appears to be an early biochemical event preceding peripheral neuropathy. The loss of MAPs immunoreactivity occurs first in dendrites and proceeds toward the perikarya. This study indicates that acrylamide not only causes axonal damage but may also induce dendritic degeneration.

The number and mean volume of neurons in the cerebral cortex of rats intoxicated with acrylamide

Acrylamide was given in an accumulated dose of 500 mg/kg to rats by intraperitoneal injection in two different dosing schedules: 50 mg/kg twice a week for 5 weeks and 33.3 mg/kg twice a week for 7.5 weeks. The effect of acrylamide intoxication on the neurons in the cerebral cortex of the rat was studied using unbiased stereological methods. A reduction of brain weight of 8% was seen in both the intoxicated groups. The volume of neocortex was significantly decreased in the experimental groups, but the density of neurons was increased resulting in an unchanged total number of neurons. The mean volume of neurons in neocortex was significantly decreased in both acrylamide intoxicated groups. There was no difference between the two different intoxication schedules. The possibility that acrylamide causes neuronal death and the effect of eventual differential cellular sensitivity is discussed.

Neurotoxicity of 1-methoxycycloheptatriene--a Purkinje cell toxicant

The toxicity of 1-methoxycycloheptatriene (1-MCHT), a sensory irritant, has been investigated in beagles. It was found to produce gross inco-ordination of the limbs at intravenous doses greater than 10 mg kg-1. The main histological abnormalities were in the cerebellum and consisted of Purkinje cell death and subsequent reactive gliosis. A few necrotic neurons were seen in the diencephalon, pons and medulla. Haematological abnormalities, e.g. leucocytosis with relative lymphopenia, were seen, while biochemical changes included hyperglycaemia and a rise in plasma aminotransferases. The no-effect dose for the histological and biochemical changes was the same. These abnormalities are compared with cerebellar changes observed in acrylamide and other toxic states.

An ACTH-(4-9) analogue, Org 2766, improves recovery from acrylamide neuropathy in rats

Org 2766 is one of a series of melanocortins (ACTH and related peptides) that exert trophic influences on the central and peripheral nervous system of the rat. We used acrylamide neuropathy in rats as an experimental model of peripheral neuropathies of the dying-back type in order to assess the potential therapeutic efficacy of Org 2766 in this type of nerve damage. The peptide reversed the delayed persistent deficit in sensory conduction velocity without preventing the initial loss of motor coordination. The recovery of apparently normal coordination was unaffected by the peptide, but resistance to a second toxic challenge suggested that recovery was more complete in the peptide-treated rats. The finding that Org 2766 improved the quality of the repair following acrylamide neuropathy, together with previous studies showing beneficial effects in neuropathies caused by cisplatin or diabetes and after mechanical trauma, strongly suggests that Org 2766 may be beneficial in the treatment of various conditions in which the nervous system has sustained damage.

Comparison of central and peripheral nervous system lesions caused by high-dose short-term and low-dose subchronic acrylamide treatment in rats

The effects of high-dose subacute acrylamide treatment of up to 50 mg/kg/day for 4 or 10 d were compared to those of subchronic exposure, up to 12 mg/kg/day for 90 d. In the subacute study, Purkinje cells, long ascending tracts of the spinal cord, optic tract terminal or preterminal regions in superior colliculus, sensory ganglion cells, and distal large-caliber peripheral axons were severely affected. Purkinje cells and fasciculus gracilis changes were the earliest lesions. In the subchronic study, the dominant lesion was confined to the distal peripheral axon, with only minor changes occurring in spinal cord and medulla. Paranodal swellings with the characteristic appearance of neurofilament aggregations were not seen. This morphological study suggests a significant difference between high- and low-dose acrylamide-induced lesions. If there is a reduced tendency for long-term low-dose acrylamide exposure to produce CNS lesions, the risk of irreversible nervous system damage would be less than that predicted from subacute studies.

The evolution of intracellular responses to acrylamide in rat spinal ganglion neurons

Acrylamide (30 mg or 50 mg/kg/day, 5 days each week) was injected intraperitoneally into rats for up to 4 weeks. Lumbar spinal ganglia, spinal cord and lumbrical muscle spindles were examined by light and electron microscopy at various times during this period. The first abnormalities in spinal ganglion neurons were seen at 7 days when an apparent increase in numbers of mitochondria, some being hypertrophic, were found in a few large light cells. This was 10 days before any significant Wallerian degeneration was found in muscle spindle sensory fibres. Mitochondrial changes became more marked with time and were later associated with RER disruption, loss of neurofilaments and peripheral displacement of the nucleus thus mimicking chromatolysis of the axon reaction. All these changes began, however, before axon degeneration. Evidence of increased satellite cell activity was maximal at 21 days. These changes are discussed in the light of the possibility that calcium entry into the cell may be seriously increased early in the intoxication as a direct result of the presence of acrylamide and that many of these cellular features are secondary responses to such an event. Distal degeneration of axons seems likely to be secondary to the perikaryal changes.

Neurotoxicity of acrylamide and related compounds in rats. Effects on rotarod performance, morphology of nerves and neurotubulin

Neurotoxic properties of acrylamide and seven related compounds in rats were studied with regard to the effects on rotarod performance, morphology of nerves and neurotubulin. Compounds used in the present study were acrylamide, N-hydroxymethylacrylamide, N-isopropylacrylamide, methacrylamide, N-methylacrylamide, crotonamide, diacetone acrylamide, and N-tert-butylacrylamide. Animals were given chemicals in their drinking water for 90 days. Deficit of rotarod performance was produced by five compounds; acrylamide, N-hydroxymethylacrylamide, N-isopropylacrylamide, methacrylamide, and N-methylacrylamide. Morphological changes in tibial and sural nerves, such as shrinkage and loss of myelinated fibres, myelin retraction, and corrugated myelin sheaths, were observed after treatment with these five compounds. Depression of the [3H]colchicine-binding to neurotubulin (the soluble protein) of sciatic nerves was detected after giving these five compounds. After acrylamide dosing, the depression progressed with time. A significant reduction of the colchicine-binding to neurotubulin was also detected in the spinal cord of both the cervical and the lumbar regions, but neither in the brain nor the cerebellum.

Ultrastructural features of the Purkinje cell damage caused by acrylamide in the rat: a new phenomenon in cellular neuropathology

Dosing rats with acrylamide leads to the formation in Purkinje cells of juxtanuclear clusters of tubular and vesicular smooth endoplastic reticulum (SER). A microtubule organizing centre forms in relation to these clusters and together they appear to move to the cell surface, where protrusions of plasmalemma form, often with overlying synaptic attachments, containing densely packed tubular and vesicular SER membranes. Usually the microtubule organizing centre immediately underlies this. Subsequently, appearances suggest that astroglial intrusions occur internal to the protrusions described above to which the tubulo-vesicular material appears to be transferred. During these events the organization of the cytoplasm of the Purkinje cell is grossly disturbed with apparent loss and disarray of rough endoplasmic reticulum (RER) and of polyribosomes. This temporal sequence of events can be followed after a single dose of acrylamide. In chronically intoxicated animals vacuolation and swelling of dendrites takes place and the Purkinje cell may die after all stages of the cellular transformations have been present. These unique events appear to be confined to Purkinje cells and are considered probably to be the result of a primary disturbance to SER synthesis caused by acrylamide. It is argued that the changes taking place in acrylamide intoxication in neurons that lead to degeneration in long axons are probably of the same general kind.