Biomedical subjects

W Slikker

Publications and source records attributed to W Slikker.

At least 37 records · Page 2Linked to original sources

PubMed2000

Transplacental pharmacokinetics and fetal distribution of 2', 3'-didehydro-3'-deoxythymidine (d4T) and its metabolites in late-term rhesus macaques.

BACKGROUND: The overall goal of human immunodeficiency virus (HIV) therapy during pregnancy is to maintain maternal health and reduce the probability of vertical transmission during gestation and delivery, while keeping toxicity risks low. Azidothymidine (AZT) is currently recommended for pregnant women infected with HIV; however, many pregnant women are unable to tolerate AZT because of toxicity. In the present study, the placental transfer and fetal accumulation of the anti-HIV compound 2',3'-didehydro-3'-deoxythymidine (d4T) and its active (triphosphorylated) and inactive (thymine and beta-aminoisobutyric acid) metabolites were examined at steady state in late-term rhesus macaques. METHODS: On the day of the hysterotomy, the mother was administered an intravenous loading dose of d4T, followed by a 3-hr steady-state intravenous infusion that also included [(3)H]d4T as a tracer. After 3 hr of infusion, the fetus was delivered by cesarean section under halothane/N(2)O anesthesia. Plasma, amniotic fluid, and tissues were analyzed for d4T and its inactive metabolites by HPLC; tissue samples were analyzed for d4T and active (phosphorylated) metabolites by strong anion-exchange HPLC. RESULTS: Maternal steady-state plasma concentrations of d4T were 1-2 microg/ml, with a fetal-to-maternal plasma ratio of 0.85 +/- 0.09. The fetal tissue distribution of radioactivity was highest in the kidney and lowest in the brain. D4T, thymine, and beta-aminoisobutyric acid were detected in all fetal tissues examined. CONCLUSIONS: Our data indicate that d4T readily crosses the placenta and is present in the fetus as parent compound or its inactive metabolites after maternal infusion. Although fetal plasma concentrations of d4T were similar to clinical d4T concentrations, no phosphorylated metabolites were detected. Teratology 62:93-99, 2000. Published 2000 Wiley-Liss, Inc.

Aminoisobutyric Acids↗

PubMed2000

Systemic administration of domoic acid-induced spinal cord lesions in neonatal rats.

Domoic acid (Dom) is a glutamate analog and a seafood toxin that has caused neurological disturbance and death in humans. Brain lesions caused by Dom have been documented in the literature, but the effect of Dom on the spinal cord has not been investigated as extensively. Systemic administration of glutamate agonists (i.e., homocysteate, kainate, and a-amino-3-hydroxy-5-methylisoxazole-4-propionic acid) caused spinal cord lesions in infant rats. In the present study, the toxic effects of Dom on the developing spinal cord are examined. Neonatal rats on Postnatal Day 7 were administered Dom subcutaneously at doses of 0.10, 0.17, 0.25, 0.33, 0.42, and 0.50 mg/kg, respectively. Motor seizures characterized by scratching, tail flicking, and swimming-like movement were induced by Dom at all doses. High doses of Dom (> or = 0.33 mg/kg) further induced a hindlimb paralysis, a forelimb tremor, and death that occurred in less than 2 hours. The percentages of death and paralysis induced by 0.33 mg/kg Dom were 47% and 65%, respectively (n = 17). At this dose, electrocorticogram was recorded and synchronized interrupted electrical activities in brains of these animals were detected. However, no brain damage was detected in these rats. Spinal cord lesions characterized by focal hemorrhage, neuronal swelling, and neuronal vacuolization were found in 73% of the animals that had shown the paralysis/tremor in their extremities, as examined 1 to 2 hours after Dom injection. These lesions were seen at all spinal cord levels. Neuronal degeneration was mainly found in the ventral and intermediate gray matter, whereas cells in the dorsal portion of the spinal cord were relatively spared. Data suggest that observed behavioral changes were due to spinal cord damage rather than seizures or brain lesions.

Animals↗

PubMed2000

An evaluation of l-ephedrine neurotoxicity with respect to hyperthermia and caudate/putamen microdialysate levels of ephedrine, dopamine, serotonin, and glutamate.

l-Ephedrine is an active ingredient in several herbal formulations with a mechanism of action similar to amphetamine and methamphetamine. However, its potential to damage dopaminergic terminals in the caudate/putamen (CPu) has yet to be fully evaluated. The studies here used in vivo brain microdialysis experiments to determine the systemic doses and extracellular brain levels of l-ephedrine necessary to produce similar increases in CPu extracellular dopamine and marked hyperthermia that were previously shown necessary for amphetamine-induced neurotoxicity in male Sprague-Dawley rats. At an environmental temperature of 23 degrees C, a single 40 mg/kg intraperitoneal (ip) dose of l-ephedrine produced marked hyperthermia (>/= 40 degrees C), peak microdialysate ephedrine levels of 7.3 +/- 1.2 microM, and a 20-fold increase in microdialysate dopamine levels. Twenty-five mg/kg produced a lesser degree of hyperthermia, peak microdialysate ephedrine levels of 2.6 +/- 0.4 microM, and a 10-fold increase in dopamine levels. Three doses of 40 mg/kg given at 3-h intervals or 4 doses of 25 mg/kg l-ephedrine given at 2-h intervals were compared with 4 doses of 5 mg/kg d-amphetamine given at 2-h intervals. Multiple doses of either ephedrine or amphetamine caused severe hyperthermia (>/= 41.3 degrees C) but striatal tissue levels of dopamine 7 days after dosing were reduced only 25% or less by ephedrine compared to the 75% reductions produced by amphetamine. The increases in CPu microdialysate levels of serotonin produced by either 4 x 25 mg/kg l-ephedrine or 4 x 5 mg/kg d-amphetamine did not significantly differ, but elevation of dopamine levels by d-amphetamine were over 2-fold times the level caused by l-ephedrine. Microdialysate glutamate levels were elevated to the same extent by either 25 mg/kg l-ephedrine or 4 x 5 mg/kg d-amphetamine. l-Ephedrine may not be as neurotoxic to dopaminergic terminals as d-amphetamine, because non-lethal doses of l-ephedrine do not sufficiently increase the CPu dopamine levels within nerve terminals or the extracellular space to those necessary for a more pronounced long-term dopamine depletion.

Animals↗

PubMed2000

A dose-response study of ibogaine-induced neuropathology in the rat cerebellum.

Ibogaine (IBO) is an indole alkaloid from the West African shrub, Tabernanthe iboga. It is structurally related to harmaline, and both these compounds are rigid analogs of melatonin. IBO has both psychoactive and stimulant properties. In single-blind trials with humans, it ameliorated withdrawal symptoms and interrupted the addiction process. However, IBO also produced neurodegeneration of Purkinje cells and gliosis of Bergmann astrocytes in the cerebella of rats given even a single dose (100 mg/kg, ip). Here, we treated rats (n = 6 per group) with either a single ip injection of saline or with 25 mg/kg, 50 mg/kg, 75 mg/kg, or 100 mg/kg of IBO. As biomarkers of cerebellar neurotoxicity, we specifically labeled degenerating neurons and axons with silver, astrocytes with antisera to glial fibrillary acidic protein (GFAP), and Purkinje neurons with antisera to calbindin. All rats of the 100-mg/kg group showed the same pattern of cerebellar damage previously described: multiple bands of degenerating Purkinje neurons. All rats of the 75-mg/ kg group had neurodegeneration similar to the 100-mg/kg group, but the bands appeared to be narrower. Only 2 of 6 rats that received 50 mg/kg were affected; despite few degenerating neuronal perikarya, cerebella from these rats did contain patches of astrocytosis similar to those observed with 75 or 100 mg/kg IBO. These observations affirm the usefulness of GFAP immunohistochemistry as a sensitive biomarker of neurotoxicity. None of the sections from the 25-mg/kg rats, however stained, were distinguishable from saline controls, indicating that this dose level may be considered as a no-observable-adverse-effect level (NOAEL).

Animals↗

PubMed2000

Cognitive tests: interpretation for neurotoxicity? (Workshop summary).

The appropriate use and interpretation of cognitive tests presents important challenges to the toxicologist and to the risk assessor. For example, intelligence cannot be measured directly; rather intelligence is quantified indirectly by scoring responses (i.e., behaviors) to specific situations (problems). This workshop, "Cognitive Tests: Interpretation for Neurotoxicity?" provided an overview on the types of cognitive tests available and described approaches by which the validity of such tests can be assessed. Unlike many tools available to the toxicologist, cognitive tests have a particular advantage. Being noninvasive and species-neutral, the same test can be performed in different mammalian species. This enhances one's ability to assess the validity of test results. Criteria for test validity include comparable responses across species as well as similar disruption by the same neurotoxicant across species. Test batteries, such as the Operant Test Battery, have indicated remarkable similarity between monkeys and children with respect to performance of certain tasks involving, for example, short-term memory. Still, there is a need for caution in interpretation of such tests. In particular, cognitive tests, especially when performed in humans, are subject to confounding by a range of factors, including age, gender, and, in particular, education. Moreover, the ability of such tests to reflect intelligence must be considered. Certain aspects of intelligence, such as the ability to plan or carry out specific tasks, are not well reflected by many of the standard tests of cognition. Nonetheless, although still under development, cognitive tests do hold promise for reliably predicting neurotoxicity in humans.

Animals↗

PubMed2000

Prevention of dopaminergic neurotoxicity by targeting nitric oxide and peroxynitrite: implications for the prevention of methamphetamine-induced neurotoxic damage.

Methamphetamine (METH) is a neurotoxic psychostimulant that produces catecholaminergic brain damage by producing oxidative stress and free radical generation. The role of oxygen and nitrogen radicals is well documented as a cause of METH-induced neurotoxic damage. In this study, we have obtained evidence that METH-induced neurotoxicity is the resultant of interaction between oxygen and nitrogen radicals, and it is mediated by the production of peroxynitrite. We have also assessed the effects of inhibitors of neuronal nitric oxide synthase (nNOS) as well as scavenger of nitric oxide and a peroxynitrite decomposition catalyst. Significant protective effects were observed with the inhibitor of nNOS, 7-nitroindazole (7-NI), as well as by the selective peroxynitrite scavenger or decomposition catalyst, 5,10,15,20-tetrakis(2,4,6-trimethyl-3,5-sulfonatophenyl)porphyrinato iron III (FeTPPS). However, the use of a nitric oxide scavenger, 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO), did not provide any significant protection against METH-induced hyperthermia or peroxynitrite generation and the resulting dopaminergic neurotoxicity. In particular, treatment with FeTPPS completely prevented METH-induced hyperthermia, peroxynitrite production, and METH-induced dopaminergic depletion. Together, these data demonstrate that METH-induced dopaminergic neurotoxicity is mediated by the generation of peroxynitrite, which can be selectively protected by nNOS inhibitors or peroxynitrite scavenger or decomposition catalysts.

3,4-Dihydroxyphenylacetic Acid↗

PubMed2000

Application of electrophysiological method to study interactions between ibogaine and cocaine.

The psychoactive indole alkaloid, ibogaine (IBO), has been investigated for over a decade concerning its reported anti-addictive properties for opioids as well as psychomotor stimulants. The mechanism for the anti-addictive action of IBO is still unclear. IBO interactions with opioid, NMDA, nicotinic, adrenergic, and serotonergic receptor sites have been suggested. The involvement of the dopaminergic system in IBO action is well documented. Increased or decreased levels of dopamine (DA) in specific brain regions following IBO pretreatment have been seen concomitantly with increased or decreased motor activity after subsequent amphetamine or cocaine administration. In this report, in vivo electrophysiological measures were monitored in awake adult male rats in order to investigate alterations of the electrocorticogram (ECoG) resulting from interactions between IBO and cocaine (COC). Rats were implanted bilaterally with bipolar ECoG electrodes. They were either injected with saline, COC alone (20 mg/kg, i.p.) or IBO (50 mg/kg, i.p.) and COC 1 hr later. The concentrations of DA, 5-HT, and their metabolites DOPAC, HVA, and 5-HIAA were assessed in the caudate nucleus in separate groups of saline-, COC-, and IBO/COC-treated rats. An alpha1 power increase was observed within 10 min after COC injection, which lasted for less than 20 min. A desynchronization over alpha2 and both beta power bands was observed throughout the recording. In IBO/COC-treated rats, a significant increase in delta, theta, and alpha1 power occurred within 20 min after COC injection (p <0.05). This effect lasted for up to an hour. DA levels significantly increased after COC only and decreased after IBO administration. A further decrease in levels of DA was observed in IBO/COC-treated rats. DA turnover increased significantly after IBO alone but was not observed after IBO/COC treatment. The alterations in ECoG and neurotransmitter levels suggest a decreased response to COC following IBO pretreatment.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1999

Incorporation of 3'-azido-3'-deoxythymidine (AZT) into fetal DNA and fetal tissue distribution of drug after infusion of pregnant late-term rhesus macaques with a human-equivalent AZT dose.

In the United States, the nucleoside analogue drug 3'-azido-3'deoxythymidine (AZT; also called zidovudine or ZDV) is given to most pregnant women who produce a positive test result for HIV-1. To investigate transplacental distribution and genotoxicity of AZT, near-term pregnant rhesus (Macaca mulatta) monkeys and their fetuses were studied. Four pregnant monkeys were continuously infused with 8 mg AZT/kg body weight for the 4 hours just prior to hysterotomy at term. This short-term AZT exposure resulted in AZT incorporation into DNA of fetal liver, lung, heart, skeletal muscle, brain, testis, and placenta, which varied between 29 and 1944 molecules of AZT/10(6) nucleotides. In contrast, values for AZT and combined metabolites, determined by radioactivity, varied between 0.94 and 5.20 microg AZT equivalents/g tissue. A fifth animal, (H076), was infused with 17.3 mg AZT/kg body weight for approximately 3 hours, followed by 1 hour without drug before hysterotomy. Similar to the 4 other monkeys, variable levels of AZT (16-147 molecules of AZT/10(6) nucleotides) were incorporated into organ DNA of H076, whereas organ tissues contained less-variable levels of AZT and metabolites (0.86-2.05 microg AZT equivalents/g tissue). For H076, at hysterotomy 1 hour after discontinuation of drug, values for AZT and the 3'-azido-3'-deoxythymidine-beta-D-glucuronide (AZTG) in fetal blood and amniotic fluid were twofold and threefold higher than those in maternal blood. Most AZT pharmacokinetic parameters in the fifth monkey were similar to those previously reported for the first 4 monkeys and those observed in a similar study of pregnant women. These data show that a short-term AZT infusion in pregnant rhesus monkeys, which have similar AZT pharmacokinetics to those present in a pregnant human, results in incorporation of drug into the DNA of placenta and most fetal organs. Data imply that the human fetus may also be subject to incorporation of AZT into DNA even after short-term AZT infusion to the mother just before delivery.

Animals↗

PubMed1999

Hyperthermia-enhanced serotonin (5-HT) depletion resulting from D-fenfluramine (D-Fen) exposure does not evoke a glial-cell response in the central nervous system of rats.

D-Fen-induced hyperthermia has been shown to coincide with an enhanced depletion of 5-HT and 5-hydroxyindole acetic acid (5-HIAA). Because these observations have relied on D-Fen exposure at multiple environmental temperatures, some have questioned the validity of the findings. Therefore, this experiment was designed to determine if the correlation between elevated body temperature and 5-HT depletion could be observed when D-Fen exposure occurred in one warm environment (28 degrees C) and to determine if a hyperthermia-enhanced glial-cell response could be evoked by D-Fen exposure. Hyperthermia-enhanced 5-HT and 5-HIAA depletion resulting from D-Fen exposure was dependent on body temperature during drug exposure. In the frontal cortex, 5-HT concentrations ranged from 3 to 45% of control values. Likewise, in the striatum and hippocampus, 5-HT concentrations ranged from 13 to 53% and 6 to 40%, respectively. The 5-HIAA concentrations had a wider range than the 5-HT concentrations for each brain region. In the frontal cortex, striatum and hippocampus, 5-HIAA ranged from 0 to 93%, 15 to 72% and 0 to 83% of control, respectively. In spite of the substantial reductions in 5-HT, there was no detectable glial-cell response. D-Fen-induced hyperthermia does not appear to cause generalized damage to neurons in the frontal cortex, striatum and hippocampus.

Animals↗

PubMed1999

Black-gold: a simple, high-resolution histochemical label for normal and pathological myelin in brain tissue sections.

A novel haloaurophosphate complex called Black-Gold has been synthesized and applied to localize myelin within the central nervous system. The technique is tailored to studies using formalin fixed non-solvent processed tissue. The technique stains large myelinated tracts dark red-brown, while the individual myelinated axons appear black. This study demonstrates how this novel tracer can be used to localize both normal and pathological myelin. Specific myelin changes associated with exposure to diverse neurotoxicants including kainic acid, domoic acid, 3-nitropropionic acid, Fluoro-Gold and isoniazid are demonstrated and characterized. This study also demonstrates how Black-Gold can be combined with other histochemical markers including Nissl stains, retrogradely transported fluorescent tracers and fluorescent markers of neuronal degeneration. Advantages associated with the Black-Gold technique include high resolution, high contrast, short histochemical processing time, and consistent reproducibility.

Animals↗

PubMed1999

Methamphetamine generates peroxynitrite and produces dopaminergic neurotoxicity in mice: protective effects of peroxynitrite decomposition catalyst.

Methamphetamine (METH)-induced dopaminergic neurotoxicity is believed to be produced by oxidative stress and free radical generation. The present study was undertaken to investigate if METH generates peroxynitrite and produces dopaminergic neurotoxicity. We also investigated if this generation of peroxynitrite can be blocked by a selective peroxynitrite decomposition catalyst, 5, 10,15, 20-tetrakis(N-methyl-4'-pyridyl)porphyrinato iron III (FeTMPyP) and protect against METH-induced dopaminergic neurotoxicity. Administration of METH resulted in the significant formation of 3-nitrotyrosine (3-NT), an in vivo marker of peroxynitrite generation, in the striatum and also caused a significant increase in the body temperature. METH injection also caused a significant decrease in the concentration of dopamine (DA), 3, 4-dihydroxyphenylacetic acid (DOPAC), and homovanillic acid (HVA) by 76%, 53% and 40%, respectively, in the striatum compared with the control group. Treatment with FeTMPyP blocked the formation of 3-NT by 66% when compared with the METH group. FeTMPyP treatment also provided significant protection against the METH-induced hyperthermia and depletion of DA, DOPAC and HVA. Administration of FeTMPyP alone neither resulted in 3-NT formation nor had any significant effect on DA or its metabolite concentrations. These findings indicate that peroxynitrite plays a role in METH-induced dopaminergic neurotoxicity and also suggests that peroxynitrite decomposition catalysts may be beneficial for the management of psychostimulant abuse.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1999

Ibogaine blocked methamphetamine-induced hyperthermia and induction of heat shock protein in mice.

Body temperature changes and heat shock protein (HSP-72) induction in the caudate nucleus were studied in female C57BL/6N mice pretreated with ibogaine (50 mg/kg) and sacrificed 48 h. after a single dose of methamphetamine (20 mg/kg). Methamphetamine injection resulted in hyperthermia and induced HSP-72 expression, whereas treatment with ibogaine alone produced hypothermia. The ibogaine followed by methamphetamine injection showed no hyperthermia and decreased HSP-72 expression. These data indicate that pretreatment with ibogaine can completely block methamphetamine-induced hyperthermia and HSP-72 expression in the striatum.

Animals↗

PubMed1999

Selenium, an antioxidant, protects against methamphetamine-induced dopaminergic neurotoxicity.

Dopaminergic changes were studied in the caudate nucleus of adult female mice after pre- and post-treatment with an antioxidant, selenium, 72 h after the multiple injections of methamphetamine (METH, 4x10 mg/kg, i.p. at 2-h interval) or an equivalent volume of saline. Selenium treatment prevented the depletion of dopamine (DA) and its metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in caudate nucleus resulting from the METH treatment. These data suggest that METH-induced neurotoxicity is mediated by free radical and selenium plays a protective role against METH-induced dopaminergic neurotoxicity.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1999

Reduced levels of catalase activity potentiate MPP+-induced toxicity: comparison between MN9D cells and CHO cells.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) has been shown to be toxic by inducing oxygen free radicals in the mammalian nervous system, especially in the nigrostriatal dopaminergic system. The present study was designed to compare the toxic effects of MPP+, the active metabolite of MPTP, in MN9D neuronal cells that exhibit relatively low levels of catalase activity, as compared to CHO cells, which exhibit high levels of catalase activity. The survival of the MN9D cells in the presence of 250 microM MPP+ was less than 10%, whereas CHO cells exhibited 70% survival at the same concentration of MPP+. The ED50 values of MPP+ in MN9D and CHO cell lines were 60-600 microM, respectively. MN9D cells contain less catalase, an enzyme believed to be involved in the detoxification of free radicals compared to CHO cells. The catalase activity was 2 Units/mg protein in MN9D cells and 30 U/mg protein in CHO cells. The catalase activity in CHO cells increased with increasing MPP+ concentrations from 100-500 microM, however, it decreased at 1 mM MPP+. In contrast, catalase activity in MN9D remained the same at all MPP+ concentrations. When the CHO cells were pre-treated with 10-25 mM 3-aminotriazole (3-AT), which inhibits catalase activity, and exposed to MPP+ at various concentrations, they became susceptible to MPP+. It is evident from these data that the differential susceptibility to MPP+ in these two cell lines are due to differences in catalase activity. In addition, the inhibition of constituentive catalase activity in CHO cells by 3-AT treatment enhances their susceptibility. In conclusion, the study demonstrates that catalase activity represents an important defence mechanism in MPTP-induced toxicity.

1-Methyl-4-phenylpyridinium↗

PubMed1999

Hyperthermia-enhanced serotonin (5-HT) depletion resulting from d-fenfluramine exposure is preventable.

Recent findings indicate that elevations in body temperature during acute d-fenfluramine (Fen) exposure enhance long-term 5-HT depletion. Therefore, we hypothesized that when repeated exposure to d-Fen produced repeated elevations in body temperature, 5-HT reductions would be greater in comparison to a single d-Fen exposure. Groups of animals were exposed to d-Fen for 1 or 4 days in a 28 degrees C environment. Exposure to d-Fen in the 28 degrees C environment induced an increase in body temperature and resulted in a long-term decrease in brain 5-HT. However, brain 5-HT was not different between the two groups. An additional experiment revealed that if the initial exposure to d-Fen does not induce elevations in body temperature, then long-term 5-HT depletion can be prevented. We conclude that the central nervous system rapidly adapts to the 5-HT depleting action of d-Fen thereby preventing further decreases in 5-HT concentrations from d-Fen exposure. In addition, this rapid adaptation circumvented the hyperthermia-enhanced 5-HT depletion that results from d-Fen exposure in a warm environment.

Animals↗

PubMed1999

Effect of manganese on the concentration of amino acids in different regions of the rat brain.

The present study was designed to determine if chronic exposure of weanlings and adult rats to Mn produces significant alterations in amino acid concentrations in different regions of the rat brain. Weanling (30 day old) and adult (90 day old) male rats were exposed to 10 and 20 mg Mn/kg body weight per day, by gavage, for 30 days. Forty-eight hours after the last dose, animals were sacrificed by decapitation and brains were dissected into different regions to determine the concentration of amino acids by HPLC/EC. A dose dependent decrease in body weight gain was found in the adult, but not in the weanling rats. Significant increases occurred in concentrations of aspartate, glutamate, glutamine, taurine and gamma-aminobutyric acid (GABA) in the cerebellum of the adult rats dosed with 20 mg/kg per day, Mn. A significant decrease in the concentration of glutamine was observed in caudate nucleus and hippocampus of weanling rats dosed with 10 mg/kg, Mn. These data suggest that chronic Mn exposure can produce a decrease in body weight gain in adult rats and alterations in amino acids in different regions of weanling and adult rat brains.

Amino Acids↗

PubMed1999

d-Fenfluramine produces neuronal degeneration in localized regions of the cortex, thalamus, and cerebellum of the rat.

d-Fenfluramine is a potent serotonin (5-HT) reuptake inhibitor/releaser and, until its recent recall, was prescribed as an anoretic agent. This study demonstrates that 10 mg/kg d-fenfluramine i.p., when administered to rats in a warm (27 degrees C) environment, produces neuronal degeneration within select brain regions. Degeneration was detected and localized using a recently developed fluorescent marker of neuronal degeneration, Fluoro-Jade. The most extensive cortical damage was in the anterior cingulate region. In the medial thalamus, degeneration was frequently seen within the intralaminar nuclei, and somewhat less frequently observed within the paraventricular nucleus, the mediodorsal nucleus, and the gelatinosis nucleus. Cerebellar damage occurred primarily in medial Purkinje cells and occasionally in granule cells or basket cells. Degeneration was not observed in either saline-injected control animals or in rats given even higher doses of 25 mg/kg d-fenfluramine but kept in a cooler environment (23 degrees C). The degeneration was clearly most prominent in animals with body temperatures of 41 degrees to 42 degrees C, but this degeneration was not seen in animals given saline that became extremely hyperthermic in a 37 degrees C environment. Behavioral signs such as tremors, myoclonus, rigidity, and splayed legs were seen in all animals with extensive neurodegeneration. The areas damaged by d-fenfluramine, when hyperthermia occurs, could play a role in the expression of the serotonin syndrome. Elevated extracellular 5-HT levels alone are probably not sufficient for neurotoxicity, and additional factors such as hyperthermia, regional specificity of 5-HT receptor subtypes, blood flow, and/or neuronal networks may be involved.

Animals↗

PubMed1998

Biologically-based dose-response model for neurotoxicity risk assessment.

Domoic acid is a tricarboxylic amino acid that is structurally-related to kainic acid and glutamic acid. It is produced by phytoplankton that may contaminate seafood. To determine domoate's toxicological effects and their pathogenesis, cynomolgus monkeys were dosed intravenously at one of a range of bolus doses from 0.25 to 4.0 mg/kg. Histochemical staining, using silver methods, revealed degenerating axons and cell bodies. Doses in the range of 0.5-1.0 mg/kg produced a small area of silver grains restricted to axons of the hippocampal CA2 stratum lucidum, the most sensitive brain area identified. Quantitation of the abundance of these silver grains yielded continuous dose-response data. A four step quantitative risk estimation approach was used: (1) determination of a dose-response model; (2) determination of the distribution of measurements (variability) about the model; (3) determination of an adverse or abnormal level with the use of the control data; and (4) estimation of the probability that a measure is beyond the abnormal level as a function of dose. The currently used safety-factor (S-F) approach, the benchmark (BM) approach and this quantitative (Q) approach was used to assess the same data set. Assuming a 5% oral absorption of domoic acid, acceptable doses would be achieved if subjects ate 200 g of seafood containing 12, 6 and 10 ppm domoic acid for the S-F, BM and Q approaches, respectively. This quantitative approach uses all the available data, takes into account the variability of the data and provides an actual risk at a given dose of domoic acid.

Animals↗