Functional Observational Battery Research Articles

Subchronic Inhalation Toxicity and Neurotoxicity Assessment of Cumene in Fischer 344 Rats

Male and female Fischer 344 rats were exposed to cumene vapor at 0, 100, 500, and 1,200 ppm for 6 h per day, 5 days per week, for 13 weeks; a satellite group received a single 6-h exposure. A subsequent 13-week study with a 4-week recovery period was conducted at 0, 50, 100, 500, and 1,200 ppm. Following the single exposure, the functional observational battery was altered at 500 and 1,200 ppm through 6 h postexposure. In the subchronic studies, there were no exposure-related changes in the functional observational battery, auditory brain stem response, brain measurements, or nervous system histopathology. Motor activity decreases seen only in male rats exposed to 500 or 1,200 ppm in the first study were not replicated in the second study. The 500-and/or 1,200-ppm groups showed transient decreases in body weight gain and food consumption, an increase in water consumption, and changes in several hematologic and clinical chemistry parameters. There were no exposure-related ophthalmologic findings or effects on spermatogenesis. Weights of liver, kidneys, and adrenal glands were increased in the 500- and 1,200-ppm groups. Renal proximal tubular cell hypertrophy, hyperplasia, and hyaline drop formation were observed in the male rats at 500 and 1,200 ppm. In conclusion, exposure to cumene vapor resulted in mild toxicity at 1,200 ppm, minimal effects at 500 ppm, and no observable effects at 50 and 100 ppm. Cumene vapor exposure was neither neurotoxic nor ototoxic in these studies.

Acute and subchronic neurotoxicity studies with tri-N-butyl phosphate in adult Sprague-Dawley rats.

Male and female adult Sprague-Dawley rats received tributyl phosphate (TBP) in corn oil by gavage in acute (single-dose) and subchronic (three-month) studies. Dosage levels in the acute study were 100, 325, and 1000 mg/kg; they were 32.5, 100, and 325 mg/kg/day in the subchronic study. Behavioral evaluations were performed in both studies, and neuropathological evaluations were performed in the three-month study only. The methods used in the studies are as described in the U.S. Environmental Protection Agency neurotoxicity guidelines. Mean body weight decreases were statistically significant compared to controls for male rats at the high-dosage level only in the acute study. Transient changes only, attributable to the general toxicity of the material, were noted in forelimb grip strength and mean activity level during the first 24 hours after dosing for 1000 mg/kg rats. In the subchronic study high-dose males and females had statistically significant body weight decreases; some mortality also was observed at this dosage level. The motor activity levels and qualitative and quantitative functional observational battery measurements were comparable between treatment and control groups, and there were no gross or neurohistopathological findings in the rats indicative of treatment-related effects. Based on these study results, TBP was not neurotoxic to rats following either acute or subchronic exposures.

Acute and Subchronic Neurotoxicity Studies with Tri-n-butyl Phosphate in Adult Sprague-Dawley Rats

Male and female adult Sprague-Dawley rats received tributyl phosphate (TBP) in corn oil by gavage in acute (single-dose) and subchronic (three-month) studies. Dosage levels in the acute study were 100, 325, and 1000 mg/kg; they were 32.5, 100, and 325 mg/kg/day in the subchronic study. Behavioral evaluations were performed in both studies, and neuropathological evaluations were performed in the three-month study only. The methods used in the studies are as described in the U.S. Environmental Protection Agency neurotoxicity guidelines. Mean body weight decreases were statistically significant compared to controls for male rats at the high-dosage level only in the acute study. Transient changes only, attributable to the general toxicity of the material, were noted in forelimb grip strength and mean activity level during the first 24 hours after dosing for 1000 mg/kg rats. In the subchronic study high-dose males and females had statistically significant body weight decreases; some mortality also was observed at this dosage level. The motor activity levels and qualitative and quantitative functional observational battery measurements were comparable between treatment and control groups, and there were no gross or neurohistopathological findings in the rats indicative of treatment-related effects. Based on these study results, TBP was not neurotoxic to rats following either acute or subchronic exposures.

Toxicological and Chemical Evaluation of Emissions From Carpet Samples

This study investigated findings that the off-gassing of certain carpets caused sensory and pulmonary irritation, changes in neurobehavioral signs, and death in exposed mice. Two standard test method measures--one for estimating sensory irritancy (ASTM-E981-84), the other for evaluating the neurotoxic potential of chemicals (functional observational battery)--were coupled with a postmortem assessment to ascertain the mechanism of toxicity. The postmortem evaluation included measurements of hemoglobin, serum clinical chemistries, blood and lung lavage white cell counts and differential, organ weights, and a gross necropsy with a microscopic evaluation of all major organs. The study evaluated three treatment groups composed of two preheated carpet emission exposures and one preheated air-control exposure. No toxic effects were associated with exposure to the off-gassing of the two tested carpets. Clinical chemistry and histopathological alterations were observed with exposure to either filter-air or carpet when compared to nonexposed unrestrained control mice, indicating that the exposure procedure caused significant effects unrelated to carpet emissions. A detailed chemical and microbial evaluation of the carpets and carpet emissions showed volatile organic compounds, pesticide residues, and microbiological flora, but at insufficient quantities to result in acute toxicity. Based on this assessment, there was no indication that exposure to emissions from these two carpets poses a serious health risk.

Toxicological and Chemical Evaluation of Emissions From Carpet Samples

This study investigated findings that the off-gassing of certain carpets caused sensory and pulmonary irritation, changes in neurobehavioral signs, and death in exposed mice. Two standard test method measures—one for estimating sensory irritancy (ASTM-E981-84), the other for evaluating the neurotoxic potential of chemicals (functional observational battery)—were coupled with a postmortem assessment to ascertain the mechanism of toxicity. The postmortem evaluation included measurements of hemoglobin, serum clinical chemistries, blood and lung lavage white cell counts and differential, organ weights, and a gross necropsy with a microscopic evaluation of all major organs. The study evaluated three treatment groups composed of two preheated carpet emission exposures and one preheated air-control exposure. No toxic effects were associated with exposure to the off-gassing of the two tested carpets. Clinical chemistry and histopathological alterations were observed with exposure to either filter-air or carpet when compared to nonexposed unrestrained control mice, indicating that the exposure procedure caused significant effects unrelated to carpet emissions. A detailed chemical and microbial evaluation of the carpets and carpet emissions showed volatile organic compounds, pesticide residues, and microbiological flora, but at insufficient quantities to result in acute toxicity. Based on this assessment, there was no indication that exposure to emissions from these two carpets poses a serious health risk.

Evaluation of a method used to test for potential toxicity of carpet emissions

After a private testing laboratory had reported mortality, neurotoxicity, and respiratory irritation in mice exposed to emissions from heated carpet in a modified application of the sensory irritation test (ASTM E981-84), the studies reported in this paper were conducted to evaluate the method used in testing for carpet toxicity and to see if the reported findings were reproducible. Mice were exposed head-only to offgasses generated by heating carpet (AT # 3) to temperatures that ranged from 37 to 70°C. Control mice were simultaneously exposed to heated air. The animals were evaluated for mortality, clinical signs and respiratory irritation. Neurotoxicity was evaluated using functional observational battery and motor activity monitoring. Pathological evaluations of organs and tissues, including the nervous system, were also conducted. The carpet samples heated to higher temperatures produced greater concentrations of total volatile organic compounds than those heated to 37°C. Both carpet-exposed and control mice displayed some effects, such as body weight loss, mortality and pathological lesions, that were due to the exposure system. There was no mortality or neurotoxicity, nor were there clinical signs or pathological lesions as a result of carpet exposures. Mice exposed to carpet heated to 70°C had slightly decreased respiratory rates and an increased incidence of breathing patterns indicative of sensory irritation. Therefore, none of the results reported by the private testing laboratory could be reproduced when this carpet was heated to temperatures below 70°C, and slight sensory irritation was the only effect observed at the 70°C test conditions. Effects from the exposure system itself made interpretation of results difficult, and concurrent controls were considered essential for interpretation of data.

Isopropanol 13-Week Vapor Inhalation Study in Rats and Mice with Neurotoxicity Evaluation in Rats

Isopropanol 13-Week Vapor Inhalation Study in Rats and Mice with Neurotoxicity Evaluation in Rats. Burleighflayer, H. D., Gill, M. W., Strother, D. E., Masten, L. W., McKee, R. H., Tyler, T. R., and Gardiner, T. (1994). Fundam. Appl. Toxicol. 23, 421-428.This study was conducted to evaluate the possible subchronic toxicity as well as neurobehavioral effects of isopropanol, a widely used industrial and commercial solvent. Five groups, each containing 10 Fischer 344 rats/sex and 10 CD-1 mice/sex, were exposed for 6 hr/day, 5 days/week, for 13 weeks to isopropanol vapor at concentrations of 0 (control), 100, 500, 1500, or 5000 ppm. An additional 15 rats/sex were assigned to the 0, 500, 1500, and 5000 ppm groups for assessment of neurobehavioral function. No exposure-related mortalities occurred during the study. The narcotic effects of isopropanol were noted only during exposures at 1500 and 5000 ppm. These signs, noted during exposures, were typically absent following exposures. The only clinical signs observed following exposures included swollen periocular tissue, perinasal encrustation, and ataxia for rats of the 5000 ppm group. Neurobehavioral evaluations indicated no changes in any of the parameters of the functional observational battery; however, increased motor activity for female rats in the 5000 ppm group was noted at Weeks 9 and 13. Decreases in body weight and body weight gain were observed for rats of the 5000 ppm group at the end of the first week of exposure. During the remaining weeks, increases in body weight and/or body weight gain were observed for rats of the 1500 and 5000 ppm groups. No exposure-related effects on body weight were noted for male mice; however, increased body weight and body weight gain were observed for female mice of the 5000 ppm group. Increases or decreases in food and water consumption generally corresponded to changes in body weight and body weight gain. Various changes in clinical pathology parameters were observed for rats and female mice of the 5000 ppm group. The only organ weight effect noted was an increased relative liver weight in both sexes of rats and female mice of the 5000 ppm group. At necropsy, there were no gross lesions determined to be exposure related. Furthermore, the only micro, scopic change observed was hyaline droplets within the kidneys of all male rats (including controls). The size and frequency of the hyaline droplets were increased for the isopropanol exposure groups compared to the control group. These differences were not clearly concentration related, although this microscopic change was most pronounced in the high-concentration group. Neuropathologic examination revealed no exposure-related lesions in the central or peripheral nervous system of exposed rats. Thus, repeated exposures to isopropanol for 13 weeks produced toxic effects only at the highest concentration and a kidney change in male rats of unknown biological significance.

A Comparison of the Acute Behavioral Effects of Alkylbenzenes Using a Functional Observational Battery in Mice

A Comparison of the Acute Behavioral Effects of Alkylbenzenes Using a Functional Observational Battery in Mice. Tegeris, J. S., and Balster, R. L. (1994). Fundam. Appl. Toxicol. 22, 240-250.The acute neurobehavioral effects of six alkylbenzenes (benzene, toluene, ethylbenzene, propylbenzene, m-xylene, and cumene) were evaluated alter 20-min inhalation exposures using a functional observational battery (FOB) in mice. In order to do this, an explicit protocol for the FOB developed for rats by Moser was adapted for use in mice with inhalation exposures. All six alkylbenzenes, in the concentration range of 2000 to 8000 ppm, produced a nearly identical profile of effects, a profile that was also produced by ip administration of the central nervous system depressant drug pentobarbital. These effects included changes in posture, decreased arousal and rearing, increased ease of handling, disturbances of gait, mobility, and righting reflex, decreased forelimb grip strength, increased landing foot splay, and impaired psychomotor coordination. The response to various sensory stimuli was also decreased by the alkylbenzenes and pentobarbital. These acute effects of alkylbenzenes were short-lived, with recovery beginning within minutes of removal from the exposure chamber. The finding that the alkylbenzenes produce a profile of neurobehavioral effects similar to that of pentobarbital is consistent with a growing body of other evidence that many solvents produce a profile of acute effects similar to that of central nervous system depressant drugs and ethanol.

A Comparison of the Acute Behavioral Effects of Alkylbenzenes Using a Functional Observational Battery in Mice

The acute neurobehavioral effects of six alkylbenzenes (benzene, toluene, ethylbenzene, propylbenzene, m-xylene, and cumene) were evaluated after 20-mm inhalation exposures using a functional observational battery (FOB) in mice. In order to do this, an explicit protocol for the FOB developed for rats by Moser was adapted for use in mice with inhalation exposures. All six alkylbenzenes, in the concentration range of 2000 to 8000 ppm, produced a nearly identical profile of effects, a profile that was also produced by ip administration of the central nervous system depressant drug pentobarbital. These effects included changes in posture, decreased arousal and rearing, increased ease of handling, disturbances of gait, mobility, and righting reflex, decreased forelimb grip strength, increased landing foot splay, and impaired psychomotor coordination. The response to various sensory stimuli was also decreased by the alkylbenzenes and pentobarbital. These acute effects of alkylbenzenes were short-lived, with recovery beginning within minutes of removal from the exposure chamber. The finding that the alkylbenzenes produce a profile of neurobehavioral effects similar to that of pentobarbital is consistent with a growing body of other evidence that many solvents produce a profile of acute effects similar to that of central nervous system depressant drugs and ethanol.

Assessing the Neurotoxic Potential of Methyl Ethyl Ketoxime in Rats

Assessing the Neurotoxic Potential of Methyl Ethyl Ketoxime in Rats. SCHULZE, G. E., AND DERELANKO, M. J. (1993). Fundam. Appl. Toxicol. 21, 476–485. The potential of methyl ethyl ketoxime (MEKO) to produce neurotoxicity following acute and subchronic exposure was studed in rats. A Functional Observational Battery, assessment of motor activity, and neuropathology evaluations were conducted in the context of acute and subchronic toxicity studies. Three independent studies are reported: a pilot time-effect study designed to determine the time course and time to peak effect following a single high dose of MEKO, a single-dose neurotoxicity study, and a subchronic (13-week) repeated-dose neurotoxicity study in rats. An acrylamide-positive control group was included in the acute and subchronic studies for comparison with MEKO. Following an acute oral exposure of MEKO at a dose level of 900 mg/kg, locomotor activity was decreased compared to control with maximum decreases occurring between 30 and 60 min following oral administration. In the acute study, transient treatment-related changes in ease of cage removal, ease of handling, and in posture and gait were observed 1 hr after dosing with 900 mg/kg MEKO, as were significant depressions in motor activity. Following a single 300 mg/kg dose, transient MEKO-related changes in gait and aerial righting reflex were noted 1 hr after dosing. All effects were reversible within 24 hr of dosing. The single 100 mg/kg dose of MEKO was without observable effects. No acrylamide-related behavioral effects were noted following a single 50 mg/kg dose. In the subchronic study, transient treatment-related changes in ease of cage removal, ease of handling, and in posture, gait, and aerial righting were observed at the 400 mg/kg/day dose level when assessments were conducted immediately after dose administration. No consistent behavioral effects were observed prior to daily dose administration even after 13 weeks of exposure, indicating a lack of cumulative behavioral effect. No consistent behavioral changes were noted at doses of 125 mg/kg/day and below. Significant dose-related decreases in red cell mass, and increases in methemoglobin levels, reticulocyte, leukocyte, Heinz body counts, and spleen weights occurred at subchronic MEKO doses of 40 mg/kg/day and higher. No MEKO-related neuropathological changes occurred. Animals receiving acrylamide at 20 mg/kg/day showed expected behavioral and neuropathological changes consistent with peripheral neuropathy. In conclusion, high doses of MEKO can produce transient and reversible changes in neurobehavioral function consistent with central nervous system (CNS) depression. No evidence of cumulative neurotoxicity was detected. The hematopoietic system was effected at doses which did not produce detectable changes in CNS function.

A neurotoxicity assessment of high flash aromatic naphtha.

Catalytic reforming is a refining process that converts naphthenes to aromatics by dehydrogenation to make higher octane gasoline blending components. A portion of this wide-boiling range hydrocarbon stream can be separated by distillation and used for other purposes. One such application is a mixture of predominantly 9-carbon aromatic molecules (C9 Aromatics, primarily isomers of ethyltoluene and trimethylbenzene), which is removed and used as a solvent also known as High Flash Aromatic Naphtha (HFAN). A program was initiated to assess the toxicological properties of HFAN since there may be human exposure, especially in the workplace. The current study was conducted to assess the potential for neurotoxicity in the rat. Adult male Sprague-Dawley rats of approximately 300 grams body weight, in groups of twenty, were exposed by inhalation to HFAN for 90 days at concentrations of 0, 100, 500, and 1500 ppm. During this period the animals were tested monthly for motor activity and in a functional observation battery. After three months of exposure, for 6 hours/day, 5 days/week, 10 animals/group/sex were sacrificed and selected nervous system tissue was examined histopathologically. No signs of neurotoxicity were seen in any of the evaluated parameters, nor was there evidence of pathologic changes in any of the examined tissues.

Assessing the Neurotoxic Potential of Methyl Ethyl Ketoxime in Rats

Assessing the Neurotoxic Potential of Methyl Ethyl Ketoxime in Rats. Schulze, G. E., and Derelanko, M. J. (1993). Fundam. Appl. Toxicol. 21, 476-485.The potential of methyl ethyl ketoxime (MEKO) to produce neurotoxicity following acute and subchronic exposure was studied in rats. A Functional Observational Battery, assessment of motor activity, and neuropathology evaluations were conducted in the context of the acute and subchronic toxicity studies. Three independent studies are reported: a pilot time-effect study designed to determine the time course and time to peak effect following a single high dose of MEKO, a single-dose neurotoxicity study, and a subchronic (13-week) repeated-dose neurotoxicity study in rats. An acrylamide-positive control group was included in the acute and subchronic studies for comparison with MEKO. Following an acute oral exposure of MEKO at a dose level of 900 mg/kg, locomotor activity was decreased compared to control with maximum decreases occurring between 30 and 60 min following oral administration. In the acute study, transient treatment-related changes in ease of cage removal, ease of handling, and in posture and gait were observed 1 hr after dosing with 900 mg/kg MEKO, as were significant depressions in motor activity. Following a single 300 mg/kg dose, transient MEKO-related changes in gait and aerial righting reflex were noted 1 hr after dosing. All effects were reversible within 24 hr of dosing. The single 100 mg/kg dose of MEKO was without observable effects. No acrylamide-related behavioral effects were noted following a single 50 mg/kg dose. In the subchronic study, transient treatment-related changes in ease of cage removal, ease of handling, and in posture, gait, and aerial righting were observed at the 400 mg/kg/day dose level when assessments were conducted immediately after dose administration. No consistent behavioral effects were observed prior to daily dose administration even after 13 weeks of exposure, indicating a lack of cumulative behavioral effect. No consistent behavioral changes were noted at doses of 125 mg/kg/day and below. Significant dose-related decreases in red cell mass, and increases in methemoglobin levels, reticulocyte, leukocyte, Heinz body counts, and spleen weights occurred at subchronic MEKO doses of 40 mg/kg/day and higher. No MEKO-related neuropathological changes occurred. Animals receiving acrylamide at 20 mg/kg/day showed expected behavioral and neuropathological changes consistent with peripheral neuropathy. In conclusion, high doses of MEKO can produce transient and reversible changes in neurobehavioral function consistent with central nervous system (CNS) depression. No evidence of cumulative neurotoxicity was detected. The hematopoietic system was effected at doses which did not produce detectable changes in CNS function.

Prolonged Neurobehavioral and Visual Effects of Short-Term Exposure to 3,3′-Iminodipropionitrile (IDPN) in Rats

Prolonged Neurobehavioral and Visual Effects of Short-Term Exposure to 3,3′-Iminodipropionitrile (IDPN) in Rats. Moser, V. C., and Boyes, W. K. (1993). Fundam. Appl. Toxicol. 21, 277-290.Strategies for neurotoxicity testing often include initial screening tests, such as a functional observational battery (FOB) and motor activity assessment, followed by detailed characterization studies. In this study, a neurobehavioral screening battery (FOB and motor activity) was used to evaluate the effects of 3-day repeated exposure to 0, 100, 200, or 400 mg/kg/day IDPN. Adult Long-Evans rats (males and females) were tested before dosing and 1, 14, 28, 56, and 91 days after the third dose. IDPN initially produced generalized CNS depression, weakness, and hypothermia. Thereafter, marked hyperactivity, increased excitability, decreased reactivity to visual and auditory stimuli, neuromuscular weakness, equilibrium changes, and a "waltzing syndrome" (vertical and lateral head movements, circling, and retropulsion) emerged and persisted for 3 months. Males were more severely affected than females. Following neurobehavioral testing, the rats were examined for visual function using flash (three intensities) and pattern (three pattern sizes by three contrast levels)-elicited visual evoked potentials (VEPs). IDPN produced changes in pattern- and flash-elicited VEPs, thus verifying predictions made from the screening tests. However, the extent of the VEP changes produced by IDPN was insufficient to account for some of the deficits detected in the FOB, which are dependent on sensory, integrative, and motor functions. Thus, profound neurological effects of IDPN were detected using this screening battery and visual effects were confirmed using VEPs. These effects, following only three doses of IDPN, lasted for at least 3 months and thus may be permanent.

Neurotoxicity Evaluation of N,N-Diethyl-m-toluamide (DEET) in Rats

Neurotoxicity Evaluation of N,N-Diethyl-m-toluamide (DEET) in Rats. Schoenig, G. P., Hartnagel, G. E., Jr., Schardein, J. L., and Vorhees, C. V. (1993). Fundam. Appl. Toxicol. 21, 355-365.The neurotoxic potential of N,N-diethyl-m-toluamide (DEET) was evaluated following acute oral administration or following multigeneration plus chronic dietary administration to the rat. For the acute study, rats were administered undiluted DEET at dose levels of 50, 200, or 500 mg/kg by gavage. A dose level of 500 mg/kg was considered to be the highest practical dose that could be evaluated in this study based upon observations of overt toxicity at 500 mg/kg and mortality at 1000 mg/kg in a dose range-finding study. The two measures of neurotoxicity evaluated in the acute study were functional observational battery (FOB) and motor activity measurements. An apparent treatment-related effect in thermal response time (increased) was noted for both sexes 1 hr after dosing at the 500 mg/kg dose level. A questionable effect on rearing activity (decreased) also was noted at the same dose level. For the multigeneration plus chronic dietary administration study, rats were administered DEET at dietary concentrations of 0, 500, 2000, or 5000 ppm continuously over two generations and then chronically for 9 months. A dietary concentration of 5000 ppm meets the criteria for a maximum tolerated dose (MTD) based on traditional chronic toxicology assessments. Evaluations included FOB, motor activity, discriminative acquisition and reversal in an M-maze, acoustic startle habituation, passive avoidance acquisition and retention, and microscopic examination of central and peripheral nervous tissue. The only effect that was considered to be possibly treatment-related was a slight increase in exploratory locomotor activity at the 5000 ppm dose level. Based on the results of these studies, the nervous system does not appear to be a selective target when DEET is administered to rats either as a single oral dose at high dose levels or chronically at the MTD.

Neurotoxicologic examination of rats exposed to 1,1,1-trichloroethane vapor for 13 weeks

Large evoked potential and EEG changes occurred in a pilot study in Fischer 344 rats during exposure to 2000 ppm of 1,1,1-trichloroethane (1,1,1-T; a cleaning solvent with anesthetic properties). In the main study, rats were evaluated for persistent nervous system effects the week following exposure to 0, 200, 630, or 2000 ppm 1,1,1-T for 6 h/day, 5 days/week, for 13 weeks. Rats were clinically examined regularly and were given a functional observational battery monthly (FOB, including forelimb and hindlimb grip performance testing). After 13 weeks of exposure, the rats were evaluated by FOB and by visual, auditory, somatosensory, and caudal nerve-evoked potentials. After functional testing, a subgroup of rats had histopathologic examination of brain, spinal cord, peripheral nerves, and limb muscles. There were no post-exposure treatment-related findings in any parameter (FOB observations plus 39 dependent variables) except for a slightly smaller forelimb grip performance in the 2000-ppm exposure group. There was no recognized toxicologic significance for the difference in forelimb grip performance; a lack of findings in any other clinical, evoked potential or morphologic parameter did not support a diagnosis of neurotoxicity.

Strategies for the Prevention of Environmental Neurotoxic Illness

Toxic chemicals in the environment can cause a wide range of neurological disease. High-dose exposures to environmental neurotoxicants have produced encephalopathy in children ingesting chips of lead-based paint, blindness in persons who ingested methanol, blindness and ataxia in persons who consumed organic mercury, spinal cord degeneration and peripheral neuropathy in persons exposed to triorthocresyl phosphate (TOCP), and Parkinsonism in persons exposed to MPTP or to manganese. Environmental neurotoxicants have also been shown to produce a wide range of subclinical neurotoxic effects, including reduction in intelligence, impairment in reasoning ability, shortening of attention span, and alternation of behavior. The first step in the prevention of environmental neurotoxicity is to test chemicals for their toxic potential. More than 70,000 chemicals are currently in commerce. However, except for pharmaceuticals, fewer than 10% of these chemicals have been tested for neurotoxicity. A logical approach to neurotoxicologic assessment of chemical substances will build on and extend currently available test systems. It will have a tiered structure. The first or screening tier will consist of tests to measure obvious structural and functional changes, often a functional observational battery. Subsequent levels of testing will be guided by the results of initial screening. Toxicologic testing must be supplemented by epidemiologic surveillance of populations exposed to known and suspect neurotoxicants. Screening programs in these populations designed to detect excessive absorption of a neurotoxic agent or subclinical neurological dysfunction can be useful in identifying affected individuals before severe disability occurs.

Toxicology of Diethylene Glycol Butyl Ether 5. Dermal Subchronic Neurotoxicity Study in Rats

Groups of Sprague-Dawley rats were treated dermally with the vehicle, distilled water or with diethylene glycol butyl ether (DGBE) at 10 or 30% v/v aq. solutions or undiluted (0.2, 0.6, or 2.0 g/kg body weight) for 13 weeks under occlusion 6 hr/day, 5 days/week, at the maximum attainable volume of 2 mL/kg. Male and female rats were examined using a functional observational battery (FOB) prestudy, at 1, 6, and 24 hr after the initiation of the first exposure, and prior to treatment on days 7, 14, 35, 63, and 91. Motor activity was determined prestudy and on nontreated days 34, 62, and 90. At the completion of treatment, six control and top dose group animals were perfused for neuropathology. There was no mortality, and the body weights and food consumption were unaffected. Five females in the top dose group had scab formation at the treatment site during the study. There were no other treatment-related clinical findings. The FOB and motor activity tests revealed no findings indicative of a neurotoxic effect, and there were no gross or neuropathological changes that were attributed to treatment. No neurotoxicity or other systemic toxicity was seen at the highest dose tested—2 g/kg/day.

Utility of a neurobehavioral screening battery for differentiating the effects of two pyrethroids, permethrin and cypermethrin

The ability of a neurobehavioral screening battery to differentiate the effects of two pyrethroids, permethrin and cypermethrin, was assessed in this experiment. Although the structures of these pesticides differ only in the α-cyano group, the behavioral syndromes associated with the Type I and II pyrethroids are quite different. The tests included a functional observational battery which is a series of subjective and quantitative measures of neurological function and behavior, and an automated measure of motor activity. Our results verified previous reports in the literature describing these different syndromes, i.e., aggressive sparring behavior, fine to whole-body tremor, hyperthermia, and decreased motor activity for the Type I pyrethroid permethrin, and pawing, burrowing, salivation, whole body tremor to choreoathetosis, hypothermia, and lowered motor activity for the Type II pyrethroid cypermethrin. In addition, we report that permethrin produced decreased grip strengths, increased resistance to capture, increased reactivity to a click stimulus, and induced head and forelimb shaking and agitated behaviors, whereas cypermethrin produced pronounced neuromuscular weakness and equilibrium changes, retropulsion, lateral head movements, alterations in responses to various stimuli, and increased urination. Although there were similarities in some effects (e.g., decreased motor activity), the pesticides differed sufficiently in their overall behavioral profiles, and severity and time course of effects, to discriminate these two compounds. Thus, this type of screening approach is sensitive enough to differentiate these pyrethroids for hazard identification purposes.

Prolonged Neurobehavioral and Visual Effects of Short-Term Exposure to 3,3'-lminodipropionitrile (IDPN) in Rats

Strategies for neurotoxicity testing often include initial screening tests, such as a functional observational battery (FOB) and motor activity assessment, followed by detailed characterization studies. In this study, a neurobehavioral screening battery (FOB and motor activity) was used to evaluate the effects of 3-day repeated exposure to 0, 100, 200, or 400 mg/kg/day IDPN. Adult Long-Evans rats (males and females) were tested before dosing and 1,14, 28, 56, and 91 days after the third dose. IDPN initially produced generalized CNS depression, weakness, and hypothermia. Thereafter, marked hyperactivity, increased excitability, decreased reactivity to visual and auditory stimuli, neuromuscular weakness, equilibrium changes, and a “waltzing syndrome” (vertical and lateral head movements, circling, and retropulsion) emerged and persisted for 3 months. Males were more severely affected than females. Following neurobehavioral testing, the rats were examined for visual function using flash (three intensities) and pattern (three pattern sizes by three contrast levels)-elicited visual evoked potentials (VEPs). IDPN produced changes in pattern- and flash-elicited VEPs, thus verifying predictions made from the screening tests. However, the extent of the VEP changes produced by IDPN was insufficient to account for some of the deficits detected in the FOB, which are dependent on sensory, integrative, and motor functions. Thus, profound neurological effects of IDPN were detected using this screening battery and visual effects were confirmed using VEPs. These effects, following only three doses of IDPN, lasted for at least 3 months and thus may be permanent.

Short-term Clinical and Neuropathologic Effects of Cholinesterase Inhibitors in Rats

Adult male Long Evans rats were given a single administration of 3 dosage levels of the organophosphorus compounds tri-ortho-tolyl phosphate (TOTP), diisopropyl fluorophosphate (DFP), phenyl saligenin phosphate (PSP), mipafox, malathion, and dichlorvos or the carbamate carbaryl. Acetylcholinesterase and neurotoxic esterase activities were inhibited in a dose-dependent manner, with the highest dosages of all of these compounds inhibiting activities of these enzymes in brain by at least 37% and 64%, respectively, at 4 and 48 hours after administration. Rats given the high doses of TOTP (1000 mg/kg), DFP (3 mg/kg), malathion (2000 mg/kg), and carbaryl (160 mg/kg) weighed significantly less than control rats 14 days after administration. A functional observational battery (FOB) was used to screen for neurotoxic effects 1, 2, and 3 weeks after exposure. All 7 test compounds were capable of causing changes in parameters indicative of behavioral and central nervous system excitability. In addition, dose-related alterations in response to approach were seen in rats given DFP, malathion, dichlorvos, and carbaryl. Mild to moderate myelinated fiber degeneration was seen in the rostral levels of the fasciculus gracilis in rats given TOTP, DFP, PSP and mipafox, but no significant neuropathologic lesions were noted in rats given dichlorvos, malathion, or carbaryl.