Behavioral evaluation of rats following low-level inhalation exposure to sarin

We evaluated the effects, in rats, of single and multiple low-level inhalation exposures to sarin. Rats were trained on a variable-interval, 56 s (VI56) schedule of food reinforcement and then exposed to sarin vapor (1.7-4.0 mg/m(3) x 60 min) or air control. The exposures did not produce clinical signs of toxicity other than miosis. Subsequently, performance on the VI56 and acquisition of a radial-arm maze spatial memory task was evaluated over approximately 11 weeks. Single exposures did not affect performance on the VI56 and had little effect on acquisition of the radial-arm maze task. Multiple exposures (4.0 mg/m(3) x 60 min/day x 3) disrupted performance on the VI56 schedule during the initial post-exposure sessions. The disruption, however, resolved after several days. Multiple exposures also produced a deficit on the radial-arm maze task in that sarin-exposed rats tended to take it longer to complete the maze and to make more errors. The deficit, however, resolved during the first three weeks of acquisition. These results demonstrate that in rats, inhalation exposure to sarin at levels below those causing overt signs of clinical toxicity can produce cognitive and performance deficits. Furthermore, the observed deficits do not appear to be persistent.     

Acute pulmonary toxicity following inhalation exposure to aerosolized VX in anesthetized rats

ABSTRACT

This study evaluated acute toxicity and pulmonary injury in rats at 3, 6 and 24?h after an inhalation exposure to aerosolized O-ethyl S-[2-(diisopropylamino)ethyl] methylphosphonothioate (VX). Anesthetized male Sprague-Dawley rats (250–300?g) were incubated with a glass endotracheal tube and exposed to saline or VX (171, 343 and 514?mg×min/m³ or 0.2, 0.5 and 0.8?LCt₅₀, respectively) for 10?min. VX was delivered by a small animal ventilator at a volume of 2.5?ml?×?70 breaths/minute. All VX-exposed animals experienced a significant loss in percentage body weight at 3, 6, and 24?h post-exposure. In comparison to controls, animals exposed to 514?mg×min/m³ of VX had significant increases in bronchoalveolar lavage (BAL) protein concentrations at 6 and 24?h post-exposure. Blood acetylcholinesterase (AChE) activity was inhibited dose dependently at each of the times points for all VX-exposed groups. AChE activity in lung homogenates was significantly inhibited in all VX-exposed groups at each time point. All VX-exposed animals assessed at 20 min and 3, 6 and 24?h post-exposure showed increases in lung resistance, which was prominent at 20 min and 3?h post-exposure. Histopathologic evaluation of lung tissue of the 514?mg×min/m³ VX-exposed animals at 3, 6 and 24?h indicated morphological changes, including perivascular inflammation, alveolar exudate and histiocytosis, alveolar septal inflammation and edema, alveolar epithelial necrosis, and bronchiolar inflammatory infiltrates, in comparison to controls. These results suggest that aerosolization of the highly toxic, persistent chemical warfare nerve agent VX results in acute pulmonary toxicity and lung injury in rats.     

Acute lung injury following inhalation exposure to nerve agent VX in guinea pigs

A microinstillation technique of inhalation exposure was utilized to assess lung injury following chemical warfare nerve agent VX [methylphosphonothioic acid S-(2-[bis(1-methylethyl)amino]ethyl) O-ethyl ester] exposure in guinea pigs. Animals were anesthetized using Telazol-meditomidine, gently intubated, and VX was aerosolized using a microcatheter placed 2 cm above the bifurcation of the trachea. Different doses (50.4 microg/m3, 70.4 micro g/m(m3), 90.4 microg/m(m3)) of VX were administered at 40 pulses/min for 5 min. Dosing of VX was calculated by the volume of aerosol produced per 200 pulses and diluting the agent accordingly. Although the survival rate of animals exposed to different doses of VX was similar to the controls, nearly a 20% weight reduction was observed in exposed animals. After 24 h of recovery, the animals were euthanized and bronchoalveolar lavage (BAL) was performed with oxygen free saline. BAL was centrifuged and separated into BAL fluid (BALF) and BAL cells (BALC) and analyzed for indication of lung injury. The edema by dry/wet weight ratio of the accessory lobe increased 11% in VX-treated animals. BAL cell number was increased in VX-treated animals compared to controls, independent of dosage. Trypan blue viability assay indicated an increase in BAL cell death in 70.4 microg/m(m3) and 90.4 microg/m(m3) VX-exposed animals. Differential cell counting of BALC indicated a decrease in macrophage/monocytes in VX-exposed animals. The total amount of BAL protein increased gradually with the exposed dose of VX and was highest in animals exposed to 90.4 microg/m(m3), indicating that this dose of VX caused lung injury that persisted at 24 h. In addition, histopathology results also suggest that inhalation exposure to VX induces acute lung injury.     

Behavioral effects of ethanol inhalation in rats

Behavioral effects of ethanol inhalation were studied on two fixed-ratio (FR) liquid-reinforced schedules and a continuous reinforcement (CRF) schedule intracranial self-stimulation (SS) in rats using the inhalational behavioral chamber designed in our laboratory. In the FR-24 schedule ethanol caused a decrease of reinforcement rate at 161 ppm and higher concentrations. In the FR-50 schedule decreases of the rate were observed at 102 ppm and 203 ppm. In the SS behavior ethanol produced a decrease in the rate of reinforcement at 603 ppm and higher concentrations. In rats of this schedule, blood ethanol concentrations were measured to be 393 micrograms/ml and 545 micrograms/ml after exposure to 600 ppm and 1200 ppm of ethanol respectively. Acute tolerance to ethanol was observed in these experiments, particularly in the FR-24 schedule. Thus ethanol inhalation could produce adequate blood concentrations so as to produce behavioral effects.     

Behavioral and biochemical consequences of perinatal exposure of mice to instant coffee: A correlative evaluation

In the present study, the lasting effects of prepartum and perinatally consumed instant coffee by female mice on the behavior as well as on the level of activities of certain enzymes in the tissues of their male offspring have been investigated. The behavioral observations of nonsocial investigation, defense, displacement, latency to threat and naso-nasal contact has decreased significantly in offspring of treated mothers, while the threat, attack, latency to threat and attack and number of fights have increased significantly. Hence, coffee has proven to be an inducer of hyperactive behavior in these offspring. Such effects are both dose dependent and duration-of-treatment dependent. Moreover, variations were detected in the level of AChE activity in the brain tissues of these offspring together with variations in the levels of AcPase and AlPase activities in their liver, kidneys and testes. Such variations in these organs have developed in utero, making these enzymes convenient markers in teratological studies.     

The effect of prolonged exposure of rats to sub-lethal dose of acetaminophen

In this report, we studied the effect of sub-lethal doses (20mg, 30mg, 100mg, 200mg and 300mg/Kg body weight) and duration of acetaminophen given intraperitoneally (i.p) to male albino rats; on the level of pc methaemoglobin and some liver function tests: Alkaline phosphatase, free and conjugated bilirubin. The study showed that the increase in pc methaemoglobin, free and conjugated bilirubin in rats treated with acetaminophen are significantly (P less than 0.05) greater than those for the control rats and that the measured parameters increase with acetaminophen concentrations. The results also show that the free bilirubin is probably displaced from plasma albumin.     

Developmental effects of inhalation exposure to 2-bromopropane in rats

2-Bromopropane (2-BP), known as a reproductive and hematopoietic toxicant in humans, was assessed for developmental toxicity. Sprague-Dawley rats were exposed by inhalation to 2-BP at a concentration of 0 (control), 125, 250, 500, or 1000 ppm for 6 h per day, 7 days per week during 2 weeks of the pre-mating period, during the mating period until copulation and during the period of gestation days 0-19. After parturition, dams were allowed to breast feed their pups until postnatal day 4. 2-BP exposure resulted in no signs of maternal toxicity as assessed by clinical observations and body weight gain. On the other hand, the inhalation exposure to 1000 ppm markedly decreased the number of pups born, although the number of implantations did not decrease. No effect of 2-BP on pups weights or survival until postnatal day 4 was found. It was found that the repeated inhalation exposure of rats to 1000 ppm 2-BP induced fetal lethality during the post-implantation period.     

Neurotoxicologic evaluation of rats after 13 weeks of inhalation exposure to dichloromethane or carbon monoxide

Male and female Fischer 344 rats were exposed to dichloromethane (methylene chloride, DCM) or carbon monoxide (CO) for 6 hr/day, 5 days/week, for 13 weeks. Since oxidative metabolism of DCM to CO and CO2 is a saturable process, DCM exposure concentrations were selected clearly below saturation (50 ppm), just below saturation (200 ppm), and well above saturation (2000 ppm). At saturation of metabolism, metabolic CO causes about 10% carboxyhemoglobinemia (COHb). Therefore, as a control for CO effects, a separate group of rats was exposed to 135 ppm CO to induce approximately 10% COHb. Postexposure functional tests included an observational battery, hindlimb grip strength, and a battery of evoked potentials (flash, auditory brainstem, somatosensory, caudal nerve). After functional tests were completed, rats from all groups were perfused with fixative and a comprehensive set of nervous tissues from the high DCM exposure group and from controls were examined by light microscopy. Although some miscellaneous functional and morphologic variations were recorded, none were related to treatment. Thus, subchronic exposures as high as 2000 ppm DCM or 135 ppm CO had no deleterious effects on any of the measures of this study.     

Behavioral and neurochemical alterations in the offspring of rats after maternal or paternal inhalation exposure to the industrial solvent 2-methoxyethanol

The industrial solvent 2-methoxyethanol (2ME) has antifertility effects in male rats at 300 ppm and is tetragenic in rats and rabbits at 50 ppm. The present research investigated if exposure of paternal or maternal animals to 25 ppm 2ME, the current U. S. permissible occupational exposure limit, would produce detectable effects in the offspring. Eighteen male young-adult Sprague-Dawley rats were exposed to 25 ppm 2ME 7 hr/day, 7 days/week for 6 weeks; they were then mated with untreated females which were allowed to deliver and rear their young. In addition, groups of 15 pregnant rats were exposed 7 hr/day on gestation days 7–13 or 14–20 and allowed to deliver and rear their young. At birth, litters were culled to 4 females and 4 males for behavioral testing of neuromotor function, activity, and simple learning ability on days 10 through 90. In addition, brains from new born and 21-day-old offspring were analyzed for neurochemical deviations from controls. No effects on paternal or maternal animals, nor on the number or weight of live offspring, were noted. Behavioral testing revealed significant differences from controls only in avoidance conditioning of offspring of mothers exposed on days 7–13. In contrast, neurochemical deviations were observed in brains from 21-day-old offspring from the paternally exposed group as well as from both maternally exposed groups; changes were numerous in the brainstem and cerebrum but were fewer in the cerebellum and midbrain. Thus it appears that both paternal and maternal inhalation of 25 ppm 2ME produces some effect which is reflected in neurochemical deviations in the offspring.     

Behavioral teratology investigation of 1-propanol administered by inhalation to rats

Due to their structural similarity to ethanol, a human teratogen, and their widespread use in industry, a series of industrial alcohols are being investigated for developmental toxicity. This paper presents the results of exposures to 7000 ppm 1-propanol, which is minimally toxic to maternal animals and produces a low incidence of teratogenicity, and to 3500 ppm 1-propanol, which is not toxic to maternal rats and produces no teratogenicity. Propanol vapors or filtered air was administered for 7 hr/day to 15 pregnant Sprague-Dawley rats throughout gestation or to 18 male rats daily for 6 weeks. Tests of offspring were: a) ascent on a wire mesh screen b) rotorod, c) open field and optically monitored activity, d) running wheel, e) avoidance conditioning, and f) progressive fixed ratio schedule of reinforcement. Brains from 10 rats per group were dissected into cerebrum, cerebellum, brainstem, and midbrain, and were assayed for protein, acetylcholine, dopamine, norepinephrine, serotonin, beta-endorphin, Met-enkephalin, and substance P. Overall, the results indicate that exposure to high concentrations of 1-propanol can affect fertility in exposed males (only 2 of 17 produced litters), but there were no consistent effects seen in the behavioral or neurochemical tests measured. This lack of effects is surprising based on predictions from the structural similarity of 1-propanol to ethanol, and on long-standing observations that toxicity (to adult animals) increases with carbon chain length among the aliphatic alcohols.     

Effects of whole-body VX vapor exposure on lethality in rats

Male and female rats were whole-body exposed to VX vapor in a 1000-L single-pass exposure chamber. Estimated exposure dosages producing lethal (LCT50) effects in 50% of exposed male and female rats were established for 10, 60, and 240 min exposure durations. A potency comparison with GB and GF shows that VX becomes increasingly more potent than these G agents with increasing exposure duration. VX is approximately 4-30 times more potent than GB and 5-15 times more potent than GF. Gender differences in the estimated median dosages were not significant at the 10, 60, and 240 min exposure durations. An empirical toxic load model was developed and the toxic load exponent for lethality (n) in the equation Cn x T = k was determined to be n = 0.92. The VX-G regeneration assay was successfully used as a biomarker for the presence of VX in the blood plasma and RBC fractions of the blood 24 h postexposure.     

Behavioral and biochemical effects of postnatal parathion exposure in the rat

Preweanling rat pups were exposed daily to parathion (1.3 mg/kg or 1.9 mg/kg) or vehicle (corn oil) on postnatal days 5-20, a time period critical to development of behavioral and biochemical parameters of the cholinergic nervous system. This exposure resulted in dose-dependent reductions in acetylcholinesterase activity and muscarinic receptor binding in the cortex. During the preweanling period, there were no differences among the groups in most reflex measures, eye opening or incisor eruption. Postweanling behavioral assessment revealed small deficits in tests of spatial memory in both the T-maze and the radial arm maze. There were no differences in neuromuscular abilities or spontaneous activity measures. Thus, biochemical and behavioral deficits in cholinergic nervous system functioning occurred in the absence of severe signs of toxicity and in the absence of generalized nonspecific behavioral disturbances.     

Renal toxicity after chronic inhalation exposure of rats to trichloroethylene

Male Long-Evans rats were exposed to 0 (controls) or 500 ppm trichloroethylene (TRI) for 6 months, 6 h daily, and 5 days a week. The TRI metabolites trichloroethanol (TCE) in blood and trichloroacetic acid (TCA) in urine were measured. Specific parameters related to the renal damage were determined in urine [biomarker for glomerular damage: high molecular weight proteins (HMW), albumin (ALB); for proximal tubular damage: N-acetyl-beta-D-glucosaminidase (NAG), low-molecular-weight-proteins (LMW)]. Significantly increased concentrations of NAG and LMW in urine of exposed rats were detected. No DNA-strand breaks in kidney cells could be detected using the comet assay, and histological examinations were performed. Histological alterations were observed in glomeruli and tubuli of exposed rats. The release of biomarkers for nephrotoxicity suggested alterations preferably in the proximal tubules of the exposed rats.     

Behavioral changes in juvenile rats after prenatal exposure to ethosuximide

Juvenile rats 4-6 weeks old exposed prenatally at days 5-20 of gestation to ethosuximide at 10 mg/kg/dams' body weights per day were examined for behavioral abnormalities. Pinning behavior in the pups aged 4-5 weeks was significantly more frequent than that in age-matched controls. However, basal activity of open-field behavior and activity inhibited by diazepam administration in the pups aged 5-6 weeks showed no difference from the controls. The intensity of stereotyped behavior induced by apomorphine (1 mg/kg, SC) was significantly greater in the pups aged 5-6 weeks than in the controls. These results indicate that prenatal exposure to ethosuximide may cause changes in the dopaminergic neurons in the central nervous system.     

Repeated exposure inhalation study of pentane in rats

Pentane (CAS No. 109-66-0) is a chemical being used as a co-solvent in a polymer production facility with potential for inhalation exposure in humans. To assess the toxicity of pentane, groups of 10 male rats each were exposed by inhalation, 6 hr/day, 5 days/week for 2 weeks to either 0 (control), 1,000, 3,000 or 10,000 ppm. Five rats per group were killed following the 10th exposure; the remaining 5/group were killed after a 14-day post-exposure recovery period. Parameters investigated were clinical signs of toxicity, functional behavior, body weights, clinical pathology, and gross and microscopic pathology including organ weights. No unusual clinical observations were seen in the pentane-treated rats, and body weights were not altered. Test rats generally exhibited normal behavioral responses in the functional observational battery. Increases in serum calcium and phosphorus concentrations were seen in rats exposed to either 3,000 or 10,000 ppm. These were reversible during the 2-week recovery period. No other clinical pathology changes were observed and no pentane-related tissue pathology was seen in any of the groups. The no-observed-adverse-effect level was 1,000 ppm with reversible clinical pathology changes produced at 3,000 and 10,000 ppm.     

Behavioral effects of sub-acute inhalation of toluene in adult rats

Reports of behavioral effects of repeated inhalation of toluene in rats have yielded inconsistent findings. A recent study from this laboratory (Beasley et al., 2010) observed that after 13 weeks of inhaled toluene (“subchronic” exposure scenario), rats showed mild but persistent changes in behavior, primarily involving acquisition of an autoshaped lever-press response. The present experiment sought to systematically replicate these findings, using a 4-week “sub-acute” exposure scenario. Adult male Long-Evans rats inhaled toluene vapor (0, 10, 100, or 1000 ppm) for 6 h/day, 5 days/week for 4 weeks. As in the subchronic study, toluene had no effect on motor activity, anxiety-related behavior in the elevated plus-maze, or acquisition of the visual discrimination. However, sub-acute toluene did not affect appetitively-motivated acquisition of the lever-press response, but did reduce accuracy of signal detection at the end of training. Analysis of the deficit in accuracy in the 1000 ppm group by means of manipulations of different task parameters suggested a greater influence of attentional impairment than visual or motor dysfunction as a source for the deficit. These results confirm a pattern of subtle and inconsistent long-term effects of repeated daily exposure to concentrations of toluene vapor of 1000 ppm and below, in contrast to robust and reliable effects of acute inhalation of the solvent at concentrations above 1000 ppm.     

Behavioral effects of subchronic inhalation of toluene in adult rats

Whereas the acute neurobehavioral effects of toluene are robust and well characterized, evidence for persistent effects of repeated exposure to this industrial solvent is less compelling. The present experiment sought to determine whether subchronic inhalation of toluene caused persistent behavioral changes in rats. Adult male Long–Evans rats inhaled toluene vapor (0, 10, 100, or 1000 ppm) for 6 h/day, 5 days/week for 13 weeks and were evaluated on a series of behavioral tests beginning 3 days after the end of exposure. Toluene delayed appetitively-motivated acquisition of a lever-press response, but did not affect motor activity, anxiety-related behavior in the elevated plus maze, trace fear conditioning, acquisition of an appetitively-motivated visual discrimination, or performance of a visual signal detection task. Challenges with acute inhalation of toluene vapor (1200–2400 ppm for 1 h) and injections of quinpirole (0.01–0.03 mg/kg) and raclopride (0.03–0.10 mg/kg) revealed no toluene-induced latent impairments in visual signal detection. These results are consistent with a pattern of subtle and inconsistent long-term effects of daily exposure to toluene vapor, in contrast to robust and reliable effects of acute inhalation of the solvent.     

Behavioral effects of exposure to endosulfan and methyl parathion in adult rats

Endosulfan (ES) and methyl parathion (MP) are widely used in Latin America, and simultaneous exposure to both products is documented. This exposure may have effects on the nervous system because their targets include the GABAergic and cholinergic systems, which are main modulators of neuronal excitability in the cortex and hippocampus. We tested whether low-level, repeated exposure of adult rats to commercial formulations containing ES and MP disrupts spatial learning in the water maze. Five groups of eight animals received subcutaneously appropriate dilutions of the commercial formulations to yield the following treatments during 10 days: saline, 25 mg/kg ES, 2 mg/kg MP (MP(2)), 25 mg/kg ES plus 1 mg/kg MP (ES+MP(1)) and 25 mg/kg ES plus 2 mg/kg MP (ES+MP(2)). In addition, markers of neurological function, renal and hepatic damage were explored as potential consequences of exposure. In the absence of overt toxicity, the groups exposed to the ES plus MP showed significantly longer escape latencies, higher number of failures to reach the platform and more time in the periphery of the tank than the control and single-exposed groups. This finding shows that commercial formulations of ES and MP have marginal effects when administered individually but can produce behavioral alterations when given in combination.     

Behavioral effects of acute exposure to tributyltin chloride in rats.

The behavioral effects of a single acute exposure to nonlethal doses of tributyltin chloride (TBTCl) were studied in male Wistar rats. The rats were given TBTCl by oral gavage at doses of 0, 6.3, 12.5, 25.0 or 50.0 mg/kg, and spontaneous motor activity (SMA) and acquisition of conditioned avoidance responses in a shuttle box were monitored. Body weight gain in the 50.0-mg/kg group was significantly lowered, but weight gain in the 6.3-, 12.5- and 25.0-mg/kg groups was comparable to that in the control group. TBTCl caused a dose-related decrease in SMA during the dark phase. The 24-h total daily and 12-h nocturnal activity was decreased at doses of 12.5 mg/kg and above. The acquisition of shock avoidance responses was inhibited in all TBTCl-treated groups in a dose-dependent manner, and the difference was significant for rats given TBTCl at doses of 25.0 mg/kg and above. The data indicate that an acute exposure to TBTCl can cause significant changes in rat behavior and suggest that SMA can serve as a sensitive index for detecting its toxicity.