Impacts of a perinatal exposure to manganese coupled with maternal stress in rats: Learning, memory and attentional function in exposed offspring.

The developmental effects of chemicals that co-occur in vulnerable populations with elevated psychological stress are of increasing concern to the public. To investigate these concerns, we developed a rodent model of co-occurring perinatal manipulations and conducted a series of cognitive assessments in male and female offspring. Manganese (Mn), a neurodevelopmental toxicant when exceeding physiological requirements, was delivered in the drinking water (0, 2, or 4 mg Mn/mL) of rats from gestational day (GD) 7 to postnatal day (PND) 22. A variable perinatal stress paradigm was applied to half of the animals from GD13 to PND9. Novel object recognition (NOR), Morris water maze (MWM), differential reinforcement of low-rates procedure (DRL) and cued and uncued choice reaction time (CRT) tests were used to assess cognitive functions in offspring. Mn (4 mg/mL) and stress impaired NOR in adolescent males but facilitated NOR performance in females. However, when stress and Mn were combined these effects were attenuated in both sexes. During training for the DRL, Mn (2 mg/mL) facilitated, while stress impaired, lever press learning in both sexes. Few effects related to the treatments were found on DRL or MWM. During cued CRT, Mn (2 and 4 mg/mL) and stress reduced accuracy in males, while stress and Mn (2 mg/mL) increased anticipatory responding and slowed decision time in both sexes. Stress combined with Mn (2 mg/mL) improved cued accuracy and decision time, and Mn attenuated the effect of stress on anticipatory responding in both sexes. Stress slowed female movement time but when combined with Mn (4 mg/mL) the effect of stress was attenuated. During uncued CRT, except for decision time (which replicated effects observed with the cued task), no other effects of Mn or its combination with stress occurred. Females remained negatively affected by stress in most uncued CRT performance measures, while stressed improved male uncued accuracy. Taken together these data do not support increased cognitive impairment produced by Mn when combined with stress. However, the effects of perinatal stress alone, on these cognitive functions may hinder the detection of effects due to chemical exposures and underscores the need to consider the psychological health and wellbeing of the mother and her environment in risk assessment for developmental neurotoxicity of chemicals.

Prenatal exposure to vapors of gasoline-ethanol blends causes few cognitive deficits in adult rats.

Developmental exposure to inhaled ethanol-gasoline fuel blends is a potential public health concern. Here we assessed cognitive functions in adult offspring of pregnant rats that were exposed to vapors of gasoline blended with a range of ethanol concentrations, including gasoline alone (E0) and gasoline with 15% or 85% ethanol (E15 and E85, respectively). Rat dams were exposed for 6.5h daily to the vapors at concentrations of 0, 3000, 6000, or 9000 ppm in inhalation chambers from gestational day (GD) 9 through 20. Cage controls (offspring of non-exposed dams that remained in the animal facility during these exposures) were also assessed in the E0 experiment, but showed no consistent differences from the offspring of air-exposed controls. Offspring were tested as adults with trace fear conditioning, Morris water maze, or appetitive operant responding. With fear conditioning, no significant effects were observed on cue or context learning. In the water maze, there were no differences in place learning or escaping to a visible platform. However, during the reference memory probe (no platform) male rats exposed prenatally to E85 vapor (6000 and 9000 ppm) failed to show a bias for the target quadrant. Across studies, females (treated and some controls) were less consistent in this measure. Males showed no differences during match-to-place learning (platform moved each day) in any experiment and females showed only transient differences in latency and path length in the E0 experiment. Similarly, no differences were observed in delayed match-to-sample operant performance of E0 males or females; thus this test was not used to evaluate effects of E15 or E85 vapors. During choice reaction time assessments (only males were tested) decision and movement times were unimpaired by any prenatal exposure, while anticipatory responses were increased by vapors of E0 (9000 ppm) and E15 (6000 and 9000 ppm), and the latter group also showed reduced accuracy. E85 vapors did not disrupt any choice reaction time measure. Finally, no response inhibition deficit was observed in a differential reinforcement of low rate (DRL) response schedule in males or females in the E15 or E85 experiments. In summary, prenatal exposure to these fuel blends produced few deficits in adult offspring on these cognitive tests. Significant effects found during a water maze probe trial and choice reaction time tests were observed at vapor concentrations of 6000 ppm or higher, a concentration that is 4-6 orders of magnitude higher than those associated with normal automotive fueling operations and garages. Similar effects were not consistently observed in a previous study of inhaled ethanol, and thus these effects cannot be attributed to the concentration of ethanol in the mixture.

Selective cognitive deficits in adult rats after prenatal exposure to inhaled ethanol.

Increased use of ethanol blends in gasoline suggests a need to assess the potential public health risks of exposure to these fuels. Ethanol consumed during pregnancy is a teratogen. However, little is known about the potential developmental neurotoxicity of ethanol delivered by inhalation, the most likely route of exposure from gasoline-ethanol fuel blends. We evaluated the potential cognitive consequences of ethanol inhalation by exposing pregnant Long Evans rats to clean air or ethanol vapor from gestational days 9-20, a critical period of neuronal development. Concentrations of inhaled ethanol (5000, 10,000, or 21,000 ppm for 6.5h/day) produced modeled peak blood ethanol concentrations (BECs) in exposed dams of 2.3, 6.8, and 192 mg/dL, respectively. In offspring, no dose-related impairments were observed on spatial learning or working memory in the Morris water maze or in operant delayed match-to-position tests. Two measures showed significant effects in female offspring at all ethanol doses: 1) impaired cue learning after trace fear conditioning, and 2) an absence of bias for the correct quadrant after place training during a reference memory probe in the Morris water maze. In choice reaction time tests, male offspring (females were not tested) from the 5000 and 10,000 ppm groups showed a transient increase in decision times. Also, male offspring from the 21,000 ppm group made more anticipatory responses during a preparatory hold period, suggesting a deficit in response inhibition. The increase in anticipatory responding during the choice reaction time test shows that inhaled ethanol yielding a peak BEC of ~200mg/dL can produce lasting effects in the offspring. The lack of a dose-related decrement in the effects observed in females on cue learning and a reference memory probe may reflect confounding influences in the exposed offspring possibly related to maternal care or altered anxiety levels in females. The surprising lack of more pervasive cognitive deficits, as reported by others at BECs in the 200mg/dL range, may reflect route-dependent differences in the kinetics of ethanol. These data show that response inhibition was impaired in the offspring of pregnant rats that inhaled ethanol at concentrations at least 5 orders of magnitude higher than concentrations observed during normal automotive transport and fueling operations, which rarely exceed 100 ppb.

Evaluation of developmental neurotoxicity of organotins via drinking water in rats: dimethyl tin.

Dimethyltin (DMT) is one of several organotins that are detected in domestic water supplies due to their use as plastic stabilizers for polyvinyl chloride (PVC) and chlorinated PVC (CPVC) products. A limited number of in vitro and in vivo studies suggest that DMT may produce developmental neurotoxicity; therefore, we initiated studies to evaluate long-term neurobehavioral changes in offspring following perinatal exposure. In the first study, female Sprague-Dawley rats were exposed via drinking water to DMT (0, 3, 15, 74 ppm) before mating and throughout gestation and lactation. Male offspring were tested for changes in: 1) preweaning learning in an associative runway task, 2) motor activity ontogeny, 3) spatial learning and retention in the Morris water maze as adults, 4) brain weight, 5) biochemical evidence of apoptosis, and 6) neuropathology. DMT toxicity was expressed as depressed maternal weight gain (74 ppm), and in the offspring, decreased brain weight (3, 74 ppm), decreased apoptosis (all concentrations), mild vacuolation in adult offspring (all concentrations), and slower learning in the water maze (15 ppm) due to altered spatial search patterns. In a second study, DMT exposure (same concentrations) occurred from gestational day 6 to weaning. Male and female offspring were tested. The high concentration again depressed maternal weight gain, decreased offspring birth weight and preweaning growth, and decreased brain weight. Increased and decreased apoptotic markers were measured, depending on age. Learning deficits were observed in the runway at postnatal day 11 (15, 74 ppm) and again in the adult offspring in the water maze (15 ppm). The results of both studies demonstrate a reproducible effect of 15 ppm perinatal DMT exposure on spatial learning. Changes in expression of apoptosis, brain weight, and the occurrence of neuropathological lesions also indicate potential neurotoxicity of DMT. These results were in contrast to earlier findings with monomethyl tin, for which only similar neuropathological lesions were observed. Thus, developmental neurotoxicity may be produced in offspring following gestational exposure to DMT in drinking water.

Influence of dosing volume on the neurotoxicity of bifenthrin.

Pyrethroids are pesticides with high insecticidal activity and relatively low potency in mammals. The influence of dosing volume on the neurobehavioral syndrome following oral acute exposure to the Type-I pyrethroid insecticide bifenthrin in corn oil was evaluated in adult male Long Evans rats. We tested bifenthrin effects at 1 and 5 ml/kg, two commonly used dose volumes in toxicological studies. Two testing times (4 and 7 h) were used in motor activity and functional observational battery (FOB) assessments. Four to eight doses were examined at either dosing condition (up to 20 or 26 mg/kg, at 1 and 5 ml/kg, respectively). Acute oral bifenthrin exposure produced toxic signs typical of Type I pyrethroids, with dose-related increases in fine tremor, decreased motor activity and grip strength, and increased pawing, head shaking, click response, and body temperature. Bifenthrin effects on motor activity and pyrethroid-specific clinical signs were approximately 2-fold more potent at 1 ml/kg than 5 ml/kg. This difference was clearly evident at 4 h and slightly attenuated at 7 h post-dosing. Benchmark dose (BMD) modeling estimated similar 2-fold potency differences in motor activity and pyrethroid-specific FOB data. These findings demonstrate that dose volume, in studies using corn oil as the vehicle influences bifenthrin potency. Further, these data suggest that inconsistent estimates of pyrethroid potency between laboratories are at least partially due to differences in dosing volume.

Neurobehavioral effects of chronic dietary and repeated high-level spike exposure to chlorpyrifos in rats.

This study aimed to model long-term subtoxic human exposure to an organophosphorus pesticide, chlorpyrifos, and to examine the influence of that exposure on the response to intermittent high-dose acute challenges. Adult Long-Evans male rats were maintained at 350 g body weight by limited access to a chlorpyrifos-containing diet to produce an intake of 0, 1, or 5 mg/kg/day chlorpyrifos. During the year-long exposure, half of the rats in each dose group received bi-monthly challenges (spikes) of chlorpyrifos, and the other half received vehicle. Rats were periodically tested using a neurological battery of evaluations and motor activity to evaluate the magnitude of the acute response (spike days) as well as recovery and ongoing chronic effects (non-spike days). Effects of the spikes differed as a function of dietary level for several endpoints (e.g., tremor, lacrimation), and in general, the high-dose feed groups showed greater effects of the spike doses. Animals receiving the spikes also showed some neurobehavioral differences among treatment groups (e.g., hypothermia, sensory and neuromotor differences) in the intervening months. During the eleventh month, rats were tested in a Morris water maze. There were some cognitive deficits observed, demonstrated by slightly longer latency during spatial training, and decreased preference for the correct quadrant on probe trials. A consistent finding in the water maze was one of altered swim patterning, or search strategy. The high-dose feed groups showed more tendency to swim in the outer annulus or to swim very close to the walls of the tank (thigmotaxic behavior). Overall, dietary exposure to chlorpyrifos produced long-lasting neurobehavioral changes and also altered the response to acute challenges.

Neurotoxicity produced by dibromoacetic acid in drinking water of rats.

An evaluation of potential adverse human health effects of disinfection byproducts requires study of both cancer and noncancer endpoints; however, no studies have evaluated the neurotoxic potential of a common haloacetic acid, dibromoacetic acid (DBA). This study characterized the neurotoxicity of DBA during 6-month exposure in the drinking water of rats. Adolescent male and female Fischer 344 rats were administered DBA at 0, 0.2, 0.6, and 1.5 g/l. On a mg/kg/day basis, the consumed dosages decreased greatly over the exposure period, with average intakes of 0, 20, 72, and 161 mg/kg/day. Weight gain was depressed in the high-concentration group, and concentration-related diarrhea and hair loss were observed early in exposure. Testing with a functional observational battery and motor activity took place before dosing and at 1, 2, 4, and 6 months. DBA produced concentration-related neuromuscular toxicity (mid and high concentrations) characterized by limb weakness, mild gait abnormalities, and hypotonia, as well as sensorimotor depression (all concentrations), with decreased responses to a tail-pinch and click. Other signs of toxicity at the highest concentration included decreased activity and chest clasping. Neurotoxicity was evident as early as one month, but did not progress with continued exposure. The major neuropathological finding was degeneration of spinal cord nerve fibers (mid and high concentrations). Cellular vacuolization in spinal cord gray matter (mostly) and in white matter (occasionally) tracts was also observed. No treatment-related changes were seen in brain, eyes, peripheral nerves, or peripheral ganglia. The lowest-observable effect level for neurobehavioral changes was 20 mg/kg/day (produced by 0.2 g/l, lowest concentration tested), whereas this dosage was a no-effect level for neuropathological changes. These studies suggest that neurotoxicity should be considered in the overall hazard evaluation of haloacetic acids.

Dopamine transporter binding in the rat striatum is increased by gestational, perinatal, and adolescent exposure to heptachlor.

Heptachlor is a persistent cyclodiene pesticide that affects GABAergic function. Recent reports indicate that heptachlor exposure also alters dopamine transporter (DAT) expression and function in adult mice. The aim of this study was to determine whether gestational, perinatal, and/or adolescent heptachlor exposure in rats altered dopamine-receptor and DAT binding. Adolescent exposure to dieldrin was included to evaluate the generality of the findings. Sprague-Dawley rats received doses (po) ranging from 0 to 8.4 mg/kg/day of heptachlor, or dieldrin, 3 mg/kg/day, during different developmental periods. There were dose-related decreases in maternal weight gain and pup survival, as well as delayed righting reflex, at heptachlor doses > or =3 mg/kg/day. There were no changes in striatal dopamine receptor-D1 ([(3)H]SCH-23390) and -D2 ([(3)H]spiperone) binding in preweanling pups exposed perinatally to heptachlor, and no differences in the response of adult rats to the motor activity-increasing effects of d-amphetamine. However, there were significant (27-64%) increases in striatal DAT binding of [(3)H]mazindol in preweanling rats exposed only gestationally. In rats exposed perinatally and/or during adolescence, there were also increases (34-65%) in striatal DAT binding at postnatal days (PND) 22, 43, and 128. Adolescent exposure to dieldrin also increased DAT binding. In other rats exposed perinatally and throughout adolescence, even the lowest dose of heptachlor 0.3 mg/kg/d increased DAT binding on PND 130. The DAT affinity for mazindol was unchanged in heptachlor-exposed striata. In vitro binding studies indicated that heptachlor (> or =10 microM) displaced mazindol binding. Thus, gestational, perinatal, and/or adolescent exposure to heptachlor produced an increase in DAT binding as early as PND 10, and this change persisted into adulthood.

Behavioral evaluation of the neurotoxicity produced by dichloroacetic acid in rats.

Dichloroacetic acid (DCA) is commonly found in drinking water as a by-product of chlorination disinfection. It is a known neurotoxicant in rats, dogs, and humans. We have characterized DCA neurotoxicity in rats using a neurobehavioral screening battery under varying exposure durations (acute, subchronic, and chronic) and routes of administration (oral gavage and drinking water). Studies were conducted in both weanling and adult rats, and comparisons were made between Long-Evans and Fischer-344 rats. DCA produced neuromuscular toxicity comprised of limb weakness and deficits in gait and righting reflex; altered gait and decreased hindlimb grip strength were the earliest indicators of toxicity. Other effects included mild tremors, ocular abnormalities, and a unique chest-clasping response (seen in Fischer-344 rats only). Neurotoxicity was permanent (i.e., through 2 years) following a 6-month exposure to high dose levels, whereas the effects of intermediate dose levels with exposures of 3 months or less were slowly reversible. The severity, specificity, and recovery of neurological changes were route, duration, and strain dependent. Fischer-344 rats were more sensitive than Long-Evans rats, and weanling rats may be somewhat more sensitive than adults. Oral gavage produced significantly less toxicity compared to the same intake level received in drinking water. Neurotoxicity was progressive with continued exposure, and was observed at exposure levels as low as 16 mg/kg/day (lowest dose level tested) when administered via drinking water in subchronic studies. The data from these studies characterize the neurotoxicity produced by DCA, and show it to be more pronounced, persistent, and occurring at lower exposures than has been previously reported. Further research should take into account these marked route, age, and strain differences.

The IPCS Collaborative Study on Neurobehavioral Screening Methods: III. Results of proficiency studies. Steering Group.

The goal of the IPCS Collaborative Study on Neurobehavioral Screening Methods was to determine the intra- and inter-laboratory reliability of a functional observational battery (FOB) and an automated assessment of motor activity in eight laboratories world-wide. The first phase of the Collaborative Study involved training the participants: evidence of training was then evaluated using positive-control compounds. The positive-control studies required the laboratories to identify, using the FOB, specific neurotoxic syndromes produced by acute exposure to p,p'-DDT, parathion, and by short-term repeated dosing with acrylamide. For the sake of expediency, only one dose of each chemical was used instead of collecting dose-response data. Motor activity test chambers were not of uniform design. The laboratories were therefore required to demonstrate adequate sensitivity by the ability to detect statistically-significant activity increases and decreases produced by triadimefon and chlorpromazine, respectively, following acute administration of a range of doses. The resulting FOB and motor activity data showed variability in the magnitude of effects obtained: some of these differences were attributed to miscommunications, difficulties with the techniques or protocol, or the limitations of having only one dose. All laboratories, however, successfully met the criteria set forth by the Study Steering Committee.

The IPCS Collaborative Study on Neurobehavioral Screening Methods: IV. Control data. Steering Group.

The goal of the International Programme on Chemical Safety (IPCS) Collaborative Study on Neurobehavioral Screening Methods was to determine the intra- and inter-laboratory reliability of a functional observational battery (FOB) and an automated assessment of motor activity in eight laboratories worldwide. The control data were crucial to the outcome of the studies in terms of sensitivity and reliability of the test measures, which in turn impact on the between-laboratory comparisons of chemical effects. In addition, analyses of control data can aid in determining endpoints that may require modification to improve their sensitivity and reliability. The control data from the eight laboratories were examined in terms of the following parameters: 1) control variability within studies for each laboratory; 2) within-laboratory replicability of control values across studies; 3) within-laboratory stability of control values over the course of testing for a given study; and 4) between-laboratory comparisons of parameters (1), (2), and (3). The analyses indicated considerable differences across endpoints, wherein some measures showed high variability and little replicability, while others were extremely reproducible. Generally, there were similar ranges of variability and replicability of control data across laboratories, although in some cases one or two laboratories were markedly different from the others. The physiological (weight, body temperature) and neuromuscular (grip strength, landing foot splay) endpoints exhibited the least variability, whereas the subjective assessments of reactivity varied the most. These data indicate a reasonable degree of comparability in the data generated in the participating laboratories.

The IPCS Collaborative Study on Neurobehavioral Screening Methods: V. Results of chemical testing. Steering Group.

The IPCS Collaborative Study on Neurobehavioral Screening Methods was undertaken to determine the intra- and inter-laboratory reliability of a functional observational battery (FOB) and an automated assessment of motor activity in eight laboratories world-wide. Following the training phase and the conduct of proficiency studies in all laboratories, participants proceeded to test the effects of seven chemicals in both single dose and four-week repeated dosing scenarios. The chemicals studied were acrylamide, bisacrylamide, p,p'-DDT, lead acetate, parathion, toluene, and triethyl tin. Participants received coded samples from a common source. In order to judge the general utility of these procedures in a diversity of testing situations, laboratories conducted the studies under their standard conditions, using their choice of rat strain and test equipment. Chemical does and time of peak effect for acute testing were determined by each laboratory: these parameters were quite similar for some chemicals, but varied greatly for others. The results of the chemical tests indicated that while there was some variability in the data on specific endpoints, all laboratories detected and characterized the effects of all but one of the known neurotoxicants. The one exception (toluene) was probably due to other factors (e.g., dose level, route of administration) rather than lack of sensitivity of the test methods. This study provides extensive data regarding the use of neurobehavioral screening methods over a range of laboratory conditions as well as the reliability, sensitivity, and robustness of the tests to detect neurotoxic potential of chemicals.

The IPCS Collaborative Study on Neurobehavioral Screening Methods: VI. Agreement and reliability of the data.

The IPCS Collaborative Study on Neurobehavioral Screening Methods was undertaken to determine the intra- and inter-laboratory reliability of a functional observational battery (FOB) and an automated assessment of motor activity in eight laboratories world-wide. The effects of seven chemicals (acrylamide, bis-acrylamide, p,p'-DDT, lead acetate, parathion, toluene, and triethyl tin) were studied during two dosing regimens: single-dose and four-week repeated dosing. All participating laboratories generally could detect and characterize the effects of known neurotoxicants, even though there were some differences in outcome on specific endpoints. The results were further evaluated to assess the agreement across laboratories in the dose-response data at the expected times of maximal effect (time of peak effect for the single-dose studies, and during or at the end of dosing for repeated-exposure studies). Percent agreement was calculated as the percentage of laboratories agreeing on an outcome (whether it be a significant dose effect or not). As an alternative approach, slopes of the dose-response functions were calculated, and reliability of those slope estimates across laboratories and chemicals was determined. Reliability was defined as the degree of agreement across laboratories (intraclass correlation coefficient) of the dose-response slopes within and between chemicals. These reliability estimates were calculated for each domain and for each endpoint. Relative reliability of the endpoints was evaluated, and hypotheses concerning the influence of outlying data were tested. The data clearly showed that reliability was not influenced by the objectivity or subjectivity of the test measure. Thus these data provide additional information regarding the reliability and robustness of the tests across the participating laboratories.

The influence of dosing volume on the toxicity of p,p'-DDT.

In the IPCS Collaborative Study on Neurobehavioral Screening Methods, the "Top Dose" (TD) of p,p'-DDT (oral gavage, in corn oil) was determined to be different depending on the volume of administration: TD = 87 mg/kg when delivered in 1 ml/kg (i.e., 87 mg/ml) vs. TD = 130.5 mg/kg when given at 5 ml/kg (26.1 mg/ml). Two acute dose-response studies were conducted, the only difference being the doses used (pre-established percentages of the TD) and dosing volume (1 and 5 ml/kg); a third study was conducted using a single dose and varying the dosing volume (1 and 5 ml/kg). In the higher-volume study, dose-response curves for almost all the affected endpoints were shifted to the right, and the effects of the highest dose were less severe compared to the lower-volume study. For example, tremors were observed in all rats dosed with 43.5 mg/kg at 1 ml/kg, but only in 40% of the dose group given 65.3 mg/kg at 5 ml/kg. The highest dose groups (100% TD) showed myoclonus in both studies, but the incidence was 100% at 87 mg/kg (1 ml/kg) compared to 60% at 130.5 mg/kg (5 ml/kg). The dose-response curves indicated that the effective doses were generally 2-5 times higher, i.e., less potent, using a volume of 5 ml/kg. In general, the profiles of effect were similar in that the Sensorimotor and Convulsive domains were significantly altered in both studies, but again the dose-response curves were shifted; these domains were affected by both 43.5 and 87 mg/kg at 1 ml/kg, but only by 130.5 mg/kg at 5 ml/kg. The Neuromuscular domain, however, was only affected in the 1 ml/kg study (at 87 mg/kg). These differences in outcome could be due to higher partitioning of DDT into the oil, or increased gut motility, both of which could be due to the larger volume of oil delivered. The findings illustrate the importance of knowing the pharmacokinetic properties of the compound in question, as well as standardization of such variables whenever direct comparisons of dose levels are conducted.

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 alpha-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.

Rat strain and stock comparisons using a functional observational battery: baseline values and effects of amitraz.

A functional observational battery (FOB) was utilized to assess the effects of 3-day exposure to the formamidine pesticide amitraz in outbred Sprague-Dawley-derived and inbred Fischer-344-derived (F344) rats (both from Charles River Laboratories) and in outbred Long-Evans rats obtained from two commercial suppliers (Charles River Breeding Laboratories and Blue Spruce Farms). Significant strain and stock differences were obtained in baseline values for one-third of the FOB measures. In most cases, F344 rats were different from the others. Characteristic signs of amitraz exposure consisting of increased excitability, hyper-reactivity, and physiological and autonomic changes were evident in all treated rats. These effects increased with repeated dosing, and many were still present 6 days after dosing. On individual measures, there were differences between the strains and stocks in terms of sensitivity and time course of amitraz effects. In general, Blue Spruce Long-Evans rats displayed more effects of amitraz and F344 rats recovered more quickly than others. Although Sprague-Dawley rats showed the least effect overall, they displayed the largest increases in the sensorimotor responses to stimuli. These data indicate that although some behavioral and physiological parameters showed strain and supplier differences, in both baseline values and the effects of amitraz, conclusions concerning its neurotoxic potential in a screening context would be similar.

Microinjection of dynorphin into the hippocampus impairs spatial learning in rats.

The effect of hippocampal dynorphin administration on learning and memory was examined in spatial and nonspatial tasks. Bilateral infusion of dynorphin A(1-8) (DYN; 10 or 20 micrograms in one microliters) into the dorsal hippocampus resulted in a dose-related impairment of spatial working memory in a radial maze win-stay task. Subsequent experiments found that acquisition of a reference memory task in the water maze was impaired by DYN injections (20 micrograms/microliters) in the dorsal hippocampus, but not in the ventral hippocampus, and that this impairment could be blocked by naloxone. In a nonspatial task, posttraining DYN injections in the dorsal hippocampus had no effect on retention of step-through passive avoidance. These results suggest that dynorphin specifically interferes with spatial learning and memory, and that this effect is mediated by opioid receptors in the dorsal hippocampus.