Validation of a photobeam system for assessment of motor activity in rats

Practical Procedure of Testing for Neurotoxicity

In the course of routinely performed subchronic toxicity studies with laboratory rodents, functional neurotoxicity, i.e., behavioral changes, usually are noted first during the daily cageside observations of all animals, Observation and neurologic examination of a few key animals provide a tentative diagnosis. Subsequent automated testing procedures for further characterization and quantifying behavioral changes might include motor activity, startle response, hurdle stepping, and maze behavior. Automated testing serves to assess the no observable effect under conditions of blind testing and provides further refinement of the diagnosis. Behavioral changes should be assessed as early as possible after onset of testing, i.e., during acute tests for mortality and the subsequent subchronic range-finding studies. Subsequent subchronic organ toxicity studies are then carried out by following a validated experimental protocol, including automated testing procedures and appropriate neuropathologic evaluation.

Large-Scale Assessment of Motor Activity in Rodents: Procedures for Routine Use in Toxicology Studies

An automated system for the routine large-scale assessment of motor activity in rats has been established in this laboratory for use in toxicity testing. This study was designed to evaluate the validity and sensitivity of motor activity measurements for routine use in toxicology studies. The effects of two known neurotoxins, acrylamide (ACR) and 3'3'-iminodipropionitrile (IDPN), were measured in rats using an automated photocell device in the context of a routine toxicology study. One hundred Sprague-Dawley rats (10/sex/group) were dosed with vehicle, ACR (10 and 30 mg/kg/day) or IDPN (50 or 125 mg/kg/day), by oral gavage 7 days per week for 5 weeks (except where otherwise indicated). Motor activity was measured in 5-min test sessions prior to initiating treatment, 6 and 24 h after the first dose, and weekly thereafter. Significant mortality occurred in high-dose ACR animals during Week 3. A 10-or 7-day recovery period was initiated after 20 or 22 daily doses for high-dose ACR and IDPN animals, respectively; after which, the high dose ACR and IDPN animals, respectively; after which, the high dose of ACE: was lowered to 20 mg/kg/day. Rapid habituation to the test environment occurred over the 5-imin testing sessions. Significant depressions in activity were observed in high-dose ACR males during Weeks 3 and 5 and in high-dose ACR females during Weeks 2-5. High-dose IDPN females showed no significant changes in activity. However, significant activity depressions were noted in males during weeks 1, 3, and 5. When depressions in activity occurred, they were apparent over the entire test session. The sensitivity of activity measures was sufficient to detect a 15% change in activity levels as compared with controls, with sufficient statistical power to meet regulatory requirements. Inclusion of motor activity assessments complements the additional parameters routinely measured in toxicology studies, augmenting hazard identification.

Network analysis of rat spatial cognition: behaviorally-established symmetry in a physically asymmetrical environment

Background

We set out to solve two inherent problems in the study of animal spatial cognition (i) What is a “place”?; and (ii) whether behaviors that are not revealed as differing by one methodology could be revealed as different when analyzed using a different approach.

Methodology

We applied network analysis to scrutinize spatial behavior of rats tested in either a symmetrical or asymmetrical layout of 4, 8, or 12 objects placed along the perimeter of a round arena. We considered locations as the units of the network (nodes), and passes between locations as the links within the network.

Principal Findings

While there were only minor activity differences between rats tested in the symmetrical or asymmetrical object layouts, network analysis revealed substantial differences. Viewing ‘location’ as a cluster of stopping coordinates, the key locations (large clusters of stopping coordinates) were at the objects in both layouts with 4 objects. However, in the asymmetrical layout with 4 objects, additional key locations were spaced by the rats between the objects, forming symmetry among the key locations. It was as if the rats had behaviorally imposed symmetry on the physically asymmetrical environment. Based on a previous finding that wayfinding is easier in symmetrical environments, we suggest that when the physical attributes of the environment were not symmetrical, the rats established a symmetric layout of key locations, thereby acquiring a more legible environment despite its complex physical structure.

Conclusions and Significance

The present study adds a behavioral definition for “location”, a term that so far has been mostly discussed according to its physical attributes or neurobiological correlates (e.g. - place and grid neurons). Moreover, network analysis enabled the assessment of the importance of a location, even when that location did not display any distinctive physical properties.

Feasibility study of the zebrafish assay as an alternative method to screen for developmental toxicity and embryotoxicity using a training set of 27 compounds

To anticipate to increased testing needs for reproductive toxicity and 3R approaches, we studied zebrafish embryo/larva as an alternative for animal testing for developmental toxicity and embryotoxicity and evaluated a training set of 27 compounds with a standardized protocol. The classification of compounds in the zebrafish embryo/larva assay, based on a prediction model using a TI (teratogenic index) cut-off value of 2, was compared to available animal and human data. When comparing the classification of compounds in the zebrafish embryo/larva assay to available animal classification, a sensitivity of 72% and specificity of 100% were obtained. The predictive values obtained in comparison to a limited set of human data were 50, 60% respectively for teratogens, non-teratogens. Overall, we demonstrated that the zebrafish embryo/larva assay, may be used as screening tool for prioritization of compounds and could contribute to reduction of animal experiments in the field of developmental toxicology.

GBR 12909 administration as a mouse model of bipolar disorder mania: mimicking quantitative assessment of manic behavior

RATIONALE

Mania is a core feature of bipolar disorder (BD) that traditionally is assessed using rating scales. Studies using a new human behavioral pattern monitor (BPM) recently demonstrated that manic BD patients exhibit a specific profile of behavior that differs from schizophrenia and is characterized by increased motor activity, increased specific exploration, and perseverative locomotor patterns as assessed by spatial d.

OBJECTIVES

It was hypothesized that disrupting dopaminergic homeostasis by inhibiting dopamine transporter (DAT) function would produce a BD mania-like phenotype in mice as assessed by the mouse BPM.

METHODS

We compared the spontaneous locomotor and exploratory behavior of C57BL/6J mice treated with the catecholamine transporter inhibitor amphetamine or the selective DAT inhibitor GBR 12909 in the mouse BPM. We also assessed the duration of the effect of GBR 12909 by testing mice in the BPM for 3 h and its potential strain dependency by testing 129/SvJ mice.

RESULTS

Amphetamine produced hyperactivity and increased perseverative patterns of locomotion as reflected in reduced spatial d values but reduced exploratory activity in contrast to the increased exploration observed in BD patients. GBR 12909 increased activity and reduced spatial d in combination with increased exploratory behavior, irrespective of inbred strain. These effects persisted for at least 3 h.

CONCLUSIONS

Thus, selectively inhibiting the DAT produced a long-lasting cross-strain behavioral profile in mice that was consistent with that observed in manic BD patients. These findings support the use of selective DAT inhibition in animal models of the impaired dopaminergic homeostasis putatively involved in the pathophysiology of BD mania.

Undertaking positive control studies as part of developmental neurotoxicity testing: a report from the ILSI Research Foundation/Risk Science Institute expert working group on neurodevelopmental endpoints

Developmental neurotoxicity testing involves functional and neurohistological assessments in offspring during and following maternal and/or neonatal exposure. Data from positive control studies are an integral component in developmental neurotoxicity risk assessments. Positive control data are crucial for evaluating a laboratory's capability to detect chemical-induced changes in measured endpoints. Positive control data are also valuable in a weight-of-evidence approach to help determine the biological significance of results and provide confidence in negative results from developmental neurotoxicity (DNT) studies. This review is a practical guide for the selection and use of positive control agents in developmental neurotoxicology. The advantages and disadvantages of various positive control agents are discussed for the endpoints in developmental neurotoxicity studies. Design issues specific to positive control studies in developmental neurotoxicity are considered and recommendations on how to interpret and report positive control data are made. Positive control studies should be conducted as an integral component of the incorporation and use of developmental neurotoxicity testing methods in laboratories that generate data used in risk decisions.

A reverse-translational approach to bipolar disorder: rodent and human studies in the Behavioral Pattern Monitor

Mania is the defining feature of bipolar disorder (BD). There has been limited progress in understanding the neurobiological underpinnings of BD mania and developing novel therapeutics, in part due to a paucity of relevant animal models with translational potential. Hyperactivity is a cardinal symptom of mania, traditionally measured in humans using observer-rated scales. Multivariate assessment of unconditioned locomotor behavior using the rat Behavioral Pattern Monitor (BPM) developed in our laboratory has shown that hyperactivity includes complex multifaceted behaviors. The BPM has been used to demonstrate differential effects of drugs on locomotor activity and exploratory behavior in rats. Studies of genetically engineered mice in a mouse BPM have confirmed its utility as a cross-species tool. In a "reverse-translational" approach to this work, we developed the human BPM to characterize motor activity in BD patients. Increased activity, object interactions, and altered locomotor patterns provide multi-dimensional phenotypes to model in the rodent BPM. This unique approach to modeling BD provides an opportunity to identify the neurobiology underlying BD mania and test novel antimanic agents.

Validation of a motor activity system by a robotically controlled vehicle and using standard reference compounds

INTRODUCTION

A series of experiments were undertaken to evaluate the accuracy, precision, specificity, and sensitivity of an automated, infrared photo beam-based open field motor activity system, the MotorMonitor v. 4.01, Hamilton-Kinder, LLC, for use in a good laboratory practices (GLP) Safety Pharmacology laboratory.

METHODS

This evaluation consisted of two phases: (1) system validation, employing known inputs using the EM-100 Controller Photo Beam Validation System, a robotically controlled vehicle representing a rodent and (2) biologic validation, employing groups of rats treated with the standard pharmacologic agents diazepam or D-amphetamine. The MotorMonitor's parameters that described the open-field activity of a subject were: basic movements, total distance, fine movements, x/y horizontal ambulations, rearing, and total rest time. These measurements were evaluated over a number of zones within each enclosure.

RESULTS

System validation with the EM-100 Controller Photo Beam Validation System showed that all the parameters accurately and precisely measured what they were intended to measure, with the exception of fine movements and x/y ambulations. Biologic validation using the central nervous system depressant diazepam at 1, 2, or 5 mg/kg, i.p. produced the expected dose-dependent reduction in rat motor activity. In contrast, the central nervous system stimulant D-amphetamine produced the expected increases in rat motor activity at 0.1 and 1 mg/kg, i.p, demonstrating the specificity and sensitivity of the system.

DISCUSSION

Taken together, these studies of the accuracy, precision, specificity, and sensitivity show the importance of both system and biologic validation in the evaluation of an automated open field motor activity system for use in a GLP compliant laboratory.

Radial arm maze performance of rats following repeated low level microwave radiation exposure

We examined the possibility of changes in "working" memory of rats following whole body exposure to microwave (MW) radiation. During each of 10 days, we exposed rats within circularly polarized waveguides for 45 min to 2450 MHz fields at whole body SARs of 0.6 W/kg (2 micros pulses, 500 pps), followed by testing in a 12 arm, radial arm maze (RAM). Rats received a preexposure injection of one of three psychoactive compounds or saline, to determine whether a compound would interact with MW exposure to affect performance in the maze. Error rate, i.e., reentry into arms already visited, and time to criterion data for 10 consecutive days of testing were analyzed by a three way analysis of variance (ANOVA) using main effects of "exposure" and "drug" and a repeated factor of "test day." Our alpha limit for significance was P <.05. Analyzes of error rates revealed no significant exposure effect, no significant drug effect and no significant interaction between the two main factors. There was a significant difference in test days, as expected, with repeated test-trial days, which indicates that learning was accomplished. There was no significant interaction of test day and the other two factors. The results of our analyzes of time to criterion data included no significant exposure effect, a significant drug effect, a significant test day effect, and a significant interaction between drug and test day factors. Post hoc analyzes of the drug factor revealed that rats treated with either physostigmine or nalrexone hydrochloride, took significantly longer to complete the maze task than rats pretreated with saline or with naloxone methodide. We conclude that there is no evidence from the current study that exposure to of MW radiation under parameters examined caused decrements in the ability of rats to learn the spatial memory task.

Neurobehavioral analysis of developmental iron deficiency in rats

Iron deficiency (ID) in early life alters the course of behavioral and cognitive development in humans, causing decreased physical activity and responsiveness to the environment. The effects of ID on behavior are similar in rats and hypothesized to be related to ID-related impairments in central dopamine pathways. The objective of this study was to examine the association between brain iron measures of dopamine function, and behavioral measures of activity and reactivity. Male and female weanling rats were fed either an iron deficient diet or control diet for 6 weeks. The iron deficient rats showed significantly decreased activity and increased anxiety-like behaviors. Iron deficient rats also showed significant decrements in brain iron content in the corpus striatum, prefrontal cortex, and midbrain and decreases in dopamine receptors and the transporter in the same areas. Multiple regression analysis showed ventral midbrain iron concentration and dopamine D(1) receptor density to be highly associated with exploration and repeated movements, respectively. In addition, the results showed anxiety-like behaviors to be related to prefrontal cortex dopamine transporter and dopamine D(1) receptor densities. We conclude from these analyses that iron concentration in dopamine containing regions and densities of dopamine receptors and the transporter, are significant predictors of measures of activity and reactivity. These observations also strengthen the argument that the Fe-dopamine link is fundamental to understanding biobehavioral difficulties seen in children with ID anemia.

Adaptation of a primate operant test battery to the rat: effects of chlorpromazine

The National Center for Toxicological Research (NCTR) Operant Test Battery (OTB) has been used extensively in rhesus monkeys to characterize the effects of drugs and toxicants on the performance of tasks designed to model several cognitive functions. Recently, the majority of the OTB tasks have been adapted for use in rats. The current study is the first to examine the effects of a prototypic pharmacological agent previously assessed in monkeys on rat OTB performance. The effects of the dopamine antagonist chlorpromazine (0.56-5.6 mg/kg, i.p.) were assessed in rats performing tasks designed to model auditory-visual-position discrimination, learning, time estimation, and appetitive motivation. All four tasks were equally sensitive to the behavioral effects of chlorpromazine. This pattern of sensitivity was very similar to that obtained when chlorpromazine was tested in monkeys performing the OTB. These data thus suggest that operant tasks designed to model cognitive functions in monkeys can also be used in rats, and that the effects of chlorpromazine on the performance of these tasks may be predictive of results obtained with monkeys. Further characterization of the rat OTB using prototypic pharmacological agents will further determine the extent to which drug effects on rat OTB performance can be generalized to primates.

Transplantation of fetal brain tissue into the site of intracerebral hemorrhage in rats

The purpose of this study was to evaluate whether transplantation of fetal forebrain tissue into the hematoma site of rats with intrastriatal hemorrhage could improve the final neurological outcome. Nine to twelve days after collagenase-induced intracerebral hemorrhage, day 14 fetal forebrain fragments were transplanted into hematoma site. Quantitative measures of behavioral function were repeatedly evaluated until the rats were killed 10 weeks after grafting. Histology was used to assess the survival of the grafts and overall brain morphology. Surviving grafts were located in the residual cavity at the hematoma site. However, comparison of rats with live transplants to control rats with no transplant, sham transplant, or dead tissue transplant revealed no statistically significant differences in any of the motor tests.

Effects of chronic episodic hypoxia on monoamine metabolism and motor activity

Chronic episodic hypoxia produces a wide array of cardiovascular dysfunctions in rats, including increases in blood pressure, heart rate, and sympathetic nerve activity. The action of episodic hypoxia might be related to low oxygen itself (hypoxemia) and/or combined with low CO2 (hypocapnia) resulting from hyperventilation. It is unknown whether or not the cardiovascular abnormalities are related to alterations in the central nervous system (CNS) that may be manifested as neurotransmitter and/or behavioral changes. In this study, we investigated effects of episodic eucapnic and hypocapnic hypoxia on monoamine metabolism in both CNS and adrenal glands, and on motor behavioral activity. Thirty-five male rats were divided into 3 groups. Experimental rats were exposed 8 h daily to varying fractional concentrations of inspired oxygen (FiO2) and carbon dioxide (FiCO2) for 35 days. These consisted of brief exposures (3-6s) of episodic (twice every min) eucapnic (3.5% FiO2 and 10% FiCO2, n = 6) or hypocapnic (3.5% FiO2 and 0% FiCO2, n = 14) hypoxia, or room air (21% FiO2 and 0.03% FiCO2, n = 15). Norepinephrine, dopamine, serotonin, and their metabolites in the hypothalamus, hippocampus, and adrenal glands were measured by high-performance liquid chromatography (HPLC). Spontaneous behavioral activity was assessed for 30 min by automated activity monitors. Episodic hypocapnic hypoxia produced a decrease in dopamine turnover and eucapnic hypoxia increased norepinephrine levels in the hypothalamus. Animals exposed to hypocapnic hypoxia also exhibited a consistent increase in horizontal (walking) and vertical (rearing) activity, as well as in total activity time. From these results, it is concluded that episodic eucapnic and hypocapnic hypoxia may affect metabolism of different neurotransmitters in the CNS.

Functional and morphological characterization of neuropathy induced with 5-lipoxygenase inhibitor CGS 21595

Peripheral toxic neuropathy induced in rats with a 5-lipoxygenase inhibitor CGS 21,595 was characterized using special functional tests and pathological procedures. Functional tests included measurement of grip strength, landing foot splay, assessment of sensorimotor and autonomic functions and monitoring of motor activity. Pathological procedures consisted of perfusion fixation, embedding in plastic, teasing of isolated nerve fibers, and light and electron microscopy. Male and female albino rats received the test article orally by gavage on 5 days per week. To characterize the development of the lesion animals treated with 1000 mg/kg were examined and sacrificed at 2-week intervals until termination at 10 weeks. In a separate study, the dose-effect relationship was examined in groups of animals treated with 50,200 or 1000 mg/kg for 10 weeks. Neurotoxicity occurred only in animals treated with 1000 mg/kg and was first detected following 4 weeks of treatment. Although there were no overt clinical signs of neurotoxicity, functional examination detected a reduction of grip strength, increased landing foot splay and reduced motor activity. Neuropathological examination revealed peripheral segmental demyelination affecting predominantly the Schwann cells in the ventral spinal nerve roots. Owing to its unusual localization in the nervous system and to subtlety of functional signs, peripheral segmental demyelination represents a special diagnostic challenge in toxicological safety studies.

Strain and housing affect cocaine self-selection and open-field locomotor activity in mice

We recently conducted an experiment to investigate the possible cooperation between genetic makeup and differential housing on cocaine self-administration in male and female C57BL/6J and DBA/2J mice. Cocaine self-selection was measured in a two-choice test with one choice being cocaine-HCl solution of 40 mg% in tap water and the other choice being plain tap water. Housing conditions began at weaning (21-23 days of age) and consisted of group housed (GH) with 2-3 mice per cage, and isolated housed (IH) with 1 mouse per cage. The results of this study revealed overall strain, sex and housing differences, with C57BL/6Js consuming more cocaine solution than DBA/2J subjects, females consuming more cocaine solution than males, and group housed consuming more than isolate housed subjects. In a second study, the effect of differential housing on open-field locomotor activity was investigated. Testing was conducted on two consecutive days, with subjects receiving an IP injection of saline on day 1, and 15 mg/kg cocaine HCl on day 2. Four behaviors were recorded, including: total distance, nosepokes, stereotypy, and margin time. Overall, the results revealed significant strain differences for stereotypy and nosepokes, and males were found to be more activated by cocaine than females. Additionally, DBA males tended to be differentially affected by housing condition, with IH showing suppressed locomotor activity as compared to GH subjects. Last, significant strain by housing interactions occurred in nosepokes and stereotypy time.

Behavioral toxicity of selected radioprotectors

Effective radioprotection with minimal behavioral disruption is essential for the selection of protective agents to be used in manned spaceflight. This overview summarizes the studies on the behavioral toxicity of selected radioprotectors classified as phosphorothioates (WR-2721, WR-3689), bioactive lipids (16, 16 dimethylprostaglandin E2(DiPGE2), platelet activating factor (PAF), leukotriene C4), and immunomodulators (glucan, synthetic trehalose dicorynomycolate, and interleukin-1). Behavioral toxicity was examined in laboratory mice using a locomotor activity test. For all compounds tested, there was a dose-dependent decrease in locomotor behavior that paralleled the dose-dependent increase in radioprotection. While combinations of radioprotective compounds (DiPGE2 plus WR-2721) increased radioprotection, they also decreased locomotor activity. The central nervous system stimulant, caffeine, was able to mitigate the locomotor decrement produced by WR-3689 or PAF.

Interlaboratory comparison of motor activity experiments: implications for neurotoxicological assessments

Motor activity is an important functional measure used in neurotoxicology. The effects of chemicals on motor activity, however, may depend on variables such as type of measurement apparatus, physical and environmental testing conditions, and many other experimental protocol and organismic variables. Due to the increasing use of motor activity in neurotoxicology, a major question concerns the potential for differences in experimental findings due to variations in sensitivity and reliability between different laboratories and devices used to measure motor activity. This study examined historical data from a number of laboratories that employed different devices and experimental protocols to measure motor activity. Four aspects of the motor activity data were compared: 1) within-laboratory control variability across time; 2) within-laboratory replicability of control data; 3) between-laboratory variability in the effects of chemicals; and 4) between-laboratory comparison of the control rates of habituation. The analyses indicated that there was a relatively restricted range of within-laboratory variability and reliability in control values, and that these ranges were comparable across laboratories. Similar profiles of habituation were also seen across the different laboratories. Moreover, in virtually every case, all laboratories were capable of detecting qualitatively similar changes in motor activity following acute exposure to a variety of chemicals. These data indicate a high degree of comparability in the data generated by the different devices and experimental protocols.

Pharmacologic and toxicologic effects of di(beta-phenylisopropyl)amine (DPIA) in rats and mice

1. Di(beta-phenylisopropyl)amine (DPIA) given i.p. to mice and rats in sublethal doses caused increased motility, mild stereotypic behavior and suppression of food intake. Repeated daily doses led to enhanced motor stimulation, and in one group, 40% lethality, indicating development of "reverse tolerance". Brain monoamine modifiers prevented DPIA-induced motor activity. 2. Treatment with toxic i.p. doses of DPIA enabled determination of the LD50, which was 106.8 mg/kg for isolated mice and 89.7 mg/kg for mice kept in aggregation after dosing. Possible antidotal agents given before a high DPIA dose (LD50) protected significantly against lethality. 3. Combinations of DPIA with (+)-amphetamine in mice at lethal doses showed a subadditive synergism. 4. Effects of DPIA on the cardiovascular system, both i.v. in anesthetized rats and in isolated atrial preparations, were mainly opposite to those of (+)-amphetamine, namely decreases in blood pressure, force of contraction and heart rate.

Validation of a radial maze test for assessing learning and memory in rats

Choice behavior of rats in a radially symmetrical 6-arm maze, without food reward, was validated for assessing changes in learning and memory following treatment with 4 psychoactive agents. The test is designed for future use in routine toxicity studies with laboratory rodents. Each radial main arm of the maze leads to a T-shaped choice-point with a blind alley on the left and a long angled alley on the right. Order of choice of the radial main arms served to score within-session working memory, by evaluating relative recency of arm reentries. The choice between blind alley and long-angled alley at the T-intersections provided a measure of between-session reference memory. Maze behavior as an indicator for impairment in learning and memory was validated by testing rats treated with d-amphetamine, chlorpromazine, scopolamine and physostigmine. Based on the above evaluations, working memory was found to be severely impaired by 0.3 and 1.0 mg/kg scopolamine, and reference memory to be improved by 0.02 mg/kg physostigmine and 1.0 mg/kg amphetamine. Locomotor activity, in terms of the total number of arm choices per test session, was altered by all substances as expected from previous reports in the literature. The test appears to be a valid and sensitive method for assessing learning and memory in the rat without the use of food reward, and thus well suited for implementation in routine toxicity studies with rodents.