Behavioral test methods workshop

Roadbumps at the Crossroads of Integrating Behavioral and In Vitro Approaches for Neurotoxicity Assessment

With the appreciation that behavior represents the integration and complexity of the nervous system, neurobehavioral phenotyping and assessment has seen a renaissance over the last couple of decades, resulting in a robust database on rodent performance within various testing paradigms, possible associations with human disorders, and therapeutic interventions. The interchange of data across behavior and other test modalities and multiple model systems has advanced our understanding of fundamental biology and mechanisms associated with normal functions and alterations in the nervous system. While there is a demonstrated value and power of neurobehavioral assessments for examining alterations due to genetic manipulations, maternal factors, early development environment, the applied use of behavior to assess environmental neurotoxicity continues to come under question as to whether behavior represents a sensitive endpoint for assessment. Why is rodent behavior a sensitive tool to the neuroscientist and yet, not when used in pre-clinical or chemical neurotoxicity studies? Applying new paradigms and evidence on the biological basis of behavior to neurobehavioral testing requires expertise and refinement of how such experiments are conducted to minimize variability and maximize information. This review presents relevant issues of methods used to conduct such test, sources of variability, experimental design, data analysis, interpretation, and reporting. It presents beneficial and critical limitations as they translate to the in vivo environment and considers the need to integrate across disciplines for the best value. It proposes that a refinement of behavioral assessments and understanding of subtle pronounced differences will facilitate the integration of data obtained across multiple approaches and to address issues of translation.

Dose and Time Response Study to Develop Retinal Degenerative Model of Zebrafish with Lead Acetate

Animal models are the silent scouts that help to understand the complex biological processes and gather data that aid our understanding of how organisms function. Various animal models are being sacrificed to assess the impact of toxic chemicals. Mortality calculations should be minimized and much data should be collected on the basis of clinical signs that can contribute to identifying robust humane endpoints linked to mortality. This study was designed to calculate the lowest possible dose of PbAc (lead acetate), a neurotoxicant, that can have a toxicological impact on the zebrafish retina and to minimize animal usage. Dose and time-dependent changes were observed in the zebrafish retina following PbAc exposure with zero mortality. Vision and visual behavior response are the foremost indicators that can be recorded to mark the risk assessment of any chemical. Therefore, the present study aims at dose and time response to find the lowest dose of PbAc affecting the zebrafish retina and its visual behavior. Zebrafish were treated for 3 weeks with four concentrations of 0.04, 0.06, 0.08, and 0.1 mg/L of PbAc for a dose-response study. Then for the time response study, two doses 0.08 and 0.1 mg/L were selected and zebrafish were exposed to those concentrations for 2 and 4 weeks. The results of qualitative and quantitative analyses of retinal histology showed that 15 days of treatment with 0.08mg/L concentration can cause appropriate damage to the photoreceptor layer. At the ultrastructural level, it was further observed that PbAc induces damage to the photoreceptors, especially the rod cells. Escape response behavior showed a significant decrease in visual response to changing contrasts in an increasing dose-dependent manner.

CNS Safety Screening Under ICH S7A Guidelines Requires Observations of Multiple Behavioral Units to Assess Motor Function

In the adoption of behavior as a critical end point in safety pharmacology and neurotoxicity screening, federal regulatory agencies have shifted the predominating scientific perspective from pharmacology back to the experimental analysis of behavior (psychology). Nowhere is this more evident than in tier I safety assessment of the central nervous system (CNS). The CNS and peripheral nervous system have multiple behavioral units of general activity. A complete picture of the motor control neural pathways cannot be measured by any one single approach. The CNS safety protocols under International Council for Harmonization of Technical Requirements for Pharmaceuticals for Human Use S7A are required to be conducted in accordance with Good Laboratory Practices by trained technical staff. The CNS safety assessments necessitate the inclusion of a thorough and detailed behavioral analysis of home cage activity, the response to handling, and transportation to and observations within an open-field apparatus with ancillary measures of basal muscle tone, muscle strength, and tremor in a functional observation battery, as well as quantitative measurements of 3-dimensional activity in an automated photobeam arena. Cost-cutting initiatives or a radical application of the "reduce use" principle of the 3 Rs only jeopardize the spirit, intent, and predictive validity of tier I safety testing assays dictated by current drug safety guidelines.

Neurobehavioral assessment of mice following repeated oral exposures to domoic acid during prenatal development

Domoic acid (DA) is an algal toxin which has been associated with significant neurotoxicity in humans, non-human primates, rodents, and marine mammals. Developmental exposure to DA is believed to result in neurotoxicity that may persist into adulthood. DA is produced by harmful algal blooms of Pseudo-nitzschia, raising concerns about the consumption of contaminated seafood. We evaluated oral exposures to DA during pregnancy in mice. Doses of 0 (vehicle), 1 or 3mg/kg/d of DA were administered by gavage to C57BL/6J mice on gestational days 10 to 17. The offspring were tested for persistent neurobehavioral consequences during early development, adolescence and adulthood. Neurobehavioral tests revealed both dose- and gender-related differences in several neurobehavioral measures, including motor coordination in the rotarod test, behavior in the elevated plus maze, circadian patterns of activity in Phenotyper cages, gait as assessed in the Catwalk, and exploratory activity in the Morris water maze. This study demonstrated significant gender-specific and persistent neurobehavioral effects of repeated prenatal oral exposures to DA at low-dose levels that did not induce toxicity in dams.

Recommendations for harmonization of data collection and analysis of developmental neurotoxicity endpoints in regulatory guideline studies: Proceedings of workshops presented at Society of Toxicology and joint Teratology Society and Neurobehavioral Teratology Society meetings

The potential for developmental neurotoxicity (DNT) of environmental chemicals may be evaluated using specific test guidelines from the US Environmental Protection Agency or the Organisation for Economic Cooperation and Development (OECD). These guidelines generate neurobehavioral, neuropathological, and morphometric data that are evaluated by regulatory agencies globally. Data from these DNT guideline studies, or the more recent OECD extended one-generation reproductive toxicity guideline, play a pivotal role in children's health risk assessment in different world areas. Data from the same study may be interpreted differently by regulatory authorities in different countries resulting in inconsistent evaluations that may lead to inconsistencies in risk assessment decisions internationally, resulting in regional differences in public health protection or in commercial trade barriers. These issues of data interpretation and reporting are also relevant to juvenile and pre-postnatal studies conducted more routinely for pharmaceuticals and veterinary medicines. There is a need for development of recommendations geared toward the operational needs of the regulatory scientific reviewers who apply these studies in risk assessments, as well as the scientists who generate DNT data sets. The workshops summarized here draw upon the experience of the authors representing government, industry, contract research organizations, and academia to discuss the scientific issues that have emerged from diverse regulatory evaluations. Although various regulatory bodies have different risk management decisions and labeling requirements that are difficult to harmonize, the workshops provided an opportunity to work toward more harmonized scientific approaches for evaluating DNT data within the context of different regulatory frameworks. Five speakers and their coauthors with neurotoxicology, neuropathology, and regulatory toxicology expertise discussed issues of variability, data reporting and analysis, and expectations in DNT data that are encountered by regulatory authorities. In addition, principles for harmonized evaluation of data were suggested using guideline DNT data as case studies.

The standardized functional observational battery: Its intrinsic value remains in the instrument of measure: The rat

The International Conference on Harmonisation's (ICH) Tripartite Guideline on Safety Pharmacology Studies for Human Pharmaceuticals has adopted the requirement that each new test substance must be tested for effects on the central nervous system prior to "first dose in man". This assessment is required to measure, at a minimum, the effects of the substance on general motor activity, behavioral changes, coordination, sensory/motor reflex responses, and body temperatures. To achieve this goal, ICH S7A recommends a neurobehavioral assessment (usually a functional observational battery (FOB) or modified Irwin test), which is generally undertaken in the rat. There seems to be a growing lack of consensus on the value of the FOB to determine CNS safety. This review highlights the importance of the time, effort and cost of training technicians to familiarize with their instrument of measure, so that each observer is better able to identify and document very subtle changes in behavior that will serve to increase the reliability and validity of these assays with respect to CNS safety assessments.

Fundamentals of neurobiology

Session 1 of the 2010 STP/IFSTP Joint Symposium on Toxicologic Neuropathology, titled "Fundamentals of Neurobiology," was organized to provide a foundation for subsequent sessions by presenting essential elements of neuroanatomy and nervous system function. A brief introduction to the session titled "Introduction to Correlative Neurobiology" was provided by Dr. Greg Hall (Eli Lilly and Company, Indianapolis, IN). Correlative neurobiology refers to considerations of the relationships between the highly organized and compartmentalized structure of nervous tissues and the functioning within this system.

Functional assays for neurotoxicity testing

Neurobehavioral and pathological evaluations of the nervous system are complementary components of basic research and toxicity testing of pharmaceutical and environmental chemicals. While neuropathological assessments provide insight as to cellular changes in neurons, behavioral and physiological methods evaluate the functional consequences of disruption of neuronal communications. The underlying causes of certain behavioral alterations may be understood, but many do not have known direct associations with specific brain pathologies. In some cases, however, rapidly expanding mouse models (transgenic, knock-out) are providing considerable information on behavioral phenotypes of altered pathology. Behavior represents the integrated sum of activities mediated by the nervous system, and functional tests used for neurotoxicity testing tap different behavioral repertoires. These tests have an advantage over pathologic measures in that they permit repeated evaluation of a single animal over time to determine the onset, progression, duration, and reversibility of a neurotoxic injury. Functional assays range from a screening-level battery of tests to refined procedures to tap specific forms of learning and/or memory. This article reviews common procedures for behavioral toxicity testing and provides examples of chemical-specific neurobehavioral-pathological correlations in order to inform interpretation and integration of neuropathological and behavioral outcomes.

A retrospective performance assessment of the developmental neurotoxicity study in support of OECD test guideline 426

OBJECTIVE

We conducted a review of the history and performance of developmental neurotoxicity (DNT) testing in support of the finalization and implementation of Organisation of Economic Co-operation and Development (OECD) DNT test guideline 426 (TG 426).

INFORMATION SOURCES AND ANALYSIS

In this review we summarize extensive scientific efforts that form the foundation for this testing paradigm, including basic neurotoxicology research, interlaboratory collaborative studies, expert workshops, and validation studies, and we address the relevance, applicability, and use of the DNT study in risk assessment.

CONCLUSIONS

The OECD DNT guideline represents the best available science for assessing the potential for DNT in human health risk assessment, and data generated with this protocol are relevant and reliable for the assessment of these end points. The test methods used have been subjected to an extensive history of international validation, peer review, and evaluation, which is contained in the public record. The reproducibility, reliability, and sensitivity of these methods have been demonstrated, using a wide variety of test substances, in accordance with OECD guidance on the validation and international acceptance of new or updated test methods for hazard characterization. Multiple independent, expert scientific peer reviews affirm these conclusions.

Identification and interpretation of developmental neurotoxicity effects

The reliable detection, measurement, and interpretation of treatment-related developmental neurotoxicity (DNT) effects depend on appropriate study design and execution, using scientifically established methodologies, with appropriate controls to minimize confounding factors. Appropriate statistical approaches should be optimized for the specific endpoints in advance, analyzing effects across time and functional domains as far as possible. If available, biomarkers of exposure are useful to assess the bioavailability of toxicants to the dam and offspring in utero and after birth. Finally, "weight of evidence" principles are used to aid assessment of the biological significance of differences from concurrent controls. These effects should be interpreted in light of available information from historical controls, positive controls, maternal and offspring systemic toxicity, and other relevant toxicological data. This review provides a framework for the integration of all these types of information in the interpretation of DNT studies.

Determining normal variability in a developmental neurotoxicity test: a report from the ILSI Research Foundation/Risk Science Institute expert working group on neurodevelopmental endpoints

With the implementation of the Food Quality Protection Act in 1996, more detailed evaluations of possible health effects of pesticides on developing organisms have been required. As a result, considerable developmental neurotoxicity (DNT) data have been generated on a variety of endpoints, including developmental changes in motor activity, auditory startle habituation, and various learning and memory parameters. One issue in interpreting these data is the level of variability for the measures used in these studies: excessive variability can obscure treatment-related effects, or conversely, small but statistically significant changes could be viewed as treatment related, when they might in fact be within the normal range. To aid laboratories in designing useful DNT studies for regulatory consideration, an operational framework for evaluating observed variability in study data has been developed. Elements of the framework suggest how an investigator might approach characterization of variability in the dataset; identification of appropriate datasets for comparison; evaluation of similarities and differences in variability between these datasets, and of possible sources of the variability, including those related to test conduct and test design. A case study using auditory startle habituation data is then presented, employing the elements of this proposed approach.

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.

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.