UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
SAB-EC-88-043
i , „ i <* « *. OPTICS OF
September 9, 1988 THE ADMINISTRATOR
Honorable Lee M. Thomas
Administrator
U. S. Environmental Protection Agency
401 M Street, SW
Washington, D. C. 20460
Dear Mr. Thomas:
The Neurotoxicology Research Review Committee of the Science
Advisory Board met February 29 and March 1, 1988 to review the
program to develop neurotoxieity methods by the Neurotoxicology
Division (NTD) of the Health Effects Research Laboratory (HERL)
in Research Triangle Park, N.C,
The Committee concluded that NTD is the leading federal
neurotoxicology research organization and, since its formation
ten years ago, has assembled an excellent staff of capable
research scientists who have established a significant record of
contributions to the field. The Committee concludes that NTD can
increase its effectiveness over the short and long term by
implementing the following scientific and administrative
recommendations:
Scientific Recommendations
1. Involve all NTD principal investigators in the
development of more detailed long range planning for methods
development research. This plan will narrow the scope of
behavioral research currently underway in NTD and permit a more
focused approach.
2. Establish a database for reference chemicals with known
neurotoxic effects. Use these same reference chemicals as pro-
totype chemicals for research in all areas.
3. utlilize field batteries of behavioral and
electrophysical tests in high-dose human exposure cases through
interactions with other agencies with access to such cases (e.g.
NIOSH and ATSDR).
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4. Emphasize research on problems associated with screening
tests for repeated low concentration exposure to potential
toxicants.
5. Emphasize research on cross species extrapolation of
toxicity data.
6, Confine the study of limbic system electrophysiological
methods to secondary tests for risk characterization rather than
using them as primary screening techniques,
Administrative Bacjanmendations
l. Develop better mechanisms for assuring budget stability.
Expenditures should be reviewed to assure that NTD is devoting
its resources to its primary mission.
2. Encourage development of funding mechanisms to purchase
equipment with unit costs between $15,000 and $50,000. At
present the acquisition of such equipment is very difficult.
3, Reorganize the management structure responsible for the
molecular toxicology elements of the program (including
neurochemistry and neuropath©logy) to assure the optimal
development and utilization of new techniques in this field. A
separate branch might be fonaed for research in cellular and
molecular toxicology.
The Committee was pleased to participate in this review and
appreciates the opportunity to be briefed on the activites of the
Neurotoxicology Division in the area of methods development. We
request that the Agency consider the advice contained here and
respond to our suggestions.
Sincerely,
Norton Nelson, Chairman
Executive Committee
Richard A. Griesemer, Chairman
Environmental Health Committee
Don McMillan, Chairman
Neurotoxicology Research
Review Committee
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REVIEW OF NEURQTQXICQLQGY METHODS DEVELOPMENT BY N1URQTQXICQLOGY
RESEARCH REVIEW COMMITTEE OF THE SCIENCE ADVISORY BOARD
The Netirotoxicology division (NTD) is the leading federal
neurotoxicology research organization, since its formation ten
years ago, it has assembled an excellent staff of capable
research scientists who have established a significant record of
contributions to the field. The NTD should continue its
leadership role in neurotoxicology and expand its overall impact
on the field through the development of critical test methods and
by addressing key issues that relate to the EPA mission. NTD has
adapted, developed, and/or refined test methods that we would
characterize as mainstream and, in some cases, innovative.
EXECUTIVE
As the leading federal neurotoxicology research
organisation, the NTD is a national asset. The NTD has focused
its attention on the most appropriate potential effects of
neurotoxic chemicals. It has developed and is validating a host
of important methods for screening chemicals for neurotoxicity .
These achievements are playing an important role in the
regulatory process and in the protection of public health.
The next decade should be a major challenge for the NTD.
The committee has made a number of recommendations which it feels
will help NTD to meet this challenge. General recommendations
include the development of better mechanisms for long range
planning, increased cooperation among research groups
(particularly with reference to coordinated attacks on
prototypical chemicals) , a stabilisation of the patterns of
funding which will allow controlled growth, the development of
better mechanisms for the acquisition of equipment and supplies,
and a better balance between long range programs and responses to
emergency problems arising from EPA program offices.
The specific research groups have developed strong programs,
although the groups could coordinate their research better than
they have done. The Neurotoxicology Screening Program has
developed and validated appropriate screening methods/
particularly in behavioral toxicology. These method are now
adequately developed to permit their use in testing chemicals of
regulatory emphasis. Work with methods development and
validation should continue with emphasis on cross species
extrapolation .
The NTD has been particularly effective in developing
electrophysiological methods. This effort should continue with
emphasis on developing a data base for prototypical compounds,
on the mechanisms underlying the evoked potential and on the
interaction of prototypical chemicals with these mechanisms using
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state-of-the-art technology. Certain of the methods under
development, such as kindling procedures and evoked potentials in
hippoeampal slices should be confined to secondary tests for risk
characterization, rather than being used as primary screens for
risk identification.
The behavioral research program is among the most nature of
NTD programs in terms of the development and validation of
appropriate methods. The focus of this group should turn to the
assessment of the consequences of repeated low->level exposure to
chemicals and to the integration of their findings with those of
other research groups.
The investigators working on methods for developmental
neurotoxicity have developed sensitive and cost-effective
methods. This group should focus on the study of prototypic
chemicals using the methods that they have developed, giving the
development of new methods a lower priority..
The program in molecular and cellular toxicology has made
particularly impressive progress in developing a rat model of
organophosphorous-induced delayed neuropathology and in activity
correlating this neuropathology with neurotoxic esterase. They
are also investigating the effects of neurotoxicants on
neurotypic and proteins. This group should focus on intergrating
its research program and findings with those of other groups.
The human functions research stands as a model program,
since its data from animal tests seem to have direct application
to similar human processes and the program has been designed with
such 'efforts in mind. Efforts to field test the screening
batteries in drug and chemical exposure groups should be a focus
for the group.
The considerable research contributions of NTD are to be
commended* Their work is generally of high scientific quality.
The international recognition that NTD's research has obtained .
strongly reinforces EPA*s decision to emphasize the development of
this Division with the Health Effects Laboratory. If NTD gives
careful attention to the long range planning of an integrated
research attack on neurotoxicity problems and receives a
stabilized budget which is adequate to permit reasonable growth
during the next decade, the NTD should continue its leadership
role.
gENESAL COMMENTS
1. A long range plan needs to be developed by NTD. The goals and
objectives of the plan should be understood and supported by all
managers and principal investigators. NTD has provided a
collegial atmosphere in which multMisciplinary research can
develop effectively, despite limitations in funds which may have
hindered the development of some disciplines. While this
atmosphere has avoided the limitations of most academic,
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industrial, or government research institutes, the lack of long
range planning appears to have led many NTD investigators to
pursue their own research interests without requiring them to
develop a common rationale for selecting and evaluating test
methods. It appears that although the Division Director has a
clear vision of the contributions of the NTD to the growth of the
field of neurotoxicology and to the EPA mission, this vision is
not always pursued by Branch management or the principal
investigators who are essentially following their own research
interests.
The lack of long range planning is a special concern since
over half the staff has 8 years or less of experience beyond
their Ph.D. While these more junior investigators are clearly
able and well trained, their vision is necessarily limited by
their experience. The committee recommends that NTD formulate a
long term plan with well defined goals for the Division in
methods development. It is important to recognize that long-term
planning needs 'frequent review and reconsideration, but it is
expected that the major goals of NTD would change infrequently.
The limited experience of junior investigators in NTD suggests
the need for an ongoing peer review process which may tafce the
form of programmatic project review by a Division advisory group,
or peer review of program initiatives by outside experts,
2. A fundamental impediment to the establishment of long range
planning by NTD is the instability of its financial support.
Unanticipated budget cuts with minimal prior notification have
both discouraged NTD from attempts at long range planning and
frustrated investigators. Greater budget stability would be an
important factor in helping the Division to set and achieve long
term goals. The level of funding for equipment and supplies
significantly restricts the research and productivity of some
scientists. The Committee recommends that NTD conduct a careful
review of NTD expenditures, including on-site contract staff,
cooperative agreements, and core research support. This would
assure that an appropriate balance exists and that the limited
funding available is directed toward those activities fundamental
to NTD's mission. The Committee also recommends that
consideration be given to finding funds for conferences such as
those in 19i9 and 1985 that addressed human test methods and test
guidelines for screening. These served effectively to direct the
field to respond to EPA's mission.
3, There is a need for certain equipment and supply items within
the Division that is not being met. The difficulty in obtaining
equipment items with unit costs in the range of $15,000 to
$50,000 and the difficulty in running laboratories with extensive
supply needs on a totally inadequate supply budget are two major
problems that impede the ability of the Division to carry out its
mission. It appears that the supplies budget is a major driving
force and it appears that important research is not carried out
because of its limits. The committee recommends that a funding
mechanism be developed for equipment in the $15,000 to $30,000
range and that four layers of headquarters review not be imposed.
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For example, reviews of on-line computer systems are carried out
at headquarters by personnel who are totally ignorant of
laboratory applications.
4. The organization of the branches is somewhat awkward, with
molecular toxicologists reporting to behaviorists and
physiologists. The disparity in disciplines nay, at times, be
detrimental to the development of the molecular toxicology
programs, including description and explanation to upper
management and competition for resources. The committee
recommends that the Health Effects Research Laboratory management
consider a minor administrative reorganization within the
Division to assure the optimal development and utilization of new
techniques in molecular toxicology (including neuropathology and
neurochemistry).
5, Interactions between the Division and EPA program offices
need to be improved. If the Division is required to respond to
frequently changing priorities (e.g., the "crisis of the'month")
as defined by various program offices, a coherent program cannot
be developed. The Division needs to be .responsive to problems
raised by program offices, but these short-term problems must be
balanced against the Division's investment in achieving long term
goals.
6. The Committee recommends that all research groups concentrate
their research on the'same prototype compounds. Much of the data
on the effects of prototypical compounds on screening tests such
as the functional observational battery may already be available
in drug company files. The Screening for Neurotoxicity
conference planned for April by the American College of
Toxicology is a prototype of a mechanism for at least identifying
such sources of data.
COMMENTS CONCERNING SPECIFIC METHODS.
A. Neurotoxicolocrv Screening Methods
The neurotoxicology screening program has been developing and
validating a wide variety of screening tests for incorporation
into a comprehensive test battery. Among the individual tests in
the battery are the functional observation battery (FOB),
automated testing of motor activity, and schedule-controlled
behavior. The tests are validated by studying, the effects of a
series of known neurotoxicants in the battery in an attempt to
develop profiles for different classes of neurotoxicants. This
is a logical approach for detecting and classifying
neurotoxicants.
The work published by the neurotoxicology screening group has
been of high'quality, with publications appearing in the better
peer-reviewed journals. The group has a good command of the
neurobehavioral toxicology literature and has developed a test
battery that is consistent with the recommendations of various
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select committees. Within the behavioral group, a critical mass
of investigators has been recruited who have shown flexibility in
their approach to problems in neurobehavioral toxicology.
The data developed by the screening group has had an
important influence on the regulatory process in neurotoxicology.
The methods developed by the group, and the chemical database it
has generated, have influenced the recommendations made to the
Agency for the development of neurotoxicity test guidelines. For
example, members of the behavioral toxicology group presented
their data to a recent meeting sponsored by the Office of
Pesticides. The expert committee assembled by the Office of
Pesticides made recommendations to that Office for neurotoxicity
test guidelines under the Federal Insecticide Fungicide and
Rodenticide Act (FIFRA) that depended heavily on the database
developed in the Behavioral Toxicology Branch of NTD, Similarly,
this database has influenced the test guidelines developed under
the Toxic Substance and Control Act (TSCA).
Thus, the neurotoxicology screening .group has been evaluating
the appropriate tests and methods for behavioral toxicity testing
and the data they have generated has influenced regulatory
recommendations. Although this has been a useful approach, a
coordinated research program on the neurobehavioral problems
likely to arise during the next decade needs to be developed.
For example, concerns that the Agency has about problems
developing from long terra low-level exposure to toxicants needs
greater emphasis. There appears to be some lack of coordination
across investigators in evaluating screening methods. For
example, different chemicals are being evaluated for acute
exposure, short-term repeated exposure and subchronic exposure
thus making it difficult to determine the degree to which
extrapolation can be Made from acute to repeated exposure. Also,
increased emphasis should be placed on species extrapolation to
provide a basis for human risk assessment. In general, the
research program is turning out high quality worJc, but the
program needs better coordination and focus.
At least some of these difficulties may have been due to the
level and variability of research funding, it is difficult to
develop a focused plan of when budget cuts are being imposed with
little advance warning.
In view of these strengths and weaknesses of the screening
program the following recommendations are made:
, 1. The screening program should develop a planning process to
determine which problems in neurotoxicology are likely to become
important in the next decade, and how these problems can best be
solved with the limited resources likely to be available.
2. Increased emphasis should be placed on problems and
mechanisms associated with repeated, low level exposure to
potential toxicants.
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3, Where applicable, there should be greater research
emphasis on cross-species extrapolation, particularly
extrapolation to humans.
a. Since many of the difficulties in the development of
extrapolation models may relate to cross-species differences in
phanaacokinetics, the NTD should increases its efforts to develop
pharmacokinetics research within the Division.
b. There is a need for closer cooperation and some
integration of methods between those investigators
developing animal models for neurotoxicity testing and those
involved with human testing and epidemiology.
4. Efforts to validate the screening tests by studying the
effects of a range of chemicals is encouraged. Efforts to
characterize the toxicity through more detailed testing and to
investigate the mechanisms underlying the toxicity are
appropriate and should continue.
Given the poor predictive power "of in yJLfcro. screening,
and the limited available resources, the present efforts should
be limited to two directions; 1) to become and stay knowledgeable
about advances in this area and 2) to utilize appropriate methods
for mechanistic studies of particular problems. It is not yet
time to expend valuable resources in a broad effort on in vitro
screening methods.
B. Electophvsioloqjcal Approaches
The NTD is presently involved in research using
electrophysiological methods with two major emphases: (l) sensory
system toxicity and (2) limbic system activity. The research in
sensory systems focuses on the visual and auditory systems.
Three testing methodologies have been developed for testing the
response of these systems to neurotonic exposures. Flash-evoked
potentials (F1P) and the pattern-reversal evoked potentials
(PREP) assess the functional status of the visual system. The
brainstem auditory evoked response (BAER) assess the functional
status of the auditory system. Two approaches to limbic system
function are also being evaluated.' These include kindling, a
model for a type of electrical activity in animals that closely
resembles certain types of human epilepsy, and evoked potential
analysis of the- perforant path-dentate gyrus portion of the
hippocampus.
1* Sensory Systems Research
An advantage of utilizing evoked potential analyses to
monitor sensory system function is that a similar analyses can be
conducted in many species, including man. In man, the techniques
are noninvasive and involve recording of electrical activity from
surface electrodes attached to the scalp. In animals, the
electrode is usually implanted in the bone overlying the brain to
provide a permanent, reusable recording site.
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Present Status
Over the past 5-8 years, NTD has concentrated upon
development of methods that would be suitable for hazard
identification. Its efforts indicate that evoked potential
approaches (FEP and PREP-visual system and BAER-auditory system)
are useful for hazard identification. Evoked potentials reflect
sensory system function and can detect perturbation in function
associated with neurotoxic insults. The methods may detect
neurotoxicity resulting fromj 1) changes in receptor function,
measured as changes in response threshold; 2) alteration of
pathway integrity measured as alteration in parts of the evoked
potential waveform or by changes in the latency of components of
the response; 3) shifts in information processing function of the
brain as measured by the amplitude of specified response
components. NTD has provided evidence that evoked response
techniques may also be sensitive to neural depression or
excitation.
In addition to developing the specific methodology to test
sensory function, NTD has also conducted research to validate
test methodology and extend the methods to new problems.
Important research has been initiated to improve the sensitivity
and reliability of the test methods and to improve their
efficiency and reduce costs. The lab has begun to establish a
database, using reference chemicals, which is essential to
defining testing reliability and redundancy. It has also
provided a fairly complete analysis of the neurophysiological
effects of selected substances such as the organotin compounds.
Equally important, NTD is studying the basic physiology
underlying the generation of the evoked response. It has
completed important basic research into the generation of the
components of the evoked response which enables the
identification of specific regions of the brain involved in
neurotoxic responses. One of the most significant areas of
research has been the program to study effects of selected
neurotoxican-ts in man and in animal models (rat) . Such
extrapolation studies are essential in validating the animal
models, and in establishing their sensitivity relative to man.
Proposed Research
The investigators at NTD have outlined the following major
areas for future research! 1) completion of a database employing
reference compounds that encompass known neurotoxic mechanisms of
action; 2) improving the understanding of the parallels between
human and animal models to selected neurotoxic agents; 3)
continuing basic research into the neural substrate underlying
evoked responses; 4) refining test procedures to improve
sensitivity and efficiency, reduce redundancy and- reduce costs.
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Recommendations
The committee recommends that NTD continue its program in
this area with the following priorities"
1. A database should be establish using reference chemicals
that encompasses the known neurotoxic effects. Reference
chemicals should be selected to include known mechanisms of
action. A data base is essential for hazard identification,
2. The physiological substrates responsible for generating
the evoked potential should be established. An understanding of
the mechanism underlying the measured response enables the
identification of specific neuronal elements affected by the
neurotoxicants,
3, Studies should be conducted to establish the parallels in
responses of the human and animal model to selected
neurotoxicants. This information will provide insight into the
validity of the animal model and should indicate the relative
sensitivity of the test species (rat) and the target species
(man). This approach provides an important opportunity to obtain
comparative data in man and animal.
4. The methodology for risk assessment should foe continually
refined. More research is needed to: a) determine what are the
critical parameters to be measured? b) determine how redundancy
can be reduced within and between procedures; c) improve
sensitivity, stability and specificity of test methods to
different types of neurotoxins; d) reduce time, labor and animals
required to achieve a desired endpoint.
5. The group should be encouraged to provide data about the
functional integrity of sensory systems for and use by the other
groups in the division (behavior, neurochemistry, neuropathology,
etc.). This will enhance interunit evaluation of various testing
approaches.
6. The group and section head are encouraged to plan for the
development of electrophysiologic approaches to more basic
assessment of neurotoxic mechanisms. The appropriateness of
state of the art technology (e.g. patch clamp, in vitro brain
slice and cell culture systems) to the long term mission of the
division should be addressed. The role that electrophysiology
can play beyond methods development is one that must be addressed
if the various components of the NTD are to grow and evolve in a
smooth, consistent manner*
Limbic .Systems Research
The limbic system is clearly sensitive to the effects many
neurotoxic agents. Its suitability and usefulness in methods
development as related to the mission of NTD has been evaluated
to some degree both by in-house studies and cooperative
agreements. There was concern as to the suitability of this
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research for purposes of hazard identification. The two
approaches to the limbic system function discussed here are
kindling and hippocampal evoked potentials,
Kindling
Kindling (experimental siezures in animals) is time and labor
intensive procedure. Its primary usefulness has been in
providing an animal model of certain types of human epilepsy and
it has been employed to a screen for anti-convulsant drugs, it
has also been shown to be sensitive to certain convulsant drugs,
including some pesticides. Although pesticides at low doses
affect kindling, the Committee agrees with the consensus at NTD
that this model is probably not suitable as a primary screening
method in neurotoxicology,' however, it may be useful as a
secondary test for characterizing neurotoxicity, or it may be of
value in assessing prenatal exposures on central nervous system
development of the offspring, or assessing the consequences of
repeated low level exposures to some chemicals. From the
scientific literature available, kindling can be predicted to be
most sensitive to neurotoxic actions that increase the
excitability of the nervous system.
Hip-P0-C_ampal Evoked Potentials
The hippocampus is a suitable region of the nervous system
for the study of evoked response analysis, particularly of the
monosynaptic perforant path dentate gyrus response. Evoked
responses of the region can be evaluated both in vitro
(hippocampal slices) and in vivo. The approaches have different
but complementary uses. Research done by the group has suggested
that the hippocampal slice is not a suitable method for primary
screening for neurotoxicity. The Committee agrees with this
opinion. The Committee.feels that these methods are more
profitably employed in studies defining mechanisms of toxic
action than in screening. A data base for hippocampal evoked
responses would be useful for comparison with data from other
testing procedures. Filling this data gap might help to
delineate the future role of these approaches for the NTD.
Recommendation
For hippocampal-ER-kindling methods, the Committee recommends
that these procedures not be used as primary screening tests for
hazard identification. They may be of value, however, for
characterization of developmental effects and/or repeated, low
level exposure effects of neurotoxins. Alternative approaches
should be considered carefully because these approaches are time
and labor-intensive. The in vitro hippocampus preparation should
be validated with prototype compounds before it is used widely.
G. Behavioral Research
It has now been recognized that neurotoxicology screening,
with available methods, can be done by studying the behavior of
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target organisms and interactions with, their environment*
Deficits in memory, coordination, judgment, or in response to
environmental changes represent threats to ability to function
efficiently or even to survive. One phase of the NTD program is
directed, for these reasons, at assessments of such behavior.
originally, NTD was charged with developing suitable
assessment Methods for behavioral toxicology. A legacy of that
original mission is an impressive range of procedures, several of
which have demonstrated their utility as neurotoxic endpoints.
This original investment in test method validation and
refinement has now advanced to a stage at which it can serve an a
source for undertaking a major responsibility of NTD — risk
characterization. Further methodological developments should not
be precluded, of course, but the focus should begin to change
from methods development to the use of the methods already
developed is risk characterization* such a shift in priorities
would enable NTD to move into a pivotal position in the new RtJRA
initiative.
At present, those aspects of the program devoted to what is
broadly called, "cognitive behavioral research" encompass a
variety of procedures, each aimed at some aspect of behavior such
as attention, learning, memory, discrimination, and so on.
Within each of these categories, several experimental approaches
are discussed. As a result, techniques tend to proliferate, but
at some cost to depth of analysis and understanding. A limited
range of chemicals is surveyed, and important parametric
manipulations are not explored.
One consequence of the tendency to proliferate tests has been
the emphasis on short-term,, high-dose treatment. EPA is
continually embroiled in disputes about the validity of extreme
doses in projecting cancer risks on the basis of animal studies.
Parallel disputes are certain to arise when the program for
reducing uncertainty in risk assessments (RURA) begins to deal
with neurotoxicity, unless the appropriate data are available.
NTD is uniquely equipped to respond to these future needs of the
agency, but it has to pursue an explicit policy of appropriate
research to do so. Bending the current work on thermoregnlation,
maze performance, flavor avoidance, and delayed response to these
aims will enhance both the research and its utility to the
agency.
The Committee recommends that the scope of research
activities be narrowed to permit a more focused approach. Such a
narrowing would permit NTD scientists to respond to questions of
concern to the agency; e,g, (1) Can behavioral endpoints be used
to trace the progressive consequences of research exposure?
(2) As toxicity unfolds, what is the correspondence between
behavioral, neurochemical, and morphological measures? (3) Would
more detailed analyses of behavioral measures afford an improved
basis for the kinds of extrapolation required for risk
assessment?
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In summary, the committee views the future of behavioral
research at NTD- as closely related to the risk evaluation
process. In accord with this view, it recommends that the
Principal Investigators responsible for these programs adopt a
focused research plan, and carefully consider integration with
other disciplines within NTD.
D. Developmental Methods
The investigators working on methods to identify and describe
developmental neurotoxicity are a talented, well-trained group
who have done a good job of identifying and implementing
promising test methods. They have developed test methods that
are cost-effective and sensitive. Scientifically, they are
productive and in touch with their fields. They interact well
with each other and with colleagues outside the agency,
The group has been less successful at developing a strategy
for assessing the usefulness of the methods that they have
selected. We recommend that they do the following;
1. The group, in conjunction with other groups, should
construct a standard list of toxic and non-toxic agents to use in
methods evaluation. The list should include prototypical agents
whose effects have been well-characterized. They should
represent agents producing a variety of injuries and mechanisms
of injury. Active agents should be tested before proceeding to
screen inactive agents or unknowns.
2. Exposure regimens (or set of regimens) appropriate to
damage the developing nervous system should be- used.
3. The group should perform a logic analysis which specifies
the possible outcomes of the proposed experiments and the
conclusions about methods which will be drawn from those
outcomes.
4. The evaluation of methods should be given a high priority
with the development of new methods receiving a lower priority.
Because new methods appear constantly, the failure to do this
will result in an endless enlargement of the methods catalogue.
The goal should be a reduction of this catalogue to those methods
most valuable for toxicity testing.
E. Molecular ajj<| Cellular Toxicology
The development of a program in immunocytochemistry is
commendable. Where possible, it is recommended that close
coordination between these studies and those involving
biochemical markers be established as a means of validating the
biochemical markers more efficiently.
The development of molecular and cellular indices of toxic
neuropathies is considered particularly promising. However, the
complexity of such systems will require critical outside
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collaborative support, and it is recommended that this be given
.priority.
The atonal transport project has the potential for providing
a sensitive index of toxieity, as well as being of mechanistic
importance. It is recousmended that emphasis be placed upon
validation of these methodologies.
1. NjjU.ropatholggy;
A particularly important direction of this group has been
studies into the biochemistry of NTS. Such studies involve
protein purification and characterization, and their technical
difficulties are exacerbated by the nature of the NT1
differential assay. While such experiments are not guaranteed to
be successful, the remarkable correlation of NTE activity (a
differential enzymatic measurement) with organophosphorous-
induced delayed neuropathy (OPDIN) makes these experiments long
overdue. This direction should be encouraged and may be one
excellent project in which outside assistance (either through
cooperative agreement, consultants, or RFP) would be appropriate*
Previously, it was believed that OPIDM, an important
neurotoxic effect in humans, could not be produced in the rat.
Thus, the chicken has been the accepted model, both increasing
the cost of studies and preventing use of the large body of
neurobiological and toxicological data in the rat. However, the
group at NfD had developed data suggesting that an QPIDN-like
neuropathology can be obtained in the rat. However, the rat
clearly differs from the human and chicken; much higher doses of
organophosphate compounds are needed, and the pathology is not
accompanied by the same degree of incapacitation. Nonetheless,
there are potential applications for such a model, and further
validation and study should be a high priority.
As these examples indicate, the research directions in
neuropathology are strong and clearly related to the mission of
NTD and the Agency. There was, however, 'a lack of integration of
this group with other disciplines. This probably is a result of
the lack of long term planning through the NTD, as well as
competition for resources.
Nenrochemistry
The neuroehemistry group brings several important strengths
to the activities of the NTD. The investigators are individually
strong, and have picked topical areas for their research. For
example, the effects of various neurotoxicants'on neurotypic and
gliotypie proteins is an important subject to understand, and the
investigators should be commended for this approach. However,
they have emphasized this approach as a general marker of
neurotoxieity, rather than as important biochemical loci whose
function needs to be understood (and which later might produce
such a marker). Nonetheless, these competent investigators are
likely to produce important information which will be even more
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useful if integrated into behavioral, physiological, and
pathological studies ongoing elsewhere in the NTD.
As with the neuropathology group, this group should
integrate their research with that of the other research groups.
There were cases where the significant expertise of this group
could have been integrated into projects ongoing by other
sections (such as with the pyrethroids).
F. Human Function lej3j5.ar_Qh
Methods development efforts in the area of human function
have concentrated on specific Agency needs for screening tests
and test batteries which can be used to assess exposures from
waste dumps or chemical spills posing a hazard to the nervous
system. Portable batteries of behavioral and
electrophysiological tests have been developed through NTD
support and the program staff recognizes the need to apply these
batteries in field situations to known neurotoxieants following
accidental exposures to assess battery usefulness under actual
field conditions.
The sensory testing program displays good breadth and depth.
The addition of speech perception to classic audiometry
recognizes the need to assess the processing capability for
patterned sounds by adopting the most important real-life
application of sound patterns. The development of olfactory
trigeminal test capabilities is also important, because of the
unigue status of this system as a warning indicator of
environmental exposures. The implementation of a tactile
sensitivity test device provides a screening test for peripheral
neuropathy, one of the problems identified most freguently
following significant chemical exposures. Because of the doubts
about the validity of the proposed device, however, it should not
be adopted without a thorough validation study. The visual and
auditory testing programs, however, are among the most forward-
looking in the Division because they assess key visual functions
and effectively integrate test methods for humans and animals.
This should be seen as a model for NTD research because it offers
an animal model which can be used in high-dose laboratory
research to identify neurotoxic chemicals in pre-market screening
with confidence that the application to humans is direct, in
addition, the low end of the dose-effect curve can be assessed in
human laboratory research, or, if an accidental spill/exposure
occurs, in affected individuals. This model should be extended
to other programs and test paradigms in NTD,
The future direction of methods development in this program
is sound, aiming at field evaluation and validation of the
screening batteries and laboratory validation of selected sensory
tests. Specific Committee recommendations ares 1) field testing
should be pursued in high-dose exposure cases in industrial or
agricultural settings; 2) test batteries should be' validated
using acute drug exposures and clinical populations; 3) plans
should be made to add vestibular test methods to provide
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capabilities for a more complete sensory analysis* (This is a
good direction as the hardware and software are available and
there is data on a range of environmental chemicals that
demonstrate unique effects using these test systems); 4) the
grotip should adopt the, Peurobehavioral Evaluation System (NES)
for testing children as planned. However, careful attention
should be given to a rationale for selecting tests to adopt from
the many available in the NES, Possible rationales would be to
select tests sensitive to generally accepted behavioral
taxonomies derived from factor analytic studies
(Fieischman/Carroll) or tests sensitive to frequently-occurring
neurotoxic effects? (5) opportunities should be sought to
integrate human and animal test methods in ways similar to visual
function testing that would require long-term planning of
cooperative research goals among the various research specialists
in NTD.
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Science Advisory Board
Neurotoxicology Research Review Committee
Dr. Donald McMillan (Chairman), Department of Pharmacology,
School of Medicine, University of Arkansas, Little RocK, AR,
7220S
Dr. W. Kent Anger, Neurobehavioral Research Section, National
Institute of Occupational Health Sciences, 4676 Columbia ParKway,
Cincinnati, OH 45226
Dr. Shane Gad, Director of Toxicology, G.D, Searle and Co., 4901
Searle Parkway, SJtofcie, IL 60077
Dr. Doyle Graham, Dean of Medical Education, Box 305, Duke
University Medical Center, Durham, NC 27710
Dr. Robert Joy, Department of Veterinary Pharmacology and
Toxicology, University of California at -Davis, Davis, CA, 95616
Dr. Richard Mailman, Department of Psychiatry and Pharmacology,
University of North Carolina School of Medicine, Chapel Hill, NC,
27514
Dr. Kenneth Reuhl, Department of Pharmacology and Toxicology,
Neurotoxicology Laboratory, College of Pharmacy, Rutgers
University, lusch Campus, Piscatawa, NJ 08855-0789
Dr. Patricia Rodier, Box 668, Department OBGYN, University of
Rochester Medical School, Rochester, NY 14642
Dr. Bernard Weiss, Box BPHYS, University of Rochester Medical
School, Rochester, N¥ 14642
Executive Secretary
Dr. C. Richard Cothern, office of the Administrator (A-101F), u*
S. Environmental Protection Agency, Washington, D.c. 20460
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