United States Prevention, Pesticides EPA712-C-96-242
Environmental Protection and Toxic Substances June 1996
Agency (7101)
&EPA Health Effects Test
Guidelines
OPPTS 870.6855
Neurophysiology:
Sensory Evoked
Potentials
'Public Draft"
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INTRODUCTION
This guideline is one of a series of test guidelines that have been
developed by the Office of Prevention, Pesticides and Toxic Substances,
United States Environmental Protection Agency for use in the testing of
pesticides and toxic substances, and the development of test data that must
be submitted to the Agency for review under Federal regulations.
The Office of Prevention, Pesticides and Toxic Substances (OPPTS)
has developed this guideline through a process of harmonization that
blended the testing guidance and requirements that existed in the Office
of Pollution Prevention and Toxics (OPPT) and appeared in Title 40,
Chapter I, Subchapter R of the Code of Federal Regulations (CFR), the
Office of Pesticide Programs (OPP) which appeared in publications of the
National Technical Information Service (NTIS) and the guidelines pub-
lished by the Organization for Economic Cooperation and Development
(OECD).
The purpose of harmonizing these guidelines into a single set of
OPPTS guidelines is to minimize variations among the testing procedures
that must be performed to meet the data requirements of the U. S. Environ-
mental Protection Agency under the Toxic Substances Control Act (15
U.S.C. 2601) and the Federal Insecticide, Fungicide and Rodenticide Act
(7U.S.C. I36,etseq.).
Public Draft Access Information: This draft guideline is part of a
series of related harmonized guidelines that need to be considered as a
unit. For copies: These guidelines are available electronically from the
EPA Public Access Gopher (gopher.epa.gov) under the heading "Environ-
mental Test Methods and Guidelines" or in paper by contacting the
OPP Public Docket at (703) 305-5805 or by e-mail:
guidelines@epamail.epa.gov.
To Submit Comments: Interested persons are invited to submit com-
ments. By mail: Public Docket and Freedom of Information Section, Office
of Pesticide Programs, Field Operations Division (7506C), Environmental
Protection Agency, 401 M St. SW., Washington, DC 20460. In person:
bring to: Rm. 1132, Crystal Mall #2, 1921 Jefferson Davis Highway, Ar-
lington, VA. Comments may also be submitted electronically by sending
electronic mail (e-mail) to: guidelines@epamail.epa.gov.
Final Guideline Release: This guideline is available from the U.S.
Government Printing Office, Washington, DC 20402 on The Federal Bul-
letin Board. By modem dial 202-512-1387, telnet and ftp:
fedbbs.access.gpo.gov (IP 162.140.64.19), or call 202-512-0132 for disks
or paper copies. This guideline is also available electronically in ASCII
and PDF (portable document format) from the EPA Public Access Gopher
(gopher.epa.gov) under the heading "Environmental Test Methods and
Guidelines."
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OPPTS 870.6855 Neurophysiology: sensory evoked potentials.
(a) Scope—(1) Applicability. This guideline is intended to meet test-
ing requirements of both the Federal Insecticide, Fungicide, and
Rodenticide Act (FIFRA) (7 U.S.C. 136, et seq.) and the Toxic Substances
Control Act (TSCA) (15 U.S.C. 2601).
(2) Background. This guideline was developed jointly between the
Office of Pesticide Programs and the Office of Pollution Prevention and
Toxics in cooperation with the Office of Research and Development of
the Environmental Protection Agency. The source material used in devel-
oping this harmonized guideline is 40 CFR 798.6855 Neurophysiology:
sensory evoked potentials.
(b) Purpose. The techniques in this guideline are designed to detect
and characterize changes in the sensory aspects of nervous system function
that result from exposure to chemical substances. The techniques involve
neurophysiological measurements from adult animals and are sensitive to
changes in the function of auditory, somatosensory (body sensation) and
visual sensory systems. These procedures can be used in two ways:
(1) To detect sensory dysfunction produced by compounds in the ab-
sence of relevant information.
(2) When there are reasons to expect that particular sensory functions
are specifically sensitive to the test compound. The procedures employed
during a particular study will be selected on a case-by-case basis depend-
ing on information available at the time of the study design, signs of tox-
icity observed during the study, and/or the purpose of the study. It will
be the responsibility of those submitting to justify the selection of a spe-
cific test from the categories of electrophysiological tests available. The
tests are adaptable so that they may be used in sum or in part, and either
alone or in conjunction with other tests including: A functional observa-
tional battery, motor activity, neuropathology, and general toxicity studies.
These studies may involve acute, subchronic, or chronic exposures.
(c) Definitions. The definitions in section 3 of the Toxic Substances
Control Act (TSCA) and the definitions in 40 CFR Part 792—Good Lab-
oratory Practice Standards apply to this test guideline. The following defi-
nitions also apply to this test guideline.
Neurotoxicity is any adverse effect on the structure or function of
the nervous system related to exposure to a chemical substance.
Toxic effect is any adverse change in structure or function of an exper-
imental animal as a result of exposure to a chemical substance.
(d) Principle of the test method. The test substance is administered
to several groups of experimental animals, each group receiving a different
dose level. Electrodes for recording brain electrical activity are temporarily
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or permanently affixed to the test animals. After electrodes are in place
and, if appropriate surgical recovery, stimuli for the visual, auditory or
somatosensory sensory systems are presented to the test animals, and the
resulting brain electrical potentials are recorded. The electrical potentials
recorded from animals treated with the test compound are compared to
those recorded from control animals. The results are interpreted regarding
the extent to which treatment with the test compound altered the normal
function of the sensory systems tested.
(e) Test procedure—(1) Animal selection—(i) Species and strain.
Testing should generally be performed in the laboratory rat, preferably a
pigmented strain. Albino strains of animals have abnormalities of the vis-
ual and auditory systems (see paragraphs (g)(4), (g)(5), and (g)(13) of this
guideline), including: The absence of pigment from the retinal pigment
epithelial layer, high incidence of spontaneous retinal pathologies, prob-
lems of photogenic retinopathy (under paragraph (g)(7) of this guideline),
abnormal pattern visual evoked potentials (under paragraph (g)(l) of this
guideline), lack of normal pigment in the stria vascularis of the cochlea
(see paragraph (g)(17) of this guideline) and differential susceptibility to
ototoxic noise and drugs from pigmented strains (under paragraphs (g)(2)
and (g)(3) of this guideline). However, it is recognized that under some
circumstances, use of another species or an albino strain may be justified.
If another species or an albino strain is used, the user must submit jus-
tification.
(ii) Age. Animals should be young adults (42-120 days of age, for
rats) at the start of exposure. Implantation of chronic electrodes in rats
younger than 60 days of age is not advised.
(iii) Sex. (A) In order to reduce the number of animals used, only
one sex is required. Male rats may be preferred because there is more
existing data on them. If, on the other hand, females are known or expected
to be more sensitive to the test agent, they may be used. The user should
provide justification for the sex selected.
(B) If females are used, they should be nulliparous and nonpregnant.
(2) Number of animals. A final sample size of at least 10 animals
should be used in each dose and control group. The number of animals
to be used should be based on appropriate statistical methods and an allow-
ance for attrition due to anticipated problems such as loss of electrode
preparations, etc. Note that the rate of attrition should be estimated based
on the experience of the laboratory performing the testing. If interim
neurophysiological evaluations are planned in long-term dosing studies,
it may be advisable to include an additional number of animals sufficient
for the interim studies. Animals should be randomly assigned to treatment
and control groups. If groups are not randomly assigned, justification must
be provided.
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(3) Control groups, (i) A concurrent ("sham" exposure) vehicle
control group is required. Subjects should be treated in the same way as
an exposure group except that administration of the test substance is omit-
ted. If the vehicle used has known or potential neuroactive properties, both
untreated and vehicle-control groups are required.
(ii) Positive control groups exhibiting functional changes in the sen-
sory systems to be tested are required in order to demonstrate the capabil-
ity of the laboratory performing the testing to conduct the procedures. Sep-
arate setups for each sensory system are acceptable, but not necessary.
In addition, for each sensory modality in vehicle or untreated control group
data, it should be demonstrated that the mean of an amplitude-sensitive
dependent measure increases monotonically as a function of stimulus in-
tensity as defined in paragraph (e)(7)(v)(D) of this guideline. Use of histor-
ical positive controls collected in the laboratory conducting the test is ac-
ceptable in order to demonstrate adequate characterization of treatment-
related changes by the approach outlined in this guideline.
(4) Dose levels and dose selection, (i) At least three dose levels
should be used in addition to the vehicle control group. Ideally, the data
should be sufficient to produce a dose-effect curve. We encourage the use
of equally spaced doses on a logarithmic scale, and a rationale for dose
selection that will enable detection of dose-effect relations to the highest
degree possible. For acute studies, dose selection may be made relative
to the establishment of a benchmark dose (BD). That is, doses may be
specified as successive fractions, e.g. 0.5, 0.25 of the BD. The BD itself
may be estimated as the highest nonlethal dose as determined in a prelimi-
nary range-finding study. A variety of test methodologies may be used
to determine a BD, and the method chosen may influence subsequent dose
selection. The goal is to use a dose level that is sufficient to be judged
a limit dose, or clearly toxic. Alternatively, the BD may be specified as
a dose of the test compound producing clear neurotoxic effects in previous
studies.
(ii) Acute studies. The high dose need not be greater than 2 g/kg.
Otherwise, the high dose should result in significant neurotoxic effects
or other clearly toxic effects, but not result in an incidence of fatalities
that would preclude a meaningful evaluation of the data. This dose may
be estimated by a BD procedure as described above, with the middle and
low dose levels chosen as fractions of the BD. The lowest dose should
produce minimal effects or, alternatively, no effects.
(iii) Subchronic and chronic studies. The high dose need not be
greater than 1 g/kg/day. Otherwise, the high dose level should result in
significant neurotoxic effects or other clearly toxic effects, but not produce
an incidence of fatalities that would preclude a meaningful evaluation of
the data. The middle and low dose should be fractions of the high dose.
The low dose should produce minimal effects, or alternatively, no effects.
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(5) Route of exposure. Selection of route may be based on several
criteria: The most likely route of human exposure, the greater likelihood
of observing effects, the practical difficulties, the likelihood of producing
nonspecific effects, and existing data regarding the test compound. Be-
cause more than one route of exposure may be important for many mate-
rials, these criteria may conflict with one another. The route that best meets
these criteria should be selected.
(6) Combined protocol. The tests described herein may be combined
with any other toxicity study, as long as none of the requirements of either
is violated by the combination.
(7) Study conduct—(i) Preparation of animals for recording. (A)
For electrophysiological recording it usually will be necessary to implant
animals with chronic in-dwelling electrodes using stereotaxic surgical pro-
cedures. In some circumstances, acute attachment of temporary electrodes
may be acceptable if criteria for humane treatment of animals, for record-
ing without undue anesthesia, and for data acceptability detailed below
can be met. Chronic implantation of electrodes will require surgical anes-
thesia and surgical techniques appropriate for the species as outlined in
current laboratory animal care guidelines under paragraph (g)(16) of this
guideline. Standard animal surgical practices should be followed as out-
lined in a number of standard references (e.g. paragraph (g)(10) of this
guideline). Once anesthetized, animals are usually placed in a stereotaxic
device in order to position the head firmly. The stereotaxic device should
be designed to prevent trauma to the tympanic membranes and, for audi-
tory studies, tympanic membranes should be examined after removal from
the stereotaxic device.
(B) Care should be taken during surgery to prevent drying of the
cornea through means such as regular application of fluids such as mineral
oil, saline, or artificial tear solution. Once the animal is positioned in the
stereotaxic device and the implantation site is prepared, the electrodes
should be positioned with reference to standard skull markings and/or to
published brain atlas coordinates (see paragraph (g)(ll) or (g)(12) of this
guideline).
(C) For recording potentials which are generated in sensory cortex,
the recording or active electrodes are to be positioned as close as possible
to the brain sites generating the response. For "far-field" potentials such
as the brainstem auditory evoked potential, which are conducted through
cranial tissues from sites relatively distant to the recording electrodes, the
location of the recording electrodes should be such as to provide good
resolution of the major waveform components, but need not be as close
as possible to the generator sites. The site of the reference electrode for
differential recordings should be indifferent with respect to stimulus-
evoked electrical activity to the extent possible. A ground electrode should
also be included. The electrodes should be made of a material that is not
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toxic to neural tissue. The electrodes should be made of a nonpolarizable
material, such as silver-silver chloride, if potentials of a frequency less
than approximately 1 Hz are to be reported. However, extra caution should
be exercised in this case to avoid toxic effects of such electrodes. Elec-
trodes should be described as to composition, size, shape, and position.
(D) Wound sites should be treated and closed so as to prevent infec-
tions and to protect the integrity of the electrodes. Following surgery, elec-
trode impedance should be measured in order to verify that electrode con-
nections are intact and functional. Following surgery, animals should be
given sufficient time to recover from the anesthetic and surgical trauma
prior to testing; ordinarily a period of one week is recommended. Prior
to testing, the wound site should be inspected for signs of infection or
inflammation, and any animal showing such signs should be removed from
the experiment.
(E) For acute studies, it is necessary to perform surgery prior to ad-
ministering the test compound. In repeated dosing, it may be necessary
to implant the electrodes during the course of treatment with the test
compound due to the limited time which electrode preparations may be
expected to remain intact. It may be advisable to prevent exposure to the
test compound on the day of surgery due to possible interactions of the
effects of the test compound and the anesthetic agent. The time between
surgical implantation of electrodes and testing should be equal for all ani-
mals or, if unequal, balanced across the treatment groups. Animals losing
electrode preparations between time of surgery and testing should be re-
moved from the study and not submitted to another surgery. At termination
of the study, postmortem examination of each animal should be used to
determine if the electrodes were incorrectly positioned, or if the presence
of epidural electrodes damaged the underlying neural tissue. If either of
these two conditions is found, the data from the involved animal should
be discarded.
(ii) Testing environment. (A) Electrophysiological testing should be
conducted in a chamber or room which is isolated from extraneous light
and noise and controlled for temperature. Background noise, light, and
room temperature should be reported. Where possible, testing should be
conducted without the use of restraint or anesthetics. The use of restraint
may be necessary when a specific orientation to, or distance from, the
stimulation equipment is required, or when movement of the animal would
interfere with recording.
(B) For auditory testing of unrestrained, unanesthetized animals,
acoustic stimuli should be of equal sound pressure level wherever the ani-
mals' ears may be placed during data acquisition. The animal enclosure
should be acoustically transparent to sound in the frequency band of the
stimulus spectrum. The use of anesthetic is permissible when consider-
ations of animal discomfort prohibit testing awake animals, and when it
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can be reasonably expected that the effects of the test agent would not
be substantially different under anesthesia. If recording is to be performed
on anesthetized animals, body temperature should be maintained within
a normal range during testing. In addition, if recording from anesthetized
animals, the power spectrum of the spontaneous electroencephalogram
(EEG) should be measured in order to control depth of anesthesia. Position
of the stimulation device or devices relative to the appropriate sensory
organs should be specified.
(iii) Electrophysiological recording. (A) Electrophysiological re-
cording procedures should follow generally accepted practice such as is
found in standard reference texts (under paragraph (g)(8) or (g)(15) of
this guideline). Typically, it is appropriate to differentially record between
active and reference electrodes using an amplifier with high common mode
rejection and high input impedance relative to that of the electrodes.
(B) Electrical shielding and grounding should be used to eliminate
activity in the electrophysiological recording at the frequency of the power
lines reflecting inductive noise. Electrophysiological amplifiers and filter
bandpass settings must be appropriate to the signal being measured. For
example, ac-coupling is appropriate for most applications, but de-coupling
should be used if steady potentials are to be measured. Analog electrical
activity is typically digitized using an analog-to-digital converter operating
at a rate at least twice, preferable higher, the highest frequency passing
the input filters. Analog or digital filtering of data is appropriate to im-
prove signal-to-noise ratios. If using analog filtering, the decay functions
of the high and low bands of the filters should be specified, and filtering
parameters should be selected to avoid amplitude reductions or phase shifts
in the frequency bands of the signal to be measured.
(iv) Signal averaging. (A) Signal averaging of the input data syn-
chronized with the stimulation is appropriate to increase the signal-to-noise
ratio. The number of trials averaged should be sufficient to yield reliable
data, and a waveform in control animals for which the maximum ampli-
tude measure to be reported at the minimum intensity stimulus is at least
50 percent greater in amplitude than the recording noise level. The dura-
tion of the sampling epoch should be sufficient to encompass all major
components of transient evoked potentials. Automated artifact rejection
routines may be employed to reject occasional spurious data provided that
no greater than 50 percent of the original trials are rejected for any given
waveform, and all final averaged waveforms for a given stimulus condition
are based on an equal number of trials.
(B) The data for cases in which greater than 50 percent of the trials
are rejected due to artifacts should be discarded, and the recording condi-
tions improved, if possible, to allow more suitable data collection. The
recording noise level should be determined in order to illustrate the signal-
to-noise ratio. Acceptable methods to do so include: examining a portion
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of the data preceding the presentation of the stimulus, but following the
last of the evoked activity from the previous stimulus in transient evoked
potentials; averaging an equal number of trials as the recording session
but without presentation of the eliciting stimulus (for visual stimuli this
should be accomplished by temporarily blocking the test subjects view
of the stimulus with an opaque material); averaging alternate trials of in-
verted polarity during the standard recording session, or reaveraging the
original raw data from the standard recording session over a similar num-
ber of trials in a manner nonsynchronous with the eliciting stimulus. The
voltage gain and temporal response properties of the electrophysiological
recording equipment should be calibrated for each experiment, or more
frequently as needed. The same recording conditions should be used on
all animals tested.
(v) Stimulation. The selection of stimulation parameters will depend
upon the specific goals of the study. Tests should include measures of
visual, auditory and somatosensory systems, unless there are reasons to
limit testing to particular aspects of sensory function. The testing of mul-
tiple sensory systems in the same animal has been demonstrated (see para-
graphs (g)(9) and (g)(14) of this guideline). The order of presentation of
the different tests to individual subjects be either random, balanced across
treatment groups, or fixed. If the test order is fixed, justification for the
test order should be provided.
(A) Visual stimuli. Visual testing should include separate tests in-
volving light flashes and patterned stimuli. Visual pattern testing should
employ stimuli with a sinusoidal spatial luminance profile, and should in-
clude a range of pattern sizes which encompass the low, middle and high
spatial frequency ranges of the contrast sensitivity function of the test spe-
cies. Techniques for recording visual evoked potentials using both flashed
(under paragraph (g)(6) of this guideline) and patterned stimuli (under
paragraph (g)(l) of this guideline) are available for laboratory rats.
(B) Auditory stimuli. Auditory testing should include a stimulus of
broadband frequency characteristics, such as a click. In addition, pure tone
stimuli reflecting the low, middle and high frequency portions of the
audiometric function of the test species should be used. Techniques for
recording auditory evoked potentials using both click and pure tone stimuli
(under paragraph (g)(14) of this guideline) are available for laboratory rats.
(C) Somatosensory stimuli. Somatosensory testing should include
electrical stimuli delivered to the tail or distal portions of the lower extrem-
ities. Techniques for recording somatosensory evoked potentials are avail-
able for laboratory rats (under paragraph (g)(14) of this guideline).
(D) Stimulus levels. (7) For studies designed to detect a change in
sensory function produced by a compound for which little is known, it
is sufficient to use a single stimulus level for each visual, auditory or
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somatosensory evoked potential. Justification for the stimulus level se-
lected should be provided. For studies designed to characterize a sensory
effect, at least three different levels of flash intensity, pattern contrast,
acoustic click stimulus sound pressure level or somatosensory stimulus
current are required for each stimulus condition. The stimulus levels
should be chosen on the basis of prior experience and/or pilot studies.
(2) In control animals, the low level should be near the response
threshold, but large enough to produce a response amplitude at least 50
percent greater than the recording noise level. Specification of the high
stimulus level varies with stimulus type. For flashed visual stimuli the high
stimulus level should either produce a maximal response, or be the maxi-
mum output available from a conventional stimulator (e.g. Grass model
PS-22 photic stimulator). For patterned visual stimuli the high stimulus
level should either produce a maximal response, or be below the highest
level of contrast within the linear range of the input-voltage/stimulus-con-
trast calibration function of the stimulus screen. For somatosensory stimuli
the high stimulus level should either produce a maximal response, or be
at or below a current which produces minimal reflexive muscle movement
or other indications of discomfort. For acoustic stimuli the high stimulus
level should be below approximately 80 decibels sound pressure level in
order to avoid production of temporary or permanent threshold shifts.
(3) For all types of stimuli, the middle stimulus level should produce
a response intermediate between high and low stimulus levels. The phys-
ical and temporal parameters of stimuli should be calibrated against known
standards for each experiment using commonly accepted procedures.
(4) Visual stimulus luminance and contrast, or for flashes integrated
power, should be calibrated with an appropriate radiometer or photometer
against a known standard. Acoustic stimuli should be calibrated for level
using equipment which meets standards of the American National Stand-
ards Institute (ANSI) for sound level meters. Stimuli should be measured
and reported as peak levels, maximum root mean square (max RMS), or
"peak equivalent" sound pressure levels. In addition, the polarity of the
electrical stimulus and the transduction system for acoustic stimuli should
be reported.
(vi) Measurement. (A) Dependent measures should be taken from
each evoked potential which are sensitive to changes of both amplitude
(voltage) and latency (time after stimulus onset) for transient evoked po-
tentials or phase for steady-state evoked potentials. Enough measures
should be taken to adequately reflect the shape of the evoked potential
in control animals.
(B) A variety of measurement schemes may be acceptable, provided
they are specified a priori, do not ignore major portions of the waveform,
yield ratio-scale values, and meet the criterion for positive controls speci-
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fied in paragraph (e)(3)(ii) of this guideline. If the measurement scheme
involves inspection of each waveform by an operator and scoring of the
waveform, the criteria for scoring should be objective and stated.
(C) The experiment also must be conducted so that the experimental
personnel are unaware of the treatment of individual animals at the time
of scoring. Measurement schemes that minimize the scoring by personnel
of each response are preferred. The same data scoring procedure must be
used on all subjects.
(D) Previously collected data demonstrating selective effects of the
test compound may be used to restrict the number of test parameters and/
or the number of measured endpoints in order to examine more restricted
hypotheses. Colonic temperature should be measured at the time of each
electrophysiological recording. Body weight should be measured on each
test day.
(vii) Acute. Testing should be timed to include the estimated time
of peak effect.
(viii) Repeated dosing. Testing should be conducted after the com-
pletion of dosing with the test compound when it can be expected that
transient effects of the final treatment have dissipated. Additional testing
may be conducted during the course of treatment in order to provide infor-
mation on the emergence of toxic effects.
(f) Data reporting and evaluation. The following should be re-
ported:
(1) Description of the test methods. This must include:
(i) Positive control data from the laboratory performing the test which
demonstrate the sensitivity of the procedure being used. Historical control
data can be critical in the interpretation of study findings. We require sub-
mission of such data to facilitate the rapid review of the significance of
the observed effects.
(ii) Procedures for calibrating the stimulation and recording equip-
ment and balancing the groups.
(2) Results. The following must be arranged by test group (dose
level).
(i) In tabular form, data must be provided showing for each animal:
(A) Its identification number.
(B) Body weight for each day tested.
(C) Values of each evoked potential dependent measure
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(D) Body temperature of the animal at the time of acquisition of each
evoked potential.
(iii) Group summary data should also be reported. Data reporting
should include in tabular form measures of central tendency and variability
for each combination of stimulus conditions and treatment with the test
compound, and the statistical significance level for effects of treatment
with the test compound associated with each set of values. The final sam-
ple size should be reported along with reasons for excluded or missing
data. The noise level should be reported. Graphic presentation of the data,
or portions thereof, may also be included. Also, samples of typical individ-
ual animal evoked potential waveforms illustrating all stimulus conditions
and the noise level, or preferably group mean waveforms of the same,
should be included.
(3) Evaluations of the data—(i) Data analysis. (A) Numerical data
analysis should include a measure of central tendency, such as mean, and
a measure of variability, such as standard error of the mean, for each stim-
ulus and dose treatment combination, and for each dependent variable.
(B) Statistical analysis should test the null hypothesis of no statis-
tically significant overall effect of treatment with the test compound across
stimulus conditions for each type of sensory evoked potential. In addition,
statistical tests for interactions between treatment with the test compound
and the manipulation of the stimulus parameters should be performed and
the results reported. The choice of statistical analysis should consider the
experimental design and address the problem of adjustments for multiple
statistical analyses.
(ii) Interpretation. The report should include an interpretation of the
neurotoxicological significance of the findings, and relate the
neurophysiological results to those of other neurotoxicological results, and
to other data to the extent possible.
(g) References. The following references should be consulted for ad-
ditional background information on this guideline.
(1) Boyes, W. K. and R. S. Dyer. Pattern reversal visual evoked po-
tentials in awake rats. Brain Research Bulletin 10:817-823 (1983).
(2) Conlee J.W. et al. Differential susceptibility to noise-induced per-
manent threshold shift between albino and pigmented guinea pigs. Hearing
Research 23:81-91 (1986).
(3) Conlee J.W. et al. Differential susceptibility to gentamicin
ototoxicity between albino and pigmented guinea pigs. Hearing Research
41:43-52(1989).
(4) Creel, D. Inappropriate use of albino animals in research. Phar-
macology and Bioochemical Behavior 12:969-977 (1980).
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(5) Creel, D. Albinism and evoked potentials: Factors in the selection
of infrahuman models in predicting the human response to neurotoxic
agents. Neurobehavioral Toxicology and Teratology 6:447-453 (1984).
(6) Dyer, R. S. and H. S. Swartzwelder. Sex and strain differences
in the visual evoked potentials of albino and hooded rats. Pharmacology
and Biochemical Behavior 9:301-306 (1978).
(7) Heywood, R. and C. Gopinath. Morphological assessment of vis-
ual dysfunction. Toxicology and Pathology 18:204-217 (1990).
(8) International Federation of Societies for Electroencephalography
and Clinical Neurophysiology. Recommendations for the Practice of Clini-
cal Neurophysiology. Elsevier Science, Amsterdam, The Netherlands
(1983).
(9) Mattsson, J. L. and R. R. Albee. Sensory evoked potentials in
neurotoxicology. Neurotoxicology and Teratology 10:435-443 (1988).
(10) Myers, R.D. Methods in Psychobiology. Academic Press, NY
(1971).
(11) Paxinos, G. and Watson, C. The Rat Brain in Stereotaxic Coordi-
nates. Academic Press, Sydney (1982).
(12) Pelligrino, L. J. et al. A Stereotaxic Atlas of the Rat Brain, 2nd
ed., Plenum, NY (1979).
(13) Prieur, D. J. Albino animals: Their use and misuse in biomedical
research. Comparative Pathology Bulletin XIV(3):l-4 (1982).
(14) Rebert, C. S. Multisensory evoked potentials in experimental and
applied neurotoxicology. Neurobehavioral Toxicology and Teratology
5:659-671 (1983).
(15) Thompson, R.F. Methods in Physiological Psychology, Vol 1:
Bioelectric Recording Techniques; Parts A, B and C. Academic Press, NY
(1973 and 1974).
(16) U.S. Department of Health and Human Services, Public Health
Service, National Institutes of Health, Publication No. 85-23, Guide for
the care and use of laboratory animals, Revised 1985.
(17) Witkop, C. J. et al. (eds), The Metabolic Basis of Inherited Dis-
eases, McGraw-Hill, NY, pp. 301-346 (1983).
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