Download Alterations in Neurobehavioral Responses in Fishes Exposed to

AMER. ZOOL., 37:354-362 (1997)
Alterations in Neurobehavioral Responses in Fishes Exposed to
Lead and Lead-chelating Agents1
DANIEL N. WEBER 2 , WENDY M. DINGEL
Marine and Freshwater Biomedical Sciences Center, University of Wisconsin,
Milwaukee, Wisconsin 53204
JOHN J. PANOS AND RHEA E. STEINPREIS
Department of Psychology, University of Wisconsin, Milwaukee, Wisconsin 53201
SYNOPSIS. Lead (Pb) is a neurotoxic element that causes behavioral dysfunction
in fishes within days of exposure to sublethal concentrations. To test the hypothesis
that internal stores of Pb have long-term behavioral effects, Pb-exposed (0.3 ppm)
fish were either treated with the Pb-chelating drug meso-2,3 dimercaptosuccinic
acid (DMSA) or returned to control conditions (0.0 ppm Pb). Swimming capacity
improved after a 7-day DMSA (1.5 ppm) exposure (ANOVA P < 0.05). Removing
fish from conditions of waterborne Pb did not achieve this result; DMSA alone
without Pb pretreatment had no significant effect. Blood Pb (BPb) levels in control
or DMSA-only fish were not detectable. Treated groups had significantly higher
BPb (ANOVA, P < 0.05): Pb-exposed fish—530.5 ± 156.7, 884.6 ± 130.0 ppm (1,
2 wks, respectively); Pb-exposed -> 0.0 ppm water—488.8 ± 67.3 ppm after 2 wks;
Pb-exposed —> 1.5 ppm DMSA—202.0 ± 116.0 ppm after 2 wks. Norepinephrine
and vanillylmandelic acid levels were altered by Pb exposure (ANOVA, P < 0.05).
Whereas removing Pb did not facilitate a return to control values, adding DMSA
did (ANOVA, P < 0.05). Temporal-spatial response patterns to a stimulus in Pb-exposed (0.1 ppm) and Pb-exposed —» 0.0 ppm Pb water groups differed from controls (0.0 ppm Pb; 0.0 ppm DMSA) for stimulus response angle, and rate and
extent of movement away from stimulus source. While the two control types were
similar for stimulus response angle and reaction time, DMSA-only controls, unlike
0.0 ppm Pb controls, did not respond as a tightly-associated group after the stimulus.
INTRODUCTION
fishes
The extensive use and mining of Pb have
been major sources of contamination in
aquatic systems (Carpenter, 1927; Czarnez' 9?5:JDflhn§er' 1 9 8 6 ;Prosl' 1989)- A s
a result, fishes, particularly those in urban
areas, have been exposed to high amounts
of Pb (Eisler, 1988; D'Antuono and Foye,
1992). Because of the importance of Pb as
a measure of overall ecosystem health in
urban rivers and lakes (D'Antuono and
Foye, 1992) and because behavioral endpoints are sensitive measures of toxicity in
(Scherer, 1992), our concerns have
been to (1) identify specific short-term effects of p b o n individual a n d social behav.
iors
( 2 ) e v a l u a t e u n d e rlying physiological
m e c h a n i s m s t h a t a r e a s s o c iated with these
behavioral alterations, (3) develop methodologies
t h a t u s e s h o rt-term behavioral
c h a n g e s t o predict adverse long-term effects
a n d ( 4 ) e x a m i n e t h e reversibility of effects
a n d t h e r o l e o f i n t e r n a , s t o r e s o f p b i n af_
fecting both
a n d individual
behavjors
This
focuses
o n locomotor
activity
'From the Symposium Behavioral Toxicology:
Mechanisms and Outcomes presented at the Annual
of Pb behavioral toxicity and the ability of Pb-chelating drugs
to reverse those effects. Weber (1991) demonstrated that Pb-exposed fathead minnows
^^S^oZJZ?T9V95anwaCs°hrnPgtoan;
D.c.
2
To whom correspondence should be addressed.
«>• Pamelas) display lower stamina. Pb decreases heme synthesis (Bolognani Fantin
et al., 1989; Tabche et al., 1990) and eryth-
tQ m o d d
354
m e chanisms
FISH NEUROBEHAVIORAL TOXICOLOGY
355
rocyte concentrations (Dawson, 1930, ber and Spieler, 1995) and Cu (Steele,
1933, 1935) in fishes within a few days. 1989) and may result from changes in unWeber (1991) observed after a 30-d Pb ex- derlying circadian rhythms of brain neuroposure edema, intralamellar hyperplasia and transmitter activity. In adult P. promelas,
increased mucus secretion in gill filaments. circadian variations of whole brain norepiCumulatively, lowered oxygen uptake and nephrine and its metabolite vanillylmandeltransport abilities, and ion exchange capac- ic acid levels showed significant changes
ities at gill surfaces (Tabche et al., 1990) between control and Pb-exposed groups
could result in decreased swimming capac- (Spieler et al., 1995).
ity. Yet, another explanation for decreased
Pb-exposed male Medaka (Oryzias latiswimming capacity is Pb-induced CNS and pes) maintain hyperactivity after being
PNS dysfunction. The medulla, a critical placed into 0.0 ppm Pb water for 17 days
site for respiratory control, contains both (Weber, unpublished). It is possible that Pb
cholinergic and catecholaminergic nuclei damaged pathways critical to controlling
that control such functions as mucus secre- this behavior. Alternatively, due to internal
tions on the gill surface, opercular stroke stores being mobilized, these neural pathfrequency, gill and systemic blood vessel ways may still be exposed to toxic levels
vasoconstriction, and heart stroke (Lagler et of Pb, thus maintaining altered states of beal, 1962; Randall, 1970; Butler and Met- havior. Previous data (Weber, 1991) indicalfe, 1983; Smith, 1984). Pb interferes cate that Pb reaches very high bioconcenwith selected muscarinic receptors in the tration factors (internal: ambient concentrabrain and may be an important mechanism tions), remains in various tissues, especially
for some Pb-induced behavioral alterations bone, even after Pb is no longer present in
(Costa and Fox, 1983; Schulte et al, 1994; the water, and may decrease from specific
tissues at a very slow rate. A similar pattern
Cory-Slechta and Pokora, 1995).
Group responses to directional stimuli of bone-Pb mobilization has been observed
are directly controlled by two interconnect- in humans (Todd et al, 1996).
Little research has been done with vered, neural pathways, the Mauthner cells
(M-cell) and lateral line system, that induce tebrates on the reversibility of lead effects
highly coordinated and uniform group on CNS function. In children exposed to Pb
movements away from the perturbation and then treated with various Pb-chelating
(Partridge, 1982; Eaton et al, 1991). This drugs, blood Pb does decrease. When chilhighly polarized, stereotypical startle reflex dren cease taking the drug, blood Pb inis controlled by the M-cell located on the creases, suggesting that internal stores are
medulla surface. Sensitive to transitory dis- being released (Graziano et al, 1988), alplacements of water, the lateral line gives though the implications for long-term beinformation to individuals regarding posi- havioral change are not clear (Eileen Helztion and velocity within a group (Partridge, ner, MacNeil Consumer Products Company,
1982). During exposure to cadmium (Cd) personal communication), During Pb-cheor copper (Cu), positions relative to others lation therapy, Frumkin and Gerr (1993)
within the group, velocity and angular dis- noted that Pb-induced depression was repersion are altered (Sullivan et al., 1978; versed. Ruff et al. (1993) observed imKoltes, 1985). To date, there have been no proved cognitive abilities in Pb-poisoned
reports on Pb effects on either neural sys- children treated with the Pb-chelating drug
tem.
meso 2,3-dimercaptosuccinic acid (DMSA).
While some neural pathways control in- Mechanisms of action were not investigated
stantaneous reactions to specific stimuli in either study. Friedheim et al. (1978) de(Eaton et al, 1991), others influence loco- scribed the efficacy of treating Pb poisoning
motor activity patterns that control specific with DMSA. Several workers investigating
circadian rhythms, e.g., anticipatory behav- Pb redistribution during DMSA chelation
ior associated with feeding schedules (We- therapy found that DMSA significantly reber and Spieler, 1995). Prolonged states of duced brain and bone Pb levels (Coryhyperactivity are induced by both Pb (We- Slechta, 1988; Jones etal, 1994; Tandon et
356
D. N. WEBER ET AL.
al., 1994), although the mode of action at
the cellular level is not clear (Goyer et al.,
1995). By decreasing levels of Pb in the
primary storage site (bone) and in those tissues critical for controlling behavior
(brain), DMSA has the potential to affect
changes in Pb-induced behavioral dysfunction. Our goal in using this drug, as a part
of a multifaceted approach to study Pb neurobehavioral toxicity in fishes, is to determine the longevity and reversibility of
Pb-induced behavioral effects. These investigations are unique in that we use fish as a
biomedical model for evaluating drug efficacy and physiological mechanisms of behavioral dysfunction.
METHODS
Blood Pb levels
As with clinical samples, whole blood
from rainbow trout {Oncorhynchus mykiss)
(approximately 250 g) was used to evaluate
Pb levels using graphite furnace atomic absorption spectrophotometry with deuterium
background correction (GBC Scientific
Equipment, Model 904AA). Blood (1.0
mL) from control (0.0 ppm Pb), Pb-exposed
(0.3 ppm for 2 wks), Pb-exposed for 2 wks
followed by 0.0 ppm Pb for 2 wks, Pb-exposed for 2 wks followed by 1.5 ppm
DMSA for 2 wks, and 1.5 ppm DMSA
alone for 2 wks to control for any druginduced effects (5 fish per group) was collected weekly from the caudal vein with a
heparinized hypodermic syringe. Samples
were diluted 1:10 in a matrix modifier of
0.2% NaH3PO4, 0.2% HNO3 and 0.5% Triton X-100. Additional 1:10 dilutions of
these samples were prepared as needed.
Samples were read at 283.3 nm to minimize
background interference normally observed
at 217 nm. Data were analyzed using ANOVA (two-way for Pb and DMSA concentrations, with replicates) with significance defined as P < 0.05. Duncan's Multiple
Range Test was used to evaluate significance of intergroup differences.
Neurotransmitter analyses
P. promelas (approx. 25 mm; 5/treatment) were exposed to either 0.0, 0.05 or
0.10 ppm Pb for 1 wk, or Pb for 1 wk followed by 0.0 ppm Pb for 1 wk, or Pb for
1 wk followed by 0.25 or 0.50 ppm DMSA
for 1 wk, or DMSA alone for 1 wk. Fish
were anesthetized in an ice-water bath.
Brains (approx. 2-10 mg wet weight) were
removed and snap-frozen in 0.1 M perchloric acid (150 uX/100 mg tissue) until homogenized. Homogenate was centrifuged at
14,800 g for 1 hr at 4°C. Supernatant was
recentrifuged with Z-spin filtering centrifuging tubes at 4,000 g for 20 min. Supernatant was injected into an HPLC with electrochemical detection. Dihydrobenzoic acid
was used as an internal standard. Mobile
phase consisted of phosphate and citrate
buffers with o-sulfonic acid as an ion-pairing agent. Data were analyzed using ANOVA (two-way for Pb and DMSA concentrations, with replicates) with significance defined as P < 0.05. Duncan's Multiple
Range Test was used to evaluate significance of intergroup differences.
Group response to a stimulus
If removing Pb from the water should
yield results similar to those seen in Pb-exposed fish, it is possible that internal stores
of Pb are an important consideration in Pb
toxicity studies. If short-term exposure to
DMSA is able to return the fish to control
behaviors, then the drug may have an important role to play in how internal stores
of Pb interact with other tissues. These experiments represent initial tests to evaluate
the ability of group responses to detect Pb
toxicity and the degree of permanent damage due to Pb exposure.
Group startle responses, were recorded
on professional quality video tape (Maxell)
by a remote camera (Sony Model
XC711RR) connected to a 13" color video
monitor (Sony, Trinitron model) and a Panasonic Super VHS video recorder with a jog
shuttle for frame-by-frame analyses. P. promelas (15 fish/group; 3-4 cm length) were
placed in each of three aerated aquaria (static-renewal, 100% water changes every second day) and allowed to acclimate for 1 wk.
The applied stimulus involved using a nylon stopper at the end of a glass rod to hit
the side of the aquarium at which the group
was congregated. At the end of each 1 wk
exposure period the area the group occupied, direction of swimming (180° = exact
357
FISH NEUROBEHAVIORAL TOXICOLOGY
opposite direction of the stimulus), and
mean distance of each fish (at snout) in the
group from the source of the stimulus were
recorded before the stimulus was applied
(to) and every 0.05 sec for 0.5 sec and then
at 1.0, 2.0, 5.0 and 10.0 sec thereafter. With
each group being its own control, this procedure was repeated after 1 wk exposure to
0.1 ppm Pb, then followed by 0.0 ppm Pb,
and finally followed by 1.0 ppm DMSA
only. To control for any drug-induced effects, an additional set was exposed to
DMSA only. Data were transformed to
mean angle and angular distribution using
formulae for circular distributions (Zar,
1974). During protocol development, we
noticed that control groups responded similarly to a stimulus regardless of time spent
in the aquarium. Therefore, separate sets to
control for time were not included.
Swimming behavior
Testing protocol for O. mykiss (approx. 7
cm standard length) followed Peterson et al.
(1987) with exposure regimes as with tests
for BPb. Data were transformed to critical
swimming velocity (Beamish, 1978) and
analyzed using ANOVA (two-way for Pb
and DMSA concentrations, with replicates)
with significance defined as P < 0.05. Duncan's Multiple Range Test was used to evaluate significance of intergroup differences.
RESULTS
Blood levels
The effect of DMSA on blood Pb (BPb)
was greater than that of simply removing
environmental Pb (Fig. 1; ANOVA, P <
0.05). However, DMSA-treated fish still
had a large concentration of Pb in their
blood after 2 weeks. Because fish erythrocytes are nucleated, it is possible that these
cells have nuclear Pb inclusions similar to
that found in catfish oocytes (Katti and
Sathyanesan, 1987). It is not clear at present
whether these Pb inclusions are a protective
mechanism for the cell or a source of internal Pb mobilization. If there are nuclear
Pb inclusions, it is not clear from these data
if DMSA interacts with them.
Pb-DMSA 2
Pb-DMSA 1
I Pb-OPb 2
5> Pb-OPb 1
I
Pb2
5
Pb1
I
DMSA 2
5
DMSA1
control 2
control 1
200
400
600
800
Blood Pb (ppb)
1000;
FIG. 1. Whole blood Pb analysis from rainbow trout
(Oncorhynchus mykiss). Fish were exposed to either
control (0.0 ppm Pb or 1.5 ppm DMSA) for two
weeks, 0.3 ppm Pb for two weeks (Pb), 0.3 ppm Pb
for one week followed by 0.0 ppm Pb for two weeks
(Pb-0), 0.3 ppm Pb for one week followed by 1.5 ppm
DMSA for two weeks (Pb-DMSA). Histogram bars =
mean values of 5 fish ± S.E. All Pb treatments are
significantly different from control and DMSA-only
values; Pb-DMSA at two weeks is significantly different from both Pb and Pb-0 (ANOVA, P < 0.05). Note:
No S.E. shown on Pb 2 because 4 of 5 fish in that
group died after 1 wk.
Whole brain neurotransmitter levels
The neurotransmitter dynamics of norepinephrine (NE) and its metabolite vanillylmandelic acid (VMA) in whole fish
brains after exposure to each of the experimental regimes is described in Figure 2. Pb
exposure results in significant decreases in
NE levels at either concentration; a significant drop in VMA occurred only at 1.0
ppm Pb (ANOVA, P < 0.05). Removal of
Pb did not ameliorate the condition (ANOVA, P > 0.05 compared to Pb-exposure
groups and P < 0.05 compared to control
groups). In the presence of DMSA, a return
to control values was observed for VMA
and a significant increase over the Pb removal group was observed for NE (ANOVA, P < 0.05 for NE and P > 0.05 for
VMA).
Swimming capacity
Individual fish tested without exposure to
either Pb or DMSA displayed no significant
change in swimming capacity; DMSA
alone also did not cause any significant
change in swimming capacity (ANOVA, P
> 0.05; Fig. 3). Fish exposed for 1 wk to
358
D. N. WEBER ET AL.
A.
Pb-DMSA
.1 Pb-DMSA
Pb-0
„, .05 Pb-DMSA
£
o>
or
a
.1 Pb-OPb
.05 Pb-OPb
DMSA
control
.05 Pb
control
40
20000
pg NE/mg brain
40000
FIG. 3. Mean critical swimming velocities in Oncorhynchus mykiss as per cent of control values ± SE
Treatments: 1 wk exposure to 0.3 ppm Pb (Pb), 1 wk
exposure to 0.3 ppm Pb followed by 1 wk exposure to
0.0 ppm Pb (Pb-0), 1 wk exposure to 0.3 ppm Pb followed by 1 wk exposure to 1.5 ppm DMSA (PbDMSA), or 1 wk exposure to 0.0 ppm DMSA followed
by 1 wk exposure to 1.5 ppm DMSA (DMSA). Each
individual fish was tested before the exposure regime
was begun and again after the exposure regime was
completed. Values shown are for the second set of
tests, i.e. increases in control values are due to exercise-induced improvements. Controls, DMSA-only,
and Pb-DMSA are significantly different from Pb and
Pb-0 (ANOVA, P < 0.05) but not from each other. SE
for the DMSA-only group = ±27.5.
.1 Pb-DMSA
o .05
Pb-DMSA
E
oi
.1 Pb-OPb
60 80 100 120 140 180
% Control
0
20000
pg VMA/mg brain
40000
Only by the addition of DMSA for 1 wk
did the critical swimming velocity return to
FIG. 2. Effects of Pb and DMSA on catecholamine near-control values (89% of control; ANOneurotransmitter dynamics in juvenile fathead minnow VA, P > 0.05). The DMSA group was also
(Pimephales promelas). Exposure regimes correspond significantly different from the two
to: control (0.0 ppm Pb or DMSA-only); 0.05 ppm Pb Pb-treated groups (ANOVA, P < 0.05).
for 2 wk; 0.1 ppm Pb for 2 wk; 0.05 ppm Pb for 1 wk Therefore, just as Pb did not alter hemoglothen 0.0 ppm Pb for 1 wk; 0.1 ppm Pb for 1 wk then
0.0 ppm Pb for 1 wk; 0.05 ppm Pb for 1 wk then 0.25 bin levels, DMSA-induced reversals of beppm DMSA for 1 wk; 0.1 ppm Pb for 1 wk then 0.5 havior may not have been due to physioppm DMSA for 1 wk. A. norepinephrine, B. vanillyl- logical changes in the blood.
mandelic acid. * = Significant difference from control;
t = Significant difference from Pb-exposed group; +
= Significant difference from Pb and no Pb group.
Significance: ANOVA, P < 0.05.
Pb displayed a 38% loss in critical swimming velocity; this value did not improve
by simply removing environmental Pb
(-36%; ANOVA, P < 0.05). This is of interest in that even a 2 wk exposure to Pb
may not significantly affect hemoglobin
concentrations in fish blood (Christensen et
al., 1977). Thus, over this time period,
changes in swimming capacity may not be
due to changes on O2 carrying capacity.
Group response to stimulus
Under conditions of 0.0 ppm Pb and 0.0
ppm DMSA fish respond to a stimulus by
swimming in a closely-knit group in the
opposite direction (Fig. 4). After one
week of Pb exposure, pre-stimulus group
size was initially larger than control
groups and the post stimulus flash expansion occupied a larger area and lasted longer, time to react to the stimulus appeared
to be longer (0.05 sec in control groups
vs. 0.15 sec in Pb-exposed groups), the
group took longer settling to a final position (10 sec vs. 2 sec for control group)
FISH NEUROBEHAVIORAL TOXICOLOGY
which was not at the opposite side of the
aquarium, i.e., there was less movement
away from the stimulus source (Fig. 5).
The response after one week of 0.0 ppm
Pb was similar to the reaction of Pb-exposed groups. With only one week of exposure to DMSA, the group again displayed a pattern similar to groups exposed
to control conditions. Because approximately 33% of the DMSA-treated fish remained near the stimulus source and the
rest moved to the other side of the aquarium, the mean distance traveled appears
to be similar to Pb-exposed groups. However, most fish within the group did react
similarly to groups under control conditions. Groups treated only with DMSA
displayed reaction times and mean stimulus response angle similar to control
groups. However, like the Pb-DMSA
group, about one-third of the fish in the
DMSA-only group did not move very far
from the stimulus source. Reaction times
of workers exposed to occupational
sources of Pb were, as with fish, increased
(Stollery, 1996). Interestingly, -y-amino
butyric acid (GABA) located in the medulla, where the M-cell is located and
where the anterior and posterior lateral
lines connect with the M-cell, is involved
with the startle response (Smith, 1984);
GABA levels in both mammalian and fish
brains are decreased by Pb (Silbergeld et
al., 1980; Katti and Sathyanesan, 1986).
CONCLUSIONS
In the experiments reported here,
Pb-exposed fishes still maintained their
disrupted behavioral patterns 1 wk after
they were transferred to aquaria in which
all environmental sources of Pb were removed, perhaps due to high internal stores
of Pb still being mobilized (Weber, 1991).
This behavioral pattern is reflected by
whole brain neurotransmitter dynamics
remaining altered even after fish were
placed in aquaria with 0.0 ppm Pb.
Whether individual behaviors, e.g., swimming capacity, or group interactions, e.g.,
startle responses, were examined, the
short-term removal of environmental Pb
did little to facilitate a return to the activity patterns observed under control con-
359
ditions. If these observations were primarily due to tissue damage, the addition
of a Pb-chelating drug would not be expected to be effective over such short exposure times. However, it was observed
that DMSA could reverse some neurobehavioral changes, specifically attenuation
of altered startle responses and reversals
of norpeinephrine levels and metabolism
even when declining BPb levels were still
high. Thus, this Pb-chelating agent may
be decreasing the internal, labile stores of
Pb that are important in affecting behavior.
Although several reversals of behavioral dysfunction were affected by DMSA,
not all Pb-induced behavioral alterations
fall into this category. Previous studies
(Weber et al., 1991) demonstrated that
psychomotor coordination in P. promelas
was adversely affected by Pb. Yet, preliminary data (unpublished) suggest that
there is no significant difference between
control groups and Pb-exposed fish placed
into water with either no Pb or no DMSA.
This may be due to the complex nature of
neural networks involved in feeding, i.e.,
olfactory, visual, neuromuscular (jaw
muscles for capturing, trunk muscles for
swimming), appetitive/motivation (hunger
status), and mechanosensory (anterior lateral line). Amelioration in only a few of
these systems may not be sufficient to
counteract long-term effects of Pb in other
neural networks.
The length of response, i.e., the fear
factor, depends upon processing centers in
the medulla. That Pb-exposed groups neither moved very far from the stimulus
source nor oriented 180° from the stimulus source, yet did return to the stimulus
source, unlike either control group, would
indicate that the fear response was quickly
attenuated by Pb; the delayed response
may be indicative of altered neurotransmitter dynamics in the M-cell and/or
slower nerve conduction velocities in the
M-cell-interneuron-muscle
pathway.
These data resemble the changes in vibrational sensitivity seen in some Pb-exposed
monkeys (Rice and Gilbert, 1995), i.e., Pb
changed the threshold level and response
time for mechanosensory neural net-
360
D. N. WEBER ET AL.
A.
B.
A.
B.
Distance Travelled
Area ot Group
Distance Travelled
Area ot Group
200-
250
0
.1
.2 .3 .4 .5 1 2 510
Time (sec)
0
.1
.2 .3 .4 .512510
Time (sec)
0
.1
.2 .3 .4 .5 1 2 510
Time (sec)
.1
2 .3 .4 .51 a 510
Time (sec)
.1
.2 .3 .4 . 5 1 2 5 1 0
Time (sec)
IV.
III.
Distance Travelled
0
Area of Group
.2 .3 .4 .51 2 510
Time (sec)
Distance Travelled
Area of Group
.2 .3 .4 . 5 1 2 5 1 0
Time (sec)
FIG. 4. Group response of fathead minnows (Pimephales promelas) to a stimulus. A. mean group direction
from stimulus (arrow) ± angular dispersion (rays surrounding arrow), and mean group distance (cm; intersection
point of rays and arrow) from stimulus source as a function of time; B. area of a group (cm2) as a function of
time after a stimulus applied. I. 1 wk exposure to 0.0 ppm Pb (control); II. 1 wk exposure to 0.1 ppm Pb; III.
1 wk exposure to 0.1 ppm Pb followed by 1 wk exposure to 0.0 ppm Pb; IV. 1 wk exposure to 0.1 ppm Pb
followed by 1 wk exposure to 1.0 ppm DMSA; V. 1 wk exposure to 0.0 ppm DMSA followed by 1 wk exposure
to 1.0 ppm DMSA.
works. Short-term treatment with DMSA
apparently modified, but did not totally
reverse, those changes. There exists, however, an alternate hypothesis that requires
additional investigation. Because DMSA
by itself, affects some parameters of the
startle response, specifically group size, it
may interact with the neurons and, therefore, directly induce reversals of Pb-induced neurobehavioral toxicity. If true,
FISH NEUROBEHAVIORAL TOXICOLOGY
V.
A.
Area of Group
Distance Travelled
0
810-
20-
25
0
.1
2 3 A .5 1 2 510
Time (sec)
0
.1
.2 .3 .4 .5 1 2 510
Time (sec)
this hypothesis might explain the higher,
albeit statistically insignificant, swimming
capacity of fish treated only with DMSA.
ACKNOWLEDGMENTS
These studies were supported by the Marine and Freshwater Biomedical Sciences
Center (University of Wisconsin-Milwaukee; NIH grant ES04184 to D. Petering),
Medical College of Wisconsin (NIH grant
ES07292 to J. Lech), EPA block grant to
Wisconsin Department of Natural Resources, and the Conservation and Research
Foundation. Special thanks to T. Egan, K.
Kosteretz, B. Wimpee and M. Zogg for
technical assistance, and S. McKay for figure preparation.
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