The Toxicologist - Society of Toxicology

activity. The dose-response curves for brain ChE and horizontal activity were significantly
different across ages. For brain ChE, the PND18 pups were more affected
than the other ages. On the other hand, RBC ChE was similarly decreased
across all ages. Older rats (12 and 24 mo) were more sensitive to decreases in horizontal
activity, especially at the higher doses, whereas the 4 mo old rats were least
sensitive. The same pattern was seen with vertical activity. In both control and
treated rats, variability of the behavioral measures was greatest in the youngest and
oldest rats, unlike ChE measures which showed similar variability across ages. Thus,
the youngest rats were the most sensitive to the ChE-inhibiting effects of carbaryl,
but older rats showed the most motor activity depression. The explanation for the
dissociation between ChE inhibition and motor activity changes across ages is unclear.
This is an abstract of a proposed presentation and does not reflect US EPA policy.
1340 EFFECTS OF GESTATIONAL & LACTATIONAL
EXPOSURE TO THE PYRETHROID PESTICIDE
DELTAMETHRIN ON NEURAL DEVELOPMENT.
M. Pine, B. Reimers, R. Mariano, D. DeVillier, T. Wagner and G. Ko. Texas
A&M University, College Station, TX.
Due to concerns over the toxicity of organophosphate and organochlorine pesticides,
their use has decreased while that of less toxic alternatives such as pyrethroid
pesticides has steadily grown. However, there is little data as to pyrethroid effects on
neural development after low dose exposure during pregnancy and lactation. The
present study measured the impact of the type II pyrethroid, deltamethrin (DM),
on brain development using the Sprague-Dawley rat model. Females were dosed
orally with 5.0 mg/kg/day DM or corn oil beginning on day 1 of pregnancy and
continuing throughout lactation (PND21). Another group was exposed to the neurodevelopmental
toxin valproic acid (VA; 400 mg/kg) by intraperitoneal injection
on embryonic day 12.5 only. DM treatment caused a significant reduction in pup
body weight while exposure to VA had no effect. We weighed the cerebral cortex,
diencephalon, hippocampus, cerebellar hemisphere, and vermis on PND21. DM
treatment resulted in decreased absolute weight of the cerebral cortex and cerebellar
hemisphere, but did not affect the relative weight (% of body weight) of these brain
regions. Interestingly, the relative weight of the cerebellar vermis from DM exposed
pups was greater than that of the controls. VA exposure resulted in a decrease in the
absolute weight of the cerebral cortex only. To assess any long term effects on behavior
and motor coordination, a minimum of two pups from each litter underwent
behavioral (somatosensory and open field) and motor coordination (rotarod)
tests on PND90. DM treated animals were less sensitive to sensory stimuli based on
their decreased removal of progressively smaller sizes of adhesives. Both VA and
DM exposed females spent more time in the center of the open field chamber as
compared to controls while males spent less time in the center. No differences were
noted in coordination (rotarod and gait analysis). These results suggest that DM exposure
adversely affects brain development at doses two times below the current
lowest observable adverse effect level of 10.0 mg/kg/day.
1341 AGE-DEPENDENT MODULATION OF SODIUM
CHANNEL LEVELS AND CALPAIN ACTIVATION
FOLLOWING ACUTE DELTAMETHRIN EXPOSURE.
J. P. Magby 1, 2 and J. R. Richardson 1, 2 . 1 Joint Graduate Program in Toxicology,
Rutgers University/UMDNJ, Piscataway, NJ and 2 Graduate School of Biomedical
Sciences, RWJMS, Piscataway, NJ.
Sodium channels (Na(v)) are a critical component of neuronal signaling and a target
of pyrethroid pesticides, which function as Na(v) agonists. Previously published
work found that the sodium channel agonist alpha-scorpion toxin causes internalization
and degradation Na(v) proteins in vitro. These effects were age-dependent,
as alpha-scorpion toxin promoted internalization of Na(v) in slices from animals at
postnatal day (PND) 12, but not at PND30. However, it is not known if this
down-regulation of Na(v) protein occurs in vivo. To determine the relevance of
these findings in intact animals, PND 12 and 30 rats (n=3-5) were dosed with
deltamethrin (0, 3, or 6 mg/kg) and sacrificed 30 min or 2 hr later for determination
of membrane levels of Na(v) by western blot. In PND 12 rats, administration
of 3 mg/kg deltamethrin resulted in a 20% reduction of membrane Na(v) levels at
30 min and a 25% reduction at 120 min in the striatum. In contrast, administration
of 3 mg/kg or 6 mg/kg deltamethrin to PND30 rats resulted in no reduction
in membrane Na(v) levels. However, recent in vitro data has found that the calcium-dependent
protease calpain can mediate cleavage of Na(v) protein, rendering
membrane levels unchanged while generating a non-functional protein. To determine
whether calpain is activated by deltamethrin, we measured spectrin cleavage,
an indicator of calpain activation. In PND12 animals deltamethrin exposure did
not result in increased spectrin cleavage. Conversely, administration of 3 or 6
mg/kg deltamethrin to PND30 rats resulted in an increase of spectrin cleavage at
30 min by 63% and 212%, respectively. These data suggest that acute deltamethrin
exposure results alterations of Na(v) protein by different mechanisms that are agedependent,
but that either mechanism may lead to interruption of neuronal signaling
and neurotoxicity. Supported by R01ES015991, P30ES 005022, and a Bristol-
Myers Squibb Predoctoral Fellowship.
1342 DELTAMETHRIN INHIBITS HUMAN VOLTAGE-
SENSITIVE CALCIUM CHANNEL ISOFORMS
EXPRESSED IN XENOPUS OOCYTES.
D. Galluzzo, E. M. Mutanguha, Z. Valentine and S. B. Symington. Biology and
Biomedical Science, Salve Regina University, Newport, RI.
Low voltage-activated (T-type) calcium channels are involved with a variety of
physiological processes including pacemaking activity and repetitive firing in neurons.
Human Cav3.1, Cav3.2 and Cav3.3 are three T-type calcium channel isoforms
that are expressed in different tissues, possess unique molecular pharmacology,
and have different voltage-dependent kinetics. Deltamethrin is a potent
CS-syndrome pyrethroid that is frequently used in agricultural and vector control
programs to control pests. In this research the effect of deltamethrin was evaluated
on Cav3.1, Cav3.2, and Cav3.3 expressed in Xenopus oocytes. The Cav3 isoforms
were verified using a combination of restriction enzymes and linearized DNA was
used as a template to transcribe cRNA using the mMessage mMachine in vitro
transcription kit. Cav3 channel expression was confirmed by two electrode voltage
clamp electrophysiology. Concentration-dependent response curves were generated
on the relative peak current remaining following perfusion of increasing concentrations
of deltamethrin. Deltamethrin was found to inhibit the peak current of all
Cav3 isoforms. Concentration-dependent response curves were generated for
Cav3.2 and Cav3.3. Preliminary results indicate that deltamethrin is a potent inhibitor
of Cav3.2 and Cav3.3. Furthermore, high concentrations of deltamethrin
inhibit Cav3.1, however, a complete concentration-dependent response has yet to
be established due to inconsistent expression of this clone. Current studies are underway
to assess the effects of deltamethrin on the voltage-dependent and steady kinetics
of Cav3.1 and Cav3.3 in comparison to already compiled data on Cav3.2.
Nevertheless, our results indicate a structural specific interaction with deltamethrin
on all three Cav3 isoforms.
1343 DIFFERENTIAL SENSITIVITY OF RAT VOLTAGE-
GATED SODIUM CHANNEL ISOFORMS TO THE
PYRETHROID INSECTICIDE TEFLUTHRIN.
D. M. Soderlund 1 , J. Choi 2 and J. Tan 3 . 1 Entomology, Cornell University, Geneva,
NY, 2 Neurology, Yale University School of Medicine, New Haven, CT and 3 Monsanto
Company, St. Louis, MO.
Voltage-gated sodium channels are important sites for the neurotoxic actions of
pyrethroid insecticides in mammals. The pore-forming α subunits of mammalian
sodium channels are encoded by a family of 9 genes, designated Nav1.1 - Nav1.9.
We used the potent pyrethroid tefluthrin as a probe of pyrethroid sensitivity in assays
of rat Nav1.2, Nav1.3, Nav1.6, Nav1.7 and Nav1.8 sodium channels expressed
in Xenopus laevis oocytes. All five isoforms were modified by tefluthrin in the resting
state. Channel activation by repeated depolarization significantly enhanced the
extent of tefluthrin modification of all isoforms except Nav1.8, indicating that
tefluthrin binds preferentially to these four isoforms either in the open state or to in
other activation-dependent channel states. For Nav1.2 and Nav1.6 channels, the
increase in apparent affinity for tefluthrin upon repetitive depolarization was more
than 10-fold. The five sodium channel isoforms segregated into two groups on the
basis of tefluthrin sensitivity, with Nav1.3, Nav1.6 and Nav1.8 forming the more
sensitive group and Nav1.2 and Nav1.7 the less sensitive group. Direct comparison
of the sensitivity of Nav1.2 and Nav1.6 channels to resting and use-dependent
modification showed that the Nav1.6 isoform was ~15-fold more sensitive to
tefluthrin modification. Less extensive data sets for the remaining 3 isoforms show
that Nav1.7 channels were somewhat less sensitive than Nav1.2 channels whereas
Nav1.3 channels were more sensitive than Nav1.6 channels. Alignment of the
amino acid sequences of these five isoforms identified two sequence polymorphisms,
located in the S6 transmembrane segments of homology domains I and II,
as possible determinants of differential sensitivity of rat sodium channel isoforms to
tefluthrin and other pyrethroids.
Supported by NIH grant R01-ES013686.
SOT 2011 ANNUAL MEETING 287