In utero exposure of mice to diesel exhaust particles affects spatial learning and memory with reduced N-methyl-D-aspartate receptor expression in the hippocampus of male offspring

Abstract

Diesel exhaust consists of diesel exhaust particles (DEPs) and gaseous compounds. Previous studies reported that in utero exposure to diesel exhaust affects the central nervous system. However, there was no clear evidence that these effects were caused by diesel exhaust particles themselves, gaseous compounds, or both. Here, we explored the effects of in utero exposure to DEPs on learning and memory in male ICR mice. DEP solutions were administered subcutaneously to pregnant ICR mice at a dose of 0 or 200μg/kg body weight on gestation days 6, 9, 12, 15, and 18. We examined learning and memory in 9-to-10 week-old male offspring using the Morris water maze test and passive avoidance test. Immediately after the behavioral tests, hippocampi were isolated. Hippocampal N-methyl-D-aspartate receptor (NR) expression was also measured by quantitative RT-PCR analysis. Mice exposed to DEPs in utero showed deficits in the Morris water maze test, but their performance was not significantly different from that of control mice in the passive avoidance test. In addition, DEP-exposed mice exhibited decreased hippocampal NR2A expression. The present results indicate that maternal DEP exposure disrupts learning and memory in male offspring, which is associated with reduced hippocampal NR2A expression.
Copyright © 2015. Published by Elsevier B.V.

Full text

Full
length
article
In
utero
exposure
of
mice
to
diesel
exhaust
particles
affects
spatial
learning
and
memory
with
reduced
N-methyl-
D
-aspartate
receptor
expression
in
the
hippocampus
of
male
offspring
Satoshi
Yokota
a,b,
*,
Akira
Sato
a
,
Masakazu
Umezawa
a
,
Shigeru
Oshio
b
,
Ken
Takeda
a
a
The
Center
for
Environmental
Health
Science
for
the
Next
Generation,
Research
Institute
for
Science
and
Technology,
Organization
for
Research
Advancement,
Tokyo
University
of
Science,
2641
Yamazaki,
Noda,
Chiba
278-8510,
Japan
b
Department
of
Hygiene
Chemistry,
School
of
Pharmaceutical
Sciences,
Ohu
University,
31-3
Misumido,
Tomita,
Koriyama,
Fukushima
963-8611,
Japan
1.
Introduction
Exposure
to
particulate
matter
(PM)
in
the
atmosphere
is
associated
with
impaired
cognitive
function
(Caldero
´n-Garcidue-
n
˜as
et
al.,
2008).
PM
exposure
causes
increased
oxidative
stress
response,
blood–brain
barrier
damage,
and
increased
amyloid-
b
deposition
in
brain
tissue,
which
suggests
a
causal
link
between
PM
exposure
and
acceleration
of
the
pathogenesis
of
neurodegen-
erative
diseases
such
as
Alzheimer’s
disease
(Block
and
Caldero
´n-
Garciduen
˜as,
2009).
These
particles,
particularly
nano-sized
PM
(<100
nm
in
aerodynamic
diameter),
may
pass
through
the
blood–brain
barrier
and
penetrate
into
brain
tissue.
Nano-sized
PM
can
also
carry
large
amounts
of
toxic
compounds,
such
as
hydrocarbons
and
metals,
on
their
surface
(Hesterberg
et
al.,
2010),
which
suggests
that
nano-sized
PM
may
cause
direct
neurotoxic
effects.
Notably,
diesel
combustion
can
produce
nano-sized
PM
(Wichmann,
2007).
Diesel
exhaust
(DE)
is
a
complex
mixture
of
diesel
exhaust
particles
(DEPs)
and
gaseous-phase
compounds.
The
soluble
organic
fraction
of
particulate
materials
in
DE
contains
more
than
1000
compounds
including
a
variety
of
polycyclic
aromatic
hydrocarbons
and
heavy
metals
(Wichmann,
2007).
The
Interna-
tional
Agency
for
Research
on
Cancer,
which
is
part
of
the
World
Health
Organization,
classified
DE
as
carcinogenic
to
humans
(Group
1),
based
on
sufficient
evidence
that
DE
exposure
is
associated
with
an
increased
risk
of
lung
cancer
(Silverman
et
al.,
2012;
Claxton,
2015).
Developmental
toxicity
following
DE
exposure
has
been
also
reported.
Prenatal
exposure
to
DE
increases
susceptibility
to
lung
inflammation
and
heart
failure
(Auten
et
al.,
2012;
Weldy
et
al.,
2013).
The
early
life
environment
can
also
affect
brain
development
(Welberg
and
Seckl,
2001).
Indeed,
we
previously
showed
that
maternal
exposure
to
DE
could
affect
monoaminergic
systems
in
various
brain
regions
of
male
offspring
in
mice
(Yokota
et
al.,
2013b).
Prenatal
exposure
to
DE
also
affected
NeuroToxicology
50
(2015)
108–115
A
R
T
I
C
L
E
I
N
F
O
Article
history:
Received
4
June
2015
Received
in
revised
form
13
August
2015
Accepted
13
August
2015
Available
online
18
August
2015
Keywords:
Diesel
exhaust
particles
Maternal
exposure
Learning
Memory
N-methyl-
D
-aspartate
receptor
Hippocampus
A
B
S
T
R
A
C
T
Diesel
exhaust
consists
of
diesel
exhaust
particles
(DEPs)
and
gaseous
compounds.
Previous
studies
reported
that
in
utero
exposure
to
diesel
exhaust
affects
the
central
nervous
system.
However,
there
was
no
clear
evidence
that
these
effects
were
caused
by
diesel
exhaust
particles
themselves,
gaseous
compounds,
or
both.
Here,
we
explored
the
effects
of
in
utero
exposure
to
DEPs
on
learning
and
memory
in
male
ICR
mice.
DEP
solutions
were
administered
subcutaneously
to
pregnant
ICR
mice
at
a
dose
of
0
or
200
m
g/kg
body
weight
on
gestation
days
6,
9,
12,
15,
and
18.
We
examined
learning
and
memory
in
9-to-10-week-old
male
offspring
using
the
Morris
water
maze
test
and
passive
avoidance
test.
Immediately
after
the
behavioral
tests,
hippocampi
were
isolated.
Hippocampal
N-methyl-
D
-aspartate
receptor
(NR)
expression
was
also
measured
by
quantitative
RT-PCR
analysis.
Mice
exposed
to
DEPs
in
utero
showed
deficits
in
the
Morris
water
maze
test,
but
their
performance
was
not
significantly
different
from
that
of
control
mice
in
the
passive
avoidance
test.
In
addition,
DEP-exposed
mice
exhibited
decreased
hippocampal
NR2A
expression.
The
present
results
indicate
that
maternal
DEP
exposure
disrupts
learning
and
memory
in
male
offspring,
which
is
associated
with
reduced
hippocampal
NR2A
expression.
ß
2015
Elsevier
Inc.
All
rights
reserved.
*Corresponding
author
at:
Department
of
Hygiene
Chemistry,
School
of
Pharmaceutical
Sciences,
Ohu
University,
31-3
Misumido,
Tomita,
Koriyama,
Fukushima
963-8611,
Japan.
Tel.:
+81
24
932
8931x5351.
E-mail
addresses:
satoshi_yokota1008@yahoo.co.jp,
s-yokota@pha.ohu-u.ac.jp
(S.
Yokota),
thanksgivingday0907@hotmail.com
(A.
Sato),
masa-ume@rs.noda.tus.ac.jp
(M.
Umezawa),
s-oshio@pha.ohu-u.ac.jp
(S.
Oshio),
takedak@rs.noda.tus.ac.jp
(K.
Takeda).
Contents
lists
available
at
ScienceDirect
NeuroToxicology
http://dx.doi.org/10.1016/j.neuro.2015.08.009
0161-813X/ß
2015
Elsevier
Inc.
All
rights
reserved.

the
morphology
of
perivascular
macrophages
and
the
surrounding
tissue
in
the
cerebral
cortex
and
hippocampus,
where
accumula-
tion
of
ultrafine
DEPs
was
observed
(Sugamata
et
al.,
2006).
This
finding
suggests
that
DEP
accumulation
may
directly
affect
the
cerebral
cortex
and
hippocampus
in
murine
adult
male
offspring.
We
hypothesized
that
prenatal
DEP
exposure
would
cause
neurotoxic
effects
in
mice.
Thus,
the
present
study
aimed
to
determine
whether
prenatal
exposure
to
DEPs
affected
cognitive
functions
in
male
offspring.
To
investigate
the
effects
of
DEPs
on
cognitive
function,
methods
such
as
intratracheal
administration
are
useful
to
mimic
DEP
inhalation.
However,
intratracheal
administration
is
associated
with
restraint
stress
and
requires
anesthesia,
both
of
which
may
also
affect
the
cognitive
function
of
the
offspring.
In
contrast,
subcutaneous
DEP
administration
can
achieve
a
certain
dose
with
repeated
treatments
during
pregnancy
without
inducing
restraint
stress
or
requiring
anes-
thesia.
Such
a
multiple
treatment
protocol
may
be
more
relevant
to
human
exposure
scenarios
than
a
single-dose
exposure
method
such
as
intratracheal
administration.
Therefore,
we
injected
DEP
suspensions
subcutaneously
into
pregnant
mice.
We
focused
on
the
effects
of
prenatal
DEP
exposure
on
locomotor
activity,
learning,
and
memory
in
male
offspring
using
behavioral
tests,
followed
by
measurement
of
N-methyl-
D
-aspartate
recep-
tor
(NR)
gene
expression.
2.
Materials
and
methods
2.1.
Characterization
of
diesel
exhaust
particles
(DEPs)
DEPs
were
collected
with
a
constant
volume
sampler
system
attached
to
the
end
of
a
dilution
tunnel
that
was
in
turn
attached
to
a
2369-cc
diesel
engine
(Isuzu
Motors,
Ltd.,
Tokyo,
Japan),
which
was
operated
at
a
speed
of
1050
rpm
at
80%
load
with
commercial
diesel
oil.
Equipment
was
provided
by
the
Japan
Anti-Tuberculosis
Association
(Tokyo,
Japan).
DEPs
were
sus-
pended
at
1
mg/mL
in
an
isotonic
sodium
chloride
solution
(pH
6.3;
Otsuka,
Pharmaceutical
Factory
Inc.,
Tokushima,
Japan)
with
0.05%
Tween
80
and
were
sonicated
for
approximately
30
min
immediately
before
administration.
To
determine
the
size
distribution
of
DEPs
in
suspension,
DEPs
were
subjected
to
dynamic
light
scattering
(DLS)
measurements
using
a
Zetasizer
Nano-ZS
system
(Malvern
Instruments
Ltd.,
Worcestershire,
UK).
A
DEP
suspension
was
also
passed
through
a
450-nm
Millex-HV
filter
(SLHV033RS;
Merck
Millipore
Ltd.,
Carrigtwohill,
Cork,
Ireland)
and
analyzed
by
DLS
to
determine
the
size
distribution
in
the
absence
of
bulk
aggregation.
2.2.
Animals
and
treatments
Thirty
pregnant
ICR
mice
obtained
from
SLC
Co.
(Shizuoka,
Japan)
were
used
throughout
the
experiments.
DEP
suspensions
(200
m
g/kg
body
weight)
were
injected
subcutaneously
into
15
pregnant
mice
on
gestation
days
6,
9,
12,
15,
and
18.
The
total
dose
of
DEPs
was
adjusted
to
approximately
1
mg/kg
body
weight.
This
dose
corresponds
to
208
days
of
exposure
to
PM
2.5
at
the
suggested
future
air
quality
daily
standard
of
25
m
g/m
3
in
the
European
Union,
assuming
that
humans
inhale
16
m
3
per
day
with
60%
alveolar
deposition
of
PM
2.5
(Invernizzi
et
al.,
2006;
Lo
¨ndahl
et
al.,
2007).
Saline
(containing
0.05%
Tween
80)
was
injected
subcutaneously
into
other
pregnant
mice
as
a
control.
After
DEP
exposure,
mothers
and
male
pups
were
maintained
in
the
same
clean
room.
After
weaning
on
postnatal
day
21,
male
mice
were
maintained
in
groups
in
their
home
cages
(5
mice/cage)
at
22

2
8C,
in
a
humidity-controlled
environment
(50

5%
humidity)
with
a
12-h
light/dark
cycle
(lights
on
from
8:00
to
20:00).
Food
and
water
were
provided
ad
libitum.
Body
weights
of
male
mice
were
recorded
at
9
(before
behavioral
tests)
and
10
(just
before
sample
collection)
weeks
of
age.
When
the
pregnant
mice
were
dissected,
residues
of
DEP
agglomerates
were
apparent
in
the
subcutaneous
tissue.
All
experiments
were
performed
in
accordance
with
National
Institutes
of
Health
(NIH,
USA)
guidelines
for
animal
experiments
and
were
approved
by
Tokyo
University
of
Science’s
Institutional
Animal
Care
and
Use
Committee.
All
samples
were
obtained
under
sodium
pentobarbital
(50
mg/kg)
anesthesia,
and
all
efforts
were
made
to
minimize
suffering.
2.3.
Behavioral
testing
Thirty
male
offspring
in
each
group
were
used
for
behavioral
tests.
All
behavioral
tests
were
conducted
between
13:00
and
17:00.
To
minimize
the
possible
effects
of
plasma
corticosterone
concentrations
on
animal
behavior
(Butte
et
al.,
1976;
Hui
et
al.,
2004)
during
the
test
period,
we
counterbalanced
the
task
by
controlling
the
order
of
animals
tested
among
the
control
and
DEP-
exposed
groups.
Behavioral
tests
were
performed
at
9
and
10
weeks
of
age.
Behavioral
tests
performed
included
the
Morris
water
maze
test
and
passive
avoidance
test.
To
avoid
carryover
effects
between
the
water
maze
test
and
passive
avoidance
test,
each
mouse
was
used
independently
in
each
behavioral
test.
This
design
does
not
change
the
interpretation
of
the
results
in
the
current
set
of
experiments.
2.3.1.
Open-field
test
Spontaneous
motor
activity
was
examined
in
an
open-field
test
performed
at
9
weeks
of
age.
Each
mouse
was
placed
in
the
corner
of
the
open-field
apparatus.
The
test
chamber
was
illuminated
at
100
lux.
Spontaneous
motor
activity
was
measured
using
a
digital
counter
with
Video
Tracking
Interface
software,
version
1.4
(Home
Cage
Video
Tracking
System,
MED
Associates
Inc.,
VT,
USA).
Using
the
video
tracking
system,
the
total
distance
traveled,
stereotype,
and
ambulatory
counts
were
recorded
in
the
chamber.
Data
were
collected
for
10
and
60
min.
2.3.2.
Morris
water
maze
test
Spatial
learning
and
memory
in
male
offspring
(9–10
weeks
of
age)
were
measured
using
a
Morris
water
maze
test.
The
Morris
water
maze
test
was
performed
as
previously
described,
with
modifications
(Kim
et
al.,
2003,
2006;
Vorhees
and
Williams,
2006).
Briefly,
mice
learned
to
swim
in
a
circular
pool
with
a
diameter
of
120
cm
and
a
height
of
25
cm.
The
pool
was
filled
with
skim
milk
diluted
in
water
(23

1
8C)
with
a
depth
of
14
cm.
The
pool
was
placed
in
a
large
testing
room,
which
was
furnished
with
various
cues
for
spatial
orientation.
These
cues
were
not
moved
throughout
the
experimental
period.
The
movement
of
each
mouse
in
the
pool
was
recorded
using
a
video
camera.
Prior
to
the
experiment,
each
mouse
was
placed
in
the
pool
and
allowed
to
swim
freely
for
60
s
without
a
platform
for
evaluation
of
swimming
performance.
A
circular
transparent
platform
(invisible
platform,
10
cm
in
diameter)
was
placed
in
the
pool,
and
its
top
surface
was
1
cm
below
the
water
level.
Two
blocks
of
trials
were
performed
daily
for
9
consecutive
days
in
a
hidden
platform
test.
In
each
trial,
the
starting
position
was
randomized
among
three
possible
positions,
except
for
the
platform
area,
which
remained
in
a
fixed
place.
The
interval
between
each
trial
was
1
h.
Each
trial
lasted
120
s
or
until
the
mice
located
the
platform.
When
the
mice
found
the
platform
within
120
s,
they
were
allowed
to
rest
for
10
s
on
the
platform.
Mice
that
could
not
find
the
platform
were
guided
to
the
platform
and
assigned
a
latency
score
of
120
s.
After
the
trial,
mice
were
placed
into
a
plastic
cage
filled
with
paper
for
drying
before
another
test
was
initiated.
The
time
to
reach
the
platform
(latency
to
escape)
was
recorded
for
each
trial
as
an
index
of
learning.
After
sequence
training
to
learn
the
platform
location,
the
platform
was
removed.
Twenty-four
hours
after
the
final
hidden
S.
Yokota
et
al.
/
NeuroToxicology
50
(2015)
108–115
109

platform
test,
a
probe
test
was
performed.
In
the
probe
test,
mice
could
swim
freely
in
the
tank,
which
was
divided
into
four
compartments
(one
compartment
was
where
the
platform
was
located
during
training).
As
a
measure
of
reference
memory,
we
recorded
the
time
that
the
mice
spent
in
the
quarter
containing
the
platform.
2.3.3.
Passive
avoidance
test
A
passive
avoidance
test
was
conducted
as
previously
described
(Kim
et
al.,
2006).
Briefly,
the
apparatus
consisted
of
a
rectangular
box
containing
one
dark
chamber
and
one
light
chamber
with
a
100
W
bulb
(20

20

20
cm).
The
dark
compartment
contained
2-mm
stainless
steel
rods
spaced
1
cm
apart
with
a
shock
generator
(ENV-414S;
Neuroscience
Inc.,
Tokyo,
Japan).
The
two
compartments
were
separated
by
a
guillotine
door
(5

5
cm).
In
the
training
test,
each
mouse
(10
weeks
old)
was
first
placed
into
the
light
chamber
and
the
guillotine
door
was
opened.
After
the
mouse
entered
the
dark
chamber,
the
door
automatically
closed
and
a
1-s
foot
shock
at
0.5
mA
was
delivered
through
the
stainless
steel
rods.
Subsequently,
the
mouse
would
learn
the
relationship
between
a
foot
shock
and
the
dark
compartment.
Mice
were
trained
to
refrain
from
entering
a
dark
area
they
would
normally
prefer
by
using
an
aversive
stimulus.
Twenty-
four
hours
after
the
training
test,
the
mice
were
tested
for
retention
by
placing
each
animal
into
the
light
chamber,
and
the
latency
to
enter
the
dark
compartment
was
measured
for
up
to
300
s.
2.4.
Total
RNA
isolation
Immediately
after
the
Morris
water
maze
test,
the
hippocam-
pus
was
isolated
(within
45
s),
frozen
in
liquid
nitrogen,
and
stored
at
80
8C.
Total
RNA
was
isolated
using
Isogen
(Nippon
Gene
Co.,
Ltd.,
Tokyo,
Japan)
according
to
the
manufacturer’s
protocol
and
suspended
in
pure
water.
The
RNA
quantity
was
determined
by
spectrophotometry
measurements
at
OD260/280
(ratio
>
1.8)
in
a
Smart
Spec
3000
(Bio-Rad
Laboratories
Inc.,
Tokyo,
Japan).
Extracted
RNA
from
each
sample
was
used
for
quantitative
RT-PCR
analysis.
2.5.
Quantitative
real-time
RT-PCR
Total
RNA
(1
m
g)
from
each
sample
was
used
as
a
template
to
synthesize
cDNA
using
M-MLV
reverse
transcriptase
(Invitrogen
Co.,
Carlsbad,
CA,
USA)
according
to
the
manufacturer’s
instruc-
tions.
Quantitative
real-time
RT-PCR
was
performed
with
SYBR
Green
Real-Time
PCR
Master
Mix
(Toyobo
Co.,
Ltd.,
Osaka
Japan)
in
an
Mx3000P
system
(Agilent
Technologies
Inc.,
Santa
Clara,
CA,
USA)
with
an
initial
hold
step
(95
8C
for
60
s)
and
40
cycles
of
a
two-step
PCR
(95
8C
for
15
s
and
60
8C
for
60
s).
At
each
cycle,
the
fluorescence
intensity
of
each
sample
was
measured
to
monitor
amplification
of
the
target
gene.
Relative
expression
levels
of
target
genes
were
calculated
for
each
sample
after
normalization
against
the
housekeeping
gene,
glyceraldehyde-3-phosphate
dehydroge-
nase
(Gapdh).
There
were
no
significant
differences
in
the
Gapdh
expression
between
groups
(data
not
shown).
Target
primers
were
custom-prepared
(Fasmac
Co.
Ltd.,
Kanagawa,
Japan)
and
the
sequences
are
shown
in
Table
2.
2.6.
Measurement
of
basal
serum
corticosterone
levels
To
measure
serum
corticosterone
levels,
we
used
an
enzyme-
linked
immunosorbent
assay
kit
(cat.
no.
ADI-900-097,
Enzo
Life
Sciences,
Inc.,
Farmingdale,
NY,
USA).
We
collected
blood
between
17:00
and
18:00.
Serum
samples
were
handled
and
stored
at
80
8C.
Detection
of
serum
corticosterone
levels
was
performed
according
to
the
manufacturer’s
established
protocol.
2.7.
Statistical
analysis
We
used
independent
litters
for
both
the
Morris
water
maze
test
and
passive
avoidance
test.
The
independent
litters
were
composed
of
one
pup
from
each
dam
from
the
control
or
DEP-
exposed
groups
(n
=
15).
Statistics
were
performed
with
the
independent
litter
as
the
statistical
unit.
Values
for
body
weight,
each
behavioral
test,
and
quantitative
RT-PCR
are
presented
as
the
mean

standard
error
of
the
mean
(S.E.M).
In
the
Morris
water
maze
test,
a
two-way
analysis
of
variance
(ANOVA)
was
used
to
evaluate
DEP
exposure
and
training
day
interaction
effects
for
dependent
variables.
For
the
water
maze
test,
statistical
significance
was
determined
by
a
subsequent
multiple
comparison
analysis
with
Fisher’s
protected
least
significant
difference
test.
Student’s
t-test
was
used
for
the
other
behavioral
tests,
body
weight,
and
quantitative
RT-
PCR
analysis
to
detect
significant
differences
between
the
control
and
DEP-exposed
groups.
Significance
was
determined
at
p
<
0.05.
3.
Results
3.1.
Characterization
of
diesel
exhaust
particles
(DEPs)
The
DEPs
consisted
of
elemental
and
organic
carbon
com-
pounds,
metals,
and
anions
(Table
1).
The
DEPs
were
of
various
sizes
(approximately
60–1700
nm
diameter)
with
a
peak
size
of
126.0

36.6
nm
and
a
polydispersity
index
(PDI)
of
0.629
(0.015)
(Fig.
1A).
The
data
on
the
size
distribution
of
the
filtered
DEPs
(through
a
450-nm
filter)
clearly
showed
the
presence
of
an
ultrafine
DEP
fraction
in
the
suspension
(Fig.
1B,
PDI:
0.171

0.014).
3.2.
Effects
of
prenatal
exposure
to
DEPs
on
litter
size
and
body
weight
of
male
offspring
DEP
exposure
had
no
significant
effects
on
litter
size
(Control:
12.8

1.8;
DEP:
12.5

2.2).
The
body
weight
of
male
Table
1
Characterization
of
the
components
of
diesel
exhaust
particles.
Constituent
(unit)
Concentration
Analysis
method
Carbon
(mg/g)
790
CHN
analysis
Organic
carbon
(mg/g)
52
CHN
analysis
Benzo(a)pyrene
(
m
g/kg)
500
GC–MS
Lead
(
m
g/g)
67
ICP-MS
Nickel
(
m
g/g)
110
ICP-MS
Zinc
(
m
g/g)
760
ICP-MS
Iron
(
m
g/g)
11,000
ICP-MS
Manganese
(
m
g/g)
250
ICP-MS
Aluminum
(
m
g/g)
170
ICP-MS
Nitrate
ion
(
m
g/g)
810
Ion
chromatography
Sulfate
ion
(
m
g/g)
8,600
Ion
chromatography
CHN
analysis,
carbon-hydrogen-nitrogen
(elemental)
analysis;
GC–MS,
gas
chromatography–mass
spectrometry;
ICP-MS,
inductively
coupled
plasma
mass
spectrometry.
Table
2
Primer
design
for
quantitative
RT-PCR.
Gene
Sequence
T
m
GAPDH:
glyceraldehyde-3-phosphate
dehydrogenase
Forward:
5
0
-TGCACCACCAACTGCTTAG-3
0
60
8C
Reverse:
5
0
-GGATGCAGGGATGATGTTC-3
0
NR2A:
N-methyl-
D
-aspartate
receptor
subunit
2A
Forward:
5
0
-GCTACGGGCAGACAGAGAAG-3
0
60
8C
Reverse:
5
0
-GTGGTTGTCATCTGGCTCA-3
0
NR2B:
N-methyl-
D
-aspartate
receptor
subunit
2B
Forward:
5
0
-GCTACAACACCCACGAGAAGAGG-3
0
60
8C
Reverse:
5
0
-GAGAGGGTCCACACTTTCC-3
0
S.
Yokota
et
al.
/
NeuroToxicology
50
(2015)
108–115
110

offspring
was
also
not
affected
by
maternal
DEP
exposure
during
the
adolescent
to
adult
period
(postnatal
day
1:
Control,
2.2

0.3
g;
DEP,
2.3

0.3
g.
9
weeks:
Control,
40.8

1.0
g;
DEP,
41.3

0.9
g.
10
weeks:
Control,
40.4

1.0
g;
DEP,
40.7

0.7
g).
No
deaths
or
malformations
were
observed
in
both
control
and
DEP-
exposed
mice.
3.3.
Effects
of
prenatal
exposure
to
DEPs
on
serum
corticosterone
levels
To
check
for
confounding
effects
of
stress
on
behavioral
endpoints,
we
measured
serum
corticosterone
levels
of
both
control
and
DEP-exposed
mice.
There
were
no
significant
differences
in
basal
plasma
corticosterone
levels
between
control
and
DEP-
exposed
mice
(data
not
shown).
3.4.
Effects
of
prenatal
DEP
exposure
on
locomotor
activity
in
male
offspring
Spontaneous
locomotor
activity
was
tested
in
the
open-field
test.
There
were
no
significant
differences
between
control
and
DEP-exposed
mice
in
total
distance
traveled
in
10
min
or
60
min
(Fig.
2A,
D).
In
addition,
there
were
no
significant
differences
between
control
and
DEP-exposed
mice
in
10-min-
and
60-min
stereotype
and
ambulatory
counts
(Fig.
2B,
C,
E,
F).
3.5.
Effects
of
prenatal
DEP
exposure
on
learning
and
memory
in
male
offspring
To
examine
hippocampus-dependent
spatial
learning
and
memory,
we
performed
a
Morris
water
maze
test.
Both
the
control
Fig.
1.
Size
distribution
of
diesel
exhaust
particles
(DEPs)
in
suspension
as
determined
by
dynamic
light
scattering.
(A)
Original
DEP
suspension
used
for
treatment
of
the
mice.
(B)
Suspension
filtered
through
a
450-nm
filter.
Values
represent
the
mean

S.E.M.
of
three
measurements.
Fig.
2.
Effects
of
prenatal
exposure
to
diesel
exhaust
particles
(DEPs)
on
spontaneous
locomotor
activity
for
(A–C)
10
min
and
(D–F)
60
min.
(A,
D)
The
total
distance
traveled
was
recorded
in
the
open-field
test.
(B,
E)
Stereotype
counts
were
recorded
in
the
open-field
test.
(C,
F)
Ambulatory
counts
were
recorded
in
the
open-field
test.
There
were
no
significant
differences
between
control
(open
bars,
n
=
30)
and
prenatally
DEP-exposed
(closed
bars,
n
=
30)
mice.
Values
represent
the
mean

S.E.M.
S.
Yokota
et
al.
/
NeuroToxicology
50
(2015)
108–115
111

and
DEP-exposed
mice
swam
well
with
the
characteristic
swimming
posture.
In
the
hidden
platform
test,
from
day
1
to
9,
all
mice
showed
a
gradual
reduction
in
the
time
taken
to
find
the
escape
platform
as
training
proceeded.
The
improvement
in
the
escape
latency
of
each
group
following
training
was
reflected
in
a
main
effect
of
day
[F
(8
,
269)
=
19.20,
p
<
0.001,
Fig.
3A].
However,
the
control
mice
found
the
platform
faster
than
the
DEP-exposed
mice
[F
(1
,
269)
=
5.06,
p
<
0.05,
Fig.
3A].
A
post
hoc
analysis
showed
significant
differences
between
control
and
DEP-exposed
mice
on
day
7,
but
not
on
day
8
and
day
9
(Fig.
3A).
In
the
probe
test,
DEP-exposed
mice
showed
significant
deficits
in
reference
memory
compared
to
control
mice
(Fig.
3B).
However,
additional
time
was
required
to
acquire
learning
in
the
present
study
compared
to
previously
published
data
(Vorhees
and
Williams,
2006)
because
we
used
ICR
mice,
which
have
poorer
performance
in
this
task
than
the
C57BL/6
mice
used
by
Vorhees
and
Williams.
Therefore,
we
used
more
than
two
cohorts
in
the
study
and
confirmed
that
the
data
were
reproducible
(data
not
shown).
Next,
we
examined
another
type
of
learning
and
memory
using
the
passive
avoidance
test
(Fig.
4A).
However,
prenatal
DEP
Fig.
3.
Effects
of
prenatal
exposure
to
diesel
exhaust
particles
(DEPs)
on
spatial
learning
and
memory.
(A)
Mice
that
were
prenatally
exposed
to
DEPs
were
slower
to
learn
the
location
of
the
hidden
platform
in
the
Morris
water
maze
test.
The
graph
represents
the
escape
latency
of
mice
trained
to
find
a
hidden
platform
in
a
water
maze.
Mice
that
were
prenatally
exposed
to
DEPs
(closed
triangles,
n
=
15)
displayed
a
longer
latency
in
every
block
(two
trials
per
day)
than
control
mice
(closed
circles,
n
=
15).
Mice
that
were
prenatally
exposed
to
DEPs
also
learned
the
acquisition
task,
although
learning
was
delayed.
(B)
Average
percentage
of
time
in
each
quadrant
in
the
probe
test
for
control
(open
bar,
n
=
15)
and
DEP-exposed
(closed
bar,
n
=
15)
mice.
DEP-exposed
mice
spent
equal
amounts
of
time
in
every
quadrant,
whereas
control
mice
spent
significantly
more
time
in
the
target
quadrant.
Values
represent
the
mean

S.E.M.
Asterisks
indicate
significant
differences
between
control
and
DEP-exposed
groups
(*p
<
0.05,
**p
<
0.01).
Fig.
4.
Effects
of
prenatal
exposure
to
diesel
exhaust
particles
(DEPs)
on
non-spatial
learning
and
memory.
(A)
Schematic
representation
of
the
passive
avoidance
apparatus.
(B)
Passive
avoidance
performance
in
control
and
DEP-exposed
mice
in
the
training
test.
(C)
Passive
avoidance
performance
in
control
and
DEP-exposed
mice
in
the
retention
test
24
h
after
the
training
test.
There
were
no
significant
differences
between
the
results
for
control
(open
bars,
n
=
15)
and
DEP-exposed
(closed
bars,
n
=
15)
mice.
Values
represent
the
mean

S.E.M.
S.
Yokota
et
al.
/
NeuroToxicology
50
(2015)
108–115
112

exposure
had
no
significant
effect
on
learning
and
memory
in
this
test
(Fig.
4B,
C).
3.6.
RT-PCR
analysis
To
examine
the
cause
of
the
spatial
learning
and
memory
deficits,
we
used
RT-PCR
to
quantify
N-methyl-
D
-aspartate
receptor
(NR)
gene
expression
in
the
hippocampus.
NR2A
expression
levels
in
the
hippocampus
of
DEP-exposed
mice
were
significantly
lower
than
those
of
the
control
(Fig.
5A).
However,
there
were
no
differences
in
hippocampal
NR2B
expression
between
control
and
DEP-exposed
mice
(Fig.
5B).
4.
Discussion
The
results
of
the
present
study
demonstrate,
for
the
first
time,
the
effects
of
prenatal
DEP
exposure
on
acquisition
and
reference
memory
in
male
offspring
in
later
life,
in
addition
to
reduced
NR2A
expression
in
the
hippocampus.
In
the
present
study,
we
adopted
repeated
maternal
DEP
administration,
as
this
approach
is
more
relevant
to
human
exposure
scenarios
than
single-dose
exposure.
Subcutaneous
injection
was
selected
because
of
the
repeated
exposure
schedule.
The
dose
used
in
the
present
study
did
not
affect
litter
size,
body
weight,
or
spontaneous
locomotor
activity
in
the
open
field
test.
However,
the
decreased
performance
in
the
Morris
water
maze
test
was
suggestive
of
impaired
spatial
learning
and
memory.
Whereas
previous
studies
noted
that
exposure
to
DE
or
DEPs
during
the
adult
period
resulted
in
behavioral
and/or
molecular
effects
on
the
central
nervous
system
in
vivo
and
in
vitro
(Gerlofs-
Nijland
et
al.,
2010;
Hartz
et
al.,
2008;
Oppenheim
et
al.,
2013;
Tobwala
et
al.,
2013;
van
Berlo
et
al.,
2010;
Win-Shwe
et
al.,
2012;
Yamagishi
et
al.,
2012),
the
present
study
addressed
potential
long-lasting
effects
of
repeated
prenatal
exposure
to
DEPs
on
the
central
nervous
system
of
adult
offspring.
This
mouse
model
of
maternal
DEP
exposure
is
unique
because
it
enables
clarification
of
the
effects
of
chronic
exposure
during
pregnancy
to
further
elucidate
environmental
factors
involved
in
DEP-
mediated
neurodegeneration.
In
rodents,
the
hippocampus
has
long
been
recognized
as
a
critical
structure
for
encoding
spatial
information
(Kesner
et
al.,
2004;
Milner
et
al.,
1998).
The
Morris
water
maze
test
demon-
strated
an
impairment
of
spatial
learning
and
reference
memory,
which
requires
a
fully
functional
hippocampus,
in
adult
male
offspring
of
mice
maternally
exposed
to
DEPs.
Additionally,
NR2A
expression
in
the
hippocampus
of
mice
maternally
exposed
to
DEPs
was
significantly
lower
than
that
of
control
mice.
These
results
are
similar
to
those
of
a
previous
study
in
which
a
significant
pathological
impairment
of
the
CA1
region
of
the
hippocampus
was
found
in
mice
exposed
to
maternal
DE
inhalation
(Sugamata
et
al.,
2006).
In
rats,
the
volume
of
dorsal
hippocampal
tissue
damage
correlates
with
the
degree
of
spatial
learning
impairment,
and
dorsal
hippocampal
lesions
result
in
more
profound
impairment
than
ventral
hippocampal
lesions
(Moser
et
al.,
1993),
and
CA1
neurons
are
important
for
spatial
learning
(Morris
et
al.,
1982).
However,
in
the
present
study,
there
were
no
differences
between
the
two
groups
in
the
passive
avoidance
test,
indicating
that
DEPs
might
affect
spatial
learning
and
memory,
but
not
non-spatial
learning
and
memory.
In
recent
years,
much
research
has
focused
on
relationships
between
neurochemistry
and
behavior.
It
is
known
that
excitatory
transmission
in
the
brain
is
mediated
by
glutamate
through
ionotropic
(NRs
and
AMPA)
and
metabotropic
(mGluR)
receptors.
In
this
regard,
the
expression
of
NRs
has
received
special
interest.
NRs
are
heteromeric
assemblies
of
a
core
NR1
subunit
and
various
modulatory
NR2
subunits.
In
the
hippocampus,
NR2A
and
NR2B
subunits
serve
as
the
major
NR2
components
in
association
with
NR1
subunits
(Monyer
et
al.,
1994).
As
NRs
are
involved
in
long-
term
potentiation
(LTP)
and
long-term
depression
(LTD),
this
receptor
type
is
important
for
spatial
learning
and
memory
(Morris
et
al.,
1986).
For
example,
transgenic
mice
lacking
the
NR2A
subunit
show
defects
in
hippocampal
LTP,
in
addition
to
impaired
hidden-platform
acquisition
and
probe
trial
performance
in
the
water
maze
test
(Sakimura
et
al.,
1995).
In
the
present
study,
prenatal
DEP
exposure
significantly
decreased
hippocampal
NR2A
expression,
which
may
be
relevant
to
the
observed
deficits
in
spatial
learning
and
memory.
However,
maternal
exposure
to
DEPs
did
not
affect
NR2B
expression.
The
NR2B
subunit
is
required
for
neuronal
pattern
formation
during
the
prenatal
period
and
for
fetal
viability
(Kutsuwada
et
al.,
1996),
whereas
NR2A
subunit
expression
(Monyer
et
al.,
1994)
and
synaptic
incorporation
(Tovar
and
Westbrook,
1999)
progressively
increase
throughout
devel-
opment.
In
general,
synaptic
NRs
play
critical
roles
in
brain
development,
plasticity,
and
pathology
(Constantine-Paton
and
Cline,
1998;
Dingledine
et
al.,
1999;
Zoghbi
et
al.,
2000).
Insertion
of
NRs
into
synaptic
sites
follows
different
mechanisms,
dependent
upon
receptor
subunit
composition.
Synaptic
insertion
of
NR2B-
containing
receptors
does
not
increase
with
increased
levels
of
NR2B
gene
expression,
whereas
synaptic
insertion
of
NR2A-
containing
receptors
requires
synaptic
activity,
which
is
promoted
by
increased
levels
of
NR2A
gene
expression
(Barria
and
Malinow,
2002).
Therefore,
prenatal
exposure
to
DEPs
might
affect
NR2A
Fig.
5.
Quantitative
analysis
of
hippocampal
N-methyl-
D
-aspartate
receptor
(NR)
subunit
mRNA
expression.
NR2A
(A)
and
NR2B
(B)
mRNA
levels
in
the
hippocampus
of
10-
week-old
male
offspring.
NR2A
mRNA
expression
levels
were
lower
in
mice
maternally
exposed
to
DEPs
than
in
control
mice.
However,
similar
NR2B
expression
levels
were
observed
in
control
and
DEP-exposed
animals.
Values
represent
the
mean

S.E.M.
Asterisks
indicate
significant
differences
between
control
and
DEP-exposed
groups
(**p
<
0.01).
S.
Yokota
et
al.
/
NeuroToxicology
50
(2015)
108–115
113

insertion
into
synapses
in
the
hippocampus
because
NR2A
expression
was
decreased
in
the
hippocampus.
Epidemiological
studies
have
indicated
that
high
concentra-
tions
of
particulate
matter,
including
DEPs,
may
contribute
to
the
onset
of
Alzheimer’s
disease
(Caldero
´n-Garciduen
˜as
et
al.,
2004,
2007,
2015).
Our
results
highlight
the
requirement
for
identifying
means
of
preventing
and
controlling
the
developmental
effects
of
maternal
exposure
to
DEPs
on
cognitive
function.
We
previously
reported
that
early
environmental
enrichment
prevented
changes
in
gene
expression
in
the
olfactory
bulb
following
DE
exposure
(Yokota
et
al.,
2013a).
The
living
environment
during
the
perinatal
period
is
of
interest
for
preventing
the
developmental
effects
of
DEPs.
Indeed,
environmental
enrichment
also
prevents
im-
pairment
of
hippocampal
function
(Beauquis
et
al.,
2013;
Hui
et
al.,
2011;
Hutchinson
et
al.,
2012;
Spires
et
al.,
2004;
Valero
et
al.,
2011;
Xie
et
al.,
2012).
Further
investigation
is
required
to
identify
further
preventative
measures
against
the
effects
of
DEP
exposure
on
cognition,
e.g.,
by
early
environmental
enrichment
or
through
other
interventions.
In
conclusion,
maternal
exposure
to
DEPs
resulted
in
changes
in
NR2A
expression
in
the
hippocampus
and
impairment
of
spatial
learning
and
memory.
Acknowledgments
We
are
grateful
to
Dr.
Shinya
Yanagita
(Tokyo
University
of
Science),
Dr.
Keisuke
Mizuo
(Sapporo
Medical
University),
and
Mr.
Nozomu
Moriya
(Hyogo
University
of
Health
Sciences)
for
experimental
assistance.
We
also
thank
Mr.
Tadashi
Udagawa
(Research
Institute
of
Tuberculosis)
for
providing
DEP
samples.
We
would
like
to
thank
Editage
(www.editage.jp)
for
English
language
editing.
This
research
was
supported
in
part
by
a
Grant-in-Aid
for
Science
Research
from
the
Japan
Society
for
the
Promotion
of
Science
(JSPS:
Satoshi
Yokota,
22.
5895)
and
a
grant
from
the
Academic
Frontier
Project
from
the
Ministry
of
Education,
Culture,
Sports,
Science,
and
Technology
of
Japan.
This
work
was
supported
by
a
Grant-in-Aid
for
JSPS
Fellows
(Satoshi
Yokota,
22.
5895)
and
in
part
by
a
Grant-in-Aid
for
Science
Research
from
the
Ministry
of
Education,
Culture,
Sports,
Science,
and
Technology
of
Japan.
This
work
was
also
supported
by
a
Grant-in-Aid
for
Health
and
Labor
Sciences
Research
Grants,
Research
on
Risk
of
Chemical
Sub-
stances,
from
the
Ministry
of
Health,
Labor,
and
Welfare,
and
a
Grant-in-Aid
for
NEXT-supported
Program
for
the
Strategic
Research
Foundation
at
Private
Universities,
2011–2015.
References
Auten,
R.L.,
Gilmour,
M.I.,
Krantz,
Q.T.,
Potts,
E.N.,
Mason,
S.N.,
Foster,
W.M.,
2012.
Maternal
diesel
inhalation
increases
airway
hyperreactivity
in
ozone-
exposed
offspring.
Am.
J.
Respir.
Cell
Mol.
Biol.
46
(4),
454–460,
http://
dx.doi.org/10.1165/rcmb.2011-0256OC.
Barria,
A.,
Malinow,
R.,
2002.
Subunit-specific
NMDA
receptor
trafficking
to
synapses.
Neuron
35
(2),
345–353,
http://dx.doi.org/10.1016/S0896-
6273(02)00776-6.
Beauquis,
J.,
Pavı
´a,
P.,
Pomilio,
C.,
Vinuesa,
A.,
Podlutskaya,
N.,
Galvan,
V.,
et
al.,
2013.
Environmental
enrichment
prevents
astroglial
pathological
changes
in
the
hippocampus
of
APP
transgenic
mice,
model
of
Alzheimer’s
disease.
Exp.
Neurol.
239,
28–37,
http://dx.doi.org/10.1016/
j.expneurol.2012.09.009.
Block,
M.L.,
Caldero
´n-Garciduen
˜as,
L.,
2009.
Air
pollution:
mechanisms
of
neuroinflammation
and
CNS
disease.
Trends
Neurosci.
32
(9),
506–516,
http://dx.doi.org/10.1016/j.tins.2009.05.009.
Butte,
J.C.,
Kakihana,
R.,
Noble,
E.P.,
1976.
Circadian
rhythm
of
corticosterone
levels
in
rat
brain.
J.
Endocrinol.
68
(02),
235–239,
http://dx.doi.org/10.1677/
joe.0.0680235.
Caldero
´n-Garciduen
˜as,
L.,
Franco-Lira,
M.,
Torres-Jardo
´n,
R.,
Henriquez-Rolda
´n,
C.,
Barraga
´n-Mejı
´a,
G.,
Valencia-Salazar,
G.,
et
al.,
2007.
Pediatric
respiratory
and
systemic
effects
of
chronic
air
pollution
exposure:
nose,
lung,
heart,
and
brain
pathology.
Toxicol.
Pathol.
35
(1),
154–162,
http://
dx.doi.org/10.1080/01926230601059985.
Caldero
´n-Garciduen
˜as,
L.,
Mora-Tiscaren
˜o,
A.,
Ontiveros,
E.,
Go
´mez-Garza,
G.,
Barraga
´n-Mejı
´a,
G.,
Broadway,
J.,
et
al.,
2008.
Air
pollution,
cognitive
deficits
and
brain
abnormalities:
a
pilot
study
with
children
and
dogs.
Brain
Cogn.
68
(2),
117–127,
http://dx.doi.org/10.1016/j.bandc.2008.04.008.
Caldero
´n-Garciduen
˜as,
L.,
Reed,
W.,
Maronpot,
R.R.,
Henrı
´quez-Rolda
´n,
C.,
Delgado-Chavez,
R.,
Caldero
´n-Garciduen
˜as,
A.,
et
al.,
2004.
Brain
inflammation
and
Alzheimer’s-like
pathology
in
individuals
exposed
to
severe
air
pollution.
Toxicol.
Pathol.
32
(6),
650–658,
http://dx.doi.org/
10.1080/01926230490520232.
Caldero
´n-Garciduen
˜as,
L.,
Vojdani,
A.,
Blaurock-Busch,
E.,
Busch,
Y.,
Friedle,
A.,
Franco-Lira,
M.,
et
al.,
2015.
Air
pollution
and
children:
neural
and
tight
junction
antibodies
and
combustion
metals,
the
role
of
barrier
breakdown
and
brain
immunity
in
neurodegeneration.
J.
Alzheimers
Dis.
43
(3),
1039–1058,
http://dx.doi.org/10.3233/JAD-141365.
Claxton,
L.D.,
2015.
The
history,
genotoxicity,
and
carcinogenicity
of
carbon-
based
fuels
and
their
emissions.
Part
3:
diesel
and
gasoline.
Mutat.
Res.
Rev.
Mutat.
Res.
763,
30–85,
http://dx.doi.org/10.1016/j.mrrev.
2014.09.002.
Constantine-Paton,
M.,
Cline,
H.T.,
1998.
LTP
and
activity-dependent
synaptogenesis:
the
more
alike
they
are,
the
more
different
they
become.
Curr.
Opin.
Neurobiol.
8
(1),
139–148,
http://dx.doi.org/10.1016/S0959-
4388(98)80017-2.
Dingledine,
R.,
Borges,
K.,
Bowie,
D.,
Traynelis,
S.F.,
1999.
The
glutamate
receptor
ion
channels.
Pharmacol.
Rev.
51
(1),
7–61.
Gerlofs-Nijland,
M.E.,
van
Berlo,
D.,
Cassee,
F.R.,
Schins,
R.P.,
Wang,
K.,
Campbell,
A.,
2010.
Effect
of
prolonged
exposure
to
diesel
engine
exhaust
on
proinflammatory
markers
in
different
regions
of
the
rat
brain.
Part
Fibre
Toxicol.
7,
12,
http://dx.doi.org/10.1186/1743-8977-7-12.
Hartz,
A.M.,
Bauer,
B.,
Block,
M.L.,
Hong,
J.S.,
Miller,
D.S.,
2008.
Diesel
exhaust
particles
induce
oxidative
stress,
proinflammatory
signaling,
and
P-
glycoprotein
up-regulation
at
the
blood-brain
barrier.
FASEB
J.
22
(8),
2723–2733,
http://dx.doi.org/10.1096/fj.08-106997.
Hesterberg,
T.W.,
Long,
C.M.,
Lapin,
C.A.,
Hamade,
A.K.,
Valberg,
P.A.,
2010.
Diesel
exhaust
particulate
(DEP)
and
nanoparticle
exposures:
what
do
DEP
human
clinical
studies
tell
us
about
potential
human
health
hazards
of
nanoparticles?
Inhal.
Toxicol.
22
(8),
679–694,
http://dx.doi.org/10.3109/
08958371003758823.
Hui,
G.K.,
Figueroa,
I.R.,
Poytress,
B.S.,
Roozendaal,
B.,
McGaugh,
J.L.,
Weinberger,
N.M.,
2004.
Memory
enhancement
of
classical
fear
conditioning
by
post-
training
injections
of
corticosterone
in
rats.
Neurobiol.
Learn.
Mem.
81
(1),
67–74,
http://dx.doi.org/10.1016/j.nlm.2003.09.002.
Hui,
J.J.,
Zhang,
Z.J.,
Liu,
S.S.,
Xi,
G.J.,
Zhang,
X.R.,
Teng,
G.J.,
et
al.,
2011.
Hippocampal
neurochemistry
is
involved
in
the
behavioural
effects
of
neonatal
maternal
separation
and
their
reversal
by
post-weaning
environmental
enrichment:
a
magnetic
resonance
study.
Behav.
Brain
Res.
217
(1),
122–127,
http://dx.doi.org/10.1016/j.bbr.2010.10.014.
Hutchinson,
K.M.,
McLaughlin,
K.J.,
Wright,
R.L.,
Bryce
Ortiz,
J.,
Anouti,
D.P.,
Mika,
A.,
et
al.,
2012.
Environmental
enrichment
protects
against
the
effects
of
chronic
stress
on
cognitive
and
morphological
measures
of
hippocampal
integrity.
Neurobiol.
Learn.
Mem.
97
(2),
250–260,
http://dx.doi.org/10.1016/
j.nlm.2012.01.003.
Invernizzi,
G.,
Boffi,
R.,
Ruprecht,
A.A.,
Barnes,
P.J.,
Kharitonov,
S.A.,
Paredi,
P.,
2006.
Real-time
measurement
of
particulate
matter
deposition
in
the
lung.
Biomarkers
11
(3),
221–232,
http://dx.doi.org/10.1080/13547500600648523.
Kesner,
R.P.,
Lee,
I.,
Gilbert,
P.,
2004.
A
behavioral
assessment
of
hippocampal
function
based
on
a
subregional
analysis.
Rev.
Neurosci.
15
(5),
333–351,
http://dx.doi.org/10.1515/REVNEURO.2004.15.5.333.
Kim,
D.H.,
Hung,
T.M.,
Bae,
K.H.,
Jung,
J.W.,
Lee,
S.,
Yoon,
B.H.,
et
al.,
2006.
Gomisin
A
improves
scopolamine-induced
memory
impairment
in
mice.
Eur.
J.
Pharmacol.
542
(1–3),
129–135,
http://dx.doi.org/10.1016/
j.ejphar.2006.06.015.
Kim,
S.R.,
Kang,
S.Y.,
Lee,
K.Y.,
Kim,
S.H.,
Markelonis,
G.J.,
Oh,
T.H.,
et
al.,
2003.
Anti-amnestic
activity
of
E-p-methoxycinnamic
acid
from
Scrophularia
buergeriana.
Brain
Res.
Cogn.
Brain
Res.
17
(2),
454–461,
http://dx.doi.org/
10.1016/S0926-6410(03)00161-7.
Kutsuwada,
T.,
Sakimura,
K.,
Manabe,
T.,
Takayama,
C.,
Katakura,
N.,
Kushiya,
E.,
et
al.,
1996.
Impairment
of
suckling
response,
trigeminal
neuronal
pattern
formation,
and
hippocampal
LTD
in
NMDA
receptor
epsilon
2
subunit
mutant
mice.
Neuron
16
(2),
333–344,
http://dx.doi.org/10.1016/S0896-
6273(00)80051-3.
Lo
¨ndahl,
J.,
Massling,
A.,
Pagels,
J.,
Swietlicki,
E.,
Vaclavik,
E.,
Loft,
S.,
2007.
Size-
resolved
respiratory-tract
deposition
of
fine
and
ultrafine
hydrophobic
and
hygroscopic
aerosol
particles
during
rest
and
exercise.
Inhal.
Toxicol.
19
(2),
109–116,
http://dx.doi.org/10.1080/08958370601051677.
Milner,
B.,
Squire,
L.R.,
Kandel,
E.R.,
1998.
Cognitive
neuroscience
and
the
study
of
memory.
Neuron
20
(3),
445–468,
http://dx.doi.org/10.1016/S0896-
6273(00)80987-3.
Monyer,
H.,
Burnashev,
N.,
Laurie,
D.J.,
Sakmann,
B.,
Seeburg,
P.H.,
1994.
Developmental
and
regional
expression
in
the
rat
brain
and
functional
properties
of
four
NMDA
receptors.
Neuron
12
(3),
529–540,
http://
dx.doi.org/10.1016/0896-6273(94)90210-0.
Morris,
R.G.,
Anderson,
E.,
Lynch,
G.S.,
Baudry,
M.,
1986.
Selective
impairment
of
learning
and
blockade
of
long-term
potentiation
by
an
N-methyl-D-aspartate
receptor
antagonist,
AP5.
Nature
319
(6056),
774–776,
http://dx.doi.org/
10.1038/319774a0.
Morris,
R.G.,
Garrud,
P.,
Rawlins,
J.N.,
O’Keefe,
J.,
1982.
Place
navigation
impaired
in
rats
with
hippocampal
lesions.
Nature
297
(5868),
681–683,
http://
dx.doi.org/10.1038/297681a0.
S.
Yokota
et
al.
/
NeuroToxicology
50
(2015)
108–115
114

Moser,
E.,
Moser,
M.B.,
Andersen,
P.,
1993.
Spatial
learning
impairment
parallels
the
magnitude
of
dorsal
hippocampal
lesions,
but
is
hardly
present
following
ventral
lesions.
J.
Neurosci.
13
(9),
3916–3925.
Oppenheim,
H.A.,
Lucero,
J.,
Guyot,
A.C.,
Herbert,
L.M.,
McDonald,
J.D.,
Mabondzo,
A.,
et
al.,
2013.
Exposure
to
vehicle
emissions
results
in
altered
blood
brain
barrier
permeability
and
expression
of
matrix
metalloproteinases
and
tight
junction
proteins
in
mice.
Part
Fibre
Toxicol.
10,
62,
http://dx.doi.org/
10.1186/1743-8977-10-62.
Sakimura,
K.,
Kutsuwada,
T.,
Ito,
I.,
Manabe,
T.,
Takayama,
C.,
Kushiya,
E.,
et
al.,
1995.
Reduced
hippocampal
LTP
and
spatial
learning
in
mice
lacking
NMDA
receptor
epsilon
1
subunit.
Nature
373
(6510),
151–155,
http://dx.doi.org/
10.1038/373151a0.
Silverman,
D.T.,
Samanic,
C.M.,
Lubin,
J.H.,
Blair,
A.E.,
Stewart,
P.A.,
Vermeulen,
R.,
et
al.,
2012.
The
diesel
exhaust
in
miners
study:
a
nested
case-control
study
of
lung
cancer
and
diesel
exhaust.
J.
Natl.
Cancer
Inst.
104
(11),
855–868,
http://dx.doi.org/10.1093/jnci/djs034.
Spires,
T.L.,
Grote,
H.E.,
Varshney,
N.K.,
Cordery,
P.M.,
van
Dellen,
A.,
Blakemore,
C.,
et
al.,
2004.
Environmental
enrichment
rescues
protein
deficits
in
a
mouse
model
of
Huntington’s
disease,
indicating
a
possible
disease
mechanism.
J.
Neurosci.
24
(9),
2270–2276,
http://dx.doi.org/10.1523/
JNEUROSCI.
1658-03.2004.
Sugamata,
M.,
Ihara,
T.,
Takano,
H.,
Oshio,
S.,
Takeda,
K.,
2006.
Maternal
diesel
exhaust
exposure
damages
newborn
murine
brains.
J.
Health
Sci.
52,
82–84,
http://dx.doi.org/10.1248/jhs.52.82.
Tobwala,
S.,
Zhang,
X.,
Zheng,
Y.,
Wang,
H.J.,
Banks,
W.A.,
Ercal,
N.,
2013.
Disruption
of
the
integrity
and
function
of
brain
microvascular
endothelial
cells
in
culture
by
exposure
to
diesel
engine
exhaust
particles.
Toxicol.
Lett.
220
(1),
1–7,
http://dx.doi.org/10.1016/j.toxlet.2013.03.023.
Tovar,
K.R.,
Westbrook,
G.L.,
1999.
The
incorporation
of
NMDA
receptors
with
a
distinct
subunit
composition
at
nascent
hippocampal
synapses
in
vitro.
J.
Neurosci.
19
(10),
4180–4188.
Valero,
J.,
Espan
˜a,
J.,
Parra-Damas,
A.,
Martı
´n,
E.,
Rodrı
´guez-A
´lvarez,
J.,
Saura,
C.A.,
2011.
Short-term
environmental
enrichment
rescues
adult
neurogenesis
and
memory
deficits
in
APP(Sw.
Ind)
transgenic
mice.
PLoS
One
6
(2),
e16832,
http://dx.doi.org/10.1371/journal.pone.0016832.
van
Berlo,
D.,
Albrecht,
C.,
Knaapen,
A.M.,
Cassee,
F.R.,
Gerlofs-Nijland,
M.E.,
Kooter,
I.M.,
et
al.,
2010.
Comparative
evaluation
of
the
effects
of
short-term
inhalation
exposure
to
diesel
engine
exhaust
on
rat
lung
and
brain.
Arch.
Toxicol.
84
(7),
553–562,
http://dx.doi.org/10.1007/s00204-010-
0551-7.
Vorhees,
C.V.,
Williams,
M.T.,
2006.
Morris
water
maze:
procedures
for
assessing
spatial
and
related
forms
of
learning
and
memory.
Nat.
Protoc.
1
(2),
848–858,
http://dx.doi.org/10.1038/nprot.2006.116.
Welberg,
L.A.,
Seckl,
J.R.,
2001.
Prenatal
stress,
glucocorticoids
and
the
programming
of
the
brain.
J.
Neuroendocrinol.
13
(2),
113–128,
http://
dx.doi.org/10.1111/j.1365-2826.2001.00601.x.
Weldy,
C.S.,
Liu,
Y.,
Chang,
Y.C.,
Medvedev,
I.O.,
Fox,
J.R.,
Larson,
T.V.,
Chien,
W.M.,
Chin,
M.T.,
2013.
In
utero
and
early
life
exposure
to
diesel
exhaust
air
pollution
increases
adult
susceptibility
to
heart
failure
in
mice.
Part
Fibre
Toxicol.
10
(1),
59,
http://dx.doi.org/10.1186/1743-
8977-10-59.
Wichmann,
H.E.,
2007.
Diesel
exhaust
particles.
Inhal.
Toxicol.
19,
241–244.
Win-Shwe,
T.T.,
Fujimaki,
H.,
Fujitani,
Y.,
Hirano,
S.,
2012.
Novel
object
recognition
ability
in
female
mice
following
exposure
to
nanoparticle-rich
diesel
exhaust.
Toxicol.
Appl.
Pharmacol.
262
(3),
355–362,
http://dx.doi.org/
10.1016/j.taap.2012.05.015.
Xie,
T.,
Wang,
W.P.,
Jia,
L.J.,
Mao,
Z.F.,
Qu,
Z.Z.,
Luan,
S.Q.,
et
al.,
2012.
Environmental
enrichment
restores
cognitive
deficits
induced
by
prenatal
maternal
seizure.
Brain
Res.
1470,
80–88,
http://dx.doi.org/10.1016/
j.brainres.2012.06.034.
Yamagishi,
N.,
Ito,
Y.,
Ramdhan,
D.H.,
Yanagiba,
Y.,
Hayashi,
Y.,
Wang,
D.,
et
al.,
2012.
Effect
of
nanoparticle-rich
diesel
exhaust
on
testicular
and
hippocampus
steroidogenesis
in
male
rats.
Inhal.
Toxicol.
24
(8),
459–467,
http://dx.doi.org/10.3109/08958378.2012.688225.
Yokota,
S.,
Hori,
H.,
Umezawa,
M.,
Kubota,
N.,
Niki,
R.,
Yanagita,
S.,
et
al.,
2013a.
Gene
expression
changes
in
the
olfactory
bulb
of
mice
induced
by
exposure
to
diesel
exhaust
are
dependent
on
animal
rearing
environment.
PLoS
One
8
(8),
e70145,
http://dx.doi.org/10.1371/journal.pone.0070145.
Yokota,
S.,
Moriya,
N.,
Iwata,
M.,
Umezawa,
M.,
Oshio,
S.,
Takeda,
K.,
2013b.
Exposure
to
diesel
exhaust
during
fetal
period
affects
behavior
and
neurotransmitters
in
male
offspring
mice.
J.
Toxicol.
Sci.
38
(1),
13–23,
http://dx.doi.org/10.2131/jts.38.13.
Zoghbi,
H.Y.,
Gage,
F.H.,
Choi,
D.W.,
2000.
Neurobiology
of
disease.
Curr.
Opin.
Neurobiol.
10
(5),
655–660.
S.
Yokota
et
al.
/
NeuroToxicology
50
(2015)
108–115
115