From the Laboratoire de Recherches Cérébrovasculaires, CNRS
UPR 646, 1FR6, Université Paris 7, France.
Correspondence to Dr Elisabeth Pinard, Laboratoire de Recherches Cérébrovasculaires, 10 Avenue de Verdun, 75010 Paris, France. E-mail pinard{at}ext.jussieu.fr
Methods—7-Nitroindazole (7-NI) was used as a selective
inhibitor of neuronal NO synthase. Global ischemia
was induced for 20 minutes in anesthetized rats following the
four-vessel occlusion model. Electroencephalogram and brain and body
temperatures were continuously monitored. All rats were thermoregulated
for the entire duration of anesthesia. 7-NI (25 mg/kg) or
its vehicle was given intraperitoneally just after
the carotid clamping and again 1 hour later. Rats were randomly divided
into four groups: (1) vehicle (n=7); (2) 7-NI (n=7); (3)
L-arginine (300 mg/kg IP)+7-NI (n=7); and (4) 7-NI
associated with warming to 37°C for 7 hours after disruption of
anesthesia to compensate for the decrease in temperature
induced by 7-NI (n=9). Seven days after ischemia, hippocampal
CA1 damage was evaluated by classic histology. The lesion was scored
with the use of a point scale, and the surviving neurons were
counted.
Results—Lesion scores were significantly lower and neuron counts
higher in the two (warmed and unwarmed) groups of rats in which 7-NI
was given alone than in vehicle- and
L-arginine+7-NI–treated rats.
Conclusions—The results indicate that 7-NI was neuroprotective in
20-minute global ischemia in rats and that the neuroprotective
effect of 7-NI was mostly due to the blockade of NO synthesis,
suggesting that NO released from neurons in ischemic conditions
has a deleterious influence on hippocampal pyramidal
neurons.
The selective and delayed hippocampal damage induced in
pyramidal neurons by transient global ischemia is
believed to be triggered by excessive glutamate release associated with
inhibition of glutamate reuptake mechanisms under conditions of energy
failure.17 The overstimulation of NMDA receptors
induces an overload of Ca2+, leading to a
persistent activation of nNOS.18 This enzyme is
present not only in hippocampal
interneurons19 20 but also in the
pyramidal neurons of the CA1/CA3 layers and in the dentate
gyrus, as shown by immunocytochemistry21 and by
in situ hybridization.22 Most in vitro studies in
cultured neurons conclude that NO is involved in NMDA toxicity, either
directly or indirectly, through its reaction with superoxide to form
the powerful cyto-oxidant, peroxynitrite.23 24 25
In addition, in vitro experiments in hippocampal slices, which enable
avoidance of direct effects on the vascular system, suggest that the
activation of nNOS is involved in ischemic degeneration in the
CA1 region.26 However, some discrepant results
were obtained under similar experimental
conditions.27
The development of a relatively selective inhibitor of
nNOS, 7-nitroindazole (7-NI),28 29 has enabled
investigators to explore in vivo the possible roles of NO released by
neurons, as opposed to L-arginine derivatives, which
nonselectively block all types of NOS, thus preventing any possible
beneficial vasodilatory effect of NO released by vascular
endothelial cells. 7-NI was found to produce
significant neuroprotection against NMDA-mediated excitotoxic striatal
lesions and also, and more effectively, against secondary excitotoxic
lesions.30 In rat focal cerebral
ischemia, a significant neuroprotection was found under 7-NI,
which was reversible by L-arginine.31
In 5-minute global ischemia in gerbils, a neuroprotective
effect of 7-NI was also demonstrated.32 However,
it was not evaluated in this study whether the NO precursor
L-arginine in excess can reverse the neuroprotective effect
of 7-NI. Thus, it was not possible to be entirely conclusive on the
role of neuronal NO generation in the detrimental consequences of
global ischemia.
To explore this problem in rats, we have chosen to study the
four-vessel occlusion model. We have attempted to determine whether
7-NI, given at the onset of ischemia, is neuroprotective in
20-minute global cerebral ischemia and whether its influence is
due to nNOS inhibition or mediated by thermal changes. Actually, 7-NI
does not modify temperature in gerbils, whereas it has been shown to
depress temperature in rats,30 and we have found
in preliminary experiments that 7-NI induced a significant decrease in
body and brain temperatures in awake rats. We have thus evaluated the
influence of hypothermia induced in a delayed fashion by 7-NI, since
hypothermia is very efficient to ensure neuroprotection in rats
submitted to global ischemia, even when its induction is
delayed.33 34 35 36
Male Wistar rats weighing 280 to 330 g (Charles River) were used
in this study. They had access to food and water ad libitum and were
housed in individual cages.
Protocol for Induction of Ischemia
On the day of the experiment, anesthesia was induced with
halothane (4% in 30% oxygen and 70% N2O) and
maintained at 1%. Body temperature was kept at 37°C by a
homeothermic blanket control unit (Harvard Apparatus)
throughout the entire period of ischemia and
postischemic recovery under anesthesia. A
33-gauge thermocouple was placed under the temporalis muscle to monitor
brain temperature. The EEG was continuously recorded. The bilateral
CCAs were isolated from surrounding tissues through a midline neck
incision, and silk ligatures were placed loosely around them.
Transient forebrain ischemia was induced by occlusion of the
CCA with the use of metal clips. The completeness of ischemia
was confirmed by the observation of a flattened EEG. At that time
halothane inhalation was discontinued. After 20 minutes of
ischemia, reperfusion was accomplished by releasing the clips.
Halothane inhalation was adjusted to 0.6% for 1 hour of recovery, and
the success of reperfusion was attested to by the recovery of some EEG
activity. The wounds were sutured and infiltrated with lidocaine, and
anesthesia was then discontinued. EEG and brain temperature
recordings were stopped just before anesthesia was
discontinued.
When the rats began to recover motor activity, they were placed in a
flexible hammock where they were free to move their head and limbs.
Body temperature was monitored for 7 hours, and then the rats were
returned to their cages. Seven days later, the brains were processed
for histological analysis of the hippocampal
damage.
Evaluation of Hippocampal Damage
In addition, the intensity of ischemic injury within the
hippocampus was quantified by counting numbers of normal-appearing
neurons per high-power field (x250) in the middle CA1 subsector. All
normal-appearing hippocampal neurons in a 490-µm length of stratum
pyramidale were counted bilaterally and averaged. Three
sections were examined per animal, and the counts were averaged. CA1
cell counts from three sham-operated animals provided an assessment of
uninjured/normal CA1. Cell counts were conducted by an observer (V.S.)
who was blinded to the experimental protocols.
Experimental Groups
Materials
Statistical Analysis
Temperature
There was no significant difference in body temperature between groups
during the entire experimental period under anesthesia, ie,
during surgery, ischemia, and 60-minute reperfusion (Figure 1
Hippocampal Damage
The statistical results of both lesion scores and neuron counts are
presented in Figure 2
The comparison of normal-appearing neuron counts between groups
confirmed that the 7-NI–treated rats, whether warmed or not, had a
significantly better histological outcome than both the
vehicle and L-arginine+7-NI–treated rats. The number of
normal-appearing neurons in the middle CA1 hippocampal subsector was
10.0±2.6 in vehicle-treated rats, 68.8±7.6 in 7-NI–treated rats
(P<0.05 versus vehicle-treated rats), 25.7±6.3 in
L-arginine+7-NI–treated rats, and 47.3±13.1 in
7-NI–treated rats in which body temperature was maintained at
approximately 37°C during the entire postanesthesia
recovery period (P<0.05 versus vehicle-treated rats).
No significant difference was measured between the two groups of
7-NI–treated rats (warmed and unwarmed), or between the 7-NI–treated
rats maintained at 37°C and the L-arginine+7-NI–treated
rats, or between the L-arginine+7-NI–treated rats and the
vehicle-treated rats.
The degree of inhibition of hippocampal NOS activity by 7-NI at the
dose and timing used in the present study was determined to be 57%
in a previous study41 in which the conversion of
[14C]L-arginine in
[14C]L-citrulline was measured with
the use of the ex vivo Bredt and Snyder assay.42
It was also previously found in the conscious rat that 7-NI does not
affect arterial blood pressure, indicating its lack of
effect on eNOS.43 44 Another study has clearly
shown that 7-NI does not inhibit eNOS present in vascular
endothelial cells since it did not modify the
cerebrovascular response to acetylcholine.31 It
is thus clear that the inhibition of nNOS was rather selective in the
present experimental conditions. Interestingly enough, some
hippocampal pyramidal neurons contain
eNOS,45 but it seems that 7-NI selectivity is
mostly cellular rather than enzymatic28 so that
7-NI probably acts on both Ca2+-dependent forms of NOS
possibly present in neurons.
The NO precursor, L-arginine, partly reversed the
neuroprotective effect of 7-NI, clearly indicating that the inhibition
of NOS activity is involved in the process of neuroprotection. Any
deleterious influence of L-arginine itself through an
enhancement of NO production can be discarded, since Kirsch et
al46 have shown that it does not affect
neurological outcome after global ischemia. The incomplete
reversion by L-arginine is probably due to the fact that
7-NI competes with L-arginine for binding to the
prosthetic heme group of NOS but also additionally affects the
pteridine site of the enzyme,47 such an effect
being reversed by tetrahydrobiopterin (BH4) only.
The transient nature of the effect of 7-NI on NOS
activity28 40 enables one to propose that the
detrimental influence of NO released by neurons occurs in the early
stages after cerebral ischemia.
The prolonged decrease in temperature induced by 7-NI does not seem to
be related to NOS activity since it was not reversed by
L-arginine and because such a hypothermic effect never
occurred with NG-substituted arginine
analogues. Neither is it due to an influence of 7-NI on brain
metabolism since the cerebral metabolic rate of
glucose was unchanged in most structures of conscious rats at 30 to 40
minutes after the injection.43 However,
glucose consumption was not explored at longer delays after 7-NI
injection. It is interesting to note that the relatively late
hypothermia induced by 7-NI did not occur in
gerbils,32 occurred irregularly in
mice,48 49 and has usually not been detected in
rats, except by Schulz et al.30 This is probably
due to the thermocontrolled conditions in which the experimental
procedures under anesthesia were performed, associated with
the absence of physiological measurements after
discontinuation of anesthesia. Hypothermia, even when
induced late (2 hours) into the reperfusion phase, has been shown to be
neuroprotective in rats submitted to global
ischemia.34 However, in this previous
study the decrease in temperature was both higher and of longer
duration than in the present study. More recently, Nurse and
Corbett36 have shown that a protracted period of
subnormal temperature during the postischemic period can
obscure the interpretation of drug studies. Their demonstration was
applied to the AMPA receptor antagonist NBQX, whose
neuroprotective effect did not take place when the
postischemic brain temperature of NBQX-treated gerbils was
regulated in the long term. In contrast, our results show that the
compensation for the prolonged 7-NI–induced hypothermia in the
postanesthesia recovery period did not significantly modify
the neuroprotective effect of 7-NI, although a tendency toward
aggravation was measured. This reinforces our conclusion that the
neuroprotection exerted by 7-NI in rat global ischemia was
mainly due to nNOS inhibition.
Such a conclusion is in good agreement with the generally hypothesized
sequence of events leading to neuronal death in transient
ischemic conditions, ie, depolarization, increase in
extracellular glutamate concentration, overstimulation of glutamate
receptors (notably NMDA receptors), increase in intracellular
Ca2+ concentration, activation of enzymes
(notably constitutively expressed NOS), release of NO (which rapidly
reacts with superoxide produced in excess during reperfusion),
formation of peroxynitrite, and nitrosylation of proteins. NO may also
damage DNA through nucleotide base deamination and may
trigger programmed cell death. However, this could be modulated by some
possible protective effects of NO, such as inhibition of NOS activity,
NMDA receptor function, and glutamate release. All these processes have
been recently reviewed in detail.6 8
The neuroprotection that we found with 7-NI in rat transient global
ischemia agrees well with the data from experiments in mice
selectively deficient in nNOS isoform15 and
supports a detrimental role of NO released by neurons. However, neither
study indicates whether the neuroprotection is permanently established
when neuronally derived NO is depleted, or whether the damage is only
delayed.
It cannot be excluded that the neuroprotective effect of 7-NI was
partly due to a cerebrovascular effect. Indeed, the possible
involvement of neuronally derived NO in the local regulation of
cerebral blood flow must be taken into account when addressing the
question of NO neurotoxicity, especially when studying hippocampal
damage, since a close association between NOS-positive neurons and
blood vessels has been found in the
hippocampus.50 Because 7-NI has been shown to
decrease blood flow in all brain structures in basal
conditions43 and to reduce the cerebrovascular
responses to hypercapnia,51 somatosensory
activation,52 and limbic
seizures,44 it is likely that it may reduce the
hyperemic phase of postischemic reperfusion. The
injury due to reperfusion after global ischemia has been
extensively studied, and free radicals, especially superoxide, were
found to play a major role in this deleterious
process.53 A reduction by 7-NI of the
postischemic hyperemia would lead to a decrease in
free radical production in a period of attenuated NO synthesis,
thus limiting the formation of cytotoxic oxidants as peroxynitrite and
being beneficial for the tissue.
In conclusion, this study provides evidence of the neuroprotective
effect of 7-NI against the delayed hippocampal damage induced by
20-minute global ischemia in rats. The present results
confirm and extend the findings obtained in rat focal ischemia
and in gerbil global ischemia. They strengthen the hypothesis
that neuronally derived NO is toxic in ischemic conditions,
since they demonstrate that L-arginine reversed the
neuroprotective effect of 7-NI, whereas normothermic
conditions during postanesthesia reperfusion did not
significantly modify the hippocampal damage.
Received December 19, 1997;
revision received February 25, 1998;
accepted March 10, 1998.
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Department
of Neurology,
University of Miami School of Medicine,
Miami, Florida
The authors report that 7-NI treatment led to a reduction in body
temperature after the discontinuation of anesthesia. However,
significant neuroprotection was also reported with 7-NI treatment
whether or not there was compensation for postanesthesia hypothermia.
Finally, L-arginine reversed the neuroprotective effects of
7-NI treatment.
This study is important because it provides novel data concerning
the ability of 7-NI treatment to promote neuroprotection of the CA1
hippocampus after global ischemia. It should be stressed, however, that
7-NI treatment was initiated immediately after the carotid clamping. We
therefore have no information concerning the "therapeutic window"
for 7-NI treatment in this experimental setting. The findings do,
however, implicate nNOS in the pathophysiology of the acute injury
process.
Recent ischemia studies have shown that neuroprotective
treatments that provide partial protection several days after the
insult may not confer long-term improvements in behavioral or
histopathological outcome. It will therefore be important in future
studies to determine whether 7-NI treatment in this ischemia model
protects against cognitive abnormalities and improves long-term
hippocampal pathology. These data will be important for future
considerations regarding the use of selective inhibitors of neuronal
NOS in clinical stroke trials.
Received December 19, 1997;
revision received February 25, 1998;
accepted March 10, 1998.
2.
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synthase inhibition in neuronal injury. In: Bar PR, Beal MF, eds.
Neuroprotection in CNS Diseases. New York, NY: Marcel Dekker
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Iadecola C, Zhang F, Xu X. Inhibition of inducible
nitric oxide synthase ameliorates cerebral ischemic damage. Am J
Physiol. 1995;268:R286–R292.
© 1998 American Heart Association, Inc.
Original Contributions
The Selective Inhibitor of Neuronal Nitric Oxide Synthase, 7-Nitroindazole, Reduces the Delayed Neuronal Damage Due to Forebrain Ischemia in Rats
Abstract
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Abstract
Introduction
Materials and Methods
Results
Discussion
References
Introduction
References
Background and Purpose—The
present study was designed to investigate whether neuronally
derived nitric oxide (NO) plays a toxic role in the cascade of cellular
events triggered by global cerebral ischemia in rats.
Key Words: cerebral ischemia • hippocampus • neuroprotection • nitric oxide
Introduction
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Abstract
Introduction
Materials and Methods
Results
Discussion
References
Introduction
References
Transient cerebral
ischemia is associated with NO
release,1 2 3 4 5 but the question of whether NO is
beneficial or toxic in this pathology remains unanswered. It is
suggested that the effect of NO depends on the stage of evolution of
the ischemic process and on the cellular source of
NO.6 The balance between the activation of two
different (neuronal and endothelial) calcium-dependent
isoforms of NOS in the acute stage of ischemia has been invoked
to explain the contradictory results obtained with nonselective NOS
inhibitors in rat focal
ischemia7 8 and in
rat9 10 and gerbil11 12 13
global ischemia. On the basis of studies in knockout mice
lacking specific NOS isoforms, it has been proposed that, in cerebral
ischemia, the activation of type 3
(endothelial) NO synthase (eNOS) is beneficial, whereas
the activation of type 1 (neuronal) NO synthase (nNOS) is
detrimental.14 15 16 NO produced by these enzymes
is involved in the relaxation of cerebral blood vessels and the
neurotoxicity of glutamate, respectively. However, no direct validation
of this hypothesis has been demonstrated in rats submitted to severe
global cerebral ischemia, which is the most widely used
model.
Materials and Methods
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Abstract
Introduction
Materials and Methods
Results
Discussion
References
Introduction
References
All experimental procedures were performed in accordance with
the National Institutes of Health Guide for the Care and Use of
Laboratory Animals. Experiments were performed under permit No.
02934 from the French Ministry of Agriculture. The protocols received
full review and approval by the CNRS Animal Care and Use Committee
before we conducted the experiments.
The rats were prepared for transient global ischemia
according to the four-vessel occlusion model.37
On the day before the experiment, the rats were anesthetized
with halothane (1.5% in 30% oxygen and 70%
N2O) and placed in a stereotaxic
frame (David Kopff). The skin and muscles over the first two cervical
vertebrae were incised and separated from the midline. Both vertebral
arteries were electrocauterized after exposure of the alar foramina
under a surgical microscope (Zeiss). In the same experimental session,
three silver electrodes were cemented to the cranial bone in order to
record the EEG on a polygraph (ECEM).
The rats underwent profound halothane anesthesia.
They were perfused through a transcardiac catheter with
heparinized saline (100 mL) followed by
paraformaldehyde 4% (400 mL) at a constant pressure of
110 to 120 mm Hg. The brains were carefully removed and incubated
with phosphate-buffered 4% paraformaldehyde for 48
hours at 4°C. They were then soaked in 30% sucrose phosphate buffer
for 48 hours. Twelve-micrometer sections were coronally cut
with a cryomicrotome (Bright) every 500 µm at the level of the
dorsal hippocampus (2.8, 3.3, 3.8 mm caudal to the bregma) and
stained with cresyl violet. The middle zone of the dorsal hippocampal
CA1 subsector was targeted for the assessment of the neuronal damage
because it is the zone most affected by the delayed neuronal
death38 and because its anatomic localization
enables different investigators to perform reproducible evaluations on
many slices. Determination of ischemic injury was performed on
three sections per animal with the use of an ocular grid under an
optical Leitz microscope at x160 magnification by three observers
blinded to the experimental protocols. They gave a score to the middle
CA1 hippocampal subsector, graded from 0 (no visible damage) to 3
(extensive pyramidal cell loss), with 1 indicating
scattered ischemic neurons and 2 indicating that approximately
one half of the pyramidal cells were lesioned.
All rats were given either 7-NI (25 mg/kg) or its vehicle
(peanut oil) intraperitoneally twice at 1-hour
intervals. The dose of 7-NI was selected on the basis of functional
studies39 and because it is the most widely used
dose in neuroprotection studies. The timing of 7-NI injection was
motivated by the transient effect of 7-NI on NOS
activity.40 The first injection was performed
just after both CCAs were clamped, and the second injection was given 1
hour later, ie, after 40 minutes of reperfusion. The rats were randomly
divided into four groups. Group 1 was given peanut oil (2 mL/kg). Group
2 was given 7-NI (25 mg/kg). Group 3 was given 7-NI with the same dose
as group 2, but L-arginine (300 mg/kg IP) was additionally
administered 30 minutes before each 7-NI injection. Group 4 was given
7-NI with the same dose and timing as group 2, but body temperature was
maintained at 37.0±0.2°C for a 7 hour-period of
postanesthesia recovery with the use of an external
lamp.
7-NI (Research Biochemical International) was suspended in
peanut oil by sonication. L-Arginine (Sigma Chemical Co)
was dissolved in normal saline, and pH was adjusted at 7.0.
Differences in temperature between groups were statistically
evaluated with a one-way ANOVA followed by Scheffé's test.
Within each group, differences in temperature changes in relation to
time were assessed with Dunnett's test. Differences in lesion scores
were analyzed by intergroup comparisons with a
nonparametric test (ANOVA followed by Tukey's test on
ranks). Differences in normal-appearing neuron counts were assessed by
ANOVA followed by Tukey's test. Differences were regarded as
statistically significant at P<0.05. All data are
presented as mean±SEM.
Results
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Abstract
Introduction
Materials and Methods
Results
Discussion
References
Introduction
References
All rats presenting electrical activity during the
ischemic period or seizure activity during the recovery were
discarded from the study. Some rats died during the ischemic
insult, and some did not recover from ischemia, indicating a
no-reflow phenomenon. No significant difference between groups was
measured in the percentage of occurrence of these phenomena.
There was no significant difference in temporalis muscle
temperature between groups in basal conditions, in ischemic
conditions, or during reperfusion under anesthesia. The
mean basal temporalis muscle temperatures were 36.4±0.1°C,
36.5±0.2°C, 36.7±0.1°C, and 36.5±0.1°C in groups 1, 2, 3, and
4, respectively. During ischemia, temporalis muscle
temperature decreased significantly by approximately 1°C in all
groups and remained significantly lowered until the end of CCA
occlusion. When the clips were released, temporalis muscle temperature
returned to its basal level within 10 minutes. No significant changes
in temporalis muscle temperature were then measured during the entire
reperfusion period under anesthesia. 
). The mean body temperatures were
37.0±0.1°C, 36.9±0.3°C, 37.1±1.7°C, and 36.9±0.8°C in
groups 1, 2, 3, and 4, respectively, under basal conditions. These
values did not significantly change under anesthesia except
in groups 1 and 4, in which a small significant increase was measured
transiently at the end of the ischemic period. However, when
anesthesia was discontinued, body temperature remained
constant in groups 1 (oil) and 4 (thermoregulated), while it rapidly
and significantly decreased in groups 2 (7-NI treatment) and 3
(L-arginine+7-NI treatment), attaining minimal values of
34.4±0.3°C and 34.7±0.9°C, respectively, 90 minutes later, ie,
approximately 3 hours after the first 7-NI injection. Body temperature
remained at this minimal level for approximately 2 hours and then
started to progressively increase, reaching its basal level within 3
hours, ie, 8 hours after the first 7-NI injection.
View larger version (21K):
[in a new window]
Figure 1. Rectal temperatures (mean±SEM) during 90 minutes
of halothane anesthesia, including a 20 minute-period of
global ischemia, and during 390 minutes of recovery after
discontinuation of anesthesia in Wistar rats given either
the vehicle, peanut oil (n=7), 7-NI (25 mg/kg IP twice at 1
hour-intervals; n=7), L-arginine (300 mg/kg IP) 30 minutes
before each 7-NI injection (n=7), or 7-NI but with thermoregulation
continued for the entire duration of postanesthesia
recovery (n=9). The arrows indicate 7-NI or oil injections.
*Significant difference at P<0.05 with the
basal value at time 0; 
, significant difference at
P<0.05 with oil-treated rats; and 
, significant
difference at P<0.05 with thermoregulated 7-NI–treated
rats.
The damage induced by ischemia in the CA1 layer of the
hippocampus was significantly higher in the vehicle-treated rats than
in the 7-NI–treated rats whether or not there was compensation for
postanesthesia hypothermia. In addition,
L-arginine reversed the neuroprotection afforded by
7-NI. . The lesion
score in the middle CA1 hippocampal subsector was 2.9±0.1 in
vehicle-treated rats, 1.3±0.4 in 7-NI–treated rats
(P<0.05 versus vehicle-treated rats), 2.3±0.2 in
L-arginine+7-NI–treated rats, and 1.6±0.2 in
7-NI–treated rats in which body temperature was maintained at
approximately 37°C during the entire postanesthesia
recovery period (P<0.05 versus vehicle-treated rats). A
statistically significant difference was also measured between
7-NI–and L-arginine+7-NI–treated rats but not between 7-NI–treated
thermoregulated rats and L-arginine+7-NI–treated rats. The number of
normal-appearing neurons in the middle CA1 hippocampal subsector was
significantly lower in each group of ischemic rats than in the
control nonischemic group (109.8±2.4).
View larger version (15K):
[in a new window]
Figure 2. Qualitative and quantitative assessments of
neuronal damage in the middle CA1 subsector of hippocampus after
20-minute global ischemia in Wistar rats divided into four
groups according to the legend of Figure 1 
. Top, Lesion scores
(mean±SEM) according to a scale of 0 (no damage) to 3 (extensive
damage). Bottom, Numbers (mean±SEM) of normal-appearing neurons in a
490-µm length of stratum pyramidale. A control group
(n=3) has been added to determine the number of neurons in
nonischemic conditions. L-arg indicates L-arginine;
, significant difference at P<0.05 with oil-treated
rats; and 
, significant difference at P<0.05 with
control nonischemic rats.
Discussion
Top
Abstract
Introduction
Materials and Methods
Results
Discussion
References
Introduction
References
The present results indicate that 7-NI given soon after the
occlusion provides significant neuroprotection against the hippocampal
damage due to severe global ischemia in rats. Furthermore, the
results indicate that this neuroprotective effect is due to the
decrease in NO released by neurons since it is reversed by
L-arginine but not by preventing postanesthesia
hypothermia.
Selected Abbreviations and Acronyms
AMPA
=
-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid
CCA
=
common carotid artery
EEG
=
electroencephalogram
eNOS
=
endothelial nitric oxide synthase
NBQX
=
2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline
7-NI
=
7-nitroindazole
NMDA
=
N-methyl-D-aspartate
NO
=
nitric oxide
NOS
=
nitric oxide synthase
Acknowledgments
This study was supported by CNRS, University of Paris 7, and by
a grant from the Direction des Recherches, Etudes et Techniques (DRET,
contract 952515A). Dr Nanri was supported by the Uehara Memorial
Foundation. We thank O. Issertial for skillful technical
assistance
References
Top
Abstract
Introduction
Materials and Methods
Results
Discussion
References
Introduction
References
1.
Malinski T, Bailey F, Zhang ZG, Chopp M. Nitric
oxide measured by a porphyrinic microsensor in rat brain after
transient middle cerebral artery occlusion. J Cereb Blood
Flow Metab. 1993;13:355–358.[Medline]
[Order article via Infotrieve]
Editorial Comment
Introduction
Top
Abstract
Introduction
Materials and Methods
Results
Discussion
References
Introduction
References
NO has been implicated in the pathobiology of various
neurological problems, including cerebral ischemia.1 2
While NO produced by endothelial NOS may improve cerebral blood flow
and outcome after cerebral thromboembolic events,3 NO
produced by neuronal or inducible NOS may initiate and/or enhance
various pathological processes felt to lead to ischemic cell
death.4 5 This study determined whether the selective
inhibition of nNOS by 7-NI would be neuroprotective in a model of
transient global ischemia in rats. Specific attention was given to the
consequences of 7-NI administration on body temperature because of the
beneficial effects of mild hypothermia in this ischemia model.
Selected Abbreviations and Acronyms
AMPA
=
-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid
CCA
=
common carotid artery
EEG
=
electroencephalogram
eNOS
=
endothelial nitric oxide synthase
NBQX
=
2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline
7-NI
=
7-nitroindazole
NMDA
=
N-methyl-D-aspartate
NO
=
nitric oxide
NOS
=
nitric oxide synthase
References
Top
Abstract
Introduction
Materials and Methods
Results
Discussion
References
Introduction
References
1.
Lipton SA, Stamler JS. Neuronal
injury or protection by nitric oxide-related species. In: Bar PR, Beal
MF, eds. Neuroprotection in CNS Diseases. New York, NY:
Marcel Dekker Inc; 1997:121–130.
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