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NEUROPHARMACOLOGY
Department of Pharmacology, Tokyo University of Pharmacy and Life Science, Tokyo, Japan
Received August 26, 2002; accepted October 1, 2002.
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Abstract |
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 Top Abstract Materials and MethodsResultsDiscussionReferences |
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). Pretreatment of scopolamine-,
benzodiazepine-, and cycloheximide-treated animals with this agent revealed
its antiamnesic effects in the passive avoidance task (Nabeshima et al.,
1990,
1991;
Doyle et al., 1993). These
findings suggest that nefiracetam is a possible nootropic drug against
dementia. The improvement is conceivably mediated through activation of the
cholinergic and/or GABAergic system in the brain
(Yamada and Nabeshima, 1996).
However, the exact mechanism for the benefit of this agent remains unclear.
Hara and Ogawa (1990) showed
that nefiracetam improved the impairment of retention of discrimination
avoidance learning in animals with iboteinic acid-induced lesions upon
treatment with the agent for 1 week. They also showed that the improvement
caused by nefiracetam was retained even 1 week after the cessation of the drug
treatment, whereas such a persistent effect was not observed in animals
treated in the same manner with tetrahydroaminoacridine, a centrally acting
cholinesterase inhibitor. This finding suggests that treatment with
nefiracetam may elicit a persistent effect on, or a substantial restoration
of, impairments of the cognition-enhancing ability of the amnesic animal. In
the present study we aimed at determining whether nefiracetam may improve
microsphere embolism-induced memory and learning dysfunction and whether the
effect, if any, may persist even after the cessation of the drug
treatment.
As neurochemical measures contributing to recovery of memory function, we
examined parameters related to the adenylyl cyclase (AC)/cAMP/protein kinase A
(PKA) system. Accumulating evidence indicates that the cAMP-mediated signal
transduction system is appreciably involved in synaptic plasticity and
long-term memory formation. For example, there are several reports showing
AC-stimulated enhancement of learning and memory function in the bar-pressing
task (Guillou et al., 1998), an
increase in Ca2+-stimulated AC activity after completion
of a spatial learning task (Guillou et
al., 1999), improvement of the experimental amnesia caused by
administration of cAMP to the lateral ventricle
(Chute et al., 1981), and PKA
inhibitor-induced impairment of memory function in the passive avoidance task
(Zhao et al., 1995). These
observations suggest that the AC/cAMP/PKA signal transduction may play an
important role in the regulation of learning and memory function. In the
present study, we focused on alterations in the AC/cAMP/PKA system in two
brain regions, i.e., the cerebral cortex and hippocampus. Both brain regions
were selected because these regions are believed to be substantially involved
in learning and memory function (DiMattia
and Kesner, 1988; Save et al.,
1992) and are quite sensitive to ischemia
(Kirino, 1982;
Smith et al., 1984).
We used microsphere-embolized (ME) rats as a model of sustained cerebral
ischemia. Microsphere-induced cerebral embolism induces the widespread
formation of small emboli in the ipsilateral hemisphere and subsequent
neuronal loss and/or development of multiple infarct areas in the brain,
particularly in the parietal cortex, striatum, and hippocampus
(Miyake et al., 1993). Thus,
this model is considered to mimic focal ischemia-induced human stroke
(Lyden et al., 1992) or
multi-infarct dementia (Naritomi,
1991). Such irreversible ischemic damage may lead to learning and
memory dysfunction (Takagi et al.,
1997; Nagakura et al.,
2002a) and to impairment of the AC/cAMP/PKA system
(Nagakura et al., 2002b),
resulting in a significant impairment of the signal transduction connecting to
the nuclear cAMP response element-binding protein (CREB) in the ME animal
(Nagakura et al., 2002b).
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Materials and Methods |
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TopAbstractMaterials and MethodsResultsDiscussionReferences |
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Microsphere Embolism. Microsphere-induced cerebral embolism was
performed by the method described previously
(Miyake et al., 1993) with
some modification. In brief, after anesthetization of animals with 35 mg/kg
sodium pentobarbital i.p., the right external carotid and pterygopalatine
arteries were temporarily occluded with strings. Seven hundred microspheres
(47.5 ± 0.5 µm in diameter, NEN-005; PerkinElmer Life Sciences,
Boston, MA), suspended in 20% dextran solution, were injected into the right
internal carotid artery through a needle connected to a polyethylene catheter
(3 French; Atom Co., Tokyo, Japan). The needle was then removed, and the
puncture wound was repaired with surgical glue (Aron 
A, Sankyo Co.,
Tokyo, Japan). Finally, the strings occluding the right external carotid and
pterygopalatine arteries were released. After the temporal occlusion of the
arteries, the blood flow was reestablished within 2 to 3 min to the areas
supplied by the right external carotid and pterygopalatine arteries.
Sham-operated (sham) rats were prepared in a similar manner by injecting
vehicle without microspheres.
Neurological Deficits. Fifteen hours after the operation, the
behavior of the operated rats was scored on the basis of paucity of movement,
truncal curvature, and forced circling during locomotion according to the
criteria described previously (Miyake et
al., 1993). The score of each item (neurological deficit) was
rated from 3 to 0 (3, very severe; 2, severe; 1, moderate; 0, little or none).
The rats with a total score of 7 to 9 points (ME rats) were used in the
present study. The neurological deficits were determined at 10:00 AM every day
up to either day 19 or day 3.
Water Maze Test. The water maze test was performed according to the
method described previously (Nagakura et
al., 2002a). The test was started on day 7 after the operation. ME
and sham animals were tested in the water maze by using a three trials/day
regimen. To eliminate rats that could not swim due to microsphere
embolism-induced injury, we performed a habituation study by placing the
surgically treated rats in a pool with a diameter of 100 cm on day 6 after the
operation. There were no animals that could not swim in the habituation test
for the first series of experiments. The water maze apparatus (model TARGET/2;
Neuroscience Co., Tokyo, Japan) consisted of a circular pool with a diameter
of 170 cm, which was filled with water to a 30-cm depth. The water temperature
was maintained at 23 ± 1°C. A hidden transparent circular platform
with a diameter of 12 cm was placed 1.5 cm below the surface of the water and
kept in a constant position in the center of one of the four quadrants of the
pool. The animals were released from three randomly assigned start locations
(excluding the platform-containing quadrant). When a rat mounted the platform,
it was kept there for 30 s. If the rat did not reach the platform, it was
transferred onto the platform by hand and kept there for 30 s. Data collection
was automated by an online video-tracking device designed to track an object
in a field. Escape latency (the time to climb onto the platform) and swimming
speed (the distance that the animals swam divided by escape time) were
determined for each trial with a behavioral tracing analyzer (BAT-2;
Neuroscience Co.). The cutoff time for each trial was set at 180 s. Each trial
was performed with an intertrial interval of approximately 1 h.
The animals that showed stroke-like symptoms and the sham animals were subjected to the water maze test on days 7 to 9 with or without nefiracetam treatment to examine the acquisition of spatial memory.
The retention test was performed on day 17 after the operation to determine whether the animals could retain the spatial navigation ability in the hidden platform test even 1 week after cessation of the drug treatment. The regimen and starting point used for this task were the same as those conducted on day 9.
The contraposition test was performed on day 18 to examine the overall cognition and short-term or working memory by assessing the ability of the animals to search for and learn a new location of the platform. The platform was moved from its previous position (the 3rd quadrant of the tank) to the opposite position (the first quadrant), and the hidden platform test was carried out by releasing the animals from the starting point of either the 2nd or 4th quadrant alternatively.
On day 19, the visible platform test was performed to examine the ability of spatial navigation of the operated animals. The platform having a striped black-and-white flag was set at 1 cm above the water surface.
Brain Membrane and Cytosolic Preparations. To determine the protein
levels of AC-I and PKA subunits, we prepared membrane fractions from animals
sacrificed at 15 h after microsphere embolism (before administration of the
drug), at day 3, and at day 19 after the visible platform test. The isolated
brain regions were homogenized in buffer A (20 mM HEPES, pH 7.4, 0.25 M
sucrose, 0.3 mM phenylmethylsulfonyl fluoride, 1 mM dithiothreitol, 1 mM EGTA,
and 1 mM MgCl2). The homogenates were centrifuged at 1000g
for 10 min. The supernatant fluid was collected and centrifuged at
100,000g for 20 min to pellet the membrane fraction. The pellets were
then resuspended in the same buffer as described above and stored at -80°C
until used. The supernatant obtained after the second centrifugation was used
as the cytosolic fraction. Determination of protein concentrations was
conducted with a protein assay kit according to the method of Bradford
(1976).
Western Immunoblot Analysis. Samples containing 5 to 50 µg of
protein were separated on an 8 or 10% polyacrylamide gel and transferred to a
polyvinylidene difluoride membrane (Immobilon polyvinylidene difluoride;
Millipore Corporation, Bedford, MA). The following primary antibodies were
used: anti-AC-I antibody (1:1000; Santa Cruz Biotechnology, Inc., Santa Cruz,
CA) and anti-PKA RII, C, or C
antibodies (1:1000; Santa
Cruz Biotechnology, Inc.). After incubation with the appropriate corresponding
secondary antibodies, the blots were developed by the enhanced
chemiluminescence detection method (Amersham Biosciences UK, Ltd., Little
Chalfont, Buckinghamshire, UK). Quantification of the immunoreactive bands was
performed by using an Image Analysis System (NIH 1.61). Care was taken to
ensure that bands to be quantified were in the linear range of response. To
minimize between-blot variability, we applied an aliquot of pooled
"control" membranes to one lane of every gel and calculated the
immunolabeling of samples relative to this standard. Immunoblotting of AC-I,
PKA RII, PKA C, and PKA C was also performed after
preabsorption of these antibodies with their respective synthetic
complementary peptides according to the method of Yamamoto et al.
(1996). These synthetic
peptides completely abolished each corresponding band (data not shown).
Experimental Protocol and Delayed Treatment with Nefiracetam. The
experimental protocol used in the present study is shown in
Fig. 1. Microspheres were
injected into rats on day 0. After assessment of stroke-like symptoms of
microsphere-injected rats, the ME or sham-operated animals were randomly
divided into four groups, i.e., nefiracetam-treated and untreated sham groups
and nefiracetam-treated and untreated ME groups. Randomization of the operated
animals was performed according to the result of the toss of a coin.
Nefiracetam (10 mg/kg/day) was administered orally from 15 h after the
operation, once daily to the agent-treated group, whereas vehicle (0.5%
carboxyl methylcellulose) was administered to the untreated group. Drug
treatment on each day was completed by 2 h before either the water maze test
for assessment of learning and memory function or tissue sampling for
immunochemical examination. This treatment was conducted until day 9 in the
first series of experiments or until day 3 in the second series. The dose used
in the present study, 10 mg/kg/day, was based on the data of Hara and Ogawa
(1990) and those obtained in
our preliminary study: treatment with 3 mg/kg/day nefiracetam shortened the
escape latency to a lesser degree than that with 10 mg/kg/day.
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The water maze test was performed from days 7 to 9 after the operation. The daily administration of nefiracetam was stopped after day 9. On day 17, the retention test was performed and on day 18, the contraposition test was conducted. On day 19, the animals were subjected to the visible water maze test and then their brain samples were isolated for determination of AC-I and PKA proteins.
In another set of experiments, the ME and sham animals were subjected to
determination of AC-I and PKA proteins at 15 h (before administration of the
agent) and day 3 after the operation. The examination at 15 h after the
operation was designed to determine the profile of neurochemical variables
before treatment and that on day 3 after the operation, to determine whether
nefiracetam might have an effect on neurochemical parameters in the ischemic
brain. Our previous studies showed that cerebral blood flow and metabolic
parameters of the ME animals were most severely impaired on day 3
(Takeo et al., 1992;
Miyake et al., 1993).
Statistical Analysis. The results were presented as means ± S.E.M. The data of neurochemical variables of nefiracetam-untreated sham-operated (S), nefiracetam-treated sham-operated (SN), nefiracetam-untreated microsphere-embolized (ME), and nefiracetam-treated microsphere-embolized (MN) animals were evaluated by using two-way analysis of variance (ANOVA) followed by post hoc Fisher's protected least significant difference (PLSD) t test. The escape latency of the water maze task was analyzed by using two-way ANOVA for repeated measures followed by post hoc Fisher's PLSD. Differences with a probability of 5% or less were considered to be significant (P < 0.05).
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Results |
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TopAbstractMaterials and MethodsResultsDiscussionReferences |
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Neurological Deficits
Changes in neurological deficits of the ME and MN rats are depicted in
Fig. 2. The neurological
deficits gradually decreased starting 3 days after the operation. No
significant improvement in the nefiracetam-treated ME animals was seen when
these animals were compared with the untreated ME ones. Sham animals,
regardless of treatment with the agent or not, did not reveal any neurological
deficits throughout the experiment.
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Effects of Nefiracetam on the Water Maze Task
Learning and Memory Function (Acquisition). In the first series of
experiments, the ME, MN, S, and SN animals were subjected to the water maze
test (acquisition) on days 7 to 9 after the operation
(Fig. 3). There were
significant differences in the escape latency by groups
(F3,24 = 23.0; P < 0.0001; n = 7
each) and by days (F8,192 = 16.2; P < 0.001;
n = 7 each). The groups by day interaction tended to be significant
(P = 0.0874). Analysis by Fisher's PLSD showed that the escape
latency of the ME rats was significantly lengthened compared with that of the
sham-operated rats from the second trial of day 7 to the third trial of day 9
(P < 0.05). The MN rats showed a significant attenuation in the
prolongation of the escape latency compared with the ME rat at the third
trials of days 8 and 9 (P < 0.05).
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The swimming speed (the distance that the animals swam divided by the escape time) in the water maze task was similar in all groups examined (Table 1).
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Retention Test. The retention test was performed on day 17 with the same regimen as that on day 9 (Fig. 4). There were significant differences in the escape latency by groups (F3,24 = 12.4; P < 0.0001; n = 7 each). Fisher's PLSD revealed that the escape latency of the ME rat from the first to third trials in the retention test was significantly lengthened compared with that of the S or SN rats (P < 0.0001). The MN rats showed a significant attenuation in the prolongation of the escape latency compared with the ME rats from the first to third trials (P < 0.05).
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Contraposition Test. On day 18, the water maze task was changed by placing the platform in the contraposition quadrant in the pool (Fig. 4). The statistical analysis by two-way ANOVA revealed a significant difference of the escape latency by groups (F3,24 = 19.6; P < 0.0001; n = 7 each) and by times (F3,72 = 16.2; P < 0.01; n = 7 each). Fisher's PLSD showed that the escape latency of the ME rat was significantly lengthened compared with that of the sham rat from the first trial to fourth trial (P < 0.01). The MN rat revealed a significant shortening of the escape latency (P < 0.05) compared with the ME rat at the first, second, and fourth trials.
Visible Platform Test. On day 19, the visible platform test was performed. There were no significant changes in the swimming speed among these groups (Table 1). One rat that belonged to the MN group did not get onto the platform within 60 s, and thus it was eliminated from the study. The escape latency of the MN rats was slightly, but significantly, lengthened compared with that of the untreated ME animals.
Effects of Nefiracetam on AC and PKA Subunit Proteins
We examined changes in the AC-I and PKA subunits of S, SN, ME, and MN rats at 15 h, day 3, and day 19 after the operation.
On day 19 in the first series of experiments, the animals were sacrificed
after the visible platform test, and AC-I in the membrane fraction and PKA
subunits in the cytosol fraction of the right cerebral cortex and hippocampus
were determined. A significant decrease in the AC-I protein in the cerebral
cortex and in the hippocampus of the ME rat was seen
(Fig. 5). Furthermore, PKA
catalytic subunit C ( cat) and PKA regulatory subunit RII
(II reg) in the cytosol of the right cerebral cortex and hippocampus of
the ME animal were decreased (Fig.
6). The delayed treatment with nefiracetam almost completely
reversed the decreases in these three variables in both regions of the ME rat.
There were no differences in these protein contents between S and SN rats.
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In another set of experiments, we determined the AC-I in the membrane fraction and PKA proteins in the cytosolic fraction of the right cerebral cortex and hippocampus of the ME and sham animals at 15 h and day 3 after the operation.
At 15 h after the operation in the second series of experiments, the
protein level of AC-I in the membrane fraction of the right hippocampus of the
ME rat was decreased significantly and that of the right cerebral cortex
tended to be decreased (Fig.
7). In contrast, no significant changes in the protein levels of
PKA C, C, and RII were seen.
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On day 3, a significant decrease in the AC-I protein level in the membrane
fraction (Fig. 8) and one in
the PKA C level in the cytosolic fraction of the right cerebral cortex
and hippocampus (Fig. 9) were
seen in the ME rat. In contrast, no changes in the PKA C and PKA
RII in either brain region of the ME rat were seen. The delayed
treatment with nefiracetam partially prevented the decrease in AC-I protein
(P < 0.05) and significantly attenuated the decrease in the PKA
C subunit in the cytosolic fraction of the right cerebral cortex and
hippocampus of the ME rat (P < 0.05).
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We also examined these protein levels in the left hemisphere. There were no significant changes in AC-I and PKA subunits in the cerebral cortex and hippocampus of the left hemispheres of the ME and sham rats.
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Discussion |
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TopAbstractMaterials and MethodsResultsDiscussionReferences |
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;
Imanishi et al., 1997) and
middle cerebral artery occlusion (Yonemori
et al., 1999; Modo et al.,
2000). Although the degree of the severity in learning and memory
dysfunction would not compare simply with that of other models, the learning
and memory dysfunction of the ME animal seems to be no less, or rather more,
long-lasting than that of the ischemia/reperfusion models mentioned above,
probably due to permanent embolism in the ME animal. The delayed treatment with nefiracetam reduced the failure in the spatial memory function in the water maze test, suggesting that this drug is capable of improving learning and memory function impaired by sustained cerebral ischemia. We conducted the retention test on day 17 after the operation to examine whether the effect of treatment may persist after cessation of the drug treatment. Notably, nefiracetam-treated ME rats revealed a significant shortening of the escape latency in the retention test. This finding suggests that this drug is capable of exerting a persistent effect on learning and memory function or of preventing the loss of spatial navigation ability due to ischemic damage in animals with sustained cerebral ischemia. Furthermore, at the first trial in the contraposition test on day 18 where the platform had been moved to the opposite quadrant, nefiracetam shortened the escape latency of the ME animal, suggesting that the overall process, including search strategy, of the drugtreated animal may be superior to that of the untreated animal. The shortened escape latency at the fourth trial in the contraposition test predicted better acquisition of shortterm memory in the nefiracetam-treated ME animal.
The question arises as to the nature of the mechanism underlying the
nefiracetam-mediated improvement of learning and memory function by
nefiracetam in ischemia-induced amnesic animals. In previous studies, we
reported the possible involvement of the AC/cAMP/PKA signal transduction
pathway in the learning and memory dysfunction of the ME animal (Nagakura et
al.,
2002b,c).
Particularly, alterations in AC-I activity and protein well correlated with
the impairment of the spatial memory function in the ME animal
(Nagakura et al., 2002a).
Furthermore, these pathophysiological alterations were attenuated by treatment
with a phosphodiesterase III inhibitor, rolipram, which augmented the cellular
cAMP content (Nagakura et al.,
2002b). Thus, we focused on the role of this system in the
nefiracetam-exerted improvement of learning and memory function in our
ischemic animals. We found that, among variables examined, only a small, but
significant, decrease in the level of AC-I protein in the right hippocampus
occurred at 15 h after the microsphere embolism (before administration of the
agent). The ME animal on day 3 revealed greater decreases in AC-I and PKA
C proteins in the hippocampus and cerebral cortex, whereas neither PKA
C nor PKA RII protein level had decreased. This finding suggests
that impairment of the signal transduction system is gradually developed in
the hippocampus and cerebral cortex along with time after microsphere
embolism. The delayed treatment with nefiracetam for 3 days attenuated these
decreases, suggesting that nefiracetam prevented the ME-induced decrease in
these protein levels. On day 19, a reduction in PKA RII protein, apart
from the decreases in AC-I and PKA C proteins, was detected, suggesting
additional damage to the PKA regulatory subunit by 19 days. The delayed
treatment from day 1 to 9 reversed these decreases almost completely on day
19, when administration of nefiracetam had already been halted. The results
suggest that this agent is capable of exerting a persistent effect on the
learning and memory function, probably by preventing the ischemia-induced
degradation of proteins involved in the AC/cAMP/PKA signal transduction.
One might attribute the decreases in the levels of membranous AC-I protein
and cytosolic PKA C, and PKA RII proteins to a drop in the number
of neurons or of an increase in the proliferation of glial cells seen after
cerebral ischemia. However, we cannot simply attribute the decrease in these
proteins to ischemia-induced global loss of neurons or gliosis, because no
decrease in PKA C protein in the cytosolic fraction of the ME animal
was detected even 19 days after microsphere embolization. Also, no alterations
in other proteins in this signal transduction system, such as AC-V/VI,
AC-VIII, and PKA regulatory units were detected under similar experimental
conditions in this model (Nagakura et al.,
2002b). Thus, whether AC subtypes and PKA subunits after ME alter
or not, might depend upon the difference in the vulnerability of each protein
to sustained ischemia.
Several investigators postulated a possible connection of the AC/cAMP/PKA
signal transduction system with the nuclear CREB in normal and
pathophysiological animals (Abel et al.,
1997; Bernabeu et al.,
1997; Cammarota et al.,
2000). Because nefiracetam prevented the microsphere
embolism-induced decrease in the levels of AC-I and PKA subunit proteins
involved in the signal transduction system even at day 19, nefiracetam is
capable of protecting the AC/cAMP/PKA signal transduction system from ischemic
damage even in the absence of treatment as long as the therapeutic dose of
this agent has been previously administered for a few days.
Several observations, including disruption of long-term memory for fear
conditioning and spatial learning in CREB knockout mice
(Bourtchuladze et al., 1994)
and disruption of long-term spatial memory by the intrahippocampal infusion of
antisense oligonucleotides to CREB
(Guzowski and McGaugh, 1997),
suggest the possible connection of CREB to learning and memory function. We
also observed a decrease in phosphorylated CREB protein in the ME rat, which
was associated with the spatial memory dysfunction in the water maze task
(Nagakura et al., 2002b), and
its reversal by treatment with rolipram
(Nagakura et al., 2002c).
Taken together, the data suggest that nefiracetam-mediated protection of the
AC/cAMP/PKA signal transduction and the following CREB-mediated transcription
may play an important role in the improvement of the spatial memory function
in sustained cerebral ischemic animals.
In summary, nefiracetam improved the spatial memory function of sustained cerebral ischemic animals in association with the prevention of the ischemia-induced damage to the AC/cAMP/PKA signal transduction, although the exact site of action of nefiracetam in this system remains unclear. The present study has proposed the possible mechanism of the effect of nefiracetam on learning and memory function.
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Acknowledgements |
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Footnotes |
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ABBREVIATIONS: AC, adenylyl cyclase; PKA, protein kinase A; ME, microsphere-embolized/nefiracetam-untreated; CREB, cAMP responsive element-binding protein; S, nefiracetam-untreated sham-operated; SN, nefiracetam-treated sham-operated; MN, nefiracetam-treated microsphere-embolized; ANOVA, analysis of variance; PLSD, protected least significant difference.
Address correspondence to: Satoshi Takeo, Ph.D., Department of Pharmacology Tokyo University of Pharmacy and Life Science 1432-1 Horinouchi, Hachioji, Tokyo 1920392, Japan. E-mail: takeos{at}ps.toyaku.ac.jp
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References |
|---|
|
TopAbstractMaterials and MethodsResultsDiscussionReferences |
|---|
Abel T, Nguyen PV, Barad M, Deuel TAS, Kandel ER, and Bourtchouladze R (1997) Genetic demonstration of a role for PKA in the late phase of LTD and hippocampus-based long-term memory. Cell 88: 615–626.[CrossRef][Medline]
Bernabeu R, Bevilaqua L, Ardenghi P, Bromberg E, Schmitz P,
Bianchin M, Izquierdo I, and Medina JH (1997) Involvement of
hippocampal cAMP/cAMP-dependent protein kinase signaling pathways in a late
memory consolidation phase of aversively motivated learning in rats.
Proc Natl Acad Sci USA
94:
7041–7046.
Bourtchuladze R, Frenguelli B, Blendy J, Cioffi D, Schutz G, and Silva AJ (1994) Deficient long-term memory in mice with a targeted mutation of the cAMP-responsive element-binding protein. Cell 79: 59–68.[CrossRef][Medline]
Bradford MM (1976) A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding. Anal Biochem 72: 248–254.[CrossRef][Medline]
Cammarota M, Bevilaqua LRM, Ardenghi P, Paratcha G, Levi deStein M, Izquierdo I, and Medina JH (2000) Learning-associated activation of nuclear MAPK, CREB and Elk-1, along with Fox production, in the rat hippocampus after a one-trial avoidance learning: abolition by NMDA receptor blockade. Mol Brain Res 76: 36–46.[Medline]
Chute DL, Villiger JW, and Kirton NF (1981) Testing cyclic AMP mediation of memory: reversal of alpha-methyl-p-tyrosine-induced amnesia. Psychopharmacology 74: 129–131.[CrossRef][Medline]
DiMattia BC and Kesner RP (1988) Spatial cognitive maps; differential role of parietal cortex and hippocampal formation. Behav Neurosci 102: 471–480.[CrossRef][Medline]
Doyle E, Regan CM, and Shiotani T (1993) nefiracetam (DM-9384) preserves hippocampal neural cell adhesion molecule-mediated memory consolidation processes during scopolamine-disruption of passive avoidance training in the rat. J Neurochem 61: 266–272.[CrossRef][Medline]
Guillou JL, Micheau J, and Jaffard R (1998) The opposite effects of cysteamine on the acquisition of two different tasks in mice are associated with bidirectional testing-induced changes in hippocampal adenylyl cyclase activity. Behav Neurosci 112: 900–908.[CrossRef][Medline]
Guillou JL, Rose GM, and Cooper DM (1999) Differential
activation of adenylyl cyclases by spatial and procedural learning.
J. Neurosci 19:
6183–6190.
Guzowski JF and McGaugh JL (1997) Antisense
oligodeoxynucleotide-mediated disruption of hippocampal cAMP response element
binding protein levels impaired consolidation of memory for water maze
training. Proc Natl Acad Sci USA
94:
2693–2698.
Hara C and Ogawa N (1990) Characteristic of learning deficit induced by ibotenic acid lesion of the frontal cortex related with the nucleus basalis of Meynert in rats, in Basic, Clinical and Therapeutic Aspects of Alzheimer's and Parkinson's Diseases (Nagatsu T, Fisher A, and Yoshida M eds), vol 1, pp 735–738, Plenum Press, New York
Hodges H (1996) Maze procedures: the radial-arm and water maze compared. Cogn Brain Res 3: 167–181.[CrossRef][Medline]
Imanishi T, Sawa A, Ichimaru Y, Miyashiro M, Kato S, Yamamoto T, and Ueki S (1997) Ameliorating effects of rolipram on experimentally induced impairments of learning and memory in rodents. Eur J Pharmacol 321: 273–278.[CrossRef][Medline]
Kirino T (1982) Delayed neuronal death in the gerbil hippocampus following ischemia. Brain Res 39: 57–69.
Lyden PD, Zivin JA, Chabolla DR, Jacobs MA, and Gage FH (1992) Quantitative effects of cerebral infarction on spatial learning in rats. Exp Neurol 116: 122–132.[CrossRef][Medline]
Miyake K, Takeo S, and Kajihara H (1993) Sustained
decrease in brain regional blood flow after microsphere embolism in rats.
Stroke 24:
415–420.
Modo M, Stroemer RP, Tang E, Veizovic T, Sowniski P, and Hodges H (2000) Neurological sequelae and long-term behevioural assessment of rats with transient middle cerebral artery occlusion. J Neurosci Methods 194: 99–109.
Nabeshima T, Tohyama K, and Kameyama T (1990) Effects of DM-9384, a pyrrolidone derivative, on alcohol- and chlordiazepoxide-induced amnesia in mice. Pharmacol Biochem Behav 36: 233–236.[CrossRef][Medline]
Nabeshima T, Tohyama K, Murase K, Ishihara S, Kameyama T, Yamasaki
T, Hatanaka S, Kojima H, Sakurai T, Takasu Y, et al. (1991)
Effects of DM-9384, a cyclic derivative, on alcohol- and
chlordiazepoxide-induced amnesia in mice. J Pharmacol Exp
Ther 257:
271–275.
Nagakura A, Miyake-Takagi K, Takagi N, and Takeo S (2002a) Impairment of adenylyl cyclase and of spatial memory function after microsphere embolism in rats. J Neurosci Res 68: 363–372.[CrossRef][Medline]
Nagakura A, Niimura M, and Takeo S (2002c) Effects of phosphodiesterase IV inhibitor rolipram on microsphere embolism-induced defects in memory function and cerebral cyclic AMP signal transduction system in rats. Br J Pharmacol 135: 1783–1793.[CrossRef][Medline]
Nagakura A, Takagi N, and Takeo S (2002b) Impairment of cerebral cAMP-mediated signal transduction system and of spatial memory function after microsphere embolism in rats. Neuroscience 113: 519–528.[CrossRef][Medline]
Naritomi H (1991) Experimental basis of multi-infarct dementia: memory impairments in rodent models of ischemia. Alzheimer Dis Assoc Disord 5: 103–111.[CrossRef][Medline]
Save E, Poucet B, Foreman N and Buhot MC (1992) Object exploration and reactions to spatial and nonspatial changes in hooded rats following damage to parietal cortex or hippocampal formation. Behav Neurosci 106: 447–456.[CrossRef][Medline]
Smith ML, Auer RN, and Siesjo BK (1984) The density and distribution of ischemic brain injury in the rat following 2–10 min of forebrain ischemia. Acta Neuropathol 64: 319–332.[CrossRef][Medline]
Takagi N, Miyake K, Taguchi T, Tamada H, Takagi K, Sugita N, and Takeo S (1997) Failure in learning task and loss of cortical cholinergic fibers in microsphere-embolized rats. Exp Brain Res 114: 279–287.[CrossRef][Medline]
Takeo S Taguchi T Tanonaka K, Miyake K, Horiguchi T, Takagi N, and
Fujimori K (1992) Sustained damage to energy metabolism of brain
regions after microsphere embolism in rats. Stroke
23:
62–68.
Yamada K and Nabeshima T (1996) Nefiracetam (DM-9384): a novel anti-amnesic drug. CNS Drugs Rev 2 (1996) 322–342.[CrossRef]
Yonemori F, Yamaguchi T, Yamada H, and Tamura A (1999) Spatial cognitive performance after chronic focal cerebral ischemia in rats. J Cereb Blood Flow Metab 19: 483–494.[Medline]
Yamamoto M, Ozawa H, Saito T, Frolich L, Riederer P, and Takahata N (1996) Reduced immunoreactivity of adenylyl cyclase in dementia of the Alzheimer type. Neuroreport 7: 2965–2970.[Medline]
Zhao WQ, Polya GM, Wang BH, Gibbs ME, Sedman GL, and Ng KT
(1995) Inhibitors of cAMP-dependent protein kinase impair
long-term memory formation in day-old chicks. Neurobiol Learn
Mem 64:
106–118.[CrossRef][Medline]
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