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 Previous Article | Next Article 
The Journal of Neuroscience, March 1, 2002, 22(5):1967-1975
Blockade of Striatal Adenosine A2A Receptor Reduces,
through a Presynaptic Mechanism, Quinolinic Acid-Induced
Excitotoxicity: Possible Relevance to Neuroprotective Interventions in
Neurodegenerative Diseases of the Striatum
Patrizia
Popoli1,
Annita
Pintor1,
Maria
Rosaria
Domenici1,
Claudio
Frank1,
Maria Teresa
Tebano1,
Antonella
Pèzzola1,
Laura
Scarchilli1,
Davide
Quarta1,
Rosaria
Reggio1,
Fiorella
Malchiodi-Albedi2,
Mario
Falchi2, and
Marino
Massotti1
Departments of 1 Pharmacology and
2 Ultrastructures, Istituto Superiore di Sanità, 299 00161 Rome, Italy
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ABSTRACT |
The aim of the present study was to evaluate whether, and by means
of which mechanisms, the adenosine A2A receptor antagonist SCH 58261 [5-amino-7-(2-phenylethyl)-2-(2-furyl)-pyrazolo[4,3-e]-1,2,4-triazolo[1,5-c]pyrimidine] exerted neuroprotective effects in a rat model of Huntington's disease. In a first set of experiments, SCH 58261 (0.01 and 1 mg/kg)
was administered intraperitoneally to Wistar rats 20 min before the
bilateral striatal injection of quinolinic acid (QA) (300 nmol/1 µl).
SCH 58261 (0.01 but not 1 mg/kg, i.p.) did reduce significantly the
effects of QA on motor activity, electroencephalographic changes, and
striatal gliosis. Because QA acts by both increasing glutamate outflow
and directly stimulating NMDA receptors, a second set of experiments
was performed to evaluate whether SCH 58261 acted by preventing the
presynaptic and/or the postsynaptic effects of QA. In microdialysis
experiments in naïve rats, striatal perfusion with QA (5 mM) enhanced glutamate levels by ~500%. Such an effect of QA was completely antagonized by pretreatment with SCH 58261 (0.01 but not 1 mg/kg, i.p.). In primary striatal cultures, bath application
of QA (900 µM) significantly increased intracellular calcium levels, an effect prevented by the NMDA receptor antagonist MK-801 [(+)-5-methyl-10,11-dihydro-5H-dibenzo [a,d]
cyclohepten-5,10-imine maleate]. In this model, bath
application of SCH 58261 (15-200 nM) tended to potentiate
QA-induced calcium increase. We conclude the following: (1) the
adenosine A2A receptor antagonist SCH 58261 has
neuroprotective effects, although only at low doses, in an excitotoxic
rat model of HD, and (2) the inhibition of QA-evoked glutamate outflow
seems to be the major mechanism underlying the neuroprotective effects
of SCH 58261.
Key words:
adenosine A2A receptors; quinolinic acid; Huntington's disease; neuroprotection; SCH 58261; striatum
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INTRODUCTION |
Adenosine is an endogenous
neuromodulator involved in the regulation of many functions within the
CNS (Phillis and Wu, 1981 ) and whose effects are mediated by at least
four distinct receptors: A1,
A2A, A2B, and
A3 (Fredholm et al., 1994). Unlike
A1 receptors, which are widely expressed in the
CNS, and A2B and A3
receptors, whose central expression is rather low, adenosine
A2A receptors are mainly expressed in the
striatum, although lower levels of expression do exist in other brain
areas, such as the cortex and the hippocampus (for review, see
Impagnatiello et al., 2000). Besides their role in the regulation of
dopamine-dependent behaviors in both normal and pathological conditions
(Ferré et al., 1997), adenosine A2A
receptors seem also to be involved in excitotoxic-neurodegenerative processes: (1) selective A2A receptor ligands
have been shown to regulate striatal glutamate release (Popoli et al.,
1995; Corsi et al., 1999, 2000); (2) the intrastriatal injection of an
adenosine A2>A1 receptor
antagonist prevented the electroencephalographic (EEG) abnormalities
induced by an excitotoxic striatal lesion in rats (Reggio et al.,
1999); (3) A2A receptor antagonists showed neuroprotective effects in models of diseases, such as brain ischemia, in which excitotoxic mechanisms are thought to play a pathogenetic role
(Gao and Phillis, 1994; Bona et al., 1997; Monopoli et al., 1998b); (4)
mice lacking A2A receptors have been reported to
be less vulnerable to ischemia- and MPTP-induced neuronal damage (Chen
et al., 1999, 2001). Together, these observations support the view that
adenosine A2A receptor antagonists may possess
neuroprotective effects in neurodegenerative diseases (Ongini et al.,
1997; Abbracchio and Cattabeni, 1999; Impagnatiello et al., 2000),
although the mechanisms responsible for such effects are still
primarily unknown. Given the anatomical distribution of
A2A receptors, their blockade could be a
particularly reliable approach in the treatment of neurodegenerative
diseases of the striatum. In particular, because adenosine
A2A receptors are selectively expressed in the
striopallidal neurons (Schiffmann et al., 1991), a population of
medium-sized spiny neurons that degenerate early in Huntington's
disease (HD) (Glass et al., 2000), it is conceivable that such
receptors may play a role in triggering neuronal death in HD. If so,
blockade of striatal A2A receptors should exert
neuroprotective effects in experimental models of the above disease.
Besides the more recent genetic models (transgenic mice expressing the
HD mutation) (Bates et al., 1997; Hodgson et al., 1999), several
"pathogenetic" models of the disease have been developed. In
particular, the model of excitotoxic striatal lesion by quinolinic acid
(QA) in the rat has been reported to mimic both the clinical and the
neuropathological features of human HD (Beal et al., 1986; Popoli et
al., 1994).
The aims of the present work were as follows: (1) to study the possible
neuroprotective influence of SCH 58261 [5-amino-7-(2-phenylethyl)-2-(2-furyl)-pyrazolo[4,3-e]-1,2,4-triazolo[1,5-c]pyrimidine], an adenosine A2A receptor antagonist showing
selectivity for striatal versus cortical and hippocampal binding sites
(Lindström et al., 1996; Lopez et al., 1999), on QA-induced
effects in rats, and (2) to investigate the mechanisms underlying such effects.
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MATERIALS AND METHODS |
Surgery
Adult male Wistar rats (250-280 gm) were used. The animals were
kept under standardized temperature, humidity, and lighting conditions,
with access to water and food ad libitum. Animal care and
use followed the directives of the Council of the European Communities
(86/609/EEC). Animals were anesthetized with Equithesin (3 ml/kg, i.p.)
and placed in a David Kopf Instruments (Tujunga, CA) stereotaxic
apparatus. Quinolinic acid (300 nmol) or vehicle (PBS) were bilaterally
injected in the striatum (coordinates: anterior, +1.7 mm; lateral, +2.7
mm; ventral,  4.8 mm from bregma and dura) by means of a Hamilton
syringe (model 701); the injection volume was 1 µl. Experimental
groups (n = 8-12 animals per group) were as follows:
sham-lesioned animals (intrastriatal injection of 1 µl vehicle);
lesioned animals (intrastriatal QA); and animals treated with SCH 58261 (0.01 and 1 mg/kg, i.p., dissolved in DMSO) 20 min before QA injection.
The doses of SCH 58261 to be used were selected on the basis of
preliminary experiments in which a wider range of doses of SCH 58261 had been tested in a limited number of animals. On the basis of such
experiments, a low-dose range (0.01-0.05 mg/kg) and an a high-dose
range (0.5-2 mg/kg) in the effects of SCH 58261 were identified, and
it was established that 0.01 and 1 mg/kg SCH 58261 were the two most
representative doses within the above ranges. To evaluate the possible
influence of SCH 58261 alone on the motor, EEG, and cognitive
parameters studied here, in separate experiments, three groups of five
rats each were treated with SCH 58261 (0.01 and 1 mg/kg, i.p.) or
vehicle (1 ml/kg) 20 min before being subjected to a sham lesion. The EEG tracing, spatial learning, and motor response to
d-amphetamine of these animals were then evaluated 3, 4, and
5 weeks after surgery, respectively.
EEG experiments
Two weeks after surgery, the animals were newly anesthetized
with Equithesin, and screw cortical electrodes were implanted at the
level of the frontal cortex and fixed with dental acrylic to the skull
surface. Five to 6 d thereafter, the animals were individually
placed in a cylindrical Plexiglas container in a soundproof
experimental room. After a 30 min habituation period, each animal was
connected to an Ote (model 10b) polygraph. The EEG was then
continuously recorded over 45 min. The methods used for EEG recording
and analysis have been described previously (Reggio et al., 1999).
Briefly, sequential power spectra of 20 sec EEG epochs (1 epoch every
minute) were analyzed by fast Fourier transformation with a frequency
resolution of 0.35 Hz (software by Enrico Staderini, IADA Sistemi,
Rome, Italy). All of the power spectra relevant to an EEG
tracing were recorded on a optical disk and then analyzed to calculate
the relative power in each frequency band. Frequency bands were as
follows: 1.2-4 Hz ( ), 4.35-7 Hz ( ), 7.35-9.5 Hz
( 1), 9.85-12.5 Hz
(2), 12.85-16 Hz ( 1), and 16.35-30 Hz
(2). One-way ANOVA and Tukey's
post hoc test were used for the statistical analysis of the results.
Motor activity recording
To measure their motor response to d-amphetamine,
5-6 weeks after surgery, the animals were placed, one per cage, in an
animal activity motor (model Automex II; Columbus Instruments,
Columbus, OH), in a soundproof experimental room. Experiments
were always performed between 9:00 A.M. and 12:00 A.M. The motor
activity of each rat, expressed as counts, was recorded on a computer
and analyzed by a computer counter software (version 3.3;
Columbus Instruments). After an habituation period of 30 min, each
animal was injected with d-amphetamine (1 mg/kg, i.p.), and
the motor activity was then recorded for an additional period of 90 min.
Evaluation of spatial learning by the Morris water maze
Experiments were performed 4-6 weeks after the lesion. A
circular black pool (100 cm diameter; 48 cm height) was filled up to 30 cm with water (23-24°C). Each experiment consisted of 18 learning
trials (two daily blocks of three consecutive trials each), over 3 consecutive days. Within each block, the rats were put into the pool
from three different starting points (one for each trial). The rats
were able to escape from the water by climbing on an invisible
platform, which was submerged under water and whose location remained
unchanged over the whole experiment. A trial was terminated as soon as
the animal found the platform or after 70 sec of unsuccessful swimming
(in this case, the animal was placed on the platform by the
experimenter). Rats were allowed to stay on the platform for 10 sec
before the next trial started. All trials were video recorded, and a
computer-assisted analysis of escape latency (i.e., the time required
to find the platform), swim distance, and swimming paths was performed
(Software Delta Sistemi, Rome, Italy). One-way ANOVA and Tukey's
post hoc test were used for the statistical analysis of the results.
In vitro hippocampal electrophysiology
To assess whether the memory impairment observed in the spatial
learning test correlated with alterations in hippocampal synaptic plasticity, experiments were performed in hippocampal slices obtained from sham, QA-lesioned, and SCH 58261-pretreated rats. The animals were
decapitated under ether anesthesia, the brain was quickly removed, and
the hippocampi were dissected free. Transverse slices (400-450
µM) were cut with a tissue chopper and maintained at room
temperature (22-24°C) in oxygenated artificial CSF (ACSF) containing (in mM): 126 NaCl, 3.5 KCl, 1.2 NaH2PO4, 1.3 MgCl2, 2 CaCl2, 25 NaHCO3, and 11 glucose, pH 7.3 (saturated with
95% O2 and 5% CO2). After
incubation for at least 1 hr, an individual slice was transferred to a
submerged recording chamber and continuously superfused at 32-33°C
with oxygenated ACSF at a rate of 3 ml/min. Field EPSPs (fEPSPs) were
recorded with a glass microelectrode filled with NaCl (2 M;
pipette resistance of 2-5 M ). A bipolar twisted NiCr-insulated
electrode (50 µm outer diameter) was used to stimulate the
medial perforant path and the Schaffer collaterals (test frequency of
0.05 Hz) while recording in the middle molecular layer of the dentate
gyrus and the apical dendritic region of CA1, respectively. The
duration of the stimulus was 100 µsec. The stimulation intensity
corresponded to that necessary to obtain a response equal to 50% of
the maximal fEPSP. In the CA1 region, early long-term potentiation
(LTP) was produced by high-frequency stimulation (HFS) administered at
100 Hz for 1 sec using the same stimulation intensity and repeated
after 15 min. In the dentate gyrus, early LTP was induced, in the
presence of 10 µM bicuculline, by two trains (frequency
of 100 Hz, 1 sec) delivered 10 sec apart to the medial perforant path
with the stimulation intensity necessary to obtain the maximal field
response. The induction of early LTP was measured 30 min after HFS as
the percentage of increase of fEPSP slope with respect to pretetanus
values. Signals were acquired with a DAM-80 AC differential amplifier
(World Precision Instruments, Sarasota, FL) and analyzed with the LTP
Software (courtesy of Dr. W.W. Anderson, University of Bristol,
Bristol, UK). Mann-Whitney U test was used for the
statistical analysis of the data.
Histological studies
Gliofibrillary acidic protein immunolocalization. The
animals (sham, QA only, and 0.01 mg/kg SCH 58261 plus QA) were
decapitated under ether anesthesia, and the brains were removed and
frozen in liquid nitrogen. Ten- to 20-µm-thick coronal sections were cut on a cryostat microtome, mounted on a slide, and fixed in 4%
paraformaldehyde in PBS containing 0.12 M
sucrose, for 15 min at room temperature. After washes in PBS, sections
were incubated with 10% fetal calf serum in PBS to abolish nonspecific
staining. gliofibrillary acidic protein (GFAP) was immunolabeled by
monoclonal antibody (1:250; Sigma, St. Louis, MO), followed by
fluoresceinated goat anti-mouse IgG (Sigma). Three sections for each
brain were examined at a Nikon (Tokyo, Japan) Optiphot microscope, and
three fields for each section (a total of nine fields for each brain) were chosen randomly in the lesion area (excluding areas of complete cell loss) recorded at 200× magnification. Images were captured by a
color CCD camera, obtaining frames of 3 mm2 (nine frames per brain). Images were
analyzed by the Optilab software (Graftek, Mirmande, France).
After background subtraction, the area occupied by GFAP-positive
staining was identified and measured. Positive areas were expressed as
percentage of total areas. Statistical comparisons were made using the
nonparametric Mann-Whitney U test.
Measurement of the lesion size. For the measurement of the
striatal lesions, two groups of animals (QA only and 0.01 mg/kg SCH
58261 plus QA) were decapitated under ether anesthesia, and the brains
were removed and frozen in liquid nitrogen. Serial 20 µm coronal
sections were cut on a cryostat microtome, stained with cresyl violet,
and examined by light microscopy. For each brain, a series of
consecutive sections taken at the level of the maximal extension of the
lesion was identified, and, within this series, the slide (or one of
the slides) showing the largest lesion was chosen for the quantitative
analysis. Images were captured by a color digital camera and analyzed
by the Optilab software (Graftek). The lesion area was expressed as
percentage of the total area of the dorsal striatum. Statistical
comparisons were made using the nonparametric Mann-Whitney
U test.
Microdialysis experiments
Under Equithesin anesthesia, naïve Wistar rats were
placed in a stereotaxic frame and implanted with a concentric dialysis probe (model CMA/12; 3 mm length; CMA Microdialysis, Solma, Sweden) into the striatum. Stereotaxic coordinates in mm from bregma, sagittal
suture, and dura, respectively, were as follows: anterior, +1.7;
lateral, +2.7; ventral, 6.2. Twenty-four hours later, the probe was
perfused at a rate of 2 µl/min with a Ringer's solution (in
mM: 147 NaCl, 2.3 CaCl2, and 4.0 KCl). After a washout period of at least 90 min, samples were collected
every 5 min into a refrigerated fraction collector (model CMA/170; CMA
Microdialysis) and then frozen until assay. Because the intracerebral
injection of QA induces tremors and convulsions in rodents, these
experiments were performed under general anesthesia (3 ml/kg
Equithesin). Each experimental group was made up of four to five
animals. Results were expressed as percentage of changes of
extracellular glutamate levels induced by probe perfusion with QA (5 mM over 30 min) with respect to basal (predrug) values
(mean of three to four samples collected after the induction of general
anesthesia). SCH 58261 (0.01 and 1 mg/kg) was administered
intraperitoneally 20 min before starting QA perfusion. At the end of
the experiments, each rat was killed with an overdose of
Equithesin, the brain was fixed with 4% paraformaldehyde, and coronal
sections (20-µm-thick) were cut to verify the probe location. The
glutamate content of all samples was measured by reverse-phase
HPLC coupled to a fluorometric detector (model LC240 at
wavelength of 335 nm and emission cutoff filter of 425 nm; PerkinElmer
Life Sciences, Emeryville, CA), using a 15 min gradient elution program
(methanol from 20 to 80% with 50 mM
NaH2PO4 and
CH3COONa) and automatic precolumn derivatization with ophthalaldehyde and -mercaptoethanol. Cysteic acid was used as
internal standard. The concentration of the standard was linear (r2 = 0.99) between 0.2 and 25 ng/10 µl. Basal glutamate levels were calculated by comparison of
sample peak height with external standard peak height, both corrected
for the internal standard peak height and expressed as 10 µl/ng
without probe recovery correction. Data were processed by two-way
ANOVA, followed by post hoc Student's t test.
Intracellular calcium measurement on primary striatal cultures
Striatal cells from 17-d-old rat embryos were mechanically
dissociated and plated in Eagle's Basal Medium with a density of ~30.000/cm2. Experiments were started
13-15 d after plating. Optical fluorimetric recordings with fura-2 AM
were used to evaluate the intracellular calcium concentration
([Ca2+]i). Fura-2
AM stock solutions were obtained by adding 50 µg of fura-2 AM to 50 µl of 75% DMSO plus 25% pluronic acid. Cells were bathed for 60 min
at room temperature with 5 µl of stock solution diluted in 1 ml of
extracellular solution (in mM: 125 NaCl, 1 KCl, 5 CaCl2, 1 MgCl2, 8 glucose,
and 20 HEPES, pH 7.35). This solution was then removed and replaced
with extracellular solution, and the dishes were quickly placed on the
microscope stage. To measure fluorescence changes, an Hamamatsu
(Shizouka, Japan) Argus 50 computerized analysis system was used,
recording every 6 sec the ratio between the values of light intensity
at 340 and 380 nm stimulation. Drugs [QA, SCH 58261, CGS 21680 (carboxyethyl phenethylamino-5'-N-ethylcarboxamido adenosine
HCl), and MK-801 ((+)-5-methyl-10,11-dihydro-5H-dibenzo [a,d]
cyclohepten-5,10-imine maleate)] were applied by directly dropping in
the bath.
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RESULTS |
Experiment 1: study of the influence of pretreatment with SCH 58261 on the effects induced by QA; experiments in striatally lesioned
rats
As a consequence of QA lesion, three of 12 animals (25%) died
within 6.5 ± 2.7 d. In animals pretreated with 0.01 mg/kg
SCH 58261, the occurrence of death was significantly delayed (20.3 ± 0.88 d; p = 0.008 versus QA alone according to
Student's t test), whereas the mortality rate was not
reduced (18.7%). Pretreatment with 1 mg/kg SCH 58261 did not
significantly affect the above parameters, although a tendency to a
reduced mortality was seen (10%; NS versus QA alone according to
Fisher's exact test). As reported previously
(Popoli et al., 1994; Reggio et al.,
1999), QA-lesioned rats show an exaggerated motor response to
d-amphetamine (Fig. 1) and a marked
reduction in EEG voltage amplitude (Figs. 2, 3), accompanied by an altered
distribution of EEG spectral power (increase in band and reductions
in and bands) (Fig. 4). The
exaggerated response to d-amphetamine is thought to depend on the loss of striatal GABAergic inhibitory projections (Rozas et al.,
1996). QA-induced EEG changes at the level of the frontal cortex, which
are very similar to those observed in HD patients (Bylsma et al.,
1994), seem to depend on the impairment of the striocortical pathway,
which follows the striatal lesion (Schwarz et al., 1992; Popoli et al.,
1994). QA-induced motor hyperactivity (Fig. 1), EEG voltage reduction
(Figs. 2, 3), and relative power distribution (Fig. 4) were fully
antagonized by pretreatment with 0.01 mg/kg SCH 58261 but not 1 mg/kg.
Animals treated with SCH 58261 before receiving a sham lesion did not
differ from sham controls in terms of motor response to
d-amphetamine (data not shown). As for EEG analysis, both
the mean EEG voltage and the relative EEG power distribution of the
animals pretreated with SCH 58261 were indistinguishable from those
observed in sham controls (data not shown). In the Morris water maze,
QA-lesioned rats showed impairment in their spatial learning
performances compared with controls. As shown by their swimming paths
(Fig. 5), whereas sham animals had
already developed a clear spatial strategy at block 5, QA-lesioned rats
did not. Such an impairment was reflected by the mean escape latencies
of lesioned rats, which were significantly higher than those of control
animals over the whole experiment (Fig.
6A). Rats pretreated
with SCH 58261 (either 0.01 or 1 mg/kg) before the lesion did not
differ from QA-lesioned animals in their mean escape latencies (Fig.
6B). A significant reduction in mean distance
traveled (70 sec/cm) was also observed in QA-lesioned versus sham rats
(1277 ± 94 and 1616 ± 93, respectively; p < 0.05 according to one-way ANOVA and Tukey's post hoc
test). Such an effect, which is an expression of QA-induced motor
impairment, was prevented by pretreatment with the lower dose of SCH
58261 only (0.01 SCH 58261, 1565 ± 82, p < 0.05 vs QA-lesioned; 1 SCH 58261, 1320 ± 77, NS vs QA-lesioned
according to one-way ANOVA and Tukey's post hoc test). Rats
treated with SCH 58261 (0.01 and 1 mg/kg) before receiving a sham
lesion did not differ from sham controls in terms of mean escape
latencies or mean distance traveled (data not shown). In
electrophysiological studies, slices from QA-lesioned rats showed no
significant alterations with respect to controls (slices from sham
animals) in basal synaptic transmission. In experiments aimed at
evaluating the induction of long-term synaptic plasticity, HFS applied
to the input fibers elicited a robust increase in fEPSP, followed by a
stable potentiation of fEPSP both in the CA1 area and in the dentate
gyrus. In the CA1 area, no differences were found in the magnitude of
potentiation between sham and QA-lesioned animals (+67.86 ± 14.88 and +53.05 ± 4.99% in sham and lesioned animals, respectively;
data not shown). Conversely, in the dentate gyrus (Fig.
7), LTP was significantly decreased in
QA-lesioned animals with respect to their sham controls (+60.91 ± 10.79 and 111.18 ± 15.29%, respectively; p < 0.05). Such a decrease in dentate LTP was not prevented by pretreatment with 0.01 mg/kg SCH 58261 (+73.6 ± 17.84%).
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Figure 1.
Influence of SCH 58261 on QA-induced motor
abnormalities. Rats lesioned with QA (LESQA) showed an
increased motor response to D-amphetamine (1 mg/kg, i.p.)
with respect to controls (SHAM). This effect was
prevented by pretreatment, 20 min before the lesion, with 0.01 (SCH 0.01) but not 1 (SCH 1) mg/kg SCH
58261 intraperitoneally. Each group was composed of 8-12 animals.
°p < 0.05 versus sham; *p < 0.05 versus QA-lesioned rats (one-way ANOVA and Tukey's post
hoc test).
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Figure 2.
Influence of SCH 58261 on QA-induced EEG voltage
reduction. The figure shows some representative EEG tracings recorded
from a sham (SHAM), a QA-lesioned
(QA), and two SCH 58261 (SCH 0.01 + QA
and SCH 1 + QA)-pretreated rats. At the level of the
frontal cortex (F-F leads), the QA-lesioned rat shows a
marked reduction in the EEG voltage amplitude compared with the sham
animal. Such a reduction is prevented in the animal that had been
pretreated, 20 min before the lesion, with 0.01 but not 1 mg/kg SCH
58261 intraperitoneally. Leads are as follows: F-F,
fronto-frontal; rF-P, right fronto-parietal;
lF-P, left fronto-parietal.
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Figure 3.
Quantitative analysis of EEG voltage amplitude.
The mean EEG voltage amplitude of rats lesioned with QA
(LESQA) is significantly reduced with respect to
controls (SHAM). This effect was prevented by
pretreatment, 20 min before the lesion, with 0.01 (SCH
0.01) but not 1 (SCH 1) mg/kg SCH 58261 intraperitoneally. For EEG recording and analysis, see Materials and
Methods. Each group was composed of 8-12 animals.
°p < 0.05 versus sham; *p < 0.05 versus QA-lesioned rats (one-way ANOVA and Tukey's post
hoc test).
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Figure 4.
Influence of SCH 58261 on QA-induced alterations
in relative EEG power distribution. Bilateral intrastriatal injection
of QA altered the distribution of total EEG power into the different
frequency bands. In particular, relative EEG power was increased in the
band and decreased in the and bands. These changes were
prevented by 0.01 (SCH 0.01) but not 1 (SCH
1) mg/kg SCH 58261 intraperitoneally. For EEG recording and
analysis, see Materials and Methods. Each group was composed of 8-12
animals. °p < 0.05 versus controls
(SHAM); *p < 0.05 versus
rats lesioned with QA (LESQA) (one-way ANOVA and
Tukey's post hoc test).
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Figure 5.
Impairment of space learning in animals lesioned
with QA. Rats were trained over six consecutive blocks of trials in the
Morris water maze. The figure shows some representative swimming paths
recorded from four sham (SHAM) and four
QA-lesioned (LES) rats during block 5. The
square indicates the location of the platform. Whereas
all sham animals were able to find the platform at this stage, most the
of QA-lesioned rats were still greatly impaired.
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Figure 6.
Pretreatment with SCH 58261 does not prevent
QA-induced impairment in place learning. The mean escape latencies of
QA-lesioned rats (LESQA) were significantly higher than
those of sham animals (SHAM) over the whole
experiment (A). Animals pretreated with SCH 58261 [0.01 (SCH 0.01) and 1 (SCH 1) mg/kg,
i.p.] did not differ significantly from QA-lesioned rats, although a
slight reduction in their escape latencies was observed in the last two
blocks of trials (B). *p < 0.05 versus sham (one-way ANOVA and Tukey's post hoc
test).
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Figure 7.
Induction of early LTP in hippocampal slices.
Pooled data (mean ± SEM) of fEPSPs (percentage of control)
plotted as a function of time. HFS (arrow) delivered to
the medial perforant path induced LTP that was significantly decreased
in QA-lesioned animals (LES; n = 8)
with respect to sham controls (SHAM;
n = 7). Pretreatment with 0.01 mg/kg SCH 58261 (SCH58261; n = 8) did not prevent
the reduction in the magnitude of LTP. The insets show
representative fEPSPs recorded before and 30 min after HFS. Each
trace is the average of three successive fEPSPs
(artifacts of stimulation have been truncated).
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In histological studies, the brain tissue surrounding necrosis induced
by quinolinic acid was characterized by a marked astrocytic hyperplasia. Whereas in the sham group GFAP immunolabeling identified sparse astrocytic elements, with few, thin cytoplasmic processes (Fig.
8A), in sections from
animals lesioned with QA, astrocytes increased in number and
dimensions, showing plump cell bodies with thicker and longer processes
(Fig. 8B). Quantification of hyperplasia revealed an
increase of GFAP-positive area (6.2 ± 0.4%; n = 4), which significantly exceeded that of the sham group (1.8 ± 0.5%; n = 4; p = 0.02). In animals
pretreated with 0.01 mg/kg SCH 58261, astrocytic hyperplasia was less
evident (Fig. 8C), and GFAP-positive areas were
significantly reduced (3.7 ± 0.43%; n = 5) with
respect to lesioned rats (p < 0.05).
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Figure 8.
Pretreatment with SCH 58261 prevents QA-induced
striatal gliosis. The figure shows representative striatal sections
obtained from a sham rat (A), a QA-lesioned rat
(B), and a rat pretreated with 0.01 mg/kg SCH
58261 (C). GFAP immunolabeling shows sparse
astrocytic elements in A and a marked astrocytic
hyperplasia in B. In C, GFAP-positive
elements are markedly reduced with respect to B.
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QA-lesioned animals showed marked striatal shrinkage and enlarged
ventricular cavities. At the core of QA lesion, areas of complete cell
loss were visible in the dorsal striatum. Such areas were surrounded by
densely packed dark-stained cells and reactive gliosis. The lesion
extended from 0.8 and +3.6 mm from bregma in the rostrocaudal axis
and showed its maximal extension between +1.4 and +2.7 mm from bregma.
At the site of its largest extension, the lesion occupied 82.9 ± 6% of the dorsal striatum (n = 6). SCH
58261-pretreated animals showed slightly enlarged ventricular cavities
and small areas of marked to complete cell loss. Most of the striatal
tissue surrounding such areas appeared normal at the light microscopy.
The lesion was maximal between +1.4 and +2.7 mm from bregma, and its
rostrocaudal extension was always included between +1.2 and +3.0 mm. At
the site of its largest extension, the lesion occupied in mean 22 ± 6.6% of the dorsal striatum (n = 8;
p < 0.05 vs QA alone). No histopathological damage was
observed in the hippocampus of QA-lesioned or SCH 58261-pretreated rats.
Experiment 2: study of the possible mechanisms of the protective
effects of SCH 58261
The excitotoxin QA is an endogenous metabolite of tryptophan,
which acts by both elevating extracellular levels of glutamate and
directly stimulating NMDA receptors (Connick and Stone, 1988; Stone, 1993; Mena et al., 2000). Thus, the possible influence of SCH
58261 on presynaptic and postsynaptic effects of QA was tested by
microdialysis experiments in naïve rats and fura-2 AM
experiments on striatal neurons, respectively.
Microdialysis experiments in naïve rats
In the striatum of naïve rats, the perfusion of QA (5 mM) through the dialysis probe dramatically increased
(approximately +500%) the extracellular levels of glutamate with
respect to basal values (Fig. 9). The
dose of QA was chosen on the basis of a previous report, showing that
QA elevated extracellular glutamate levels in the rat cortex when
injected in the low millimolar range (Connick and Stone, 1988). The
effects of QA were fully prevented by intraperitoneal injection (20 min
before starting the perfusion of QA) of 0.01 mg/kg SCH 58261. At the
dose of 1 mg/kg, SCH 58261 did not influence QA-stimulated glutamate
release (Fig. 9).
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Figure 9.
Influence of SCH 58261 on QA-evoked glutamate
outflow in the rat striatum. Microdialysis probes were inserted in the
striatum of naïve rats. Probe perfusion with QA (5 mM over 30 min) dramatically increased extracellular
glutamate levels with respect to basal values. Pretreatment with SCH
58261 (SCH) (0.01 mg/kg, i.p.) completely
prevented QA-stimulated glutamate outflow. The higher dose of SCH 58261 (1 mg/kg) did not influence the effects of QA perfusion. The
bar indicates the period of QA perfusion through the
probe. The time of injection of SCH 58261 is indicated by the
arrow. Each experimental group was made up of four to
five animals. °p < 0.01 versus QA.
|
|
Fura-2 AM experiments on striatal neurons
In striatal neurons, bath application of 900 µM QA
markedly raised
[Ca2+]i: the mean
340/380 ratio measured at the time of peak effect (average of 50 cells
from four different experiments) was 4.01 ± 0.19. The effect of
QA was potentiated by 15-200 nM SCH 58261. The mean
340/380 ratio with 30 nM SCH 58261 plus QA
(n = 53/4) was 5.56 ± 0.23 (p < 0.05 vs QA alone according to Student's
t test). Bath application of the selective adenosine
A2A receptor agonist CGS 21680 (100 nM) reduced the effect of QA (mean 340/380 ratio,
0.96 ± 0.66; p < 0.05 vs QA alone;
n = 34 cells from three experiments). The NMDA receptor
antagonist MK-801 (100 µM) fully prevented
QA-induced effects (n = 38 cells from three
experiments). Single representative experiments performed with QA, SCH
58261 plus QA, CGS 21680 plus QA, and MK-801 plus QA are shown in
Figure 10.
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[in this window]
[in a new window]
|
Figure 10.
Measurement of intracellular calcium in striatal
neurons. Optical fluorimetric recordings with fura-2 AM were performed
to evaluate changes in intracellular calcium levels
[Ca2+]i in rat striatal neurons. Bath
application of 900 µM QA induced a sustained
[Ca2+]i increase (A) that is
significantly potentiated by preapplication of 30 nM SCH
58261 (B) and reduced by the selective
A2A receptor agonist CGS 21680 (100 nM)
(C). The effects of QA were fully prevented by
bath application of the NMDA receptor antagonist MK-801 (100 µM) (D). Each panel
shows a single representative experiment (average of 8-14 cells from
the same dish). Ratio, Ratio between the values of light
intensity at 340 and 380 nm stimulation.
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|
| |
DISCUSSION |
Two main findings arise from this study: (1) the adenosine
A2A receptor antagonist SCH 58261 shows
neuroprotective effects in an excitotoxic rat model of HD; and (2) the
inhibition of QA-evoked increase in extracellular glutamate seems to be
the main mechanism of the effects elicited by SCH 58261.
The finding that SCH 58261 significantly prevented most of the effects
induced by the intrastriatal injection of an excitotoxin is in line
with some findings suggesting that activation of
A2A receptors could participate in the generation
of excitotoxicity. Adenosine A2A receptor
agonists have been reported indeed to stimulate glutamate release in
the rat striatum (Popoli et al., 1995; Corsi et al., 1999). Moreover,
in previous experiments, we observed that the intrastriatal injection
of the adenosine A2A receptor agonist CGS 21680, together with QA, potentiated QA-induced mortality in a dose-dependent
way (50, 75, and 83% of mortality after 3, 6, and 12 nmol QA plus CGS
21680, respectively; P. Popoli, A. Pèzzola, and R. Reggio,
unpublished results). Thus, although only a single compound was tested
in the present investigation, on the basis of the above observations,
the protective effects exerted by SCH 58261 can be actually ascribed to
a blockade of adenosine A2A receptors. On the
other hand, SCH 58261 is a specific and selective
A2A receptor ligand, because in binding studies it showed A2A receptor affinity in the low
nanomolar range (Ki of 2.3 nM), lower A1 receptor
affinity (Ki of 121 nM), and no affinity for A3
receptors up to micromolar concentrations (Zocchi et al., 1996; Varani
et al., 1998). Moreover, in a recent study, [3H]SCH 58261 has been reported to
directly and selectively label striatal A2A
receptors after peripheral administration in rodents (El Yacoubi et
al., 2001).
Striatal perfusion with 5 mM QA dramatically increased
extracellular glutamate levels. An abnormal glutamate outflow is
thought to play a crucial role in triggering the cellular events
leading to excitotoxic neuronal death (Choi, 1988; Choi and Rothman,
1990; Rossi et al., 2000). The observation that SCH 58261 fully
prevented the QA-induced increase in glutamate levels when administered at the same dose (0.01 mg/kg, i.p.), which was effective in protecting QA-lesioned animals, suggests that the reduction of QA-stimulated glutamate outflow plays a major role in the effects of the drug. Although it has been observed that an increase in glutamate
extracellular levels may be not a good index of excitotoxicity
(Obrenovitch et al., 2000) and that reducing glutamate release does not
necessarily imply neuroprotection (Calabresi et al., 2000), a
contribution of increased glutamate outflow in inducing excitotoxic
neuronal death cannot be ruled out. An inhibition of evoked glutamate
release has been reported indeed to parallel the neuroprotective
effects of some compounds (O'Neill et al., 2000; Mauler et al., 2001). Thus, the modulation of glutamate outflow can well be invoked to
explain the neuroprotective effects of SCH 58261, although alternative
mechanisms, such as a possible regulation of excessive microglial cell
activation (Fiebich et al., 1996; Picano and Abbracchio, 2000), should
also be taken into account.
According to the present findings, a possible influence of SCH 58261 on
the postsynaptic, NMDA agonistic effects of QA should be ruled out. In
fact, bath application of SCH 58261 did amplify the increase in
intracellular Ca2+ levels induced by QA on
striatal neurons. Conversely, the adenosine A2A
receptor agonist CGS 21680 attenuated QA-induced effects in the same
preparation. The present results are in line with previous reports
showing that CGS 21680 inhibits the conductance of NMDA receptor
channels in rat neostriatal neurons (Nöremberg et al., 1997). The
fact that an adenosine A2A receptor antagonist
can exert protective effects while potentiating QA-stimulated
intracellular calcium increase is not entirely surprising, because the
NMDA agonistic effects of QA seem to contribute poorly to the toxic effect of this compound. In fact, the removal of corticostriatal projections did reduce QA-induced neuronal death in the rat striatum by
~90% (Orlando et al., 2001). Thus, a reduction of glutamatergic input to the striatum is likely to represent the major step in protecting neurons from QA.
As for the finding that 1 mg/kg SCH 58261 was no longer able to prevent
QA-induced effects, the most obvious explanation would be that
adenosine receptors other than A2A (i.e.,
adenosine A1 receptors, whose blockade would be
detrimental in models of excitotoxicity) (Phillis, 1995; Ongini and
Schubert, 1998) may also be blocked by higher doses of SCH 58261. As a
possible alternative explanation, the occurrence of peripheral effects
after the administration of the higher dose of SCH 58261 might play a
role in the inversely dose-related effects of the drug. Interestingly,
after intraperitoneal administration in rats, SCH 58261 did not induce
hemodynamic changes up to the dose of 0.1 mg/kg, although it increased
blood pressure and heart rate starting from the dose of 1 mg/kg
(Monopoli et al., 1998a). Thus, low doses of SCH 58261 might have
protective effects in excitotoxic processes by the inhibition of
adenosine A2A receptor-stimulated glutamate
release, whereas higher doses could also block adenosine
A2A receptor-mediated effects on blood pressure
(Stella et al., 1996) and on platelet aggregation (Dionisotti et al.,
1992), thus eventually reducing blood and nutrient supply to the
compromised brain area (Jones et al., 1998) and further stimulating
glutamate release.
The inability of SCH 58261 to prevent QA-induced impairment in place
learning and dentate LTP deserves some consideration. Whereas the motor
and EEG alterations induced by QA seem to depend directly on the
striatal damage (Schwarz et al., 1992; Popoli et al., 1994; Rozas et
al., 1996), the reduced ability to learn the location of an invisible
platform in the water maze is rather related to an impairment of
hippocampal function (Devan and White, 1999). Thus, both the impaired
performance in the Morris maze and the reduced dentate LTP can be
considered the expression of an "indirect" hippocampal dysfunction,
which most probably depends on the QA-induced reduction in the
functional link between the hippocampus and the striatum (Devan and
White, 1999). If so, even a mild striatal damage may be able to perturb
the functional connection between these two structures, which would
explain the inability of SCH 58261 to influence "cognitive"
("hippocampal") parameters. This view is supported by the
observation that cognitive alterations, such as loss of visuospatial
abilities, occur in preclinical stages of HD, when the extent of
striatal damage may be still insufficient to bring about the onset of
motor symptoms (Bamford et al., 1995; Lawrence et al., 1998).
Interestingly, although animals pretreated with SCH 58261 were not
protected in terms of place learning impairment, their distance
traveled was comparable with that of control animals. Because the
reduction in mean distance traveled observed in QA-lesioned rats is an
expression of QA-induced motor impairment (Block et al., 1993), this
finding confirms that pretreatment with SCH 58261 does prevent the
motor ("striatal") effects of QA lesion. Another implication of
this finding is that QA-induced motor deficits are not responsible for
the poor performances of lesioned rats in the Morris maze, because SCH
58261-treated rats still showed an impaired place learning despite
their normal values in terms of distance traveled.
In conclusion, the present data show that blockade of striatal
adenosine A2A receptor by SCH 58261 exerts
neuroprotective effects in QA-lesioned rats. They also show, for the
first time, that the neuroprotective effects of SCH 58261 are
paralleled by an inhibition of QA-induced glutamate outflow. Because
the bilateral striatal lesion by QA may be considered a model of HD and
QA in itself may have a pathogenetic role in this disease (Stone,
2001), the finding of a beneficial effect of SCH 58261 (at least at low doses) in this model suggests that striatal adenosine
A2A receptors could represent an interesting
target for the development of neuroprotective strategies for HD. This
hypothesis appears even more intriguing in the light of a very recent
report showing that, in striatal cells expressing mutant
huntingtin (a genetic cellular model of HD), adenosine
A2A receptor signaling (i.e.,
A2A-stimulated adenylyl cyclase) is aberrantly
increased (Varani et al., 2001). Interestingly, changes in
A2A receptor signaling were much more evident in
cells expressing truncated mutant huntingtin, which is significantly more toxic than the full-length protein. Thus, an aberrant increase in
A2A receptor signaling seems to be specifically
associated with the expression of mutant huntingtin cytotoxicity. This
finding, together with the selective expression of adenosine
A2A receptors in the population of striatal
neurons that degenerate in early phases of HD (Glass et al., 2000),
supports the hypothesis that A2A receptors may
play a role in the pathogenesis of HD. Given the limitations of the QA
lesion as a model of HD, the therapeutic potential of adenosine
A7 2A receptor antagonists in such disease, for
which only symptomatic treatments are available to date (Marshall and
Shoulson, 1997), is worthy to be confirmed in more relevant models.
| |
FOOTNOTES |
Received July 30, 2001; revised Nov. 1, 2001; accepted Dec. 12, 2001.
Correspondence should be addressed to Patrizia Popoli, Department of
Pharmacology, Istituto Superiore di Sanità, Viale Regina Elena,
299 00161 Rome, Italy. E-mail: patrizia.popoli{at}iss.it.
| |
REFERENCES |
-
Abbracchio MP,
Cattabeni A
(1999)
Brain adenosine receptors as target for therapeutic intervention in neurodegenerative diseases.
Ann NY Acad Sci
890:79-92[Web of Science][Medline].
-
Bamford KA,
Caine ED,
Kido DK,
Cox C,
Shoulson I
(1995)
A prospective evaluation of cognitive decline in early Huntington's disease: functional and radiographic correlates.
Neurology
45:1867-1873[Abstract/Free Full Text].
-
Bates GP,
Mangiarini L,
Mahal A,
Davies SW
(1997)
Transgenic mouse models of Huntington's disease.
Hum Mol Genet
6:1633-1637[Abstract/Free Full Text].
-
Beal MF,
Kowall NW,
Ellison DW,
Mazurek MF,
Swartz KJ,
Martin JB
(1986)
Replication of the neurochemical characteristics of Huntington's disease by quinolinic acid.
Nature
321:168-171[Medline].
-
Block F,
Kunkel M,
Schwartz M
(1993)
Quinolinic acid lesion of the striatum induces impairment in spatial learning and motor performances in rats.
Neurosci Lett
149:126-128[Web of Science][Medline].
-
Bona E,
Adén U,
Giland E,
Fredholm BB,
Hagberg H
(1997)
Neonatal cerebral hypoxia-ischemia: the effect of adenosine receptor antagonists.
Neuropharmacology
36:1327-1338[Web of Science][Medline].
-
Bylsma FW,
Peyser CE,
Folstein SE,
Ross C,
Brandt J
(1994)
EEG power spectra in Huntington's disease: clinical and neuropsychological correlates.
Neuropsychologia
32:137-150[Web of Science][Medline].
-
Calabresi P,
Picconi B,
Saulle E,
Centonze D,
Hainsworth A,
Bernardi G
(2000)
Is pharmacological neuroprotection dependent on reduced glutamate release?
Stroke
31:766-773[Abstract/Free Full Text].
-
Chen JF,
Huang Z,
Ma J,
Zhu J,
Moratalla R,
Standaert D,
Moskowitz MA,
Fink SJ,
Schwarzschild MA
(1999)
A2A adenosine receptor deficiency attenuates brain injury induced by transient focal ischemia in mice.
J Neurosci
19:9192-9200[Abstract/Free Full Text].
-
Chen JF,
Xu K,
Petzer JP,
Staal R,
Xu YH,
Belstein M,
Sonsalla PK,
Castagnoli K,
Castagnoli Jr N,
Schwarzschild MA
(2001)
Neuroprotection by caffeine and A2A adenosine receptor inactivation in a model of Parkinson's disease.
J Neurosci
21:RC143(1-6).
-
Choi DW
(1988)
Glutamate neurotoxicity and diseases of the nervous system.
Neuron
1:623-634[Web of Science][Medline].
-
Choi DW,
Rothman SM
(1990)
The role of glutamate neurotoxicity in hypoxic-ischemic neuronal death.
Annu Rev Neurosci
13:171-182[Web of Science][Medline].
-
Connick JH,
Stone TW
(1988)
Quinolinic acid effects on amino acid release from the rat cerebral cortex in vitro and in vivo.
Br J Pharmacol
93:868-876[Web of Science][Medline].
-
Corsi C,
Melani A,
Bianchi L,
Pepeu G,
Pedata F
(1999)
Striatal A2A adenosine receptors differentially regulate spontaneous and K+-evoked glutamate release in vivo in young and aged rats.
NeuroReport
10:687-691[Web of Science][Medline].
-
Corsi C,
Melani A,
Bianchi L,
Pedata F
(2000)
Striatal A2A adenosine receptor antagonism differentially modifies striatal glutamate outflow in vivo in young, aged rats
NeuroReport
11:2591-2595[Web of Science][Medline].
-
Devan BD,
White NM
(1999)
Parallel information processing in the dorsal striatum: relation to hippocampal function.
J Neurosci
19:2789-2798[Abstract/Free Full Text].
-
Dionisotti S,
Zocchi C,
Varani K,
Borea PA,
Ongini E
(1992)
Effects of adenosine derivatives on human and rabbit platelet aggregation. Correlation of adenosine receptor affinities and antiaggregatory activity.
Naunyn Schmiedebergs Arch Pharmacol
346:673-676[Medline].
-
El Yacoubi M,
Ledent C,
Parmentier M,
Ongini E,
Costentin J,
Vaugeois JM
(2001)
In vivo labelling of the adenosine A2A receptor in mouse brain using the selective antagonist [3H]SCH 58261.
Eur J Neurosci
14:1567-1570[Web of Science][Medline].
-
Ferré S,
Fredholm BB,
Morelli M,
Popoli P,
Fuxe K
(1997)
Adenosine-dopamine receptor-receptor interactions in the basal ganglia.
Trends Neurosci
20:482-487[Web of Science][Medline].
-
Fiebich BL,
Biber K,
Lieb K,
van Calker D,
Berger M,
Bauer J,
Gebicke-Haerter PJ
(1996)
Cyclooxygenase-e expression in rat microglia is induced by adenosine A2a-receptors.
Glia
18:152-160[Web of Science][Medline].
-
Fredholm BB,
Abbracchio MP,
Burnstock G,
Daly JW,
Harden TK,
Jacobson KA,
Leff P,
Williams M
(1994)
Nomenclature and classification of purinoceptors.
Pharmacol Rev
46:143-156[Web of Science][Medline].
-
Gao Y,
Phillis JW
(1994)
CGS 15943, an adenosine A2 receptor antagonist, reduces cerebral ischemic injury in the mongolian gerbil.
Life Sci
55:PL61-PL65[Web of Science][Medline].
-
Glass M,
Dragunow M,
Faull RLM
(2000)
The pattern of neurodegeneration in Huntington's disease: a comparative study of cannabinoid, dopamine adenosine and GABAA receptor alterations in the human basal ganglia in Huntington's disease.
Neuroscience
97:505-519[Web of Science][Medline].
-
Hodgson JG,
Agopyan N,
Gutekunst CA,
Leavitt BR,
LePiane F,
Singaraja R,
Smith DJ,
Bissada N,
McCutcheon K,
Nasir J,
Jamot L,
Li XJ,
Stevens ME,
Rosemond E,
Roder JC,
Phillips AG,
Rubin EM,
Hersch SM,
Hayden MR
(1999)
A YAC mouse model for Huntington's disease with full-length mutant huntingtin, cytoplasmic toxicity, and selective striatal neurodegeneration.
Neuron
23:181-192[Web of Science][Medline].
-
Impagnatiello F,
Bastia E,
Ongini E,
Monopoli A
(2000)
Adenosine receptors in neurological disorders.
Emerg Ther Targets
4:635-664.
-
Jones PA,
Smith RA,
Stone TW
(1998)
Protection against kainate induced excitotoxicity by adenosine A2A receptor agonists and antagonists.
Neuroscience
85:229-237[Web of Science][Medline].
-
Lawrence AD,
Hodges JR,
Rosser AE,
Kershaw A,
ffrench-Constant C,
Rubinstein DC,
Robbins TW,
Sahakien BJ
(1998)
Evidence for specific cognitive deficits in preclinical Huntington's disease.
Brain
121:1329-1341[Abstract/Free Full Text].
-
Lindström K,
Ongini E,
Fredholm BB
(1996)
The selective A2A receptor antagonist SCH 58261 discriminates between two different binding sites for [3H]-CGS 21680 in the rat brain.
Naunyn Schmiedebergs Arch Pharmacol
354:539-541[Web of Science][Medline].
-
Lopez LV,
Cunha R,
Ribeiro JA
(1999)
ZM 241385, an adenosine A2A receptor antagonist, inhibits hippocampal A1 receptor responses.
Eur J Pharmacol
383:395-398[Web of Science][Medline].
-
Marshall FJ,
Shoulson I
(1997)
Clinical features and treatment of Huntington's disease.
In: Movement disorders: neurologic principles and practice (Watt RL,
Koller WC,
eds), pp 491-502. New York: McGraw-Hill.
-
Mauler F,
Fahrig T,
Horvath E,
Jork R
(2001)
Inhibition of evoked glutamate release by the neuroprotective 5-HT(1A) receptor agonist BAY x 3702 in vitro and in vivo.
Brain Res
888:150-157[Medline].
-
Mena FV,
Baab PJ,
Zielke CL,
Zielke HR
(2000)
In vivo glutamine hydrolysis in the formation of extracellular glutamate in the injured rat brain.
J Neurosci Res
60:632-641[Medline].
-
Monopoli A,
Casati C,
Lozza G,
Forlani A,
Ongini E
(1998a)
Cardiovascular pharmacology of the A2A adenosine receptor antagonist, SCH 58261, in the rat.
J Pharmacol Exp Ther
285:9-15[Abstract/Free Full Text].
-
Monopoli A,
Lozza G,
Forlani A,
Mattavelli A,
Ongini E
(1998b)
Blockade of adenosine A2A receptors results in neuroprotective effects in cerebral ischaemia in rats.
NeuroReport
9:3955-3959[Web of Science][Medline].
-
Nöremberg W,
Wirkner K,
Illes P
(1997)
Effect of adenosine and some of its structural analogues on the conductance of NMDA receptor channels in a subset of rat neostriatal neurones.
Br J Pharmacol
122:71-80[Web of Science][Medline].
-
Obrenovitch TP,
Urenjak J,
Zilkha E,
Jay TM
(2000)
Excitotoxicity in neurological disorders: the glutamate paradox.
Int J Dev Neurosci
18:281-287[Web of Science][Medline].
-
O'Neill MJ,
Bogaert L,
Hicks CA,
Bond A,
Ward MA,
Ebinger G,
Ornstein PL,
Michotte Y,
Lodge D
(2000)
LY 377770, a novel iGlu5 kainate receptor antagonist with neuroprotective effects in global, focal cerebral ischaemia
Neuropharmacology
39:1575-1588[Medline].
-
Ongini E,
Schubert P
(1998)
Neuroprotection induced by stimulating A1 or blocking A2A adenosine receptors: an apparent paradox.
Drug Dev Res
45:387-393.
-
Ongini E,
Adami M,
Ferri C,
Bertorelli R
(1997)
Adenosine A2A receptors and neuroprotection.
Ann NY Acad Sci
825:30-48[Web of Science][Medline].
-
Orlando LR,
Alsdorf SA,
Penney Jr JB,
Young AB
(2001)
The role of group I and group II metabotropic glutamate receptors in modulation of striatal NMDA and quinolinic acid toxicity.
Exp Neurol
167:196-204[Medline].
-
Phillis JW
(1995)
The effects of selective A1 and A2a adenosine receptor antagonists on cerebral ischemic injury in the gerbil.
Brain Res
705:79-84[Web of Science][Medline].
-
Phillis JW,
Wu PH
(1981)
The role of adenosine and its nucleotides in central synaptic transmission.
Prog Neurobiol
16:187-239[Web of Science][Medline].
-
Picano E,
Abbracchio MP
(2000)
Adenosine, the imperfect endogenous anti-ischemic cardio-neuroprotector.
Brain Res Bull
52:75-82[Web of Science][Medline].
-
Popoli P,
Pèzzola A,
Domenici MR,
Sagratella S,
Diana G,
Caporali MG,
Bronzetti E,
Vega J,
Scotti de Carolis A
(1994)
Behavioural and electrophysiological correlates of the quinolinic acid rat model of Huntington's disease.
Brain Res Bull
35:329-335[Medline].
-
Popoli P,
Betto P,
Reggio R,
Ricciarello G
(1995)
Adenosine A2A receptor stimulation enhances striatal extracellular glutamate levels in rats.
Eur J Pharmacol
287:215-217[Web of Science][Medline].
-
Reggio R,
Pèzzola A,
Popoli P
(1999)
The intrastriatal injection of an adenosine A2 receptor antagonist prevents frontal cortex EEG abnormalities in a rat model of Huntington's disease.
Brain Res
831:315-318[Medline].
-
Rossi DJ,
Oshima T,
Attwell D
(2000)
Glutamate release in severe brain ischaemia is mainly by reversed uptake.
Nature
403:316-321[Medline].
-
Rozas G,
Liste I,
Lopez-Martin E,
Guerra MJ,
Kokaia M,
Labandiera-Garcia JL
(1996)
Intrathalamic implants of GABA-releasing polymer matrices reduce motor impairments in rats with excitotoxically lesioned striata.
Exp Neurol
142:323-330[Medline].
-
Schiffmann SN,
Jacobs O,
Vanderhaeghen J-J
(1991)
Striatal restricted adenosine A2 receptor (RDC8) is expressed by enkephalin but not by substance P neurons: an in situ hybridization histochemistry study.
J Neurochem
57:1062-1067[Web of Science][Medline].
-
Schwarz M,
Block F,
Topper R,
Sontag KH,
Noth J
(1992)
Abnormalities of somatosensory evoked potentials in the quinolinic acid model of Huntington's disease: evidence that basal ganglia modulate sensory cortical input.
Ann Neurol
32:358-364[Web of Science][Medline].
-
Stella L,
De Novellis V,
Berrino L,
d'Amico M,
Rossi F
(1996)
Evidence that A(2a) and not A(2b) purinoceptors are coupled to production of nitric oxide in the regulation of blood pressure.
Environ Toxicol Pharmacol
2:327-329.
-
Stone TW
(1993)
Neuropharmacology of quinolinic and kinurenic acids.
Pharmacol Rev
45:309-379[Abstract].
-
Stone TW
(2001)
Endogenous neurotoxins from tryptophan.
Toxicon
39:61-73[Medline].
-
Varani K,
Cacciari B,
Baraldi PG,
Dionisotti S,
Ongini E,
Borea PA
(1998)
Binding affinity of adenosine receptor agonists and antagonists at human cloned A3 adenosine receptors.
Life Sci
63:PL81-PL87.
-
Varani K,
Rigamonti D,
Sipione S,
Camurri A,
Borea PA,
Cattabeni F,
Abbracchio MP,
Cattaneo E
(2001)
Aberrant amplification of A2A receptor signaling in striatal cells expressing mutant huntingtin.
FASEB J
15:1245-1247[Free Full Text].
-
Zocchi C,
Ongini E,
Conti A,
Monopoli A,
Negretti A,
Baraldi PG,
Dionisotti S
(1996)
The non-xanthine heterocyclic compound, SCH 58261, is a new potent and selective A2A receptor antagonists.
J Pharmacol Exp Ther
276:398-404[Abstract/Free Full Text].
Copyright © 2002 Society for Neuroscience 0270-6474/02/2251967-09$05.00/0
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ABSTRACT
INTRODUCTION
