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Vol. 280, Issue 2, 1094-1101, 1997
Department of Physiology and Pharmacology, Section of Molecular Neuropharmacology, Karolinska Institutet, Stockholm, Sweden
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Abstract |
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 Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References
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The effect of adrenalectomy on the expression of adenosine receptors
and their mRNA in rat brain was examined using quantitative autoradiography and in situ hybridization.
1,3-[3H]Dipropyl-8-cyclopentylxanthine
([3H]DPCPX), a selective adenosine A1
receptor antagonist, and [3H]CGS 21680, a selective
adenosine A2A receptor agonist, were used as radioligands.
One week after adrenalectomy, the expression of mRNA for adenosine
A1 receptors was significantly decreased, as was the number
of binding sites for [3H]DPCPX. These effects were
significantly counteracted by replacement treatment with dexamethasone
(1.5 mg/kg i.p., twice daily). Addition of GTP caused a similar
increase of [3H]DPCPX binding in sham-operated rats,
adrenalectomized rats and rats adrenalectomized and treated with
dexamethasone. Moreover, no differences in displacement of
[3H]DPCPX by the adenosine receptor agonist
N6-(R-phenylisopropyl)adenosine
were found among these groups. Adrenalectomy did not significantly
affect the number of [3H]CGS 21680 binding sites in
striatum or the mRNA encoding adenosine A2A receptors. No
changes in the affinity of [3H]CGS 21680 for adenosine
A2A receptors or in the potency of the adenosine receptor
agonist 2-chloroadenosine to displace [3H]CGS 21680 were
found. Dexamethasone treatment decreased cAMP formation induced by the
nonselective adenosine agonist
5
-N-ethylcarboxamidoadenosine in Jurkat cells, which
express adenosine A2B receptors, but did not alter it in
PC-12 cells, which express mostly A2A receptors. The
results suggest that endogenous corticosteroids positively regulate the
expression of adenosine A1 receptors, at least partly at
the transcriptional level. In contrast, corticosteroids do not regulate
the expression of adenosine A2A receptors.
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Introduction |
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Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References
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Corticosteroids acting on
mineralocorticoid and glucocorticoid receptors, both of which bind to
DNA (Evans and Arriza, 1989
), regulate the transcription of many genes,
including those for receptors. Thus, it has been shown that
corticosteroids, via glucocorticoid receptors, can increase
the mRNA expression and responsiveness of beta-2 adrenergic
receptors in DDT1 MF-2 cells (Collins et al.,
1988), and it is well documented that corticosteroids can regulate mRNA
and receptor expression in vivo. Removal of endogenous corticosteroids by adrenalectomy has, for example, been shown to
significantly affect both mRNA and receptor density for
5-hydroxytryptamine1A and 
-aminobutyric
acidA receptors in the rat hippocampus (Chalmers et
al., 1993; Orchinik et al., 1994), a region in the
central nervous system where both mineralocorticoid and glucocorticoid receptors are expressed (McEwen et al., 1968; Chao et
al., 1989; Cintra et al., 1994). Whereas
mineralocorticoid receptors are expressed at high levels only in
hippocampus, glucocorticoid receptors are widely distributed, with high
to moderate levels in, for example, hippocampus and cerebral and
cerebellar cortex and striatum (Cintra et al., 1991, 1994).
In the latter region glucocorticoid receptors are involved in the
transcriptional regulation of cannabinoid receptors and the
neuropeptides proenkephalin and protachykinin (for review, see Chao and
McEwen, 1990; Mailleux and Vanderhaeghen, 1993; Angulo and McEwen,
1994).
Adenosine is a potent endogenous neuromodulator that has been suggested
to act as an endogenous neuroprotective agent (Rudolphi et
al., 1992), as a regulator of seizure susceptibility (Dragunow, 1988), as an endogenous analgetic (Sawynok, 1995) and in the regulation of sensorimotor control (for review, see Ferré et al.,
1992; Fredholm, 1995). Adenosine in physiological concentrations exerts its action in the brain mainly via the G protein-coupled
adenosine A1 and A2A receptors (Rudolphi
et al., 1992). Adenosine A1 receptors are widely
distributed in the central nervous system, with high levels of
expression in glucocorticoid receptor-rich areas like hippocampus and
cerebral and cerebellar cortex (Goodman and Snyder, 1982; Fastbom
et al., 1987). Adenosine A2A receptors and their corresponding mRNAs have a more restricted distribution and are mostly
found in striatum. A2A receptors are colocalized with
dopamine D2 receptors in -aminobutyric acid-ergic
medium-sized neurons that also contain enkephalin (Schiffmann et
al., 1991; Fink et al., 1992). These striatal neurons
also show high levels of immunoreactivity for glucocorticoid receptors
(Cintra et al., 1991). These data suggest that
glucocorticoids may regulate adenosine receptors in the brain. Indeed,
there is some evidence that stressful stimuli, which are known to
affect glucocorticoid levels, can influence A1 receptors
(Boulenger et al., 1984, 1986) in the central nervous system.
Gerwins and Fredholm (1991) showed that in vitro treatment
with the synthetic steroid dexamethasone increases the number of adenosine A1 receptors and enhances A1
receptor-mediated responses in smooth muscle cells. However, it is not
known whether such a regulation of adenosine A1 receptors
occurs at the transcriptional level or whether it occurs in the central
nervous system in vivo. There is likewise no information
about the role that corticosteroids have in the regulation of adenosine
A2A receptors. In the present study, we investigated the
effects of adrenalectomy on the expression of adenosine A1
and A2A receptors and their corresponding mRNA in rat
brain.
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Materials and Methods |
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Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References
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Animals and treatment. The experiments were approved by the regional animal ethics committee. Male Sprague-Dawley rats (ALAB, Stockholm, Sweden) weighing 200 to 230 g were used. The rats were housed two per cage and maintained on a 12/12-hr light/dark cycle. All rats had free access to food and drinking water.
Bilateral adrenalectomy was performed via a lumbar approach under chloral hydrate (400 mg/kg) anesthesia. Sham operations were identical to adrenalectomy, but the adrenal glands were left intact. The adrenalectomized rats received 0.9% NaCl for daily drinking and were injected i.p. twice daily (10:00 A.M. and 5:00 P.M.) with either 1 ml of dexamethasone (1.5 mg/kg; Sigma, LabKemi, Stockholm, Sweden), dissolved in saline and a few drops of Tween 80, or vehicle. At 10:00 A.M. on day 7, rats were briefly anesthetized with CO2 and killed by decapitation. The brains were rapidly dissected out and frozen at
80°C. Sagittal
sections (10- or 14-µm thick) were made and thaw-mounted on
poly-L-lysine (50 mg/ml)- or gelatin-coated slides.
In situ hybridization.
The 48-mer A1
adenosine receptor probe was complementary to nucleotides 985 to 1032 of the rat A1 receptor (Mahan et al., 1991). The
44-mer A2A probe was complementary to nucleotides 916 to
959 of the dog RDC8 cDNA (Schiffmann et al., 1990). The
48-mer preproenkephalin probe was complementary to nucleotides 388 to 435 of the rat preproenkephalin gene (Yoshikawa et al.,
1984). The specificity of each probe was tested earlier (Johansson
et al., 1993, 1994). The oligodeoxyribonucleotides
(Scandinavian Gene Synthesis, Köping, Sweden) were radiolabeled,
using terminal deoxyribonucleotidyl transferase (Amersham, Solna,
Sweden) and 
-35S-dATP (DuPont-NEN, Stockholm, Sweden),
to a specific activity of about 109 cpm/µg.
Slide-mounted, 14-µm sections were hybridized in a cocktail containing 50% formamide (Fluka, Buchs, Switzerland), 4× SSC (1× SSC
is 0.15 M NaCl, 0.015 M sodium citrate), 1× Denhardt's solution, 1%
sarcosyl, 0.02 M sodium phosphate (pH 7.0), 10% dextran sulfate, 0.5 mg/ml yeast tRNA (Sigma, LabKemi), 0.06 M dithiothreitol, 0.1 mg/ml
sheared salmon sperm DNA and 107 cpm/ml probe. After
hybridization for 16 hr at 42°C, the sections were washed four times
for 15 min each in 1× SSC at 55°C (A1 probe and
preproenkephalin probe) or 45°C (A2A probe), dipped
briefly in water, 70% ethanol, 95% ethanol and 99.5% ethanol and
air-dried. Finally the sections were apposed to Hyperfilm 
-max film
(Amersham) for 1 week (preproenkephalin probe) or 3 weeks
(A1 and A2A probe).
Ligand-binding autoradiography.
For receptor
autoradiography, 10-µm sections were preincubated in 170 mM Tris-HCl
buffer containing 1 mM EDTA and 2 U/ml adenosine deaminase (calf
intestine; Boehringer, Mannheim, Germany) at 37°C for 30 min.
Sections were then washed twice for 10 min at 23°C in 170 mM Tris-HCl
buffer with 10 mM MgCl2 for A2 receptors or 1 mM MgCl2 for A1 receptors. Incubations were
performed for 2 hr at 23°C in Tris-HCl buffer containing the
radioligand at the appropriate concentration, 2 U/ml adenosine
deaminase and 1 mM MgCl2 with or without 100 µM GTP for
A1 or 10 mM MgCl2 with or without 1000 µM GTP
for A2 receptors. The ligand used for A1
receptors was [3H]DPCPX (0.125, 0.25, 0.5, 1, 2.5 and 5 nM, 60-80 Ci/mmol; DuPont-NEN), and the ligand for the study of
A2A receptors was [3H]CGS 21680 (0.5, 1.25, 2.5, 5, 10 and 20 nM, 48.1 Ci/mmol; DuPont-NEN). Nonspecific binding
was defined with 20 µM (R)-PIA (Boehringer, Mannheim,
Germany) (for A1 receptors) or 20 µM 2-chloroadenosine (Sigma, LabKemi) (for A2A receptors). Displacement studies
were performed with (R)-PIA (10
10,
109, 108 and 107 M) for
A1 receptors (0.5 nM DPCPX) and with 2-chloroadenosine (109, 108, 107 and
106 M) for A2 receptors (2.5 nM CGS 21680).
Sections were then washed twice for 5 min each in ice-cold Tris-HCl,
dipped quickly three times in ice-cold distilled water and dried at
4°C over a strong fan. The dried sections, together with plastic
tritium standards (Amersham), were apposed to 3Hyperfilm
(Amersham) for 5 weeks.
In vitro assays. PC-12 cells were grown in Dulbecco's modified Eagle's medium supplemented with penicillin, streptomycin, L-glutamine and 5% fetal calf serum/10% horse serum at 37°C in 5% CO2/95% air. Jurkat cells were maintained in RPMI 1640 medium supplemented with penicillin, streptomycin, L-glutamine and 7.5% fetal calf serum. Cells were subcultured (5 × 104 cells/ml) for 12 hr before addition of dexamethasone (100 nM). Cells were then incubated for 24 hr.
After being washed twice with assay medium, aliquots (0.5 × 105 cells, 0.35 ml) were transferred to test tubes. NECA (108 to 103 M; Sigma, LabKemi), a potent
nonselective adenosine receptor agonist, was added, together with 30 µM levels of the phosphodiesterase inhibitor rolipram (Research
Biochemicals Inc., Natick, MA), to a final volume of 0.5 ml. To amplify
the response, Jurkat cells were studied in the presence of 10 µM
forskolin (van der Ploeg et al., 1996). Reactions were
terminated, after 10 min of incubation at 37°C, by addition of
perchloric acid to a final concentration of 0.4 M. Samples were
neutralized with KOH, and the cAMP content in the supernatants was
determined with a protein-binding assay (Nordstedt and Fredholm,
1990), where bound [3H]cAMP was separated from free by
rapid filtration over glass fiber filters (Skatron AS, Tranby, Norway).
Data analysis. The films from the in situ hybridization and autoradiographic studies were analyzed with a microcomputer imaging device system (Imaging Research, St. Catharine's, Canada). The system was calibrated with a Kodak density wedge when films from in situ hybridization experiments were analyzed, and the results are presented as optical density values. For films from ligand-binding autoradiographic studies, the optical density values were converted to binding density (femtomoles per milligram of gray matter) by using calibrated plastic standards (Amersham) and the specific activity of the respective radioligand.
Statistics. When measurements were done in several regions of the rat brain, an overall analysis was performed with two-way ANOVA (treatment × region) (GraphPad PRISM, San Diego, CA). Additionally, for individual regions a one-way ANOVA followed by Bonferroni's correction for pairwise comparisons was used (GraphPad InStat; ISI Software, San Diego, CA). A two-tailed, unpaired, Student's t test was used for analysis of the in vitro studies (GraphPad InStat; ISI Software). P values of <.05 were considered significant.
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Results |
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Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References
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Effect of adrenalectomy on preproenkephalin mRNA.
To verify
that the adrenalectomy and the treatment with dexamethasone did
influence the central nervous system, we examined the expression of
preproenkephalin mRNA in caudate putamen; previous reports
(e.g., Chao and McEwen, 1990; Mailleux and
Vanderhaeghen, 1993) demonstrated clear-cut effects on this
neuropeptide. As seen in figure 1, the expected decrease
in preproenkephalin mRNA was observed after adrenalectomy, and the
effect of adrenalectomy was reversed by the chosen dose of
dexamethasone.
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Effects of adrenalectomy on the expression of adenosine
A1 receptors and corresponding mRNA in rat
brain.
In agreement with previous studies (e.g.,
Johansson et al., 1993), there was a widespread distribution
of both [3H]DPCPX binding and mRNA encoding
adenosine A1 receptors (fig. 2). Also in
agreement with previous data (Johansson et al., 1993), we
found that there was no exact correspondence between the distribution of A1 receptors, as determined by [3H]DPCPX
binding, and the distribution of A1 receptor mRNA. As discussed elsewhere (e.g., Johansson et al.,
1993), this difference may be accounted for by the fact that
A1 receptors are present in many nerve terminals, where
they regulate transmitter release (Fredholm and Dunwiddie, 1988),
whereas mRNA is found mainly in cell bodies.
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).
It was previously found that drug treatment can influence not only
total receptor number, as assessed by antagonist binding, but also the
coupling to G proteins (e.g., Green and Stiles, 1986; Fastbom and Fredholm, 1990; Hoppe and Lohse, 1995). We therefore examined whether adrenalectomy altered the ability of GTP to influence [3H]DPCPX binding or the affinity of an agonist for the
binding sites. However, as illustrated in figure 4A,
none of the groups differed in the potency with which
(R)-PIA, an agonist at adenosine receptors, displaced
[3H]DPCPX binding. Moreover, addition of 100 µM GTP to
the incubation solution increased the binding to similar extents in the
three different treatment groups (fig. 4B).
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Effects of adrenalectomy on the expression of adenosine
A2A receptors and corresponding mRNA in rat
brain.
In agreement with previous results (e.g.,
Johansson et al., 1993), expression of adenosine
A2A receptors and their corresponding mRNA was much higher
in caudate putamen than in other brain regions (fig. 5).
The respective Bmax and
Kd values for
[3H]CGS 21680 binding were 403 ± 13.4 fmol/mg
gray matter and 2.74 ± 0.28 nM for adrenalectomized rats,
392 ± 11.8 fmol/mg gray matter and 2.99 ± 0.27 nM for
sham-operated rats and 377 ± 15.5 fmol/mg gray matter and
3.09 ± 0.38 nM for adrenalectomized rats treated with
dexamethasone, respectively. These values were not significantly different, nor were there any significant differences in
A2A receptor mRNA expression among the three groups. A
similar decrease in [3H]CGS 21680 binding was found in
all three groups when 1000 µM GTP was added to the incubation
solution; the decreases were 47%, 46% and 57% in adrenalectomized,
sham-operated and adrenalectomized/dexamethasone-treated rats,
respectively. The adenosine agonist 2-chloroadenosine displaced [3H]CGS 21680 binding with similar potencies in all three
groups. The IC50 values were 59.9 ± 24.8 nM for
adrenalectomized rats, 71.8 ± 28.3 nM for sham-operated rats and
78.6 ± 25.5 nM for adrenalectomized rats treated with
dexamethasone.
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Effects of dexamethasone on NECA-induced cAMP formation in PC-12
and Jurkat cells.
The lack of significant effect of adrenalectomy
or dexamethasone on A2A receptors in the striatum is in
apparent contrast to the previous finding that A2
receptor-mediated effects in DDT1 MF-2 cells are
down-regulated by dexamethasone (Gerwins and Fredholm, 1991). To ensure
that the discrepancy is not caused by a difference in the type of assay
used (binding vs. cAMP measurements), we examined whether
dexamethasone could affect cAMP responses mediated by A2A
receptors in PC-12 cells. However, dexamethasone did not have any
significant effect on NECA-induced cAMP responses in PC-12 cells (fig.
6A). The cAMP response in DDT1 MF-2 cells
may be due to stimulation of A2B rather than
A2A receptors. A2B receptors are found in
Jurkat cells (van der Ploeg et al., 1996). In these cells,
treatment with dexamethasone (100 nM) for 24 hr significantly decreased
the cAMP formation after stimulation with NECA at 104,
105 or 107 M (fig. 6B).
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Discussion |
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Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References
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Our main finding is that adrenal steroids regulate the expression of adenosine A1 receptors not only in vitro but also in vivo. The number of adenosine A1 receptors was decreased after adrenalectomy. The effect of adrenalectomy was counteracted by daily dexamethasone injections, indicating that it is due to loss of endogenous glucocorticoids. Although decreases in adenosine A1 receptors after adrenalectomy were observed in most brain regions, the magnitude of the effect differed among brain areas. Significant decreases of Bmax values were found only in caudate putamen and frontoparietal cortex. However, when adrenalectomized rats that received no glucocorticoid replacement were compared with rats that were given dexamethasone, significant differences in receptor number were found in caudate putamen, frontoparietal cortex, stratum radiatum of CA3, ventrolateral thalamus and the molecular layer of cerebellar cortex. There was no direct correspondence between the number of glucocorticoid receptors and the alterations in adenosine A1 receptor density in the examined regions.
A complicating factor for the interpretation of these region-specific differences is that many adenosine A1 receptors are located on nerve terminals in regions distinct from those where the cell bodies are located. Glucocorticoids might therefore regulate the transcription and translation of adenosine A1 receptors in the cell bodies but the consequent alterations in receptor number would be found mostly in nerve terminal regions. In fact, results concerning adenosine A1 receptor mRNA are consistent with this view (see below).
In agreement with several previous studies, GTP markedly increased the
binding of the receptor antagonist [3H]DPCPX (Fastbom and
Fredholm, 1990; Parkinson and Fredholm, 1992). The reason is that
adenosine receptor agonist ligands, including the endogenous ligand
adenosine, bind in a pseudoirreversible manner to the receptors in the
presence of magnesium when GTP levels are low. This tightly bound
adenosine cannot be removed by addition of the enzyme adenosine
deaminase. When GTP (or GDP) is added in concentrations approaching
physiological levels, the bound adenosine rapidly dissociates and the
antagonist radioligand can gain access to the receptor (see Parkinson
and Fredholm, 1992). The difference in [3H]DPCPX binding
in the presence and absence of GTP therefore reflects the number of
A1 receptors tightly associated with the holotrimeric G
protein. The present data thus indicate that this proportion is not
altered by adrenalectomy or by dexamethasone.
There were significant overall effects of adrenalectomy and of
dexamethasone not only on the number of A1 receptors but
also on the expression of A1 receptor mRNA. The effect of
dexamethasone was most pronounced in the granular layer of gyrus
dentatus and the pyramidal layer of CA1. These two hippocampal regions,
along with the granular layer in cerebellum, express the highest levels of glucocorticoid receptors in the brain (Cintra et al.,
1994). It therefore seems reasonable to assume that altered
transcription of the A1 receptor gene can account for at
least part of the change in the amount of receptor protein.
There are several reasons for believing that corticosteroids regulate
adenosine A1 receptors mainly via glucocorticoid
receptors and not via mineralocorticoid receptors. First,
dexamethasone treatment reversed the decrease in adenosine
A1 receptors induced by adrenalectomy and, because
dexamethasone binds to glucocorticoid receptors with much higher
affinity than to mineralocorticoid receptors (Chao et al.,
1989), this compound mainly reveals effects mediated via the
glucocorticoid receptor. Second, adrenalectomy down-regulated adenosine
A1 receptors in several brain regions that are known to
express high levels of glucocorticoid receptors but only low levels of
mineralocorticoid receptors. Third, Gerwins and Fredholm (1991) found
up-regulation of adenosine A1 receptors in vitro
after stimulation of glucocorticoid, but not mineralocorticoid, receptors. In fact, the changes in adenosine receptors were smallest in
the hippocampal area, where mineralocorticoid receptors are most
abundant. This might indicate that mineralocorticoid receptors and
glucocorticoid receptors play opposing roles in the regulation of
adenosine A1 receptors. Another possibility is that
heterodimeric mineralocorticoid and glucocorticoid receptors have
different effects, compared with the homodimers (see Trapp and
Holsboer, 1996).
The adenosine A1 receptor gene has been shown to contain at
least four exons (Ren and Stiles, 1995), which can generate two different transcripts that are expressed in a tissue-specific manner
(Ren and Stiles, 1995). It is not known how these are regulated, but it
is interesting to note that there are several AP-1 consensus sites. It
has been shown in vitro that activated glucocorticoid receptors can interact with AP-1 (Schule et al., 1990;
Yang-Yen et al., 1990; Beato et al., 1995).
Whereas glucocorticoid altered A1 receptors, it had no
apparent effect on A2A receptors or on A2A
receptor mRNA. This could not be ascribed to a lack of effect on gene
transcription in striatal adenosine A2A receptor-containing
neurons, because a significant alteration was found in the level of
mRNA coding for the coexisting neuropeptide preproenkephalin. Indeed,
preproenkephalin mRNA and adenosine A2A receptor mRNA are
expressed in the same subpopulation of striatal neurons (Schiffmann
et al., 1991).
This lack of effect of dexamethasone on A2A receptors is in
apparent contrast to the findings of Yingling et al. (1994)
on cAMP responses to adenosine analogs in PC-18 cells. We therefore examined the effect of dexamethasone treatment on cAMP responses to an
adenosine analog in PC-12 cells. We previously showed that, in the
clone used, the response can be accounted for by stimulation of
A2A receptors (van der Ploeg et al., 1996). Our
findings confirmed the results on striatal A2A receptors
but differed from those reported for PC-18 cells. We have no good
explanation for this apparent discrepancy, but it should be noted that
Yingling and coworkers used (R)-PIA as an agonist despite
the fact that it is more potent on A1 receptors than on
A2A receptors. Furthermore, it was found that the
enhancement of (R)-PIA-stimulated cAMP responses was
markedly reduced by inclusion of a phosphodiesterase inhibitor, suggesting that part of the effect was due to down-regulation of this
enzyme (Yingling et al., 1994). In our experiments, the phosphodiesterase inhibitor rolipram was used.
Our experiments in PC-12 cells were run in parallel with experiments in
Jurkat cells, which express mainly adenosine A2B receptors, rather than A2A receptors (van der Ploeg et al.,
1996). In contrast to the results in PC-12 cells, the functional
responses in Jurkat cells were decreased after dexamethasone. These
findings provide further evidence for a down-regulation of
A2B receptors. They also suggest that the functional
A2 effects reported previously in DDT1 MF-2
cells (Gerwins and Fredholm, 1991) may reflect alterations in
A2B receptors. Although further studies on A2B
receptors are needed, the data thus indicate that glucocorticoid
effects on adenosine receptors can range from up-regulation
(A1 receptor) or no effect (A2A receptor) to
down-regulation (A2B receptor).
The present data thus show that endogenous and exogenous
glucocorticoids regulate the number of adenosine A1
receptors at least in part by altering the expression of the
corresponding mRNA in rat brain. In contrast, no effects on adenosine
A2A receptors or their mRNA were found. It is tempting to
speculate that the alterations in adenosine A1 receptors
can have functional consequences, because these receptors are known to
modulate many brain functions. For example, adenosine A1
receptors modulate seizure activity (Dragunow, 1988), and it is
possibly relevant that dexamethasone treatment increases the threshold
of the adenosine receptor antagonist theophylline to cause seizures
(Hoffman et al., 1994). If adenosine A1
receptors are important there, then it can be predicted that adrenalectomy would render animals more susceptible to these and other
effects of adenosine A1 receptor antagonists.
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Acknowledgments |
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We thank Dr. A. Cintra for help with the adrenalectomy and Susanne Ahlberg for help with the cAMP measurements in PC-12 and Jurkat cells.
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Footnotes |
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Accepted for publication October 21, 1996.
Received for publication August 13, 1996.
1 Recipient of a doctoral fellowship from the Knut and Alice Wallenberg Foundation.
Send reprint requests to: Per Svenningsson, Department of Physiology and Pharmacology, Karolinska Institutet, S-171 77 Stockholm, Sweden.
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Abbreviations |
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ANOVA, analysis of variance;
cAMP, cyclic AMP;
CGS 21680, 2-[p-(2-carbonylethyl)phenylethylamino]-5-N-ethylcarboxamidoadenosine;
DPCPX, 1,3-dipropyl-8-cyclopentylxanthine;
NECA, 5-N-ethylcarboxamidoadenosine;
(R)-PIA, N6-(R-phenylisopropyl)adenosine;
SSC, standard saline citrate.
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References |
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Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References
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-nucleotidase in the brain of some commonly used experimental animals.
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