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-Aminobutyric AcidA Receptor Subunit Expression throughout Pregnancy1
Department of Obstetrics, Gynecology, and Reproductive Sciences (E.F., S.H.M.), Center for Reproductive Sciences (E.F., S.H.M.), and Metabolic Research Unit (S.H.M.), University of California, San Francisco, California 94143
Address all correspondence and requests for reprints to: Synthia H. Mellon, Ph.D., Department of Obstetrics and Gynecology, University of California, Box 0556, San Francisco, California 94143-0556. E-mail: mellon{at}cgl.ucsf.edu
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
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-aminobutyric acid (GABA)-ergic stimulation. A new subunit
of the GABAA receptor, 
, has recently been identified as
being particularly abundant in the rat uterus. Reduced derivatives of
progesterone, such as the 3
,5-reduced derivative termed
allopregnanolone, modulate GABAA receptor activity and
neuronal inhibition by modulating the frequency and duration of
GABAA channel opening. This modulation depends on the
specific subunit composition of the GABAA receptor. In
particular, assembly of recombinant and 
GABAA
receptor subunits into a functional GABAA receptor have
been reported to reduce sensitivity to allopregnanolone. As
allopregnanolone works through the GABAA receptor to reduce
uterine contraction, we hypothesized that incorporation of the
-subunit into this receptor in the uterus might change the
sensitivity of the GABAA receptor to allopregnanolone and
modulate parturition. We therefore determined the expression of
GABAA receptor subunit messenger RNAs (mRNAs) in rat uteri
from various gestational ages and determined the physiological
properties of the receptors. GABAA -subunit mRNA
abundance was constant throughout gestation, but decreased at the onset
of labor. Other GABAA subunits fluctuated differently
during pregnancy: GABAA 1-subunit mRNA
expression increased, whereas 2- and -subunit mRNA
expression decreased during pregnancy, and ß3-subunit
mRNA only appeared on postpartum day 1. We determined how
allopregnanolone affected the binding of muscimol, a ligand for the
GABAA receptor, to rat uterine GABAA receptors
throughout pregnancy. Allopregnanolone caused the greatest increase in
muscimol binding to uterine GABAA receptors at 19.5 days
gestation and the least increase during labor, a time when and
1 receptor subunit mRNA concentrations were low, and
and 2 receptor subunit mRNA concentrations were high.
Thus, the subunit composition of the GABAA receptor differs
in rat uteri throughout gestation. These changes may also affect the
sensitivity of the GABAA receptor to allopregnanolone and
thus contribute to the regulation of parturition. |
Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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,5-reduced metabolite of
progesterone, has a much stronger effect than progesterone on
inhibition of uterine contraction (2, 3). As
allopregnanolone works through the -aminobutyric
acidA (GABAA) receptor and
not through the classical progesterone receptor (4, 5),
uterine contraction may be modulated through
GABAA receptor function.
GABAA receptors have been identified in both the
uterine myometrium and endometrium (6).
There are 16 known GABAA receptor subunits,
1–6, ß1–3,
1–3, , 
, and 
(7, 8),
and the localization of many of these has been mapped in the rat brain
(9, 10, 11). The GABAA receptor is
composed of five subunits that form an ion-gated chloride channel. The
function of the GABAA receptor is modulated not
only by GABAA binding, but also modulated by
benzodiazepines, barbiturates, convulsants, and neurosteroids that
include the 3,5- and 3,5ß-reduced derivatives of
progesterone (12, 13, 14, 15, 16). The degree to which each class of
compound affects GABA receptor function depends on the subunit
composition of the receptor. For example, expression of -subunit
complementary DNA (cDNA) in cells transfected with combinations of
1, 6,
ß3, 2
GABAA receptor subunit cDNAs affects the
neurosteroid-induced modification of the recombinant
GABAA receptor (17). Expression of
the 4-subunit in functional
GABAA receptors results in decreased sensitivity
to benzodiazepines (18, 19, 20, 21, 22) and increased sensitivity to
allopregnanolone (23). Hence, neurosteroid modulation of
chloride flux through the GABAA receptor is
affected by the combination of its many subunits. The regulation of
subunit expression, the regulation of assembly of subunits into
functional receptors, and the ultimate physiological function of the
receptor are still not well understood.
A new GABAA receptor subunit, named , was
recently identified (24). The -subunit is unique in
that it is abundantly expressed in the uterus, but not in other
tissues. In addition, the assembly of this subunit into a recombinant
GABAA receptor may change the sensitivity of the
receptor to allopregnanolone (24, 25). Circulating
concentrations of allopregnanolone change dramatically during pregnancy
(26, 27) and may affect uterine contractility. In
addition, changes in expression of the -subunit may affect the
function of the uterine GABAA receptor. Hence, we
determined the expression of the GABAA and
other GABAA subunits in rat uteri from various
gestational ages and examined the correlation between the change in
subunit combination and the physiological properties of the
receptor.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Cloning GABAA -subunit and rat
3-hydroxysteroid dehydrogenase (3HSD) cDNAs
First strand cDNA was made by RT of total RNA from nonpregnant
rat uteri, using Moloney murine leukemia virus reverse transcriptase
and random primers. cDNA was amplified by PCR using the primers shown
in Table 1
. PCR products were purified by
agarose gel electrophoresis, and the bands of the interest were cut out
and purified by column chromatography on QIAGEN columns
(Chatsworth, CA). Purified PCR fragments were cloned into pBluescript
KS (Stratagene, La Jolla, CA). These subcloned DNAs were
used as template DNAs to make RNA probes for the ribonuclease (RNase)
protection assays.
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-subunit
HindIII/XbaI cDNA fragment [nucleotides (nt)
148–363] and full-length 3HSD cDNA (1000 bp) were subcloned into
pKS. GABAA plasmid DNA was linearized with
HindIII. 3HSD plasmid DNA was digested with
EcoRI, which digests full-length 3HSD cDNA at 853 bp.
Both linear plasmids were transcribed with T7 RNA polymerase in the
presence of [-32P]UTP. The 251-nt
GABAA -subunit complementary RNA (cRNA) probe
contained 215 nt of GABAA -subunit cRNA
sequence and 36 nt of vector sequence; the 187-nt 3HSD cRNA probe
contained 147 nt of 3HSD cRNA sequence and 40 nt of vector sequence.
Both probes were purified by deoxyribonuclease I treatment and ethanol
precipitation. RNA samples (35 µg) were combined with the
32P-labeled cRNA probes, hybridized overnight at
42 C in buffer (2 M NaCl, 200
mM PIPES, and 5 mM EDTA, pH
6.4), treated with RNase A (20 µg/ml at 37 C for 30 min), extracted
with the phenol/chloroform, precipitated with ethanol, and loaded onto
7 M urea/6% acrylamide electrophoresis gels.
Plasma membrane preparation for GABAA
receptor binding assay
Uterine plasma membranes from timed pregnant rats were prepared
as previously described (28). Uterine tissue was
homogenized in 50 mM Tris-HCl (pH 7.4) and centrifuged at
800 x g for 10 min at 4 C. The supernatant was
collected by filtering through a double layer of cheese cloth and was
centrifuged at 40,000 x g at 4 C for 30 min. The
pellets were swollen in 5 mM Tris-HCl (pH 7.4)
for 25 min on ice and then centrifuged at 40,000 x g
for 30 min again to obtain the pellets. Pellets were washed three
additional times, and the final pellets were stored at -70 C for 3
days before the experiment.
[3H]Muscimol binding assays on rat
uterine membrane GABAA receptors
Binding assays were performed as previously described
(28). Uterine membrane protein concentrations were
measured using bicinchoninic acid protein assay reagent (Pierce Chemical Co., Rockford, IL). Two hundred micrograms of the
plasma membrane samples and [3H]muscimol in
various concentrations (1–300 nM) were incubated for 15
min on ice in a total volume of 500 µl 50 mM Tris-HCl (pH
7.4). Nonspecific binding was determined in the presence of 1
mM GABA. The reaction was terminated by adding 4 ml
ice-cold assay buffer (50 mM Tris-HCl, pH 7.4), followed by
vacuum filtration through glass-fiber filters (GF/C,
Whatman, Clifton, NJ). The filters were washed three times
with 4 ml ice-cold assay buffer, and the radioactivity retained on
filters was counted by liquid spectrometry. Data were analyzed by
Scatchard analysis to determine the
[3H]muscimol binding to
GABAA receptors.
[3H]Muscimol was purchased from NEN Life Science Products (Boston, MA), GABA was obtained from RBI
(Natick, MA), and other reagents were purchased from Sigma
(St. Louis, MO).
To determine the effect of allopregnanolone on muscimol binding to GABAA receptors, 200 µg of the uterine plasma membranes of timed pregnant rats were incubated with [3H]muscimol (10 nM for high affinity site or 100 nM for low affinity site) and 0.1 µM allopregnanolone in assay buffer (50 mM Tris-HCl, pH 7.4) for 15 min on ice. Samples were assayed in triplicate for each gestational age, and the binding experiments were repeated four times using different uterine membrane preparations. Plasma membranes of each gestational age were obtained from at least three individuals and mixed together in each membrane preparation. Data are presented as the mean ± SE, and statistical analysis was performed using ANOVA, followed by Fisher’s protected least significant difference test, with P < 0.05 considered significant.
Semiquantitative PCR
The primers used to amplify the different
GABAA receptor subunits, some previously used by
others to amplify GABAA receptor subunits by
RT-PCR (29), are listed in Table 1
. First strand cDNAs
were made by RT from 1 µg RNA from rat uteri at various gestational
ages. cDNAs from the various gestational ages were made at the same
time to control for potential experimental errors. cDNAs were amplified
by PCR. The linearity of PCR amplification reactions for each primer
pair was determined by collection of PCR reactions at five cycle
intervals, separation of PCR-amplified products by agarose gel
electrophoresis, and analysis of PCR products using a computer program
(ImageQuant program, Molecular Dynamics, Inc., Sunnyvale,
CA). Reactions using GAPDH primers were included in each reaction as a
control for the quality and quantity of RNA in each sample. Positive
controls of the PCR conditions and reactions used rat brain cDNA
prepared from a nonpregnant animal, and reactions were performed
simultaneously with PCR reactions using rat uterine cDNA. PCR products
were loaded onto 2% agarose gels containing 0.2 µg/ml ethidium
bromide. To compare the intensities of the cDNA products, gels were
scanned and analyzed using an ImageQuant analysis program
(Molecular Dynamics, Inc.).
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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-subunit messenger RNA
(mRNA)-subunit mRNA was expressed in the adult
rat uterus (24). Using RNase protection assays, we
determined whether the GABAA -subunit mRNA was
expressed in the pregnant rat uterus, and whether the abundance of this
mRNA was altered throughout pregnancy (Fig. 1). mRNA was present at 13.5 days
gestation (Fig. 1A), the earliest time tested. Its abundance at this
time was almost the same as that in the nonpregnant rat. mRNA
abundance increased slightly between 13.5 and 19.5 days of pregnancy
(Fig. 1A) and started decreasing at 21.5 days of pregnancy (Fig. 1B).
The most notable change in mRNA abundance was seen at parturition,
when its abundance decreased dramatically. At 1 day postpartum,
mRNA expression increased slightly (Fig. 1B), but was still less than
that seen in a uterus from a nonpregnant rat (Fig. 1B). Thus, mRNA
is abundant in the rat uterus throughout pregnancy and falls
dramatically at the end of pregnancy.
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HSD mRNA-reductase and 3HSD. As local allopregnanolone synthesis may
affect uterine GABAA receptor function, we
determined the abundance of uterine 3HSD mRNA during pregnancy (Fig. 2). The abundance of 3HSD mRNA
increased from 15.5 days of pregnancy until 21.5 days of pregnancy.
Unlike mRNA abundance, 3HSD mRNA did not change further during
labor. At 1 day postpartum, 3HSD expression decreased to a level
comparable to that seen in nonpregnant rats.
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are likely
to be required to form a functional GABAA
receptor. Receptors containing or lacking or other
GABAA receptor subunits may be differentially
sensitive to allopregnanolone (13, 14, 22, 24, 25, 30, 31, 32). Therefore, we analyzed uterine expression of several
GABAA subunit mRNAs during pregnancy to determine
whether the mRNAs for any of these subunits changed in a manner similar
to that seen for the -subunit (Fig. 3). A summary of the PCR data from Fig. 3A is shown in graph form in Fig. 3B. Relative levels of mRNA
expression from the RT-PCR are included as a comparison with the
expression of the other GABAA receptor subunit
mRNAs, and the abundance of each subunit mRNA was compared with that of
GAPDH, whose concentration was constant throughout pregnancy, during
labor, and postpartum. mRNA for the 1-subunit
showed a transitional change during pregnancy in the rat uterus. The
expression of the 1-subunit increased from
13.5 days until 19.5 days of pregnancy. After that time, it decreased
and remained low, even at 1 day postpartum (Fig. 3, A and B). By
contrast, 2-subunit mRNA decreased during
pregnancy, and after 19.5 days of pregnancy, the expression increased
(Fig. 3, A and B).
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). We confirmed that
the 419-bp amplified fragment we identified was indeed a
ß3 DNA fragment by restriction enzyme digestion
of the amplified products. XhoI digestion of this product
yielded DNA fragments of 260 and 159 bp, the expected sizes for
ß3-subunit DNA (data not shown).
-Subunit expression decreased slightly during pregnancy (15.5–21.5
days of pregnancy), and it increased at the onset of labor and 1 day
postpartum to a level greater than that seen in nonpregnant rats (Fig. 3A). We also examined the expression of other
GABAA receptor subunits,
4 and 2, but did not
detect expression of those subunits in the uteri from rats at any stage
of pregnancy or from nonpregnant rats despite their strong expression
in the rat brain (not shown).
[3H]Muscimol binding to rat uterine
GABAA receptors
To determine the nature of the binding sites of
GABAA receptors in the uterus, we performed
Scatchard analyses for [3H]muscimol binding on
the uterine plasma membranes from nonpregnant rats. We analyzed our
data using the two-site model for [3H]muscimol
binding, as described for GABAA receptors from
rat brain cortexes (33). The high affinity binding site
for muscimol shows a Kd of 1.79 nM
and a binding capacity (Bmax) of 4.9 pmol/mg
protein, and the low affinity site shows a Kd of
52.6 nM and a Bmax of 12.1 pmol/mg
protein. These values are similar to muscimol binding to
GABAA receptors from rat brains (33, 34).
Effect of allopregnanolone on
[3H]muscimol binding in the various
gestational samples
We determined whether the changes we observed in rat uterine
mRNA concentrations resulted in functionally different receptors.
Hence, we determined whether there were differences in the ability of
allopregnanolone to alter [3H]muscimol binding
to rat uterine GABAA receptors during pregnancy.
In the absence of allopregnanolone (control binding; Fig. 4A, 
), the high affinity muscimol site
showed a biphasic change in binding during pregnancy. Specific muscimol
binding increased from 118.3 ± 17.3 fmol/mg protein in
nonpregnant rat uteri to 130.8 ± 14.8 fmol/mg protein at 15.5
days of pregnancy. This binding decreased from 15.5 days of pregnancy
until 21.5 days of pregnancy, when binding was 106.8 ± 15.2
fmol/mg protein. After delivery (postpartum day 1), muscimol binding to
GABAA receptors increased to 129.5 ± 23.9
fmol/mg protein. These changes did not reach significance
(P < 0.05).
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, 
) in uteri from pregnant rats at the
middle vs. the end of gestation. At 19.5 days gestation,
allopregnanolone increased muscimol binding to 149.5 ± 5.9 fmol/mg
protein. From 19.5 days of pregnancy to labor, there was a decrease in
muscimol binding to GABAA receptors in the
presence of allopregnanolone. This binding differed significantly (Fig. 4A, asterisks; P < 0.05) between 15.5 days
gestation and labor, between 19.5 and 21.5 days gestation, and between
19.5 days gestation and labor (Fig. 4A). The sensitivity of the
GABAA receptor to allopregnanolone decreased at
the end of gestation and during labor, such that there was a decrease
in muscimol binding at those times.
We compared binding of muscimol to the high affinity
GABAA receptor in the presence of
allopregnanolone vs. that in the absence of allopregnanolone
and plotted these results as percent binding vs. time of
gestation (Fig. 4B). The results show that at 19.5 days of pregnancy,
allopregnanolone caused a 21% increase in muscimol binding compared
with muscimol binding without allopregnanolone stimulation. This
increased binding was significantly different from that in samples from
uteri during labor and on postpartum day 1, which were less sensitive
to allopregnanolone than at any other gestational age (Fig. 4B, asterisks; P < 0.05).
At the low affinity site of the GABAA receptor,
muscimol binding did not vary appreciably during pregnancy, during
labor, on postpartum day 1, or in the nonpregnant animal (Fig. 4C).
There appeared to be a biphasic change in muscimol binding during
pregnancy, as there was for the high affinity
GABAA receptor, and the receptor appeared to be
the least sensitive at 21.5 days of pregnancy, like the high affinity
receptor. These differences did not reach significance. In addition,
there was no significant effect of allopregnanolone in the specific
binding of [3H]muscimol to
GABAA receptors at any time during pregnancy
(Fig. 4, C and D).
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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-hydroxy-5-reduced
metabolite of progesterone, is even more potent than progesterone in
inhibiting uterine contractions, and it mediates its action through the
GABAA receptor. Studies in vivo in rat
brains and in cell transfection assays using recombinant
GABAA subunit cDNAs have shown that different
combinations of GABAA subunits result in
GABAA receptors that are more or less sensitive
to allopregnanolone modulation (13, 14, 22, 24, 25, 30, 31, 32). One subunit, , is particularly abundant in the
uterus, and recent experiments (24, 25) demonstrated that
the GABAA receptor subunit, when combined with a
ß3subunit, resulted in a GABAA
receptor that was less sensitive to allopregnanolone than a receptor
that did not contain the -subunit. Hence, we hypothesized that both
the synthesis of allopregnanolone in situ in the uterus and
the expression of specific subunits of the GABAA
receptor that are more sensitive to allopregnanolone may operate to
make the uterus quiescent during pregnancy and more contractile at
parturition.
Our studies have now demonstrated that the different uterine
GABAA receptor subunit mRNAs fluctuate
differently during pregnancy. Our data suggest that -subunit mRNA
expression throughout pregnancy did not vary appreciably from that seen
in the uterus from a nonpregnant rat. However, -subunit mRNA did
decrease considerably during labor. These data suggest that the
expression of the -subunit may correlate with parturition.
Decreases in uterine -subunit mRNA expression during pregnancy and
sharp increases during labor may also affect uterine contractility.
Others have shown that incorporation of the -subunit of the
GABAA receptor produces a receptor that is less
sensitive to the modulating effect of another neurosteroid,
allotetrahydrodeoxycorticosterone (17), that functions at
the GABAA receptor in a similar fashion to
allopregnanolone. Thus, decreased synthesis of the -subunit mRNA in
the uterus during pregnancy may lead to a GABAA
receptor that has increased sensitivity to allopregnanolone, and
increased synthesis of this subunit at the onset of labor may create a
GABAA receptor that has decreased sensitivity to
allopregnanolone. These data further suggest that assembly of
GABAA receptor subunits into functional receptors
may change during pregnancy, and that the resulting receptor may have
properties that are distinct at the time of the onset of labor.
Others have shown pregnancy-induced fluctuations in
GABAA receptors from rat brains (26, 27). In those studies the most notable changes were found in the
2L receptor subunit, which decreased during
pregnancy, increased during delivery, and returned to control levels 2
days after delivery. Unlike the rat brain, we detected no form of the
receptor subunit (neither 2L nor
2S) at any time in the pregnant or nonpregnant
rat uterus. In addition, whole brain concentrations of
1, 2,
3, 4,
ß1, ß2,
ß3, and 2S mRNAs did
not change throughout pregnancy, whereas we detected changes in
1- and 2-subunits in
the rat uterus. Thus, both uterine and brain
GABAA receptor subunit concentrations fluctuate
during pregnancy, and they fluctuate independently.
The sensitivity of the rat uterine GABAA receptor to its ligands and to the modulating effects of neurosteroids does change during pregnancy. Our data confirm those shown previously that [3H]muscimol binding to uterine GABAA receptor increased on day 15 of gestation compared with that in nonpregnant animals (28). Our data further demonstrate that the [3H]muscimol binding to high affinity sites shows the greatest binding at 15.5 days of pregnancy and the least binding at 21.5 days of pregnancy. However, the sensitivity of the high affinity site to allopregnanolone (allopregnanolone/control) was the greatest at the end of pregnancy, at 19.5 days of pregnancy, and the sensitivity to allopregnanolone was least during labor.
It is unclear how this sensitivity changes, but we believe that it is
directly related to the concentration of uterine
GABAA receptor subunits. Sensitivity to
allopregnanolone at 19.5 days of pregnancy was greatest when
1- and -subunit expression was greatest,
and when 2- and -subunit expression was
least. By contrast, the sensitivity of the GABAA
receptor was least around parturition, a time when
1- and -subunits were expressed to a lesser
extent and when 2- and -subunits were
expressed to a greater extent. Ligand binding studies from others
demonstrate that membranes from human embryonic kidney 293 cells
transfected with ß3- and -subunit cDNAs had
reduced receptor sensitivity to allopregnanolone compared with
membranes from cells transfected with only the
ß3 cDNA (24). However, we detected
ß3 mRNA in the rat uterus only on postpartum
day 1, a time when -subunit mRNA was expressed to the least extent.
These data suggest that ß3-subunit may not
affect the function of the GABAA receptor
containing a -subunit, and hence, the binding data using cloned
GABAA receptor ß3- and
-subunits do not reflect in vivo uterine physiological
conditions. Alternatively, the data may suggest that postpartum,
increased expression of the ß3-subunit may play
a role in the decreased sensitivity of the GABAA
receptor to the stimulatory effect of allopregnanolone.
It has been suggested that most of the functional
GABAA receptors in the brain contain combinations
of /ß/- or /ß/-subunits (35, 36), and
recently it was suggested that -subunit coassembles with -, ß-,
-subunits to form functional GABA receptors (25). Our
experiments did not detect ß1 or
ß2 mRNAs in any uterine sample and could only
detect ß3 mRNA in a postpartum uterine sample.
There is no information about the functional subunit combination of
GABAA receptor in the uterus. Because the
-subunit has high sequence similarities with ß-subunits (37%) and
because the -subunit is particularly abundant in the uterus, we
believe that the -subunit is crucial for functional
GABAA receptor formation in the uterus.
The role of the -subunits in GABAA receptor
function have been studied in the brain. Previous investigators have
shown that the GABAA
1-subunit mRNA decreased from 19 days of
pregnancy and 1 day postpartum in the magnocellular oxytocin neuron
located in the supraoptic nucleus of the hypothalamus (37, 38). 2-Subunit expression did not
change during this period, but increased after delivery (during 2 weeks
of lactation). The decrease in the ratio of
1/2-subunit mRNAs
correlated with a decrease in allopregnanolone potentiation and an
increase in the decay time constant of the GABAA
receptor-mediated inhibitory postsynaptic currents in these cells. We
found that the 1- and
2-subunit mRNAs in the uterus changed in a
fashion similar to that in the supraoptic nucleus, suggesting that
these subunit mRNAs may be regulated by similar factors or may be
coordinately regulated in both the brain and uterus during pregnancy.
The fluctuation of these subunits in the uterus may also result in
increased potentiation by allopregnanolone during pregnancy when
1 is increased and 2
is decreased, and decreased potentiation during labor and postpartum,
when 1 is decreased and
2 is increased.
The physiological significance of high affinity site and low affinity
site of the GABAA receptor is still unclear, but
the high affinity site seemed to be more sensitive to allopregnanolone
in our rat uterine [3H]muscimol binding assays.
These changes in sensitivity did not correlate with expression of the
-subunit, but did correlate with expression of the
1- and
2-subunits.
During pregnancy, not only does progesterone increase, but its
metabolism to allopregnanolone also increases (39, 40). In
pregnant women, the plasma concentration of
5-dihydroprogesterone(5-pregnan-3,2odione) (5DHP) is
extremely high. During the third trimester of pregnancy, the blood
production rate of 5DHP may exceed 100 mg/24 h (41).
Maternal plasma 5DHP is derived mainly from fetal metabolism of
progesterone synthesized in the syntiotrophoblast. 5DHP is then
secreted from the trophoblast, preferentially entering the maternal
compartment (41). The uterus may then convert
trophoblast-derived 5DHP into increasing concentrations of
allopregnanolone, as our RNase protection assay showed that the uterine
expression of 3HSD mRNA increased during pregnancy. Increased local
synthesis of allopregnanolone coupled with increased sensitivity of
GABAA receptors to allopregnanolone at the end of
pregnancy may allow the uterus to be its most quiescent toward the end
of pregnancy (19.5 days gestation). Decreases in allopregnanolone
synthesis at the end of pregnancy, together with further changes in
GABAA receptor subunit composition that result in
a receptor less sensitive to allopregnanolone may signal the onset of
labor.
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Footnotes |
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2 Present address: Department of Obstetrics and Gynecology, Osaka
University Graduate School of Medicine 2–2 Yamadaoka, Suita, Osaka
565-0871, Japan.
Received August 23, 2000.
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References |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
amino butyric
acidA receptor systems. Biol Reprod 45:266–272[Abstract]
aminobutyric acidA
receptors in the rabbit: a novel mechanism? J Endocrinol 131:427–434-aminobutyric
acidA receptors to neurosteroids. J
Neurochem 57:1818–1821[CrossRef][Medline]
subunit inhibits neurosteroid modulation of GABAA
receptors. J Neurosci 16:6648–66564 subunit. FEBS Lett 289:227–230[CrossRef][Medline]
4 subunit: identification of a unique
diazepam-insensitive binding site. Eur J Pharmacol 291:319–325[CrossRef][Medline]
4ß32,
42, or
1ß32
subunits. Eur J Pharmacol 304:155–162[CrossRef][Medline]
-aminobutyric acidA receptors containing the
4 subunit. Mol Pharmacol 50:670–678[Abstract]
4 subunit suppression prevents
withdrawal properties of an endogenous steroid. Nature 392:926–930[CrossRef][Medline]
-aminobutyric acidA
receptor 4 subunit expressed in Xenopus
laevis oocytes. Mol Pharmacol 50:1364–1375[Abstract]
-aminobutyric acid(A) receptors. Mol
Pharmacol 56:598–610-aminobutyric acid type A
receptor in rat brain during pregnancy and after delivery. Proc Natl
Acad Sci USA 95:13284–13289-OH-5-pregnan-20-one using a
pseudopregnancy model alters the kinetics of hippocampal
GABAA-gated current and increases the
GABAA receptor 4 subunit
in association with increased anxiety. J Neurosci 18:5275–5284-aminobutyric acid
receptor-gated chloride ion channels: evidence for multiple steroid
recognition sites. Mol Pharmacol 37:263–270[Abstract]
-Dihydroprogesterone formation in human placenta from
5-pregnan-3ß/-ol-20-ones and 5-pregnan-3ß-yl-20-one sulfate.
J Steroid Biochem Mol Biol 63:155–163[CrossRef][Medline]
-hydroxysteroid dehydrogenase. Mol
Endocrinol 5:823–828 subunit in rat brain GABAA receptors. Neuron 3:745–753[CrossRef][Medline]
2 polypeptide of rat
-aminobutyric acidA receptors. J
Neurochem 56:1717–1722[CrossRef][Medline]
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 K. Mizuta, D. Xu, Y. Pan, G. Comas, J. R. Sonett, Y. Zhang, R. A. Panettieri Jr., J. Yang, and C. W. Emala Sr. GABAA receptors are expressed and facilitate relaxation in airway smooth muscle Am J Physiol Lung Cell Mol Physiol, June 1, 2008; 294(6): L1206 - L1216. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 W F Symmans, D J Fiterman, S K Anderson, M Ayers, R Rouzier, V Dunmire, J Stec, V Valero, N Sneige, C Albarracin, et al. A single-gene biomarker identifies breast cancers associated with immature cell type and short duration of prior breastfeeding Endocr. Relat. Cancer, December 1, 2005; 12(4): 1059 - 1069. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A. Parizek, M. Hill, R. Kancheva, H. Havlikova, L. Kancheva, J. Cindr, A. Paskova, V. Pouzar, I. Cerny, P. Drbohlav, et al. Neuroactive Pregnanolone Isomers during Pregnancy J. Clin. Endocrinol. Metab., January 1, 2005; 90(1): 395 - 403. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 S. R. Bair and S. H. Mellon Deletion of the Mouse P450c17 Gene Causes Early Embryonic Lethality Mol. Cell. Biol., June 15, 2004; 24(12): 5383 - 5390. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
E. P. Tierney, S. Tulac, S.-T. J. Huang, and L. C. Giudice Activation of the protein kinase A pathway in human endometrial stromal cells reveals sequential categorical gene regulation Physiol Genomics, December 16, 2003; 16(1): 47 - 66. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 G. Charpigny, M.-J. Leroy, M. Breuiller-Fouche, Z. Tanfin, S. Mhaouty-Kodja, Ph. Robin, D. Leiber, J. Cohen-Tannoudji, D. Cabrol, C. Barberis, et al. A Functional Genomic Study to Identify Differential Gene Expression in the Preterm and Term Human Myometrium Biol Reprod, June 1, 2003; 68(6): 2289 - 2296. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 P. Seth, D. Porter, J. Lahti-Domenici, Y. Geng, A. Richardson, and K. Polyak Cellular and Molecular Targets of Estrogen in Normal Human Breast Tissue Cancer Res., August 15, 2002; 62(16): 4540 - 4544. [Abstract] [Full Text] [PDF]
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|
 D. Matsui, M. Sakari, T. Sato, A. Murayama, I. Takada, M. Kim, K.-i. Takeyama, and S. Kato Transcriptional regulation of the mouse steroid 5{alpha}-reductase type II gene by progesterone in brain Nucleic Acids Res., March 15, 2002; 30(6): 1387 - 1393. [Abstract] [Full Text] [PDF]
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