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Cortical  -Aminobutyric Acid Levels Across the Menstrual Cycle in Healthy Women and Those With Premenstrual Dysphoric Disorder
A Proton Magnetic Resonance Spectroscopy Study
C. Neill Epperson, MD;
Kristin Haga, PhD;
Graeme F. Mason, PhD;
Edward Sellers, MD;
Ralitza Gueorguieva, PhD;
Wenjiang Zhang, PhD;
Erica Weiss, MD;
Douglas L. Rothman, PhD;
John H. Krystal, MD
Arch Gen Psychiatry. 2002;59:851-858.
ABSTRACT
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Background There is increasing support for the hypothesis that gonadal steroids
involved in the regulation of the human menstrual cycle modulate  -aminobutyric
acid (GABA) neuronal function. This study tests the hypothesis that cortical
GABA neuronal function, reflected in brain GABA concentrations, fluctuates
across the menstrual cycle in healthy women and those with premenstrual dysphoric
disorder (PMDD) and that a menstrual cycle phase–dependent abnormality
in brain GABA concentrations in women diagnosed as having PMDD would reflect
altered central response to circulating gonadal and neuroactive steroids.
Methods Fourteen healthy menstruating women and 9 women diagnosed as having
PMDD were recruited from a women's behavioral health research program located
at a university-based medical center. The women underwent serial proton magnetic
resonance spectroscopic measurements of occipital cortex GABA levels across
the menstrual cycle (primary outcome measure) and had blood drawn for gonadal
hormone and neurosteroid levels determined on each scan day (secondary outcome
measure).
Results There was a significant group x phase interaction with most of
the finding explained by the reduction in cortical GABA levels during the
follicular phase in those with PMDD compared with healthy controls. Cortical
GABA levels declined across the menstrual cycle in healthy women, whereas
women with PMDD experienced an increase in cortical GABA levels from the follicular
phase to the mid luteal and late luteal phases. Significant between-group
differences in the relationship between hormones and GABA were observed for
estradiol, progesterone, and allopregnanolone.
Conclusions These data strongly suggest that the GABAergic system is substantially
modulated by menstrual cycle phase in healthy women and those with PMDD. Furthermore,
they raise the possibility of disturbances in cortical GABA neuronal function
and modulation by neuroactive steroids as potentially important contributors
to the pathogenesis of PMDD.
INTRODUCTION
PRECLINICAL STUDIES have increasingly defined the neural targets for
gonadal steroids, such as estradiol and progesterone, and their neurosteroid
precursors and derivatives.1-4
For example, the 3 -reduced biosynthetic derivatives of progesterone,
3-hydroxy-5-pregnan-20-one (allopregnanolone) and 3-hydroxy-5 -pregnan-20-one
(pregnenolone), are potent -aminobutyric acid A (GABAA)
receptor facilitators, increasing the frequency and duration of the chloride
ionophore channel opening.4 In healthy women,
menstrual cycle–related changes in cognitive function, mood, and drug
sensitivity may be attributable to fluctuations in the hormonal modulation
of -aminobutyric acid (GABA) systems.5-7
Alterations in GABA neuronal function have been implicated in the pathophysiology
of premenstrual dysphoric disorder (PMDD), a luteal phase–specific syndrome
characterized by moderate-to-severe alterations in mood, behavior, and physical
well-being that impairs the personal, professional, and/or social functioning
of 3% to 7% of premenopausal women.8 Plasma
GABA levels are reduced across the menstrual cycle in women with PMDD compared
with healthy controls who experience an increase in plasma GABA levels from
the follicular to luteal phases.9 Additionally,
women with PMDD demonstrate a luteal phase–specific decrease in the
behavioral and physiologic response to administration of GABAA
receptor agonists.6-7 Measurement
of cortical excitability using transcranial magnetic stimulation demonstrates
an increase in cortical inhibition in healthy controls in the mid luteal phase
compared with the mid follicular phase to a degree comparable to that observed
after administration of GABA-enhancing drugs.10
The fact that women with PMDD did not demonstrate an increase in cortical
inhibition during the mid luteal phase provides additional evidence of phase-specific
reduction in GABAA receptor function11
in this population. Preclinical findings demonstrating alterations in the
number of 4 subunits and sensitivity of GABAA receptor on
withdrawal of chronically administered allopregnanolone12
provide a compelling model for the mechanism by which neurosteroids may mediate
GABA neuronal changes across the menstrual cycle.
Further support for a neurosteroid-GABA hypothesis in the pathogenesis
of PMDD comes from treatment studies that demonstrate the preferential responsivity
of PMDD to selective serotonin reuptake inhibitors (SSRIs). The SSRI-induced
increases in cerebrospinal fluid and brain allopregnanolone in patients with
major depression13 and in rats,14
respectively, are likely due to the stimulatory effect of SSRIs on 3-hydroxysteroid
oxoreductase, the rate-limiting enzyme in the biosynthesis of allopregnanolone.15 Although luteal phase deficits in allopregnanolone
are associated with greater symptom severity in women with PMDD,16-17
most studies have found no difference between women with premenstrual syndrome
and PMDD and their healthy counterparts with respect to luteal phase levels
of gonadal steroids and allopregnanolone.17-19
Failure to demonstrate a significant effect of diagnosis on plasma neuroactive
steroids does not necessarily detract from the importance of these steroids
in the pathogenesis of PMDD because a dissociation between peripheral and
brain levels of allopregnanolone has been demonstrated in rodents.20-21
Quantitative, localized, repeatable, noninvasive measurements of human
cortical GABA levels are now possible.22 These
advances in proton magnetic resonance spectroscopy (1H-MRS) permit
direct tests of the hypothesis that human cortical GABA levels fluctuate across
the menstrual cycle and that PMDD is associated with abnormalities in GABA
neuronal function. The aims of this study are 3-fold: (1) to determine whether
there are menstrual cycle phase– and diagnosis-specific fluctuations
in cortical GABA levels in normal menstruating women and women with PMDD,
(2) to assess menstrual cycle–related fluctuations in plasma neuroactive
steroids, and (3) to examine the relationship between plasma neuroactive steroids
and cortical GABA levels. We chose the occipital cortex as our region of interest
for this study based on previous evidence that GABAergic-modulating substances
(benzodiazepines, alcohol, vigabatrin) and psychiatric disorders (unipolar
depression and panic disorder) were associated with altered GABA levels in
this region.23-25
PARTICIPANTS AND METHODS
PARTICIPANTS
Twenty-three regularly menstruating women, 9 with PMDD (age, 26-39 years;
mean age, 34.6 years) and 14 healthy controls (age, 21-45 years; mean age,
30.1 years), participated in this study after giving written informed consent
using forms and procedures approved by the Yale University School of Medicine
Human Investigations Committee, New Haven, Conn. All participants were recruited
through local advertising and were paid for their participation. Participants
had not been pregnant or taking hormonal contraceptives for at least 10 months
and had not taken psychotropic drugs for more than 5 years. Two participants
with PMDD had previously taken fluoxetine hydrochloride for major depressive
episodes.
All participants underwent a diagnostic interview using the Structured
Clinical Interview for Diagnosis based on DSM-IV.26 Women with PMDD were excluded if they had an Axis
I psychiatric or substance abuse or dependence disorder within the previous
2 years or a lifetime history of bipolar disorder or psychosis. Healthy controls
were without personal or family (first-degree relative) history of a confirmed
psychiatric disorder (by participant report). Table 1 summarizes participant characteristics. Participants did
not differ significantly with respect to age at presentation, age at menarche,
parity, or menstrual cycle length.
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Table 1. Participant Characteristics*
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All women were screened prospectively for 2 to 3 consecutive menstrual
cycles using the Daily Record of Severity of Problems to rate severity of
mood and physical symptoms.27 The Daily Record
of Severity of Problems is a 24-item daily diary that solicits information
regarding the severity of mood, cognitive, behavioral, and physical symptoms
and level of interference in the personal, professional, and interpersonal
life domains. Each symptom is rated on a scale of 1 (not present) to 6 (extreme).
All women with PMDD had at least a 50% increase in severity of at least 4
mood symptoms in the luteal phase (average score for 7 days before onset of
menses) compared with the follicular phase (average score days 5-11). No symptom
was rated higher than a 3 (mild) on days 5 to 11, and 4 symptoms were rated
at least a 4 (moderate) in severity for at least 2 of the 7 days before onset
of menses.
TIMING OF 1H-MRS SCANS
Scans were scheduled to coincide with the period of low gonadal steroid
levels (days 3-8; early to mid follicular phase), highest gonadal steroid
levels (3-8 days after luteinizing hormone surge; mid luteal phase), and the
period of gonadal steroid withdrawal (1-5 days before onset of menses; late
luteal phase). Timing of the luteinizing hormone surge was determined using
a commercially available urine luteinizing hormone kit (Answer, Carter-Wallace,
New York, NY). Blood was obtained for gonadal steroid and neurosteroid determination
on each scan day. Serum was assayed for estradiol and progesterone levels
by a commercial laboratory (Clinical Laboratory Partners, Hartford, Conn)
to confirm menstrual cycle phase. The GABA data were not included in any statistical
analysis that included menstrual cycle phase (operationalized group) when
hormone levels could not confirm the desired phase. Follicular phase scan
data from 1 participant with PMDD and 2 healthy controls were excluded from
phase-specific analyses secondary to having estradiol levels of more than
100 pg/mL (367 pmol/L) (indicative of late follicular phase). Data from 2
mid luteal phase scans (1 PMDD participant, 1 healthy control) were omitted
from analyses because of a progesterone level of 299 ng/dL (9.5 nmol/L) or
less.
All women participating in the study abstained from drinking alcohol
for at least 48 hours before each 1H-MRS scan and had minimal (none
to 3 drinks per week) alcohol use at baseline with the exception of one participant
with PMDD who regularly drank 10 glasses of wine per week. One participant
with PMDD reported smoking 5 to 7 cigarettes per day but abstained from smoking
for at least 5 hours before each scan. Daily ratings during the scan month
continued to confirm PMDD diagnosis for those included in the study.
MRS METHODS
Studies were performed with a 2.1-T magnet (Oxford Magnetic Technology,
Oxford, England) with a 1-m bore and a spectrometer (Bruker Avance; Bruker
Instruments, Billerica, Mass). Participants lay supine with the occipital
cortex against an 8-cm surface coil tuned to the 1H-MRS frequency
of 89.67 MHz. Gradient-echo scout images of the participant's brain were obtained
for participant positioning, and a 1.5 x 3 x 3-cm3
voxel centered on the midline of the occipital cortex, 1.5 cm deep from the
dura, was chosen for 1H-MRS. Automated first- and second-order
shimming was applied in the volume of interest.28
Detection of the 3.0 ppm of GABA C4 resonance was performed for 20 minutes
using J-editing.22 Briefly, pairs of subspectra
were obtained, one with a frequency selective inversion pulse applied to the
GABA C3 resonance and one without the inversion pulse. The subspectra were
subtracted to obtain difference spectra that contained total GABA (combined
measure of GABA and the GABA-containing dipeptide homocarnosine). Localization
was achieved with selective excitation, 3-dimensional, image-selected, in
vivo spectroscopy, outer volume suppression, and a surface spoiler coil. The
spectral acquisition parameters were as follows: repetition time, 3.39 seconds;
echo time, 68 milliseconds; sweep width, 1500 Hz; and acquisition time, 510
milliseconds. The free induction decay was zero-filled to 32 K, processed
with 3-Hz lorentzian broadening, and Fourier transformed. The GABA signal
was then integrated over a 0.30-ppm bandwidth at 3.00 ppm, and the creatine
signal was integrated over a 0.20-ppm bandwidth at 3.00 ppm in the GABA-inverted
spectrum. The GABA concentration was calculated as described previously.22 Figure 1 depicts representative spectra obtained during the follicular phase from 1
participant with PMDD and 1 healthy control using 1H-MRS.
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Figure 1. Example of -aminobutyric
acid (GABA) spectra obtained from the occipital cortex during the follicular
phase of 1 healthy control (A) and 1 woman with premenstrual dysphoric disorder
(B). The arrows indicate the GABA peak. Cho indicates choline; Cr, creatine;
and ppm, parts per million.
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GONADAL STEROID AND NEUROSTEROID DETERMINATION
Serum estradiol and progesterone levels were determined in a commercial
laboratory using heterogeneous competitive magnetic separation assay with
a lower limit of detection (LOD) of 30.7 pmol/L and immunoassay techniques
with a within-run coefficient of variation of 8.1% at the LOD for estradiol
and an LOD of 0.32 nmol/L and coefficient of variation of 9.3% for progesterone.
Neurosteroids, including pregnenolone, 5-dihydroprogesterone (5DHP),
and allopregnanolone, were determined using gas chromatography–mass
spectroscopy (GC-MS) modified from Hubbard et al.29
GC-MS Conditions
The mass spectrometer was a Perkin Elmer Turbomass (negative chemical
ionization mode). The gas chromatograph (GC) was an Autosystem XL (Quadrex
Corp, New Haven, Conn) equipped with a methylsilicone column (15 m x
0.25 mm inside diameter) with a 0.05-m film thickness. The initial gas chromatograph
oven temperature was 150°C, followed by 230°C at 30°C/min, then
to 250°C at 1.0°C/min, and finally to 320°C at 30°C/min. Ultrahigh-purity
helium was the carrier gas. The gas chromatograph was operated in the splitless
mode for the first 0.7 min and then was switched to a split flow. The injection
port flow was 1.0 mL min. Methane was used as the reagent gas for negative
chemical ionization. The injector and transfer-line temperatures were maintained
at 300°C and 310°C, respectively. Selected ions of m/z (mass/charge)
460, m/z 462, and m/z 466 were monitored.
Steroid Extraction and Separation
Steroids in plasma were extracted by solid phase extraction using C18
columns. For plasma samples, the internal standard solution was added, followed
by an aliquot of methanol and water (proportion, 50/50), then diluted with
deionized water to a final concentration of 5% methanol. Samples were then
extracted with C18 columns equilibrated with methanol. The steroid fraction
was eluted with methanol, then evaporated to dryness at 40°C.
Steroids were derivatized according to the method of Hubbard et al29 and were reacted in the following order: 50 µL
of 2% carboxymethoxylamine hemihydrochloride in pyridine at 60°C for 45
minutes, a volume of 25 µL each of 20% pentafluorobenzyl bromide in
acetonitrile and 20% disopropylethylamine in acetonitrile at 45°C for
20 minutes, and 25 µL of acetonitrile and 50 µL of bis(trimethylsilyl)trifluoroacetamide
at 40°C for 30 minutes. After each step, the reaction mixture was dried
under nitrogen.
All neurosteroids for participants with PMDD and healthy controls were
batch run under the same laboratory conditions. The ranges of between-day
coefficient of variation for duplicate repeats of samples performed throughout
several months were 3.6% to 15% for 5DHP, 5.5% to 27% for pregnenolone,
and 8.4% to 22% for allopregnanolone.
STATISTICAL METHODS
Mixed models were used to analyze the data on GABA and neuroactive steroid
levels.30-31 This approach takes
into account correlations between repeated measurements on the same participant
and is unaffected by data missing at random. Before analysis, all outcomes
were checked to ensure that they resembled a normal distribution using normal
probability plots and Kolmogorov-Smirnov test statistics. Log transformations
were used when data exhibited positive skewness.
Differences in GABA levels across the 3 phases between the 2 groups
(aim 1) were tested in a computer program (SAS PROC MIXED; SAS Institute,
Cary, NC) by fitting a mixed model with a random effect for participant and
fixed effects for group, phase, and group x phase interaction. If the
group x phase interaction effect was significant at the .05 level, follow-up
individual comparisons between the groups at each phase were performed. Bonferroni
correction was used for multiple post hoc comparisons.
Similarly, overall and phase between-group differences for each gonadal
steroid and neurosteroid (aim 2) were tested by fitting a separate mixed-effects
model with the same fixed and random effects described herein. Because phase
was an effect in these models, the analyses were performed on the operationalized
sample (the results were essentially the same for the entire sample).
The relationship between GABA and each steroid (aim 3) was estimated
by fitting a separate mixed model with GABA as the response variable, with
a random effect for participant and fixed effects for group, steroid, and
group x steroid interactions. Because phase and steroids are usually
highly correlated, phase was not used as an effect in this model, and the
analysis was performed on the entire sample. When a significant difference
in the relationship between GABA and a gonadal steroid or neurosteroid was
observed (a significant group x steroid interaction), a graph with regression
line for each group was created to illustrate the effect.
RESULTS
GABA data were obtained in the follicular phase for 8 women with PMDD
and 12 healthy controls, in the mid luteal phase for 7 women with PMDD and
11 healthy controls, and in late luteal phase for 7 women with PMDD and 9
healthy controls. Reasons for not obtaining GABA measurements at all 3 time
points include inability to coordinate scanner availability with participant's
menstrual cycle or schedule (n = 4), participant movement in the scanner (n
= 1), and dropout after the second scan (n = 1). Most women underwent scanning
first in the follicular phase; however, 3 healthy controls underwent scans
in an alternate sequence. One healthy control had follicular and late luteal
phase scans in one cycle and the mid luteal phase scan in a subsequent cycle
2 months later. There was no significant between-group differences in the
timing of the mid luteal (t test; t11 = 0.69, P = .51) and late luteal
phase (t9 = 1.67, P = .13) scans with respect to the number of days after luteinizing
hormone surge.
MENSTRUAL CYCLE FLUCTUATIONS IN GABA LEVELS
Mean GABA, gonadal steroid, and neurosteroid levels are given in Table 2. For the operationalized sample,
there was a significant group x phase interaction (F2,25
= 17.9, P<.001) for the cortical GABA data, explained
mainly by a significant difference in follicular phase GABA levels (F1,25 = 27.8, P<.001) (Figure 2). These findings continued to be significant when age was
added as a covariate or when those undergoing scanning in an alternate sequence
were removed from the analysis. There were no significant group differences
in the mid luteal phase (F1,25 = -0.20, P = .65) or the late luteal phase (F1,25 = 0.71, P = .41) (Table 2).
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Table 2. Cortical -Aminobutyric Acid (GABA) and Peripheral Gonadal
Hormone and Neurosteroid Levels Across the Menstrual Cycle in Women With Premenstrual
Dysphoric Disorder (PMDD) and Healthy Controls*
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Figure 2. Proton magnetic resonance spectroscopic
findings of cortical -aminobutyric acid (GABA) levels across the menstrual
cycle in women with premenstrual dysphoric disorder (PMDD) and healthy controls.
Error bars indicate SD.
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Examining GABA data by group, healthy menstruating women experienced
a significant decrease in cortical GABA levels from the follicular phase to
both the mid luteal phase (F1,25 = 18.2, P<.001)
and the late luteal phase (F1,25 = 21.2, P<.001).
In contrast, a significant increase in cortical GABA from the follicular phase
to both the mid luteal phase (F1,25 = 8.9, P<.006) and the late luteal phase (F1,25 = 9.2, P = .005) occurred in the women with PMDD. There was no
significant between-group difference in the absolute magnitude of the change
in cortical GABA levels from the follicular to mid luteal phase (t11 = 0.69, P = .51).
To examine potential effects of subtle between-group differences that
may have been imposed by scanning women at different points in the luteal
phase with respect to their peak hormone levels and variation in menstrual
cycle length, we examined the GABA data with the day of cycle scanned standardized
to a 28-day cycle (day of cycle scanned/cycle length x 28). GABA data
based on the standardized day of cycle variable were analyzed using a mixed-effects
model with a random intercept and a random slope for participant and fixed
effects for group, day, and group by day. The findings from this analysis
again demonstrated a significant group x day interaction (F1,11 = 39.5, P<.001). History of major depression
(n = 3) did not seem to have an impact on cortical GABA levels.
MENSTRUAL CYCLE FLUCTUATIONS IN GONADAL STEROIDS AND NEUROSTEROIDS
Sufficient data were obtained for estradiol, progesterone, pregnenolone,
5DHP, and allopregnanolone to allow for meaningful analysis of impact
on cortical GABA levels and/or between-group differences in hormone levels.
All variables except 5DHP were log transformed to eliminate positive
skewness. Results for progesterone, estradiol, pregnenolone, and allopregnanolone
are given in Table 2. With respect
to between-group differences in hormone levels, significant group x
phase interaction occurred for pregnenolone (F2,26= 3.7, P = .03), progesterone (F2,25 = 5.0, P = .01), and estradiol (F2,25 = 3.96, P = .03). Between-group differences for these hormones occurred in
the late luteal phase (pregnenolone: F1,26 = 7.9, P = .009; progesterone: F1,25 = 10.3, P = .004; and estradiol: F1,25 = 6.77, P = .02), although the late luteal difference in estradiol did not
pass the conservative Bonferroni correction. Analysis of between-group difference
in 5DHP levels was limited to the mid luteal phase secondary to limited
sensitivity of the assay to detect follicular phase levels. Women with PMDD
had significantly higher levels of 5DHP in the mid luteal phase than
healthy controls (F1,12 = 5.3, P = .04).
RELATIONSHIP BETWEEN PLASMA NEUROACTIVE STEROIDS AND CORTICAL GABA
LEVELS
Significant between-group differences in the relationship between hormones
and GABA were observed for estradiol (F1,31 = 13.1, P = .001), progesterone (F1,31 = 13.8, P = .001), allopregnanolone (F1,31 = 8.7, P = .01), and the progestrone-allopregnanolone ratio (F1,31
= 5.9, P = .02). Pregnenolone and the pregnenolone-allopregnanolone
ratio had no significant overall or by group impact on GABA levels. As follow-up
to the significant interaction tests, separate regression lines were estimated
for healthy controls and participants with PMDD and are shown in Figure 3. Estradiol ( = -.23;
95% confidence interval [CI], -.42 to -.05), progesterone (
= -.12; 95% CI, -.21 to -.04), and allopregnanolone (
= -.19; 95% CI, -.34 to -.05) were significantly negatively
associated with GABA levels in healthy controls, whereas estradiol and progesterone
were significantly positively associated with GABA levels in participants
with PMDD (for estradiol: = .36; 95% CI, .08-.63; and for progesterone:
= .13; 95% CI, .02-.25). The relationship between cortical GABA levels and
allopregnanolone in the PMDD group was not significant ( = .12; 95%
CI, -.04 to .28).
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Figure 3. Mixed-model analyses of covariance
revealed significant between-group differences in the relationship between
the following hormones (on log scale) and -aminobutyric acid (GABA):
estradiol (A) (F1,31 = 13.1, P = .001), progesterone
(B) (F1,31 = 13.8, P = .001), and allopregnanolone
(C) (F1,31 = 8.7, P = .01). In the healthy controls,
estradiol ( = -.23; 95% confidence interval [CI], -.42 to -.05),
progesterone ( = -.12; 95% CI, -.21 to -.04), and
allopregnanolone ( = -.19; 95% CI, -.34 to -.05) were
negatively correlated with cortical GABA levels. In the group with premenstrual
dysphoric disorder (PMDD), there was a positive correlation between cortical
GABA levels and estradiol ( = .36; 95% CI, .08-.63) and progesterone
( = .13; 95% CI, .02-.25) and no significant relationship with allopregnanolone
( = .12; 95% CI, -.04 to .28). To convert estradiol to pg/mL,
divide by 3.67; progesterone to ng/dL, divide by 0.0318.
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COMMENT
To our knowledge, this report presents the first direct measurement
of the cortical level of a neurotransmitter across the menstrual cycle in
healthy women and women with PMDD. The most striking finding in this study
was the effect of diagnosis on the menstrual cyclicity seen in cortical GABA
levels in both groups. Cortical GABA levels decreased across the menstrual
cycle in healthy women, whereas the opposite occurred in women with PMDD.
These findings were not altered by participant age, whether the data were
analyzed for the operationalized group or for the entire sample, or whether
the data were analyzed based on day of cycle instead of menstrual cycle phase.
Women with PMDD have reduced cortical GABA levels during the follicular phase,
but they are not significantly different from healthy counterparts during
the mid or late luteal phase. These findings are consistent with those of
Schmidt et al,32 who suggest that the pathophysiologic
processes responsible for the symptoms associated with PMDD may not be restricted
to the late luteal phase. Furthermore, the magnitude of the change in GABA
levels from follicular to mid luteal phase was significant in both groups,
suggesting that most of the group x phase finding cannot be accounted
for by cortical GABA changes in one participant group alone.
Factors other than diagnosis or menstrual cycle phase that may have
influenced our findings include potential for instability in the GABA measurement
or, alternatively, the presence of a first scan effect. Each of these alternative
explanations is improbably based on previous data that the interscan variation
in cortical GABA levels in men who underwent scanning several times in 1 month
is 0.10 mmol/kg brain.22 Furthermore, the group
x phase findings for the GABA data were unchanged when women who underwent
scanning in an alternate sequence were removed from the analysis.
The decline in cortical GABA levels from the follicular to luteal phase
seen in healthy controls in the present study is in contrast to the plasma
GABA findings of Halbreich et al9 and suggests
that peripheral measures of GABA function may not accurately reflect central
function. Likewise, we did not detect a difference in cortical GABA levels
in those women with PMDD and a history of major depression compared with those
without such history; however, our sample size may have been a limiting factor.
The relationship between cortical GABA levels and symptoms in PMDD is
in contrast to that of major depression and panic disorder, where symptomatic
episodes are associated with reduced occipital cortex GABA.24-25
Our follicular phase GABA levels in the PMDD group (mean ± SD, 0.78
± 0.23 mmol/kg brain) were substantially lower than those reported
for women with major depression (melancholic subtype) (1.10 ± 0.66
mmol/kg brain)33-34 and a group
of men and women with panic disorder (1.08 ± 0.30 mmol/kg).24 In contrast, during the mid and late luteal phases
when our participants were symptomatic, their GABA levels were not unlike
those of the healthy controls in the present study. Although these findings
suggest that follicular phase GABA levels distinguish women with PMDD from
those with major depression and support the diagnostic distinction between
major depression and PMDD, these findings need to be confirmed in a study
of cortical GABA levels in MDD in which menstrual cycle phase is clearly defined.
Of interesting, our finding of a decrease in cortical GABA levels in healthy
controls as the endogenous levels of the neurosteroid GABA agonists rise is
consistent with 1H-MRS findings demonstrating a reduction in cortical
GABA levels in healthy controls after a single oral dose of 0.5 mg of the
GABA agonist clonazepam.24
The fact that allopregnanolone levels did not distinguish women with
PMDD from healthy counterparts is consistent with most studies17-19
but not all.35-36 Our finding
of higher late luteal phase estradiol and progesterone levels in the PMDD
group can be contributed to having studied a greater proportion of these women
(50% vs 33%) more than 3 days before the onset of menstrual flow.
In the present study, the relationship between gonadal steroids and
cortical GABA levels in healthy women was opposite to that seen in those with
PMDD. For healthy women, the rise in estradiol, progesterone, and allopregnanolone
levels in the mid luteal phase signaled a decrease in cortical GABA levels
that persisted, despite hormonal declines in the late luteal phase. This pattern
would be consistent with the hypothesis that these or related hormones directly
or indirectly depress GABA synthesis, perhaps via their facilitation of GABAA function. However, cautious interpretation of this finding is warranted
for several reasons. First, it is curious that estradiol, which is a GABAA antagonist1-2 and would
be expected to oppose the GABA neuronal effects of the 3-reduced progesterone
metabolites, appeared in this study to have either the same directional effect
or a weaker antagonistic effect on GABA levels. Second, the gonadal steroid
levels, which were determined in a commercial laboratory, are known to increase
in a predictable fashion from the follicular to mid luteal phase. These expected
hormonal fluctuations may have enhanced the likelihood of obtaining a significant
correlation between hormones and GABA levels, giving the appearance of driving
the GABA levels down or up in the healthy controls and participants with PMDD,
respectively.
With these caveats considered, the rise in cortical GABA levels across
the menstrual cycle and the positive correlation between gonadal steroid levels
and cortical GABA levels in participants with PMDD could have several explanations.
First, PMDD may be associated with an abnormality in GABAA receptor
function that conveys attenuated GABA neuronal sensitivity to the inhibition-enhancing
effects of agents that typically facilitate GABAA receptor function.
This hypothesis would be consistent with the literature suggesting a luteal
phase–specific decrease in cortical inhibition11-12
and reduced sensitivity to the behavioral and physiologic effects of a benzodiazepine6 and the neurosteroid pregnanolone7
administration in women with PMDD. Our finding that allopregnanolone had a
significant impact on cortical GABA levels in healthy controls but not those
with PMDD is consistent with these findings. Preclinical studies12
suggest this phenomenon may be secondary to allopregnanolone-induced expression
of the 4 subunit of GABAA, which conveys reduced sensitivity
to the facilitatory effects of agonists for this receptor.
This study parallels other human studies that indicate that benzodiazepine
administration24 and inhibition of GABA catabolism25 depress GABA levels, presumably by depression of
the expression or function of the GABA synthetic enzyme glutamic acid decarboxylase
67 (GAD67). Continuing with this theory, these findings suggest
that feedback inhibition of GAD67 by GABAA receptor
agonists outweighs the stimulatory effects of estradiol on GAD67
activity reported in some brain regions in rodents.37-38
For example, the rise in cortical GABA levels across the menstrual cycle could
reflect the induction of factors that reduce GABAA receptor function
in the luteal phase and contribute to anxiety in patients with PMDD.
However, this study has several limitations that influence interpretation
of its results. This study was unable to differentiate whether fluctuations
in cortical GABA levels reflect changes in GABA synthesis or GABA turnover.
This distinction may become possible as carbon 13 MRS techniques are developed
for directly measuring these processes.39 The
naturalistic design of this study limits the ability to determine the impact
of individual hormones on cortical GABA levels. This could be rectified by
conducting 1H-MRS studies in menstruating women using gonadotropin-releasing
hormone agonists with add-back paradigm to isolate the effects of individual
hormones on cortical GABA levels. Finally, although the occipital cortex receives
input from many cortical and limbic regions, it is not generally implicated
in the pathogenesis of mood disorders. Therefore, the findings of this study
may be "downstream" from the neural circuitry of mood regulation.
In summary, this study documented menstrual cycle–related changes
in cortical neurochemistry in healthy women. Future studies will be needed
to further characterize the nature and functional consequences of this phasic
GABAergic modulation in healthy women. This finding also highlights the importance
of incorporating menstrual cycle phase within clinical research designs involving
menstruating women.
This study also begins the important and complicated process of mapping
the neurochemical determinants of PMDD. Premenstrual dysphoric disorder presents
unique challenges to the study of brain chemistry. Postmortem studies of cortical
neurotransmitter systems in PMDD are probably impossible for several reasons:
(1) valid diagnosis requires prospective assessment during multiple menstrual
cycles; therefore, retrospective assessments from unintentional deaths are
not likely to be useful; (2) life-threatening illnesses generally impair the
regulation of the menstrual cycle and therefore prevent the use of brain tissue
collected from young women; and (3) the onset of menopause prevents the use
of brain tissue collected from elderly patients. Therefore, in conjunction
with a solid foundation in preclinical research, molecular brain imaging,
despite its limitations, seems uniquely suited for exploring the neurochemistry
of PMDD.
AUTHOR INFORMATION
Submitted for publication October 19, 2001; final revision received
March 7, 2002; accepted March 15, 2002.
This study was funded in part by the National Institute of Mental Health
(grant K23 MH01830-01) (Dr Epperson); the National Alliance for Research in
Schizophrenia and Depression (Young Investigator Award) (Drs Weiss, Epperson,
and Mason); and the National Institute of Neurological Disorders and Stroke
(grant T32 NS07416-01) (Dr Haga). Additional support for this study came from
the Department of Veterans Affairs (National Center for Post-traumatic Stress
Disorder, Alcohol Research Center) and the National Institute of Alcohol Abuse
and Alcoholism (grants P50 AA12870-01 and KO2 AA 00261-01).
Dr Epperson thanks Peter Schmidt, MD, and Robert H. Purdy, PhD, for
their insightful mentorship. In addition, we thank Kathryn Czarkowski, MS,
for her help in recruiting and managing participants and Shani Osbourne, BA,
for her technical support.
Corresponding author and reprints: C. Neill Epperson, MD, Yale Behavioral
Gynecology Program, Departments of Psychiatry and Obstetrics and Gynecology,
Yale University School of Medicine University Towers, Suite 2H, 100 York St,
New Haven, CT 06511 (e-mail: neill.epperson{at}yale.edu).
From the Departments of Psychiatry (Drs Epperson, Haga, Mason, Gueorguieva,
Weiss, and Krystal), Obstetrics and Gynecology (Dr Epperson), Diagnostic Radiology
(Dr Rothman), and Epidemiology and Public Health (Dr Gueorguieva), Yale University
School of Medicine, New Haven, Conn; and Department of Pharmacology, University
of Toronto School of Medicine, Toronto, Ontario (Drs Sellers and Zhang).
REFERENCES
| |
1. Majewska MD. Neurosteroids: endogenous bimodal modulators of the GABAA
receptor: mechanism of action and physiologic significance. Prog Neurobiol. 1992;38:379-395.
FULL TEXT
|
ISI
| PUBMED
2. Baulieu EE, Schumacher M. Synthesis and function of neurosteroids. In: Genazzani AR, Petraglia F, Purdy RH, eds. The Brain: Source and Target for Sex Steroid Hormones. New York, NY:
Parthenon Publishing Group; 1996:5-24.
3. McEwen BS, Alves SE. Estrogen actions in the central nervous system. Endocr Rev. 1999;20:279-307.
FREE FULL TEXT
4. Majewska MD, Harrison NL, Schwartz RD, Barker JL, Paul SM. Steroid hormone metabolites are barbiturate-like modulators of the
GABA receptor. Science. 1986;232:1004-1007.
FREE FULL TEXT
5. McCormick CM, Teillon SM. Menstrual cycle variation in spatial ability: relation to salivary
cortisol levels. Horm Behav. 2001;39:29-38.
FULL TEXT
| PUBMED
6. Sundstrom I, Nyberg S, Backstrom T. Patients with premenstrual syndrome have reduced sensitivity to midazolam
compared to control subjects. Neuropsychopharmacology. 1997;17:370-381.
FULL TEXT
|
ISI
| PUBMED
7. Sundstrom I, Andersson A, Nyberg S, Ashbrook D, Purdy RH, Backstrom T. Patients with premenstrual syndrome have a different sensitivity to
a neuroactive steroid during the menstrual cycle compared to control subjects. Neuroendocrinology. 1998;67:126-138.
FULL TEXT
|
ISI
| PUBMED
8. Yonkers KA. The association between premenstrual dysphoric disorder and other mood
disorders. J Clin Psychiatry. 1997;58(suppl):19-25.
9. Halbreich U, Petty F, Yonkers K, Kramer GL, Rush AJ, Bibi KW. Low plasma gamma-aminobutyric acid levels during the late luteal phase
of women with premenstrual dysphoric disorder. Am J Psychiatry. 1996;153:718-719.
FREE FULL TEXT
10. Smith MJ, Adams LF, Schmidt PJ, Rubinow DR, Wassermann EM. Effects of ovarian hormones on human cortical excitability. Ann Neurol. 2002;51:599-603.
FULL TEXT
|
ISI
| PUBMED
11. Smith MJ, Greenberg BD, Adams LF, Schmidt PJ, Rubinow DR, Wassermann EM. Menstrual-related changes in cortical excitability in women with PMS
and controls [abstract]. Biol Psychiatry. 2002;47(suppl):69S.
12. Smith SS, Gong QH, Hsu F, Markowitz RS, French-Mullen JM, Li X. GABAA receptor -4 subunit suppression prevents withdrawal
properties of an endogenous steroid. Nature. 1998;392:926-929.
FULL TEXT
| PUBMED
13. Uzunova V, Sheline Y, Davis JM, Rasmusson A, Uzunov DP, Costa E, Guidotti A. Increase in the cerebrospinal fluid content of neurosteroids in patients
with unipolar major depression who are receiving fluoxetine or fluvoxamine. Proc Natl Acad Sci U S A. 1998;95:3239-3244.
FREE FULL TEXT
14. Uzunov DP, Cooper TB, Costa E, Guidotti A. Fluoxetine-elicited changes in brain neurosteroid content measured
by negative ion mass fragmentography. Proc Natl Acad Sci U S A. 1996;93:12599-12604.
FREE FULL TEXT
15. Griffin LD, Mellon SH. Selective serotonin reuptake inhibitors directly alter activity of neurosteroidogenic
enzymes. Proc Natl Acad Sci U S A. 1999;96:13512-13517.
FREE FULL TEXT
16. Backstrom T, Sanders D, Leask R, Davidson D, Warner P, Bancroft J. Mood, sexuality, hormones, and the menstrual cycle, II: hormone levels
and their relationship to the premenstrual syndrome. Psychosom Med. 1983;45:503-507.
FREE FULL TEXT
17. Wang M, Seippel L, Purdy RH, Backstrom T. Relationship between symptom severity and steroid variation in women
with premenstrual syndrome: study on serum pregnenolone, pregnenolone sulfate,
5-pregnane-3,20-dione and 3-hydroxy-5-pregnan-20-one. J Clin Endocrinol Metab. 1996;81:1076-1082.
ABSTRACT
18. Rubinow DR, Hoban MC, Grover GN, Galloway DS, Roy-Bryne P, Andersen R. Changes in plasma hormones across the menstrual cycle in patients with
menstrually related mood disorder and in control subjects. Am J Obstet Gynecol. 1988;158:5-11.
ISI
| PUBMED
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