The principal finding from this study is that PMDD is associated with a clear increase in baseline startle magnitude in the luteal phase compared to the follicular phase, while healthy female controls do not show cyclic changes in this measure of physiologic arousal. Although our finding in women with PMDD is novel, results from the healthy controls in this study are consistent with those from other laboratories (
Swerdlow et al, 1997;
Jovanovic et al, 2004). Given the heightened baseline startle and the negative emotional state of women with PMDD during the luteal phase, our finding that affective modulation of the ASR magnitude is intact and consistent in women with PMDD is intriguing. Together these findings suggest that, for women with PMDD, the luteal phase is a period of physiologic hyperarousal that may serve to magnify the intensity of emotional states without altering the valence of these affective states.
Several factors may have contributed individually or in concert to these findings. As mentioned previously, an organism’s emotional and perceptual state has a dramatic and well-documented impact on the ASR, with pleasant states diminishing and adverse states accentuating, the amplitude of the eye blink (
Davis et al, 1997; reviewed by
Koch, 1999;
Lang et al, 1990,
Schmid et al, 1995). Our PMDD subjects were symptomatic during the luteal-phase startle study when their ASR magnitude was most pronounced. However, the relatively asymptomatic (with respect to their primary PMDD symptoms) follicular phase was associated with a baseline ASR that was similar to that seen in healthy controls. This state-dependent accentuation of baseline startle in women with PMDD is similar to that seen in individuals with posttraumatic stress disorder (PTSD) when studied at baseline and then under conditions of contextual threat. Although exaggerated startle response is one of the symptoms of PTSD, a number of studies have found a normal (
Grillon et al, 1996;
Orr et al, 1997) baseline startle when individuals with PTSD are studied in ‘safe’ conditions. However, when placed in the dark or in the context of threat of electric shock, the ASR magnitude is more consistently accentuated (
Morgan et al, 1995).
This distinction is important as the ASR increases, seen with anxious anticipation and/or stress arising from a contextual threat, are thought to be mediated by input from the bed nucleus of the stria terminalis (BNST;
Davis and Shi, 1999). The BNST is a basal forebrain structure that is highly responsive to gonadal steroids (
Isgor et al, 2002;
Auger and Vanzot, 2006), is rich in GABAergic neurons (
Herman et al, 2004) and glutamatergic projections (
Dumont and Williams, 2004). A recent study in rodents suggests that fear-potentiated startle, which is mediated by the amygdala, is not modulated by estrogen, progesterone or allopregnanolone (ALLO). However, in a rodent model of stress/anxiety, ALLO and progesterone (presumably via ALLO) reversed the ASR accentuating effects of corticotropin releasing hormone (CRH) infused into the BNST (
Toufexis et al, 2004). Compared to healthy controls and to themselves in the follicular phase, the PMDD subjects in our study were significantly more anxious/tense and irritable during the luteal phase and, as such, did not appear to require any external provocation (unpleasant picture viewing) to exhibit a heightened arousal. That we did not find a significant correlation between physiologic (ASR magnitude) and behavioral (STAI and DRSP) measures is consistent with a number of other startle studies (
Dichter et al, 2004;
Grillon et al, 1996,
1998a), and may reflect an insufficient sample size rather than a true absence of a relationship. Alternatively, startle and subjective ratings may reflect distinct processes. Startle is a low-level response and verbal report of anxiety involves more elaborate cognitive activity. This latter explanation is consistent with findings that the amygdala can be activated without alteration in conscious mood (
Morris et al, 1998).
Menstrual cycle fluctuations in neuroactive steroids could also contribute directly to alterations in the ASR by modulating neurotransmitters and/or brain regions involved in the startle reflex (
Koch, 1999) or the emotional modulation thereof (
Van Nobelen and Kokkinidis, 2006). Through a series of elegant experiments, Gulinello and colleagues have demonstrated that timing and length of progesterone and ALLO exposure or withdrawal are critical with respect to the anxiolytic properties of ALLO and the pharmacologic profile of the GABA
A receptor (
Gulinello et al, 2002,
2003;
Gulinello and Smith, 2003). Acute (minutes) and long-term (>5 days) administration of progesterone or ALLO is anxiolytic in male and female rodents (according to behavior in the elevated plus maze task), and does not lead to increases in α4 GABA
A receptor subunit configuration which is associated with diminished benzodiazepine sensitivity (
Gulinello and Smith, 2003). However, short-term administration (48 h) leads to an increase in anxiety, α4 subunit expression, and benzodiazepine insensitivity. Pertinent to our present study, female rodents exposed to short-term administration (
Gulinello and Smith, 2003) or withdrawal (
Gulinello et al, 2003) of either steroid demonstrate accentuation of the ASR that was correlated with anxiety-like behavior in the elevated plus maze (
Gulinello and Smith, 2003).
That the length of progesterone and ALLO exposure may be critical with respect to its modulation of the ASR magnitude is interesting in light of our present data and those from
Swerdlow et al (1997), indicating that the acoustic startle magnitude remains consistent across the highly divergent neuroendocrine milieu of the menstrual cycle in healthy human females. It is difficult to extrapolate from rodent to human the exact duration of exposure necessary to make the switch between the anxiolytic and anxiogenic profiles of ALLO. However, one could assume that our healthy subjects who were studied a mean of 5.5 days post-ovulation were captured during the ‘chronic’ phase of progesterone/ALLO exposure. Nevertheless, both our PMDD and healthy control subjects were studied a similar number of days post-ovulation and had similar luteal-phase progesterone levels. Thus timing in relationship to ovulation and/or quantitative differences in peripheral progesterone concentrations cannot explain the disparate findings in ASR magnitude between women with PMDD and healthy controls.
Instead, we suggest that luteal-phase accentuation of the ASR magnitude in women with PMDD reflects the aberrant interaction between neuroactive steroids and brain function. This neuroendocrine milieu contributes to the emergence of PMDD symptoms (
Schmidt et al, 1998) and what appears to be the phase-specific heightening of physiologic arousal. The notion that women with PMDD demonstrate altered central nervous system response to normal menstrual cycle-related fluctuations in neuroactive steroids is supported by the findings of numerous other groups using a wide range of experimental methods including hormonal manipulations (
Schmidt et al, 1998), transcranial magnetic stimulation (TMS;
Smith et al, 2003), and pharmacologic challenges (
Sundstrom et al, 1998,
1999). Women with PMDD show a depressive response to administration of exogenous ovarian steroids (
Schmidt et al, 1998), demonstrate a luteal phase-specific decrease in neuronal inhibition and enhanced facilitation with TMS (
Smith et al, 2003), and exhibit a luteal-phase subsensitivity to GABA
A receptor agonist administration (
Sundstrom et al, 1998,
1999;
Sundstrom-Poromaa et al, 2003). Together with the finding that menstrual cycle-related fluctuations in occipital cortex GABA concentrations are altered in women with PMDD (
Epperson et al, 2002), there is a growing body of literature in humans that implicates GABAergic dysregulation in the pathogenesis of PMDD and perhaps the physiologic hyperarousal seen here in women with PMDD during the luteal phase.
In addition to direct modulation of brain systems involved in the ASR, neuroactive steroids may have indirect effects on the ASR via the hypothalamic pituitary adrenal (HPA) axis which mediates the organism’s stress response. Interestingly, GABAergic neurons in the BNST as well as preoptic area and hypothalamus can inhibit outflow from the parvocellular paraventricular nucleus neurons and, thus, reduce adrenocorticotropin hormone (ACTH) secretion (
Tringali et al, 2004;
Herman et al, 2004). Although estrogen and progesterone have been shown in some studies to enhance and diminish HPA axis activation (
Fonseca et al, 2001;
Patchev et al, 1994), respectively, ALLO concentrations in plasma and brain increase as a result of stress (
Barbaccia et al, 1997,
2001), perhaps as a compensatory mechanism. Women with PMDD fail to demonstrate the normal increase in ALLO seen in healthy subjects under conditions of stress (
Monteleone et al, 2000;
Girdler et al, 2001;
Droogleever Fortuyn et al, 2004;
Lombardi et al, 2004), or during HPA axis activation with ACTH administration (
Genazzani et al, 1998;
Lombardi et al, 2004). In the context of this study, the acoustic startle procedure can be viewed as mildly stress inducing. However, without cerebral spinal fluid and/or plasma levels of ALLO both immediately before and after the procedure, we were not able to determine whether the procedure was sufficiently stressful to increase ALLO production in healthy controls or whether women with PMDD lacked this response.
Between-group differences in the perception of stress or the number of stressors in the weeks surrounding each of the test sessions was not directly assessed. However, several studies indicate that women with significant premenstrual mood symptoms report life events as more stressful and/or less positive during the premenstruum than compared to the follicular phase of the menstrual cycle (
Gallant et al, 1992;
Woods et al, 1998), although they do not experience an increased frequency of stressful life events compared to healthy menstruating women or males (
Schmidt et al, 1990;
Lewis, 1995). Thus, it is the perception of events as more stressful that could render women with PMDD in a more aversive state and heighten their baseline response to the startle procedure. However, if the enhanced baseline ASRs were merely a matter of negative perceptions or affect, we would have anticipated that women with PMDD would have had an altered response to affective modulation of the ASR magnitude.
Although our findings in women with PMDD of a state and menstrual cycle phase-dependent heightening of baseline ASR in the presence of intact affective modulation of ASR are intriguing, lessons learned from the growing acoustic startle literature suggest that these findings are preliminary until replicated. However, these findings begin to address the proverbial chicken or the egg question; namely whether the negative mood state itself or the abnormal neuroendocrine milieu that mediated the negative mood state of the luteal phase alters the ASR physiology. The intact affective modulation of the ASR seen in women with PMDD in this study would suggest that the latter is more critical in PMDD. Studies in which women also undergo fear-potentiated startle would help to tease apart brain areas that may be more or less responsive to gonadal hormone and neurosteroid fluctuations in women with PMDD, and lead to further knowledge regarding the complex pathogenesis of this disorder. In addition, a measure of perceived stress of the procedure and/or peristudy life events would contribute valuable information regarding the potential impact of menstrual cycle- and/or diagnosis-specific changes in stress on physiologic arousal.
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