The 5-HT1D/1B receptor agonist sumatriptan enhances fear of simulated speaking and reduces plasma levels of prolactin

Abstract

This study measured the effects of the preferential 5-HT1D/1B receptor agonist sumatriptan in healthy volunteers who performed the Simulated Public Speaking Test (SPST), which recruits the neural network involved in panic disorder and social anxiety disorder. In a double-blind, randomised experiment, 36 males received placebo (12), 50 mg (12) or 100 mg (12) of sumatriptan 2 h before the SPST. Subjective, physiological and hormonal measures were taken before, during and after the test. The dose of 100 mg of sumatriptan increased speech-induced fear more than either a 50mg dose of the drug or placebo. The largest dose of sumatriptan also enhanced vigilance more than placebo, without any change in blood pressure, heart rate or electrical skin conductance. Sumatriptan decreased plasma levels of prolactin. A significant but moderate increase in plasma cortisol after SPST occurred, independent of treatment. Because sumatriptan decreases 5-HT release into the extracellular space, the potentiation of SPST-induced fear caused by the drug supports the hypothesis that 5-HT attenuates this emotional state. As acute administration of antidepressants has also been shown to enhance speaking fear and increase plasma prolactin, in contrast to sumatriptan, the 5-HT regulation of stress-hormone release is likely to be different from that of emotion.

Keywords

Serotonin 5-HT1D/1B receptor sumatriptan anxiety public speaking hypothalamic–pituitary–adrenal axis

Introduction

Human experimental models are very useful tools in translational medicine because they are an intermediate step between basic and clinical research. In the last two decades, our research group conducted a series of pharmacological studies (de Oliveira et al., 2011; Garcia-Leal et al., 2010; Graeff et al., 1985; Guimarães et al., 1987, 1997; Hetem et al., 1996; Silva et al., 2001; Zuardi et al., 1993) of the role of serotonin (5-HT) in unconditioned fear using the Simulated Public Speaking Test (SPST) (Guimarães et al., 1989; McNair et al., 1982). This test consists of the performance of a speech in front of a videocamera in which the participant can see himself/herself on a monitor.

As previously discussed (Deakin and Graeff, 1991; Graeff, 2010), it is supposed that public speaking evokes unconditioned fear, activating brain regions responsible for the organisation of defensive responses to immediate threats. This proposal is based on the fact that the fear of public speaking is highly prevalent (Furmark et al., 1999; Stein et al., 1994, 1996) and SPST is distressful in all of the volunteers, independent of the personality anxiety trait (Palma et al., 1994).

A significant neuroimaging study of defensive behaviour in healthy volunteers showed that when a virtual predator is in close proximity or makes actual contact with the virtual prey, brain activation shifts from the prefrontal cortex to the midbrain periaqueductal grey matter (Mobbs et al., 2007). In addition, preclinical reported evidence suggests that 5-HT inhibits neuronal systems in the dorsal periaqueductal grey (DPAG) matter, reducing the expression of proximal defence reactions that are related to panic (Graeff, 2004).

The SPST has also been related to Panic Disorder (PD) and Social Anxiety Disorder (Graeff, 2010). This hypothesis was based on the SPST pharmacological response to drugs that interfere with serotonergic neurotransmission (Deakin et al., 1992, 1994). Accordingly, the results obtained in healthy volunteers showed that the acute administration of drugs that reduce serotonergic activity increased SPST-induced fear (Garcia-Leal et al., 2010; Guimarães et al., 1987; Silva et al., 2001), which corresponds to the worsening of panic symptoms observed at the beginning of PD treatment with antidepressants (Kent et al., 1998). Antidepressants are believed to enhance serotonergic activity after chronic use but are also believed to reduce the same activity after acute administration due to the preferential stimulation of autosomic 5HT1A receptors (Guimarães et al., 1987). In contrast, increasing the release of 5-HT with d-fenfluramine reduced the same fear (Hetem et al., 1996), which corresponds with the clinical improvement that is observed in PD patients as a result of taking this drug (Hetem et al., 1993; Solyom, 1994).

Sumatriptan has high affinity for 5-HT1D > 5-HT1B > 5-HT 1A receptors (Deleu and Hanssens, 2000) and is clinically used for the treatment of migraines (Dodick and Martin, 2004). Therefore, it can be used as a tool to study serotonergic functions in humans. Acute administration of sumatriptan to obsessive compulsive disorder (OCD) patients, in which 5-HT1D receptors are assumed to play a critical role (Zohar et al., 2004), exacerbated obsessive compulsive symptoms (Gross-Isseroff et al., 2004; Stein et al., 1999; Stern et al., 1998); however, there was a negative report (Pian et al., 1998). To the best of our knowledge, the effect of sumatriptan in PD was tested in just one study, and the acute administration of sumatriptan worsened panic symptoms and increased anxiety (Amital et al., 2005).

Challenge studies with sumatriptan in healthy volunteers did not cause subjective alterations compared with placebo (Gross-Isseroff et al., 2004; Pallanti et al., 2010). However, animal studies showed that either stimulation of the 5-HT1B receptor by pharmacological agonists (Lin et al., 2002; Sari, 2004) or overexpression of this receptor produces anxiety-like behaviour (Clement et al., 1996).

Because sumatriptan has not yet been used for the investigation of human experimental fear, this study aims to measure the psychological and physiological effects of acutely administered sumatriptan in healthy volunteers that underwent the SPST. Because the stimulation of 5-HT1D/1B presynaptic receptors by sumatriptan decreases 5-HT release (Davidson and Stamford, 1995; Hoyer and Middlemiss, 1989), we hypothesised that sumatriptan would increase SPST-induced fear. Among the physiological measures, plasma levels of prolactin and cortisol were assessed, as the release of these hormones is enhanced by 5-HT (Gross-Isseroff et al., 2004; Pinessi et al., 2003; Raap and Van de Kar, 1999; van Praag et al., 1987; Yatham and Steiner, 1993). Therefore, a decrease in plasma levels of both hormones is expected to occur following the acute administration of sumatriptan.

Methods and materials

Participants

The sample was composed of healthy male volunteers, at least 18 years of age, with at least eight years of formal education, recruited from students of the local university community. The study was approved by the local ethics committee and an informed consent form was signed by all the participants.

The study was publicised through advertisements, and the volunteers who expressed an interest in participating were initially subjected to a screening telephone interview, in which the procedures involved in the study were briefly explained and some exclusion criteria (described below) were evaluated. Those who retained their interest in participating in the study and who did not meet any of the exclusion criteria were invited for an in-person interview, the Mini International Neuropsychiatric Interview (MINI) (Sheehan et al., 1998), translated into Portuguese (Amorim, 2000). The interviews were conducted by a trained nurse to exclude any current or past psychiatric diagnosis. We also excluded participants with histories that included the following: illicit drug use or the use of medication within two weeks prior to the experiments; excessive consumption of alcohol (> 20 U/week), caffeine (> 6 cups of coffee/day) or cigarettes (> 10 cigarettes/day); body mass index (BMI) under 18.5 or above 25; and participation in research involving experimental drug intake within the previous two months. Because of the contraindication of sumatriptan for patients with heart disease, all volunteers were previously subjected to an electrocardiogram.

As depicted in Figure 1, 36 healthy male volunteers between 19 and 32 years of age (mean = 25.60; SD = 3.40) were submitted to the experimental session.

Although the presence of a current psychiatric diagnosis had been previously ruled out, the presence of sub-clinical depressive and anxious symptoms was also evaluated by the Beck Depression Inventory (BDI) (Beck et al., 1961), translated and adapted into Portuguese (Gorenstein and Andrade, 1996), and the Beck Anxiety Inventory (BAI) (Beck et al., 1988), translated and adapted into Portuguese (Cunha, 2001). The Brazilian version (Biaggio et al., 1976) of the State-Trait Anxiety Inventory-Trait form (STAI-T) (Spielberger, 1983) was used to measure the tendency of each participant to react with more or less anxiety.

Subjective measures

Two self-applicable instruments were used to evaluate subjective anxiety during the experimental session: the Portuguese version (Zuardi and Karniol, 1981) of the Visual Analogue Mood Scale (VAMS) (Norris, 1971) and the Bodily Symptoms Scale (BSS) (Zuardi et al., 1993). As described previously (Garcia-Leal et al., 2010; Parente et al., 2005), the VAMS is composed of 16 items, and for each item, the subject is asked to mark a point on a 100-mm line between two adjectives of opposite meaning that represents his present feelings. The middle of this line represents his normal mood. The items are distributed into four factors, named as follows: 1) anxiety, composed of the items calm–excited, relaxed–tense, and tranquil–troubled; 2) sedation, composed of alert–drowsy and attentive–dreamy; 3) cognitive impairment, composed of quick-witted–mentally slow, proficient–incompetent, energetic–lethargic, clear-headed–muzzy, gregarious–withdrawn, well-coordinated–clumsy, and strong–feeble; and 4) discomfort, composed of the items interested–bored, happy–sad, contented–discontented, and amicable–antagonistic (Parente et al., 2005; Zuardi et al., 1993).

The BSS consists of 21 items that describe somatic complaints related to anxiety, with six levels of possible responses (no symptoms to extremely marked symptoms), namely, fatigue, weakness, lethargy, headache, muscle tension, tremor, hunger, thirst, coordination difficulty, perspiration, palpitation, dyspnoea, agitation, urinary urgency, nausea, dry mouth, blurred vision, dizziness, defecation urgency, dysuria and parenthesis (Zuardi et al., 1993).

Physiological measures

Skin conductance

A computer-controlled, voltage constant (0.6 V) module with automatic back-off (Contact Precision Instruments, UK) was used to measure skin conductance. Electrodes (Beckman, UK) were fixed with adhesive tape, and contact with the skin was established through high conductance gel (KY gel, Johnson & Johnson, Brazil). The skin conductance level (SCL) and the number of spontaneous fluctuations (SFs) of the skin conductance were evaluated.

Arterial blood pressure and heart rate

Systolic blood pressure (SBP) and diastolic blood pressure (DBP) were measured with a Becton–Dickinson sphygmomanometer and heart rate (HR) was quantified by counting the pulse rate.

Plasma cortisol and prolactin measurement

The blood samples were centrifuged at 3000 rpm and plasma was kept frozen at −20°C until the time of cortisol and prolactin assays. All samples from an individual were analysed in duplicate in the same assay. Plasma cortisol was determined by radioimmunoassay after extraction with ethanol, as described previously (Santiago et al., 1996), and prolactin was measured by solid-phase, two-site chemiluminescent immunometric assay (DELFIA 80/505, Wallac Oy, Turku, Finland). The assay sensitivity and intra- and inter-assay coefficients of variation were as follows: 1.20 µg/dL, 3.94 and 10.40% for cortisol, and 0.50 ng/mL, 0.36 and 4.26% for prolactin.

Experimental design

The participants were asked to avoid eating, drinking or smoking for one hour before the session; to not drink alcohol for 48 hours before the experimental session; to avoid stress activities (for example, a competition or an academic test) on the day of and in the morning before the session; and to sleep for at least six hours. The participants were also instructed to take a light lunch around noon. The procedures of the experimental session can be observed in Table 1. The session started at 14:00, following the methodology of a previous study (Garcia-Leal et al., 2010), due to the circadian rhythm of cortisol. At this time, cortisol is falling, so it is easier to observe the response of cortisol, avoiding a ceiling effect that could occur if the assessment were performed in the morning, when cortisol levels are high. Prolactin levels are high during the night, and they sharply decrease early in the morning so that circadian rhythm effects were likely to be negligible during the experimental session.

Table 1.

Timetable of the experimental session, beginning at 14:00.

Time in minutes	Procedure
0–15	Instructions about the cannulation, psychological and physiological measures and drug intake
15–30	Cannulation
30–60	Rest
60–74	(B) Basal measures (VAMS, BSS, BP, HR, skin conductance, cortisol and prolactin)
74–75	Drug intake
75–195	Rest
195–210	(Pt) Pre-test measures (VAMS, BSS, BP, HR, skin conductance, cortisol and prolactin)
210–220	Instructions about the SPS
220–222	(Pr) Speech preparation (skin conductance)
222–232	(Pr) Preparation measures (VAMS, BSS, BP, HR)
232–234	(S) Speech performance (skin conductance)
234–244	(S) Performance measures (VAMS, BSS, BP, HR)
244–246	Continuation of speech (skin conductance)
246–251	0 min post-test cortisol and prolactin
251–261	Rest
261–276	15 min post-test (VAMS, BSS, BP, HR, skin conductance, cortisol and prolactin)
276–286	30 min post-test (VAMS, BSS, cortisol and prolactin)
286–306	Rest
306–316	60 min post-test (VAMS, BSS, cortisol and prolactin)

VAMS: Visual Analogue Mood Scale; BSS: Bodily Symptoms Scale; BP: blood pressure; HR: heart rate; SPS: simulated public speaking.

The procedures involved in the experimental session have been described in previous studies (Garcia-Leal et al., 2005, 2010; Parente et al., 2005). As observed in Table 1, in the beginning of the experimental session, instructions were provided regarding the cannulation, subjective and physiological measures, and drug intake. After the written consent of the participant was obtained, an antecubital vein was punctured by means of a flexible catheter (abbocath) and the venous access was maintained throughout the procedure with saline solution. The subjects remained at rest and were not allowed to sleep or eat during the testing session. After 30 minutes of rest, physiologic and subjective basal measures (B) were performed, and immediately thereafter, capsules containing either placebo or 50 or 100 mg of sumatriptan were orally administered in a random, double-blind manner. Placebo and sumatriptan capsules were prepared by the hospital pharmacist, who was not involved with the project. The treatment groups were identified at the end of the data collection. Two-hour intervals were necessary to reach the ideal plasmatic concentration of sumatriptan; physiologic and subjective pre-test measures (Pt) were then taken, and the second part of the informed consent form was provided. The subject was then informed that he would have 2 min to prepare a speech about the city’s public transportation system, following the methodology of previous studies (Garcia-Leal et al., 2010; Parente et al., 2005). This subject matter was intended to be an emotionally neutral topic of common knowledge, thus excluding the possibility that the theme of the speech would evoke fear. Each participant was also told that the speech would be recorded on videotape and later analysed by a psychologist. After the written agreement of the volunteer was obtained, physiologic and subjective preparation measures (Pr) were taken before the participant began the speech in front of the camera. During the speech, the participant observed his own image on the TV screen. After 2 min, the volunteer was interrupted, and the physiologic and subjective performance measures (S) were taken. Two more minutes of the speech were recorded, and physiologic and subjective post-test measures (0, 15’, 30’ e 60’) were taken 0, 15, 30 and 60 min after the end of the speech.

Data analysis

Data analysis was performed with the Statistical Package for the Social Sciences (SPSS) program. VAMS factors, the total score of BSS, the cortisol and prolactin plasma levels, HR, SBP and DBP, the SCL and the total number of SFs were subjected to two-factor (factors group and phases), repeated measures ANCOVA, with the basal measures as covariates. The degrees of freedom of the repeated factors were corrected by the Huynh–Feldt epsilon. Post-hoc comparisons were conducted by one-way analysis of variance (ANOVA), followed by the Bonferroni test, or, in the case of repeated measures, by paired t-tests. The values of SCL were converted into natural logarithms (logns), with the addition of the constant value of 0.01. Age, years of study, BMI and total score of BDI, BAI, STAI-T were analysed by one-factor ANOVA. Values of p < 0.05 were considered to be significant. Three participants (two in the group that received 100 mg of sumatriptan and one of the placebo group) were excluded from statistical analysis due to errors in the completing of VAMS, and one volunteer in the 100 mg group was excluded from statistical analysis due to a failure to fill in the BSS.

Results

Participants

Table 2 shows the characteristics of the participants that were distributed in the three treatment groups. No differences among the experimental groups were found with regard to age, BMI, schooling, depressive (BDI) or anxious complaints (BAI), or anxiety trait (STAI-T).

Table 2.

Characteristics of the experimental subjects.

Characteristics	Placebo (n =12 )	Sumatriptan 50mg (n =12)	Sumatriptan 100mg (n =12)
Age	26.27 ± 1.25^a	24.75 ± 0.64	25.90 ± 1.00
BMI	24.76 ± 0.60	23.83 ± 0.95	24.35 ± 0.77
Years of study	14.55 ± 0.65	15.25 ± 0.45	15.50 ± 0.46
STAI-T	33.36 ± 2.40	30.67 ± 1.38	34.20 ± 2.24
BDI	5.45 ± 0.95	4.92 ± 0.93	4.10 ± 1.07
BAI	4.18 ± 1.63	1.92 ± 0.40	2.10 ± 0.58

Mean ± SEM.

BMI: body mass index; STAI-T: State Trait Anxiety Inventory-Trait; BDI: Beck Depression Inventory; BAI: Beck Anxiety Inventory.

Subjective measures

Figure 2 shows the effect of simulated public speaking (SPS) on the subjective states, as assessed by the VAMS factors.

Anxiety factor

The SPST differentially increased anxiety as a function of treatment (phase × treatment interaction F (6.60, 96.0) = 2.53; p = 0.022). The participants that received 100 mg of sumatriptan were more anxious than those that received placebo at the preparation (p = 0.007) and speech (p = 0.006) phases, and they were more anxious than those that received 50 mg of sumatriptan at the speech phase (p = 0.023).

Sedation factor

Sedation also differentially decreased according to drug treatment (phase × treatment interaction F (8.1, 117.43) = 133.07; p < 0.001). During the preparation (p = 0.008) and speech (p = 0.003) phases, the participants that received 100 mg of sumatriptan were less sedated (more vigilant) than placebo controls.

Cognitive impairment factor

There were no significant effects of either treatment or phase and no significant interaction between the two factors.

Discomfort factor

The SPS caused discomfort in all of the groups (phase factor F (4.66, 135.20) = 12.25; p < 0.001), but a significant difference in discomfort among the treatments was found (treatment factor F(2, 29) = 5.26; p = 0.011) independent of phase. The participants that received 100 mg of sumatriptan reported more discomfort than those that received 50 mg of sumatriptan throughout the experimental session (p = 0.020).

BSS

There was a nearly significant effect of phase (phase factor F (5.00, 145.00) = 2.01; p = 0.081), but no significant main effect of treatment with regard to the occurrence of bodily symptoms; there was also no significant phase × treatment interaction (data not shown).

Physiological measures

Plasma cortisol

Figure 3 shows changes in the plasma cortisol levels throughout the experimental session (phase factor F (3.03, 97.15) = 3.51; p = 0.018). There was no significant effect of treatment or significant phase × treatment interaction. An analysis with all participants, independent of treatment (n = 36) with comparisons among phases (paired t-test), showed that plasma cortisol levels significantly decreased from the basal to pre-test phase (t = 6.35, df = 35; p < 0.001), increased from the pre-test phase to immediately after the speech (t =2.91, df = 35; p = 0.006), and fell again from 15 to 30 min after the end of the speech (t = 3.23, df = 35; p = 0.003).

Plasma prolactin

A significant difference in plasma prolactin levels among treatments was found (treatment factor F (2, 32) = 7.40; p = 0.039). There was no significant effect of phase or a significant phase × treatment interaction. The participants that received 100 mg of sumatriptan had lower plasma prolactin levels than those that received placebo (p = 0.035) and 50 mg (p = 0.005). These data are illustrated in Figure 3.

Skin conductance

Table 3 shows that the SPST increased the SCL (phase factor F (2.13, 61.85) = 17.33; p < 0.001) and the number of SFs (phase factor F (2.98, 86.49) = 12.76; p < 0.001). Neither a significant main effect of treatment nor a significant phase × treatment interaction for these measures was found.

Table 3.

Physiological parameters.

Experimental Group	Phase	Skin conductance level (µS)		Spontaneous fluctuations		Systolic blood pressure (mmHg)		Diastolic blood pressure (mmHg)		Heart rate (bpm)
Placebo	Basal	1.78	±0.21	12.09	±2.09	124.58	±3.11	68.75	±2.04	69.42	±2.45
	Pre-test	1.88	±0.18	9.00	±1.48	125.92	±3.80	73.67	±2.72	60.83	±2.09
	Preparation	2.37	±0.18	19.73	±2.51	128.67	±3.37	77.17	±3.35	65.58	±3.18
	Speech	2.55	±0.15	20.86	±2.33	129.17	±3.65	78.92	±2.36	65.25	±3.15
	Final^a	2.47	±0.16	8.45	±1.69	123.92	±3.95	72.75	±3.10	62.25	±2.49
Sumatriptan 50mg	Basal	1.73	±0.14	5.75	±1.47	122.73	±3.28	66.91	±2.27	68.18	±2.20
	Pre-test	1.84	±0.16	7.67	±1.30	126.55	±3.52	70.27	±2.54	65.45	±3.27
	Preparation	2.42	±0.12	17.67	±2.87	125.73	±4.05	72.64	±2.57	64.27	±3.03
	Speech	2.57	±0.10	18.46	±1.87	124.18	±3.40	72.09	±2.26	64.91	±3.34
	Final^a	2.50	±0.09	7.50	±7.50	128.73	±3.47	71.91	±2.29	64.55	±2.64
Sumatriptan 100mg	Basal	1.61	±0.12	6.70	±1.70	122.50	±4.26	68.30	±2.10	68.30	±3.12
	Pre-test	1.51	±0.17	6.50	±1.35	125.20	±3.93	72.80	±2.11	62.80	±3.47
	Preparation	2.13	±0.12	13.90	±2.44	130.60	±5.94	76.30	±2.73	69.40	±4.39
	Speech	2.28	±0.13	17.05	±3.25	127.90	±3.93	78.80	±2.62	68.30	±3.97
	Final^a	2.07	±0.14	6.30	±1.59	126.80	±4.89	78.20	±3.01	61.60	±2.89

15 min after the speech, µS: micro Siemens.

Arterial blood pressure and heart rate

There were no significant effects of phase or treatment on SBP and no significant phase × treatment interaction; the same was found for DBP and HR (Table 3).

Discussion

The main behavioural findings of the present study are the results that show that the acute administration of sumatriptan increased the fear and vigilance response during the SPST, as measured by the anxiety and sedation factors of the VAMS scale, respectively. It is important to note that the VAMS anxiety index increases with either fear or anxiety. As discussed elsewhere (Graeff, 2010), fear and anxiety are subjectively similar emotional states, but they can be neurobiologically distinguished.

Because sumatriptan preferentially stimulates presynaptic 5-HT1D/1B receptors that physiologically inhibit 5-HT release into the extracellular space (Davidson and Stamford, 1995; Hoyer and Middlemiss, 1989), these effects are likely to be due to decreased serotonergic activity. In particular, the present results show that the magnitude of the VAMS anxiety factor was increased by sumatriptan at the preparation and speech phases of the experimental session. A similar effect has been reported following the acute administration of the antidepressants clomipramine (Guimarães et al., 1987) and nefazodone (Silva et al., 2001). Although the therapeutic action of antidepressants is attributed to increased serotonergic activity, this is achieved only after repeated drug administration for several weeks. Following acute drug administration, it is assumed that the stimulation of 5-HT1A somatodendritic autoreceptors that inhibit neuronal firing predominates, resulting in less 5-HT released into the extracellular space (Piñeyro and Blier, 1999). Consequently, the enhancement of VAMS anxiety factor caused by the acute administration of the antidepressants was attributed to decreased serotonergic activity (Guimarães et al., 1987; Silva et al., 2001). The similar effect of sumatriptan that is currently described supports this interpretation because the latter drug decreases 5-HT by a different mechanism, namely, the stimulation of presynaptic 5-HT1D/1B receptors that inhibit 5-HT release (Davidson and Stamford, 1995; Hoyer and Middlemiss, 1989). Nevertheless, because sumatriptan also has a considerable affinity for 5-HT1A receptors (Deleu and Hanssens, 2000), at least part of its fear-enhancing effect could be due to the stimulation of autosomic 5-HT1A receptors.

An enhancement of SPST-induced fear was also observed after the administration of another antidepressant, the highly potent and selective 5-HT reuptake inhibitor escitalopram (Garcia-Leal et al., 2010). However, in this case, the magnitude of the response was not changed by the drug treatment, but rather, its duration was prolonged. Because the 5-HT2A/2C receptor antagonist ritanserin had the same type of effect (Guimarães et al., 1997), the delayed return of the anxiety increase, determined by public speaking, may also be attributed to the 5-HT deficit. Nevertheless, we cannot provide a good explanation for the difference between this response profile and that of the aforementioned drugs.

The action of sumatriptan on the peripheral 5HT1D/1B receptor was reported to relieve pain and to increase blood pressure through vasoconstriction (Dodick and Martin, 2004). Increases in blood pressure could cause anxiety, but in the present results, blood pressure level was not affected by sumatriptan. Furthermore, we would expect pain relief to decrease, rather than increase, anxiety. Therefore, it is unlikely that the peripheral 5HT1D/1B actions of sumatriptan are responsible for the presently observed increase in SPST-induced fear.

Assuming that the SPST engages neuronal circuits that organise proximal defence and trigger panic attacks (Deakin et al., 1992, 1994) the present results indicate that sumatriptan should aggravate PD. In agreement with this, the reported results showed that the oral acute administration of 100 mg of sumatriptan to panic patients enhanced subjective panic symptoms, as measured by the Panic Symptom Inventory; increased anxiety, as measured by the Hamilton Anxiety Rating Scale and the National Institute of Mental Health Anxiety Scale; and increased pulse rate (Amital et al., 2005). This is in agreement with animal studies that reported the anxiogenic effects of sumatriptan (Lin et al., 2002). A further clinical implication of the present results addresses the frequent comorbidity between migraines and depressive and anxiety disorders (Felbinger et al., 2009; Stewart et al., 1994). In this regard, another reported study showed that the occurrence of panic-like symptoms in patients with migraines that were treated with sumatriptan was associated with higher baseline levels of anxiety (Loi et al., 1996). Thus, clinicians should be aware that sumatriptan can trigger panic-like symptoms in patients with migraines and associated anxiety symptoms.

Regardless of the experimental phase of the session, the volunteers that received 100 mg of sumatriptan reported more discomfort than those treated with 50 mg of sumatriptan. In the original VAMS scale, this factor is named ‘contentment’ (Bond et al., 1974), and the component items, interested–disinterested, sad–happy, satisfied–dissatisfied, and hostile–friendly, are more closely associated with mood than with anxiety. Following this line of reasoning, it may be suggested that the reduced availability of serotonin caused by sumatriptan increases depressive mood. Reinforcing this possibility, a former study showed that healthy volunteers of both genders treated with d-fenfluramine, a drug that increases 5-HT availability, reported less discomfort in the anticipatory and final phases of the SPST compared with the group treated with placebo (Hetem et al., 1996). As a caveat, however, one should note that a difference between the groups that received sumatriptan and placebo was not presently found.

Although both escitalopram (Garcia-Leal et al., 2010) and sumatriptan (present results) increase SPST-induced fear, the hormonal response to each of these drugs is different. While escitalopram has been shown to raise plasma cortisol and prolactin levels immediately after the task, sumatriptan did not presently affect the serum levels of cortisol, and it lowered prolactin levels, independent of the experimental phase. These results indicate that escitalopram acts on two subpopulations of 5-HT neurons with a different mechanism of action: in the mesolimbic serotonergic system that regulates emotion, the drug would decrease 5-HT, whereas in 5-HT- neurons that regulate the hormonal response to stress, escitalopram would elevate 5-HT (Lowry 2002; Lowry et al., 2005). Acute administration of other antidepressant drugs also increases the release of stress hormones (Yatham and Steiner, 1993). The present results, which showed that sumatriptan increases SPST-induced fear and decreases prolactin, indicate that, unlike antidepressants, sumatriptan similarly decreases serotonergic activity in both subpopulations of 5-HT-containing neurons.

As to the neural mechanisms involved in the effects of serotonergic drugs on prolactin, it is known that the arcuate nucleus, located in the mediobasal hypothalamus, is dense in neuroendocrine neurons and receives 5-HT projections from both the dorsal and median raphe nuclei (van de Kar and Lorens, 1979; Willoughby and Blessing, 1987). In this region, 5-HT interacts with dopaminergic neurons (Alex and Pehek, 2007), and 5-HT1B receptor stimulation seems to facilitate dopamine action (Hållbus et al., 1997; Hudzik et al., 2003; Yan and Yan, 2001), which inhibits prolactin release (Freeman et al., 2000). Thus, a possible explanation is that the decrease in extracellular 5-HT induced by sumatriptan would enhance dopamine action and, as a consequence, would decrease prolactin release.

Although prolactin seems to regulate the stress response (Lennartsson and Jonsdottir, 2011; Drago et al., 1989), in the present results, the SPST test did not increase plasma levels of prolactin. The magnitude of the prolactin response to the Trier Social Stress Test (TSST), a model of psychological stress that is similar to the SPST, was shown to be significantly related to the degree of hypothalamic–pituitary–adrenal axis and cardiovascular activation, indicating that individual differences observed in the prolactin response to stress are dependent on the stress-induced level of physiological activation (Lennartsson and Jonsdottir, 2011). Because the cortisol response to SPST was mild (see below) in the present experiment, it would be expected that the prolactin response to public speaking stress would also be small, or even absent. Among others, one factor that could influence the prolactin response to stress is trait anxiety. Healthy subjects with high trait anxiety and even patients with PD show a reduced prolactin response to public speaking or to hypoglycaemia (Jezova et al., 2004, 2010). However, in our study, the volunteers did not have high trait anxiety, as measured by STAI-T (Table 2).

The presently observed rise in cortisol levels immediately after the test, independent of drug treatment, disagrees with previously reported results that showed that the SPST did not affect cortisol, prolactin (Garcia-Leal et al., 2005, 2010) or adrenocorticotropic hormone (ACTH) (de Oliveira et al., 2011) levels. However, we must acknowledge that although the presently observed effect is statistically significant, it is of a low magnitude, considering the degree of the task’s stress. The cortisol response to the SPST shows a large variability, and the activation of the hypothalamic–pituitary–adrenal axis is related to the stressor; thus, the greater the threat of social evaluation and the lack of control of the situation, the greater the cortisol response (Dickerson and Kemeny, 2004). Accordingly, a further study showed that after a speech there was an increase in cortisol only in the group that performed the speech in front of evaluators who expressed a negative opinion about the task, compared with the group that performed the speech in front of an appraiser who did not express his opinion and with volunteers who conducted the speech alone in the laboratory (Dickerson et al., 2008).

The lack of effect of sumatriptan on the cortisol response observed in the present study is contrary to previously reported data that showed a reduction in plasma cortisol after acutely administered sumatriptan to healthy volunteers at rest (Entwisle et al., 1995; Gross-Isseroff et al., 2004; Pinessi et al., 2003). However, there is also one study that showed no changes in cortisol plasma levels after sumatriptan intake (Boeles et al., 1997).

This study has several limitations, including the relatively small sample size and the composition of the sample, as it comprised only men with a high school level of education. Although the obtained results support the initial hypothesis regarding the role of serotonin in the processing of unconditioned fear and in the pathogenesis of PD and social anxiety disorder, further studies are needed to establish a deeper understanding of the role of the 5-HT1D/1B receptor in normal and pathological anxiety.

In conclusion, the present results show that the acute administration of sumatriptan increased the subjective fear generated by the SPST. This increase was likely due to a decreased release of 5-HT caused by the agonist action of sumatriptan on 5-HT1D/1B presynaptic receptors. These results agree with the hypothesis that 5-HT inhibits the neural mechanisms that underlie this fear response, which are supposedly the same as those that organise proximal defence, trigger panic attacks and social anxiety disorder and lie in the DPAG (Deakin and Graeff, 1991; Graeff et al., 1996). The observed reduction in plasma levels of prolactin following sumatriptan is likely to be due to the impaired serotonergic activation of prolactin release. No drug effect on cortisol plasma level was observed, although a mild increase occurred in all experimental groups, likely in response to the SPST.

Footnotes

Acknowledgements

The authors are indebted to Lucila Leico Kagohara Elias, MD, PhD, Margareth Castro, MD, PhD for cortisol and prolactin measuring and to Mr José Roberto Silva and Mrs Albina Verceze Bortolieiro for technical assistance.

Conflict of interest

The authors declare no conflict of interest.

Funding

This research was supported by ‘Fundação de Amparo à Pesquisa do Estado de São Paulo’ (grant number FAPESP-2007/03685-3), CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior) (research fellowship to MGR), the ‘Fundação de Amparo ao Ensino, Pesquisa e Assistência do Hospital das Clínicas de Ribeirão Preto’ (FAEPA) and ‘Conselho Nacional de desenvolvimento Científico e Tecnológico’ (CNPq) (research fellowships to FGG and CMD-B).

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