Connecting dots in disorders of gut-brain interaction: the interplay of stress and sex hormones in shaping visceral pain

Cardiac Vagal Efficiency Is Enhanced by Percutaneous Auricular Neurostimulation in Adolescents With Nausea: Moderation by Antidepressant Drug Exposure

OBJECTIVES

Percutaneous electrical nerve field stimulation (PENFS) is an effective treatment for disorders of gut-brain interaction (DGBI), proposed to influence vagal pathways. Cardiac metrics such as respiratory sinus arrythmia (RSA) and vagal efficiency (VE) can noninvasively assess parasympathetic output. Commonly used antidepressant drugs inhibit vagal signaling and may interfere with PENFS. This study examined immediate effects of active compared to sham PENFS on cardiac vagal function in adolescents with chronic nausea with and without concurrent drug therapy.

MATERIALS AND METHODS

Participants (n = 84) were randomized to active (3.2 V, 1-10 Hz) or sham PENFS within an 8-week prospective, double-blind clinical trial. Subjects underwent posture challenges to elicit a vagal response before and after PENFS device placement mid-way through the study. RSA, mean heart period (HP), and VE were calculated from electrocardiogram recordings. Exposure to antidepressant drugs was recorded.

RESULTS

The mean (SD) age was 15.61 (2.07) years (83% female). Fifty percent were treated with antidepressants. PENFS neurostimulation enhanced VE in patients without antidepressant exposure (mean increase after PENFS stimulation =7.56 [95% CI: 0.26, 14.86], d = 0.30, 17% increase) but not in those treated with antidepressants (mean change = -5.30 [95% CI:-14.28, 3.68]). Sham PENFS did not produce significant VE changes regardless of medication use (both p > 0.40). There were no significant effects on RSA or HP.

CONCLUSIONS

Acute enhancement of cardiac VE is demonstrated with PENFS in patients not exposed to chronic antidepressant drug therapy. Findings indicate that VE is a sensitive metric for rapid assessment of PENFS effects but raise concern for possible interaction or interference by standard of care medications.

TRIAL REGISTRATION

Clinicaltrials.gov #: 1064187-2.

Differential brainstem connectivity according to sex and menopausal status in healthy male and female individuals

BACKGROUND

Brainstem nuclei play a critical role in both ascending monoaminergic modulation of cortical function and arousal, and in descending bulbospinal pain modulation. Even though sex-related differences in the function of both systems have been reported in animal models, a complete understanding of sex differences, as well as menopausal effects, in brainstem connectivity in humans is lacking. This study evaluated resting-state connectivity of the dorsal raphe nucleus, right and left locus coeruleus complex (LCC), and periaqueductal gray (PAG) according to sex and menopausal status in healthy individuals. In addition, relationships between systemic estrogen levels and brainstem-network connectivity were examined in a subset of participants.

METHODS

Resting-state fMRI was performed in 47 healthy male (age, 31.2 ± 8.0 years), 53 healthy premenopausal female (age, 24.7 ± 7.3 years; 22 in the follicular phase, 31 in the luteal phase), and 20 postmenopausal female participants (age, 54.6 ± 7.2 years). Permutation Analysis of Linear Models (5000 permutations) was used to evaluate differences in brainstem-network connectivity according to sex and menopausal status, controlling for age. In 10 males and 17 females (9 premenopausal; 8 postmenopausal), estrogen and estrogen metabolite levels in plasma and stool were determined by liquid chromatography-mass spectrometry/mass spectrometry. Relationships between estrogen levels and brainstem-network connectivity were evaluated by partial least squares analysis.

RESULTS

Left LCC-executive control network connectivity showed an overall sex difference (p = 0.02), with higher connectivity in females than in males; however, this was mainly due to differences between males and premenopausal females (p = 0.008). Additional sex differences were dependent on menopausal status: PAG-default mode network (DMN) connectivity was higher in postmenopausal females than in males (p = 0.04), and PAG-sensorimotor network (SMN) connectivity was higher in premenopausal females than in males (p = 0.03) and postmenopausal females (p = 0.007). Notably, higher free 2-hydroxyestrone levels in stool were reliably associated with higher PAG-SMN and PAG-DMN connectivity in premenopausal females (p < 0.01).

CONCLUSIONS

Healthy females show higher brainstem-network connectivity involved in cognitive control, sensorimotor function, and self-relevant processes than males, dependent on their menopausal status. Further, 2-hydroxyestrone, implicated in pain, may modulate PAG connectivity in premenopausal females. These findings may relate to differential vulnerabilities to chronic stress-sensitive disorders at different life stages.

Sex differences in the reactivity of gastric myoelectrical activity and heart rate variability as putative psychophysiological markers in human pain research

Background

This study explored the potential of electrogastrography (EGG) and heart rate variability (HRV) as psychophysiological markers in experimental pain research related to the gut-brain axis. We investigated responses to the experience of pain from the visceral (rectal distension) and somatic (cutaneous heat) pain modalities, with a focus on elucidating sex differences in EGG and HRV responses.

Methods

In a sample of healthy volunteers (29 males, 43 females), EGG and ECG data were collected during a baseline and a pain phase. Data were analyzed for changes in gastric myoelectrical activity and cardiac autonomic regulation, with special attention to sex-specific patterns and correlations with perceptual responses to visceral and somatic pain stimuli, assessed by visual analogue scale ratings.

Results

Acute pain induced significant instability in EGG slow-wave frequency and amplitude, increased tachygastria, and decreased normogastric spectral power, without evidence of sex differences. HRV analyses revealed increases in SDNN, RMSSD, and pNN50 during pain, indicating sympathovagal regulation changes. While there were no significant sex differences in EGG responses, only female participants exhibited significant correlations between visceral pain unpleasantness and EGG alterations. HRV measures, particularly time-domain parameters, showed sex differences, independent of pain-induced autonomic reactivity.

Conclusion

The experience of pain in the lower abdominal region may induce impaired gastric motility. EGG and HRV are sensitive to acute pain and offer insight into pain mechanisms along the gut-brain axis. While EGG responses were consistent across sexes, HRV revealed sex-specific differences, suggesting that autonomic regulation and gastric motility may be modulated differently by pain and psychosocial factors. Further research in patients with chronic visceral pain is warranted.

Differential brainstem connectivity according to sex and menopausal status in healthy men and women

Background Brainstem nuclei play a critical role in both ascending monoaminergic modulation of cortical function and arousal, and in descending bulbospinal pain modulation. Even though sex-related differences in the function of both systems have been reported in animal models, a complete understanding of sex differences, as well as menopausal effects, in brainstem connectivity in humans is lacking. This study evaluated resting-state connectivity of the dorsal raphe nucleus (DRN), right and left locus coeruleus complex (LCC), and periaqueductal gray (PAG) according to sex and menopausal status in healthy individuals. In addition, relationships between systemic estrogen levels and brainstem-network connectivity were examined in a subset of participants. Methods Resting-state fMRI was performed in 50 healthy men (age, 31.2 ± 8.0 years), 53 healthy premenopausal women (age, 24.7 ± 7.3 years; 22 in the follicular phase, 31 in the luteal phase), and 20 postmenopausal women (age, 54.6 ± 7.2 years). Permutation Analysis of Linear Models (5000 permutations) was used to evaluate differences in brainstem-network connectivity according to sex and menopausal status, controlling for age. In 10 men and 17 women (9 premenopausal; 8 postmenopausal), estrogen and estrogen metabolite levels in plasma and stool were determined by liquid chromatography-mass spectrometry/mass spectrometry. Relationships between estrogen levels and brainstem-network connectivity were evaluated by partial least squares analysis. Results Left LCC-executive control network (ECN) connectivity showed an overall sex difference (p = 0.02), with higher connectivity in women than in men; however, this was mainly due to differences between men and pre-menopausal women (p = 0.008). Additional sex differences were dependent on menopausal status: PAG-default mode network (DMN) connectivity was higher in postmenopausal women than in men (p = 0.04), and PAG-sensorimotor network (SMN) connectivity was higher in premenopausal women than in men (p = 0.03) and postmenopausal women (p = 0.007). Notably, higher free 2-hydroxyestrone levels in stool were associated with higher PAG-SMN and PAG-DMN connectivity in premenopausal women (p < 0.01). Conclusions Healthy women show higher brainstem-network connectivity involved in cognitive control, sensorimotor function, and self-relevant processes than men, dependent on their menopausal status. Further, 2-hydroxyestrone, implicated in pain, may modulate PAG connectivity in premenopausal women. These findings may relate to differential vulnerabilities to chronic stress-sensitive disorders at different life stages.

Gut-Brain Axis: Focus on Sex Differences in Neuroinflammation

In recent years, there has been a growing interest in the concept of the "gut-brain axis". In addition to well-studied diseases associated with an imbalance in gut microbiota, such as cancer, chronic inflammation, and cardiovascular diseases, research is now exploring the potential role of gut microbial dysbiosis in the onset and development of brain-related diseases. When the function of the intestinal barrier is altered by dysbiosis, the aberrant immune system response interacts with the nervous system, leading to a state of "neuroinflammation". The gut microbiota-brain axis is mediated by inflammatory and immunological mechanisms, neurotransmitters, and neuroendocrine pathways. This narrative review aims to illustrate the molecular basis of neuroinflammation and elaborate on the concept of the gut-brain axis by virtue of analyzing the various metabolites produced by the gut microbiome and how they might impact the nervous system. Additionally, the current review will highlight how sex influences these molecular mechanisms. In fact, sex hormones impact the brain-gut microbiota axis at different levels, such as the central nervous system, the enteric nervous one, and enteroendocrine cells. A deeper understanding of the gut-brain axis in human health and disease is crucial to guide diagnoses, treatments, and preventive interventions.

Smooth muscle contractile responses to bile acids in mouse ileum require TGR5 but not ASBT

Background

Many disorders of gut-brain interaction (DGBIs) are more prevalent in women than men and feature alterations in gastrointestinal motility and bile acid homeostasis. Mechanisms by which bile acids regulate gastrointestinal motility are poorly characterized. We recently validated an adapted tissue bath technique using everted mouse ileum, which revealed differential contractile responses to ursodeoxycholic acid (UDCA) and deoxycholic acid (DCA). Here, we aimed to determine whether these responses are dependent on host sex, the plasma membrane bile acid receptor TGR5, or the apical sodium-dependent bile acid transporter ASBT.

Methods

Ileal segments from male and female mice were everted and suspended in tissue baths. Contractile responses to physiologic concentrations of UDCA and DCA were quantified with or without TGR5 or ASBT inhibitors. Phosphorylation of extracellular signal-regulated kinase (ERK) and myosin light chain (MLC), markers of TGR5 activation and smooth muscle contraction, respectively, were assessed with western blot.

Results

There were no sex differences in the dose-dependent contractile responses to bile acids. At 100 μmol/L, UDCA but not DCA increased MLC phosphorylation and increased contractility. TGR5 inhibition decreased ERK phosphorylation and led to decreases in contractility, phosphorylated MLC, and surprisingly, total MLC. ASBT inhibition did not affect contractile responses.

Conclusion

Differential effects of UDCA and DCA on ileal smooth muscle contractility are not dependent on host sex or ASBT-mediated transport. Bile acids signal through mucosal TGR5, which regulates smooth muscle contractility by complex mechanisms. Understanding how bile acids differentially regulate gastrointestinal motility could facilitate new therapeutic options for specific DGBIs.

Hydrocortisone Differentially Affects Reinstatement of Pain-related Responses in Patients With Chronic Back Pain and Healthy Volunteers

Despite the crucial role of effective and sustained extinction of conditioned pain-related fear in cognitive-behavioral treatment approaches for chronic pain, experimental research on extinction memory retrieval in chronic pain remains scarce. In healthy populations, extinction efficacy of fear memory is affected by stress. Therefore, we investigated the effects of oral hydrocortisone administration on the reinstatement of pain-related associations in 57 patients with non-specific chronic back pain (CBP) and 59 healthy control (HC) participants in a differential pain-related conditioning paradigm within a placebo-controlled, randomized, and double-blind design. Participants' skin conductance responses indicate hydrocortisone-induced reinstatement effects in HCs but no observable reinstatement in HCs receiving placebo treatment. Interestingly, these effects were reversed in patients with CBP, that is, reinstatement responses were only observed in the placebo and not in the hydrocortisone group. Our findings corroborate previous evidence of stress-induced effects on extinction efficacy and reinstatement of fear memory in HCs, extending them into the pain context, and call for more research to clarify the role of stress in fear extinction and return of fear phenomena possibly contributing to treatment failure in chronic pain treatment. PERSPECTIVE: Opposing effects in HCs and patients with non-specific CBP may be associated with changes in the patients' stress systems. These findings could be of relevance to optimizing psychological, extinction-based treatment approaches.

Multimodal therapies and strategies for the treatment of interstitial cystitis/bladder pain syndrome in Taiwan

Interstitial cystitis/bladder pain syndrome (IC/BPS) is a chronic disease characterized by bladder pain, frequency, and nocturia. The most common pathologies include chronic inflammation and bladder urothelium dysfunction. According to the bladder condition with or without Hunner's lesions, IC/BPS can be divided into "IC" in patients with Hunner's lesion (HIC) and "BPS" in those without Hunner's lesion (NHIC). Previous studies have reported greater central sensitization and interorgan cross-talk in patients with NHIC. Multimodal treatments have been recommended in clinical guidelines under the biopsychosocial model. The bladder-gut-brain axis has also been speculated, and multimodal therapies are necessary. Unfortunately, currently, no treatment has been reported durable for IC/BPS. Patients with IC/BPS usually experience anxiety, depression, holistic physical responses, and even threats to social support systems. The lack of durable treatment outcomes might result from inadequate diagnostic accuracy and differentiation of clinical phenotypes based on the underlying pathophysiology. Precision assessment and treatment are essential for optimal therapy under definite IC/BPS phenotype. This article reviewed currently available literature and proposed a diagnosis and treatment algorithm. Based on bladder therapy combined with suitable physical and psychological therapies, a well-grounded multimodal therapy and treatment algorithm for IC/BPS following a diagnostic protocol are indispensable.

Nocebo effects in visceral pain: concept and design of the experimental randomized-controlled pain study 'NoVis'

The role of psychological factors in the pathophysiology and treatment of chronic visceral pain in disorders of gut-brain interactions (DGBI) is increasingly appreciated. Placebo research has underscored that expectations arising from the psychosocial treatment context and from prior experiences shape treatment responses. However, effects of negative expectations, i.e., nocebo effects, as they are likely crucial elements of DGBI patients' clinical reality, have thus far only rarely been investigated in the context of visceral pain, with untapped potential for improved prevention and treatment. The experimental randomized-controlled pain study "NoVis," carried out within the Collaborative Research Center (CRC) 289 ("Treatment Expectation"), aims to close gaps regarding the generation and persistence of nocebo effects in healthy volunteers. It is designed to elucidate effects of negative expectations in a multiple-threat paradigm with intensity-matched rectal distensions and cutaneous thermal stimuli, allowing to test nocebo effects in the visceral and somatic pain modalities. Negative expectations are experimentally induced by elements of doctor-patient communication (i.e., instruction) and/or by surreptitious amplification of symptom intensity (i.e., experience/learning) within a treatment context. Accordingly, the repeated measures between-subject design contains the between-group factors "treatment instruction" (negative vs. control) and "treatment experience" (negative vs. control), with volunteers randomized into four experimental groups undergoing several pain stimulation phases (repeated factor). This allows to compare the efficacy of instruction vs. experience, and more importantly, their combined effects on the magnitude of negative expectations and their impact on pain responses, which we expect will be greatest for the visceral modality. After a Baseline, short-term effects are assessed during a test phase accomplished on study day 1 (Test-1 Phase). To explore the persistence of effects, a second test phase is accomplished 1 week later (Test-2 Phase). Effects of negative expectations within and across pain modalities are assessed at the subjective and objective levels, with a focus on psychophysiological and neuroendocrine measures related to stress, fear, and anxiety. Since nocebo effects can play a considerable role in the generation, maintenance, or worsening of chronic visceral pain, and may even constitute risk factors for treatment failure, knowledge from experimental nocebo research has potential to improve treatment outcomes in DGBI and other clinical conditions associated with chronic visceral pain.