Preliminary report: modulation of parasympathetic nervous system tone influences oesophageal pain hypersensitivity

Pharmacological and other treatment modalities for esophageal pain

Treatment of esophageal pain remains a major challenge for the clinician. Although many patients have heartburn and may respond to proton pump inhibitors, there in an unmet need for other treatment modalities in patients where there are no obvious pathological findings. Although analgesics are the mainstay in esophageal pain treatment, many patients are nonresponders to these drugs. The current concise review focuses on other systems affecting pain processing, where better understanding may serve as a framework for therapy. These are the parasympathetic nervous system, exercise, and personality profiles. Finally, treatment with analgesics for functional chest pain remains a challenge, and an overview of treatment with antidepressive drugs is provided.

Understanding the sensory irregularities of esophageal disease

Symptoms relating to esophageal sensory abnormalities can be encountered in the clinical environment. Such sensory abnormalities may be present in demonstrable disease, such as erosive esophagitis, and in the ostensibly normal esophagus, such as non-erosive reflux disease or functional chest pain. In this review, the authors discuss esophageal sensation and the esophageal pain system. In addition, the authors provide a primer concerning the techniques that are available for investigating the autonomic nervous system, neuroimaging and neurophysiology of esophageal sensory function. Such technological advances, whilst not readily available in the clinic may facilitate the stratification and individualization of therapy in disorders of esophageal sensation in the future.

What goes around comes around: novel pharmacological targets in the gut-brain axis

The gut and the brain communicate bidirectionally through anatomic and humoral pathways, establishing what is known as the gut-brain axis. Therefore, interventions affecting one system will impact on the other, giving the opportunity to investigate and develop future therapeutic strategies that target both systems. Alterations in the gut-brain axis may arise as a consequence of changes in microbiota composition (dysbiosis), modifications in intestinal barrier function, impairment of enteric nervous system, unbalanced local immune response and exaggerated responses to stress, to mention a few. In this review we analyze and discuss several novel pharmacological targets within the gut-brain axis, with potential applications to improve intestinal and mental health.

Modulation of vagal tone enhances gastroduodenal motility and reduces somatic pain sensitivity

BACKGROUND

The parasympathetic nervous system, whose main neural substrate is the vagus nerve, exerts a fundamental antinociceptive role and influences gastrointestinal sensori-motor function. Our research question was to whether combined electrical and physiological modulation of vagal tone, using transcutaneous electrical vagal nerve stimulation (t-VNS) and deep slow breathing (DSB) respectively, could increase musculoskeletal pain thresholds and enhance gastroduodenal motility in healthy subjects.

METHODS

Eighteen healthy subjects were randomized to a subject-blinded, sham-controlled, cross-over study with an active protocol including stimulation of auricular branch of the vagus nerve, and breathing at full inspiratory capacity and forced full expiration. Recording of cardiac derived parameters including cardiac vagal tone, moderate pain thresholds to muscle, and bone pressure algometry, conditioned pain modulation using a cold pressor test and a liquid meal ultrasonographic gastroduodenal motility test were performed.

KEY RESULTS

Cardiac vagal tone increased during active treatment with t-VNS and DSB compared to sham (p = 0.009). In comparison to sham, thresholds to bone pain increased (p = 0.001), frequency of antral contractions increased (p = 0.004) and gastroduodenal motility index increased (p = 0.016) with active treatment. However, no effect on muscle pain thresholds and conditioned pain modulation was seen.

CONCLUSIONS & INFERENCES

This experimental study suggests that this noninvasive approach with combined electrical and physiological modulation of vagal tone enhances gastroduodenal motility and reduces somatic pain sensitivity. These findings warrant further investigation in patients with disorders characterized with chronic pain and gastrointestinal dysmotility such as functional dyspepsia and irritable bowel syndrome.

Influence of Interoceptive Fear Learning on Visceral Perception

OBJECTIVES

Interoceptive fear learning and generalization have been hypothesized to play a key role in unexplained abdominal and esophageal pain in patients with functional gastrointestinal disorders. However, there is no experimental evidence demonstrating that fear learning and generalization to visceral sensations can be established in humans and alter visceral perception.

METHODS

In a novel fear learning-generalization paradigm, an innocuous esophageal balloon distension served as conditioned stimulus (CS), and distensions at three different pressure levels around the pain detection threshold were used as generalization stimuli. During fear learning, the CS was paired with a painful electrical stimulus (unconditioned stimulus) in the conditioning group (n = 30), whereas in the control group (n = 30), the unconditioned stimulus was delivered alone. Before and after fear learning, visceral perception thresholds for first sensation, discomfort, and pain and visceral discrimination sensitivity were assessed.

RESULTS

Fear learning was established in the conditioning group only (potentiated eye-blink startle to the CS (t(464.06) = 3.17, p = .002), and fear generalization to other stimulus intensities was observed (t(469.12) = 2.97, p = .003; t(464.29) = 4.17, p < .001). The thresholds for first sensation habituated in the control group, whereas it remained constant in the conditioning group (F(1,43) = 9.77, p = .003).

CONCLUSIONS

These data show that fear learning using visceral stimuli induces fear generalization and influences visceral perception. These findings support the idea that in functional gastrointestinal disorder, fear learning and generalization can foster gastrointestinal-specific anxiety and contribute to visceral hypersensitivity.

Vagus Nerve and Vagus Nerve Stimulation, a Comprehensive Review: Part III

Vagus nerve stimulation (VNS) is currently undergoing multiple trials to explore its potential for various clinical disorders. To date, VNS has been approved for the treatment of refractory epilepsy and depression. It exerts antiepileptic or antiepileptogenic effect possibly through neuromodulation of certain monoamine pathways. Beyond epilepsy, VNS is also under investigation for the treatment of inflammation, asthma, and pain. VNS influences the production of inflammatory cytokines to dampen the inflammatory response. It triggers the systemic release of catecholamines that alleviates the asthma attack. VNS induces antinociception by modulating multiple pain-associated structures in the brain and spinal cord affecting peripheral/central nociception, opioid response, inflammation process, autonomic activity, and pain-related behavior. Progression in VNS clinical efficacy over time suggests an underlying disease-modifying neuromodulation, which is an emerging field in neurology. With multiple potential clinical applications, further development of VNS is encouraging.