The optimal order of stimulation modalities and reproducibility of the multimodal esophageal stimulation paradigm

Disruption of the brain-esophagus axis in obese patients with heartburn

Obesity is a risk factor for gastroesophageal reflux disease. Studies addressing the brain-esophagus axis in obese are lacking. In obese with and without heartburn, we assessed: (i) the brain responses to esophageal acid perfusion during functional brain imaging; (ii) esophageal impedance baseline before and after acid perfusion; and (iii) abdominal fat distribution. In this exploratory study, 26 obese underwent functional magnetic resonance imaging (fMRI) of the brain combined with esophageal acid perfusion. Esophageal impedance baseline was determined before and after fMRI, followed by tomographic quantification of the abdominal fat. Among 26 obese (54% men, 39.7 years old, 33.5 kg/m2), there were 17 with heartburn and 9 without heartburn. Before fMRI, the esophageal impedance baseline was lower in obese with heartburn than without heartburn (median 1187 vs. 1890 Ω; P = 0.025). After acid perfusion, impedance baseline decreased in obese with heartburn (from 1187 to 899 Ω; P = 0.011) and was lower in this group than in obese without heartburn (899 vs. 1614 Ω; P = 0.001). fMRI task-residual analysis showed that obese with heartburn presented higher functional connectivity in several brain regions than obese without heartburn. Abdominal fat area did not differ between obese with and without heartburn either for total (72.8 ± 4.4% vs. 70.3 ± 6.0%; P = 0.280), subcutaneous (42.2 ± 9.0% vs. 37.4 ± 9.0%; P = 0.226), or visceral (30.6 ± 7.9% vs. 33.0 ± 7.8%; P = 0.484). In subjects with obesity, the brain-esophagus axis is disrupted centrally with higher functional brain connectivity and peripherally with decreased esophageal mucosa integrity in the presence of heartburn.

The role of serotonin in the control of esophageal sensitivity assessed by multimodal stimulation in health

BACKGROUND

Esophageal hypersensitivity is considered an important pathophysiological mechanism in refractory gastroesophageal reflux disease (GERD) patients. Serotonin (5-HT) plays an important role in the regulation of GI (gastrointestinal) secretion, motility and sensitivity. Previous studies found that altered 5-HT availability has no clear effects on esophageal/GI sensations. Our aim was therefore to investigate the role of 5-HT in esophageal sensitivity in healthy volunteers (HV).

METHODS

Esophageal sensitivity to thermal, mechanical, electrical, and chemical stimuli was assessed in 3 different placebo-controlled studies. In the first study, the effect of citalopram (40 mg; 5-HT reuptake inhibitor; intravenous) was investigated (n = 14). In the second study, the effect of buspirone (20 mg; 5HT1A agonist; oral) was investigated (n = 10). In the third study, acute tryptophan depletion (ATD) was used to decrease 5-HT levels to investigate the effect of reduced 5-HT availability on esophageal sensitivity (n = 15).

KEY RESULTS

No difference was observed in esophageal sensitivity after the administration of citalopram or buspirone (all p > 0.06). In contrast, pain perception threshold to chemical stimulation was increased after ATD (p = 0.017, Cohen's d+ = 0.67). No effect was found on the first perception or pain tolerance threshold. ATD had no influence on esophageal sensitivity to thermal, mechanical, and electrical stimulation compared with placebo.

CONCLUSIONS AND INFERENCES

ATD, which induces 5-HT depletion, significantly decreased pain perception threshold during chemical stimulation, without affecting sensitivity to mechanical, thermal, or electrical stimulation. These findings confirm the involvement of 5-HT in the control of esophageal acid sensitivity, but identifying the receptors involved requires more ligands and studies.