Vagal afferent activation induces salivation and swallowing-like events in anesthetized rats

Changes Over Time in Masseter Muscle Activity, Symptoms of Discomfort, Stress Level and Salivary Flow Rate Following Intra-Oesophageal Acid Infusion

BACKGROUND

Intra-oesophageal acid stimulation increases masseter muscle activity. However, the infusion speeds used in previous studies are significantly slow, with minimal acid volume (30 mL over 30 min). Additionally, it is unclear how masseter muscle activity, symptoms of discomfort, stress levels and saliva quantity change over time.

OBJECTIVES

The time course of masseter muscle activity, heartburn and discomfort symptoms, salivary cortisol concentration to assess stress, autonomic nervous system (ANS) activity and saliva quantity under the influence of intra-oesophageal acid infusion were evaluated at a faster injection rate and larger volume than in previous studies.

METHODS

Ten healthy adults underwent polygraphic monitoring, consisting of electromyography of the masseter muscle and electrocardiography during intra-oesophageal acid infusion (10 mL/min, 10 min). Symptoms of heartburn and discomfort were assessed using the visual analogue scale (VAS), and saliva quantity was measured. Friedman's test was used for multiple comparisons.

RESULTS

Masseter muscle activity, VAS scores for heartburn and discomfort, as well as saliva quantity during the 10-min acid infusion, increased significantly compared with that before acid infusion (p < 0.001, 0.001, 0.019 and 0.047, respectively) and decreased 10 and 20 min after acid infusion (p = 0.004, 0.004 and 0.007, respectively). No significant changes were observed in the salivary cortisol concentration or ANS activity.

CONCLUSION

Intra-oesophageal acid infusion stimulated symptoms of heartburn and discomfort and increased masseter muscle activity and saliva production, which may not be related to psychological stress.

Gastroesophageal reflux disease in preterm infants: unmet needs

INTRODUCTION

Many preterm present somatic symptoms including aerodigestive and cardiorespiratory manifestations, in combination with irritability and/or distress, which are often attributed to gastroesophageal reflux (GER), albeit for unclear reasons.

AREAS COVERED

We searched in PubMed, Google Scholar, and MEDLINE for guidelines, reviews, and randomized controlled trials up to March 2024.

EXPERT OPINION

The diagnosis of GER-disease (GERD) in preterm is challenging because manifestations are atypical and diagnostic investigations difficult and not devoid of risk for adverse events. In case of vomiting or regurgitation, GER as a consequence of anatomical or metabolic conditions should be considered. Although many preterm infants are treated with proton pump inhibitors, this is seldom needed. Low-quality evidence for alginates is available, but needs further evaluation. There is a need for an effective and safe prokinetic favoring esophageal clearance, increasing lower esophageal sphincter pressure and stimulating gastric emptying. Non-drug treatment such as feeding adaptations (volume, duration, and composition) and positional changes are insufficiently applied. Thickened formula is not indicated in preterm babies. In case none of the above recommendations did result in sufficient improvement, and if documentation of acid GER is not possible, a 2-4 week trial of a proton pump inhibitor is acceptable.

Effects of Intraoperative Vagal Nerve Stimulation on the Gastrointestinal Microbiome in a Mouse Model of Amyotrophic Lateral Sclerosis

The gastrointestinal microbiota (GM) plays a fundamental role in health and disease and contributes to the bidirectional signaling between the gastrointestinal system and brain. The direct line of communication between these organ systems is through the vagus nerve. Therefore, vagal nerve stimulation (VNS), a commonly used technique for multiple disorders, has potential to modulate the enteric microbiota, enabling investigation and possibly treatment of numerous neurologic disorders in which the microbiota has been linked with disease. Here we investigate the effect of VNS in a mouse model of amyotrophic lateral sclerosis (ALS). B6SJL-Tg(SOD1*G93A)^dl1Gur (SOD1^dl) and wildtype mice underwent ventral neck surgery to access the vagus nerve. During surgery, the experimental group received 1 h of VNS, whereas the sham group underwent 1 h of sham treatment. The third (control) group did not undergo any surgical manipulation. Fecal samples were collected before surgery and at 8 d after the initial collection. Microbial DNA was sequenced to determine the GM profiles at both time points. GM profiles did not differ between genotypes at either the initial or end point. In addition, VNS did not alter GM populations, according to the parameters chosen in this study, indicating that this short intraoperative treatment is safe and has no lasting effects on the GM. Future studies are warranted to determine whether different stimulation parameters or chronic use of VNS affect GM profiles.

Neurons with diverse phenotypes project from the caudal to the rostral nucleus of the solitary tract

The nucleus of the solitary tract is a potential site for taste-visceral interactions. Connections from the caudal, visceral area of the nucleus (cNST) to the rostral, gustatory zone (rNST) have been described, but the phenotype of cells giving rise to the projection(s) and their distribution among rNST subdivisions are unknown. To determine these characteristics of the intrasolitary pathway, we injected pan-neuronal and floxed AAV viruses into the cNST of mice expressing cre in glutamatergic, GABAergic, or catecholaminergic neurons. Particular attention was paid to the terminal field distribution in rNST subdivisions by simultaneously visualizing P2X2 localized to gustatory afferent terminals. All three phenotypically identified pathways terminated in rNST, with the density greatest for glutamatergic and sparsest for catecholaminergic projections, observations supported by retrograde tracing. Interestingly, cNST neurons had more prominent projections to rNST regions medial and ventral to P2X2 staining, i.e., the medial and ventral subdivisions. In addition, GABAergic neurons projected robustly to the lateral subdivision and adjacent parts of the reticular formation and spinal trigeminal nucleus. Although cNST neurons also projected to the P2X2-rich central subdivision, such projections were sparser. These findings suggest that cNST visceral signals exert stronger excitatory and inhibitory influences on local autonomic and reflex pathways associated with the medial and ventral subdivisions compared to weaker modulation of ascending pathways arising from the central subdivision and ultimately destined for the forebrain.