Firing characteristics of swallowing interneurons in the dorsal medulla during physiologically induced swallowing in perfused brainstem preparation in rats

The impact of physical therapy on dysphagia in neurological diseases: a review

A neurogenic dysphagia is dysphagia caused by problems with the central and peripheral nervous systems, is particularly prevalent in conditions such as Parkinson's disease and stroke. It significantly impacts the quality of life for affected individuals and causes additional burdens, such as malnutrition, aspiration pneumonia, asphyxia, or even death from choking due to improper eating. Physical therapy offers a non-invasive treatment with high efficacy and low cost. Evidence supporting the use of physical therapy in dysphagia treatment is increasing, including techniques such as neuromuscular electrical stimulation, sensory stimulation, transcranial direct current stimulation, and repetitive transcranial magnetic stimulation. While initial studies have shown promising results, the effectiveness of specific treatment regimens still requires further validation. At present, there is a lack of scientific evidence to guide patient selection, develop appropriate treatment regimens, and accurately evaluate treatment outcomes. Therefore, the primary objectives of this review are to review the results of existing research, summarize the application of physical therapy in dysphagia management, we also discussed the mechanisms and treatments of physical therapy for neurogenic dysphagia.

Sustained Effects of Capsaicin Infusion into the Oropharynx on Swallowing in Perfused Rats

OBJECTIVES

To examine the sustained effects of oropharyngeal capsaicin stimulation on the regulation of swallowing, we recorded the swallowing-related nerve activities during continuous infusion of capsaicin solution into the oropharynx.

METHODS

In 33 in situ perfused brainstem preparation of rats, we recorded the activities of the vagus, hypoglossal, and phrenic nerves during fictive swallowing. The interburst intervals (IBIs) of the swallowing-related nerves during sequential pharyngeal swallowing (sPSW) elicited by electrical stimulation of the superior laryngeal nerve (SLN) during concurrent capsaicin stimulation of 10, 1, and 0.1 μM (n = 28) were compared with those during oropharyngeal infusion of saline (control) (n = 5).

RESULTS

The IBIs during SLN-induced sPSW were reduced at 5 min after initiation of continuous infusion of 10 and 1 μM capsaicin solution. The IBIs showed significant decreases to -25.8 ± 6.9%, -25.9 ± 5.3, -18.3 ± 3.7, and -12.0 ± 1.6 at 30 min following 1 μM capsaicin stimulation at SLN stimulus conditions at 5 Hz of 1.2 times threshold, 10 Hz of 40 μA, 5 Hz of 60 μA, and 10 Hz of 60 μA, respectively. Continuous capsaicin stimulation of 0.1 μM solution did not show significant sustained effects.

CONCLUSION

Pharmacological stimulation of capsaicin could provide time-dependent effects on the likelihood of swallowing, particularly subserving sustained facilitation of swallowing reflex with appropriate concentration of capsaicin.

LEVEL OF EVIDENCE

NA Laryngoscope, 134:305-314, 2024.

Postinspiratory complex acts as a gating mechanism regulating swallow-breathing coordination and other laryngeal behaviors

Breathing needs to be tightly coordinated with upper airway behaviors, such as swallowing. Discoordination leads to aspiration pneumonia, the leading cause of death in neurodegenerative diseases. Here we study the role of the postinspiratory complex, (PiCo) in coordinating breathing and swallowing. Using optogenetic approaches in freely breathing-anesthetized ChATcre, Vglut2cre and co-transmission of ChATcre/Vglut2FlpO mice reveals this small brainstem microcircuit acts as a central gating mechanism for airway protective behaviors. Activation of PiCo during inspiration or the beginning of postinspiration triggers swallow behavior, while there is a higher probability for stimulating laryngeal activation when activated further into expiration, suggesting PiCo's role in swallow-breathing coordination. PiCo triggers consistent swallow behavior and preserves physiologic swallow motor sequence, while stimulates laryngeal activation variable to stimulation duration. Sufficient bilateral PiCo activation is necessary for gating function since activation of only a few PiCo neurons or unilateral activation leads to blurred behavioral response. Viral tracing experiments reveal projections from the caudal nucleus of the solitary tract (cNTS), the presumed swallow pattern generator (SPG), to PiCo and vice versa. However, PiCo does not directly connect to laryngeal muscles. Investigating PiCo's role in swallow and laryngeal coordination will aid in understanding discoordination in breathing and neurological diseases.

Effect of pharmacological inhibition of the pontine respiratory group on swallowing interneurons in the dorsal medulla oblongata

OBJECTIVES

To examine the role of neurons of the pontine respiratory group (PRG) overlapping with the Kölliker-Fuse nucleus in the regulation of swallowing, we compared the activity of swallowing motor activities and interneuron discharge in the dorsal swallowing group in the medulla before and after pharmacological inhibition of the PRG.

METHODS

In 23 in situ perfused brainstem preparation of rats, we recorded the activities of the vagus (VNA), hypoglossal (HNA), and phrenic nerves (PNA), and swallowing interneurons of the dorsal medulla during fictive swallowing elicited by electrical stimulation of the superior laryngeal nerve or oral water injection. Subsequently, respiratory- and swallow-related motor activities and single unit cell discharge were assessed before and after local microinjection of the GABA-receptor agonist muscimol into the area of PRG ipsilateral to the recording sites of swallowing interneurons.

RESULTS

After muscimol injection, the amplitude and duration of swallow-related VNA bursts decreased to 71.3 ± 2.84 and 68.1 ± 2.76 % during electrically induced swallowing and VNA interburst intervals during repetitive swallowing decreased. Similar effects were observed for swallowing-related HNA. The swallowing motor activity was similarly qualitatively altered during physiologically induced swallowing. All 23 neurons were changed in either discharge duration or frequency after PRG inhibition, however, the general discharge patterns in relation to the motor output remained unchanged.

CONCLUSION

Descending synaptic inputs from PRG provide control of the primary laryngeal sensory gate and synaptic activity of the PRG partially determine medullary cell and cranial motor nerve activities that govern the pharyngeal stage of swallowing.