Participation of the nucleus tractus solitarius in the therapeutic effect of electroacupuncture on post-stroke dysphagia through the primary motor cortex

BACKGROUND

Post-stroke dysphagia (PSD), a common and serious disease, affects the quality of life of many patients and their families. Electroacupuncture (EA) has been commonly used effectively in the treatment of PSD, but the therapeutic mechanism is still under exploration at present. We aim to investigate the effect of the nucleus tractus solitarus (NTS) on the treatment of PSD by EA at Lianquan (CV23) through the primary motor cortex (M1).

METHODS

C57 male mice were used to construct a PSD mouse model using photothrombotic technique, and the swallowing function was evaluated by electromyography (EMG) recording. C-Fos-positive neurons and types of neurons in the NTS were detected by immunofluorescence. Optogenetics and chemical genetics were used to regulate the NTS, and the firing rate of neurons was recorded via multichannel recording.

RESULTS

The results showed that most of the activated neurons in the NTS were excitatory neurons, and multichannel recording indicated that the activity levels of both pyramidal neurons and interneurons in the NTS were regulated by M1. This process was involved in the EA treatment. Furthermore, while chemogenetic inhibition of the NTS reduced the EMG signal associated with the swallowing response induced by activation of M1 in PSD mice, EA rescued this signal.

CONCLUSION

Overall, the NTS was shown to participate in the regulation of PSD by EA at CV23 through M1.

Inhibition of Water-Evoked Swallowing During Noxious Mechanical Stimulation of Tongue in Anesthetized Rats

Dysphagia is sometimes accompanied by pain. Because orofacial structures subserve mastication and swallowing, orofacial pain might impair both functions. Tongue biting can occur not only accidentally while eating but also in some pathological conditions. However, it remains unclear whether noxious mechanical stimulation of the tongue affects swallowing. To explore this question, we evaluated the effects of lingual pinch stimulation on the initiation of swallowing evoked by distilled water (DW) infusion with a flow rate of 5.0 µL/s for 20 s into the pharyngolaryngeal region in anesthetized rats. The swallowing reflex was identified by electromyographic (EMG) bursts in the suprahyoid muscles which include the anterior belly of the digastric muscle, mylohyoid and geniohyoid muscles, and laryngeal elevation by visual inspection. The number of DW-evoked swallows during pinch stimulation was significantly smaller than that in a control condition or during pressure stimulation. The onset latency of the first swallow during pinch stimulation was significantly longer than that in the control condition. DW-evoked swallowing was almost abolished following bilateral transection of the superior laryngeal nerve (SLN) compared with the control condition, suggesting that the SLN plays a crucial role in the initiation of DW-evoked swallowing. Finally, electrophysiological data indicated that some SLN-responsive neurons in the nucleus tractus solitarii (nTS) exhibited delayed latency from a single SLN stimulation during lingual pinch stimulation. These results suggest that noxious mechanical stimulation of the tongue inhibits the initiation of swallowing and modulates neuronal activity in the nTS.

Excitatory neurons in paraventricular hypothalamus contributed to the mechanism underlying acupuncture regulating the swallowing function

Paraventricular hypothalamus (PVH) is demonstrated to regulate stress, feeding behaviors, and other related homeostatic processes. However, no direct evidence has been investigated for the role of PVH in swallowing function. Acupuncture therapy at Lianquan (CV23) acupoint has been reported to improve the swallowing function in clinical trials, but its underlying mechanism still needs to be uncovered. Thus, we aimed to explore whether PVH involved the acupuncture mediated regulating swallowing function. Chemogenetics, electromyography (EMG) recording, and immunofluorescence staining methods were combined to demonstrate that neurons in PVH could be activated by electroacupuncture (EA) stimulation at CV23, and this neuronal cluster was represented as excitatory neurons. Furthermore, we mapped both the inputs and outputs of PVH neurons using viral tracing. The neurons in PVH projected with the brain regions, including parabrachial nucleus (PBN) and the solitary tract nucleus (NTS), which both participated in the swallowing process. The EA function regulating the swallowing was attenuated after inhibiting the neurons in PVH in the post stroke dysphagia. In conclusion, this study suggested that EA at CV23 could regulate swallowing function involving the excitatory neurons in PVH.

Creation and Initial Validation of the Caregiver Analysis of Reported Experiences with Swallowing Disorders (CARES) Screening Tool

Purpose Dysphagia is a debilitating condition with widespread consequences. Previous research has revealed dysphagia to be an independent predictor of caregiver burden. However, there is currently no systematic method of screening for or identifying dysphagia-related caregiver burden. The aim of this study was to develop a set of questions for a dysphagia-related caregiver burden screening tool, the Caregiver Analysis of Reported Experiences with Swallowing Disorders (CARES), and pilot the tool to establish preliminary validity and reliability. Method The questionnaire was developed through an iterative process by a team of clinical researchers with expertise in dysphagia, dysphagia-related and general caregiver burden, and questionnaire design. A heterogenous group of 26 family caregivers of people with dysphagia completed the CARES, along with the Eating Assessment Tool (EAT-10), the International Dysphagia Diet Standardisation Initiative Functional Diet Scale (IDDSI-FDS), and the Zarit Burden Interview (ZBI). Information on construct validity, item fit, convergent validity, internal consistency, and reliability was determined via Rasch analysis model testing, Cronbach's alpha, and Spearman's rho calculations. Results The final CARES questionnaire contained 26 items divided across two subscales. The majority of the questionnaire items fit the model, there was evidence of internal consistency across both subscales, and there were significant relationships between dysphagia-specific burden (CARES) and perceived swallowing impairment (EAT-10), general caregiver burden (ZBI), and diet restrictiveness (IDDSI-FDS). Conclusions Results from the current study provide initial support for the validity and reliability of the CARES as a screening tool for dysphagia-related burden, particularly among caregivers of adults with swallowing difficulties. While continued testing is needed across larger groups of specific patient populations, it is clear that the CARES can initiate structured conversations about dysphagia-related caregiver burden by identifying potential sources of stress and/or contention. This will allow clinicians to then identify concrete methods of reducing burden and make appropriate referrals, ultimately improving patient care.

Involvement of capsaicin-sensitive nerves in the initiation of swallowing evoked by carbonated water in anesthetized rats

Capsaicin powerfully evokes the swallowing reflex and is a known therapeutic agent for improving dysphagia and preventing aspiration pneumonia. However, the role of capsaicin-sensitive nerves in the initiation of swallowing evoked by various natural stimuli remains unclear. To explore this question, we blocked laryngeal capsaicin-sensitive nerves following the coapplication of QX-314 and capsaicin (QX/Cap), and investigated the effects on swallowing evoked by mechanical and chemical stimulation in anesthetized rats. Swallows were evoked by capsaicin, carbonated water (CW), distilled water (DW), and punctate mechanical stimulation using von Frey filaments applied topically to the larynx. Swallows were documented by recording electromyographic activation of the suprahyoid and thyrohyoid muscles. The initiation of swallowing by capsaicin was strongly suppressed at 5 min following QX/Cap treatment and returned in a time-dependent manner. CW-evoked swallows at 5 min following QX/Cap treatment were significantly diminished compared with before and 30 min after treatment. In contrast, DW-evoked and mechanically evoked swallows were unchanged by QX/Cap treatment. Furthermore, CW-evoked swallows were virtually abolished by transection of the superior laryngeal nerves and significantly decreased by the topical application of acid-sensing ion channel-3 (ASIC3) inhibitor APETx2, but they were not affected by the nonselective transient receptor potential channel inhibitor ruthenium red or the ASIC1 inhibitor mambalgin-1. Taken together, we speculate that capsaicin-sensitive nerves play an important role in the initiation of CW-evoked swallows.NEW & NOTEWORTHY The initiation of swallowing evoked by laryngeal capsaicin and carbonated water application was diminished by the coapplication of QX-314 and capsaicin. Carbonated water-evoked swallows were also abolished by transection of the superior laryngeal nerves and were inhibited by the acid-sensing ion channel-3 inhibitor. Capsaicin-sensitive nerves are involved in the initiation of carbonated water-evoked swallows.