GABA receptor-mediated inhibition of reflex deglutition in the cat

Mapping research trends regarding the mechanism of dysphagia from 1993 to 2023: a bibliometrics study and visualization analysis

As a common consequence of various neurogenic disorders, dysphagia has a significant impact on the quality of life for patients. To promote the development the field of swallowing, it will be helpful to clarify the pathological and therapeutic mechanisms of dysphagia. Through visual analysis of related papers from 1993 to 2023 in the Web of Science Core Collection (WoSCC) database, the research status and development trend of the pathogenesis of dysphagia were discussed. The co-occurrence study was finished using CiteSpace 6.2 R4 software, including keywords, countries, institutions, and authors. Finally, 1,184 studies satisfied the inclusion requirements. The findings of the visualization analysis suggested that aspiration and gastroesophageal reflux disease would be the areas of greatest interest for researchers studying the mechanism of dysphagia. As for the latest occurred research trends, fMRI, signals and machine learning emerging into the field of view of researchers. Based on an analysis of country co-occurrence, United States, Japan and China rank the top three, in terms of the number of publications on dysphagia. University System of Ohio is the organization that has published the most amount of articles regarding the mechanism of dysphagia. Other highly published schools in the top three include State University System of Florida and Northwestern University. For the prolific authors, German, Rebecca Z published the most articles at present, whose own research team working closely together. Several closely cooperating research teams have been formed at present, including the teams centered around German, Rebecca Z, Warnecke, Tobias and Hamdy Shaheen. This study intuitively analyzed the current research status of the mechanism of dysphagia, provided researchers with research hotspots in this field.

Estimating the Risk of Pneumonia in Patients With Schizophrenia Newly Receiving Clozapine: A Nationwide Cohort Study

PURPOSE/BACKGROUND

Patients with schizophrenia are vulnerable to pneumonia. Clozapine is associated with the greatest risk of pneumonia. We investigated the risk factors of pneumonia in patients with schizophrenia who use clozapine.

METHODS/PROCEDURES

We used a large cohort of patients with schizophrenia (N = 22,774) who newly use clozapine (baseline). We divided the data set into a training cohort (entry between 1998 and 2008, n = 18,496) and test cohort (entry between 2009 and 2012, n = 4278), where 483 and 168 patients developed pneumonia requiring hospitalization within 1 year after baseline, respectively. For prediction, we developed a static model using Cox proportional hazards regression and a dynamic model using Cox regression with time-dependent modeling. Areas under receiver operating curves (AUCs) for the predictive model were estimated in the training cohort and then in the test cohort for validation.

FINDINGS/RESULTS

Based on the baseline characteristics, the static model for predicting pneumonia in 3 periods (90, 180, and 365 days) was unsatisfactory (AUCs, 0.64, 0.64, and 0.65, respectively). The predictors were older age, male sex, history of nonpsychiatric hospitalization, dementia, asthma, and tuberculosis within 1 year before baseline. However, the results were improved (AUCs, 0.83, 0.79, and 0.77, respectively) after control for time-dependent variables, namely, duration of clozapine use and concomitant medications (ie, benzodiazepines, valproic acid, systemic corticosteroids).

IMPLICATIONS/CONCLUSIONS

Several risk factors for predicting subsequent pneumonia after initial use of clozapine were explored, including older age, male, history of nonpsychiatric hospitalization, dementia, asthma, tuberculosis, benzodiazepines, valproic acid, systemic corticosteroids, and the use duration of clozapine. Clinical staff can use the risk factors to administer evidence-based treatment.

Benzodiazepines and risk of pneumonia in schizophrenia: a nationwide case-control study

OBJECTIVES

To investigate the relationship between benzodiazepine and risk of developing pneumonia in patients with schizophrenia, whose benzodiazepine dosage and usage frequency was higher than that of the general population.

METHODS

We conducted a nested case-control study to assess the association between benzodiazepine use and pneumonia among patients with schizophrenia. By using the Taiwan National Health Insurance Research Database, we identified a schizophrenia cohort comprising 34,929 patients during 2000-2010. Within the schizophrenia cohort, 2501 cases of pneumonia and 9961 matched control patients (1:4 ratio) were identified. Benzodiazepine exposure was categorized by drug, treatment duration, and daily dose. Conditional logistic regression models were used to examine the association between benzodiazepine exposure and the risk of pneumonia.

RESULTS

The current use (within 30 days) of midazolam led to the highest pneumonia risk (adjusted risk ratio = 6.56, P < 0.001), followed by diazepam (3.43, P < 0.001), lorazepam (2.16, P < 0.001), and triazolam (1.80, P = 0.019). Furthermore, nearly all the benzodiazepines under current use had a dose-dependent effect on pneumonia risk. The risk of pneumonia was correlated with the affinities of γ-aminobutyric acid A α1, α2, and α3 receptors.

CONCLUSIONS

Benzodiazepines had a dose-dependent relationship with pneumonia in patients with schizophrenia. The differences in risk and mechanism of action of the individual drugs require further investigation. Clinicians should be aware of the early signs of pneumonia in patients with schizophrenia receiving benzodiazepines.

Central inhibition of initiation of swallowing by systemic administration of diazepam and baclofen in anaesthetized rats

Dysphagia is caused not only by neurological and/or structural damage but also by medication. We hypothesized memantine, dextromethorphan, diazepam, and baclofen, all commonly used drugs with central sites of action, may regulate swallowing function. Swallows were evoked by upper airway (UA)/pharyngeal distension, punctate mechanical stimulation using a von Frey filament, capsaicin or distilled water (DW) applied topically to the vocal folds, and electrical stimulation of a superior laryngeal nerve (SLN) in anesthetized rats and were documented by recording electromyographic activation of the suprahyoid and thyrohyoid muscles and by visualizing laryngeal elevation. The effects of intraperitoneal or topical administration of each drug on swallowing function were studied. Systemic administration of diazepam and baclofen, but not memantine or dextromethorphan, inhibited swallowing evoked by mechanical, chemical, and electrical stimulation. Both benzodiazepines and GABA_A receptor antagonists diminished the inhibitory effects of diazepam, whereas a GABA_B receptor antagonist diminished the effects of baclofen. Topically applied diazepam or baclofen had no effect on swallowing. These data indicate that diazepam and baclofen act centrally to inhibit swallowing in anesthetized rats.NEW & NOTEWORTHY Systemic administration of diazepam and baclofen, but not memantine or dextromethorphan, inhibited swallowing evoked by mechanical, chemical, and electrical stimulation. Both benzodiazepines and GABA_A receptor antagonists diminished the inhibitory effects of diazepam, whereas a GABA_B receptor antagonist diminished the effects of baclofen. Topical applied diazepam or baclofen was without effect on swallowing. Diazepam and baclofen act centrally to inhibit swallowing in anesthetized rats.

Overstimulation of the inhibitory nervous system plays a role in the pathogenesis of neuromuscular and neurological diseases: a novel hypothesis

Based upon a thorough review of published clinical observations regarding the inhibitory system, I hypothesize that this system may play a key role in the pathogenesis of a variety of neuromuscular and neurological diseases. Specifically, excitatory overstimulation, which is commonly reported in neuromuscular and neurological diseases, may be a homeostatic response to inhibitory overstimulation. Involvement of the inhibitory system in disease pathogenesis is highly relevant, given that most approaches currently being developed for treating neuromuscular and neurological diseases focus on reducing excitatory activity rather than reducing inhibitory activity.

Effects of morphine and midazolam on pharyngeal function, airway protection, and coordination of breathing and swallowing in healthy adults

BACKGROUND

Drugs used for sedation in anesthesia and intensive care may cause pharyngeal dysfunction and increased risk for aspiration. In this study, the authors investigate the impact of sedative doses of morphine and midazolam on pharyngeal function during swallowing and coordination of breathing and swallowing.

METHODS

Pharyngeal function, coordination of breathing and swallowing, and level of sedation were assessed by manometry, videoradiography, measurements of respiratory airflow, and a visual analog scale in 32 healthy volunteers (age 19 to 35 yr). After baseline recordings, morphine (0.1 mg/kg) or midazolam (0.05 mg/kg) was administered intravenously for 20 min, followed by recordings at 10 and 30 min after the end of infusion.

RESULTS

Pharyngeal dysfunction, seen as misdirected or incomplete swallowing or penetration of bolus to the airway, increased after morphine infusion to 42 and 44% of swallows compared with 17% in baseline recordings. Midazolam markedly increased incidence of pharyngeal dysfunction from 16 to 48% and 59%. Morphine prolonged apnea before swallowing, and midazolam increased the number of swallows followed by inspiration.

CONCLUSION

Morphine and midazolam in dosages that produce sedation are associated with increased incidence of pharyngeal dysfunction and discoordinated breathing and swallowing, a combination impairing airway protection and potentially increasing the risk for pulmonary aspirations.

Diagnosis and management of oropharyngeal Dysphagia and its nutritional and respiratory complications in the elderly

Oropharyngeal dysphagia is a major complaint among older people. Dysphagia may cause two types of complications in these patients: (a) a decrease in the efficacy of deglutition leading to malnutrition and dehydration, (b) a decrease in deglutition safety, leading to tracheobronchial aspiration which results in aspiration pneumonia and can lead to death. Clinical screening methods should be used to identify older people with oropharyngeal dysphagia and to identify those patients who are at risk of aspiration. Videofluoroscopy (VFS) is the gold standard to study the oral and pharyngeal mechanisms of dysphagia in older patients. Up to 30% of older patients with dysphagia present aspiration-half of them without cough, and 45%, oropharyngeal residue; and 55% older patients with dysphagia are at risk of malnutrition. Treatment with dietetic changes in bolus volume and viscosity, as well as rehabilitation procedures can improve deglutition and prevent nutritional and respiratory complications in older patients. Diagnosis and management of oropharyngeal dysphagia need a multidisciplinary approach.

Involvement of ERK phosphorylation in brainstem neurons in modulation of swallowing reflex in rats

In order to evaluate the neuronal mechanisms underlying functional abnormalities of swallowing in orofacial pain patients, this study investigated the effects of noxious orofacial stimulation on the swallowing reflex, phosphorylated extracellular signal-regulated kinase (pERK) and gamma-aminobutyric acid (GABA) immunohistochemical features in brainstem neurons, and also analysed the effects of brainstem lesioning and of microinjection of GABA receptor agonist or antagonist into the nucleus tractus solitarii (NTS) on the swallowing reflex in anaesthetized rats. The swallowing reflex elicited by topical administration of distilled water to the pharyngolaryngeal region was inhibited after capsaicin injection into the facial (whisker pad) skin or lingual muscle. The capsaicin-induced inhibitory effect on the swallowing reflex was itself depressed after the intrathecal administration of MAPK kinase (MEK) inhibitor. No change in the capsaicin-induced inhibitory effect was observed after trigeminal spinal subnucleus caudalis lesioning, but the inhibitory effect was diminished by paratrigeminal nucleus (Pa5) lesioning. Many pERK-like immunoreactive neurons in the NTS showed GABA immunoreactivity. The local microinjection of the GABA(A) receptor agonist muscimol into the NTS produced a significant reduction in swallowing reflex, and the capsaicin-induced depression of the swallowing reflex was abolished by microinjection of the GABA(A) receptor antagonist bicuculline into the NTS. The present findings suggest that facial skin-NTS, lingual muscle-NTS and lingual muscle-Pa5-NTS pathways are involved in the modulation of swallowing reflex by facial and lingual pain, respectively, and that the activation of GABAergic NTS neurons is involved in the inhibition of the swallowing reflex following noxious stimulation of facial and intraoral structures.

Effects of injecting GABAergic agents into the medullary reticular formation upon swallowing induced by the superior laryngeal nerve stimulation in decerebrate cats

The purpose of this study was to elucidate the role of the GABAergic system in the medullary reticular formation (MRF) in the control of swallowing. In acutely decerebrated cats (n = 12), swallowing was induced by electrical stimulation (0.3-6 V at 10-20 Hz for 10-20 s every minute) applied to the superior laryngeal nerve (SLN). The stimulus intensity was adjusted so that swallowing was induced two or four times during the period of the stimulation. Bicuculline, a GABA(A) receptor antagonist, was then injected (0.10-0.15 microl, 5 mM) into the MRF through a stereotaxically placed glass micropipette. In a total of 62 injections, 19 injections (30.6%) increased the frequency of SLN-induced swallowing when it was injected into the lateral part of the MRF corresponding to the nucleus reticularis parvocellularis (NRPv). In eight of the effective injections (42.1%) which increased the frequency of SLN-induced swallowing, SLN stimulation also induced coughing. With two injections, stimulation of the SLN-induced coughing but not facilitation of swallowing. On the other hand, an injection of 0.10-0.15 microl of 5 mM muscimol, a GABA(A) receptor agonist, into the NRPv decreased the frequency of SLN-induced swallowing. These results suggest that the NRPv neurons which are responsible for evoking swallowing are under the tonic inhibitory control of the GABAergic system.

Swallowing-like activity elicited in vitro in neonatal rat organ attached brainstem block preparation

The purpose of this study was to induce swallowing in an in vitro neonatal rat brainstem preparation and to analyze the circuit. When we applied GABA(A) receptor antagonist (bicuculine methiodide, BIC) into the the nucleus tractus solitarius (NTS) in the organ attached brainstem preparation of neonatal (0-3 days after birth) rats, jaw closing movement, palatal lifting, and tongue peristalsis-like movement were seen, subsequent to elevation of the tip of the tongue and anterior movement of the larynx (closure of the trachea). The NTS has been proposed to be a critical locus for swallowing pattern generation in mammals. Electrical stimulation into the NTS or the vagal afferent nerve (X) following an application of BIC (10 microM) to the recording chamber initiated the same organ movement. This movement caused temporary inhibition of respiratory activity that was simultaneously recorded from the fourth cervical ventral nerve (C4). We were also able to elicit this activity in a whole organ (from lip to stomach, midline intact) preparation, whose oral cavity was filled with dye (pontamine sky-blue 3 mM, 50 microl), using each of the three types of stimulation. The esophagus, which was never stained by spontaneous respiratory movements, was stained only after the experimental stimulation. We concluded that the activity elicited was swallowing-like activity and the smallest circuit for swallowing pattern generation exists in this preparation.

Brain stem control of swallowing: neuronal network and cellular mechanisms

Swallowing movements are produced by a central pattern generator located in the medulla oblongata. It has been established on the basis of microelectrode recordings that the swallowing network includes two main groups of neurons. One group is located within the dorsal medulla and contains the generator neurons involved in triggering, shaping, and timing the sequential or rhythmic swallowing pattern. Interestingly, these generator neurons are situated within a primary sensory relay, that is, the nucleus tractus solitarii. The second group is located in the ventrolateral medulla and contains switching neurons, which distribute the swallowing drive to the various pools of motoneurons involved in swallowing. This review focuses on the brain stem mechanisms underlying the generation of sequential and rhythmic swallowing movements. It analyzes the neuronal circuitry, the cellular properties of neurons, and the neurotransmitters possibly involved, as well as the peripheral and central inputs which shape the output of the network appropriately so that the swallowing movements correspond to the bolus to be swallowed. The mechanisms possibly involved in pattern generation and the possible flexibility of the swallowing central pattern generator are discussed.