Enhancement of swallowing motor activity by the ACE inhibitor imidapril in an arterially perfused rat preparation

Optical imaging of neurons related to fictive swallowing using GCaMP6f in an arterially perfused rat preparation

OBJECTIVE

It is difficult to comprehensively study the activity patterns and distribution of neurons in the brainstem that control the act of swallowing, as they are located deep in the brain. In this study, we aimed to evaluate the usefulness of calcium imaging using GCaMP6f in arterially perfused preparations to study the activity of swallowing-related neurons in the brainstem.

METHODS

Arterially perfused rat preparations were prepared 3-4 weeks after the injection of a neuron-specific virus expressing GCaMP6f. Fictive swallowing was induced by repetitive electrical stimulation of the superior laryngeal nerve (SLN). Simultaneously, the activity of GCaMP6f-expressing neurons in the dorsal brainstem, between 0.1 and 4.8 mm rostral to the obex, was assessed by changes in the intracellular calcium concentration using confocal laser microscopy.

RESULTS

Neurons responding to stimulation of the SLN included swallowing-related neurons (48%), which showed an increase in fluorescence intensity at the time of swallowing bursts in the cervical vagus nerve, and stimulation-related neurons (52%), which showed an increase in fluorescence intensity through stimulation, regardless of the swallowing bursts. Despite a broad search area, swallowing-related neurons were localized exclusively in and around the solitary nucleus. In contrast, most stimulation-related neurons were located in the brainstem reticular formation, which is more rostral than the solitary nucleus.

CONCLUSIONS

Calcium imaging using GCaMP in arterially perfused rat preparations is useful for an efficient search of the activity pattern and distribution of neurons located in a wide area of the brainstem.

Involvement of ghrelin in the regulation of swallowing motor activity in an arterially perfused rat preparation

Ghrelin, a peripheral peptide produced in the stomach, is involved in the neural networks that control food intake. Alterations in motor components, such as swallowing, are believed to be significant in the regulation food intake by orexigenic signals. However, there has been no detailed investigation of the relationship between ghrelin and swallowing activities induced in motor nerves innervating the pharyngeal and laryngeal muscles. In this study, we examined the effects of ghrelin administration on swallowing motor activity in arterially perfused rats. Injection of distilled water (0.5 ml) into the oral cavity or electrical stimulation of the superior laryngeal nerve evoked swallowing motor activity in the cervical vagus nerve. Administration of ghrelin (6 nM), but not des-acylated ghrelin (6 nM), into the perfusate increased the peak burst amplitude and burst duration, and shortened the first burst interval of water injection-induced swallowing. These ghrelin-induced changes in swallowing motor activity were blocked by the administration of JMV2959 (6 µM), a growth hormone secretagogue receptor antagonist. In preparations in which the hypothalamus was removed, ghrelin had no effect on swallowing motor activity. Furthermore, ghrelin-induced changes were counteracted by the administration of BIBO3304 (1 µM) or L-152,804 (1 µM), antagonists of neuropeptide Y Y1 and Y5 receptors, respectively, which are essential for ghrelin-induced enhancement of food intake. Ghrelin also increased the peak burst amplitude and burst duration of the swallowing motor activity evoked by electrical stimulation of the superior laryngeal nerve, although the effects of ghrelin on the number of swallowing bursts and burst intervals varied with stimulus intensity. These results suggest that ghrelin enhances the magnitude and frequency of bursts of swallowing motor activity by acting via the hypothalamic neural network, and that neuropeptide Y Y1 and Y5 receptors are involved in this enhancement.

Association Between Antihypertensive Use and Hospitalized Pneumonia in Patients With Stroke: A Korean Nationwide Population-Based Cohort Study

BACKGROUND

We aimed to examine the association between antihypertensive use and the incidence of hospitalized pneumonia in patients with a history of stroke.

METHODS

In this case-crossover study, we obtained data from the Korean National Health Insurance Service-National Sample Cohort database. We included the data of patients with history of stroke who were admitted with a disease code of pneumonia. We analyzed the patients' exposure to antihypertensives in the 30 (single case period), 90-120, and 150-180 days (2 control periods) before the onset of pneumonia using conditional logistic regression analysis. Additionally, sensitivity analysis and subgroup analysis according to diabetes status, age, and documented disability were performed.

RESULTS

Angiotensin II receptor blocker (ARB) use was associated with a reduced risk of hospitalized pneumonia (adjusted odds ratio [OR] [95% confidence interval; 95% CI]: 0.718 [0.576-0.894]). However, the use of angiotensin converting enzyme inhibitors and other antihypertensives were not associated with a change in hospitalized pneumonia incidence (adjusted OR [95% CI]: 0.902, [0.603-1.350] and 0.788 [0609-1.018], respectively). Subgroup analysis revealed that ARB use was associated with a reduced incidence of hospitalized pneumonia in patients with a history of stroke who were older than 65 years, but not in younger (≤ 65 years) group (adjusted OR [95% CI]: 0.687 [0.536-0.880]).

CONCLUSION

ARB use is associated with a reduced incidence of hospitalized pneumonia in patients with a history of stroke, especially in older adults.

Responses evoked by electrical stimulation of the brainstem reticular formation in the jaw-opening and hypoglossal motor nerves of an arterially perfused rat preparation

The interneuronal system in the brainstem reticular formation plays an important role in elaborate muscle coordination during various orofacial motor behaviors. In this study, we examined the distribution in the brainstem reticular formation of the sites that induce monosynaptic motor activity in the mylohyoid (jaw-opening) and hypoglossal nerves using an arterially perfused rat preparation. Electrical stimulation applied to 286 and 247 of the 309 sites in the brainstem evoked neural activity in the mylohyoid and hypoglossal nerves, respectively. The mean latency of the first component in the mylohyoid nerve response was significantly shorter than that in the hypoglossal nerve response. Moreover, the latency histogram of the first component in the hypoglossal nerve responses was bimodal, which was separated by 4.0 ms. The sites that induced short-latency (<4.0 ms) motor activity in the mylohyoid nerve and the hypoglossal nerve were frequently distributed in the rostral portion and the caudal portion of the brainstem reticular formation, respectively. Such difference in distributions of short-latency sites for mylohyoid and hypoglossal nerve responses likely corresponds to the distribution of excitatory premotor neurons targeting mylohyoid and hypoglossal motoneurons.