Yozo Miyaoka

Diuresis mediated by the superior laryngeal nerve in rats

Diuresis mediated by the superior laryngeal nerve (SLN) was investigated using pentobarbital-anesthetized rats. A marked increase in urine flow was induced by application of water to the larynx. The diuretic effect of water was conspicuous during the first 30 min after the application and lasted for more than 1 hr. In contrast, a 160 mM solution of NaCl produced only slight diuresis. After bilateral sectioning of the SLNs, water-induced diuresis was considerably reduced. The results suggest that water fibers contained in the SLN may make a major contribution to the diuresis.

Responses of Neurons in the Parabrachial Region of the Rat to Electrical Stimulation of the Superior Laryngeal Nerve and Chemical Stimulation of the Larynx

The responsiveness of the parabrachial region to electrical stimulation of the superior laryngeal nerve was first examined in anesthetized rats. Action potentials were recorded in 30 parabrachial sites by single and train electrical pulses to the superior laryngeal nerve. The average latency, from the onset of stimulation to the first action potentials, was 9.9 ms (range, 6.5-18.8 ms). The responsiveness of parabrachial neurons to chemical stimulation of the laryngeal region was next examined using anesthetized, immobilized, and artificially ventilated rats in which the chorda tympani and glossopharyngeal nerves were bilaterally sectioned. Taste stimuli were applied to the laryngeal region through a tracheal tube and rinsed with 0.15 NaCl. A total of 66 responses were recorded from 26 neurons. The most effective stimulus for these neurons was 0.03 M hydrochloric acid, followed by 0.01 M quinine hydrochloride, 0.5 M sodium chloride, 0.5 M sucrose, and distilled water. Seven responses were derived from 0.15 NaCl. These neurons were mainly located in a posterodorsolateral part of the parabrachial nucleus. These results suggest that chemical signals from the laryngeal region are transmitted to the parabrachial nucleus through the superior laryngeal nerve.

Changes in water intake following pharyngolaryngeal deafferentation in the rat

The role of afferent information arising from the pharyngolaryngeal region in the regulation of water intake was evaluated in rats. The animals received picric application to the mucosa of either the pharyngolaryngeal or the hard palate region. Water intake of the pharyngolaryngeal treated animals was reduced significantly, while no reduction in water intake was shown in the control and hard palate treated animals.

Responses of parabrachial nucleus neurons to chemical stimulation of posterior tongue in chorda tympani-sectioned rats

Responses of parabrachial nucleus (PBN) neurons (n = 43) to chemical stimulation of the posterior tongue were recorded in chorda tympani (CT)-sectioned rats and compared with those (n = 45) in CT-intact. The chemical stimuli used were 0.5 M sucrose, 0.5 M sodium chloride (NaCl), 0.03 M hydrochloric acid (HCl), 0.01 M quinine hydrochloride, and distilled water. These stimuli were applied to an area posterior to the intermolar eminence of the tongue. Neurons of CT-sectioned rats responsive to the chemical stimuli were located in more caudal areas of the PBN compared with those of CT-intact. Numbers of responses to the five stimuli and breadth of responsiveness to the four basics were not different between both groups of rats. However, average response magnitudes of the neurons in CT-sectioned rats were lower than those in CT-intact. In both groups of rats, the response magnitudes to NaCl and HCl were larger than those to the other three stimuli, and responses to NaCl and those to HCl were highly correlated. It is suggested that glossopharyngeal fibers responding strongly to acids and salts are likely to be the main source of PBN responses from the posterior tongue.

Influence of Heartbeat on Voluntary Movement

The phase relationship between heartbeat and self-paced voluntary movement was evaluated on a key-tapping task while recording an electrocardiogram (ECG). The task was performed by either a rhythmic or a random manner with either the right or the left hand. The frequency of key-tapping movements was most just after the R-peak of the ECG in all conditions and decreased with increasing the interval from the R-peak in the left-hand conditions. The results suggest that the key-tapping movement might be paced by afferent signals arising from heartbeat.

Hypotonic diuresis following oropharyngeal stimulation with water in humans

The role of oropharyngeal mechanisms in body water regulation was studied in 12 human males by measuring urine output and osmolality before and after drinking a very small volume of distilled water (0.15 ml/kg b.w.t.). Hypotonic diuresis was resulted only in the subjects (n = 6) who drank only sufficient water to keep their oropharynx moist continually over a 20 min period but not in those who (n = 6) drank the same volume of water within several seconds. Sham verbal instructions on drinking induced no changes in subjects examined. These results suggest that oropharyngeal afferents alone, and neither gastric afferents nor psychosomatic effects, may account for hypotonic diuresis following water intake in man.

Autonomic nervous reflexes in respiration elicited by mechanical stimulation of the velopharyngeal region in rabbits.

Reflex increases in peak activity of the diaphragm and expiratory pharyngeal muscles were recorded in lightly anesthetized and vagotomized rabbits by gentle mechanical stimulation of the nasal surface of the soft palate and of the posterior wall of the nasopharynx. No noticeable change in diaphragmatic activity was evoked by gentle mechanical stimulation of the oral surface of the soft palate and of the posterior wall of the oropharynx. The present results suggest that afferent signals from mechanoreceptors of the velopharyngeal region may contribute to reflex augmentation of respiration.

SENSATION OF THIRST IN NORMAL AND LARYNGECTOMIZED MAN

The purpose of this study was to evaluate the role of the larynx in sensation of thirst and to identify precise areas responsible for the sensation in normal and laryngectomized groups. The present analysis showed that the laryngectomized group was less aware of the sensation and less able to localize it than the normal group. Both groups localized the sensation from the base of the tongue to the larynx as well as in the pharynx.

Differences in Drinking Behavior between Normal and Laryngectomized Man

The properties of drinking in normal and laryngectomized groups were examined. Drinking associated with meals was more frequent in the 76 young and 37 older normal subjects than the 25 laryngectomized persons. The laryngectomized group preferred tea and coffee to water to alleviate thirst sensation, while such a preference was hardly seen in either normal group. Results suggest that the larynx may contribute not only to thirst sensation but may be associated with preference in drinking.

Reflexogenic Areas for Velopharyngeal Closure in Rabbits

Abstract. Responsive areas for velopharyngeal closure were examined by recording diaphragmatic and superior pharyngeal constrictor activities of anesthetized rabbits. Pressure stimulation was applied with a cotton applicator to the mucosae of three pharyngeal areas: the anterior (palatal) and posterior walls of the nasopharynx and the posterior wall of the oropharynx. The intensity and duration of the stimulation were around 9.0 gf and 0.43 sec, respectively. Velopharyngeal closure was elicited more frequently from the posterior wall of the nasopharynx than the other two areas tested. The higher responsiveness of the posterior wall of the nasopharynx for velopharyngeal closure is suggested to be attributed to higher density and/or lower threshold of pressure receptors in this area than those in the other two areas tested. Possible physiological implications of the present results are discussed.