Kyuhachiro Shimada

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.

Differential controls of small and large motor unit activity in the masseter muscle with incisal stimulation in humans.

The activity of masseter motor units with different spike amplitudes was recorded and reflex responses by force stimulation of an incisor were analyzed in humans. The effects of reflex responses varied depending on the level of prestimulus firing frequency (background activity, BGA). When small amplitude motor units and large amplitude motor units were tested at the same level of BGA, the former tended to exhibit excitatory reflexes and the latter inhibitory ones.

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.

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.

Masticatory muscle activities during rhythmic jaw movement associated with tooth contact in lightly anesthetized rats

Rhythmic jaw movements were observed in lightly anesthetized rats when a bitable object was placed between the maxillary and mandibular incisors. To elicit the jaw movements, an initiating stimulus was required. A successful stimulus was to push on the mandible at the incisors in both opening and posterior directions. This may be a suitable movement for studying mastication because of the following properties: (i) The rhythmic jaw movements could not continue without tooth contact. (ii) The timing pattern of the electromyographic activity of the masseter and digastric muscles and the tooth contact was similar to that of human mastication. (iii) Frequency of the movements was independent of hardness of the object placed between the incisors, though oral stimulation easily stopped the movement as did a noxious stimulus applied around the oral cavity. We conclude that peripheral activation, which may be generated by tooth contact, is as essential to the rhythmic jaw movement as central activation.

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.

Vagal control of pharyngeal constrictor activity in rabbits.

Abstract. The neural control mechanism of pharyngeal constrictor (PC) activity of rabbits was examined in relation to vagal afferents. The average firing rate of single PC units of unilaterally vagotomized animals increased from 0.52 to 8.83 spikes/sec by cooling of the intact vagus nerve at 5°C. Time courses of increases in PC and diaphragmatic (Dia) activities were examined during the period from the start of vagal cooling to the time when the PC reached the maximum firing rate. Although Dia activity linearly increased along with the respiratory cycles, PC activity slowly increased during the first three-quarters of the period and rapidly increased during the last quarter. The result suggests that more impulses in the vagus nerve are required to be blocked by cooling at a lower temperature for eliciting an increase in PC activity compared with that in Dia activity. The increase in PC activity evoked by bilateral vagotomy (from 0.30 to 10.07 spikes/sec) was not different from that by vagal cooling. The presumable afferent nerve fibers responsible for the increase in PC activity were discussed.