Seiji Takagi

Convergence of laryngeal afferents with different natures upon cat NTS neurons

To clarify the convergence of laryngeal afferents within the nucleus tractus solitarius (NTS) in the cat, we examined in the medulla the response characteristics of superior laryngeal nerve (SLN) fibers and NTS neurons to mechanical and chemical stimulation applied to laryngeal mucosa by extracellular recordings. The response was recorded in 75 SLN primary afferent fibers (PAFs) and 92 NTS neurons. PAFs of the SLN consisted of numerous monomodal mechanosensitive fibers and a small number of chemosensitive and polymodal fibers. On the other hand, the majority of NTS neurons had a polymodal nature. Thus, laryngeal information is considered to be integrated in modality into NTS neurons. All mechanosensitive fibers received information from a small restricted field in the larynx. On the contrary, each NTS neuron responded to mechanical stimulation over a wide laryngeal field, indicating that information from different sites spatially converge on NTS neurons. Our results suggest that caudal NTS neurons play a cardinal role in integrating laryngeal afferents, which are thought to elicit laryngeal reflexes.

Surgical Treatment for Dysphagia of Neuromuscular Origin

There are a number of surgical procedures which can be used to improve swallowing in selected dysphagic patients. These include: vocal fold augmentation or medialization, cricopharyngeal myotomy, laryngeal suspension, intrahyoid myotomy, lateral thyrolaminectomy and tracheoesophageal separation procedures. This article describes these various procedures and their appropriate application to selected dysphagic patients. Results of a study of the location of the recurrent laryngeal nerve in relation to the cricopharyngeal muscle are also presented.

Crossing inputs of the superior laryngeal nerve afferents to medullary swallowing-related neurons in the cat

To understand the neural mechanism for generation of synchronous activity on both sides during swallowing, we examined the convergence of inputs from the bilateral superior laryngeal nerves (SLNs) in the urethane-anesthetized cat medulla and we also examined the changes in swallowing outputs after a longitudinal brain-stem split in decerebrate cats. Twenty-six (31%) of 84 swallowing-related neurons (SRNs) that were oligosynaptically activated by ipsilateral SLN stimulation and recorded mostly in the reticular formation received contralateral inputs, which were confirmed by orthodromic spike responses (n = 16) or were detected as subliminal facilitatory or inhibitory inputs (n = 10) using conditioning-test stimuli. The rate of convergence of inputs from bilateral SLNs in these SRNs was significantly higher than that (4%) in the SRNs that were regarded as sensory-relay neurons in the nucleus tractus solitarius (NTS). The SRNs receiving signals from the contralateral SLN were located diffusely from the NTS and the adjacent reticular formation to the nucleus ambiguus (NA) and the reticular formation dorso-medial to the NA. A midsagittal split from 3 mm caudal to 6 mm rostral to the obex could change symmetrical swallowing to unilateral swallowing. Thus the crossing projections to the contralateral SRNs appear to contribute to symmetrical swallowing.

Adenoid cystic carcinoma of the lacrimal gland with wide and severe myoepithelial differentiation

Adenoid cystic carcinoma (ACC) of the lacrimal gland is the second most common epithelial tumor for which different biologic courses can be predicted by histologic criteria. Three main types of growth patterns, cribriform; tubular; and solid have been identified. Tumors with solid components frequently follow a more aggressive clinical course and show worse prognosis than those with other patterns. We herein report a case of ACC with wide and severe myoepithelial differentiation arising from the lacrimal gland and presenting with aggressive clinical behavior. Postoperative radiotherapy may be the treatment of choice to control residual lesions and provide long-term survival even in the case of incomplete resection. Despite extensive surgery and radiation therapy, the prognosis of these tumors, especially with solid components, remains extremely poor. Accurate diagnosis is important because tumor histopathology is generally believed to be the most significant factor in patient survival.

Characteristics of laryngeal receptors analyzed by presynaptic recording from the cat medulla oblongata

In order to clarify the neural mechanisms for the protective laryngeal reflex, we conducted physiological analysis of laryngeal sensory receptors. In the present study, presynaptic unit activities, which might accurately reflect characteristics of the laryngeal receptor, were recorded with a glass microelectrode in the nucleus of the tractus solitarius of the medulla oblongata in ketamine-urethane anesthetized cats, and the responses to the mechanical and/or chemical stimuli were analyzed. From the results, it was demonstrated that highly sensitive mechanoreceptors and polymodal receptors exist in the laryngeal mucosa; they are particularly numerous in the laryngeal surface of the epiglottis and arytenoid region, and uncommon in the vocal fold. Mechanoreceptors on the laryngeal mucosa were classified into a rapidly adapting group and a slowly adapting group, while all polymodal receptors adapted rapidly to mechanical stimulation. These results suggest that these non-specific polymodal and rapidly adapting receptors may correspond to more superficial receptors such as free nerve endings and some taste buds, and also monomodal slowly adapting mechanoreceptors may correspond to deeper terminals in the subepithelium. It is also considered possible that the structures and the characteristics of these receptors are appropriate to elicit the protective laryngeal reflexes by non-specifically detecting various kinds of stimuli.