Kazutomo Kitajima

Cortical and subcortical vestibular response to caloric stimulation detected by functional magnetic resonance imaging

The posterior insula, central sulcus, and inferior parietal lobule including the intraparietal sulcus have been considered the vestibular cortex based on functional brain mapping in humans as well as experiments in lower primates. The same regions receive optokinetic, visual, and proprioceptive projections. We examined the cortical and subcortical projection of vestibular activity with visual and proprioceptive input eliminated during caloric stimulation (CS), using functional magnetic resonance imaging (fMRI). Single-shot gradient-echo echoplanar image (EPI) volumes were sensitive to BOLD contrast in oblique orientation. We adopted a pharmacokinetic model for analysis of imaging data from 10 subjects as a group. The insular gyrus, intraparietal sulcus, superior temporal gyrus, hippocampus, cingulate gyrus, and thalamus showed activation by CS. Cortical and subcortical activation during CS in the present study was observed within regions less precisely delineated by other methods. As intraparietal sulcus activation showed right hemispheric dominance, this region may have an oculomotor projection as well as the vestibular input.

Vocal shimmer in sustained phonation of normal and pathologic voice.

Vocal shimmer during sustained phonation was measured in normal subjects and patients with laryngeal polyps, using the mean amplitude difference between consecutive cycles expressed in dB. A small laboratory computer was then used for measuring each discrete amplitude and for data processing. The results showed some overlap between the values for two groups studied, but nevertheless it appears that the measured value may be a useful index in screening for laryngeal disorders and for definitive diagnosis of such disorders.

Vasopressin and oxytocin receptor mRNAs are expressed in the rat inner ear.

THE cause of endolymphatic hydrops, a characteristic finding in Menières disease, is not known. To study the possible involvement of the neurohormones vasopressin and oxytocin in this condition, we investigated whether transcripts of the genes encoding the arginine vasopressin (AVP) and oxytocin receptors are expressed in the rat inner ear. Utilizing the reverse transcription-polymerase chain reaction (RT-PCR) method, primers specific for each receptor showed a single message band of the expected size in the rat inner ear. When the PCR products were cloned, the sequences were identical to those of the real-type (V2) AVP receptor and oxytocin receptor transcripts. The finding of vasopressin and oxytocin receptor mRNAs in the inner ear suggests that these neurohypophyseal hormones may have roles in the regulation of inner ear fluid. In particular, the presence of vasopressin receptor mRNA in the inner ear supports the hypothesis of a relationship between high plasma vasopressin levels and endolymphatic hydrops.

Studies of Cochlear Blood Flow in Guinea Pigs with Endolymphatic Hydrops

Laser Doppler flowmetry was used to assess cochlear blood flow (CoBF) in guinea pigs with experimental endolymphatic hydrops following intravenous infusion of 5 types of drugs: 50% glycerol, 70% isosorbide, 20% mannitol, 7% sodium bicarbonate, and 1% diphenidol. The magnitude of the CoBF changes following infusion tended to be smaller in the hydropic ears than in the normal control ears. A significant reduction in CoBF changes was observed in hydropic ears infused with isosorbide and sodium bicarbonate. These results suggest that the cochlear microvascular sensitivity to various stimuli such as drug infusion is reduced in hydropic ears. This may result from atrophy of the stria vascularis which is often observed in the hydropic ears of guinea pigs. Thus it seems likely that the same reaction occurs in the inner ear of patients with Ménière’s disease in whom atrophy of the stria vascularis is also presumed to exist in conjunction with extensive endolymphatic hydrops. Therefore, it seems probable that the function of the microvasculature of the stria vascularis is impaired in the inner ear of patients with Ménière’s disease, resulting in the slow progressive deterioration of the inner ear with time.

Regulation of inner ear fluid in the rat by vasopressin.

The anti-diuretic hormone vasopressin has been shown to be important in regulating inner ear fluid. The diuretic hormone, CNP, and its receptor, ANP-B receptor, may also function in the regulation of inner ear fluid. To determine whether vasopressin directly affects the fluid level, we infused this hormone to rat and assay of V2-AVP receptor mRNA by semiquantitative RT-PCR demonstrated a significantly lower level of this transcript in vasopressin-infused animals than in saline-infused animals. The levels of CNP and ANP-B receptors mRNA, however, were the same in both groups of rats. Results suggest that high plasma levels of vasopressin may be a principal causal factor of endolymphatic hydrops in Menieres disease, perhaps by down-regulating the number of vasopressin receptors.

Cricothyroid distance and vocal pitch. Experimental surgical study to elevate the vocal pitch.

To establish an experimental basis for surgical approximation of the anterior cricothyroid distance which aims at raising the vocal pitch, the relationship between vocal pitch and the cricothyroid distance was analyzed in voices produced with excised human larynges (four male and two female larynges). Within the framework of the experimental conditions, the following conclusions were drawn: 1) The vocal pitch expressed in semitones was almost linearly related to the cricothyroid distance, with an increase of 0.15 to 0.90 semitones per millimeter of cricothyroid approximation. 2) The rise in vocal pitch reached a plateau when the force applied to shorten the cricothyroid distance reached 30 to 50 gm.

Estimation of Subglottal Pressure with Intraoral Pressure

A method of estimating subglottal pressure through intraoral pressure has been reported in the literature. In order to determine its clinical usefulness, however, the method should be tested against direct measurements made on subjects with pathologic larynges. The present study was designed to compare intraoral pressure versus subglottal pressure, as measured with a sensing tube inserted through a tracheal stoma. Results showed that intraoral pressure of /i:pi:/ was almost equivalent to subglottal pressure of /i:/ when the latter was smaller than about 25 cmH20. When subglottal pressure exceeded this value, however, the intraoral pressure was smaller than the subglottal pressure. We conclude that the magnitude of subglottal pressure is not invariably identical with intraoral pressure.

Laryngeal phonatory reflex. The effect of anesthetization of the internal branch of the superior laryngeal nerve: Acoustic aspects.

The laryngeal phonatory reflex through the internal branch of the superior laryngeal nerve (SLN) was investigated by means of anesthetization of the nerve, after which acoustic signals were subjected to computer analysis to determine how anesthesia affected basic vocal parameters. Results showed that the anesthetization did not affect the abrupt cycle-to-cycle frequency changes and also did not influence the gross control of the fundamental frequency. But slower fluctuation of the fundamental frequency increased following anesthesia. From these results, it is suggested that the anesthetization of the internal branch of the SLN may derange the fine control mechanism of the larynx without affecting overall or gross performance of the phonatory apparatus.

Immunohistochemical localization of choline acetyltransferase of a peripheral type in the rat larynx

As shown in the accompanying paper, choline acetyltransferase, so far the best histochemical marker for identifying cholinergic structures, has at least one alternative splice variant. The variant, termed pChAT because of its preferential expression in peripheral organs, encouraged us to study peripheral, probably cholinergic, cells and fibers by immunohistochemistry using an antiserum against a peptide specific for pChAT. We chose the larynx of the rat, since cholinergic innervation in this organ has been well established by physiological studies, but not sufficiently by chemical neuroanatomy. Neuronal somata positive for pChAT were found in the intralaryngeal ganglia. Our double staining study indicated that these somata always possessed acetylcholinesterase activity, while the reverse did not hold true. Nerve fibers positive for pChAT were distributed widely in the intrinsic laryngeal muscles, laryngeal glands, blood vessels and laryngeal mucosa. In the intrinsic laryngeal muscles, pChAT-positive terminals were apposed closely to motor end-plates which were stained positively for acetylcholinesterase activity. Denervation experiments revealed that there were three types of pChAT-positive fibers in the larynx: (1) special visceral efferent fibers to the intrinsic laryngeal muscles, which decreased dramatically in number after vagotomy; (2) parasympathetic postganglionic fibers near the laryngeal glands and blood vessels, which appeared unaffected after vagotomy or cervical sympathectomy: and (3) afferent fibers innervating the laryngeal mucosa, which reduced markedly in number after vagotomy performed distal, but not proximal, to the nodose ganglion. Such afferent fibers remained unchanged following the neonatal capsaicin treatment, suggesting their independence from those containing substance P.

Clinical Outcome of Laryngotracheal Separation for Intractable Aspiration Pneumonia

Objectives: To confirm that laryngotracheal separation (LTS) is a satisfactory treatment for patients with intractable aspiration pneumonia, even though it does not require tracheoesophageal anastomosis. Study Design: Retrospective. Methods: Nine patients with intractable aspiration pneumonia underwent LTS at our institution from 1996 to 1999. Two patients underwent postoperative barium swallow radiography. Results: Neither halitosis nor stimulation of the cough reflex occurred due to pooled secretions in the blind pouch of the proximal tracheal segment. Barium swallow radiography confirmed that the secretions drained within 40 min by swallowing or a change in patient position. Conclusion: LTS is a satisfactory solution to the problem of chronic aspiration. Neither pooled secretions in the proximal tracheal segment nor fistula formation were significant postoperative problems.