A complex muscle fiber network in the cricothyroid muscle: a scanning electron microscopic study.

OBJECTIVES: To examine the three-dimensional ultrastructure of cricothyroid (CT) muscle fibers to elucidate their morphologic characteristics with regard to the specific functions of the muscle. STUDY DESIGN: An anatomic animal study. METHODS: The CT muscles of five adult rats were processed using the HCl-hydrolysis method to remove the peri- and intramuscular connective tissue components. The fine muscle fiber arrangements were observed by scanning electron microscopy. RESULTS: Complex muscle fiber interconnections (myomyous junctions) were identified in the muscles. Myomyous junctions were characterized by the connection of many villous processes that were 1 to 2 mum in diameter and 2 to 4 mum in length with a serrated appearance at the ends of a lateral branch or a bifurcating trunk of the muscle fibers. CONCLUSIONS: Myomyous junctions form a complex muscle fiber network, which is thought to synchronize the activity of the CT muscle fibers. This is the first three-dimensional demonstration of the muscle fiber network in the CT muscle; this network may play a major role in the functional specificity of the CT muscle.

Effects of antioxidants on auditory nerve function and survival in deafened guinea pigs.

Based on in vitro studies, it is hypothesized that neurotrophic factor deprivation following deafferentation elicits an oxidative state change in the deafferented neuron and the formation of free radicals that then signal cell death pathways. This pathway to cell death was tested in vivo by assessing the efficacy of antioxidants (AOs) to prevent degeneration of deafferented CNVIII spiral ganglion cells (SGCs) in deafened guinea pigs. Following destruction of sensory cells, guinea pigs were treated immediately with Trolox (a water soluble vitamin E analogue)+ascorbic acid (vitamin C) administered either locally, directly in the inner ear, or systemically. Electrical auditory brainstem response (EABR) thresholds were recorded to assess nerve function and showed a large increase following deafness. In treated animals EABR thresholds decreased and surviving SGCs were increased significantly compared to untreated animals. These results indicate that a change in oxidative state following deafferentation plays a role in nerve cell death and antioxidant therapy may rescue SGCs from deafferentation-induced degeneration.

Scanning electron microscopic study of the muscle fiber arrangement in the rat cricopharyngeal muscle.

CONCLUSIONS: Myomyous junctions comprise a complex muscle fiber network, which is thought to synchronize the activity of the cricopharyngeal (CP) muscle fibers. Myomyous and myotendinous junctions explain the heterogeneity in muscle fiber length which contributes to the efficient behavior of the muscle. This scanning electron microscopy (SEM) study demonstrated the complex muscle fiber arrangement of the CP muscle and improved on the previous description of its morphological specificity. OBJECTIVE: To examine the 3D ultrastructure of the inferior pharyngeal constrictor muscle fibers to obtain further knowledge of their morphological characteristics with regard to the specific functions of the muscle in deglutition. MATERIAL AND METHODS: Six adult rats were used. Their CP and thyropharyngeal (TP) muscles were obtained and processed using the HCl hydrolysis method to remove i.m. connective tissue. The fine muscle fiber structure was observed by means of SEM. RESULTS: Multifaceted muscle fiber interconnections (myomyous junctions) were identified in the CP muscle. The myomyous junctions were characterized by the tight connection of many finger-like processes at the ends of a lateral branch or bifurcating trunk of the muscle fibers. In addition, muscle fibers occasionally tapered and ended within the muscle belly, forming myotendinous junctions. The TP muscle lacked these structures.

Ganglion cells in the posterior cricoarytenoid muscle of the rat following experimental denervation.

OBJECTIVE: To investigate morphological changes of the i.m. ganglion cells in the posterior cricoarytenoid (PCA) muscle of the rat following denervation of the recurrent laryngeal nerve. MATERIAL AND METHODS: The recurrent laryngeal nerve on the left side of the rat was resected. Three weeks after transection, the PCA muscle was removed for morphological study using light and electron microscopy. RESULTS: No morphological changes were found in the i.m. ganglion cells in the PCA muscle, even though the myelinated nerve fibers were destroyed and had disappeared in ramified i.m. bundles. Around the cell body, numerous non-myelinated nerve fibers were found; these contained a large number of clear, spherical synaptic vesicles approximately 50 nm in diameter and several dense-cored vesicles approximately 100 nm in diameter. In contrast, neuromuscular junctions in most muscle fibers with partially disoriented and/or disintegrated myofibrils showed degenerative figures. In some instances, however, multiple nerve terminals were detected in contact with the postsynaptic membrane. Like the varicose swellings of non-myelinated nerve fibers around the ganglion cell body, these nerve terminals contained, in addition to clear synaptic vesicles (50 nm in diameter), several dense-cored vesicles (100 nm in diameter). CONCLUSION: We suggest that i.m. ganglion cells in the rat PCA muscle may supply postganglionic nerve fibers to the denervated neuromuscular junctions after transection of the nerve.

Delayed neurotrophic treatment preserves nerve survival and electrophysiological responsiveness in neomycin-deafened guinea pigs.

Benefits of cochlear prostheses for the deaf are dependent on survival and excitability of the auditory nerve. Degeneration of deafferented auditory nerve fibers is prevented and excitability maintained by immediate replacement therapy with exogenous neurotrophic factors, in vivo. It is important to know whether such interventions are effective after a delay following deafness, typical for the human situation. This study evaluated the efficacy of brain-derived neurotrophic factor (BDNF) and ciliary neurotrophic factor axokine-1 analogue (CNTF Ax1) application, 2 or 6 weeks postdeafening, in preventing further degeneration and a decrease in excitability. Guinea pigs were deafened and implanted with intracochlear stimulating electrodes, a scala tympani cannula-osmotic pump system, and auditory brainstem response (ABR) recording electrodes. Subjects received BDNF + CNTF Ax1 or artificial perilymph (AP) treatment for 27 days, beginning at 2 or 6 weeks following deafening. Electrical (E) ABR thresholds increased following deafening. After 1 week, in the 2-weeks-delayed neurotrophic factor treatment group, EABR thresholds decreased relative to AP controls, which were statistically significant at 2 weeks. In the 6-week delay group, a tendency to enhanced EABR sensitivity began at 2 weeks of treatment and increased thereafter, with a significant difference between neurotrophic factor- and AP-treated groups across the treatment period. A clear, statistically significant, enhanced survival of spiral ganglion cells was seen in both neurotrophic factor treatment groups relative to AP controls. These findings demonstrate that BDNF + CNTF Ax1 can act to delay or possibly even reverse degenerative and, likely apoptotic, processes well after they have been activated. These survival factors can rescue cells from death and enhance electrical excitability, even during the period of degeneration and cell loss when the spiral ganglion cell population is reduced by >50% (6 weeks). It is noteworthy that this same degree of ganglion cell loss, secondary to receptor damage, is typically observed after a period equivalent to some years of deafness in humans.

Restoring vocal fold movement after transection and immediate suturing of the recurrent laryngeal nerve with local application of basic fibroblast growth factor: an experimental study in the rat.

OBJECTIVE: To evaluate the effects of basic fibro-blast growth factor (bFGF) on the recovery of vocal fold movement and the attenuation of laryngeal muscle atrophy after transection of the recurrent laryngeal nerve (RLN). STUDY DESIGN: Quantitative assessment of vocal fold movement using the video cassette recorder (VCR) image-analysis method and histologic examination of the laryngeal muscle. METHODS: Fifty-eight Wistar rats underwent RLN transection and one of the following three procedures: 1) transection of the RLN alone (transection group, n = 18), 2) suture of the nerve stumps followed by local administration of phosphate-buffered saline (PBS) solution using an osmotic pump (PBS group, n =20), or 3) suture of the nerve stumps followed by local administration of bFGF (FGF group, n = 20). Vocal fold movements were recorded with VCR by way of a rigid endoscope, and the VCR images were analyzed on a computer. Histologic changes in the thyroarytenoid (TA) muscle were evaluated by measuring the cross-sectional area of the muscle and average size of muscle fibers. RESULTS: In the transection group, vocal fold movement did not recover, and atrophy of the TA muscle gradually progressed after sectioning the nerve. In contrast, vocal fold movement as assessed by VCR image-analysis recovered in some cases in the immediate suturing groups, more markedly in the FGF group (34.1 +/- 29.1%) than in the PBS group (5.5 +/- 7.9%) (P <.05). Histologically, atrophy of the laryngeal muscle was significantly attenuated by the local administration of bFGF. CONCLUSION: bFGF facilitates regeneration of the transected RLN and attenuation of intrinsic laryngeal muscle atrophy, thereby restoring laryngeal function.

Age-related remodeling of the hypopharyngeal constrictor muscle and its subneural apparatuses: a scanning electron microscopical study in rats.

Age-related remodeling of the hypopharyngeal constrictor muscle was studied by comparing the morphological features of the subneural apparatus (SNA) of the thyropharyngeal (TP) and cricopha ryngeal (CP) muscles in young and old rats. Scanning electron microscopy revealed that the TP and CP muscles had both gutter- and depression-type SNAs, although different proportions of the two types of apparatus were found in each muscle. In young-adult rats, the gutter-type SNA was predominant in the TP muscle, whereas in the CP muscle the depression type was predominant. By contrast, in old rats, the depression-type SNA was predominant in the TP muscle, while no such transformation of the dominant SNA was noted in the CP muscle. In addition, the number of type IIb and type I muscle fibers was lower and greater, respectively, in older animals compared with those of younger animals. Furthermore, there were more type IIc fibers in the TP muscle of old rats, but no difference in the CP muscle between young and old animals. These findings suggest that the transformation of SNAs and the muscle fibers of the hypopharyngeal constrictor muscle takes place during aging and that their remodeling processes differ in the TP and CP muscles.

The distribution of ganglion cells in the posterior cricoarytenoid muscle of the normal adult rat. A light and electron microscopic study.

We employed by light and electron microscopy to examine the innervation of the posterior cricoarytenoid muscle of the adult rat. The laryngeal nerve was found to often bifurcate into two different bundles. One contained large myelinated (motor) nerve fibers, which were located along the frontal (ventral) muscle surface and entered the muscle at its middle portion to form neuromuscular contacts with individual muscle fibers. The other nerve bundle consisting of clustered ganglion cells (20-30 microm in diameter) and their associated nonmyelinated and small-sized myelinated nerve fibers were mainly found on the dorsal side of the muscle and often ran along the peripheral clefts or depressions of the muscle surface. The nerve bundle often extended side branches, which entered the muscle to be distributed among muscle fibers and near arterioles. Some ganglion cells are considered to enter the muscle, accompanied by branched nerves. Intramuscular ganglion cells and their associated nerve fibers examined by electron microscopy were similar in fine structure to perimuscular ganglion cells and their associated nerve fibers. Nerve fibers contained abundant clear synaptic vesicles which were cholinergic in nature, and often formed synapses with both neighboring axons and the cell body of the ganglion cells. These findings suggest that, in the rat posterior cricoarytenoid muscle, perimuscular and intramuscular ganglion cells exist and may be involved in innervating and contracting smooth muscle cells of the arterioles, thus regulating the blood flow or intravascular pressure.

Protection and regrowth of the auditory nerve after deafness: neurotrophins, antioxidants and depolarization are effective in vivo.

Deafness, with loss of sensory (hair) cells, results in progressive pathophysiological changes ending in the degeneration of most auditory nerve neurons. It is now possible to consider these events in the broader context of anti-apoptotic survival factors in the peripheral and central nervous system. One consequence of deafferentation of a neuron is the loss of neurotrophins that can lead to a change in oxidative state (formation of free radicals), changes in intracellular Ca(2+), and an up-regulation of apoptotic genes. Interventions that can modify availability of neurotrophins, [Ca(2+)](I), and/or free radical formation or their destructive effects, may preserve the auditory nerve. Some interventions (neurotrophins) may also lead to a regrowth of neurites. Studies in this area are of basic value and also of immediate clinical interest for the application of the cochlear prosthesis to the severe and profoundly deaf, since the benefits of this prosthesis are directly dependent on auditory nerve survival and the proximity of stimulating electrode to neuron. We, and others, have found that auditory nerve degeneration can be prevented by chronic electrical stimulation. We have demonstrated in vivo that this effect can be blocked by tetrodotoxin, thus indicating that propagated action potentials are a necessary condition, and by verapamil (Ca(2+) channel blocker), supporting in vitro studies by others, indicating that L-type Ca(2+) channels are necessary for stimulation-induced rescue of the deafferented auditory nerve. The intensities of electrical stimulation required for rescue are at levels sufficient to express the intermediate-early gene c-fos which can initiate transcription of anti-apoptotic genes and pathways, and up-regulate expression of neurotrophins that may act in an autocrine manner to protect the nerve from death. We, and others, have found that chronic local delivery (osmotic pump and microcannulation of the inner ear fluid spaces) of individual neurotrophins and cocktails of factors can also enhance survival of the deafferented nerve, and some can also initiate a regrowth of degenerated peripheral processes of the nerve into the region of the destroyed sensory epitheliae. Recently, we have shown that this rescue can occur with delayed intervention, after degeneration of some neurons has begun, more closely mimicking the human clinical situation. Finally, we have shown that interventions with antioxidants may also be effective in preventing pathophysiological changes of the auditory nerve following deafness. These studies in the auditory periphery support the 'neurotrophic factor hypothesis' as proposed as a general mechanism underlying neurodegenerative and age-related pathology of the central nervous system. Additional animal studies can yield a rational scientific basis to justify human trials, with a goal to maintain auditory cell survival and initiate and direct fiber growth to the next generation of prosthesis. Intimate contact between electrode and a dense population of auditory neurons should greatly enhance the benefits of these devices for the profoundly deaf.

Causes of recurrent laryngeal nerve paralysis.

OBJECTIVE: Persistent hoarseness due to recurrent laryngeal nerve paralysis (RLNP) reduces the quality of life unless it is adequately treated. This study examined the indications for phonosurgical intervention in patients with RLNP. MATERIALS AND METHODS: The medical records of the Ehime University Hospital, Ehime, Japan, from October 1976 until December 1997 were reviewed retrospectively to identify patients with RLNP. The data collected included age, gender, paralyzed side, and cause of paralysis. RESULTS: Four hundred and sixty-six patients with RLNP were identified: 262 males and 204 females. Unilateral RLNP was present in 422 patients, while 44 presented with bilateral RLNP. The incidence was relatively high in the 7th and 8th decades, and was twice as high in male patients as in female patients. The 466 patients were divided into 2 groups: Group 1 included 225 patients seen before January 1987, and Group 2 included 241 patients seen after this date. The number of patients with postoperative RLNP was significantly higher in Group 2 (124 of 239 patients) than in Group 1 (65 of 227 patients) (P<0.05). Surgery for cardiovascular disease, esophageal cancer, and skull base and thyroid gland tumors contributed to this increased incidence of postoperative RLNP. CONCLUSIONS: Patients with persistent unilateral RLNP require appropriate treatment for hoarseness, regardless of its cause. Since the incidence of RLNP related to surgery was significantly increased in Group 2, phonosurgery has become more important for improving the quality of life of these patients.