Stapedius Research Articles

茎乳突孔注入法によるアミノ配糖体抗生剤の聴器毒性評価と毒性発現機序に関する実験的研究

The ototoxicity of various aminoglycoside antibiotics was evaluated after a single injection into the facial nerve through the stylomastoid foramen and a mechanism of the inner ear damage was studied in rabbits. Tobramycin (TOB), gentamicin (GM), kanamycin (KM), amikacin (AMK) and dibekacin (DKB) were dissolved 100mg/ml respectively, and their 0.04ml were given. Histological findings of the hair cell in 24 hours and 10 days after the injection was observed by the surface preparation technique with a phase contrast microscope. The concentration of these drugs in perilymph and tympanic cavity was concurrently measured by the bioassay method.No hair cell damage was observable in any rabbit decapitated 24 hours after the injection. In the animals decapitated 10 days after the injection, however, the outer hair cells were damaged. The damage of the outer hair cell caused by TOB and GM was more severe than that by KM, AMK, or DKB. These results coincide with the ototoxicic evaluation of these drugs by general administration. There were no differences in the perilymph concentration between these drugs. Therefore it is thought that the difference of the ototoxicity resulting from the aminoglycoside antibiotics is due to the difference of their own otoxicities to the hair cells and not to the difference of their accumulation in the perilymph.In order to clarify a mechanism of inner ear damage after the injection into the facial nerve, the serial horizontal sections of the temporal bones after an injection of indian ink 0.04ml were observed histopathologically. The indian ink was transudated into the tympanic cavity from the dehiscence of the facial nerve and along the stapedius muscle and the auricular branch of the vagus nerve. The indian ink was also observed in the intracranial space and inner auditory canal. There was high concentration of the drugs in perilymph and tympanic cavity. It is concluded that the inner ear damage after the injection of aminoglycoside antibiotics into the facial nerve through the stylomastoid foramen is caused by the drugs, which arrived in the perilymph along the cochlear nerve and through the round and oval window from the tympanic cavity.

Delineating the facial nerve from the stapedius muscle.

Delineating the facial nerve from the stapedius muscle.

The stapedius muscle of the squirrel monkey

Contraction of the stapedius muscle (the acoustic reflex) is useful in the clinical diagnosis of various auditory disorders. In an effort to better understand the basic innervation of the acoustic reflex we are presently studying its neuroanatomy in the squirrel monkey (Saimiri sciureus). Since the morphology of the squirrel monkey stapedius muscle (SMSM) has not been previously described, we will present here our own findings from eleven muscles observed under light (LM) and transmission electron microscopy (TEM). Squirrel monkeys were perfused intracardially with either 10% neutral buffered formalin or 3% buffered glutaraldehyde. The stapedius muscles were dissected out under the operating microscope. For LM, the muscles were embedded in JB-4 plastic and cut serially at 5 micra and for TEM, the muscles were processed as previously described (2).The topography of the SMSM in the middle ear is similar to the human (3). The muscle attaches to the posterior side of the stapes' head by a thin collagenous tendon that extends almost midway into the muscle in a postero- ventral direction.

Histochemical characteristics of rabbit stapedius muscle

A histochemical analysis of rabbit stapedius muscle fibers was conducted using the myofibrillar ATPase and NADH-tetrazolium reductase techniques. Two different fiber types, type 1 and type 2b, were identified. The functional significance of the results is discussed.

The locations of stapedius and tensor tympani motoneurons in the cat.

The numbers and locations of motoneurons to the stapedius and tensor tympani muscles were determined by retrograde transport of horseradish peroxidase. Stapedius motoneurons lay outside the traditionally recognized facial nucleus, in several distinct locations: (1) in the interface between the facial nucleus and the superior olive; (2) in a thin, scattered lamina of somewhat smaller cells spread dorsal to the facial nucleus; and (3) in a cluster located ventromedial to the rostral third of the facial nucleus. Some cells also lay dorsal to the superior olive or scattered in the reticular formation, just medial to the descending loop of the facial nerve. Tensor tympani motoneurons also lay outside the traditionally recognized trigeminal motor nucleus, in an area just ventral to it. Both motoneuron pools were large, producing innervation ratios that establish stapedius and tensor tympani among the most finely innervated muscles yet studied. The degree of intermingling of large and small cells in these pools may explain, in part, why it has been easier to identify slow muscle fibers physiologically in tensor tympani than in stapedius.

Identification of the motoneurons innervating the stapedius muscle in Gallus gallus: a horseradish peroxidase study.

The location of the stapedial motoneurons in Gallus gallus was investigated by means of the retrograde transport of HRP, injected into the stapedius muscle. The labeled neurons are located in both the ventral and dorsal divisions of the VII nerve nucleus, in a lateral and ventral position respectively, facing the superior olivary nucleus. The neurons are distributed in two size classes. The functional implications of these findings are discussed, in relation both to the absence of the acoustic stapedial reflex in birds and to the functional properties of the stapedius muscle.

Ｂｅｌｌ麻ひとアブミ骨筋反射 ＩＩ 麻ひ経過におけるアブミ骨筋反射各種パラメーター値の推移について

In 34 cases with unilateral Bell's palsy which had both normal hearing and tympanogram of Type A, crossed SR was evaluated chronologically under the same stimulus range of sound pressure level by means of the oscilloscope to record the entire pattern of sound-induced waveform in addition to SR threshold. Amplitude, reflex contraction time (RCT) and reflex relaxation time (RRT) induced were set up for measurements as a parameter.The present investigations are chiefly concerned with how these parameters, described above, change according to the time course of facial palsy, on one hand, and on the other hand, which parameters can be the best indicators to reflex the recovery of the paralysis. Results obtained are as follows. 1. As for chronologic changes of SR parameters, on the paretic side, SR threshold decreases rapidly, amplitude increases, RCT is shortened and RRT is prolonged gradually according to the time course of facial palsy. 2. On the normal side, SR threshold increases, amplitude decreases and RRT is shortened gradually according to the time course of facial palsy. 3. RRT, on the normal side, is prolonged temporarily within 20 days after the onset of facial palsy. 4. Amplitude and RRT on the paretic side, and RRT on the normal side can be used for the prognostic diagnosis of facial palsy as the one of the best parameters to indicate the rcovery signs of facial palsy. 5. The function of stapedius nerve and muscle on the paretic side is reflected indirectly in SR parameters on the normal side. Therefore, if the time course of SR parameters on the normal side is investigated, the time course of the function of stapedius nerve and muscle on the paretic side can be made clear even before the restoration of SR.

Effect of the acoustic reflex on inner ear damage induced by industrial noise.

Shipyard noise is a variable noise which induces permanent threshold shift (PTS) in exposed workers. In humans, the stapedius reflex has been found to be very stable in this type of exposure. Temporary threshold shift (TTS) in the absence of stapedius reflex has been found to extend downwards through the speech-frequencies instead of showing a high frequency dip as when the stapedius reflex is normal. The features of PTS produced by the same type of noise was investigated in rabbits with and without functioning middle ear muscles. The auditory sensitivity was measured by auditory brain stem response (ABR) and by the stapedius reflex response. Middle ear muscle function was blocked by denervation of the stapedius muscle or by general anesthesia. With normal middle ear reflex very little PTS was found. When the muscles were inactivated during the noise exposure the PTS was very extensive and covered the mid frequency range. On the basis of previous findings in humans and the present animal study it is suggested that the features of the stapedius reflex should be considered both in assessment of individual susceptibility and design of optimal acoustic environments.

Evaluation of tensor tympani muscle dominance in the biphasic acoustic reflex.

The Acoustic reflex frequently causes a biphasic change in impedance at onset. Understanding the cause of the biphasic response is important for establishing a physiological basis for the clinical measurement of reflex latency. The decrease in impedance at onset may be due to uncoupling of impedance contributed by the cochlea. Subsequent increases in impedance predominantly reflect stapedius muscle activity. The clinical implications of this physiologic model are discussed.

Acoustic reflex patterns according to different intensity and different duration of white noise (WN) stimuli.

The data were gathered by connecting the output from a middle ear impedance meter (Amplaid 702) to the computer and averaging section of the Amplaid MK VI which was also used as an acoustic stimuli generator. The stimuli consisted of white noise bursts having different peak equivalent sound pressures (115, 105, 95, 85 dB SPL) and different durations (from 1000 to 3 msec). The parameters examined were: stapedius muscle contraction latency time; muscle fibre recruitment time, i.e. the interval between the onset of contraction and its maximum; duration of contraction; amplitude of maximum contraction. An evaluation was also made as to the "efficiency" of contraction, expressed as the function of duration and amplitude. The authors discuss the different patterns of "efficiency" curve achieved at various intensity levels by stimuli of different duration.

Results of stapes operations with preservation of the stapedius muscle tendon.

The material consisted of 195 operated otosclerotic ears. In 101 ears the stapedial tendon was left intact and in 94 ears it was divided. The follow-up period was approximately 8.0 years. The stapedius reflex was tested in 85 ears with intact tendon and in 25 with divided tendon. It was elicited in 50 of the former but in none of the latter. Both bone and air conduction thresholds were postoperatively poorer in ears with preserved tendon than in the ears with divided tendon. Revision surgery was performed in 19 ears, 13 of which had an intact stapedial tendon. The reason for reoperating was usually the fixation of the stapedial crus at the oval window margin. The crus may have shifted because of the pull exerted by the stapedial muscle. In spite of the better circulation to the stapes and the long process of the incus, and of possible protection against loud noises, we cannot, in the light of our experiences, recommend preservation of the stapedius muscle tendon.

Stapedius reflex in curarized subjects: an index of neuromuscular weakness.

To examine the validity of the acoustical stapedial reflex (AR) as an index of neuromuscular weakness, the AR was measured along with other indices of muscle strength during administration of d-tubocurarine (dTc) to six healthy subjects. AR decreased immediately after each dTc dose and preceded changes in handgrip strength and respiratory muscle strength, but the peak effects of each dose similarly affected AR and other muscle strength. The findings with electrocutaneous stimulation and effects on growth function of the AR indicate that dTc affects primarily stapedius muscle contraction, the efferent portion of the reflex arc, and does not affect afferent or central portions of the reflex. We therefore conclude that the AR is a valid index of the integrity of neuromuscular transmission which promptly reflects early phase weakness. Unlike other measures of muscle strength, AR testing does not depend on subject cooperation, and involves no discomfort. The test therefore provides a useful means of assessing neuromuscular weakness.

The Avian Stapedius Muscle

The influence of the solitary avian middle ear muscle, the m. stapedius, on auditory sensitivity and sound transmission was investigated in the domestic chicken, Gallus gallus. Electrophysiological recordings of inner ear microphonic potentials (MP) were made in order to determine the effects of calibrated, mechanically induced stapedius muscle (SM) tension changes on sounds reaching the auditory receptor cells. The maximum MP responses recorded during the pre-tension measurements were on the order of 200 microV and were linear (on a log-log scale) over a range of 40-100 dB SPL. Tension levels of 50-400 mN in the SM caused a reduction of up to 20 dB in the MP at frequencies throughout the auditory spectrum. It is concluded that the SM of Aves serves to protect the inner ear receptor cells against overstimulation. In addition to attenuating the amplitude of the MP response, SM tension changes caused significant changes in the phase of the signals reaching the inner ear. The magnitude of attenuation in the ipsilateral MP response to 200-400 mN of tension was found to be similar to the interaural attenuation that occurs when sound is transmitted to the ipsilateral ear from the contralateral ear via the intracranial passageway. The similarity in MP amplitude changes resulting from SM tension and intracranial transmission suggests that the SM may be involved in interaural interaction and thereby may aid in sound localization.

A histochemical characterization of muscle fiber types in the middle ear muscles of the cat. 1. The stapedius muscle.

The muscle fiber content of the stapedius muscle of the cat was determined histochemically using a combination of oxidative enzymes and glycolytic markers. The major fiber type present was determined to be the fast oxidative glycolytic type (FOG; 77%). Two other types of fiber were found that could not be placed into any of the classical muscle fiber categories. One of these fibers had little staining for actomyosin ATPase (1', 13%) while the other stained densely for this enzyme (2', 10%). These fibers could also be separated using fiber diameter as a criterion. The mean diameters of these different fibers were 22.8 Mm+/-6.3 (FOG fiber type), 14.8 micrometers+/-3.7 (1' fiber) and 14.9 micrometers+/-5.5 (2' fiber). Since the predominant fiber type (FOG) is adapted for fast contraction and fatigue resistance, the stapedius muscle of the cat is probably capable of fast repetitive contractions, a conclusion that fits well with much of the physiological data. Due to the fact that the 2' fibers were always paired with the 1' fibers, it is conceivable that these pairs may represent some specialized sensory structures (i.e. unencapsulated muscle spindles).

Effects of linear frequency modulated ramps on stapedius muscle reflex (SMR) in children

Thirty 6-year-old children with normal hearing, speech discrimination, and SMRs to tones and noise were given FM stimulation. A 2000-Hz tone was presented at 15 dB + SMR threshold until SMR decayed. The frequency was either modulated upward (to 40000 Hz) or downward (to 1000 Hz) in 100 ms for a series of intensity steps until a full contralateral SM contraction was recorded. Decay of the tonal SMR preceded FM testing at each step. The reciprocal to the 2000-Hz rising ramp was also employed and presented re the 4000-Hz tonal SMR. Ramps were filtered to equate intensity. All FM ramps induced a reactivation of the SMR. When equated at the percent of full contraction the 2000-Hz rising ramp had a larger dynamic range than either the falling or reciprocal conditions. The SMR waveform morphology varied with sound intensity. At high levels the SMR onset and offset was fast and the amplitude high, but as the sound intensity decreased onset and offset times increased and amplitudes reduced resulting in a broadening of the waveform.

Phasor admittance measurements of the middle ear

Conventional techniques for the measurement of the acoustic admittance of the middle ear are heavily dependent upon the mobility of the most flaccid parts of the tympanic membrane and relatively insensitive to abnormalities of the ossicular chain. This paper describes a method which has been developed to characterize the vibratory properties of the tympanic membrane and the ossicular chain separately. The technique is based on the analysis of trajectories traced by the middle-ear admittance phasor as either the external ear canal pressure, or the stapedius muscle tension, is modified. Consequently, the tympanic membrane and ossicular chain are each characterised by means of a natural frequency and damping ratio. Normative data are presented from 68 ears screened for middle-ear disease. The results indicate that the two measures are each relatively consistent between subjects, yet the two measures within subjects are independent of one another. Thus they provide tractable measures of middle-ear status.

A new type of striated muscle in mammalian body: Morphological, histochemical, and x-ray microanalytical observations of stapedius muscle in guinea pig

The guinea pig stapedial muscle presented an uncommon ultrastructural organization compared with its skeletal muscles or the stapedial muscles from other species. In the majority of muscle fibers the cross-sectional area was small (5–20 μm φ) and the nuclei were centrally located. Golgi complexes and centrioles were frequently found near the nuclei. The mitochondria had a dense matrix and contained a large number of dense granules, adjacent to the internal membranes. Nerves were found among the muscle fibers and had end plates with excessive numbers of vesicles. Capillaries appeared in a small number. Degenerating and split muscle fibers were common. The muscle fiber composition based on its stainability for myofibrillar ATPase exhibited the presence of type I and type II fibers, the latter with subtypes A, B, and C. Elemental analysis performed on unfixed cryosections revealed an extremely low potassium and high calcium and sodium concentrations. The highest concentrations of calcium and phosphorus were found in the mitochondrial areas. The quadriceps muscle of guinea pig was analyzed simultaneously and its elemental composition was similar to that found in ordinary striated skeletal muscles from rat and man.

Ultrastructure and elemental composition of the stapedius muscle in guinea pig.

Muscules stapedius in guinea pig was investigated with regard to morphology and elemental composition. The muscle fibers are multinucleated, contain a high amount of ribosomes, and a centriole is often found adjacent to the cell nucleus. Intramitochondrial inclusion bodies occur adjacent to cristae mitochondriales. Both type I and type II fibres occur, the latter with all three subtypes. Elemental analysis from the myofibrillar area revealed unexpected low concentration of K and high concentrations of NA, P, and Ca.

Basic contraction properties of the avian stapedius muscle.

The basic contraction properties of the solitary avian middle ear muscle, the M. stapedius, was investigated in chicken, Gallus gallus, by a sensitive tension transducer. Previous experimental studies on the in situ muscle preparation revealed both fast and slow components in the muscle's physiological responses. In the present study, brief electrical stimulus pulses delivered to the "isolated" M. stapedius elicited rapid twitch contractions with average tension levels of 46 mN for maximal stimulation. The contraction time was 15 ms, the half relaxation time was 15 ms and the total twitch time was 54 ms. Repetitive stimulation (2.5-200 Hz) revealed maximum summation of responses at 10-20 Hz and apparent complete fusion at 160 Hz. Peak tension at 160 Hz ranged from 150 mN to 200 mN. The twitch tetanus ratio was found to be 0.25. In earlier experiments with an in situ preparation, a slow component was observed in the physiological responses. However, this slow component was not seen in the single twitch responses or the responses or the response to repetitive stimulation in the present study. The M. stapedius of Gallus gallus was found to be a "fast" muscle by conventional terminology. Its contraction time is slightly shorter than the contraction times of the M. stapedius in mammals such as the cat (21 ms) and the rabbit (22 ms). These findings are consistent with earlier morphological studies which show the M. stapedius of Gallus gallus to have the features of a fast twitch muscle.

Animal models of tinnitus.

There are few physiological data available on the origin and nature of tinnitus. It is not even known whether tinnitus associated with cochlear pathology is a manifestation of increased or decreased activity in the cochlear nerve. In previous investigations of cochlear pathology, the spontaneous neural activity has generally been found to be depressed. In the present experiments, an animal model has been established by the administration of sodium salicylate in doses producing blood concentrations that evoke tinnitus in humans. Under these conditions, changes occur in cochlear nerve-fibre thresholds and tuning, similar to those obtained in other types of cochlear pathology. However, under salicylate, the distribution of spontaneous discharge shifts significantly to higher rates than normal. These changes are accompanied in some, but not all, fibres by changes in the temporal patterns of discharge suggestive of excitation. In the second animal model studied, a normal guinea-pig that had a naturally occurring continuous tonal emission, analogous to that recently recorded in human "physiological" tinnitus, was investigated in detail. The emitted signal was recorded in the ear-canal acoustic pressure and in the round-window potential. Several lines of evidence point to the signal as being cochlear in origin, including: its resistance to muscular paralysis and section of the stapedius muscle; the effects of changes in middle-ear pressure; its reversible elimination by hypoxia; and its suppression by tones of higher frequency.