Upper airway motor outputs during vomiting versus swallowing in the decerebrate cat

Hair cells in the basilar papilla of birds have the capacity to regenerate after injury. Methods commonly used to induce cochlear damage are systemic application of ototoxic substances such as aminoglycoside antibiotics or loud sound. Both methods have disadvantages. The systemic application of antibiotics results in damage restricted to the basal 50% of the papilla and has severe side effects on the kidneys. Loud sound damages only small parts of the papilla and is restricted to the short hair cells. The present study was undertaken to determine the effect of local aminoglycoside application on the physiology and morphology of the avian basilar papilla. Collagen sponges loaded with gentamicin were placed at the round window of the cochlea in adult pigeons. The time course of hearing thresholds was determined from auditory brain stem responses elicited with pure tone bursts within a frequency range of 0.35-5.565 kHz. The condition of the basilar papilla was determined from scanning electron micrographs. Five days after application of the collagen sponges loaded with gentamicin severe hearing loss, except for the lowest frequency tested, was observed. Only at the apical 20% of the basilar papilla hair cells were left intact, all other hair cells were missing or damaged. At all frequencies there was little functional recovery until day 13 after implantation. At frequencies above 1 kHz functional recovery occurred at a rate of up to 4 dB/day until day 21, beyond that day recovery continued at a rate below 1 dB/day until day 48 at the 5.6 kHz. Below 1 kHz recovery occurred up to day 22, the recovery rate was below 2 dB/day. A residual hearing loss of about 15-25 dB remained at all frequencies, except for the lowest frequency tested. At day 20 new hair cells were seen on the basilar papilla. At day 48 the hair cells appeared to have recovered fully, except for the orientation of the hair cell bundles. The advantage of the local application of the aminoglycoside drug over systemic application is that it damages almost all hair cells in the basilar papilla and it has no toxic side effects. The damage is more extensive than with systemic application.     

Expression of novel potassium channels in the chick basilar papilla

Ionic currents are critical for the functioning of the inner ear auditory sensory epithelium. We set out to identify and molecularly clone the genes encoding the channels responsible for several currents in the chick basilar papilla. Here we describe an inward-rectifying K+ channel, cKir2.3, present in both hair cells and support cells in the apical end of the chick basilar papilla. The biophysical properties of the human ortholog, hKir2.3, are similar to those of an inward-rectifying channel found in the apical end of the chick basilar papilla, suggesting that this channel may contribute to the corresponding current. Additionally, we describe two new members of the Kv6 subfamily of putative regulatory voltage-gated K channels, cKv6.2 and cKv6.3. Both are expressed in hair cells in the apical end of the chick basilar papilla; cKv6.2 is also strongly expressed in support cells and in the brain.     

Sound damage and gentamicin treatment produce different patterns of damage to the efferent innervation of the chick cochlea

Both sound exposure and gentamicin treatment cause damage to sensory hair cells in the peripheral chick auditory organ, the basilar papilla. This induces a regeneration response which replaces hair cells and restores auditory function. Since functional recovery requires the re-establishment of connections between regenerated hair cells and the central nervous system, we have investigated the effects of sound damage and gentamicin treatment on the neuronal elements within the cochlea. Whole-mount preparations of basilar papillae were labeled with phalloidin to label the actin cytoskeleton and antibodies to neurofilaments, choline acetyltransferase, and synapsin to label neurons; and examined by confocal laser scanning microscopy. When chicks are treated with gentamicin or exposed to acoustic overstimulation, the transverse nerve fibers show no changes from normal cochleae assayed in parallel. Efferent nerve terminals, however, disappear from areas depleted of hair cells following acoustic trauma. In contrast, efferent nerve endings are still present in the areas of hair cell loss following gentamicin treatment, although their morphological appearance is greatly altered. These differences in the response of efferent nerve terminals to sound exposure versus gentamicin treatment may account, at least in part, for the discrepancies reported in the time of recovery of auditory function.     

Ultrastructural, physiological, and molecular defects in the inner ear of a gene-knockout mouse model for autosomal Alport syndrome

It is well documented that damage to the chick cochlea caused by acoustic overstimulation or ototoxic drugs is reversible. Second-order auditory neurons in nucleus magnocellularis (NM) are sensitive to changes in input from the cochlea. However, few experiments studying changes in NM during cochlear hair cell loss and regeneration have been reported. Chicks were given a single systemic dose of gentamicin, which results in maximal hair cell loss in the base of the cochlea after 5 days. Many new hair cells are present by 9 days. These new hair cells are mature but not completely recovered in organization by 70 days. We counted neurons in Nissl-stained sections of the brainstem within specific tonotopic regions of NM, comparing absolute cell number between gentamicin- and saline-treated animals at both short and long survival times. Our data suggest that neuronal number in rostral NM parallels hair cell number in the base of the cochlea. That is, after a single dose of gentamicin, we see a loss of both cochlear hair cells and NM neurons early, followed by a recovery of both cochlear hair cells and NM neurons later. These results suggest that neurons, like cochlear hair cells, can recover following gentamicin-induced damage.     

Laparoscopic surgery combined with preservation of the spleen for distal pancreatic tumors

BACKGROUND: Hair follicle preservation for the purpose of delayed application would help us to transplant hair follicles more efficiently. METHODS: Isolated single hair follicles were preserved at 4 degrees C in four different solutions. Viability of preserved follicles was judged by organ culture and cell culture. In addition, a small number of hair follicles were transplanted into athymic mice. RESULTS. By cell culture, both dermal papilla and outer root sheath cells could be cultivated after 7 days of preservation. Hair follicles preserved for 48 hours showed a significant increase of hair shafts in organ culture. Those preserved for 7 days regrew well when transplanted into athymic mice. CONCLUSION: Preservation of hair follicles at 4 degrees C could be one option to prepare many follicular units at one time for transplantation.     

Hair bundle morphology on surviving hair cells of the chick basilar papilla exposed to intense sound

Exposure to intense sound produces a well-defined "patch" lesion on the chick basilar papilla in which 30-35% of the short hair cells are lost. The present study compares various aspects of sensory hair bundle morphology on surviving hair cells in the patch lesion with hair bundles from matched locations on nonexposed control papilla immediately after removal from the exposure and 12-days post exposure. The height and thickness of the hairs, the total number of hairs in the bundle, the width of the bundle, and the area and perimeter of the apical surface of the hair cell were quantified from scanning electron microscope photomicrographs. An attempt was also made to determine if there was a consistent microstructure to the pattern of hair cell loss within the lesion area. Similar observations in 12-day recovered ears are also presented. The results indicated that stereocilia height increased and width decreased on surviving hair cells in the exposed ear. The width of the hair bundle, the hair cell surface area, and perimeter also decreased. However, the number of hairs per cell remained unchanged, and there was no evidence of any consistent organization to the hair cell loss within the patch across a number of specimens. These observations indicated that the hair bundles on short hair cells underwent changes as a consequence of intense sound exposure. The results after 12 days of recovery were complicated by developmental changes on the papilla and incomplete maturation of the newly regenerated hair cells. It remains to be seen whether these changes were the result of cell sampling in the sound-damaged ear or were due to true structural alterations within the sensory hairs themselves.     

High-frequency auditory feedback is not required for adult song maintenance in Bengalese finches

Male Bengalese finches do not normally change their vocal patterns in adulthood; song is stereotyped and stable over time. Adult song maintenance requires auditory feedback. If adults are deafened, song will degrade within 1 week. We tested whether feedback of all sound frequencies is required for song maintenance. The avian basilar papilla is tonotopically organized; hair cells in the basal region encode high frequencies, and low frequencies are encoded in progressively apical regions. We restricted the spectral range of feedback available to a bird by killing either auditory hair cells encoding higher frequencies or those encoding both high and low frequencies and documented resultant changes in song. Birds were treated with either Amikacin alone to kill high-frequency hair cells or Amikacin and sound exposure to target hair cells across the entire papilla. During treatment, song was recorded from all birds weekly. After treatment and song recording, evoked-potential audiograms were evaluated on each bird, and papillas were evaluated by scanning electron microscopy. Results showed that hair cell damage over 46-63% of the basal papilla and the corresponding high-frequency hearing loss had no effect on song structure. In birds with hair cell damage extending further into the apical region of the papilla and corresponding low-frequency and high-frequency hearing loss, song degradation occurred within 1 week of beginning treatment and was comparable with degradation after surgical deafening. We conclude that either low-frequency spectral cues or temporal cues via feedback of the song amplitude envelope are sufficient for song maintenance in adult Bengalese finches.     

Pathophysiological mechanisms of hearing loss

An understanding of auditory transduction in the ear can contribute to a better comprehension of the pathophysiological mechanisms which give rise to hearing loss. The incoming sound sets up a mechanical traveling wave which begins at the base and progresses along the basilar membrane, reaching a point of maximal displacement. The region of maximal displacement is a function of stimulus frequency. The mechanical displacement, by directly opening ion channels in the stereocilia of the hair cells, induces changes in the electrical potential of the hair cells. This initial stage is called mechano-electrical transduction, and in the normal ear, is followed by a stage of electro-mechanical transduction based on the ability of the outer hair cells to respond to the electrical changes induced in them with a change in their length. This "electromotility" presumably provides mechanical feedback to the basilar membrane, augmenting its mechanical displacement. This is called the cochlear amplifier, providing the ear with improved sensitivity and frequency discrimination. Most forms of sensori-neural hearing losses (affecting the inner ear) are due to a lesion to some part of this cochlear amplifier (e.g. noise induced hearing loss, ototoxic drugs) and are therefore characterized by auditory threshold elevations and poorer frequency discrimination.     

Chick auditory terminals contain dynorphin-like immunoreactivity

Dynorphin-like immunoreactivity (DYN-I) was studied in the auditory brain stem of chick hatchlings using an antiserum to dynorphin-B. DYN-I was found in a few small cells in the nucleus laminaris (NL) and in the superior olive (SO). Dendrites in NL also appeared immunostained. DYN-I, however, was especially prominent in the cochlear nucleus magnocellularis (NM). A few DYN-I somata could be found within NM particularly in medial regions of this nucleus. Most DYN-I, however, was localized to calyceal-type structures, reminiscent of primary auditory nerve terminals, surrounding nerve cell bodies in NM. To determine whether DYN-I is contained within auditory end-bulbs of Held, the basilar papilla (avian cochlea) was removed unilaterally. After 5 days survival, there were very few DYN-I terminals in NM on the operated side of the brain compared with the unoperated side. This novel finding suggests that primary auditory nerve terminals in NM may contain the opioid peptide, dynorphin.     

Nonscarring hair loss disorders: the basis for recognition and treatment

Hair loss can be assessed objectively by examining a hair pull sample for stage of growth and hair shaft diameter, getting an estimate of average daily hair loss, and mapping scalp hair density. The history of the loss, the clinical picture, and the growth stage and diameter of the hair when lost all help to establish the type of loss. Hair regrowth occurs without treatment in most types of hair loss. There is as yet no effective treatment for pattern or senescent alopecia, although in women the loss can now be retarded somewhat.     

Ototoxicity of sodium nitroprusside

Nitric oxide (NO) not only has normal physiological roles like vasodilation and neurotransmission in the living organism, it could also have possible neurodestructive effects under certain pathological conditions. The present study aimed to determine whether direct exposure of guinea pig cochlea to a NO donor like sodium nitroprusside (SNP), or a nitric oxide synthase (NOS) inhibitor like N(G)-nitro-L-arginine methyl ester (L-NAME), would cause damage to the auditory hair cells. A piece of gelfoam was placed on the round window of the right ear of adult albino guinea pigs. It was then soaked with 0.1 ml of SNP (3.4 microM), 0.1 ml of L-NAME (9.3 microM or 18.5 microM) or 0.1 ml of injection water, the vehicle used to dissolve the above chemicals. Twelve animals receiving SNP were perfused 1 day, 2, 3 and 7 days later, with three animals being used for each survival period. Six animals receiving L-NAME were allowed to survive up to 7 days before perfusion. Eight animals receiving injection water or 0.45% saline were used as controls. With the scanning electron microscope, the inner and outer hair cells were counted over a 1 mm length of the basilar membrane in each turn of every cochlea. The results showed that, in animals treated with L-NAME at both concentrations stated, no significant loss of either inner or outer hair cells was noted in any part of the cochlea studied. However, as early as 1 day after SNP treatment, a striking loss of inner and outer hair cells was observed in the three lower turns of the cochlea. Damage to the outer hair cells was extended to the apical turn with increasing survival period, but no significant loss of inner hair cells was evident in the apical turn at any of the survival periods studied. To rule out the possibility that the effects were due to the presence of cyanide, a metabolite of SNP, hydroxycobalamin was introduced into the scala tympani of three animals through a cannula-osmotic pump device during SNP treatment. There was no significant difference in the results between the groups with and without hydroxycobalamin infusion 7 days after SNP treatment. The present study suggests that an excessive production of NO in the inner ear could lead to extensive loss of hair cells.     

Acoustic trauma causes reversible stiffness changes in auditory sensory cells

A common cause of hearing impairment is exposure to loud noise. Recent research has demonstrated that the auditory mechanosensory cells are essential for normal hearing sensitivity and frequency selectivity. However, little is known about the effect of noise exposure on the mechanical properties of the auditory sensory cells. Here we report a significant reduction in the stiffness and cell length of the outer hair cells after impulse noise exposure, suggesting that mechanical changes at the cellular level are involved in noise-induced hearing loss. There is a recovery of the cellular stiffness and cell length over a two-week period, indicating an activation of cellular repair mechanisms for restoring the auditory function following noise trauma. The reduced stiffness observed at the cellular level is likely to be the cause for the downward shift of the characteristic frequency seen following acoustic trauma. The deterioration and the recovery of the mechanical properties of outer hair cells may form important underlying factors in all kinds of noise-induced hearing loss.     

Regulation of proteoglycan and hyaluronan synthesis by elevated level of intracellular cyclic adenosine monophosphate in peritubular cells from immature rat testis

The morphology of the basilar papilla of the emu was investigated quantitatively with light and scanning electron microscopical techniques. The emu is a member of the Paleognathae, a group of flightless birds that represent the most primitive living avian species. The comparison of the emu papilla with that of other, more advanced birds provides insights into the evolution of the avian papilla. The morphology of the emu papilla is that of an unspecialised bird, but shows the full range of features previously shown to be typical for the avian basilar papilla. For example, the orientation of the hair cells' sensitive axes varied in characteristic fashion both along and across the papilla. Many of the quantitative details correlate well with the representation of predominantly low frequencies along the papilla. The most distinctive features were an unusually high density of hair cells and an unusual tallness of the hair-cell bodies. This suggests that the evolution of morphologically very short hair cells, which are a hallmark of avian papillae, is a recent development in evolution. The small degree of differentiation in hair-cell size contrasts with the observation that a significant number of hair cells in the emu lack afferent innervation. It is therefore suggested that the development of functionally different hair-cell types in birds preceded the differentiation into morphologically tall and short hair cells.     

Correspondence between middle frequency auditory loss in vivo and outer hair cell shortening in vitro

The aromatic hydrocarbon, toluene, has been reported to disrupt auditory system function both in occupational epidemiological and in laboratory animal investigations. This agent, along with several other organic solvents, impairs hearing preferentially at middle frequencies - a finding that distinguishes these agents from the traditional high frequency impairment observed with ototoxic drugs such as aminoglycoside antibiotics and cisplatin. Prior investigations performed in vivo have identified the outer hair cell as a probable target for toluene exposure. The purpose of this investigation was to determine directly whether outer hair cells isolated from the guinea pig cochlea show morphological alterations consistent with the toxic response seen in physiological studies with toluene exposure. The effect of toluene superfusion on outer hair cell shortening was assessed for cells harvested from different locations within the cochlea. Control studies included assessment of cell shortening among outer hair cells exposed to trimethyltin and cells exposed to benzene. Trimethyltin disrupts high frequency hearing preferentially and benzene does not produce hearing loss in vivo. Toluene at a concentration of 100 microM produced a marked shortening of outer hair cells although the effect was significantly greater among cells isolated from the apical half of the cochlea than from the basal half of the cochlea. By contrast, trimethyltin at the same concentration produced a preferential shortening among outer hair cells from the base of the cochlea. Benzene (100 microM) did not disrupt outer hair cell length of cells harvested from the apex. The results indicate that intrinsic features of outer hair cells contribute significantly to the site of ototoxic impairment observed in vivo for toluene.     

The level dependence of response phase: observations from cochlear hair cells

Hair cell responses are recorded from third turn of the guinea pig cochlea in order to define the relationship between hair cell depolarization and position of the basilar membrane. Because the latter is determined locally, using the cochlear microphonic recorded in the organ of Corti (OC) fluid space, no corrections are required to compensate traveling wave and/or synaptic delays. At low levels, inner hair cells (IHC) depolarize near basilar membrane velocity to scala vestibuli reflecting the free standing nature of their stereocilia. At high levels, the time of depolarization changes rapidly from velocity to scala vestibuli to the scala tympani phase of the basilar membrane response. This change in response phase, recorded in the fundamental component of the IHC response, is associated with a decrease in response magnitude. The absence of this behavior in OC and outer hair cell responses implies that basilar membrane mechanics may not be responsible for these response patterns. Because these features are reminiscent of the magnitude notches and the large phase shifts observed in single unit responses at high stimulus levels, they provide the IHC correlates of these phenomena.     

Failure of complex supplementation of minimal cultures to elicit a shift-up response in Pseudomonas putida

Primary cell cultures are established from 8-day quail embryo livers. During the first three days the culture is made up of areas of epithelial-like cells and scattered fibroblasts. The cytoplasm of the epithelial cells shows a high glycogen content as detected by the PAS reaction controlled with salivary amylase digestion. During the following days an important increase in the number of fibroblastic cells is observed. After 6-7 days of cultivation, the epithelial cells have disappeared and the culture is entirely fibroblastic. PAS technique does not show any trace of glycogen in these cultures which have been prolonged up to 45 days. Six-to 45-day primary cultures entirely made up of fibroblasts were associated with hepatic or pulmonary mesenchyme in organotypic culture for 3-4 days. In some cases the explant was first cultivated in vitro for 2 days and then grafted into a 5-day-old chick embryo on the chorioallantoic membrane for 6 days. In the secondary cultures hepatocytes showing an epithelial arrangement and a high glycogen content were observed. It appears from this observation that some of the primary culture fibroblasts are in fact dedifferentiated parenchymal cells. Such a dedifferentiation is a reversible phenomenon since the cells retain the ability to express their initial determination if they are placed in convenient environmental conditions. The role of the specific tissular arrangement in the stability of the differentiated state is discussed.     

Time course of nerve-fiber regeneration in the noise-damaged mammalian cochlea

The time course of events which are essential for nerve-fiber regeneration in the mammalian cochlea was determined using a group of chinchillas that had been exposed for 3.5 hr to an octave band of noise with a center frequency of 4 kHz and a sound pressure level of 108 dB. The animals recovered from 40 min (0 days) to 100 days at which times their inner ears were fixed and the organs of Corti prepared for phase-contrast and bright-field microscopy as plastic-embedded flat preparations. Selected areas identified in the flat preparations were semi-thick and thin sectioned at radial or tangential angles for examination by bright-field and transmission electron microscopy. The following time-ordered events appeared critical for nerve-fiber regeneration: (1) The area of the basilar membrane in which regeneration had a possibility of occurring showed signs of severe injury. Outer hair cells degenerated first followed by outer pillars, inner pillars, inner hair cells and other supporting cells; (2) Myelinated nerve fibers in the osseous spiral lamina became fragmented, starting at the distal ends of the fibers. This degeneration gradually extended back to Rosenthal's canal; (3) Fibrous processes, originating from Schwann-like cells in the osseous spiral lamina, extended laterally on the basilar membrane; (4) Schwann cells lined up medial to the habenulae perforata in the areas of severest damage, apparently ready to migrate through the habenulae onto the basilar membrane; (5) Schwann-cell nuclei appeared on the basilar membrane beneath the developing layer of squamous epithelium which was in the process of replacing the degenerated portion of the organ of Corti; (6) Regenerated nerve fibers with thin myelin sheaths or a simple investment of Schwann cell cytoplasm appeared in areas of total loss of the organ of Corti; and (7) The myelin sheaths on the regenerated nerve fibers gradually became thicker.     

When your patients lose their hair

1. Hair loss, even when it occurs gradually, is usually accompanied by psychologic discomfort. For some chemotherapy patients, the prospect of hair loss is viewed with more dread than any of the other physical discomforts that accompany chemotherapy. 2. The pattern and extent of hair loss cannot be accurately predicted for a given patient. Chemotherapy causes alopecia by damaging hair stem cells and hair follicles making the hair brittle and causing scalp hair to break off or fall out. 3. Education and support of the patient is highly significant in helping the patient adjust to hair loss. Nurses can inform the patient in advance of anticipated hair loss, suggest techniques for coping with hair loss, and encourage alternate methods of expressing sexuality.     

Frequency tuning of basilar membrane and auditory nerve fibers in the same cochleae

Responses to tones of a basilar membrane site and of auditory nerve fibers innervating neighboring inner hair cells were recorded in the same cochleae in chinchillas. At near-threshold stimulus levels, the frequency tuning of auditory nerve fibers closely paralleled that of basilar membrane displacement modified by high-pass filtering, indicating that only relatively minor signal transformations intervene between mechanical vibration and auditory nerve excitation. This finding establishes that cochlear frequency selectivity in chinchillas (and probably in mammals in general) is fully expressed in the vibrations of the basilar membrane and renders unnecessary additional ("second") filters, such as those present in the hair cells of the cochleae of reptiles.     

Regeneration of cochlear efferent nerve terminals after gentamycin damage

Chickens recover auditory function after hair cell loss caused by ototoxic drug damage or acoustic overstimulation, indicating that mechanisms exist to reestablish appropriate neuronal connections to regenerated hair cells. However, despite similar hair cell regeneration times, hearing recovery takes substantially longer after aminoglycoside than after sound damage. We have therefore begun examining damage and regeneration of efferent nerve terminals by immunolabeling whole-mount cochleae for differentially localized synaptic proteins and by visualizing the distribution of label with confocal microscopy. In undamaged cochleae, the synaptic proteins synapsin and syntaxin show similar distribution patterns corresponding to the large cup-like terminals on short hair cells. After gentamycin administration, these terminals are disrupted as hair cells are lost, leaving smaller, more numerous synapsin-reactive structures in the sensory epithelium. Syntaxin reactivity remains associated with the extruded hair cells, indicating that the presynaptic membrane is still attached to the postsynaptic site. In contrast, after sound damage, both synapsin and syntaxin reactivity are lost from the epithelium with extruded hair cells. As regenerated hair cells differentiate after gentamycin treatment, the synapsin labeling associated with cup-like efferent endings reappears but is not completely restored even after 60 d of recovery. Thus, efferent terminals are reestablished much more slowly than after sound damage (), consistent with the prolonged loss of hearing function. This in vivo model system allows comparison of axonal reconnection after either complete loss (sound damage) or partial disruption (gentamycin treatment) of axon terminals. Elucidating the differences in recovery between these injuries can provide insights into reinnervation mechanisms.