Cbl-associated protein regulates assembly and function of two tension-sensing structures in Drosophila.

Cbl-associated protein (CAP) localizes to focal adhesions and associates with numerous cytoskeletal proteins; however, its physiological roles remain unknown. Here, we demonstrate that Drosophila CAP regulates the organization of two actin-rich structures in Drosophila: muscle attachment sites (MASs), which connect somatic muscles to the body wall; and scolopale cells, which form an integral component of the fly chordotonal organs and mediate mechanosensation. Drosophila CAP mutants exhibit aberrant junctional invaginations and perturbation of the cytoskeletal organization at the MAS. CAP depletion also results in collapse of scolopale cells within chordotonal organs, leading to deficits in larval vibration sensation and adult hearing. We investigate the roles of different CAP protein domains in its recruitment to, and function at, various muscle subcellular compartments. Depletion of the CAP-interacting protein Vinculin results in a marked reduction in CAP levels at MASs, and vinculin mutants partially phenocopy Drosophila CAP mutants. These results show that CAP regulates junctional membrane and cytoskeletal organization at the membrane-cytoskeletal interface of stretch-sensitive structures, and they implicate integrin signaling through a CAP/Vinculin protein complex in stretch-sensitive organ assembly and function.

Neither endocochlear potential nor tegmentum vasculosum are affected in hearing impaired belgian waterslager canaries.

We previously showed that the Belgian Waterslager canary strain is affected by a hereditary hearing loss that is associated with a reduced number of hair cells and hair cell pathologies in the basilar papilla. Since hair cell pathologies were also present in the sacculus, Weisleder et al. (1994) suggested that these birds are afflicted by Scheibe's like dysplasia, a cochleo-saccular defect. In mammals, cochleo-saccular defects are characterized primarily by the lack of an endocochlear potential and abnormalities in the Stria vascularis which only secondarily lead to hair cell loss (Steel and Bock, 1983; Steel, 1994; 1995). Here we report the endocochlear potential of six ears from three non-Belgian Waterslager canaries and three ears of two Belgian Waterslager canaries to decide if Waterslager canaries are affected by a cochleo-saccular or by a neuroepithelial defect. The mean endocochlear potential was 17.6+/-2. 5 mV in the non-Waterslager canaries and 20.3+/-0.6 mV in Waterslager canaries. In addition, and consistent with the presence of a normal endocochlear potential, light microscopy of the tegmentum vasculosum provided no evidence for pathology. These data show that Belgian Waterslager canaries are affected by a neuroepithelial rather than a cochleo-saccular inner ear defect.

Inner-ear abnormalities and their functional consequences in Belgian Waterslager canaries (Serinus canarius).

Recent reports of elevated auditory thresholds in canaries of the Belgian Waterslager strain have shown that this strain has an inherited auditory deficit in which absolute auditory thresholds at high frequencies (i.e. above 2.0 kHz) are as much as 40 dB less sensitive than the thresholds of mixed-breed canaries and those of other strains. The measurement of CAP audiograms showed that the hearing deficit is already present at the level of the auditory nerve (Gleich and Dooling, 1992). Here we show gross abnormalities in the anatomy of the basilar papilla of Belgian Waterslager canaries at the level of the hair cell. The extent of these abnormalities was correlated with the amount of hearing deficit as measured behaviorally.

Threshold changes in auditory brainstem response (ABR) due to the administration of kanamycin in dogs.

Auditory brainstem response (ABR) is a useful method in evaluating auditory function in human. To investigate the ABR threshold is more effective than to pursue the trends in each component of ABR. In this study, tone burst sound stimuli were employed and the ABR threshold shift caused by kanamycin administration was investigated in dogs. In a series of monitoring of ABR against short-period auditory lesions, changes in the ABR waveform after intravenous administration of kanamycin were detected. These changes returned gradually and were reversible. The changes in ABR against long-period auditory function disorder were perceived by an increase in the ABR threshold. The ABR threshold shift occurred earlier in the high frequency sounds than in the lower frequency sounds. This is why amino glycoside antibiotics damage the cochlear hair cells in the basal layer and lead to the loss of hearing selectively for high frequency tones. These findings suggest that tracing of the ABR threshold by tone bursts could provide information that has a specificity for frequency in hearing tests and is a useful method in clinical veterinary medicine or/and toxicological tests.

Auditory-evoked responses of dogs with different hearing abilities.

Sixteen dogs were separated into three groups, based on clinical impressions of their abilities to hear and historical information pertaining to their hearing loss: group I (n = 7) had normal hearing, group II (n = 4) had reduced hearing and group III (n = 5) were deaf. Monaural clicks of alternating polarities were used to elicit brainstem auditory-evoked responses. The responses of the normal group and of the reduced hearing group consistently had four major peaks (I, II, III-IV, V) with latencies similar to those previously reported in dogs with normal hearing. No difference (p greater than or equal to 0.05) was found in mean latencies of the four major waveforms when comparing the normal group with the reduced hearing group. Significant reductions in mean amplitudes of waves I (p less than 0.01) and II (p less than 0.025) were found in the reduced hearing group. No recognizable waves could be recorded from the deaf group, indicating a lack of peripheral auditory function.

Brain stem auditory-evoked responses in the dog.

Brain stem auditory-evoked responses (BAER) were recorded from 58 dogs that did not have a known history of hearing problems. The BAER wave forms had an overall mean amplitude approximately 3.0 microV and typically consisted of a series of 4 to 5 vertex-positive peaks (peaks I through V). When acoustic clicks having intensities of 60-dB hearing level (decibels relative to the subjective hearing threshold) were used as stimuli, peak I had a latency of 1.49 +/- 0.13 ms; peak II, 2.32 +/- 0.14 ms; peak III, 3.01 +/- 0.25 ms; peak IV, 4.22 +/- 0.27 ms; and peak V, 5.55 +/- 0.37 ms. Latency values were influenced by a number of nonpathologic factors, including stimulus intensity and the body temperature of the dog. As stimulus intensity was decreased, there was a lengthening of the latency of each peak coupled with a decrease in the overall amplitude of BAER. Decreases in rectal temperature caused a similar lengthening of peak latencies. Age may have an influence on BAER, but under the conditions of the present study, the effect was not significant.

Brain stem auditory-evoked response in the nonanesthetized horse and pony.

The brain stem auditory-evoked response (BAER) was measured in 10 horses and 7 ponies under conditions suitable for clinical diagnostic testing. Latencies of 5 vertex-positive peaks and interpeak latency and amplitude ratio on the 1st and 4th peaks were determined. Data from horses and ponies were analyzed separately and were compared. The stimulus was a click (n = 3,000) ranging from 10- to 90-dB hearing level (HL). Neither horses nor ponies responded with a BAER at 10 dB nor did they give reliable responses at less than 50 dB. The 2nd of the BAER waves appeared in the record at lower stimulus intensities than did the 1st wave for the horse and pony. Horses and ponies had a decreasing latency for all waves, as a result of increasing stimulus intensity. Latencies were shorter for the ponies than for the horses at all stimulus intensities for the 1st, 2nd, 3rd, and 4th waves, but not the 5th wave. At 60-dB HL, the mean latencies for the 1st through 5th wave, respectively, for the horse were 1.73, 3.08, 3.93, 4.98, and 6.00 ms and for the pony 1.48, 2.73, 3.50, 4.56, and 6.58 ms. Interpeak latencies, 1st to 4th wave, averaged 3.22 ms (horse) and 3.11 ms (pony) for all stimulus intensities from 50- to 90-dB HL and had a tendency to decrease slightly as stimulus intensity increased. Amplitude ratios (4th wave/1st wave) were less than 1 for all stimulus intensities in the horse. In the pony, the ratio was less than 1 at greater than or equal to 70-dB HL and greater than 1 at less than or equal to 60-dB HL.

Ototoxic potential of gentamicin in ponies.

Ototoxicosis was evaluated in 6 healthy ponies given 5 mg of gentamicin/kg of body weight, q 8 h, IM. Ponies 1, 2, and 3 were dosed for 7 days and ponies 4, 5, and 6 were dosed for 14 days. Serum peak and trough concentrations of gentamicin were measured by radioimmunoassay at regular intervals. Brain stem auditory-evoked responses were recorded every 5 days up to 60 days after the first dose to monitor auditory function. Although serum gentamicin concentrations were within or above the accepted clinical therapeutic range, loss of auditory function was not observed at the frequency range (1 to 4 kHz) tested. Serum chemical values remained within the accepted clinical range and no evidence of nephrotoxicosis was observed. Seemingly, gentamicin given IM to healthy ponies was safe and had minimal risk of side effects.

Otoacoustic emission in a dog.

A 7-month-old female Poodle was evaluated for a sound continuously emanating from its left ear. The frequency and intensity of the tone was matched by use of a multifrequency audiometer. The frequency and intensity of the sound were 9,594 Hz and 45.5 decibels sound pressure level, respectively. On the bases of normal brain stem auditory-evoked responses and behavioral response to sound, the dog was believed to have normal hearing in both ears. Emission of sound from an ear, referred to as an otoacoustic emission, is a condition that has been reported in human beings and small animals. Successful treatment in human patients with drugs and masking sounds is difficult, and treatment has not been reported in animals. This condition in dogs is not considered life-threatening.

Prevalence of behavioral changes associated with age-related cognitive impairment in dogs.

OBJECTIVE: To determine the prevalence of age-related behavioral changes, namely impairment, in a randomly chosen population of dogs. DESIGN: Age-stratified cohort study. ANIMALS: 97 spayed female and 83 castrated male dogs that were 11 to 16 years old. PROCEDURE: Data on possible impairment in 4 behavioral categories (ie, orientation in the home and yard, social interaction, house training, and sleep-wake cycle) linked to cognitive dysfunction were obtained from dog owners, using a structured telephone interview. Hospital records of dogs had been screened to exclude dogs with dysfunction in organ systems that may cause behavioral changes. Dogs with behavioral impairment were those with > or = 2 signs of dysfunction within a category. Dogs with impairment in 1 category were considered mildly impaired and those with impairment in > or =2 categories were considered severely impaired. RESULTS: Age by sex interactions for dogs with impairment in any category were not significant, and, therefore, data on castrated males and spayed females were pooled for analyses across ages. The prevalence of age-related progressive impairment was significant in all categories. The percentage of 11- to 12-year-old dogs with impairment in > or = 1 category was 28% (22/80), of which 10% (8/80) had impairment in > or = 2 behavioral categories. Of 15- to 16-year-old dogs, 68% (23/34) had impairment in > or =1 category, of which 35% (12/34) had impairments in > or = 2 categories. There were no significant effects of body weight on the prevalence of signs of dysfunction in the behavioral categories. CONCLUSIONS AND CLINICAL RELEVANCE: Data collected provide estimates of the prevalence of various degrees of age-related behavioral changes associated with cognitive dysfunction in dogs. Age-related behavioral changes may be useful indicators for medical intervention for dogs with signs of cognitive impairment.

Predicting behavioral changes associated with age-related cognitive impairment in dogs.

OBJECTIVE: To monitor the progression of age-related behavioral changes in dogs during a period of 6 to 18 months and to determine whether signs of dysfunction in any of 4 behavioral categories can be used to predict further impairment. DESIGN: Age-stratified cohort study. ANIMALS: 63 spayed female and 47 castrated male dogs 11 to 14 years of age. PROCEDURE: Data were collected from randomly selected dog owners who were interviewed by telephone twice at a 12- to 18-month interval; data were included if the dog had lived > or = 6 months between interviews. The interview focused on signs of impairment in the following behavioral categories: orientation in the home and yard, social interactions with human family members, house training, and the sleep-wake cycle. Dogs were determined to have impairment in 0 behavioral categories (on the basis of < or = 1 sign for each category), impairment in 1 category (> or = 2 signs of dysfunction in that category), or impairment in > or = 2 categories. RESULTS: Between interviews, 22% (16/73) of dogs that did not have impairment in a category at the time of the first interview developed impairment in that category by the time of the second interview. Forty-eight percent (13/27) of dogs that had impairment in 1 category at the time of the first interview developed impairment in > or = 2 categories by the time of the second interview and were significantly more likely to develop impairment in > or = 2 categories, compared with dogs that initially had impairment in 0 categories. Dogs with 1 sign of dysfunction in orientation were significantly more likely to develop impairment in that category, compared with dogs that had 0 signs of dysfunction in orientation. CONCLUSIONS AND CLINICAL RELEVANCE: Age-related behavioral changes in dogs are progressive. Clinicians should consider trying to predict which dogs are most likely to become progressively impaired during the subsequent 6 to 18 months.

Hearing in the dog as assessed by auditory brainstem evoked potentials.

Auditory brainstem evoked potentials were used to test hearing in dogs. A technique is described which can be carried out normally on conscious or sedated animals. Eleven normal adults, eight normal puppies and four deaf animals were rested. Reproducible brainstem evoked potentials were readily obtained from the normal adult dogs except when they became fractious (unsedated animals only). Usually the evoked waveform consisted of four peaks (I to IV) occurring in the first five milliseconds after the delivery of an auditory stimulus. In adults, the brainstem threshold for clicks varied between 5 and 25 dB normal hearing level. Brainstem evoked potentials were not detected in puppies at two weeks old but occurred at three weeks old. Between three and seven weeks of age the latencies of waves I and IV and the interval between these waves became shorter, to resemble the adult waveform. No brainstem evoked potentials were detected in the four deaf animals.

Normative auditory brainstem response data for bone conduction in the dog.

Auditory brainstem response (ABR) is a valuable tool for the diagnosis of hearing disorders in dogs, but is hampered by the lack of published normative data. The aim of the present study was to obtain normative data for bone conduction, without masking, under clearly defined conditions. Subjects comprised 20 Dalmatians and 20 Jack Russell terriers. Two methods were investigated: holding the bone vibrator against the head by hand or by applying a 500 g weight. The results revealed no difference in hearing threshold between the two breeds or for the two methods of applying the bone vibrator to the head. The mean hearing threshold was close to 0 decibels re normal hearing level (dB nHL), which is the biological norm for humans. Hence, bone conduction thresholds can be used for confirmation of conductive hearing impairment in the dog, in the same way as in humans.

Investigation of hearing impairment in Cavalier King Charles spaniels using auditory brainstem response audiometry.

Auditory brainstem response audiometry was used to investigate nine Cavalier King Charles spaniels with a history of hearing impairment. Successful recordings were made in all cases. In eight of the dogs, the hearing impairment was between 40 and 85 decibels re normal hearing level. In addition to confirming the degree of impairment in each ear, information was obtained concerning the site of the lesion. The auditory brainstem technique may have an important role to play in assessing treatment outcome. Other applications include screening animals used in breeding programmes as well as working dogs requiring good binaural hearing.

Ototoxicity in dogs and cats.

A variety of drugs in veterinary use have side effects that can potentially damage the senses of hearing or balance in animals. A large body of literature exists on the incidence and mechanisms of ototoxicity in experimental animals and in humans, but little is documented in domestic dogs and cats. However, the generality of these adverse actions across species allows one to extrapolate and provide the veterinarian with insight into possible complications of chemotherapy.

Ototoxicity in dogs and cats.

Ears are special sense organs whose principal functions are hearing and maintaining equilibrium. Aminoglycoside antibiotics, erythromycin, polymyxin B, and cisplatin can affect either or both of these functions by binding with, injuring, and/or destroying special receptor cells associated with these functions. Severe hearing loss manifests itself as deafness, whereas loss of equilibrium will present as abnormal righting reflexes, nausea, and vomiting. Damage is proportional to levels of these ototoxins in the endolymphatic fluids. Evidence suggests that toxicity may be influenced by endolymphatic calcium concentrations, and levels of cAMP and cGMP are altered in specialized cochlear cells during ototoxicity, suggesting an additional mechanism for ototoxicity. The administration of salicylates and loop diuretics may potentiate the action of ototoxins, especially aminoglycoside antibiotics, probably by increasing the levels of these toxins in the endolymphatic fluid. Although many of these assessments have been made in laboratory animals, applicability may also be expected in small domestic animals, and extreme care should be taken in prescribing potentially ototoxic drugs to small animals. Cochlear damage from ototoxic compounds occurs initially in the cells detecting high-frequency sounds located at the lower basal region. In aging dogs and humans, this sensitivity of receptors in the lower basal region is enhanced. Early auditory damage is detectable by BAER and cochlear microphonic potentials. Vestibular responses can also be detected early as vestibular ocular reflexes and visual-vestibulo-ocular reflexes. Early detection is especially important because early changes can sometimes be reversible. Cavinton (apovincaminic acid) and fosfomycin represent examples of experimental agents being evaluated in laboratory animals for application as potential treatments to limit the ototoxicity associated with various drugs.

Inherited hearing defects in mice.

Mouse mutants with hearing impairment are useful for elucidating the pathological processes underlying auditory system defects, as well as for understanding the normal process of auditory development and sensory transduction. Deaf mouse mutants are also valuable for identifying the responsible genes by positional cloning, and are used to expedite the search for genes involved in human deafness. The distribution of candidate genes for deafness across the mouse genome is presented, together with a summary of the key features of the mutants involved. Genetic defects affecting hearing can be grouped into broad categories according to their pathological features. These categories include middle ear defects, morphogenetic inner ear defects, central auditory system defects, peripheral neural defects, neuroepithelial defects, cochleo-saccular defects, and late onset hearing loss. The biological features and molecular basis of each type of hearing impairment are described. Finally, the effects of mutations in orthologous genes involved in the auditory system in humans and mice are compared.