Maturation of the auditory system in clinically normal puppies as reflected by the brain stem auditory-evoked potential wave V latency-intensity curve and rarefaction-condensation differential potentials

A comparison of the brainstem auditory evoked response in healthy ears of unilaterally deaf dogs and bilaterally hearing dogs

AIMS

Auditory plasticity in response to unilateral deafness has been reported in various animal species. Subcortical changes occurring in unilaterally deaf young dogs using the brainstem auditory evoked response have not been evaluated yet. The aim of this study was to assess the brainstem auditory evoked response findings in dogs with unilateral hearing loss, and compare them with recordings obtained from healthy dogs.

METHODS

Brainstem auditory evoked responses (amplitudes and latencies of waves I, II, III, V, the V/I wave amplitude ratio, wave I-V, I-III and III-V interpeak intervals) were studied retrospectively in forty-six privately owned dogs, which were either unilaterally deaf or had bilateral hearing. The data obtained from the hearing ears in unilaterally deaf dogs were compared to values obtained from their healthy littermates.

RESULTS

Statistically significant differences in the amplitude of wave III and the V/I wave amplitude ratio at 75 dB nHL were found between the group of unilaterally deaf puppies and the control group. The recordings of dogs with single-sided deafness were compared, and the results showed no statistically significant differences in the latencies and amplitudes of the waves between left- (AL) and right-sided (AR) deafness.

CONCLUSIONS

The recordings of the brainstem auditory evoked response in canines with unilateral inborn deafness in this study varied compared to recordings from healthy dogs. Future studies looking into electrophysiological assessment of hearing in conjunction with imaging modalities to determine subcortical auditory plasticity and auditory lateralization in unilaterally deaf dogs are warranted.

Brainstem auditory evoked responses in an equine patient population. Part II: foals

Background

Reports of the use of brainstem auditory evoked response (BAER) as a diagnostic modality in foals have been limited.

Hypothesis/Objectives

To describe BAER findings and associated causes of hearing loss in foals.

Animals

Study group 18 foals (15 neonatal, 3 nonneonatal), control group (5 neonatal foals).

Methods

Retrospective. BAER records from the Clinical Neurophysiology Laboratory were reviewed from the years of 1982 to 2013. Peak latencies, amplitudes, and interpeak intervals were measured when visible. Clinical data were extracted from the medical records. Foals were grouped under disease categories. Descriptive statistics were performed.

Results

Ten neonatal foals had complete absence of BAER bilaterally and 5 had findings within reference range. Abnormalities were associated with common neonatal disorders such as sepsis, neonatal encephalopathy, neonatal isoerythrolysis, and prematurity. BAER loss also was observed in foals with specific coat color patterns such as completely or mostly white with blue irides or lavender with pale yellow irides. An American Miniature foal with marked facial deformation also lacked BAER bilaterally. One nonneonatal foal with an intracranial abscess had no detectable BAER peaks bilaterally, and 2 older foals, 1 with presumed equine protozoal myeloencephalitis and the other with progressive scoliosis and ataxia, had BAER within normal limits.

Conclusions and Clinical Importance

In neonatal foals, BAER deficits commonly are complete and bilateral, and associated with common neonatal disorders and certain coat and eye color patterns. Sepsis, hypoxia, bilirubin toxicity, and prematurity should be investigated as potential causes of auditory loss in neonatal foals.

Auditory steady-state evoked potentials (ASSEPs): a study of optimal stimulation parameters for frequency-specific threshold measurement in dogs

OBJECTIVE

To define the optimal stimulation parameters (AM/FM vs AM alone and modulation rate) for frequency-specific threshold measurements using ASSEPs in dogs. Dependent variables were thresholds and recording times needed to obtain a response at threshold. To compare the ASSEP threshold results obtained with the optimal stimulation parameters to those obtained with the Tone-Burst/Auditory Brainstem Response (TB/ABR) combination.

METHODS

Thirty-two sedated Beagle puppies were tested at 5 audiometric frequencies (0.5-8 kHz) and 6 ASSEP modulation rates (21-199 Hz).

RESULTS

The ASSEP threshold-modulation rate functions had a high-pass profile with corner frequencies of 101 Hz for 0.5, 1 and 2 kHz carriers and of 151 Hz for 4 and 8 kHz carriers. AM stimuli did not yield higher thresholds than the AM/FM ones except at 1 kHz. Modulation type had no effect on testing duration. Audiometric profiles were obtained much more rapidly with ASSEPs than with TB/ABRs (mean: 50 vs 135 min). Both ASSEP and TB/ABR provided thresholds estimates characterized by low intersubject variability.

CONCLUSIONS

ASSEPs are a valid and rapid method for audiometric assessment in sedated dogs.

SIGNIFICANCE

ASSEPs offer a new, competitive tool for frequency-specific assessment of hearing in the canine species.

Brain stem auditory potentials evoked by clicks in the presence of high-pass filtered noise in dogs

This study evaluates the effects of a high-frequency hearing loss simulated by the high-pass-noise masking method, on the click-evoked brain stem-evoked potentials (BAEP) characteristics in dogs. BAEP were obtained in response to rarefaction and condensation click stimuli from 60 dB normal hearing level (NHL, corresponding to 89 dB sound pressure level) to wave V threshold, using steps of 5 dB in eleven 58 to 80-day-old Beagle puppies. Responses were added, providing an equivalent to alternate polarity clicks, and subtracted, providing the rarefaction-condensation potential (RCDP). The procedure was repeated while constant level, high-pass filtered (HPF) noise was superposed to the click. Cut-off frequencies of the successively used filters were 8, 4, 2 and 1 kHz. For each condition, wave V and RCDP thresholds, and slope of the wave V latency-intensity curve (LIC) were collected. The intensity range at which RCDP could not be recorded (pre-RCDP range) was calculated. Compared with the no noise condition, the pre-RCDP range significantly diminished and the wave V threshold significantly increased when the superposed HPF noise reached the 4 kHz area. Wave V LIC slope became significantly steeper with the 2 kHz HPF noise. In this non-invasive model of high-frequency hearing loss, impaired hearing of frequencies from 8 kHz and above escaped detection through click BAEP study in dogs. Frequencies above 13 kHz were however not specifically addressed in this study.

N3 potentials in response to high intensity auditory stimuli in animals with suspected cochleo-saccular deafness

We describe a previously un-reported vertex-negative potential evoked by high intensity click auditory stimuli in some dogs and cats with suspected cochleo-saccular deafness. Brainstem auditory evoked potential tracings from 24 unilaterally or bilaterally deaf animals, 22 dogs and 2 cats, among which 21 belonged to breeds with high prevalence of suspected or histologically confirmed cochleo-saccular deafness, were studied retrospectively. Values for latency, amplitude and threshold of this potential in dogs were 2.15+/-0.23 ms, 0.49+/-0.25 microV, and 91.9+/-4.7 dB NHL, respectively (mean+/-SD). Latency and threshold values in cats were in the mean+/-2 SD range of the dog values. Sensitivity to click stimulus polarity and to click stimulus delivery rate pointed towards a neural potential instead of a receptor potential. The vertex-negative wave observed in these animals shares all characteristics with the N3 potential described in some deaf humans with cochlear deafness, where it is presumed to arise from saccular stimulation. The combined degeneration of cochlea and sacculus usually reported in deaf white dogs and cats suggest that N3 may have a different origin in these species.

Inner ear histopathology in “nervous Pointer dogs” with severe hearing loss

Ten puppy dogs (82, 131 or 148 days-old) from a Pointer cross-colony, exhibiting a juvenile severe hearing loss transmitted as an autosomal recessive trait, were used for histopathological characterization of the inner ear lesion. Immunostaining with calbindin, Na,K-ATPase, cytokeratins, S100, S100A1 and S100A6 antisera were helpful in identifying the different cell types in the degenerated cochleae. Lesions, restricted to the Corti's organ and spiral ganglion, were bilateral but sometimes slightly asymmetrical. Mild to severe lesions of the Corti's organ were unevenly distributed among the different parts of the middle and basal cochlear turns while the apical turn remained unaffected at 148 days. In 82 day-old puppies (n = 2), severe lesions of the Corti's organ, meaning that it was replaced by a layer of unidentifiable cells, involved the lower middle and upper basal turns junction area, extending in the upper basal turn. Mild lesions of the Corti's organ, with both hair and supporting cells abnormalities, involved the lower middle turn and extended from the rest of upper basal turn into the lower basal turn. The outer hair cells (ohc) were more affected than the inner hair cell (ihc). The lesions extended towards the basal end of the cochlea in the 131 (n = 5) and 148 (n = 3) day-old puppies. Additionally, the number of spiral ganglion neurons was reduced in the 131 and 148 day-old puppies; it is earlier than observed in most other canine hereditary deafness. These lesions were interpreted as a degeneration of the neuroepithelial type. This possible animal model might provide information about progressive juvenile hereditary deafness and neuronal retrograde degeneration investigations in human.

Postnatal maturation of the dog stria vascularis-- an immunohistochemical study

The lateral wall of the dog cochlear duct was investigated by classical staining and immunohistochemistry for NaK/ATPase beta2 isoform, cytokeratins (Cks), vimentin, nestin, and S100A6 during the postnatal cochlear maturation, i.e., from birth to postnatal day 110. The dog stria vascularis was immature at birth. Fine melanin granules were evident in the stria from the second week of life, and melanin concentration increased drastically beyond the first month. The marginal cells were NaK/ATPase- and Ck-positive; intermediate cells were either nestin- and S100A6-positive or vimentin-positive; the basal cells were vimentin-positive; the capillary endothelium showed vimentin and nestin labeling; the cell layer underlying the stria was nestin-positive. The fibrocytes of the spiral ligament and spiral prominence expressed nestin and vimentin. The epithelial cells overlaying the spiral prominence and the external sulcus were Ck-positive, and transiently nestin- and vimentin-positive. Double immunolabeling, for S100A6 and either nestin, vimentin, or NaK/ATPase, and for nestin and vimentin suggested the presence of two distinct intermediate cell types. The results enabled us to differentiate the cell types forming the lateral wall of the dog cochlear duct, and to follow their postnatal maturation. This study may form a basis for future investigations about spontaneous cochleosaccular degeneration in dogs. This species is an important companion animal, and a possible model for the study of comparable diseases in humans.

An original inner ear neuroepithelial degeneration in a deaf Rottweiler puppy

Histopathological investigation was conducted on both inner ears from a 4.5-month-old Rottweiler puppy with electrophysiologically confirmed bilateral deafness. The lesions were restricted to the organ of Corti and spiral ganglion that both displayed severe degenerative changes. The outer hair cells were less affected than the inner hair cells. The number of spiral ganglion neurons was reduced, and remaining neurons were altered. The basal and middle cochlear turns were more affected than the apical one. The vestibules were normal. Immunostaining with calbindin, calretinin, S100A1 and S100A6 polyclonal antisera was helpful in identifying different cell-types in the degenerated cochlea. The early and severe spiral ganglion cell degeneration is an uncommon finding no matter the species. Such lesions bear significance within the frame of cochlear implants technology for deaf infants.

Immunolocalization of the calcium binding S100A1, S100A5 and S100A6 proteins in the dog cochlea during postnatal development

The immunolocalization of three members of the S100 calcium-binding protein family was investigated in the dog cochlea during normal postnatal development. Sections of decalcified and paraffin-embedded cochleae from 16 beagle puppies aged from birth to 3 months were treated with polyclonal antisera raised against the human recombinant S100A1, S100A5, and S100A6 proteins. At birth, in the dog cochlea, S100A1 was expressed in the immature Deiter's cells, and slightly in the pillar cells. From the second week, S100A1 was detected in the supporting structures of the organ of Corti, i.e. the Deiter's, the pillar, the border, and the Hensen's cells, and in the reticular membrane. From birth onwards, S100A5 remained a neuronal-specific protein, only located in a subpopulation of neurons in the spiral ganglion. S100A6 was not expressed at birth. From the second week of life, the Schwann cells and nerve sheaths in the modiolus, in the spiral ganglion, and running in the direction of the organ of Corti exhibited S100A6-labeling. From the 12th postnatal day, some scattered intermediate cells started to express S100A6 protein in the stria vascularis. The number of labeled intermediate cells increased during the third week. At adult stage, the intermediate cells were S100A6-stained with cytoplasmic labeling throughout the stria vascularis from the base to the apex of the cochlea. None of the other cochlear structures expressed the S100 proteins under study during the postnatal development of the dog cochlea. The S100A1, S100A5, S100A6 immunostaining was limited to specific cell types in dog cochlea. These S100 proteins were useful markers in the study of supporting cells, neurons, nerve fibers sheaths and stria vascularis (S100A6) during the normal postnatal development of the dog cochlea.