Brainstem auditory evoked response in the ferret (Mustela putorius)

Brainstem Auditory Evoked Potentials in Raccoon Dogs (Nyctereutes procynoides)

Raccoon dogs (Nyctereutes procynoides) are canids indigenous to Eastern Asia being one of the most invasive non-native animals in Europe and potential vectors for several hazardous parasitic and viral diseases. To present, there is a lack of studies regarding objective techniques used to appreciate the integrity and functionality of the nervous system in this species. Brainstem auditory evoked potentials (BAER) is a cost-effective, quick and noninvasive technique to assess the functionality of nervous system. The aim of the study is to provide reference values and evaluates the reliability of BAER recording with needle electrodes in clinically healthy raccoon dogs. Nine individuals were investigated for BAER under xylazine and ketamine general anesthesia. Four waves (I, II, III and V) were identified and evaluated for latencies, morphologically similarity to those previously reported for other species (dogs, horses, cats, and ferret). Our data can be used in further studies to asses objectively the auditory system function in raccoon dogs.

The in-air auditory thresholds of the eurasian otter (Lutra lutra, L. 1758) as determined by auditory brainstem responses

As of yet there is no literature record of the hearing range of the Eurasian otter (Lutra lutra, L. 1758), a key species for natural conservation efforts in Europe. We recorded in-air pure tone hearing thresholds of anaesthetized otters using auditory brainstem responses (ABR) and report the results of the Eurasian otter. The recorded potentials showed the typical mammalian auditory brainstem response consisting of 5 distinct positive peaks during the first 10 ms after stimulus onset. At 80 dB SPL the hearing ranged from around 200 Hz to 32 kHz, with lowest thresholds around 4 kHz.

Congenital Peripheral Vestibular Syndrome in a Domestic Ferret (Mustela putorius furo)

A 3-month-old intact female ferret (Mustela putorius furo) was presented with a 2-month history of ataxia. On physical examination, the ferret had difficulty standing upright. During the neurologic examination, the patient had a left head tilt and positional strabismus, circled to the left, and was ataxic. Results of the complete blood count were consistent with a mild normocytic normochromic anemia. Initial treatment was supportive. Magnetic resonance imaging was performed and revealed an asymmetry of the inner ears. A brainstem auditory evoked response test was also performed. History, clinical signs, and diagnostic test results indicated that the ferret was suffering from congenital peripheral vestibular syndrome and left-sided deafness. Congenital disease should be considered in the differential diagnosis of young ferrets with peripheral vestibular syndrome. Supportive care and physiotherapy can improve balance and motor function, leading to an acceptable quality of life.

Auditory brainstem response in tammar wallaby (Macropus eugenii)

Auditory brainstem responses (ABR) elicited by click and tonal stimuli were recorded from the tammar wallaby (Macropus eugenii), a marsupial mammal. The morphology, threshold, amplitude, and latency of ABRs recorded in the tammar wallaby are similar to those of other marsupials and mammals used in auditory research, including humans. Thresholds determined by an algorithm employing cross-correlation and by conventional visual detection methods were comparable. The findings from this study indicate that tammar wallaby is a suitable model for auditory research and that algorithms employing cross-correlation are useful for detection of the ABR waveform.

Cellular generators of the binaural difference potential in cat

In humans, lateralization and fusion of binaurally presented clicks are correlated with the latency and amplitude of the binaural difference potential (BDP) (e.g., Furst et al., 1985). The BDP is derived by subtracting the brainstem auditory evoked potential (BAEP) for binaural stimulation from the sum of the BAEPs for left and right monaural stimulation. Our aim in this work was to determine the cellular generators of the BDP and thus identify cells that may be crucial for specific types of binaural sound processing. To this end, we injected kainic acid into the superior olivary complex (SOC) or the cochlear nucleus (CN) in cats and examined the effects of the resulting lesions on the click-evoked BDP. Lesions confined to the anterior anteroventral CN (AVCNa) substantially reduced the BDP, while lesions primarily involving more posterior parts of the CN had little or no effect. BDP reductions occurred for lesions involving either high (> 10 kHz) or lower (< 10 kHz) characteristic frequency (CF) regions of the AVCNa (as well as the posterior CN). Lesions involving the SOC reduced the BDP and, in one case, eliminated the high-pass filtered (270 Hz cutoff) BDP. Combining these results with published information about the physiology and anatomy of auditory brainstem cells, we conclude that: (1) spherical cells in the AVCNa are essential for BDP production, (2) the earliest part of the BDP is generated by medial superior olive (MSO) principal cells which receive spherical cell inputs, (3) a later part is probably generated by the cellular targets of MSO principal cells and, (4) the cells involved in BDP generation have CFs above, as well as below, 10 kHz. Since humans, like cats, have a well-developed MSO, we suggest that the MSO may also be essential for BDP production in humans. Thus, perceptual correlates of the BDP, binaural fusion and click lateralization, apparently involve the MSO.

Morphology of retinal axon arbors induced to arborize in a novel target, the medial geniculate nucleus. II. Comparison with axons from the inferior colliculus

Specific neonatal lesions in ferrets can induce retinal axons to project into the medial geniculate nucleus (MGN). In the accompanying paper (Pallas et al., this issue), we described the morphology of these retinal ganglion cell axons. Those results and others (Roe et al. [1993] J. Comp. Neurol. 334:263) suggest that these axons belong to the W class of retinal axons. In this paper, the retino-MGN axons are compared with the normal inputs to the MGN from the brachium of the inferior colliculus (BIC). We first sought to determine further the extent to which a novel target might influence retinal axon arbor morphology. The second issue concerns retinal topography. Ferrets with retinal projections to the MGN have a two-dimensional retinotopic map in the MGN and the primary auditory cortex rather than the one-dimensional tonotopic map normally present (Roe et al. [1990] Science 250:818). To investigate whether there might be an anatomical substrate for a two-dimensional retinotopic map in the MGN, we compared the space-filling characteristics of the retino-MGN axons with the IC-MGN axons. Our results show that the branched retino-MGN axons resemble normal retinal W axons much more closely than they resemble the normal inputs to MGN. In addition, most of the axon arbors from the BIC are elongated along the rostrocaudal (isofrequency) axis, whereas the branched retino-MGN axons are more spatially restricted, suggesting an anatomical substrate for a retinotopic map in the MGN of the rewired ferrets.

Age-related hearing impairment in senescence-accelerated mouse (SAM)

The auditory brainstem response and histopathology of the cochlea were investigated in an accelerated senescence-prone strain, SAM-P/1 mice and a senescence-resistant strain, SAM-R/1 mice. Each strain displayed an age-related auditory loss expressed as elevated thresholds similar to human hearing loss in that high-frequency losses occurred earlier than middle- or low-frequency losses. SAM-P/1 showed a more rapid decline of hearing with age than did SAM-R/1. Interpeak intervals I-III and I-IV were prolonged with age in both strains, especially at high frequency. The prolongation was more marked in SAM-P/1 than in SAM-R/1. The decrease in amplitude of wave I observed in both strains was greater in SAM-P/1 than in SAM-R/1. The auditory function assessed by thresholds, interpeak intervals and amplitudes of wave I in SAM-P/1 at 12 months of age corresponded roughly to that in SAM-R/1 at 20 months of age. In morphological studies, there was an age-related decrease in the cell density as well as in the size of spiral ganglion neurons in both strains, but these changes were more pronounced in SAM-P/1 than in SAM-R/1. These results reveal that age-related hearing impairment associated with morphological changes in the cochlea is manifested earlier and progresses more rapidly in SAM-P/1 than in SAM-R/1. Thus, the SAM-P/1 strain should prove useful as a model of presbycusis.

Auditory brainstem responses in ferrets following unilateral cochlear removal

To examine the effect of unilateral or asymmetric hearing loss on the developing brain, ferrets had the right cochlea removed at postnatal day (P)5, P25, P40 or P90. Auditory brainstem responses (ABR) to free-field click stimulation were obtained before and after cochlear removal in the P40 and P90 groups, and from P28 in the other groups. Acute cochlear removal did not lead to any change in the morphology of the ABR waveform or to any change in the ABR threshold in response to stimulation on the side of the intact ear. There was a small, progressive increase in the latency of the four main waves of the ABR. Long-term survival following cochlear removal did not lead to any change in ABR waveform or threshold, or to any further change in wave latency, regardless of age at the time of removal or survival time (up to 1-2 years). In contrast to initial expectations based on previous single-unit studies, these results suggest that cochlear removal in infancy does not produce any large compensatory change in the functional organization of the auditory brainstem.

Comparison of the developmental changes of the brainstem auditory evoked response (BAER) in taurine-supplemented and taurine-deficient kittens

A similar development of the brainstem auditory evoked response is present in taurine-supplemented and taurine-deficient kittens between the second postnatal week and the third month of life. Between birth and the second postnatal week kittens from mothers fed the 1% taurine diet showed earlier maturation of the brainstem auditory evoked response as indicated by lower threshold, shorter P1 latency and shorter central conduction time when compared to the kittens from mothers fed the 0.05% taurine diet. These results suggest an important role of taurine in the anatomical and functional development of the auditory system.

Effects of stimulus repetition rate on ABR threshold, amplitude and latency in neonatal and adult Mongolian gerbils

The ABR wave forms of 16-day-old and adult Mongolian gerbils were evoked by click stimuli presented at rates ranging from 1 to 80/sec. Wave I and wave IV thresholds were determined for each of 5 click rates. Amplitudes and latencies of waves I and IV were measured at each of 7 click rates and 3 intensity levels (15, 40 and 65 dB above threshold). Thresholds for waves I and IV in the adult gerbil and wave I in the 16 day gerbil were unaffected by changes in stimulus repetition rate. Neonatal wave IV thresholds were unaffected by click rate for rates below 25/sec but increased approximately 7 dB/decade increase in click rate when rate exceeded 25/sec. Increasing click rate produced greater reductions in ABR amplitude among neonates than adults for both waves I and IV. Decreases in amplitude due to increasing rate were independent of intensity level in both neonatal and adult subjects. Increasing rate produced similar increases in wave I latency among 16 day and adult subjects, but produced much greater increases in wave IV latency among neonates. Stimulus intensity level and click rate acted independently on wave I and wave IV latency in adult subjects and wave I latency in neonates. However, an interaction between rate and intensity was observed with respect to neonatal wave IV latency.

Auditory brainstem of the ferret: maturation of the brainstem auditory evoked response

A longitudinal study of developmental changes in the brainstem auditory evoked response (BAER) was made on 19 ferrets between postnatal days 25 (P25) and 50. Responses to free-field click stimuli were recorded from anaesthetized animals, and compared with data obtained from 8 adult ferrets. A reproducible BAER was first recordable on P27, although the response onset was generally later in smaller animals. BAER onset preceded eye opening, which started on P32. Adult-like thresholds were observed in all animals by P40, but the age at which they were attained was also dependent on size. The BAER in the adult ferret consists of 4 main vertex-positive peaks occurring in the first 5 ms following transient acoustic stimulation. In the youngest animals the presence of an additional peak (between II and III) and the slurring of peaks III and IV were consistent features. The individual peaks undergo an asymmetrical pattern of development, with mean peak I latency attaining an adult value at P40, while mean peak IV latency is still 115% of the mean adult value at that age. BAERs could routinely be recorded using high stimulus presentation rates (greater than 40/s), though an increase in absolute and interpeak latencies occurred, the extent of which decreased with age. The pattern of BAER development in the ferret is compared with that in other species, and the concept of the 'silent period' (period between conception and onset of hearing) as a standard unit of auditory development is introduced.