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PubMed1987

Quantitative distribution of the glycine receptor in the auditory brain stem of the gerbil.

The concentration and relative distribution of glycine receptors were determined for gerbil brain stem auditory nuclei using 3H-strychnine and quantitative autoradiographic techniques. Significant binding was observed in the anteroventral cochlear nucleus, the dorsal cochlear nucleus, the lateral superior olivary nucleus, and the inferior colliculus. A non-uniform distribution of binding was seen in 3 of these nuclei, such that the greatest concentration of glycine receptors was located in the high-frequency regions. An analysis of neuron soma density suggested that the amount of post-synaptic membrane could partially explain the distribution of receptor.

Animals↗
PubMed2006

Microsurgical anatomy of the cochlear nuclei.

OBJECTIVE: The dorsal and ventral cochlear nuclei are exposed when treating lesions involving the fourth ventricle and the cerebellopontine angle. Precisely locating the nuclei is important in the placement of the auditory brainstem implantation and in intraoperative monitoring of auditory evoked potentials. This study examined the microsurgical anatomy of the cochlear nuclei. METHODS: The relationships and the surgical approaches to the nuclei were examined in 20 formalin-fixed specimens with the aid of an operating microscope. RESULTS: The dorsal cochlear nucleus is located in the floor of the lateral recess of the fourth ventricle on the posterior surface of the inferior cerebellar peduncle where it produces a prominence, the auditory tubercle. The ventral cochlear nucleus is positioned on the lateral surface of the inferior cerebellar peduncle where it often straddles the anterior edge of the foramen of Luschka at the junction of the lateral recess and cerebellopontine angle and produces less of a prominence on the surface of the brainstem than on the dorsal nucleus. CONCLUSION: Both the dorsal and ventral cochlear nuclei can be exposed after opening the foramen of Luschka and the lateral recess of the fourth ventricle by the retrosigmoid or translabyrinthine approach. The dorsal cochlear nucleus is positioned so that it would be damaged by a tumor within or approaches to the floor of the lateral recess. The ventral cochlear nucleus is positioned so that it would be vulnerable to damage by tumors within or operative approaches to the cerebellopontine angle. The dorsal cochlear nucleus and the adjacent intraventricular part of the ventral cochlear nucleus have anatomic characteristics that make them the preferable site of placement for the auditory brain stem implant.

Cochlear Nucleus↗
PubMed1996

Electrically induced fos-like immunoreactivity in the auditory pathway of the rat: effects of survival time, duration, and intensity of stimulation.

The goal of the present study was to establish how Fos-like immunoreactivity (FLI) elicited in the rat auditory pathway by unilateral electric stimulation of the cochlea is affected by the following experimental parameters: duration and intensity of stimulation, duration of survival time after offset of stimulation. The dense FLI found in the ipsilateral dorsal cochlear nucleus, as well as the moderate FLI found in the contralateral dorsal cochlear nucleus and in the posteroventral cochlear nucleus on both sides, were consistent after survival times ranging from 0 to 2-3 h, but they significantly decreased after longer survival times (5 and 6 h). In the same nuclei, FLI was increased even by short durations of stimulation (5 and 10 min) as compared to control rats, although FLI progressively increased for longer stimulation (20 and 45 min). In the auditory thalamus, FLI was found mainly in the peripeduncular nucleus, the dorsal and medial divisions of the medial geniculate body, whereas its ventral division was virtually devoid of immunoreactive neurons. This pattern of FLI distribution in the auditory thalamus persisted even after relatively long survival times (5 and 6 h). In both the cochlear nucleus and auditory thalamus, the density of FLI slightly increased in parallel with the intensity of stimulation. In other auditory nuclei, such as the inferior colliculus and the nucleus of the lateral lemniscus, there was no simple relation between the density of FLI and the three tested experimental parameters. Thus, the distribution and density of FLI did not vary in parallel in the various nuclei of the auditory pathway as a function of the tested experimental parameters; different patterns of FLI changes were instead observed in different auditory nuclei.

Action Potentials↗
PubMed1991

Experience with the Nucleus multichannel cochlear implant.

We have seen using the Nucleus multichannel cochlear implant since 1984, with more than 200 patients operated. Out of 152 adults, ten have ailed, either because of explants, or because of other causes especially psychological causes. Out of 53 children, only one child seldom wears his device. For the post-lingual adults, the vocal training is very short, during the three weeks hospitalisation necessary to place and to check the implant. The children need a much longer training period, which takes place in a special and pluridisciplinary cochlear implant center.

Adolescent↗
PubMed1991

Distribution of choline acetyltransferase immunoreactive axons and terminals in the rat and ferret brainstem.

A survey was made of the density of the cholinergic innervation of different parts of the brainstem of the rat and ferret. Sections of rat and ferret brainstems were stained for choline acetyltransferase (ChAT) immunoreactivity by using a sensitive immunocytochemical method. Adjacent sections were stained for acetylcholinesterase activity or Nissl substance. The density of the distribution of fine calibre, varicose ChAT-positive axons, assumed to represent cholinergic terminals, was categorised arbitrarily into high, medium, or low. A high density of ChAT-positive terminals was found in all or parts of these structures: interpeduncular nucleus, superficial grey layer of the superior colliculus (ferret), intermediate layers of the superior colliculus, lateral part of the central grey (rat), an area medial to the parabigeminal nucleus (rat), pontine nuclei, ventral tegmental nucleus (rat), midline pontine reticular formation, and an area ventral to the exit point of the 5th nerve (ferret). A medium density of ChAT-positive terminals was observed in all or parts of: the substantia nigra zona compacta (ferret), ventral tegmental area (ferret), superficial grey layer of the superior colliculus, intermediate and deep layers of the superior colliculus, lateral central grey, area medial to the parabigeminal nucleus, inferior colliculus, dorsal tegmental nucleus, ventral tegmental nucleus (ferret), pontine nuclei, ventral nucleus of the lateral lemniscus (ferret), midline pontine reticular formation, ventral cochlear nucleus, dorsal cochlear nucleus, lateral superior olive, spinal trigeminal nuclei, prepositus hypoglossal nucleus, lateral reticular nucleus, paragigantocellular nucleus, and the dorsal column nuclei including the cuneate, external cuneate, and gracile nuclei. A low density of ChAT-positive terminals was seen throughout the remainder of the brainstem of the rat and ferret, but these terminals were absent from the medial superior olive, substantia nigra zona reticulata (rat), and the central part of the ferret lateral superior olive. A pericellular-like distribution of ChAT-positive terminals was observed in the ventral cochlear nucleus and in association with some of the cells of the nucleus of the mesencephalic tract of the trigeminal nerve. A climbing fibre type arrangement of ChAT-positive terminals was found in the substantia nigra zona compacta (ferret) and medial reticular formation. In general, the distribution of staining for AChE activity reflected that of the distribution of ChAT immunoreactivity in the brainstem, except in a few regions where there were also species differences in the distribution of ChAT-positive terminals, e.g., in the superficial grey layer of the superior colliculus and in the substantia nigra.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

In vitro modulation of somatic glycine-like immunoreactivity in presumed glycinergic neurons.

Previous studies indicate that tuberculoventral and cartwheel cells in the dorsal cochlear nucleus as well as a group of stellate cells in the ventral cochlear nucleus are likely to be glycinergic. To test whether these neurons contain higher levels of free glycine than cells that are probably not glycinergic, immunocytochemical studies with antibodies against glycine conjugates were undertaken on slices of the murine cochlear nuclear complex. Present results show that the cell bodies of all three groups of neurons are immunolabeled. However, the somatic labeling of the tuberculoventral and cartwheel cells can be modulated by experimental conditions. In slices fixed immediately after cutting, many cell bodies in the deep layer of the dorsal cochlear nucleus (DCN), presumably tuberculoventral neurons, are labeled. As a slice is incubated in vitro, cell bodies in the deep layer of the DCN lose their glycine-like immunoreactivity. After 7 hours in vitro, labeled cells are absent in the deep DCN, but the immunoreactivity can be regained by electrically stimulating the auditory nerve for 20 minutes. The loss of immunoreactivity is prevented by electrical stimulation, by axotomy, and by inclusion of 0.8 microM tetrodotoxin, or 1 microM strychnine, or 50 microM colchicine or 50 microM beta-lumicolchicine in the bathing saline. Cartwheel cells retain their immunoreactivity during incubation in vitro without electrical stimulation, but lose it under two conditions. One is following a cut across the ventral cochlear nucleus (VCN) that severs most of their granule cell input, and the other is the inclusion of tetrodotoxin in the bathing saline. The labeling of cell bodies in the ventral cochlear nucleus and of puncta and processes is not changed by any of these experimental manipulations.

Animals↗
PubMed2000

Changes in stimulation levels over time in nucleus 22 cochlear implant users.

The purpose of this study was to evaluate changes that occur over time in the electrical stimulation levels of cochlear implant users. A retrospective review of program summaries for 26 postlingually deafened adult Nucleus cochlear implant users was completed. Program summaries were used to assess changes in electrical stimulation at threshold (T) and maximum comfort (C) levels. Comparisons were made at intervals including the subject's initial stimulation and 2-week, 3-month, 6-month, 1-year, and most recent programming sessions. Five patients had 5 years or more of implant use; 8 patients had 3 to 5 years or more of implant use; and the remainder had been using their implant for 2 to 3 years. No patient with less than 2 years of implant use was included. Results indicated that changes in stimulation levels occur gradually over time. Although the changes in stimulation levels from one programming session to the next were not significant, the changes in current requirements for both T and C levels were found to be significant when we compared the 6-month and most recent programming intervals.

Adult↗
PubMed1980

Development of the brain stem in the rat. III. Thymidine-radiographic study of the time of origin of neurons of the vestibular and auditory nuclei of the upper medulla.

Groups of pregnant rats were injected with two successive daily doses of 3H-thymidine from gestational days 12 and 13 (E12 + 13) until the day before parturition (E21 + 22). In adult progeny of the injected rats the proportion of neurons generated on specific embryonic days was determined quantitatively in the vestibular and auditory nuclei of the upper medulla. In the vestibular nuclei, neurons are generated between days E11 and E15 in an overlapping sequential order, yielding a lateral-to-medial and a rostral-to-caudal internuclear gradient. In the lateral vestibular nucleus peak production time is day E12; in the superior nucleus, E13; in the inferior nucleus, E13 and E14; and in the medial nucleus, E14. The early generation of neurons of the lateral vestibular nucleus may reflect the early differentiation of the circuit from the gravity receptors (utricle) to neurons of the spinal cord controlling postural balance. The later production of neurons of the superior vestibular nucleus may reflect the subsequent differentiation of the circuit from the rotational receptors (semicircular canals) to the neurons of the brain stem controlling eye movements. The generation time of neurons of the nucleus prepositus hypoglossi overlaps with that of the medial vestibular nucleus. The neurons of the anteroventral and posteroventral cochlear nuclei are produced from days E13 to E17, with no temporal differences between the two nuclei. The neurons of the dorsal cochlear nucleus are generated over a very long time span, beginning on day E12 and extending into the postnatal period. There is a sequence in the production of neurons forming the different layers of the dorsal cochlear nucleus in the following order: pyramidal cells, cells of the inner layer, cells of the outer layer and, finally, cells of the granular layer. There is also a sequential production of neurons in four nuclei of the superior olivary complex. In the lateral trapezoid nucleus peak production time is day E12; in the medial superior olivary nucleus, day E13; in the medial trapezoid nucleus, day E15; and in the lateral superior olivary nucleus, day E16. This order yields a medial-to-lateral gradient in the dorsal aspect of the superior olivary complex, and a lateral-to-medial gradient ventrally. These mirror-image gradients were also seen intranuclearly in the lateral superior olivary nucleus and the medial trapezoid nucleus. The cytogenetic gradients could not be related to tonotopic representation; however, they could be related to the lateral location of ipsilateral cochlear nucleus input to the lateral superior olivary nucleus and the medial location of the contralateral cochlear nucleus input to the medial trapezoid nucleus.

Animals↗
PubMed1999

The effect of frequency allocation on phoneme recognition with the nucleus 22 cochlear implant.

HYPOTHESIS: Phoneme recognition performance in patients implanted with the Nucleus 22 cochlear implant is affected by the frequency-to-electrode assignment. BACKGROUND: Multiple electrodes in modern cochlear implants are intended to deliver frequency-specific information to different tonotopic locations along the cochlea. However, the relation between the electrode locations, distribution of frequency information, and performance has not been explored thoroughly. METHODS: Ten listeners were tested on vowel and consonant identification tasks immediately after receiving each of the 15 speech processors. Experimental processors were created with 4, 7, and 20 activated electrodes. Five different frequency allocations were tested with all electrode conditions. RESULTS: For 7- and 20-electrode maps, best vowel recognition performance was obtained with frequency tables 7 and 9, with subjects showing best performance with the table with which they were most familiar. With 4-electrode maps, no change in vowel recognition performance was observed as a function of the frequency allocation. Consonant scores showed only a small effect of frequency allocation across all processors. Results were similar across listeners with different electrode insertion depths. CONCLUSION: The allocation of frequency ranges to electrodes in the Nucleus-22 cochlear implant can affect vowel recognition, when more than four electrodes are used, but is less important for consonant recognition. The allocation of frequency ranges to electrodes is an important factor in multichannel implants with more than four electrodes. The similarity of results across implant listeners with different electrode insertion depths implies that the optimal frequency allocation is one that best matches the allocation to which they've become accustomed, rather than one that matches the original tonotopic location of the electrodes.

Adult↗
PubMed2003

Correlation between NRT measurement and behavioural levels in patients with the Nucleus 24 cochlear implant.

Aim of this study was to determine the relationship between the electrically evoked whole nerve action potential (EAP) and T- and C-level for subjects using the Nucleus 24 cochlear implant system. EAP thresholds were measured using the Neural Response Telemetry system of the Nucleus 24 device. Twelve Nucleus 24 cochlear implant users took part in this study. EAP thresholds were compared with the behavioural measures of T- and C-levels used to programme the speech processor. The EAP and the T- and C-levels were obtained, on the same day, 1 month after cochlear implant activation. EAP thresholds were seen to fall between the T- and C-level. On average, EAP thresholds fell at 72% of the map dynamic range. The majority of absent answers were found in three of the 12 patients, and out of a total of 195 activated electrodes an EAP was recorded in 169. These data show that Neural Response Telemetry is a valuable clinical tool in the Nucleus cochlear implant system, providing information concerning integrity of the implant and status of the peripheral auditory nerves.

Adolescent↗
PubMed1994

Inhibition of discharge in inferior colliculus, AII cortex and Ep cortex after presentations of click stimuli.

A temporally related reduction of discharge in response to 70-dB clicks was identified in secondary auditory (AII) cortex (48-56 ms after click), posterior ectosylvian (Ep) cortex (40-56 ms after click) and inferior colliculus (IC) (56-76 ms after click). Units in primary auditory (AI) cortex, dorsal cochlear nucleus (DCN) and ventral cochlear nucleus (VCN) did not demonstrate a significant reduction of discharge at comparable periods. Neurons of AI cortex showed increased activity 36-40 ms after click. The timing of the periods of inhibited discharge in AII, Ep and IC, taken with the earlier activation of AI, supported the hypothesis of an inhibitory auditory pathway emanating from AI, affecting secondary auditory cortical regions and IC.

Acoustic Stimulation↗
PubMed1995

Auditory brainstem responses of CBA/J mice with neonatal conductive hearing losses and treatment with GM1 ganglioside.

Exogenous administration of GM1 ganglioside to CBA/J mice with a neonatal conductive hearing loss ameliorates the atrophy of spiral ganglion neurons, ventral cochlear nucleus neurons, and ventral cochlear nucleus volume. The present investigation demonstrates the extent of a conductive loss caused by atresia and tests the hypothesis that GM1 ganglioside treatment will ameliorate the conductive hearing loss. Auditory brainstem responses were recorded from four groups of seven mice each: two groups received daily subcutaneous injections of saline (one group had normal hearing; the other had a conductive hearing loss); the other two groups received daily subcutaneous injections of GM1 ganglioside (one group had normal hearing; the other had a conductive hearing loss). In mice with a conductive loss, decreases in hearing sensitivity were greatest at high frequencies. The decreases were determined by comparing mean ABR thresholds of the conductive loss mice with those of normal hearing mice. The conductive hearing loss induced in the mice in this study was similar to that seen in humans with congenital aural atresias. GM1 ganglioside treatment had no significant effect on ABR wave I thresholds or latencies in either group.

Acoustic Stimulation↗
PubMed1994

Central trajectories of type II (thin) fibers of the auditory nerve in cats.

This paper describes the central projections of thin fibers of the auditory nerve in cats. Both thin (type II) and thick (type I) fibers are labeled by extracellular injections of horseradish peroxidase (HRP) into the auditory nerve. Type I and almost all type II fibers bifurcate upon reaching the auditory nerve root of the cochlear nucleus. For a given bundle of auditory nerve fibers labeled by a discrete injection of HRP, bifurcations of type II and type I fibers are restricted to a narrow region of the nerve root. After the bifurcation, the pathways of type II branches within the anteroventral cochlear nucleus (AVCN) and posteroventral cochlear nucleus (PVCN) are similar to those of type I branches. This similarity in bifurcation and course of type I and type II fibers was observed in the ventral as well as dorsal parts of the ventral cochlear nucleus. The complete axonal course of most type II fibers could not be reconstructed, however, due to fading of the reaction product. Type II fibers produce very few collaterals in the cochlear nucleus (CN), but possess many 'en passant' swellings along their main processes and collaterals. Compared with type II fibers previously studied in mice (Berglund and Brown, 1989; 1994; Brown and Ledwith, 1990), cat type II fibers are similar in their general projections within the main body of the nucleus and in the frequency of 'en passant' swellings per length of fiber, but cat fibers have a higher percentage of 'complex' or pedunculated 'en passant' swellings.

Animals↗
PubMed1997

Results from a pilot study using the nucleus CI24M/SP5 cochlear implant system.

OBJECTIVE: To conduct a pilot study in adults with the Nucleus CI24M/SP5 cochlear implant system. PATIENTS AND METHODS: Eight postlingually deafened adults who had received little or no benefit from conventional hearing aids, equipped with the Nucleus CI24M/SP5 cochlear implant system. RESULTS AND CONCLUSIONS: The results indicate that most of the subjects were able to perform well in speech recognition tests. The test performances appeared to be strongly affected by the duration of deafness. The speech processor's four user-selectable program memories have been extremely useful for the subjects to evaluate variations to the speech coding strategies in ordinary surroundings outside of the laboratory. The telemetry functions of the new implant provide a set of useful clinical and research tools for gathering greater insights into the in-situ operation of the implant.

Adult↗
PubMed2006

[Observation of auditory brainstem response and distortion product otoacoustic emission on the animal model of autoimmune auditory neuropathy].

OBJECTIVE: To set up an animal model of autoimmune auditory neuropathy and to observe the auditory brainstem response (ABR) and distortion product otoacoustic emission (DPOAE) in guinea pigs. METHODS: The spiral ganglion and the cochlear nerve were obtained and purified by electrophoresis from 250 normal guinea pigs. The purified cochlear nerve antigen was mixed with an equal volume of complete Freunds adjuvant for immunization. Seventy guinea pigs were divided into three groups: experiment group (50 guinea pigs), control group (10 guinea pigs), normal group (10 guinea pigs). ABR, DPOAE, serum IgG levels, and morphological changes of spiral ganglion cells and the cochlear nucleus were observed. The protein expressions of the antigen were examined by immunohistochemistry and the super-structure of the auditory nerve were observed. RESULTS: The threshold of ABR response increased ranged from 10 to 25 dB in 32% (32/100 ears) of the guinea pigs. The peak latencies of waves I , III and the interpeak latency I approximately III were prolonged in the hearing loss group of guinea pigs. Prolonged peak latency of wave III was noted in hearing loss group at 2 and 3 weeks post immunization and slowly decreased to normal peak latency. The amplitude of DPOAE was no difference in the guinea pigs. The levels of serum IgG increased significantly compared with those of the control group. Inflammatory cell infiltration was observed in the cochlear nerve and the number of spiral ganglion cells detected. On the contrary, inflammatory cell infiltration was not observed in the cochlear nucleus. The cell densities and the across-sectional areas of neurons in anteroventral cochlear nucleus and posteroventral cochlear nucleus were no difference in the guinea pigs. The antigen protein distributed strictly in cochlear nerve and the spiral ganglion. Some demyelinated areas in cochlear nerve was observed in this group. The threshold of ABR response in 68% guinea pigs (68/100 ears) did not increase. The data of DPOAE and the serum IgG levels show no difference compared with the control group. There were not pathological observation in spiral ganglion cells, cochlear nucleus and cochlear nerve. CONCLUSION: An animal model of autoimmune auditory neuropathy has been set up successfully and the character of the ABR and DPOAE was observed.

Animals↗
PubMed1989

Gustatory innervation in the rabbit: central distribution of sensory and motor components of the chorda tympani, glossopharyngeal, and superior laryngeal nerves.

Although rabbits have been used extensively in neurophysiological studies of the gustatory system, there is little information about the anatomical organization of taste in this species. Afferent and efferent central connections of three nerves innervating oral or laryngeal taste buds in the rabbit, including the chorda tympani (CT), the lingual-tonsillar branch of the glossopharyngeal (IX), and the superior laryngeal nerve (SLN), were traced by means of horseradish peroxidase neurohistochemistry. After entering the brainstem, most afferent fibers of CT, IX, and SLN turned caudally in the solitary tract, with fibers of the CT terminating in the nucleus of the solitary tract from 1.0 mm rostral to 3.8 mm caudal to the caudal border of the dorsal cochlear nucleus. There was terminal label from the CT also in the principal trigeminal nucleus. There was terminal label from the CT also in the principal trigeminal nucleus and the oral and intermediate divisions of the spinal trigeminal nucleus. Preganglionic parasympathetic cell bodies of the superior salivatory nucleus were labeled retrogradely in the reticular formation ventral to the rostral pole of the solitary nucleus. Afferent fibers of the IXth nerve terminated in the solitary nucleus from 0.6 mm rostral to 5.0 mm caudal to the caudal border of the dorsal cochlear nucleus. There were also labeled terminals in the principal trigeminal nucleus and in all three divisions of the spinal trigeminal nucleus. Cell bodies composing the inferior salivatory nucleus were labeled in and around the solitary nucleus and subadjacent reticular formation just rostral to the caudal border of the dorsal cochlear nucleus. There were also a few lightly labeled cells within the nucleus ambiguus at its most rostral extent. Afferent fibers of the SLN terminated in the solitary nucleus from 1.2 to 6.8 mm caudal to the dorsal cochlear nucleus. There was also some terminal label in the intermediate and caudal divisions of the spinal trigeminal nucleus. Many cells were retrogradely labeled in the nucleus ambiguus following application of HRP to the SLN and a few cells were labeled in and around the solitary nucleus just caudal to the dorsal cochlear nucleus. These three nerves show an overlapping rostral to caudal distribution of afferent input within the nucleus of the solitary tract that may be related to their gustatory and visceral functions.

Animals↗
PubMed1994

Physiological evidence for ipsilateral inhibition in the lateral superior olive: synaptic responses in mouse brain slice.

The incidence of ipsilateral inhibition in the lateral superior olive (LSO) was examined in a brain slice preparation of the mouse superior olivary complex. A 400 microns brain slice was taken in the frontal plane and maintained in a warm, oxygenated saline solution. Intracellular recordings were made from the LSO with micropipettes filled with 4 M potassium acetate. Synaptic responses were elicited by electrical stimulation of the trapezoid body in different slices at various locations between the cochlear nucleus and the ipsilateral superior olivary complex (SOC). The results show that ipsilateral stimulation can evoke inhibitory as well as excitatory postsynaptic potentials. The ipsilateral IPSPs have short latencies and are elicited by stimulation of the trapezoid body at any point along its course between cochlear nucleus and LSO. Short-latency IPSPs can also be produced by direct stimulation of the ventral cochlear nucleus itself. Ipsilateral IPSPs are blocked by low concentrations of the glycine antagonist, strychnine. In addition, bath application of sodium pentobarbital in one case eliminated ipsilateral IPSPs without eliminating EPSPs. The results suggest that there is a rapidly conducting, glycinergic pathway from cochlear nucleus through the trapezoid body to the LSO on the same side of the brain. This pathway is probably served by either a direct projection from the ventral cochlear nucleus to the LSO or an indirect one from cochlear nucleus to LSO through the lateral nucleus of the trapezoid body (LNTB).

Action Potentials↗
PubMed1984

Auditory brainstem anomalies in albino cats: II. Neuronal atrophy in the superior olive.

In a previous paper (Brain Res., 260:1-9, 1983) we reported that albino cats show abnormal auditory brainstem evoked responses that appear to arise from structural defects in or near the superior olivary complex. In the present study, neuronal cross-sectional area in brainstem nuclei was compared in albino and normally pigmented adult cats. The albinos were true tyrosinase-negative (cc) and should not be confused with the deaf white cat (W); the albinos are not deaf. Neurons in the medial superior olivary nucleus (MSO) of albinos were, on average, 41% smaller than in pigmented animals; there was no overlap in the neuronal size distributions for the two groups of animals. Cell size in the lateral superior olive, medial nucleus of the trapezoid body, ventral nucleus of the lateral lemniscus, anteroventral cochlear nucleus, dorsal cochlear nucleus, and facial nucleus was also smaller (by 9-21%) in albinos than in pigmented animals but none of these differences was statistically reliable. In the abducens nucleus, neurons were 12% larger in albinos than in pigmented animals, demonstrating that neuronal size in the albinos is not uniformly smaller. Several lines of evidence suggest that the auditory system defects in albinos are related to abnormal pigmentation rather than to other gene effects. It is possible that a subtle pigment-related disruption of inner ear development in albinos results in a central cascade of atrophic changes along the auditory pathway.

Animals↗