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At least 19 recordsLinked to original sources

PubMed1979

Development and degeneration of hearing in the C57/b16 mouse: relation of electrophysiologic responses from the round window and cochlear nucleus to cochlear anatomy and behavioral responses.

In disorders of the auditory organ associated with hearing loss, a correlation of the anatomical, behavioral and electrophysiological studies furnishes the investigator several parameters of study to better comprehend the hearing mechanism and the various anatomical structural dysfunctions that relate to the hearing loss. Mice are interesting to study because they carry several types of genes for hereditary deafness. Until recently, it was very difficult to train mice for behavioral hearing threshold testing; however, having developed such a method, the next step was to study the normal mice in these three parameters and extend the studies to mice with hereditary hearing loss. The type of mouse studied in this research was the C57/b16 strain which carries such a gene. The results of the studies indicate that the results of the behavioral and electrophysiological studies relate well to each other, and that light microscopic studies (if taken alone) do not furnish us with the actual functional capability of the structures of the inner ear. It is recommended (and it would be most valuable) that efforts should be made to collect and study human temporal bones with all three parameters of study for a better understanding of the structures of the human inner ear. Reference is made and recommendations given as to the parameters of studies while performing human electrocochleography.

Acoustic Stimulation↗

PubMed1977

Aspartic acid and glutamic acid levels in the cochlear nucleus after auditory nerve lesion.

Aspartic acid, glutamic acid and alanine were measured in the cochlear nucleus after lesioning the auditory nerve by cochlear ablation. Ultrastructural analysis of the cochlear nucleus showed that most primary auditory terminals were degenerating one day after cochlear ablation; the terminals were enlarged and the number of synaptic vesicles was reduced. Primary auditory terminals were virtually gone three days after cochlear ablation. Aspartic acid decreased after cochlear ablation in parallel with the morphological degeneration of the primary auditory terminals. The level of total aspartic acid in the cochlear nucleus had decreased more than 8% one day after cochlear ablation and more than 30% after two days, and remained at this level up to 28 days. Glutamic acid also decreased in the cochlear nucleus after cochlear ablation but not in parallel with the morphological degeneration of the primary auditory terminals. Following a slight increase one day after cochlear ablation, total glutamic acid decreased about 10% after two days and continued to decrease slowly through to day 28. Alanine dropped slowly after cochlear ablation and not in parallel with the degeneration of the primary terminals. Levels of other amino acids measured were unchanged or had increased two days after cochlear ablation. Aspartic acid and glutamic acid did not decrease in the superficial layers of the dorsal cochlear nucleus, an area receiving little or no primary innervation.

Alanine↗

PubMed1976

Dynamic properties of excitation and two-tone inhibition in the cochlear nucleus studied using amplitude-modulated tones.

The dynamic properties of excitation and two-tone inhibition in the cochlear nucleus were studied from extracellularly recorded unit responses to two simultaneously presented tones. One tone was presented at the unit's characteristic frequency, CF, the other at the unit's best inhibitory frequency, BIF. One or both of the tones were amplitude-modulated with pseudorandom noise. The system under study is in general nonlinear, but can be considered to function as a linear system for small changes in sound intensity around a certain operating point. The dynamic properties are likely to be different at different operating points. A suitable method for the study of dynamic properties of such a system employs tones that are amplitude-modulated with pseudorandom noise. In the present study, the dynamic properties were assessed by cross-correlating the unit discharge rate with the modulation. This was accomplished by computing the cross-covariance function between a period of noise and a period histogram of the discharges, the histogram being locked to the periodicity of the pseudorandom noise. In this way, it has been shown in previous works (Moller, 1973, 1974b), that the cross-covariance function is a valid approximation of the system's impulse response function at a certain sound intensity, provided the modulation is kept at a low value. In the present study the computed cross-covariance function is thus an approximation of the change in discharge rate of the cochlear nucleus units in response to a brief increase in stimulus intensity. As the response of the system under the given circumstances is approximately that of a linear system, the integrated cross-covariance is an approximation of the system's step response function, i.e the change in discharge rate that resulte from a hypothetical step increase in stimulus intensity. The results of the present study can be summarized as follows: 1. The impulse and step response functions computed from the responses to the modulated inhibitory tone of the great majority of units from which recording was made were found to be virtual mirror images of those obtained when the excitatory tone was modulated, the inhibitory response being somewhat smaller in amplitude than the excitatory. 2. When both tones were modulated simultaneously, the step response function was approximately the algebraic sum of the two responses obtained when the tones were modulated singly, further indicating that the system functions as a linear system when the stimulus amplitude is varied slightly around a certain operating point. 3. The shape of the cross-covariance functions is similar for all three stimulus situations, but varies with stimulus intensity and is different in different units. 4. The implication of the results is that the inhibition studied may either originate from the inhibition (suppression) seen in primary fibers or it may be the result of a true neural inhibition in the cochlear nucleus that occurs without any interneurons.

Animals↗

PubMed1978

Functional characteristics of cochlear nucleus in behaving cat examined by acoustic masking of electrical stimuli.

1. Cats were trained, using an operant procedure, to detect and respond to electrical stimulation delivered in the vicinity of the cochlear nucleus. The electrical stimuli were presented both in silence and in synchrony with repeated noise bursts to determine whether detection thresholds for the electrical stimuli were elevated by the acoustic masking noise. 2. For stimulation sites centered within auditory structures (cochlear nucleus or acoustic nerve root), the acoustic maskers caused a consistent elevation of the electrical detection thresholds. For stimulation sites that were in or bordered on nonacoustic neural structures (e.g., vestibular), the acoustic maskers caused little or no elevation of electrical detection thresholds. 3. The magnitude of the acoustic masking effect was monotonically related to the intensity of the acoustic masker across the range of intensities tested. 4. The magnitude of the masking effect was strongly dependent on the relative timing of the stimulus pulse and the masker noise burst. Maximum masking occurred when the pulse just followed the onset of the neural activity in cochlear nucleus evoked by the masker burst. Less masking occurred when the electrical pulse occurred at the middle or end of the masker burst, and still less when the pulse occurred just prior to the onset (backward masking) or just after the offset (forward masking) of the masker burst. 5. The magnitude of the masking effect also depended on the frequency of the acoustic masker. For tone bursts, masking was maximal for each electrode at a particular frequency and declined monotonically for masker frequencies above or below the optimal frequency. 6. It is concluded that the masking of an electrical stimulus by an acoustic stimulus depends on a direct interaction between the neural responses evoked by the two stimuli, and that similar central, neural interactions may contribute to acoustic masking of acoustic stimuli. It is also concluded that the technique of masking an electrical stimulus by an acoustical stimulus is a precise and useful tool for the study of sensory-neural organization in intact behaving animals.

Animals↗

PubMed1977

[Damage of the cochlea and of the cochlear nucleus after the application of aminoglycosid antibiotics--a comparative light-, transmission- and scanning electronmicroscopic study in the guinea pig (author's transl)].

Ototoxic alterations were studied in the guinea pig organ of Corti and in the cochlear nucleus after high administrations of aminoglycosid antibiotics (Gentamicin/Tobramycin, 150 mg/kg body weight/day or Amikacin 300 mg/kg body weight for 10 days). After survival times up to 22 days the animals were examined. By means of morphology degeneration was found in the cochlear nucleus before we could state it in the organ of Corti. After longer survival times, when we observed heavy degeneration in the organ of Corti we found only a few myelin figures of axons in the cochlear nerve. Cochlear nucleus: As an early sign of degeneration alterations in the mitochondria were found. Compared with the organ of Corti the damage was less widespread in the second order neurons of the afferent auditory pathways, their dendrites or nerve endings. Quantitative calculations however, were not performed. In axosomatic synapses we could observe a way of degeneration which was not reported before in damage caused by aminoglycosid antibiotics. Free postsynaptic densities were observed to be invaginated into the neuron as a probable way of sequestration. As well we could observe reoccupation of the synaptic sites by a probable sliding of neighbouring nerve endings into the free intracellular space. (Similar observations were reported first by Gentschev and Sotelo [1973] after ablation of the cochlear nerve in rats.

Aminoglycosides↗

PubMed1976

Choline acetyltransferase, glutamate decarboxylase and tyrosine hydroxylase in the cochlea and cochlear nucleus of the guinea pig.

Activities of choline acetyltransferase (ChAC), glutamate decarboxylase (GAD) and tyrosine hydroxylase (TH), enzymes catalyzing the synthesis of acetylcholine (ACh), gamma-aminobutyric acid (GABA) and catecholamines, respectively, were measured in the cochlea and cochlear nucleus of the guinea pig. ChAc activity in the organ of Corti, third turn, was 1270 pmole ACh formed/min/mg protein (ChAc, 1270) and was higher than in turn 4 (ChAc, 543). ChAc activity was higher when the preparation included the inner hair cell region than when not. GAD activity in samples of turn 3 and 4 combined was low, 0.17 nmole GABA formed/min/mg protein (GAD, 0.17). All 3 enzymes were low in auditory nerve: ChAc, 1.7, GAD, 0.10 and TH, 1.0 pmole DOPA formed/min/mg protein. In the cochlear nucleus, the values were: ChAc, 129, GAD, 1.70 and TH, 2.7. The findings on the distribution of ChAc activity in the organ of Corti fit the hypothesis that the olivocochlear nerve fibers are cholinergic. Because of low GAD in the cochlea, GABA is unlikely to be transmitter in the organ of Corti. Similarly, it is unlikely that ACh, GABA or a catecholamine is a transmitter between the auditory nerve and the cochlear nucleus.

Acetyltransferases↗

PubMedDate not supplied

Coding of time-varying sounds in the cochlear nucleus.

The results presented in the present paper show that single nerve cells in the cochlear nucleus have different discharge patterns in response to tones whose frequency varies rapidly compared to tones with slowly varying frequency. Moreover, small, rapid changes in the intensity of a tone are reproduced in such a way that a modulation of a few decibels can give rise to a nearly 100% modulation in the discharge pattern. Amplitude modulation is reproduced in the discharge pattern of these neurons throughout a large intensity range, in many units more than 70 dB. This intensity range is much larger than the intensity range where the mean discharge rate is a function of the sound intensity, meaning that changes in frequency as well as in intensity are enhanced in these units. Though no doubt but a small part of the processing that occurs in the cochlear nucleus, such information seems likely to be extracted somewhat differently by different neurons.

Acoustic Stimulation↗

PubMed1978

Distribution of gamma-aminobutyric acid, glycine, glutamate and aspartate in the cochlear nucleus of the rat.

The distributions of gamma-aminobutyric acid (GABA), glycine, glutamate and aspartate were measured in cochlear nuclei of two rats by quantitative histochemical mapping procedures. The levels and distributions in the two rats were comparable, and resembled those previously reported for cat cochlear nucleus. The results are consistent with a concept that these putative transmitter amino acids have similar levels and distributions in the cochlear nucleus among mammals.

Aminobutyrates↗

PubMed1976

Descending inputs to caudal cochlear nucleus in cats: a horseradish peroxidase (HRP) study.

After HRP injections into the octopus cell area of the cat cochlear nucleus, only periolivary neurons of the superior olivary complex (SOC) reacted. Elongate neurons in the lateral periolivary nuclei (ipsilateral to the injection) and multipolar neurons in ventromedial periolivary regions (contralateral to the injection) contained granules. No neurons in the main SOC nuclei or higher auditory nuclei reacted, despite a wide range of HRP concentrations. Thus, neurons from the SOC to the octopus cell area of the cochlear nucleus seem to be entirely periolivary and not entirely equivalent to neurons providing collaterals to the olivocochlear bundle.

Animals↗

PubMed1976

Dynamic properties of primary auditory fibers compared with cells in the cochlear nucleus.

The dynamic properties of the responses of single primary auditory fibers were compared with those of single cells in the cochlear nucleus. The stimuli were tones (at the unit's characteristic frequency, CF) that were amplitude-modulated with pseudorandom noise. The dynamic properties were described by the cross-covariance and integrated cross-covariance functions between the recorded discharge rate and the modulation. These two measures have earlier been shown to be valid approximations of the system's impulse and step response function, i.e. the change in discharge rate in response to a short impulsive increase (or decrease) in the stimulus intensity and a step increment (or decrement) in the stimulus intensity. The cross-covariance function computed from the responses of fibers had a narrower peak than that of cells indicating that a brief change in stimulus intensity gives rise to a faster change in the discharge rate of fibers than that of cells. The nodulation of the discharge rate of cells for a certain degree of amplitude modulation of the sound is usually greater than that of cells. The modulation of the discharge rate of cells for a certain degree of amplitude modulation of the sound is usually greater than that of fibers. The range of stimulus intensities where a change in stimulus intensity gives rise to a change in discharge rate rate is smaller for fibers (about 30 dB) than what was shown earlier for cells (70-80 dB). The cross-covariance function computed from the slow wave responses recorded from the surface of the cochlear nucleus in response to an amplitude-modulated tone has individual peaks that reflect distinct classes of units with regard to latency of unit dishcarges.

Acoustic Stimulation↗

PubMed1975

Degenerative alterations in the ventral cochlear nucleus of the guinea pig after impulse noise exposure. A preliminary light and electron microscopic study.

Guinea pigs were exposed to the noise of 40 shots of an alarm pistol held at a distance of about 60 cm. The ventral cochlear nuclei were studied in phase contrast and electron microscopy after both survival periods and longer periods of up to 55 days survival. Marked degeneration of primary cochlear nerve endings and of synapting secondary neurons of the posterior caudal part of the ventral cochlear nucleus (AVCN) and the octupus cell area (OCA) of the posterior ventral cochlear nucleus (PVCN) was found most distinctly after 5-55 days. As criteria of degeneration of the second neuron of the afferent auditory pathway we used: 1. The loss of the synapting nerve endings, mainly 'shrinking". 2. The formation of huge mitochondria in the second order neurons and their dendrites. 3. The phagocytosis by glial cells of nerve endings, of the second order neurons and of their dendrites. After 5 days survival time no distinct changes were found in the granular cell area of PVCN, where as all stages of degeneration could be found in OCA at this time. In the discussion of these findings it is concluded that additional studies of the morphology of the cochlear nuclei seem necessary, as these may lead to a better understanding of the pathology of hearing following heavy noise exposure.

Animals↗

PubMed1978

[Lamellar structure of the dorsal cochlear nucleus in rats].

The lamellar ultrastructure of the dorsal cochlear nucleus (DCN) was studied in frontal ultrathin wide sections of the nucleus which were placed on lead aprons and included all the nucleus layers. The electron-microscopic description of the different cell types and distribution of the axonal terminals are presented. Large branchy axonal terminals (6-8micron) with small spherical synaptic vesicles 40-50 nm in diameter, small terminals (1-3 micron) with spherical synaptic vesicles (45-60 nm) and thin unmyelinated axons prevail in the surface and middle layers of the neuropile as compared to the deep layer. The number of the myelinated axons and large oval terminals 4-6 micron in diameter with central distribution of mitochondria and neurofilaments as well as with spherical synaptic vesicles 50-60 nm in diameter increased from the middle layer to the deep one. The number of granular cells was larger in the surface and middle layers than in the deep one. The functional significance of each terminal type is discussed.

Animals↗

PubMed1977

An ultrastructural analysis of neurites in the basal lamina of capillaries in the chinchilla cochlear nucleus.

In an ultrastructural study of the chinchilla anteroventral cochlear nucleus (AVCN), we found innervated capillaries in the layer of granule cells that comprises the dorsolateral portion of the AVCN and forms a cap over the principal portion of the nucleus. In 66% of 215 capillaries we examined in the granule cell layer of various levels of the AVCN, we found structures having ultrastructural features of axons that (1) were within the brain parenchyma and were in direct contact with the pericapillary basal lamina, or (2) were separate fro, the adjacent neuropil and, often in the company of astrocytic processes, were completely enveloped by the pericapillary basal lamina. An analysis of serial sections confirmed that neurites within the pericapillary basal lamina were in continuity with neurites in the brain parenchyma. Most neurites within the basal lamina of capillaries were next to pericytes, but some neurites were next to endothelial cells. None of the neurites adjoining capillaries had the abundance of synaptic vesicles typical of autonomic vasomotor nerve endings and synaptic terminals. Consequently, they may be sensory, responding perhaps to changes in hydrostatic pressure or chemical composition of the blood or cerebrospinal fluid. However, we cannot exclude the possibility that neurites which accompany capillaries in the AVCN terminate elsewhere. In the AVCN the innervation of capillaries is restricted to the superficial layer of granule cells. In none of 177 capillaries of the principal portion of the AVCN did we find an example of a neurite in contact with the pericapillary basal lamina, a pericyte, or an endothelial cell, although it was sometimes necessary to examine specimens at various angles of tilt to confirm that the pericapillary glial sleeve was continuous. Furthermore, we found no innervated blood vessels among 266 capillaries examined in the granular and molecular layers of the cerebellar cortex.

Animals↗

PubMed1977

Development of the octopus cell area in the cat ventral cochlear nucleus.

The octopus cell area (OCA) of the posteroventral cochlear nucleus was studied electron microscopically in kittens. The adult OCA, a region of morphologically homogeneous neurons receiving heterotypic synapses from the cochlea, was used to define the mature state. The OCA reaches cytological maturity at three weeks postnatally, after progression through four stages, defined on the basis of octopus cell cytology (including relative numbers of somatic and dendritic filopodia and spines) and the frequency, ultrastructure and location of previously defined synaptic terminals. Octopus cell size was also studied in rapid Golgi impregnations. The OCA from birth through three postnatal days (stage 1) showed small neurons, few identifiable synaptic types, small, mostly unmyelinated axons, mitotic cells and undifferentiated glia. Between the fourth and seventh postnatal days (stage 2) distinct type 1 and type 2 endings appeared and dendrites thickened, expanded peripherally and developed mature spines. During stage 3 (8-19 days) loss of filopodia, increased somatic spicules, larger somas and clearer differentiation of type 1 and type 2 synapses occurred. After three postnatal weeks (stage 4) the OCA contained morphologically mature octopus cell somas, all three synaptic types ending upon somas and thick basal dendrites, and fascicles of myelinated fibers. Although cytologically mature, the OCA at this stage (about 20-35 days) is substantially smaller than the adult OCA. This smaller size will facilitate further study of OCA synaptic organization.

Animals↗

PubMed1978

Survey of intracellular recording in the cochlear nucleus of the cat.

Intracellular recordings were made in the cochlear nucleus of anesthetized cats. In anterior passes, one never obtained sustained depolarizations from 'primary-like' units. For 'chopper' units, however, it was possible to record sustained depolarizations accompaneid by spikes that lasted as long as the tone burst. 'Pauser, 'buildup' and 'on' units also had spike responses that could be accompanied by sustained depolarizations. For 'pauser', 'buildup' and 'on' units, hyperpolarization was not seen during the times when no spike discharges appeared so long as the tone bursts were at the characteristic frequency of the units.

Acoustic Stimulation↗

PubMed1978

Discharge patterns in the cochlear nucleus of the chinchilla following noise induced asymptotic threshold shift.

Chinchillas were exposed to an 86 dB SPL octave band of noise centered at 4.0 kHz for 3.5--5 days. The noise elevated the hearing thresholds between 4.0 and 16.0 kHz to between 60 and 75 dB SPL. Measurements from single neurons in the cochlear nucleus revealed abnormalities in the response properties of neurons with characteristic frequencies (CF) above 2.0 kHz. Units above 2.0 kHz had elevated thresholds (between 50 and 90 dB SPL) and broad tuning curves due to a greater loss in sensitivity near CF than at lower frequencies. The tuning curve Q10dB values for high frequency neurons were generally less than 3.0 and approached the Q10dB values for basilar membrane displacement. Spontaneous activity rates in units above 2.0 kHz were also low. In a few units, the threshold for single tone inhibition was significantly lower than that for excitation; the best inhibitory frequencies were always below 2.0 kHz. Two-tone inhibition was present in both low and high threshold neurons, but its strength was not assessed. Cochleagrams obtained 12 hours postexposure revealed discrete hair cell lesions in the basal third of the cochlea. The locations of the lesions were consistent with the frequencies of maximum hearing loss. The behavioral thresholds and the thresholds at CF of the most sensitive units were within 10--15 dB of each other. The results indicate that intense sounds reduce the sensitivity, frequency selectivity and spontaneous activity of units in the cochlear nucleus. The findings are similar to those obtained in auditory nerve fibers with ototoxic drugs and hypoxia.

Acoustic Stimulation↗

PubMed1979

Coding of increments and decrements in stimulus intensity in single units in the cochlear nucleus of the rat.

The response of single units in the cochlear nucleus when confronted with step increments and step decrements in stimulus intensity was studied in the rat using tones that were amplitude modulated with square waves or with pseudorandom noise. Cycle histograms of the responses to tones modulated with square waves revealed that the probability of firing increased as a result of step increments in stimulus intensity for tones at characteristic frequency (CF) and that the probability of firing decreased as a result of step decrements. When two tones were presented simultaneously, one at CF and one at the unit's best inhibitory frequency (BIF), and one or the other of the tones was modulated, the modulation of the cycle histogram of the responses was greater than when only one tone was presented. Modulation of the inhibitory tone gave rise to histograms that were mirror images of the histograms of the responses to modulation of the excitatory tone. An increase in probability of firing always occurred at a faster rate than a decrease, independent of whether the increase was brought about by increase in the intensity of the excitatory tone or by a decrease in the intensity of the inhibitory tone. The cycle histograms of the responses to square wave-modulated tones and the step response estimated from the responses to tones amplitude-modulated with pseudorandom noise showed a greater similarity when the cycle histograms depicted the case of an increase in the probability of firing than when they concerned a decrease in the probability of firing.

Animals↗

PubMed1978

Internal organization of membranes at end bulbs of Held in the anteroventral cochlear nucleus.

The end of bulb of Held in the rostral ventral cochlear nucleus of the chinchilla and guinea pig was studied with the freeze-fracture technique. The end bulb has multiple, small active zones which are uniformly distributed within the calyceal portion of this terminal. Single or small groups of active zones are surrounded by enlarged channels of extracellular space often containing processes of astrocytes. Small plasmalemmal deformations occur at these active zones. The number of these deformations is thought to be indicative of exocytotic transmitter release because they are more frequent in animals fixed in a noisy environment compared to animals fixed in a quiet environment. Thus, our study provides a basis for the quantitative study of changes in transmitter secretion at a central nervous system synapse driven by a controllable natural stimulus. The postsynaptic active zone at end bulbs resembles other excitatory synapses in the central nervous system in having an aggregate of large particles on the external membrane leaflet. This junctional aggregate of particles is coextensive with the presynaptic active zone and with the postsynaptic density seen in thin sections. Several perisynaptic aggregates of particles are deployed around each active zone on the external membrane leaflet. These irregularly-shaped aggregates occur preferentially opposite the channels of enlarged extracellular space and along the edge of the end bulb and are not components of intercellular junctions or plasmalemmal contacts with cytoplasmic organelles. Although the function of the different particle aggregates on the postsynaptic membrane is not clear, our findings provide a basis for studying the factors controlling and maintaining their structure as well as more evidence that a consistent relationship exists between types of synaptic action and structure of the postsynaptic membrane.

Acoustic Stimulation↗