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Biomedical subjects

R Klinke

Publications and source records attributed to R Klinke.

At least 37 records · Page 2Linked to original sources
PubMed1997

Response of the primary auditory cortex to electrical stimulation of the auditory nerve in the congenitally deaf white cat.

Neural activity plays an important role in the development and maintenance of sensory pathways. However, while there is considerable experience using cochlear implants in both congenitally deaf adults and children, little is known of the effects of a hearing loss on the development of the auditory cortex. In the present study, cortical evoked potentials, field potentials, and multi- and single-unit activity evoked by electrical stimulation of the auditory nerve were used to study the functional organisation of the auditory cortex in the adult congenitally deaf white cat. The absence of click-evoked auditory brainstem responses during the first weeks of life demonstrated that these animals had no auditory experience. Under barbiturate anaesthesia, cortical potentials could be recorded from the contralateral auditory cortex in response to bipolar electrical stimulation of the cochlea in spite of total auditory deprivation. Threshold, morphology and latency of the evoked potentials varied with the location of the recording electrode, with response latency varying from 10 to 20 ms. There was evidence of threshold shifts with site of the cochlear stimulation in accordance with the known cochleotopic organisation of AI. Thresholds also varied with the configuration of the stimulating electrodes in accordance with changes previously observed in normal hearing animals. Single-unit recordings exhibited properties similar to the evoked potentials. Increasing stimulus intensity resulted in an increase in spike rate and a decrease in latency to a minimum of approximately 8 ms, consistent with latencies recorded in AI of previously normal animals (Raggio and Schreiner, 1994). Single-unit thresholds also varied with the configuration of the stimulating electrodes. Strongly driven responses were followed by a suppression of spontaneous activity. Even at saturation intensities the degree of synchronisation was less than observed when recording from auditory brainstem nuclei. Taken together, in these auditory deprived animals basic response properties of the auditory cortex of the congenitally deaf white cat appear similar to those reported in normal hearing animals in response to electrical stimulation of the auditory nerve. In addition, it seems that the auditory cortex retains at least some rudimentary level of cochleotopic organisation.

Adult↗
PubMed1997

Loss of auditory function in transgenic Mpv17-deficient mice.

The transgenic mouse strain Mpv17 develops severe morphological degeneration of the inner ear and nephrotic syndrome at a young age (Meyer zum Gottesberge et al., 1996; Weiher et al., 1990). The audiograms (1-32 kHz) of Mpv17-negative mice were determined from auditory brain stem responses in young (2 months) and old (7 months) animals. Audiograms of age-matched wild-type mice with the same genetic background, but wild-type at the Mpv17 locus, were also determined. Furthermore, young Mpv17-negative mice that carried a human Mpv17 homologue gene were studied. NMRI mice served as a reference for normal hearing. Mpv17-negative mice suffer from severe sensorineural hearing loss as early as 2 months after birth. In the old Mpv17-negative mice no responses could be elicited at all. The 2 month old wild-type mice had normal audiograms, at 7 months only high threshold responses were seen. The poor audiograms of the Mpv17-negative mice are assumed to be the functional correlate of the morphological degeneration of the cochlea described earlier (Meyer zum Gottesberge et al., 1996). The finding that 2 out of 4 Mpv17-negative mice with the human Mpv17 gene had normal audiograms, shows that the gene inactivation can be functionally compensated by the human Mpv17 gene product.

Age Factors↗
PubMed1997

Discharge properties of pigeon single auditory nerve fibers after recovery from severe acoustic trauma.

The time course of recovery of compound action potential (CAP) thresholds was observed in individual adult pigeons after severe acoustic trauma. Each bird had electrodes implanted on the round window of both ears. One ear was exposed to a tone of 0.7 kHz at 136-142 dB SPL for 1 hr under general anesthesia. Recovery of CAP audiograms was monitored twice a week after trauma. Single unit recordings from auditory nerve fibers were made after 3 weeks and after 4 or more months of the exposure. The CAP was abolished immediately after overstimulation in all animals. Based on the temporal patterns of functional recovery of the CAP three groups of animals were identified. The first group was characterized by fast functional recovery starting immediately after trauma followed by a return to pre-exposure values within 3 weeks. In the second group, slow functional recovery of threshold started 1-2 weeks after trauma followed by a return to pre-exposure values by 4-5 weeks. A mean residual hearing loss of 26.3 dB at 2 kHz remained. The third group consisted of animals that did not recover after trauma. Three weeks after the exposure, tuning curves of single auditory nerve fibers were very broad and sometimes irregular in shape. Their thresholds hovered around 120 dB SPL. Spontaneous firing rate and driven rate were much reduced. Four or more months after exposure, the thresholds and sharpness of tuning of many single units were almost completely recovered. Spontaneous firing rate and driven rate were comparable to those of control animals. In the slow recovery group neuronal tuning properties showed less recovery, especially at frequencies above the exposure frequency. Thresholds and sharpness of tuning were normal at frequencies below the exposure frequency, but were much poorer at frequencies above the exposure. Spontaneous firing rate was much reduced in fibers with high characteristic frequencies. In fast recovering animals, the papilla was repopulated with hair cells after 4 months. In slow recovering animals, short (abneural) hair cells were still missing over large parts of the papilla after 4 months of recovery. Residual short (abneural) hair cell loss was largest at two areas, one more basal and the other more apical to the characteristic place of the traumatizing frequency. The results show that, in adult birds, functional recovery from severe damage to both short (abneural) and tall (neural) hair cells occurs. However, the onset of recovery is delayed and the time course is slower than after destruction of short (abneural) hair cells alone. Also, recovery is incomplete, both functionally and morphologically. There is residual permanent hearing loss, and regeneration of short (abneural) hair cells is incomplete.

Action Potentials↗
PubMed1997

The central auditory system and auditory deprivation: experience with cochlear implants in the congenitally deaf.

In the present paper we briefly review the response of the central auditory system to auditory deprivation and describe recent experimental and clinical experience with cochlear implants. While the central auditory system undergoes marked changes in response to auditory deprivation, it would appear that at least a rudimentary cochleotopic organisation is maintained at the level of the brainstem and auditory cortex in animals deafened from birth. Moreover, recent studies have demonstrated the ability of the central auditory system to undergo functional reorganisation in response to changes in the pattern of afferent activity. Clinical experience has shown that deaf children with little or no prior auditory experience can obtain significant benefit from cochlear implants, provided the device is fitted at a young age. Furthermore, factors predicting successful clinical outcomes with these devices reflect the importance of auditory experience, either prior to an acquired loss or with the use of a cochlear implant. These findings suggest that functional reorganisation within the central auditory pathway can at least partially account for improvements in clinical performance over time.

Adult↗
PubMed1997

Basic neurophysiology of cochlear-implants.

Cochlear implants work because the fibers of the auditory nerve can be stimulated electrically. Currently used multi-channel electrodes distribute the stimuli to different cochlear places (place principle) and provide information on the fine-time structure of the acoustic stimulus thus allowing periodicity analysis by the central nervous system. The paper treats the limitations of current cochlear implant technologies and discusses conceivable improvements.

Auditory Pathways↗
PubMed1996

Regeneration after tall hair cell damage following severe acoustic trauma in adult pigeons: correlation between cochlear morphology, compound action potential responses and single fiber properties in single animals.

The time course of recovery of compound action potential (CAP) thresholds was observed in individual adult pigeons after severe acoustic trauma. Pigeons were overstimulated with a tone of 0.7 kHz and 136-142 dB SPL presented to one ear for 1 h under general anesthesia. Recovery of CAP audiograms was monitored at regular intervals after trauma. A new semi-stereotaxic approach to the peripheral part of the auditory nerve was developed. This permitted activity from single auditory nerve fibers to be recorded over a wide range of characteristic frequencies (CFs), including high CFs, without having to open the inner ear. Single unit recordings were made after three weeks and after 4 or more months of recovery. The time course of recovery, the single unit properties, and the morphological status of the basilar papilla were correlated. The CAP was abolished in all animals after overstimulation. Three groups of animals were identified according to the functional recovery of the CAP thresholds recorded at regular intervals with implanted electrodes: Group 1: Fast functional recovery starting immediately after trauma, followed by recovery to pre-exposure values within 3 weeks. Group 2: Slow functional recovery of threshold starting 1-2 weeks after trauma and ending 4-5 weeks after trauma. A mean residual hearing loss of 26.3 dB at 2 kHz remained. Group 3: No recovery of CAP thresholds up to 8 months after trauma. Three weeks after trauma, very few responsive neurons were found in groups 2 and 3. Tuning curves were very broad and sometimes irregular in shape. Thresholds were very high, around 120 dB SPL. Spontaneous firing rate was much reduced, especially in neurons with high CFs. After 4 or more months of recovery, the response properties of single units in group 1 had only partially recovered. Thresholds and sharpness of tuning of many single units were normal: however, in general they were still poorer than in control animals. Spontaneous firing rate was comparable to control animals. Neurons from animals in group 2 showed less recovery, especially at frequencies above the exposure frequency. Thresholds and sharpness of tuning were normal at frequencies below the exposure frequency, but were much poorer at frequencies above the exposure. Spontaneous firing rate was much reduced in fibers with high CFs. The basilar papilla in animals without recovery showed total loss of the sensory epithelium. The basal lamina of the basilar membrane, however, remained intact and was covered with cuboidal cells. In fast recovering animals, the papilla was repopulated with hair cells after 4 months. In slow recovering animals, short (abneural) hair cells were still missing over large parts of the papilla after 4 months of recovery. Residual short (abneural) hair cell loss was largest at two areas, one more basal and the other more apical to the characteristic place of the traumatizing frequency. The results show that functional recovery from severe damage to both short (abneural) and tall (neural) hair cells occurs in adult birds. However, the onset of recovery is delayed and the time course is slower than after destruction of short (abneural) hair cells alone. Furthermore recovery is incomplete, both functionally and morphologically. There are residual permanent hearing losses and regeneration of short (abneural) hair cells is incomplete.

Acoustic Stimulation↗
PubMed1996

Development of activity patterns in auditory nerve fibres of pigeons.

Little is known about inner ear development in pigeons. This paper addresses the question of maturation in activity patterns of pigeon auditory nerve fibres, Pigeons that were 1, 2 and 4 weeks and 1, 2, 3 and 4 years old were investigated. Adult-like activity patterns are found 4 weeks post-hatching. Spontaneous activities of fibres in immature animals (about 40 spikes/s) are half that found in adults. Spontaneous discharge rate does not increase with decreasing characteristic frequency (CF) of the fibre if the animals are immature. Rate threshold are less sensitive in immature animals. Differences between the age groups are generally significant if the CFs of the fibres are below 1.3 kHz. Sharpness of tuning is already adult-like in l-week-old animals. Inter-spike time interval histograms (ISTH) of auditory fibres recorded in animals of all age groups often show Poisson-like distributions. Preferred intervals are found in 10% of the ISTHs of fibres in immature animals but in 30% of adults. Cross-correlations between heart beats of the animal and spontaneous activities show good correlation for about 70% of the fibres in immature animals. With the growth of the animals, the number of fibres showing correlation of spontaneous activities and heart beats decreases to about 40%. The basilar papilla of a 1-week-old animal is smaller than in an adult animal (by 10% in length and by 10% in width), judge by scanning electron microscopy (SEM), Changes of activity patterns in this study are likely to be a result of maturation of the middle ear. In addition to the latter, development of the inner ear is conceivable.

Aging↗
PubMed1995

Rate-intensity-functions of pigeon auditory primary afferents.

Rate-intensity-functions (RI-functions) were determined in 150 primary auditory afferents in anaesthetized pigeon. Acoustic stimulation was either at characteristic frequency (CF) or half an octave below or above CF. Stimulated at CF, 37% of the fibres showed saturating RI-functions, whereas 50% showed sloping and 13% straight RI-functions. In the sloping RI-functions, a bend was found about 20 dB above the fibres' thresholds. For non-CF stimuli, the general shape of the RI-functions remained constant. However, the maximum evoked discharge rates were lower for frequencies below CF and higher for frequencies above CF. The data show that a population of neurones, the sloping and straight ones, code stimulus intensities over a wide intensity range. In combination with the scatter of the thresholds, intensity ranges greater than 100 dB are conceivable. It was concluded that the nonlinearities found in pigeon are not caused by basilar membrane (BM) mechanics, rather an origin at the hair cell-afferent nerve fibre system has to be considered.

Acoustic Stimulation↗
PubMed1995

Middle latency responses to acoustical and electrical stimulation of the cochlea in cats.

The middle latency responses (MLR) to acoustical stimulation (A-MLR) as well as to electrical stimulation (E-MLR) of the inner ear were recorded in pentobarbital-anaesthetised cats. Monopolar and bipolar MLR recordings were performed with electrodes located at different places on the primary auditory cortex (AI). The cochlea was electrically stimulated (ES) through a single round-window electrode or through a multichannel intracochlear implant. The slope of amplitude-intensity functions of the A-MLR was steeper when the stimulus frequency of the acoustical stimuli corresponded to the tonotopical recording place on the auditory cortex. Other response properties (waveshape, thresholds and latencies) were related to the recording site and stimulus frequency in only two-thirds of animals. Parameters of E-MLRs evoked by high-frequency ( > 4 kHz) and low-intensity ES in hearing cats, which produced an electrophonic effect, were similar to parameters of acoustically evoked MLRs. In deafened cats, the properties of responses to extracochlear ES were different from those recorded to acoustical stimulation and they were almost uniform in all cortical places. Variations in thresholds, in latencies and in the slope of the amplitude-intensity functions of the E-MLRs recorded in individual tonotopical cortical places were observed when the auditory nerve was stimulated with different configurations of electrodes through a multichannel intracochlear implant.

Acoustic Stimulation↗
PubMed1995

A functional map of the pigeon basilar papilla: correlation of the properties of single auditory nerve fibres and their peripheral origin.

The purpose of the investigation was to correlate the functional properties of primary auditory fibres with the location of appertaining receptor cells in the avian basilar papilla. The functional properties of 425 single afferent fibres from the auditory nerve of adult pigeons were measured. The peripheral innervation site of 39 fibres was identified by intracellular labelling and correlated with the fibre's functional properties. Mean spontaneous firing rate (SR, 0.1-250/s) was distributed monomodally (mean: 91 +/- 47/s) but not normally. Characteristic frequencies (CFs) were in the range of 0.02-4 kHz. SR, threshold at CF (4-76 dB SPL) and sharpness of tuning (Q10 dB, 0.1-8.8) varied systematically with CF. For a given CF there was a strong correlation of threshold and Q10 dB and of threshold and SR. Labelled fibres innervated different hair cell types over 93% of the length and 97% of the width of the basilar papilla. The majority of fibres innervated hair cells located between 30 and 70% distance from the apex and 0 and 30% distance from the neural edge of the papilla. CFs are mapped tonotopically from high at the base to low at the apex of the papilla, with a mean mapping constant of 0.63 +/- 0.05 mm/octave (in vivo). The highest CF at the base extrapolates to 5.98 +/- 1.17 kHz. The lowest CF mapped at the apex is 0.021 kHz. From the data, together with data from mechanical measurements (Gummer et al., 1987), a frequency-place function of the pigeon papilla was calculated. Transverse gradients of threshold at CF and of Q10 dB were observed across the width of the papilla. Thresholds were lowest and sharpness of tuning was highest above the neural limbus at a distance of 23% from the neural edge of the papilla. Hair cells in this sensitive strip are the tallest and narrowest ones across the width of the papilla. They are packed most densely and receive the largest number of afferent fibres. Fibres innervating (mostly short) hair cells on the free basilar membrane were spontaneously active and responsive to sound. Their Q10 dB was less than average but their sensitivity and SR were comparable to the mean population values. It is concluded that functional properties change gradually not only along the length but also across the width of the pigeon basilar papilla. The results support the idea that sharp frequency tuning of avian primary auditory fibres involves tuning mechanisms supplementary to the tuning of the free part of the basilar membrane.

Acoustic Stimulation↗
PubMed1994

Artifact-free application of drugs into the avian endolymphatic space.

A push-pull system is described that allows artifact-free application of drugs into very small volumes such as, e.g., the endolymphatic space of the inner ear. The system consists of two syringes, the pistons of which are fixed together and driven by an Oriel motordrive. The syringes are connected to the pipette holders and microcapillaries by PVC tubes. One capillary is used to expel a certain volume, whilst the other one aspirates the same volume. A balanced exchange of fluids within a given space without an overall change in volume is therefore possible.

Action Potentials↗
PubMed1994

Effects of endolymphatic and perilymphatic application of salicylate in the pigeon. I: Single fiber activity and cochlear potentials.

The effects of salicylate on the mammalian cochlea function are well documented. However, there is a lack of reports on salicylate effects on the avian auditory periphery and it might well be that salicylate is not ototoxic at all in submammalian vertebrates. We therefore recorded single fiber activities, compound action potential (CAP) and endocochlear potential (EP) during application of salicylate (calculated final concentration of about 2-18 mmol/l) into the scala media of pigeons. We furthermore recorded CAP and EP during perilymphatic perfusion of salicylate (2-20 mmol/l). Salicylate applied into the scala media led to an elevation of tip threshold in single fibers ranging from 5 to 35 dB. The characteristic frequencies of the fibers were not changed. This effect on auditory nerve fibers was reflected in an elevation of CAP thresholds. The mean spontaneous discharge rate was either slightly increased or remained unchanged in the majority of fibers. Perilymphatic salicylate perfusion also led to an elevation of CAP thresholds that was reversible following subsequent perfusion with artificial perilymph. The EP remained unchanged in both application modes. The effects of salicylate were dose dependent and more pronounced in the mid- to high-frequency range. These results are consistent with an action of salicylate on the process (electrical or mechanical, or both) responsible for the sensitivity and frequency selectivity in the avian peripheral hearing organ.

Action Potentials↗
PubMed1994

Effects of endolymphatic and perilymphatic application of salicylate in the pigeon. II: Fine structure of auditory hair cells.

Large doses of salicylate are known to cause reversible ototoxic effects including fine structural alterations of the auditory hair cells in mammals. To investigate possible fine structural correlates of salicylate effects on pigeon auditory hair cells, the basilar papillae following perilymphatic or endolymphatic application of salicylate were fixed and processed for transmission electron microscopy. The pigeon auditory hair cells possessed organelles typically described in avians. A single or multi-layered array of cisternae along the cytoplasmic side of the lateral plasma membrane, i.e. subsurface cisternae that are characteristic for mammalian outer hair cells, was not seen. The most prominent fine structural alterations of hair cells after salicylate application were an increase in the luminal width of smooth and rough endoplasmic reticulum as well as the frequent occurrence of prominent single-membrane-bound vesicles filled with electron-dense bodies. Based on the assumption that subsurface cisternae represent a specialized form of endoplasmic reticulum, the present findings indicate that the structural correlates of salicylate toxicity are similar in mammalian and avian auditory hair cells.

Animals↗
PubMed1994

Preferred intervals in birds and mammals: a filter response to noise?

Quasi-periodic spontaneous activity (preferred intervals, PIs) has been reported from avian primary auditory afferents. In mammals, PIs have not been reported, as yet. As the length of PIs is close to 1/characteristic frequency, it has been suggested that this type of spontaneous activity indicates particular mechanisms in avian inner ear transduction. However, the present paper shows that pigeon auditory fibres possessing preferred intervals in their spontaneous activity always belong to the most sensitive and the most sharply-tuned fibres recorded. This leads to the assumption that preferred intervals are the response of narrow-band filters to noise. This view is supported by three additional findings: (i) Near-threshold noise provokes PIs in avian fibres that show no spontaneous PIs. (ii) Similarly, PIs can also be evoked in mammalian (gerbil) auditory afferents by low level noise. (iii) Phase-locking of auditory afferents can be achieved by sound stimuli 10-20 dB below rate threshold. It is argued that no conclusions may be drawn from the presence of PIs about the nature of the underlying filter.

Acoustic Stimulation↗
PubMed1994

Discharge pattern in the auditory nerve evoked by vowel stimuli: a comparison between acoustical and electrical stimulation.

Single channel cochlear implants only transmit the time structure of the electrically coded input signal. All nerve fibres show similar thresholds for monopolar round window stimulation, i.e., activation does not depend on their site of origin. To investigate the fine structure of the firing pattern elicited by stimulation with an analogue coded speech processing system (VIENNA 1-channel implant), cats were electrically stimulated with German steady-state vowels at the round window. Single fibre activity was recorded from primary auditory fibres and period histograms were calculated. The electrically evoked impulse patterns were compared with those from acoustic stimulation with the same vowels. With acoustic stimulation, the response of a fibre depends on the individual characteristic frequency (CF) with regard to the fundamental F0 and the formants F1, F2 and F3 of the vowels, the spontaneous activity of the fibre and the sound level. The evoked firing pattern was used to calculate period histograms, the frequency content of which was analysed by Fourier transformation. With electrical stimulation in the threshold range, an action potential is strongly synchronized to a cathodic peak of the current within one period of F0. With increasing current level 3-5 impulses can be locked to the same period. The timing of the short intervals is determined by the relative refractory period and current peaks (negative or positive) caused by the dominant higher formant F2 or F3. The acoustically evoked patterns are specific for the CF of the neuron and represent the spectral information of the different vowels.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗
PubMed1994

The course and morphology of efferent nerve fibres in the papilla basilaris of the pigeon (Columba livia).

This paper describes the course and morphology of efferent fibres in an avian cochlea. Horseradish peroxidase stained efferent fibres in the pigeon papilla basilaris were identified by Nomarski optics and camera lucida drawings. There are at least two types of efferent fibres: Large thick fibres take mainly a transversal course and contact short and intermediate hair cells over the free basilar membrane as well as hyaline cells. Large efferent fibres contact both hair cells and hyaline cells. Small thin fibres contact short or intermediate hair cells over the free basilar membrane or tall hair cells over the neural limbus. A physiological consequence of the findings is that efferent activity will concomitantly lead to a contraction of hyaline cells and a hyperpolarization of hair cells.

Animals↗