Biomedical subjects

R Rübsamen

Publications and source records attributed to R Rübsamen.

At least 19 recordsLinked to original sources

PubMed1998

Cortical perineuronal nets in the gray short-tailed opossum (Monodelphis domestica): a distribution pattern contrasting with that shown in placental mammals.

Extracellular matrix proteoglycans accumulated in perineuronal nets and in certain neuropil zones have been shown to influence the immediate neuronal microenvironment, and to contribute to the chemoarchitectonic characteristics of neuronal networks. Studies in different placental mammals, including the human, have suggested that the major principles of extracellular matrix distribution remained constant during phylogenesis of the different mammalian strains. However, the comparison of matrix distribution between various species also indicates that striking deviations from the basic pattern may occur, although their functional significance appears unknown as yet. This study examines the extracellular matrix in the forebrain of a basic American marsupial, which has evolved independently of placental mammals for more than 100 million years. Brain sections obtained from adult gray short-tailed opossums (Monodelphis domestica) were stained for extracellular matrix components using the N-acetylgalactosamine-binding lectin Wisteria floribunda agglutinin (WFA), a polyclonal antibody against chondroitin sulfate proteoglycans (CSPG), and biotinylated hyaluronectin for the detection of hyaluronan. In subcortical regions, the distribution patterns of WFA-stained and CSPG-immunoreactive perineuronal nets were similar to those reported previously in placental mammals. In contrast, a unique distribution was found in the neocortex. This distribution was characterized by the presence of perineuronal nets around pyramidal cells and matrix components within the adjacent neuropil that together form a continuously labeled zone in layer V. Weakly stained nets ensheathed less numerous pyramidal cells in the upper layers II/III and a few multipolar cortical neurons. Dual staining experiments showed that cortical net-associated neurons were rarely immunopositive for parvalbumin. This fact, in addition to the predominant association of extracellular matrix components with layer V pyramidal cells, differentiates the neocortex in Monodelphis from that of all placental mammals studied to date. Regarding the basic phylogenetic position of this marsupial species it remains to be shown if these distribution characteristics of extracellular matrix may represent also a basic feature of cortical organization.

Acetylgalactosamine↗

PubMed1998

Development of single- and two-tone responses of anteroventral cochlear nucleus neurons in gerbil.

Responses of anteroventral cochlear nucleus (AVCN) neurons in developing gerbils were obtained to single-tone stimuli, and two-tone stimuli elicited by best frequency probes presented over a range of intensities. Neurons displayed Type I, Type I/III, and Type III receptive field patterns. Best frequencies ranged from 1.5 to 10.0 kHz. Two-tone suppression (2TS) was first observed in 5 of 16 neurons examined at 14 dab. and in all neurons examined in gerbils aged 15 to 60 dab. Suppression areas grew larger, and discharge rate reductions became greater with age. Features of the two-tone responses that were highly correlated with single-tone responses across age groups include maximum rate reductions and suppression area thresholds. The intensity level of the CF probe-tone also influenced these features of 2TS. Maximum rate reductions to below spontaneous rate levels of activity were common across age groups. Results suggest that the cochlear amplifier is present and fundamentally adult-like by 15 dab for the regions of the cochlea coding the mid frequencies in gerbil. Over the subsequent week, contributions to the developing two-tone responses by the cochlear amplifier increase slightly. Two-tone responses are influenced by central inhibitory mechanisms as early as 14 dab.

Acoustic Stimulation↗

PubMed1996

Anatomical and physiological investigation of auditory input to the superior colliculus of the echolocating megachiropteran bat Rousettus aegyptiacus.

The objective of this study was to investigate whether a representation of auditory space in the superior colliculus (SC) of the echolocating megachiropteran bat (Rousettus aegyptiacus) exists. Additionally the subcortical auditory connectivity of the SC was investigated. A total of 207 units were recorded in five awake animals while presenting acoustic stimuli (white noise, clicks, and pure tones) at different positions in space. Six units responded to acoustic stimulation. Three of these located within the superficial layers and one located in the intermediate layers were classified as omnidirectional units. Two units were located within the deep layers. One was classified as a hemifield unit, and the other as a frontal unit. All units responded phasically to acoustic stimulation with a latency of 4-150 ms. None of them could be activated by visual stimuli. We further examined the interaction of paired auditory and visual stimulation in 116 visually responsive units. Responses to visual stimulation were markedly altered by acoustic stimulation in 5 units. The influence of the acoustic stimuli was temporally and spatially restricted, and resulted either in a reduction or an elevation of unit responsiveness. Horseradish peroxidase was injected into the SC of eight animals to investigate the auditory subcortical connectivity of the SC. Retrograde labeling in auditory structures was rare compared with labeling found in nonauditory structures (e.g., retina, substantia nigra, parabigeminal nucleus). In auditory structures retrograde labeling was found mainly in the external nucleus of the inferior colliculus and in the nucleus of the brachium of the inferior colliculus. To a lesser extent it was found in the nucleus sagulum and in the area medial to the lemniscal nuclei. In one case the dorsal nucleus of the lateral lemniscus and the anterolateral periolivary nucleus were labeled. Our results reveal only a sparse auditory input into the SC of the flying fox, R. aegyptiacus. On the basis of single-unit recordings, we did not find an elaborate representation of auditory space as it is described for several other species. The existence of auditory and bimodal neurones, in combination with their response properties, nonetheless indicate that there might be a representation of auditory space in the SC of R. aegyptiacus.

Acoustic Stimulation↗

PubMed1995

Binaural response characteristics in isofrequency sheets of the gerbil inferior colliculus.

The spatial distribution of neurons with different binaural response properties was studied in two isofrequency areas of the inferior colliculus (IC) of the gerbil (Meriones unguiculatus). Single units were recorded in dorsomedial-to-ventrolaterally oriented electrode penetrations at different rostrocaudal positions, within a low (1-2 kHz; N = 108) and a high (23-27 kHz; N = 90) 'iso-frequency' sheet. Response types were not equally represented within the two layers. Within low-frequency regions, 41% of the units were excited following sound stimulation of either ear (EE), 21% received an excitatory input from one and an inhibitory input from the other ear (EI), and 12% were monaural (E0), while within high-frequency regions the distribution was 20% EE, 47% EI and 18% E0. However, the spatial arrangement of EE, EI and E0, within the dorsomedial-to-ventrolateral extent of the isofrequency sheets, was on the whole comparable within the two regions: EE-units were accumulated dorsomedially and EI-units ventrolaterally in the respective isofrequency sheets. E0-units were distributed equally within the low-frequency sheet but occurred more frequently in the middle part of the high-frequency lamina. About equal proportions of the units (low frequencies 9%; high frequencies 7%) had complex binaural response characteristics and were characterized as E/IE. In the rostrocaudal dimension of the nucleus, orderly arrangement of different unit types was less obvious. The results show that there is a tendency for grouping of different binaural unit types within the inferior colliculus. However, these unit types are not strictly segregated. Furthermore, it was shown that, despite the differences found in low- and high-frequency sites, there is a common scheme of 'binaural representation' across frequencies within the IC. Provided that EE-, EI-, and monaural response characteristics originate from separate sources, the data point to a convergence of binaural brainstem afferents within the IC.

Acoustic Stimulation↗

PubMed1995

Effects of furosemide on distortion product otoacoustic emissions and on neuronal responses in the anteroventral cochlear nucleus.

1. The objective of this study was to precisely evaluate the relationship between the threshold of neurons in the anteroventral cochlear nucleus (AVCN) and the properties of distortion product otoacoustic emissions (DPOAEs). Response areas of multiunit clusters in the AVCN and DPOAEs in the ear canal were measured alternately in the adult gerbil during furosemide-induced changes of the endocochlear potential. Stimulus frequencies of the probe tones for DPOAE measurement were in the range of f1 = 1.7-7.6 kHz and f2 = 2.0-9.0 kHz; the ratio f2:f1 was always 1.18. Stimulus amplitudes were varied in 5-dB steps from 30 to 80 dB SPL, with either equal amplitudes (L1 = L2) or unequal, with L1 set 10 dB above L2. Multiunit response areas were determined from cluster responses to a series of 100-ms tone bursts presented with a pseudo-random sequence in frequency and intensity. 2. Changes in the multiunit discharge properties after 50-75 mg/kg furosemide injection were as follows: the best frequency (BF) threshold increased from initial values in the range of 20-30 dB SPL to 50-80 dB SPL at 10-20 min postinjection and then recovered fully by 60-90 min. The spontaneous discharge activity decreased to zero before any changes in the frequency threshold curve were observed and did not return to initial values for several hours. Likewise, total discharge rates of stimulus elicited responses were reduced and tended to stay reduced even after BF threshold had fully recovered. 3. From the DPOAE measurements, the changes observed in the cubic distortion tone (CDT, 2f1-f2) emission after furosemide injection were as follows: at high levels of the probe tones, changes in the emission intensities generally stayed within a 10-dB range. The CDT amplitudes for low stimulus levels, however, were typically reduced by up to 40 dB, but recovered (depending on the furosemide dosage) by approximately 60-90 min. 4. At low to moderate stimulus levels of 40-60 dB SPL, there was a near perfect, minute-by-minute covariation of the ear canal CDT amplitude and the BF threshold measured in the AVCN. A 10-dB increase in threshold was associated with a 5- to 7-dB decrease in the CDT emission. 5. The optimum stimulus parameter set for the noninvasive estimation of cochlear performance from the CDT response was for stimulus amplitudes L1 = 50, L2 = 40 dB SPL. 6. This experiment demonstrates that CDT emissions at low stimulus levels are very good predictors of the thresholds of cochlear afferents, but this validity is lost for BF thresholds greater than approximately 60-70 dB SPL. 7. The ear canal CDT amplitude is better correlated with the BF threshold sensitivity of neuronal response areas in the AVCN than with the spontaneous discharge rate or absolute above-threshold discharge rates.

Animals↗

PubMed1995

Glutamatergic inhibition of voltage-operated calcium channels in the avian cochlear nucleus.

The auditory nerve serves as the only excitatory input to neurons in the avian cochlear nucleus, nucleus magnocellularis (NM). NM neurons in immature animals are dependent upon auditory nerve signals; when deprived of them, many NM neurons die, and the rest atrophy. Auditory nerve terminals release glutamate, which can stimulate second messenger systems by activating a metabotropic glutamate receptor (mGluR). Therefore, it is possible that the effectors of mGluR-stimulated signal transduction systems are needed for NM neuronal survival. This study shows that mGluR activation in NM neurons attenuates voltage-dependent changes in [Ca2+]j. Voltage-dependent Ca2+ influx was also attenuated by increasing cAMP with forskolin, VIP, or 8-bromo-cAMP, indicating that mGluR activation may stimulate adenylate cyclase. The main results may be summarized as follows. NM neurons possess high voltage-activated Ca2+ channels that were modulated by quisqualate, glutamate, and (+/-)trans-ACPD, in that order of potency. Glutamatergic inhibition of Ca2+ influx was not blocked by L-AP3 or L-AP4, which antagonize the actions of mGluRs in other neural systems; it was blocked by serine-O-phosphate. Finally, the attenuation of voltage-dependent Ca2+ influx was duplicated by cAMP accumulators. Since NM neurons have high rates of spontaneous activity and higher rates of driven activity, the expression of this mGluR turns out to be very valuable: without it, [Ca2+]j could reach lethal concentrations. These results provide an important clue as to the identity of an intracellular signal that may play an important role in NM neuronal survival.

Animals↗

PubMed1994

GABAergic terminals in nucleus magnocellularis and laminaris originate from the superior olivary nucleus.

The auditory brainstem nuclei, angularis (NA), magnocellularis (NM), and laminaris (NL) of the chicken, Gallus, contain terminals that stain for antibodies against the inhibitory neurotransmitter, gamma-aminobutyric acid (GABA). Some of these terminals originate from cells surrounding nucleus magnocellularis. Results from this study indicate that the majority of the GABAergic terminals found in NA, NM and NL originate from the superior olivary nucleus (SON). Injections of cholera toxin and horseradish peroxidase show that superior olivary nucleus (SON) neurons, which respond to pure tones, project bilaterally to NA, NM, and NL. NA and NL are reciprocally connected with the SON. More NA cells project to the SON than NL cells. While SON neurons project to NM, NM neurons do not project axons back to the SON. The configuration of SON terminals in NA, NM and NL matches the pattern of GABA-immunoreactive puncta seen in these three nuclei: they surround individual NM cells, congregate in the dendritic neuropil of NL, and blanket the NA. The data indicate that NA, NM and NL may be affected by two different inhibitory cell types: local interneurons and SON neurons. Patterns of connectivity described in this report suggest that the activity of NA cells could influence NM and NL cell physiology. Specifically, increases in NA cell activity could augment the effects of GABAergic SON neurons on NM and NL. Hence, binaural perception in the chicken may be more dependent upon changes in intensity cues than previously believed.

Acoustic Stimulation↗

PubMed1994

Growth of central nervous system auditory and visual nuclei in the postnatal gerbil (Meriones unguiculatus).

The objective of the present study was, by using the Mongolian gerbil (Meriones unguiculatus) as an animal model, to provide data on the growth dynamics of central auditory and visual nuclei and to relate the growth of these structures to the growth of the entire brain. So far, no such systematic study has been performed in any mammalian species. The knowledge of the rates of development of central nervous sensory structures might be useful for understanding the contribution of the central nervous system to maturation of sensory processing. Increases in volumes of nuclei and changes in their shape were analyzed for animals at the day of birth (P0); at postnatal days P7, P15, P22, P28; and in the third month (P90). The auditory nuclei investigated were the cochlear nucleus, the superior olivary complex, the nuclei of the lateral lemniscus, the inferior colliculus, and the medial geniculate body. From the visual system, the superior colliculus and the lateral geniculate body were studied. At P15 (shortly after the onset of central auditory responsiveness), the volumes of all auditory nuclei examined reached only 60-70% of their adult sizes; i.e., they showed considerable growth afterwards. At the same time (shortly before the animals open their eyes), the visual nuclei had almost reached their adult sizes (superior colliculus, 91%; lateral geniculate nucleus, 97%). These data demonstrate that different sensory nuclei contribute in highly different fashions to brain growth. There are system-specific differences in growth dynamics between central auditory and visual nuclei. However, the absolute growth of nuclei in both sensory systems relates to the brain regions. The data do not support the idea of a peripheral-to-central gradient in the growth of central auditory nuclei.

Aging↗

PubMed1994

The postnatal development of frequency-place code and tuning characteristics in the auditory midbrain of the phyllostomid bat, Carollia perspicillata.

This report describes the postnatal development of hearing range, auditory sensitivity and tonotopy within the inferior colliculus (IC) of a mammal specialized for ultrasonic hearing. The experimental animal, Carollia perspicillata, has an adult hearing range of 7-110 kHz (characteristic frequencies) but lack any significant overrepresentation of a limited frequency band as known for rhinolophoid bats and Pteronotus. The audiogram of the newborn Carollia includes characteristic frequencies from 8 to 76 kHz, which is about 65% of the adult hearing range. As in adults, low frequencies are represented in the dorsolateral portion of the IC. However, at birth the ventromedial IC is non-responsive to acoustic stimulation up to intensities of 90 dB SPL. During development there is a progressive conversion of non-responsive IC areas into acoustically responsive slabs with characteristic frequencies above 76 kHz along the dorsolateral to ventromedial (low-to-high frequency) IC axis. This development is superimposed by a non-uniform shift of characteristic frequency: a decrease of CFs in dorsolateral regions, and an increase of CFs in ventromedial areas. The results suggest a bidirectional shift of frequency representation along the cochlear tonotopic axis.

Acoustic Stimulation↗

PubMed1992

Postnatal development of central auditory frequency maps.

In the early postnatal period of many mammals and in the perihatching period of chicks the auditory ranges are restricted to the species-specific low- and mid-frequency ranges. During subsequent development, the high frequency hearing expands (depending on the species) by 1-4 octaves. Adult-like audition is established between the 4th and the 7th week. It is still discussed controversially, how the extension of the auditory ranges relates to the maturation of orderly frequency representation in the cochleae of the respective species. The present review summarizes investigations of the development of tonotopy in nuclei of the central auditory system, and discusses how the centrally acquired data might contribute to the understanding of the maturation of cochlear stimulus transduction and to the development of frequency maps.

Animals↗

PubMed1992

Setting complex tasks to single units in the avian auditory forebrain. I: Processing of complex artificial stimuli.

In the auditory forebrain (field L) of the European starling (Sturnus vulgaris), single unit responses were recorded for a wide range of complex stimuli, comprising different forms of amplitude and frequency modulation. About two-third of the units locked to sinusoidal modulation regardless of whether frequency (SFM) or amplitude (SAM) was modulated. On average, however, frequency led to stronger synchronization. Both the proportion of phase locking and its mean strength showed a low-pass dependence on modulation frequency. The lower efficiency of amplitude modulation is also visible in unit responses when SAM is combined with (random) frequency modulation. For the assessment of response strength and its comparison across the tested repertoire of complex stimuli, a new index (REX) is introduced which primarily weighs similarity of the spike trains in identically repeated stimulus runs. Applied to a set of 311 field L neurons, also this approach discloses the two stimulus classes lacking frequency modulation (pure tone and SAM) as the least effective. A new measure for response latency, the Effective Response Delay (ERD), based on the spike-triggered analysis of responses to randomly frequency-modulated sounds (RFM), reflects physiological delays better than conventional latency. So, ERD correction of SAM and SFM Period Histograms allowed to disclose response effective stimulus ranges independent of modulation frequency.

Acoustic Stimulation↗

PubMed1992

Setting complex tasks to single units in the avian auditory forebrain. II. Do we really need natural stimuli to describe neuronal response characteristics?

The response characteristic of auditory forebrain neurons in the European starling was established both with artificial stimuli (AS) and a conspecific territorial song as a natural stimulus (NS1). Applying experimenter-centred statistical methods for response detection and for scaling response strength, and spike-triggered analyses for the delimitation of the key sound parameters (spectrotemporal receptive field STRF, Aertsen et al. 1980) the study aimed at disclosing differences in the processing of the two stimulus classes, AS and NS. With the STRF as reference, we find congruence (1) in the best frequency with those determined under sweep and bandpass noise stimulation, (2) in response latency, and (3) in response-intensity dependence, further similarity in the overall frequency characteristic. Partitioning the song into 42 acoustically defined segments allowed to further delimit the response criteria under natural stimulation. They are easily understood from the AS response characteristics: (1) In the neuronal sample as a whole, long segments are more effective than short and, among the short, loud segments are more effective than faint; (2) Units showing their best excitatory response to AS in a certain frequency band are most probably excited by segments with a high proportion of their power concentrated upon or near this band; (3) Units with a slow (build-up) AS response react to a lower number of song segments than those dynamically following AS transients. Our data give no hint towards adaptive, feature detection properties of single neurons in field L. Instead, these neurons appear to base their response solely on the short-time spectrotemporal structure of the stimulus, irrespective of its natural or artificial origin.

Acoustic Stimulation↗

PubMed1990

Ontogenesis of auditory fovea representation in the inferior colliculus of the Sri Lankan rufous horseshoe bat, Rhinolophus rouxi.

This report describes the ontogenesis of tonotopy in the inferior colliculus (IC) of the rufous horseshoe bat (Rhinolophus rouxi). Horseshoe bats are deaf at birth, but consistent tonotopy with a low-to-high frequency gradient from dorsolateral to ventromedial develops from the 2nd up to the 5th week. The representation of the auditory fovea is established in ventro-medio-caudal parts of the IC during the 3rd postnatal week (Fig. 3). Then, a narrow frequency band 5 kHz in width, comprising 16% of the bat's auditory range, captures 50-60 vol% of the IC (Fig. 3c). However, foveal tuning is 10-12 kHz (1/3 octave) lower than in adults; foveal tuning in females (65-68 kHz) is 2-3 kHz higher than in males (62-65 Khz). Thereafter, foveal tuning increases by 1-1.5 kHz per day up to the 5th postnatal week, when the adult hearing range is established (Figs. 4, 5). The increase of sensitivity and of tuning sharpness of single units also follows a low-to-high frequency gradient (Fig. 6). Throughout this development the foveal tuning matches the second harmonic of the echolocation pulses vocalised by these young bats. The results confirm the hypothesis of developmental shifts in the frequency-place code for the foveal high frequency representation in the IC.

Acoustic Stimulation↗

PubMed1990

Audiovocal interactions during development? Vocalisation in deafened young horseshoe bats vs. audition in vocalisation-impaired bats.

Horseshoe bats (Rhinolophus rouxi) were deafened in their 3rd-5th postnatal week. Subsequently their vocalisations were monitored to evaluate the impact of audition on the development of echolocation pulses. Hearing impairment affected the echolocation pulses as follows: the frequency of the constant frequency (CF) component was altered by between +4 kHz and -14 kHz, and the dominance of the second harmonic of the pulses was neutralised by a relative increase in intensity of the first and third harmonics. A second experiment focused on possible influences of acoustical self-stimulation with echolocation pulses on the establishment of auditory fovea representation in the inferior colliculus (IC). Frequency control of echolocation pulses was disrupted by larynx denervation. Thereafter, the bats produced multiharmonic echolocation signals (4-11 harmonics) varying in frequency. IC tonotopy, however, as monitored by stereotaxic electrophysiology, showed the same developmental dynamics as seen in control specimens (Fig. 10). Both experiments indicate that throughout postnatal development echolocation pulses are under auditory feedback control, whereas maturation of the auditory fovea and shifts in its frequency tuning represent an innate process. The significance of this postnatal development might be the adjustment of the vocal motor system of each bat to the frequency of its 'personal' auditory fovea.

Animals↗

PubMed1989

Ontogenesis of tonotopy in inferior colliculus of a hipposiderid bat reveals postnatal shift in frequency-place code.

The postnatal development of midbrain tonotopy was investigated in the inferior colliculus (IC) of the south Indian CF-FM bat Hipposideros speoris. The developmental progress of the three-dimensional frequency representation was determined by systematic stereotaxic recordings of multiunit clusters from the 1st up to the 7th postnatal week. Additional developmental measures included the tuning characteristics of single units (Figs. 3f; 4f; 5f), the analysis of the vocalised pulse repertoire (Figs. 3e, 4e, 5e), and morphometric reconstructions of the brains of all experimental animals (Fig. 1). The maturation of auditory processing could be divided into two distinct, possibly overlapping developmental periods: First, up to the 5th week, the orderly tonotopy in the IC developed, beginning with the low frequency representation and progressively adding the high frequency representation. With regard to the topology of isofrequency sheets within the IC, maturation progresses from dorsolateral to ventromedial (Figs. 3c, 4c). At the end of this phase the entire IC becomes specialised for narrowly tuned and sensitive frequency processing. This includes the establishment of the 'auditory fovea', i.e. the extensive spatial representation of a narrow band of behaviorally relevant frequencies in the ventromedial part of the IC. In the 5th postnatal week the auditory fovea is concerned with frequencies from 100-118 kHz (Fig. 4c, d). During subsequent development, the frequency tuning of the auditory fovea increases by 20-25 kHz and finally attains the adult range of ca. 125-140 kHz. During this process, neither the bandwidth of the auditory fovea (15-20 kHz) nor the absolute sensitivity of its units (ca. 50 dB SPL) were changed. Further maturation occurred at the single unit level: the sharpness of frequency tuning increased from the 5th to the 7th postnatal weeks (Q-10-dB-values up to 30-60), and upper thresholds emerged (Figs. 4f, 5f). Although in the adult the frequency of the auditory fovea matches that of the vocalised pulses, none of the juvenile bats tested from the 5th to the 7th weeks showed such a frequency match between vocalisation and audition (Figs. 4e, 5e). The results show that postnatal maturation of audition in hipposiderid bats cannot be described by a model based on a single developmental parameter.

Acoustic Stimulation↗

PubMed1987

Ontogenesis of the echolocation system in the rufous horseshoe bat, Rhinolophus rouxi (audition and vocalization in early postnatal development).

1. The development of vocalization and hearing was studied in Sri Lankan horseshoe bats (Rhinolophus rouxi) during the first postnatal month. The young bats were caught in a nursing colony of rhinolophids in which birth took place within a two week period. 2. The new-born bats emitted isolation calls through the mouth. At the beginning these calls consisted of pure tones with frequencies below 10 kHz (Fig. 1). During the first postnatal week the call frequency increased to about 15 kHz, and the fundamental was augmented by two to four harmonics. No evoked potentials to pure tone stimuli could be elicited in the inferior colliculus of this age group, i.e., auditory processing at the midbrain level was not demonstrable. 3. Evoked potentials were first recorded in the second week, broadly tuned to 15-45 kHz, with a maximum sensitivity between 15-25 kHz. In the course of the second week, however, higher frequencies up to 60 kHz became progressively incorporated into the audiogram (Fig. 3). The fundamental frequency of the multiharmonic isolation calls, emitted strictly through the mouth, increased to about 20 kHz. 4. In the bats' third postnatal week an increased hearing sensitivity (auditory filter) emerged, sharply tuned at frequencies between 57 and 60 kHz (Fig. 4e). The same individuals were also the first to emit long constant frequency echolocation calls through the nostrils (Fig. 4c). The energy of the calls was arranged in harmonic frequency bands with the second harmonic exactly tuned to the auditory filter. These young bats continued to emit isolation calls through the mouth, which were, however, not harmonically related to the echolocation calls (Fig. 4b, d). 5. During the fourth week, both the auditory filter and the matched echolocation pulses (the second harmonic) shifted towards higher frequencies (Fig. 5). During the fifth week the fundamental frequency of the calls was progressively attenuated, and both the second harmonic of the pulses and the auditory filter reached the frequency range typical for adult bats of 73-78 kHz (Fig. 6). 6. The development of audition and vocalization is discussed with regard to possible interactions of both subsystems, and their incorporation into the active orientation system of echolocation.

Aging↗

PubMed1987

Tonotopic organization and functional characterization of the auditory thalamus in a songbird, the European starling.

1. The diencephalic auditory nucleus of the European starling, the nucleus ovoidalis, shows rostrocaudal and dorsoventral diameters of 500-800 microns and a mediolateral diameter of 800-1000 microns. This small and sharply delimited nucleus is composed of densely packed neurons. 2. Its tonotopic organization consists of evenly spaced isofrequency contours, with best frequencies decreasing ventrally. The frequency range was found to be 150 Hz to 7030 Hz. 3. Apart from tonotopic organization, other characteristics of single units demonstrate the uniformity of the neuronal population. Units have high spontaneous activities (mean 61 pps; Fig. 4a), and show mainly stimulus correlated tonic discharge patterns. In most cases, excitatory frequency bands are enclosed by inhibitory frequency bands. 4. Single units were tested, applying various stimulus classes differing in time structure (BPN, sine, FM up, FM down, SFM, SAM) but sharing a common frequency band. All neurons tested responded to all classes. Evaluation of stimulus class preference, however, revealed that BPN and SFM caused the strongest responses, whereas FM and SAM were less effective. 5. Comparison of the single unit responses in the ovoid nucleus with those known for avian auditory forebrain and midbrain centres strongly suggests a relay function for the diencephalic nucleus.

Animals↗

PubMed1986

Control of echolocation pulses by neurons of the nucleus ambiguus in the rufous horseshoe bat, Rhinolophus rouxi. I. Single unit recordings in the ventral motor nucleus of the laryngeal nerves in spontaneously vocalizing bats.

The vocal motor control of the larynx was studied with single unit recordings from the efferent motor nucleus (nucleus ambiguus) in the CF-FM-bat Rhinolophus rouxi, spontaneously emitting echolocation sounds. The experiments were performed in a stereotaxic apparatus that allowed differentiation of activities in the recorded nucleus depending on the electrode position (Fig. 1). Echolocation calls and respiration activity were monitored simultaneously, thus it was possible to compare the time course of the motor control activity during respiration with and without concurrent vocalization. Unit discharges were classified as laryngeal motoneuron activity according to their correlation with the time course (onset and end) of echolocation calls and their discharge rate as: Pre-off-tonic, pre-off-phasic, off-pauser, off-tonic, on-chopper, on-tonic, prior-tonic and inhibitory (Fig. 4). The on-chopper and on-tonic discharge patterns were assigned to the motor activity of the lateral cricoarytenoid muscle and the off-pauser and off-tonic discharge patterns to the motor activity of the posterior cricoarytenoid muscle controlling the time course of vocal pulses. Motoneuron activities recorded under the condition of systematically shifted frequencies in the emitted echolocation calls were investigated in Doppler-shift compensating bats responding to electronically simulated echoes. Of all neurons classified as motor control, only units of the pre-off-tonic discharge type (cricothyroid muscle) changed their activity with frequency shifts in the vocalized pulses; they showed a positive linear correlation with the emitted sound frequency (Fig. 6). In addition, single unit activities in strict synchronization to vocalization were recorded, that by their low discharge rate were not valid as motor control, and were considered to represent activities of interneurons or internuclear neurons connecting the nucleus ambiguus with other vocalization- and respiration-centers (Fig. 3c). Electric lesions in the brain stem and iontophoretically applied horseradish peroxidase (HRP) served as references for localization and morphological identification of the recording sites in cell stained brain slices.

Animals↗