Temporal and spatial coding of periodicity information in the inferior colliculus of awake chinchilla (Chinchilla laniger)

Amplitude modulation responses and onset latencies of multi-unit recordings and evoked potentials were investigated in the central nucleus of inferior colliculus (ICC) in the awake chinchilla. Nine hundred and one recording sites with best frequencies between 60 and 30 kHz showed either phasic (18%), tonic (25%), or phasic-tonic (57%) responses. Of 554 sites tested for responses to modulation frequencies 73% were responsive and 57% showed clear preference for a narrow range of modulation frequencies. Well defined bandpass characteristics were found for 32% of rate modulation transfer functions (rate-MTFs) and 36% of synchronization MTFs (sync-MTFs). The highest best modulation frequency (BMF) of a bandpass rate-MTF was 600 Hz. Neurons with phasic responses to best-frequency tones showed strong phase coupling to modulation frequencies and were dominated by bandpass rate-MTFs and sync-MTFs. Most neurons with tonic responses showed bandpass tuning only for sync-MTFs. Both BMFs and onset latencies changed systematically across frequency-band laminae of the ICC. Low BMFs and long latencies were located medially and high BMFs and short latencies laterally. Latency distributions obtained with evoked potentials to clicks showed a similar gradient to the multi-unit data. These findings are in line with previous findings in different animals including humans and support the hypothesis that temporal processing results in a topographic arrangement orthogonal to the spectral processing axis, thus forming a second neural axis of the auditory system.     

Analysis of information-bearing elements in complex sounds by auditory neurons of bats

Communication sounds of higher animals, including humans, often consist of three information-bearing elements, constant-frequency (or pure tone), frequency-modulated, and noise components. For communication and echolocation, bats and dolphins emit sounds including these three elements. Echoes returning from different objects overlap each other and show complex envelopes and structures. Analysis of complex sound is very essential for these animals. In order to explore the neural mechanisms of the analysis of complex sounds, two problems were particularly studied: (1) how single neurons respond to each of the information-bearing elements composing complex sounds, and (2) how single neurons respond to the complex sounds consisting of these elements.

In both the inferior colliculus and the auditory cortex of bats, neurons exist which resond either to only one of the three elements, to two of the three, or to all of them. Most of the characteristics of these various types of neurons, which are not found in the cochlear nucleus, can be explained by interaction between excitation and inhibition. In the neurons which are specialized to analyze the information-bearing elements, the structure of complex sound is an important factor for excitation.     

Perception of distorted "R" sounds in the synthesized speech of children and adults

Adult and Child manifolds were generated by synthesizing 5 X 5 matrices of /Cej/ type utterances in which F2 and F3 frequencies were systematically varied. Manifold stimuli were presented to 11 graduate-level speech-language pathology students in two conditions: (a) a rating condition in which stimuli were rated on a 4-point scale between good /r/ and good /w/; and (b) a labeling condition in which stimuli were labeled as "R," "W," "distorted R," or "N" (for none of the previous choices). It was found that (a) stimuli with low F2 and high F3 frequencies were rated 1.0-1.4; those with high F2 and low F3 frequencies were rated 3.6-4.0 were labeled as "R"; (c) none of the Child manifold stimuli were labeled as distorted "R" and one of the Adult manifold stimuli approached a level of identification that approached the percentage of identification for "R" and "W"; and (d) rating and labeling tasks were performed with a high degree of reliability.     

Frequency selectivity of phase-locking of complex sounds in the auditory nerve of the rat

Frequency selectivity of single auditory nerve fibers in the auditory nerve of the rat was studied using pseudorandom noise as the stimulus. The noise was lowpass filtered ternary m-sequences. Period histograms of the discharges of single auditory nerve fibers, locked to the periodicity of the noise, were cross-correlated with one period of the noise to obtain estimates of the impulse response. These cross-correlograms were subsequently Fourier transformed to obtain estimates of the frequency transfer functions. Earlier results obtained using noise that was based on binary sequences as the stimulus showed a systematic dependence on stimulus intensity of the bandwidth and center frequency of the computer transfer functions. The results of the present study confirmed this dependence and showed that a linear model based upon first-order cross-correlations fit the histograms of response. It is concluded that phase-locked activity of single auditory nerve fibers accurately reproduces the half-wave rectified motion of the basilar membrane over a large range of sound intensities.     

Behavioral hearing range of the chinchilla

The audiograms of three chinchillas were determined using pure tones ranging from 32 Hz to 45 kHz. The animals were tested with a conditioned avoidance procedure in which their heads were fixed within the sound field by requiring them to place their mouths on a water spout. At a level of 60 dB SPL the average hearing range extended from 50 Hz to 33 kHz with none of the animals able to hear 45 kHz at 89 dB. Overall, the audiogram of the chinchilla appears to resemble the human audiogram more closely than do other rodent audiograms. An analysis of ten published chinchilla audiograms indicates that those procedures which do not fix an animal within the sound field may overestimate their sensitivity.     

Hyperlipidemia and noise in the chinchilla

Chinchillas were maintained on a 1% cholesterol diet for 6 months. Auditory Brainstem Response (ABR) measurements were obtained before and at 1, 3, 5, and 6 months after initiation of diet. Compound Action Potential (AP) measurements were obtained at sacrifice at 6 months. A significant reduction in ABR was seen at 5 months-on-diet. At 5 months, the animals were exposed to a 2 octave bandpass noise centered at 1 kHz at 105 dB for 220 min. One month following noise exposure, the cholesterol-fed animals exhibited a greater ABR latency shift at low intensities, and an elevated AP threshold at higher frequencies, vis-à-vis a control group.     

Glycoconjugates in the chinchilla tubotympanum.

Various biotinylated lectins were used to characterize and semiquantitate glycoconjugate residues in the tubotympanum. Epithelial goblet cells were stained predominantly by WGA, LFA, SNA, RCA-I, Con-A, LCA, SBA, PHA-E, and UEA; this finding suggests they contain alpha-neuraminic acid, beta-galactose, alpha-mannose, N-acetyl alpha-galactosamine, and alpha-fucose. Glandular mucous cells were stained predominantly by WGA, LFA, SNA, and RCA-I; this finding suggests that they contain alpha-neuraminic acid and beta-galactose. The glandular serous cells were stained predominantly by Con-A, WGA, and LFA; this finding suggests that they produced alpha-mannose and alpha-neuraminic acid that represented serum-type glycoprotein. The positive staining of epithelial goblet cells and glandular mucous cells with PNA after neuraminidase digestion suggests that they produced mucin-type glycoproteins. The staining of the mucous blanket by WGA, LFA, SNA, RCA-I, LCA, PNA, SBA, PHA-E, and UEA suggests the presence of alpha-neuraminic acid, beta-galactose, N-acetyl alpha-galactosamine, and alpha-fucose. The epithelial cell (nonsecretory) surface was stained largely by WGA, LFA, SNA, RCA-I, Con-A, and LCA; this finding suggests the presence of alpha-neuraminic acid, beta-galactose, and alpha-mannose.     

Primary vestibular projections in the chinchilla

The central projections of fibers from the vestibular nerve were studied in 19 chinchillas after horseradish peroxidase labelling. In addition, the limits of the vestibular nuclei and the anatomical characteristics of their neurons were also studied. All five vestibular nuclei received primary afferents, but there were extensive areas of them that received very little or no projections at all, such as the rostral part of the superior vestibular nucleus, the dorsocaudal part of the lateral vestibular nucleus, the caudal half of the medial vestibular nucleus and the caudalmost aspect of the dorsal vestibular nucleus.     

Primary vestibular projections in the chinchilla

Summary The central projections of fibers from the vestibular nerve were studied in 19 chinchillas after horseradish peroxidase labelling. In addition, the limits of the vestibular nuclei and the anatomical characteristics of their neurons were also studied. All five vestibular nuclei received primary afferents, but there were extensive areas of them that received very little or no projections at all, such as the rostral part of the superior vestibular nucleus, the dorsocaudal part of the lateral vestibular nucleus, the caudal half of the medial vestibular nucleus and the caudalmost aspect of the dorsal vestibular nucleus.Presented at the First European Congress of Oto-Rhino-Laryngology and Cervico-Facial Surgery, Paris, 26–29 September 1988     

The formation of learning sets by the chinchilla in an auditory discrimination task

The performance of 9 chinchillas (Chinchilla lanigera) in a completely computer-automated sound-discrimination experiment was observed using stimulus pairs from a library of 180 complex sounds. Each sound of a pair was 0.2-2.08 sec in duration, separated by an interval of 250 +/- 125 msec. A modified "go/no go" paradigm was used. Licking behavior at a water-delivery tube was occasioned by keeping Ss at about 85% of ad-lib weight by water deprivation. After habituation and blank-trials training stages, sound discrimination was required: If the sounds of a pair were identical, no response was required; if they were different, a fleeing response (crossing a mid-cage barrier) was required. Each problem set utilized a different sound pair, for a total of 90 problems. Therefore, Ss learned to perform general auditory discriminations, not sound-specific discriminations. The chinchillas quickly learned to respond, but not at a rate consistently higher than 75 %-correct. The results were compared to those of other studies of sensory discrimination in monkey and chinchilla. Suggestions were made for minor improvement of the paradigm for use in future sound-discrimination tasks.     

Pathogenesis of experimental aural cholesteatoma in the chinchilla

Histopathological observation of celloidin serial sections of the chinchilla middle ear after treatment with propylene glycol disclosed the development of severe inflammation of the middle ear mucosa and tympanic membrane, papillary proliferation of the epidermis of the tympanic membrane and external auditory meatus, and retraction and adhesion of the tympanic membrane. The findings for the tympanic membrane, impedance testing and histopathological examination suggested that there were two types of acquired cholesteatoma formation, probably with a difference in the pathogenesis. In one type, the proliferated epidermal layer of the tympanic membrane penetrated into the middle ear cavity making tympanic perforations. In the other type, there was progressive retraction of the tympanic membrane forming a retraction pocket. We discuss the two different patterns of cholesteatoma development.     

Immunohistochemical localization of fibronectin in the chinchilla cochlea

The purpose of this study was to better understand the molecular composition of the cochlea. Fibronectin (FN), a well characterized adhesive glycoprotein, was localized by immunofluorescence microscopy in fresh and fixed cochlear tissues, and in fixed kidney tissue, using a polyclonal, affinity-purified, rabbit, anti-fibronectin antibody and a secondary antibody coupled to FITC. The FN antibody was free from cross-reactivity with other known basement membrane and cell matrix molecules. FN reactivity in the cochlea was most intense in the basilar membrane, latero-basal borders of Boettcher's cells, otic capsule, endothelial basement membranes (particularly those of the stria vascularis), and as a diffuse, fan-shaped network radiating into the spiral ligament. Little FN labelling was present in the epithelial basement membranes. Negative control tissue showed no immunoreactivity; whereas, positive kidney control tissue showed appropriate FN immunoreactivity in the mesangium of the glomerulus. The most significant finding of this study was that FN is a major component of the basilar membrane and its distribution appears to correspond to the amorphous ground substance. FN was not localized in the organ of Corti or at the tips of the hair-cell stereocilia.     

Gentamicin uptake in the chinchilla inner ear

Studies of transtympanic gentamicin have focused on clinical use and outcomes. This study presents evidence of bilateral uptake and retention of gentamicin in certain inner ear cells and structures following transtympanic gentamicin application. Middle ear application of gentamicin was performed by either minipump (Alza model, 2002) or transtympanic injection in a chinchilla model. Histological sections of decalcified temporal bones were stained to identify the distribution of gentamicin. Using both anti-gentamicin immunohistochemistry and autoradiography of tracer amounts of tritiated gentamicin, Scarpa’s and spiral ganglion cells, stria vascularis, and vestibular dark cells of the injected ear were found to have higher levels of gentamicin and retain it within cell bodies while staining levels fell to background levels in the rest of the injected ear over the course of 14 days. There was no evidence of an apical to basal gradient of anti-gentamicin staining within the spiral ganglion. Contralateral inner ear cells showed light anti-gentamicin staining. Cell bodies in the ipsilateral dorsal cochlear nucleus bordering the cochlear aqueduct (CA) showed a lateral to medial gradient of gentamicin staining, suggesting the CA as a potential site of transfer of gentamicin to the contralateral ear. Direct effects of aminoglycosides on ganglion cells may have implications on both the success of cochlear implantation in patients deafened following systemic aminoglycoside therapy and on the advisability of clinical practices of transtympanic gentamicin therapy and ototopic aminoglycoside treatment.     

Immunolocalization of tenascin in the chinchilla inner ear

Tenascin was immunolocalized in the chinchilla cochlea and vestibular system to better understand the functional morphology of the inner ear. Inner ear tissues were fixed with acetone, decalcified and cryosectioned. Indirect immunofluorescence, using antibodies directed against human tenascin epitopes, were used to detect tenascin. As a positive control, tenascin immunoreactivity was found in kidney, cortical mesangial cells and the extracellular matrix of glomeruli and medullary tubule interstitial spaces, concurring with previously reported results. In the cochlea, tenascin immunoreactivity was present in osteocytes, the mesothelial cells underlying the basilar membrane (BM) and within the fibrous matrix of the BM. Greater reactivity was observed in the mesothelial cells than in the fibrous matrix of the BM. In the vestibular system, tenascin immunoreactivity formed a diffuse band directly beneath the basal lamina of the ampullary and otoconial organs. Tenascin immunoreactivity was also observed in cup-shaped regions between the type I vestibular hair cells and their surrounding VIII nerve calyces in the ampullary and otoconial organs. This is the first report of the anatomical distribution of tenascin in the adult, mammalian inner ear, other than our previously published abstract P.A. Santi and D. Swartz, Soc. Neurosci. Abstr. 23 (1997) 731.     

Sound-induced priming of the chinchilla auditory system.

Exposure of the auditory system to either continuous or interrupted nontraumatic noises, often collectively referred to as priming exposures, has been shown, in a number of experimental paradigms, to reduce the susceptibility of the auditory system to noise-induced hearing and sensory cell loss from a subsequent traumatic exposure. Using auditory evoked potentials to obtain pure-tone thresholds and cochleograms to quantify sensory cell losses, the issue of priming-induced protective effects was examined in the chinchilla. Priming was accomplished with either a continuous noise or with a continuous noise followed by an interrupted noise. Trauma was induced by exposure to high-level impacts over a 5-day period that resulted in an asymptotic threshold shift. A comparison of the two groups of primed subjects with an unprimed control group showed that there were some statistically significant reductions in the asymptotic response of the primed groups to the traumatic exposure but no differences in permanent changes in thresholds among the three groups 30 days following the traumatic exposure. There were, however, some statistically significant, frequency-specific, reductions in outer hair cell loss in the primed groups. When conditioning was followed by the interrupted exposure that produced a threshold shift toughening effect, the conditioning protocol had no effect on the response of subjects to the interrupted exposure. There were also no differences in thresholds or sensory cell loss between the two primed groups 30 days post-trauma. Priming protocols may have different effects on the development of noise-induced trauma that are dependent on the nature of the traumatic stimulus, that is, long-term high-level impact noise exposure versus acute continuous noise exposure.     

The vascular pattern of the chinchilla cochlea.

The vasculature of the chinchilla cochlea was demonstrated with injected Prussian blue contrast. By and large, the vascular pattern is similar to other mammals. The vasculature appears to be richly developed, but separate types of vessels appear to be of small caliber. Particular findings for the chinchilla cochlea were the veins of the scala tympani, formed by a merging of collecting venules, running parallel to the spiral modiolar vein. Furthermore, no vessel of the basilar membrane under the tunnel of Corti was found, and which, when present, is of such great presumed importance for the oxygen supply to the organ of Corti. The scala vestibuli wall appears to be supplied completely arterially, in contrast with that of other mammals. The stria vascularis is broad and well developed, both at the apex and at the basal end.     

Morphological correlates of aging in the chinchilla cochlea

The inner ears from 80 chinchillas ranging in age from premature to 19.2 years were examined as plastic-embedded flat preparations to determine the morphological changes associated with aging. Three of the four forms of human presbycusis defined by Schuknecht were found in the chinchillas. All animals had losses of sensory cells or sensory presbycusis. Inner (IHCs) and outer hair cells (OHCs) degenerated at a rate of about 0.29% and 1.0% per year, respectively. Age-related degeneration of inner (IPs) and outer pillars (OPs) occurred at a much slower rate. In four animals (5%) the dendritic processes of some of the spiral ganglion cells had degenerated in areas where the loss of sensory cells was minimal. This pathological change is likely equivalent to neural presbycusis. Six animals (7.5%) had regions of degeneration of the stria vascularis or strial presbycusis. The other common finding in the aging cochleas was the presence of lipofuscin or age pigment. Lipofuscin deposits were found to accumulate in the subcuticular region of OHCs, IPs and OPs, near the endolymphatic surfaces of many of the supporting cells and in the epithelial cells of Reissner's membrane. The IHCs accumulated much less lipofuscin. The morphological changes seen in the ears of aging chinchillas were qualitatively similar to those seen in the temporal bones of aging humans although the magnitude of the changes was considerably less. These results suggest that some of the damage found in aging human cochleas may be due to aging plus exposure to one or more ototraumatic agents.     

Tonotopic mapping in auditory cortex of the chinchilla

Using single-unit electrophysiological methods we have mapped sound frequency (or cochleotopic) representation in the auditory cortex of the chinchilla. We describe the surgical approach to expose this area. We report on maps from six subjects and note a considerable variation in shape between individuals. In general, the primary area has a cochleotopic/tonotopic organization in which low frequencies are represented rostrally and higher frequencies caudally. Neurons in the primary area have latency and tuning properties comparable to other mammalian species. A region anterior to the primary (AI) auditory area has a reverse tonotopic map and may be analogous to the anterior auditory field (AAF) reported in other species.