Auditory cortical regions show resting-state functional connectivity with the default mode-like network in echolocating bats.

Echolocating bats are among the most social and vocal of all mammals. These animals are ideal subjects for functional MRI (fMRI) studies of auditory social communication given their relatively hypertrophic limbic and auditory neural structures and their reduced ability to hear MRI gradient noise. Yet, no resting-state networks relevant to social cognition (e.g., default mode-like networks or DMLNs) have been identified in bats since there are few, if any, fMRI studies in the chiropteran order. Here, we acquired fMRI data at 7 Tesla from nine lightly anesthetized pale spear-nosed bats (Phyllostomus discolor). We applied independent components analysis (ICA) to reveal resting-state networks and measured neural activity elicited by noise ripples (on: 10 ms; off: 10 ms) that span this species' ultrasonic hearing range (20 to 130 kHz). Resting-state networks pervaded auditory, parietal, and occipital cortices, along with the hippocampus, cerebellum, basal ganglia, and auditory brainstem. Two midline networks formed an apparent DMLN. Additionally, we found four predominantly auditory/parietal cortical networks, of which two were left-lateralized and two right-lateralized. Regions within four auditory/parietal cortical networks are known to respond to social calls. Along with the auditory brainstem, regions within these four cortical networks responded to ultrasonic noise ripples. Iterative analyses revealed consistent, significant functional connectivity between the left, but not right, auditory/parietal cortical networks and DMLN nodes, especially the anterior-most cingulate cortex. Thus, a resting-state network implicated in social cognition displays more distributed functional connectivity across left, relative to right, hemispheric cortical substrates of audition and communication in this highly social and vocal species.

Refinement of systemic guinea pig deafening in hearing research: Sensorineural hearing loss induced by co-administration of kanamycin and furosemide via the leg veins.

Auditory disabilities have a large impact on the human population worldwide. Research into understanding and treating hearing disabilities has increased significantly in recent years. One of the most relevant animal species in this context is the guinea pig, which has to be deafened to study several of the hearing pathologies and develop novel therapies. Applying kanamycin subcutaneously and furosemide intravenously is a long-established method in hearing research, leading to permanent hearing loss without surgical intervention at the ear. The intravenous application of furosemide requires invasive surgery in the cervical area of the animals to expose the jugular vein, since a relatively large volume (1 ml per 500 g body weight) must be injected over a period of about 2.5 min. We have established a gentler alternative by applying the furosemide by puncture of the leg veins. For this, custom-made cannula-needle devices were built to allow the vein puncture and subsequent slow injection of the furosemide. This approach was tested in 11 guinea pigs through the foreleg via the cephalic antebrachial vein and through the hind leg via the saphenous vein. Frequency-specific hearing thresholds were measured before and after the procedure to verify normal hearing and successful deafening, respectively. The novel approach of systemic deafening was successfully implemented in 10 out of 11 animals. The Vena saphena was best suited to the application. Since the animals' condition, post leg vein application, was better in comparison to animals deafened by exposure of the Vena jugularis, the postulated refinement that reduced animal stress was deemed successful.

Dual Drug Delivery in Cochlear Implants: In Vivo Study of Dexamethasone Combined with Diclofenac or Immunophilin Inhibitor MM284 in Guinea Pigs.

Cochlear implants are well established to treat severe hearing impairments. Despite many different approaches to reduce the formation of connective tissue after electrode insertion and to keep electrical impedances low, results are not yet satisfying. Therefore, the aim of the current study was to combine the incorporation of 5% dexamethasone in the silicone body of the electrode array with an additional polymeric coating releasing diclofenac or the immunophilin inhibitor MM284, some anti-inflammatory substances not yet tested in the inner ear. Guinea pigs were implanted for four weeks and hearing thresholds were determined before implantation and after the observation time. Impedances were monitored over time and, finally, connective tissue and the survival of spiral ganglion neurons (SGNs) were quantified. Impedances increased in all groups to a similar extent but this increase was delayed in the groups with an additional release of diclofenac or MM284. Using Poly-L-lactide (PLLA)-coated electrodes, the damage caused during insertion was much higher than without the coating. Only in these groups, connective tissue could extend to the apex of the cochlea. Despite this, numbers of SGNs were only reduced in PLLA and PLLA plus diclofenac groups. Even though the polymeric coating was not flexible enough, MM284 seems to especially have potential for further evaluation in connection with cochlear implantation.

Infection Studies with Airway Organoids from Carollia perspicillata Indicate That the Respiratory Epithelium Is Not a Barrier for Interspecies Transmission of Influenza Viruses.

Bats are a natural reservoir for many viruses and are considered to play an important role in the interspecies transmission of viruses. To analyze the susceptibility of bat airway cells to infection by viruses of other mammalian species, we developed an airway organoid culture model derived from airways of Carollia perspicillata. Application of specific antibodies for fluorescent staining indicated that the cell composition of organoids resembled those of bat trachea and lungs as determined by immunohistochemistry. Infection studies indicated that Carollia perspicillata bat airway organoids (AOs) from the trachea or the lung are highly susceptible to infection by two different porcine influenza A viruses. The bat AOs were also used to develop an air-liquid interface (ALI) culture system of filter-grown epithelial cells. Infection of these cells showed the same characteristics, including lower virulence and enhanced replication and release of the H1N1/2006 virus compared to infection with H3N2/2007. These observations agreed with the results obtained by infection of porcine ALI cultures with these two virus strains. Interestingly, lectin staining indicated that bat airway cells only contain a small amount of alpha 2,6-linked sialic acid, the preferred receptor determinant for mammalian influenza A viruses. In contrast, large amounts of alpha 2,3-linked sialic acid, the preferred receptor determinant for avian influenza viruses, are present in bat airway epithelial cells. Therefore, bat airway cells may be susceptible not only to mammalian but also to avian influenza viruses. Our culture models, which can be extended to other parts of the airways and to other species, provide a promising tool to analyze virus infectivity and the transmission of viruses both from bats to other species and from other species to bats. IMPORTANCE We developed an organoid culture system derived from the airways of the bat species Carollia perspicillata. Using this cell system, we showed that the airway epithelium of these bats is highly susceptible to infection by influenza viruses of other mammalian species and thus is not a barrier for interspecies transmission. These organoids provide an almost unlimited supply of airway epithelial cells that can be used to generate well-differentiated epithelial cells and perform infection studies. The establishment of the organoid model required only three animals, and can be extended to other epithelia (nose, intestine) as well as to other species (bat and other animal species). Therefore, organoids promise to be a valuable tool for future zoonosis research on the interspecies transmission of viruses (e.g., bat → intermediate host → human).

Purification of Fibroblasts From the Spiral Ganglion.

Using cultures of freshly isolated spiral ganglion cells (SGC) is common to investigate the effect of substances on spiral ganglion neurons (SGN) in vitro. As these cultures contain more cell types than just neurons, and it might be beneficial to have cochlear fibroblasts available to further investigate approaches to reduce the growth of fibrous tissue around the electrode array after cochlear implantation, we aimed at the purification of fibroblasts from the spiral ganglion in the current study. Subcultivation of the primary SGC culture removed the neurons from the culture and increased the fibroblast to glial cell ratio in the preparations, which was revealed by staining for vimentin, the S100B-protein, and the 200-kD neurofilament. We performed direct immunolabeling for the Thy1-glycoprotein and the p75NGFR-enabled fluorescence-based cell sorting. This procedure resulted in a cell culture of cochlear fibroblasts with a purity of more than 99%. The received fibroblasts can be subcultivated for up to 10 passages before proliferation rates drop. Additionally, 80% of the cells survived the first attempt of cryopreservation and exhibited a fibroblast-specific morphology. Using the described approach provides a purified preparation of cochlear fibroblasts, which can now be used in vitro for further investigations.

Is humane slaughtering of rainbow trout achieved in conventional production chains in Germany? Results of a pilot field and laboratory study.

BACKGROUND: Rainbow trout, Oncorhynchus mykiss, is an important fish in European freshwater aquaculture. This industry sector is dominated by small family-owned enterprises located in rural areas. A large percentage of rainbow trout produced by these small enterprises is marketed directly and killed on demand and not processed in commercial processing plants. EU and national regulations stipulate that fish shall be stunned prior to killing and slaughter. The overall objective of this study was to monitor how stunning interventions were integrated into the production chains of German conventional trout aquaculture in order to safeguard animal welfare during stunning and killing. For this, the stunning and slaughtering processes were monitored on 18 rainbow trout farms in various German federal states. During the on-farm research, (i) the stunning success, (ii) injuries related to the stunning procedure, (iii) duration between stunning and killing, and (iv) visible responses at the time of slaughtering were assessed as welfare indicators. In addition, haematological and biochemical blood parameters were measured as indicators for physiological stress. Due to the fact that stunning interventions should induce a loss of consciousness in fish, in a laboratory study, it was examined whether the absence of the brainstem/ behavioural responses, opercular movements (OM) or eye-rolling reflex (vestibulo-ocular reflex, VOR) was correlated with the stage of insensibility. RESULTS: The majority of rainbow trout farms applied manual percussion (38%) or electrical stunning (48%), while on 14% of the farms, the fish were stunned by electrical stunning which was immediately followed by manual percussion. After percussive stunning, about 92.3% of the rainbow trout displayed no OM or VOR as brainstem/ behavioural indicators of consciousness. This percentage varied on farms which applied electrical stunning. While on the majority of farms, 95 to 100% of the fish were unconscious according to the observation of brainstem/ behavioural indicators, the stunning intervention was less effective on farms where rainbow trout were stunned at current densities below 0.1 A dm2 or for a few seconds only. The laboratory study confirmed that the absence of brainstem/ behavioural indicators correlated with the absence of visually evoked responses (VER) of the brain to light stimuli as a neuronal indicator of insensibility. Therefore, the brainstem/ behavioural signs can be used to interpret the stage of insensibility in rainbow trout. A stage of insensibility could safely be induced by exposing portion-sized rainbow trout to an electric current density above 0.1 A dm2. This was not influenced by the orientation of the electric field. CONCLUSIONS: In conventional aquaculture, rainbow trout can effectively be stunned by manual percussion or electrical stunning. Consciousness can be monitored by the absence of opercular movements or the eye-rolling reflex, which are lost approximately at the same time as neurological responses like VER. For safeguarding animal welfare during stunning and killing of rainbow trout in conventional production processes, the stunning process requires careful attention and the operating personnel need to be trained in using the stunning devices and recognising indicators of consciousness.

The in-air auditory thresholds of the eurasian otter (Lutra lutra, L. 1758) as determined by auditory brainstem responses.

As of yet there is no literature record of the hearing range of the Eurasian otter (Lutra lutra, L. 1758), a key species for natural conservation efforts in Europe. We recorded in-air pure tone hearing thresholds of anaesthetized otters using auditory brainstem responses (ABR) and report the results of the Eurasian otter. The recorded potentials showed the typical mammalian auditory brainstem response consisting of 5 distinct positive peaks during the first 10 ms after stimulus onset. At 80 dB SPL the hearing ranged from around 200 Hz to 32 kHz, with lowest thresholds around 4 kHz.

Stunning of common carp: Results from a field and a laboratory study.

BACKGROUND: Common carp Cyprinus carpio is an important food fish in Central Europe, which in some regions is consumed as part of local tradition. The majority of carp are sold by small retailers and not processed in commercial processing plants. The overall objective of this study was to monitor how animal welfare is safeguarded during the stunning and slaughtering of carp for retail sale. For this, the stunning and slaughtering process was monitored on 12 carp farms. Four welfare-related parameters were assessed: (i) stunning success, (ii) injuries related to the applied stunning method, (iii) time between stunning and slaughter, and (iv) visible responses of carp during slaughtering. In addition, indicators of physiological stress were measured. In order to analyse whether the absence of behavioural indicators of consciousness after electrical stunning was correlated with unconsciousness a complementary laboratory study was performed. Here, carp were exposed to electrical current densities between 0.09 and 0.41 A/dm2. The presence of behavioural responses and visually-evoked responses (VER) in the electro-encephalogram in response to light flashes as indicators for an absence of consciousness was recorded. RESULTS: The carp farms applied manual percussive (18%) or electrical (23%) stunning methods, while the majority of farms used a combination of electrical stunning immediately followed by manual percussive stunning (59%). In the latter condition, 92.6% of stunned carp displayed no behavioural indicators of consciousness and significantly fewer injuries related to mishits compared to sole percussive stunning. In the laboratory study, behavioural indicators of consciousness recovered in carp between 1 and 9 min following removal of the electrical current. However, VER could be recorded already at 30 ± 8 s post stunning. This indicates a fast recovery of carp from electrical stunning when exposed to current densities in the range of those generated by commercially available stunning instruments for fish. CONCLUSIONS: Under field conditions, percussion (applied manually) and electrical stunning might be poor inducers of unconsciousness before slaughter, while a combination was most effective. In order to undertake improvements in electrical stunning, further investigations into the current density, required for inducing prolonged insensibility in carp during electrical stunning, are needed.

Establishment of a long-term spiral ganglion neuron culture with reduced glial cell number: Effects of AraC on cell composition and neurons.

BACKGROUND: Sensorineural deafness is mainly caused by damage to hair cells and degeneration of the spiral ganglion neurons (SGN). Cochlear implants can functionally replace lost hair cells and stimulate the SGN electrically. The benefit from cochlear implantation depends on the number and excitability of these neurons. To identify potential therapies for SGN protection, in vitro tests are carried out on spiral ganglion cells (SGC). NEW METHOD: A glial cell-reduced and neuron-enhanced culture of neonatal rat SGC under mitotic inhibition (cytarabine (AraC)) for up to seven days is presented. Serum containing and neurotrophin-enriched cultures with and without AraC-addition were analyzed after 4 and 7 days. RESULTS: The total number of cells was significantly reduced, while the proportion of neurons was greatly increased by AraC-treatment. Cell type-specific labeling demonstrated that nearly all fibroblasts and most of the glial cells were removed. Neither the neuronal survival, nor the neurite outgrowth or soma diameter were negatively affected. Additionally neurites remain partly free of surrounding non-neuronal cells. COMPARISON WITH EXISTING METHOD: Recent culture conditions allow only for short-term cultivation of neonatal SGC and lack information on the influence of non-neuronal cells on SGN and of direct contact of neurites with test-materials. CONCLUSIONS: AraC-addition reduces the number of non-neuronal cells and increases the ratio of SGN in culture, without negative impact on neuronal viability. This treatment allows longer-term cultivation of SGC and provides deeper insight into SGN-glial cell interaction and the attachment of neurites on test-material surfaces.

Neuronal Survival, Morphology and Outgrowth of Spiral Ganglion Neurons Using a Defined Growth Factor Combination.

OBJECTIVES: The functionality of cochlear implants (CI) depends, among others, on the number and excitability of surviving spiral ganglion neurons (SGN). The spatial separation between the SGN, located in the bony axis of the inner ear, and the CI, which is inserted in the scala tympani, results in suboptimal performance of CI patients and may be decreased by attracting the SGN neurites towards the electrode contacts. Neurotrophic factors (NTFs) can support neuronal survival and neurite outgrowth. METHODS: Since brain-derived neurotrophic factor (BDNF) is well known for its neuroprotective effect and ciliary neurotrophic factor (CNTF) increases neurite outgrowth, we evaluated if the combination of BDNF and CNTF leads to an enhanced neuronal survival with extended neurite outgrowth. Both NTFs were added in effective high concentrations (BDNF 50 ng/ml, CNTF 100 ng/ml), alone and in combination, to cultured dissociated SGN of neonatal rats for 48 hours. RESULTS: The neuronal survival and neurite outgrowth were significantly higher in SGN treated with the combination of the two NTFs compared to treatment with each factor alone. Additionally, with respect to the morphology, the combination of BDNF and CNTF leads to a significantly higher number of bipolar neurons and a decreased number of neurons without neurites in culture. CONCLUSION: The combination of BDNF and CNTF shows a great potential to increase the neuronal survival and the number of bipolar neurons in vitro and to regenerate retracted nerve fibers.

The scotopic and photopic visual sensitivity in the nocturnal tree frog Agalychnis callidryas.

The red-eyed tree frog (Agalychnis callidryas) is endemic to the rainforests of Central America. During the night, it hunts for insects in the treetops whereas at daytime, the frogs rest under leaves. In the present study we determined the relative visual sensitivity spectrum of this nocturnal frog species by ERG recordings in both the dark- and light-adapted state. In both the scotopic- and photopic-sensitivity curve, we found only minor individual variations among the tested individuals. The sensitivity maximum of the scotopic curve was determined at 500 nm, which matches the absorption properties of the RH1-visual pigment expressed in the red rods of frogs. The sensitivity maximum of the photopic curve was found at 545 nm which is close to the absorption maximum of the LWS pigment type expressed in most cones of the frog retina. The threshold curves determined by ERG recordings here reveal no unusual features in the sensitivity spectrum of the red-eyed tree frog that could be interpreted as adaptations for its strictly nocturnal life style.

Biocompatibility of silver containing silica films on Bioverit® II middle ear prostheses in rabbits.

For several centuries silver is known for its antibacterial effects. The middle ear is an interesting new scope for silver application since chronic inflammations combined with bacterial infection cause complete destruction of the fragile ossicle chain and tympanic membrane. The resulting conductive deafness requires tympanoplasty for reconstruction. Strategies to prevent bacterial growth on middle ear prostheses are highly recommended. In this study, rabbits were implanted with Bioverit® II middle ear prostheses functionalized with silver containing dense and nanoporous silica films which were compared with pure silica coatings as well as silver sulfadiazine cream applied on nanoporous silica coating. The health status of animals was continuously monitored; blood was examined before and after implantation. After 21 days, the middle ears were inspected; implants and mucosal samples were processed for electron microscopy. Autopsies were performed and systemic spreading of silver was chemically analyzed exemplarily in liver and kidneys. For verification of direct cytotoxicity, NIH 3T3 cells were cultured on similar silver containing silica coatings on glass up to 3 days. In vitro a reduced viability of fibroblasts adhering directly on the samples was detected compared to cells growing on the surrounding plastic of the same culture dish. In transmission electron microscopy, phagocytosed silver silica fragments, silver sulfadiazine cream as well as silver nanoparticles were noticed inside endosomes. In vivo, clinical and post mortem examinations were inconspicuous. Chemical analyses showed no increased silver content compared to controls. Mucosal coverages on almost all prostheses were found. But reduction of granulation tissue was only obvious around silver-coated implants. Single necroses and apoptosis in the mucosa were correlated by intracellular accumulation of metallic silver. For confirming supportive healing effects of middle ear implants, silver ion aggregates need to be tested in the future to optimize biocompatibility while assuring bactericidal effects in the middle ear.

Highly biocompatible behaviour and slow degradation of a LDH (layered double hydroxide)-coating on implants in the middle ear of rabbits.

Chronic inflammation can irreversibly damage components of the ossicular chain which may lead to sound conduction deafness. The replacement of impaired ossicles with prostheses does not reduce the risk of bacterial infections which may lead to loss of function of the implant and consequently to additional damage of the connected structures such as inner ear, meninges and brain. Therefore, implants that could do both, reconstruct the sound conduction and in addition provide antibacterial protection are of high interest for ear surgery. Layered double hydroxides (LDHs) are promising novel biomaterials that have previously been used as an antibiotic-releasing implant coating to curb bacterial infections in the middle ear. However, animal studies of LDHs are scarce and there exist only few additional data on the biocompatibility and hardly any on the biodegradation of these compounds. In this study, middle ear prostheses were coated with an LDH compound, using suspensions of nanoparticles of an LDH containing Mg and Al as well as carbonate ions. These coatings were characterized and implanted into the middle ear of healthy rabbits for 10 days. Analysis of the explanted prostheses showed only little signs of degradation. A stable health constitution was observed throughout the whole experiment in every animal. The results show that LDH-based implant coatings are biocompatible and dissolve only slowly in the middle ear. They, therefore, appear as promising materials for the construction of controlled drug delivery vehicles.

In vitro and in vivo evaluation of a hydrogel reservoir as a continuous drug delivery system for inner ear treatment.

Fibrous tissue growth and loss of residual hearing after cochlear implantation can be reduced by application of the glucocorticoid dexamethasone-21-phosphate-disodium-salt (DEX). To date, sustained delivery of this agent to the cochlea using a number of pharmaceutical technologies has not been entirely successful. In this study we examine a novel way of continuous local drug application into the inner ear using a refillable hydrogel functionalized silicone reservoir. A PEG-based hydrogel made of reactive NCO-sP(EO-stat-PO) prepolymers was evaluated as a drug conveying and delivery system in vitro and in vivo. Encapsulating the free form hydrogel into a silicone tube with a small opening for the drug diffusion resulted in delayed drug release but unaffected diffusion of DEX through the gel compared to the free form hydrogel. Additionally, controlled DEX release over several weeks could be demonstrated using the hydrogel filled reservoir. Using a guinea-pig cochlear trauma model the reservoir delivery of DEX significantly protected residual hearing and reduced fibrosis. As well as being used as a device in its own right or in combination with cochlear implants, the hydrogel-filled reservoir represents a new drug delivery system that feasibly could be replenished with therapeutic agents to provide sustained treatment of the inner ear.

Differential sensitivity of bat cells to infection by enveloped RNA viruses: coronaviruses, paramyxoviruses, filoviruses, and influenza viruses.

Bats (Chiroptera) host major human pathogenic viruses including corona-, paramyxo, rhabdo- and filoviruses. We analyzed six different cell lines from either Yinpterochiroptera (including African flying foxes and a rhinolophid bat) or Yangochiroptera (genera Carollia and Tadarida) for susceptibility to infection by different enveloped RNA viruses. None of the cells were sensitive to infection by transmissible gastroenteritis virus (TGEV), a porcine coronavirus, or to infection mediated by the Spike (S) protein of SARS-coronavirus (SARS-CoV) incorporated into pseudotypes based on vesicular stomatitis virus (VSV). The resistance to infection was overcome if cells were transfected to express the respective cellular receptor, porcine aminopeptidase N for TGEV or angiotensin-converting enzyme 2 for SARS-CoV. VSV pseudotypes containing the S proteins of two bat SARS-related CoV (Bg08 and Rp3) were unable to infect any of the six tested bat cell lines. By contrast, viral pseudotypes containing the surface protein GP of Marburg virus from the family Filoviridae infected all six cell lines though at different efficiency. Notably, all cells were sensitive to infection by two paramyxoviruses (Sendai virus and bovine respiratory syncytial virus) and three influenza viruses from different subtypes. These results indicate that bat cells are more resistant to infection by coronaviruses than to infection by paramyxoviruses, filoviruses and influenza viruses. Furthermore, these results show a receptor-dependent restriction of the infection of bat cells by CoV. The implications for the isolation of coronaviruses from bats are discussed.

Central auditory processing during chronic tinnitus as indexed by topographical maps of the mismatch negativity obtained with the multi-feature paradigm.

This study aimed to compare the neural correlates of acoustic stimulus representation in the auditory sensory memory on an automatic basis between tinnitus subjects and normal hearing (NH) controls, using topographical maps of the MMNs obtained with the multi-feature paradigm. A new and faster paradigm was adopted to look for differences between 2 groups of subjects. Twenty-eight subjects with chronic subjective idiopathic tinnitus and 33 matched healthy controls were included in the study. Brain electrical activity mapping of multi-feature MMN paradigm was recorded from 32 surface scalp electrodes. Three MMN parameters for five deviants consisting frequency, intensity, duration, location and silent gap were compared between the two groups. The MMN amplitude, latency and area under the curve over a region of interest comprising: F3, F4, Fz, FC3, FC4, FCz, and Cz were computed to provide better signal to noise ratio. These three measures could differentiate the cognitive processing disturbances in tinnitus sufferers. The MMN topographic maps revealed significant differences in amplitude and area under the curve for frequency, duration and silent gap deviants in tinnitus subjects compared to NH controls. The current study provides electrophysiological evidence supporting the theory that the pre-attentive and automatic central auditory processing is impaired in individuals with chronic tinnitus. Considering the advantages offered by the MMN paradigm used here, these data might be a useful reference point for the assessment of sensory memory in tinnitus patients and it can be applied with reliability and success in treatment monitoring.

Structure and possible functions of constant-frequency calls in Ariopsis seemanni (Osteichthyes, Ariidae).

In the 1970s, Tavolga conducted a series of experiments in which he found behavioral evidence that the vocalizations of the catfish species Ariopsis felis may play a role in a coarse form of echolocation. Based on his findings, he postulated a similar function for the calls of closely related catfish species. Here, we describe the physical characteristics of the predominant call-type of Ariopsis seemanni. In two behavioral experiments, we further explore whether A. seemanni uses these calls for acoustic obstacle detection by testing the hypothesis that the call-emission rate of individual fish should increase when subjects are confronted with novel objects, as it is known from other vertebrate species that use pulse-type signals to actively probe the environment. Audio-video monitoring of the fish under different obstacle conditions did not reveal a systematic increase in the number of emitted calls in the presence of novel objects or in dependence on the proximity between individual fish and different objects. These negative findings in combination with our current understanding of directional hearing in fishes (which is a prerequisite for acoustic obstacle detection) make it highly unlikely that A. seemanni uses its calls for acoustic obstacle detection. We argue that the calls are more likely to play a role in intra- or interspecific communication (e.g. in school formation or predator deterrence) and present results from a preliminary Y-maze experiment that are indicative for a positive phonotaxis of A. seemanni towards the calls of conspecifics.

Nanoporous silica coatings as a drug delivery system for ciprofloxacin: outcome of variable release rates in the infected middle ear of rabbits.

HYPOTHESIS: The present study was performed to examine the impact of the release rate of ciprofloxacin from prostheses coated with nanoporous silica layers on the outcome of an acute bacterial infection of the middle ear of rabbits. BACKGROUND: Middle ear prostheses are often implanted in an infectious environment because of chronic otitis media and cholesteatoma. Bacterial colonization leads to healing disorders after surgery and may lead to the extrusion of the implants. Nanoporous silica layers appear promising as a drug delivery system for antibiotics placed on implants. Before clinical applications can be envisioned, it is necessary to find an optimal release rate. METHODS: White New Zealand rabbits were provided unilaterally with either a "slow release" or a "burst release" ciprofloxacin-containing middle ear Bioverit II prosthesis. After implantation, the middle ears were infected with a solution of Pseudomonas aeruginosa. Afterwards, animals were monitored clinically and, after 3 months, sacrificed to perform necropsy and microbiologic examinations. RESULTS: In the "slow release" group, 7 of 12 animals had to be euthanized preterm because of their poor clinical condition compared with 2 of 12 animals of the "burst release" group (p < 0.05). Clinical and microbiologic examination also showed a better outcome for animals of the burst release group. CONCLUSION: A burst release of ciprofloxacin from middle ear implants is important to combat a perioperative infection with Ps. aeruginosa in the middle ear model of the rabbit.

UHV-alginate as matrix for neurotrophic factor producing cells--a novel biomaterial for cochlear implant optimization to preserve inner ear neurons from degeneration.

HYPOTHESIS: Ultra high viscous (UHV-) alginate is a suitable matrix for brain-derived neurotrophic factor (BDNF) producing cells, enabling cell survival and BDNF release out of the matrix and subsequent protection of auditory neuronal cells. BACKGROUND: Cochlear implant (CI) target cells, spiral ganglion cells (SGC), undergo a progressive degeneration. BDNF prevents SGC from degeneration but has to be delivered locally to the inner ear for months. A permanent growth factor application may be realized via a cell-based drug delivery system. Encapsulation of this delivery system into a matrix could avoid immune response of the recipient, migration, and uncontrolled proliferation of the cells. METHODS: NIH3T3-fibroblasts producing endogenous BDNF were incorporated in UHV-alginate. The survival of the cells in the alginate was examined by cell counts of cryogenic slices, and the BDNF production was determined by performing ELISA. The supernatant of the alginate-cell culture was added to primary SGC culture, and the neuroprotective effect of the produced BDNF was observed performing SGC counts. RESULTS: BDNF-producing cells cultivated in UHV-alginate survived for up to 30 days, which was the latest time point observed. The BDNF concentration in cell culture medium, produced from in UHV-alginate incorporated fibroblasts and released out of the alginate matrix into the medium, was significantly increased after 30 days of cultivation. Supernatant of 7 days incubated UHV-alginate containing NIH3T3/BDNF cells significantly increased the SGC survival in vitro. CONCLUSION: This study demonstrates UHV-alginate to be a suitable scaffold for BDNF-producing fibroblasts. UHV-alginates are a promising biomaterial for cochlear implant biofunctionalization.

Layered double hydroxides as efficient drug delivery system of ciprofloxacin in the middle ear: an animal study in rabbits.

Chronic otitis media is a common disease often accompanied by recurrent bacterial infections. These may lead to the destruction of the middle ear bones such that prostheses have to be implanted to restore sound transmission. Surface coatings with layered double hydroxides (LDHs) are evaluated here as a possibility for drug delivery systems with convenient advantages such as low cytotoxicity and easy synthesis. Male New Zealand White rabbits were implanted with Bioverit(®) II middle ear prostheses coated with the LDH Mg(4)Al(2)(OH)(12)(SO(4))(2)·6H(2)O impregnated with ciprofloxacin. 12 (group 1) were directly infected with Pseudomonas aeruginosa and another 12 (group 2) 1 week after the implantation. Clinical outcome, blood counts, histological analyses and microbiological examination showed an excellent antimicrobial activity for group 1, whereas this effect was attenuated in animals where infection was performed 1 week after implantation. This is the first study to demonstrate an efficient drug delivery system with an LDH coating on prostheses in the middle ear.