Ventral approach to the rat middle ear for otologic research

Otitis media: recent advances in otitis media vaccine development and model systems

Otitis media is an inflammatory disorder of the middle ear caused by airways-associated bacterial or viral infections. It is one of the most common childhood infections as globally more than 80% of children are diagnosed with acute otitis media by 3 years of age and it is a common reason for doctor's visits, antibiotics prescriptions, and surgery among children. Otitis media is a multifactorial disease with various genetic, immunologic, infectious, and environmental factors predisposing children to develop ear infections. Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis are the most common culprits responsible for acute otitis media. Despite the massive global disease burden, the pathogenesis of otitis media is still unclear and requires extensive future research. Antibiotics are the preferred treatment to cure middle ear infections, however, the antimicrobial resistance rate of common middle ear pathogens has increased considerably over the years. At present, pneumococcal and influenza vaccines are administered as a preventive measure against otitis media, nevertheless, these vaccines are only beneficial in preventing carriage and/or disease caused by vaccine serotypes. Otitis media caused by non-vaccine serotype pneumococci, non-typeable H. influenza, and M. catarrhalis remain an important healthcare burden. The development of multi-species vaccines is an arduous process but is required to reduce the global burden of this disease. Many novel vaccines against S. pneumoniae, non-typeable H. influenza, and M. catarrhalis are in preclinical trials. It is anticipated that these vaccines will lower the disease burden and provide better protection against otitis media. To study disease pathology the rat, mouse, and chinchilla are commonly used to induce experimental acute otitis media to test new therapeutics, including antibiotics and vaccines. Each of these models has its advantages and disadvantages, yet there is still a need to develop an improved animal model providing a better correlated mechanistic understanding of human middle ear infections, thereby underpinning the development of more effective otitis media therapeutics. This review provides an updated summary of current vaccines against otitis media, various animal models of otitis media, their limitations, and some future insights in this field providing a springboard in the development of new animal models and novel vaccines for otitis media.

Improved postauricular surgical approach to the round window of rats

OBJECTIVES

Research using rat as an in-vivo model has played an important role in otological research. The rat ear anatomy has been described; however, detailed surgical procedures to access the temporal bone are limited. The authors present a technique to approach the inner ear of rat that was standardized by cadaveric dissections and later replicated in living animals.

METHODS

Adult Wistar albino rats were dissected via the post-auricular approach. The emphasis was on early identification of the facial nerve that formed a reliable landmark for the tympanic bulla, which in turn houses the round window and stapedial artery. The point of identification of facial nerve was postero-inferior to the external auditory meatus. The procedure was then repeated in living animals.

RESULTS

Seventeen cadaveric rats were dissected. Initially, the investigators attempted to identify the facial nerve at its crossing over the external auditory meatus. However, that method was found to be unsatisfactory. The facial nerve was then attempted to be identified in its course postero-inferior to the external auditory meatus. The technique improved drastically, and the facial nerve was identified promptly and reliably. The procedure was then repeated in seven living rats under general anaesthesia. The major issues encountered were bleeding from the stapedial artery, hematoma of the pinna in one rat.

CONCLUSION

This study suggests that the post-auricular approach is a feasible and less time consuming route for round window drug delivery experiments in Wistar albino rats. Recognition of anatomical landmarks, particularly the facial nerve is the key to surgery.

Auditory cortical plasticity in cochlear implant users

Cochlear implants are one of the most successful neuroprosthetic devices that have been developed to date. Profoundly deaf patients can achieve speech perception after complete loss of sensory input. Despite the improvements many patients experience, there is still a large degree of outcome variability. It has been proposed that central plasticity may be a major factor in the different levels of benefit that patients experience. However, the neural mechanisms of how plasticity impacts cochlear implant learning and the degree of plasticity's influence remain unknown. Here, we review the human and animal research on three of the main ways that central plasticity affects cochlear implant outcomes.

Middle ear structure and transcanal approach appropriate for middle ear surgery in rabbits

The current study aimed to investigate the middle ear structure and surgical approach appropriate for middle ear surgery in rabbits. A total of eight healthy New Zealand rabbits (16 ears) were dissected under a surgical microscope. The dimensions of the auditory canal and the middle ear were measured. In the present study, the transcanal surgical approach to the middle ear in rabbits was performed without complications, the anatomical landmarks in the auricle and the external auditory canal were apparent, no large vessels were present in the surgical zone and the bleeding was minor. Furthermore, the surgical procedure did not require removal of large bone sections of the external auditory canal. Additionally, the constitution of the ossicular chain, the leverage ratio of the ossicular chain and the constitution of ligaments and muscles in rabbits were similar to humans. Otherwise, the facial nerve canal in rabbits was more prominent compared with humans and the mobility of pars flaccida in rabbits was more noticeable compared with humans. The results of the current study indicate that the transcanal surgical approach was suitable to study the middle ear in rabbits. Furthermore, the rabbit middle ear may be used as a model for ossicular surgery and facial nerve research.

Animal models of acute otitis media - A review with practical implications for laboratory research

Considerable animal research has focused on developing new strategies for the prevention and treatment of acute otitis media (AOM). Several experimental models of AOM have thus been developed. A PubMed search of the English literature was conducted from 1975 to July 2016 using the search terms "animal model" and "otitis media" from which 91 published studies were included for analysis, yielding 123 animal models. The rat, mouse and chinchilla are the preferred animals for experimental AOM models with their individual advantages and disadvantages. The most common pathogens used to create AOM are Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis. Streptococcus pneumoniae (types 3, 23 and 6A) and non-typeable Haemophilus influenzae (NTHi) are best options for inoculation into rat and mouse models. Adding viral pathogens such as RSV and Influenza A virus, along with creating ET dysfunction, are useful adjuncts in animal models of AOM. Antibiotic prophylaxis may interfere with the inflammatory response without a significant reduction in animal mortality.

Polymeric nanoparticles loaded with dexamethasone or α-tocopheryl succinate to prevent cisplatin-induced ototoxicity

The aim of this work is the development of highly protective agents to be administered locally within the middle ear to avoid cisplatin-induced ototoxicity, which affects to 100% of the clinical patients at ultra-high concentrations (16mg/kg). The protective agents are based on polymeric nanoparticles loaded with dexamethasone or α-tocopheryl succinate as anti-inflammarory and anti-apoptotic molecules. Dexamethasone and α-tocopheryl succinate are poorly soluble in water and present severe side effects when systemic administered during long periods of time. Their incorporation in the hydrophobic core of nanoparticles with the appropriate hydrodynamic properties provides the desired effects in vitro (lower cisplatin-induced toxicity, decreasing of caspase 3/7 activity, and lower IL-1β release) and in vivo (reducing the hearing loss at the local level). The local administration of the nanoparticles by bullostomy provides an adequate dose of drug without systemic interference with the chemotherapeutic effect of cisplatin.

STATEMENT OF SIGNIFICANCE

100% of the cancer patients receiving ultra-high doses of CDDP (16mg/kg) suffer severe hearing loss, being a limiting factor in antineoplastic treatments. In this paper we describe the application of polymeric nanoparticles loaded with dexamethasone or α-tocopheryl succinate to palliate the cisplatin ototoxicity derived from chemotherapy treatment. These new nanoparticles, that encapsulate, transport, and deliver dexamethasone or α-tocopheryl succinate in the middle ear, are able to partially prevent ototoxicity derived from high doses of CDDP. This is an interdisciplinary study in which in vitro and in vivo experiments are described and extensively discussed. The importance of the results opens an excellent opportunity to the translation to the clinic.

Retroauricular Approach for Targeted Cochlear Therapy Experiments in Wistar Albino Rats

Background:

As the idea of stem cell technology in the treatment of sensorial hearing loss has emerged over the past decades, the need for in vivo models for related experiments has become explicit. One of the most common experimental models for inner ear stem cell delivery experiments is the Wistar albino rat.

Aims:

To investigate the surgical anatomy of the temporal bone of the Wistar albino rat with respect to the dissection steps, operative techniques and potential pitfalls of surgery.

Study Design:

Animal experimentation.

Methods:

Adult Wistar albino rats were operated on via the retroauricular approach under an operation microscope. The anatomy of the temporal bone, the surgical route to the temporal bulla and the inner ear were investigated. Technical details of surgical steps, complications and potential pitfalls during the surgery were noted.

Results:

The study group consisted of 40 adult Wistar albino rats. The mean times to reach the bulla and to achieve cochleostomy were 4.3 (2-13 min) and 7.5 min (3.5-22 min), respectively. The mean width of the facial nerve was 0.84 mm (0.42-1.25 mm). The stapedial artery lay nearly perpendicular to the course of the facial nerve (88-93 °C). There were three major complications: two large cochleostomies and one massive bleed from the stapedial artery.

Conclusion:

The facial nerve was the key anatomical landmark in locating the bulla. By retrograde tracing of the facial nerve, it was possible to find the bulla ventral (inferior) to the main trunk. The facial nerve trunk was the upper limit when drilling the bulla. By dissecting the main trunk of the facial nerve and retracting cranially, a large drilling space could be achieved. Our results suggest that the retroauricular approach is an effective, feasible route for inner ear drug delivery experiments in Wistar albino rats.

A physiological and behavioral system for hearing restoration with cochlear implants

Cochlear implants are neuroprosthetic devices that provide hearing to deaf patients, although outcomes are highly variable even with prolonged training and use. The central auditory system must process cochlear implant signals, but it is unclear how neural circuits adapt-or fail to adapt-to such inputs. The knowledge of these mechanisms is required for development of next-generation neuroprosthetics that interface with existing neural circuits and enable synaptic plasticity to improve perceptual outcomes. Here, we describe a new system for cochlear implant insertion, stimulation, and behavioral training in rats. Animals were first ensured to have significant hearing loss via physiological and behavioral criteria. We developed a surgical approach for multichannel (2- or 8-channel) array insertion, comparable with implantation procedures and depth in humans. Peripheral and cortical responses to stimulation were used to program the implant objectively. Animals fitted with implants learned to use them for an auditory-dependent task that assesses frequency detection and recognition in a background of environmentally and self-generated noise and ceased responding appropriately to sounds when the implant was temporarily inactivated. This physiologically calibrated and behaviorally validated system provides a powerful opportunity to study the neural basis of neuroprosthetic device use and plasticity.

Otoprotective properties of 6α-methylprednisolone-loaded nanoparticles against cisplatin: In vitro and in vivo correlation

6α-Methylprednisolone-loaded surfactant-free nanoparticles have been developed to palliate cisplatin ototoxicity. Nanoparticles were based on two different amphiphilic pseudo-block copolymers obtained by free radical polymerization and based on N-vinyl pyrrolidone and a methacrylic derivative of α-tocopheryl succinate or α-tocopherol. Copolymers formed spherical nanoparticles by nanoprecipitation in aqueous media that were able to encapsulate 6α-methylprednisolone in their inner core. The obtained nanovehicles were tested in vitro using HEI-OC1 cells and in vivo in a murine model. Unloaded nanoparticles were not able to significantly reduce the cisplatin ototoxicity. Loaded nanoparticles reduced cisplatin-ototoxicity in vitro being more active those based on the methacrylic derivative of vitamin E, due to their higher encapsulation efficiency. This formulation was able to protect hair cells in the base of the cochlea, having a positive effect in the highest frequencies tested in a murine model. A good correlation between the in vitro and the in vivo experiments was found.

FROM THE CLINICAL EDITOR

Cisplatin is a commonly used chemotherapeutic agent against many cancers clinically. However, one of the significant side-effects remains ototoxicity. Here, the authors presented their data on using 6α-methylprednisolone-loaded nanoparticles in the reduction of ototoxicity in in-vitro and in-vivo experiments. Early promising results should enable further refinement of adopting this new approach in future experiments.

A melting method for RNA extraction from the mucosal membrane of the mouse middle ear

PURPOSE

There is much confusion surrounding the methods of RNA extraction from the middle ear mucosa of mice. In this study, we worked to develop a "melting method," which is faster, purer, and more reliable than other methods in common use.

MATERIALS AND METHODS

Thirty-two ears were used for this study. Light microscopy with hematoxylin-eosin staining of the bullae, scanning electron microscopy (SEM), spectrophotometer analysis, and reverse transcription polymerase chain reaction were performed before and after melting the half lateral bullae, which were detached from the temporal bone by using a lateral retroauricular approach.

RESULTS

Each resected half bulla contained a well distributed mucosal membrane. After a TRIzol melting duration of 10-30 minutes, only mucosal marker (MUC5AC) was expressed without bony marker (total osteocalcin). The same results were determined from SEM.

CONCLUSION

This melting method, compared with stripping and irrigation methods, is effective and offers an easier, more robust approach to extracting RNA from the middle ear mucosal membranes of mice.

Systematic review of animal models of middle ear surgery

Animal models of middle ear surgery help us to explore disease processes and intervention outcomes in a manner not possible in patients. This review begins with an overview of animal models of middle ear surgery which outlines the advantages and limitations of such models. Procedures of interest include myringoplasty/tympanoplasty, mastoidectomy, ossiculoplasty, stapedectomy, and active middle ear implants. The most important issue is how well the model reflects the human response to surgery. Primates are most similar to humans with respect to anatomy; however, such studies are uncommon now due to expense and ethical issues. Conversely, small animals are easily obtained and housed, but experimental findings may not accurately represent what happens in humans. We then present a systematic review of animal models of middle ear surgery. Particular attention is paid to any distinctive anatomical features of the middle ear, the method of accessing the middle ear and the chosen outcomes. These outcomes are classified as either physiological in live animals, (e.g., behavioural or electrophysiological responses), or anatomical in cadaveric animals, (e.g., light or electron microscopy). Evoked physiological measures are limited by the disruption of the evoking air-conducted sound across the manipulated middle ear. The eleven identified species suitable as animal models are mouse, rat, gerbil, chinchilla, guinea pig, rabbit, cat, dog, sheep, pig and primate. Advantages and disadvantages of each species as a middle ear surgical model are outlined, and a suggested framework to aid in choosing a particular model is presented.

Lentivirus carrying the Atoh1 gene infects normal rat cochlea

Lentivirus carrying the Atoh1 gene can infect Corti's organ and express a hair-like cell surface marker in the supporting cell area. However, expression of the gene carried by adenovirus is instantaneous, which undoubtedly limits its clinical application. Lentivirus acts as a carrier that can stably and continuously express genes. In this study, the cochlear structure and hearing level were not affected, and Atoh1 gene carried by lentivirus promoted the production of hair-like cells in the cochlear supporting cell area. This led to expression of the hair-like cell surface marker myosin 7a 30 days after lentivirus carrying Atoh1 was microinjected into the cochlear round window of rats.

Mouse cochleostomy: a minimally invasive dorsal approach for modeling cochlear implantation

OBJECTIVES/HYPOTHESIS

The murine model has been used extensively to model and study human deafness. Technical difficulty in the surgical approach due to the small size of the tympanic bulla and a robust stapedial artery has limited its application for studies of cochlear implantation and electrical stimulation. We describe a minimally traumatic, stapedial artery-sparing approach to the round window that may be used to access the mouse cochlea for acute or chronic studies of implantation and stimulation.

STUDY DESIGN

Animal model.

METHODS

Fifteen C57BL6J mice were used to validate this approach. Auditory brainstem response threshold and distortion product otoacoustic emissions were obtained preoperatively and 2 weeks postoperatively to determine hearing preservation results.

RESULTS

The approach provided excellent exposure for round-window implantation. Substantial hearing was preserved in all animals with a mean postimplantation auditory brainstem response threshold increase of 27.8 dB. Otoacoustic emissions were lost in subjects with the largest threshold shifts.

CONCLUSIONS

Residual hearing after cochlear implantation is a determinant of success both with standard cochlear implant electrodes and with electrodes designed to optimize hearing preservation. Here, we have preserved usable hearing after implantation of C57BL6J mice, an endogenous model of human presbycusia. The murine model may become a powerful tool to assay the effects of cochlear intervention in different genetic backgrounds.

Stapedectomy in sheep: an animal model for surgical training

HYPOTHESIS AND BACKGROUND

Stapedectomy is a surgical technique that requires progressive training. The external and middle ear of sheep have a close resemblance to the human and have been previously used as surgical training models. In our project we describe the anatomy of the middle and external ear in sheep focusing on surgical landmarks and technique in order to determine whether the sheep's ear is an adequate model for stapedectomy training.

MATERIALS AND METHODS

We reviewed the literature on sheep anatomy and use of sheep as an otologic surgical model. Macroscopic sections as well as temporal bone computed tomography were obtained. Stapedectomy was performed on 40 sheep, using 4 mm platinum piston prosthesis, by first year residents.

RESULTS

Most of the structures in the sheep's middle ear are similar to those in humans although their size is about two thirds smaller. Incus long process is shorter, thicker, and closer to the malleus body, making the piston insertion and adjustment more difficult. The median surgical time of stapedectomy was reduced from 70 (52.5-100.3) minutes to 39.5 (35.5-48) minutes after completing training. There was also a reduction in rate of complications (flap disruption, incus dislocation, and footplate mobilization).

CONCLUSION

Sheep ears constitute a cheap, easy to obtain and anatomically adequate model for stapedectomy training.

Click-evoked responses in vestibular afferents in rats

Sound activates not only the cochlea but also the vestibular end organs. Research on this phenomenon led to the discovery of the sound-evoked vestibular myogenic potentials recorded from the sternocleidomastoid muscles (cervical VEMP, or cVEMP). Since the cVEMP offers simplicity and the ability to stimulate each labyrinth separately, its values as a test of human vestibular function are widely recognized. Currently, the cVEMP is interpreted as a test of saccule function based on the assumption that clicks primarily activate the saccule. However, sound activation of vestibular end organs other than the saccule has been reported. To provide the neural basis for interpreting clinical VEMP testing, we employed the broadband clicks used in clinical VEMP testing to examine the sound-evoked responses in a large sample of vestibular afferents in Sprague-Dawley rats. Recordings were made from 924 vestibular afferents from 106 rats: 255 from the anterior canal (AC), 202 from the horizontal canal (HC), 177 from the posterior canal (PC), 207 from the superior vestibular nerve otolith (SO), and 83 from the inferior nerve otolith (IO). Sound sensitivity of each afferent was quantified by computing the cumulative probability of evoking a spike (CPE). We found that clicks activated irregular afferents (normalized coefficient of variation of interspike intervals >0.2) from both the otoliths (81%) and the canals (43%). The order of end organ sound sensitivity was SO = IO > AC > HC > PC. Since the sternocleidomastoid motoneurons receive inputs from both the otoliths and the canals, these results provide evidence of a possible contribution from both of them to the click-evoked cVEMP.

Effects of NasoPore Packing in the Middle Ear Cavity of the Guinea Pig

Objective. To evaluate the effects of NasoPore after packing of the middle ear in guinea pigs.

Study Design. A randomized, prospective, controlled animal study.

Setting. University laboratory.

Subjects and Methods. Forty-one guinea pigs were divided into 3 groups. In group 1 (n = 12), the middle ears of animals were unilaterally implanted with NasoPore, leaving the contralateral middle ears packed with absorbable gelatin sponge soaked in a solution containing kanamycin and furosemide as an ototoxicity-positive control; group 2 (n = 17) underwent the same experimental protocol as group 1, except the gelatin sponge was unsoaked; in group 3 (n = 12), NasoPore was inserted unilaterally and no packing material was placed into the contralateral ear. Auditory brainstem responses (ABRs) were performed preoperatively and 3 months after the procedure. The surface preparation and scanning electron microscopy (SEM) were assessed 3 months postoperatively, whereas pathology of middle ear was analyzed in 5 samples of group 2.

Results. ABR thresholds of the contralateral ear significantly increased in group 1 and were slightly shifted in group 2 compared with the NasoPore-packed and nonpacked ears 3 months postoperatively. The NasoPore-packed middle ears were found to have less fibrosis and inflammation and less thickened bone and tympanic membranes than Gelfoam-packed ears. Surface preparations and SEM showed no ototoxicity in the inner ear of NasoPore-packed ears.

Conclusion. NasoPore appears to be effective for use in otosurgery. It caused less fibrosis in the middle ear than conventional packing agents and no ototoxicity to the inner ear.

Direct drug application to the round window: A comparative study of ototoxicity in rats

Objective: To assess the validity of inducing ototoxicity in rats by applying a sponge soaked in kanamycin and furosemide on the round window.

Study Design: Basic, randomized, nonblind experimental study.

Setting: Animal models of cochlear damage and reliable methods of local drug delivery are fundamental to study hearing loss and to design new therapies.

Subjects and Methods: Four experimental groups of six Wistar rats with different methods of drug administration were used: (1) injection of subcutaneous kanamycin (400 mg/kg) and intravenous furosemide (100 mg/kg); (2) local application of a sponge soaked in saline close to the round window; (3) animals for which the sponge was soaked in a solution containing kanamycin (200 mg/mL) and furosemide (50 mg/mL); and (4) sham-operated rats. The tympanic bulla was exposed using a ventral approach, and a bullostomy was performed to visualize the round window membrane. Cochlear function was assessed by measuring the auditory brainstem response, and hearing thresholds in response to click and tone burst stimuli were determined as peak and interpeak latencies. At the end of the study, cochlear histology was analyzed.

Results: Systemic administration of kanamycin and furosemide induced profound hearing loss and severe hair cell damage. Local delivery of these ototoxic drugs caused comparable damage but avoided the systemic side effects of the drug. Sham-operated and saline control animals did not experience functional alterations.

Conclusion: Situating a sponge soaked in kanamycin and furosemide on the round window membrane through the ventral approach is a reliable method to provoke local ototoxicity in rats.

Conhecimento da anatomia da orelha de cobaias e ratos e sua aplicação na pesquisa otológica básica

O uso de mostras animais é importante na pesquisa otológica e o conhecimento da anatomia de sua orelha permite sua utilização adequada. OBJETIVO: Estudar a anatomia da orelha da cobaia e do rato por microscopia óptica de luz (MOL) e microscopia eletrônica de varredura (MEV) e suas vantagens anatômicas na pesquisa otológica básica. MATERIAL E MÉTODO: Os ossos temporais, as bulas timpânicas e cócleas de três cobaias e ratos albinos foram fotografados e analisados ao MOL e MEV. RESULTADOS: O rato não é tão simples de manipular como a cobaia, e freqüentemente apresenta otite média. O rato apresenta uma junção frágil da bula timpânica, duas e meia espiras na cóclea e a membrana timpânica não veda todo o conduto auditivo externo. A cobaia possui uma bula inteiriça, martelo e bigorna fundidos e três e meia espiras na cóclea. Pela MEV a cobaia e o rato possuem Membrana Tectória, Membrana de Raissner e o Órgão de Corti. As Células de Hensen estão presentes somente na cobaia. CONCLUSÃO: A cobaia foi considerada de fácil manipulação para a microdissecção, pelo tamanho e rigidez do osso temporal, e para experimentos cirúrgicos envolvendo o estribo, janela oval e a membrana timpânica. Pela MEV nota-se semelhança entre cobaia e rato, podendo ambos serem utilizados em estudos da orelha interna.

Understanding the anatomy of ears from guinea pigs and rats and its use in basic otologic research

The use of animal samples is important in otologic research and understanding the anatomy of their ears help make proper use of them in research projects. Aim: to study guinea pig’s and rat’s ears under light microscopy(LM) and scanning electron microscopy(SEM) and understand their anatomical advantages in basic otologic research. Materials and methods: The temporal bones, tympanic bullas and cochleas from three albino guinea pigs and rats were photographed and analyzed under LM and SEM. Results: Rats aren’t as simple to handle as guinea pigs, and often present with otitis media. Rats have a fragile junction of the tympanic bulla, two and half turns in the cochlea, and their tympanic membranes do not seal off the entire external auditory canal. Guinea pigs have full bullas, their incus and malleus are fused and they have three and half cochlear turns. Under SEM, guinea pigs and rats have Tectori Membrane, Raissner’s Membrane and the Organ of Corti. Only guinea pigs have Hensen’s Cells. Conclusion: Guinea pigs were considered easy to handle for microdissection purposes because of the size and robustness of their temporal bones, and for surgical experiments involving the stapes, the oval window and the tympanic membrane. Under SEM there are similarities guinea pigs and rats, and both can be used in inner ear studies.

Morphological sequence of Plastipore extrusion in experimental otitis media

OBJECTIVES

Plastipore prostheses are still used by many surgeons, although the functional results are controversial. The aim of this study was the morphological analysis of Plastipore material performance in the middle ear of rats, with special attention to extrusion.

METHODS

Twenty-four Wistar rats were given implants made of commercially available Plastipore and assigned to 3 groups: group A, with implantation in a healthy middle ear; group B, with implantation and cauterization of the nasopharyngeal orifice of the eustachian tube (hypoventilation); and group C, with implantation, cauterization of the eustachian tube, and bacterial inoculation with Pseudomonas aeruginosa.

RESULTS

The pathological study showed in nearly all cases the disintegration of the biomaterial. Adhesion between the biomaterial and bone could be seen in 1 rat from group C (hypoventilation and infection). In group C, the Plastipore was in contact with the tympanic membrane in 1 case and was extruding in 2 animals. Different phases of extrusion were defined. No extrusion was observed in the other groups.

CONCLUSIONS

The sequential stages of Plastipore extrusion are demonstrated. Infection seems to be the most important factor in Plastipore extrusion in our model.

Tissular changes induced by Pseudomonas aeruginosa in an otitis media rat model with tubal obstruction

CONCLUSIONS

This is a suitable model for the study of different features of middle ear inflammation. This model allows manipulations inside the middle ear while preserving relevant structures such as the tympanic membrane, and provides a useful model for the study of interactions between bacterial infection and eustachian tube dysfunction.

OBJECTIVES

Analysis of early and late histological features in an experimental model of Pseudomonas aeruginosa middle ear inoculation in the rat designed for the study of middle ear procedures.

MATERIALS AND METHODS

Thirty Wistar rats were inoculated with Pseudomonas aeruginosa in the tympanic bulla followed by the cauterization of the eustachian tube. Culturing of middle ear effusion was carried out at 7 days follow-up and at sacrifice. Processing of the temporal bones for light microscopy was performed at 7, 14, 30 and 60 days.

RESULTS

Early cultures were positive in most cases, thus proving that middle ear inflammation was due to the presence of inoculated Pseudomona aeruginosa. Mucoperiosteal inflammatory changes similar to those observed in human middle ear infection were seen. Acute inflammatory cell infiltration was seen at 7 and 14 days, gradually decreasing to chronic inflammatory changes with fibroplasia at 60 days. Bone resorption was observed at 7 and 14 days, changing to a bony deposition at 30 and 60 days.

Cochlear implantation in rats: a new surgical approach

The laboratory rat has been used extensively in auditory research but has had limited use in cochlear implant related research due mainly to the surgically restricted access to the scala tympani. We have developed a new surgical method for cochlear implantation in rats. The key to this protocol was cauterizing the stapedial artery (SA) and making a small cochleostomy near the round window in order to enlarge the surgical access to the scala tympani. Five normal hearing Hooded Wistar rats were used to investigate the effect of cauterizing the SA on hearing and auditory nerve survival. Results showed that cauterizing the SA was surgically feasible, afforded excellent exposure of the round window niche for cochleostomy, and did not adversely affect acoustic thresholds measured electrophysiologically. Moreover, there was no difference in spiral ganglion cell densities for any cochlear turn when compared with the contralateral control ears. Three deafened rats were subsequently implanted with a scala tympani electrode array using this new surgical approach. Electrically evoked auditory brainstem responses using bipolar stimulation, and subsequent cochlear histopathology demonstrated that cochlear implantation using a custom-made rat electrode array was safe and effective. The surgical approach presented in this paper presents a safe and effective procedure for acute or chronic cochlear implantation in the rat model.

Anti-adhesive properties of polytetrafluoroethylene (Gore-Tex) in middle ear surgery. An experimental study

CONCLUSIONS

Polytetrafluoroethylene (PTFE) may represent a material that prevents adhesions when implanted in the middle ear. This characteristic can be used to improve the design of prostheses.

OBJECTIVE

Prostheses in the middle ear have a relatively high failure rate due to extrusion, deformation and adhesion. Adhesion of prostheses to the walls of the tympanic cavity is the commonest cause of long-term hearing loss. The anti-adhesive properties of PTFE have been previously studied in abdominal and vascular surgery. To the best of our knowledge, this is the first work in which the properties of PTFE have been studied in the context of middle ear pathology.

MATERIAL AND METHODS

In order to induce otitis media with effusion, 27 Wistar rats underwent a technique based on permanent cauterization of the pharyngeal Eustachian tube. PTFE was subsequently implanted in the middle ear. Rats that underwent cauterization without implantation and cauterization with implantation of hydroxyapatite and Plastipore were included as controls.

RESULTS

Histopathological study of the tympanic bullae at 15 and 90 days after implantation demonstrated good biocompatibility of the PTFE implant under the analyzed conditions, with formation of a capsule around the material and no adhesions between the ear tissues and the prosthesis.

Pseudomonas aeruginosa infection in the hypoventilated middle ear: an experimental model

CONCLUSION

This is a suitable model for studying different aspects of the pathophysiology of chronic suppurative otitis media.

OBJECTIVE

To analyze the methodological features of an animal model of chronic suppurative otitis media induced by intratympanic inoculation of Pseudomonas aeruginosa.

MATERIAL AND METHODS

Otitis media was induced by inoculation of P. aeruginosa through the inferior aspect of the rat bulla and cauterization of the Eustachian tube via a transpalatal approach. Inspection of the tympanic membrane, culturing of middle ear effusion and processing of the temporal bones for light microscopy were performed.

RESULTS

Abnormal otomicroscopic findings and persistence of infection were correlated with the histopathological changes found in middle ear tissues.

Development of interface in hydroxyapatite implanted in the middle ear of the rat: a light and scanning microscopy study

OBJECTIVE

The aim of this work is to study the chronology in the biological covering of the hydroxyapatite bioprostheses in the healthy middle ear of the rat.

STUDY DESIGN AND SETTING

Dense hydroxyapatite is implanted into the middle ear of 45 Long-Evans rats, between stapes and tympanic membrane. The sample was divided into 3 groups for morphologic, functional, and chemical studies at 15 days, 3 months, and 6 months after surgery, respectively.

RESULTS

The short-term studies reveal that the prostheses is surrounded by a fibrous epithelial tissue referred as the interface; it presents a marked inflammatory reaction that decreases gradually in the medium-term and long-term studies; in this way, we observe a progressive adhesion between implant and the contact tissues.

CONCLUSIONS AND SIGNIFICANCE

This model has enabled us to study the cell reaction produced by the contact of the prostheses with bone and soft tissue and their impact on the functional qualities of the prostheses.