Chronic tympanic membrane perforation represents a prevalent otological condition, necessitating a reliable animal model for the validation and safety assessment of surgical techniques and materials employed in myringoplasty. This prospective study involved the establishment of chronic tympanic membrane perforation animal models in 16 chinchillas. A thermic myringotomy was conducted on the right ear (study group), followed by cold instrument myringotomy, coupled with the topical application of mitomycin C and dexamethasone solution on the left ear (control group). Results revealed that tympanic membrane perforations in the study group persisted for a minimum of 4 weeks in 93.7% of cases and extended to 12 weeks in 62.5% of the cases. In contrast, all tympanic membrane perforations in the control group were present at 4 weeks, with only 37.5% persisting after 12 weeks, although statistical tests did not find significant differences between the two groups (chi-square: p-value = 0.157, Kruskal-Wallis: p-value = 0.093, Mann-Whitney: p-value = 0.121). The thermic myringotomy employed to induce chronic tympanic membrane perforation in animals demonstrated efficiency and sustainability. This model, characterized by stability and reproducibility, holds promise for future experimental applications in the field.

Chinchillas are a relatively novel research model compared with other rodent species. They require special considerations when it comes to their husbandry and daily care. Chinchillas tend to be shy animals that are well adapted to masking clinical signs of illness. These characteristics can make them a difficult species to maintain in a research setting. The authors\' institution has maintained chinchillas and established standardized daily animal care procedures for them. Chinchillas are most commonly used for auditory research. They are often used to study the mechanism of different induced auditory conditions or injuries as well as exploration for potential alleviating treatments. Often, tested therapeutics have demonstrated potentially beneficial effects but have not been applied in the specific condition or injury of interest. The development of new applications for therapeutics can lead to groundbreaking discoveries, but testing of new therapeutic applications is often initially performed in an animal model without knowing how the therapeutic will behave in the species. During testing, unexpected adverse events may manifest that require more focused monitoring and supportive care. This scenario occurred when adverse effects were observed in a chinchilla blast-injury model after receiving an acylated glucagon-like peptide-1 (GLP-1) receptor agonist. The study involved evaluation of this therapeutic over an extended amount of time after inducing a controlled pressurized blast-injury followed by multiple repeated hearing tests under anesthesia. Chinchillas enrolled in the study exhibited several clinical signs including weight loss, lethargy, labored breathing, neurologic abnormalities, decreased appetite or decreased fecal output, and otitis. Five primary abnormalities were reported on pathology: aspiration pneumonia, hepatic steatosis, right ventricular dilation, pancreatitis, and tubulointerstitial nephritis. Initially abnormal clinical signs, early mortality rates, and pathology were attributed to multiple anesthetic events. However, a retrospective analysis evaluating the association of different study variable exposures in a stratified comparison demonstrated that the early mortality rates were actually associated with the therapeutic drug given for the first time in this species. In this study, we describe the detailed findings of the retrospective analysis and explore different strategies that can be incorporated to maintain good animal welfare and decrease early animal loss.

OBJECTIVE: We report the in vivo biodistribution and ototoxicity of cationic liposomal-ceftriaxone (CFX) delivered via ear drop formulation in adult chinchilla.
METHODS: CFX was encapsulated in liposomes with size of ∼100 nm and surface charge of +20 mV. 100 μl liposomes or free drug was applied twice daily in both external ear canals of adult chinchillas for either 3 or 10 days. Study groups included free ceftriaxone (CFX, Day 3: n = 4, Day 10: n = 8), liposomal ceftriaxone (CFX-Lipo, Day 3: n = 4, Day 10: n = 8), and a systemic control group (Day 3: n = 4, Day 10: n = 4). Ceftriaxone delivery to the middle ear and systemic circulation was quantified by HPLC assays. Liposome transport was visualized via confocal microscopy. Auditory brainstem response (ABR) tests and cochlear histology were used to assess ototoxicity.
RESULTS: Liposomal ceftriaxone (CFX-Lipo) displayed a ∼658-fold increase in drug delivery efficiency in the middle ear relative to the free CFX (8.548 ± 0.4638% vs. 0.013 ± 0.0009%, %Injected dose, Mean ± SEM). CFX measured in blood serum (48.2 ± 7.78 ng/ml) following CFX-Lipo treatment in ear was 41-fold lower compared to systemic free-CFX treatment (1990.7 ± 617.34 ng/ml). ABR tests and histological analysis indicated no ototoxicity due to the treatment.
CONCLUSIONS: Cationic liposomal encapsulation results in potent drug delivery across the tympanic membrane to the middle ear with minimal systemic exposure and no ototoxicity.

Few instances of neoplastic formations in the liver of chinchillas have been found, even though the species is widely used in different scientific experiments. In the present article we investigate the anatomical features of the chinchilla\'s liver using CT and three dimension (3D) imaging. For the trials we used 12 (six males and six females) clinically healthy chinchillas all at 18 months of age. The animals were positioned in dorsal recumbency. We used Th8 to L2 vertebrae and the sternum as bone markers for the transverse CT study. The investigated anatomical landmarks for the CT coronal study were the vertebrae, costal arch, soft abdominal wall, diaphragm, stomach and the right kidney. 3D reconstructions were accomplished with a specific imaging software. On transverse and coronal CT images, the chinchilla\'s liver was composed of lobus hepatis sinister lateralis, \'middle lobe\'-without proper Latin term in NAV 2017, lobus hepatis dexter and lobus caudatus. The \'middle lobe\' was separated into the \'left middle lobe\' and the \'right middle lobe\'. Lobus hepatis dexter consisted of lobus hepatis dexter medialis and lobus hepatis dexter lateralis. There was an anatomical relation between the liver, fundus ventriculi and corpus ventriculi. Proc. caudatus was in close contact with the right kidney. Vesica fellea was elongated and ellipsoid. 3D reformatted images confirmed the results obtained by transverse and coronal CT studies. The CT density of the liver in HU was 195.6 ± 73.1. The CT and 3D reconstructed images were visualized at high resolution. This data could be used as a basis for further morphological and imaging studies.

Otitis media (OM) is one of the most globally pervasive pediatric conditions. Translocation of nasopharynx-resident opportunistic pathogens like nontypeable Haemophilus influenzae (NTHi) assimilates into polymicrobial middle ear biofilms, which promote OM pathogenesis and substantially diminish antibiotic efficacy. Oral or tympanostomy tube (TT)-delivered antibiotics remain the standard of care (SOC) despite consequences including secondary infection, dysbiosis, and antimicrobial resistance. Monoclonal antibodies (mAb) against two biofilm-associated structural proteins, NTHi-specific type IV pilus PilA (anti-rsPilA) and protective tip-region epitopes of NTHi integration host factor (anti-tip-chimer), were previously shown to disrupt biofilms and restore antibiotic sensitivity in vitro. However, the additional criterion for clinical relevance includes the absence of consequential microbiome alterations. Here, nine chinchilla cohorts (n = 3/cohort) without disease were established to evaluate whether TT delivery of mAbs disrupted nasopharyngeal or fecal microbiomes relative to SOC-OM antibiotics. Cohort treatments included a 7d regimen of oral amoxicillin-clavulanate (AC) or 2d regimen of TT-delivered mAb, AC, Trimethoprim-sulfamethoxazole (TS), ofloxacin, or saline. Fecal and nasopharyngeal lavage (NPL) samples were collected before and several days post treatment (DPT) for 16S sequencing. While antibiotic-treated cohorts displayed beta-diversity shifts (PERMANOVA, P < 0.05) and reductions in alpha diversity (q < 0.20) relative to baseline, mAb antibodies failed to affect diversity, indicating maintenance of a eubiotic state. Taxonomic and longitudinal analyses showed blooms in opportunistic pathogens (ANCOM) and greater magnitudes of compositional change (P < 0.05) following broad-spectrum antibiotic but not mAb treatments. Collectively, results showed broad-spectrum antibiotics induced significant fecal and nasopharyngeal microbiome disruption regardless of delivery route. Excitingly, biofilm-targeting antibodies had little effect on fecal and nasopharyngeal microbiomes.

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OBJECTIVE: Frequency selectivity is a fundamental property of the peripheral auditory system; however, the invasiveness of auditory nerve (AN) experiments limits its study in the human ear. Compound action potentials (CAPs) associated with forward masking have been suggested as an alternative to assess cochlear frequency selectivity. Previous methods relied on an empirical comparison of AN and CAP tuning curves in animal models, arguably not taking full advantage of the information contained in forward-masked CAP waveforms.
METHODS: To improve the estimation of cochlear frequency selectivity based on the CAP, we introduce a convolution model to fit forward-masked CAP waveforms. The model generates masking patterns that, when convolved with a unitary response, can predict the masking of the CAP waveform induced by Gaussian noise maskers. Model parameters, including those characterizing frequency selectivity, are fine-tuned by minimizing waveform prediction errors across numerous masking conditions, yielding robust estimates.
RESULTS: The method was applied to click-evoked CAPs at the round window of anesthetized chinchillas using notched-noise maskers with various notch widths and attenuations. The estimated quality factor Q10 as a function of center frequency is shown to closely match the average quality factor obtained from AN fiber tuning curves, without the need for an empirical correction factor.
CONCLUSIONS: This study establishes a moderately invasive method for estimating cochlear frequency selectivity with potential applicability to other animal species or humans. Beyond the estimation of frequency selectivity, the proposed model proved to be remarkably accurate in fitting forward-masked CAP responses and could be extended to study more complex aspects of cochlear signal processing (e.g., compressive nonlinearities).

This article reviews the development, hand-rearing, feeding, housing, and social behavior of common pet rodent species (rats, mice, hamsters, gerbils, guinea pigs, chinchillas, and degus). In addition, common gastrointestinal, respiratory, cardiovascular, dermatologic, musculoskeletal, neurologic, and ophthalmic disorders in pediatric pet rodents are reviewed. Preventative care and indications for spaying and neutering are discussed.

We measure bone-conduction (BC) induced skull velocity, sound pressure at the tympanic membrane (TM) and inner-ear compound-action potentials (CAP) before and after manipulating the ear canal, ossicles, and the jaw to investigate the generation of BC induced ear-canal sound pressures and their contribution to inner-ear BC response in the ears of chinchillas. These measurements suggest that in chinchilla: i.) Vibrations of the bony ear canal walls contribute significantly to BC-induced ear canal sound pressures, as occluding the ear canal at the bone-cartilaginous border causes a 10 dB increase in sound pressure at the TM (PTM) at frequencies below 2 kHz. ii.) The contributions to PTM of ossicular and TM motions when driven in reverse by BC-induced inner-ear sound pressures are small. iii.) The contribution of relative motions of the jaw and ear canal to PTM is small. iv.) Comparison of the effect of canal occlusion on PTM and CAP thresholds point out that BC-induced ear canal sound pressures contribute significantly to bone-conduction stimulation of the inner ear when the ear canal is occluded.

BACKGROUND: External-ear amplification (EEA) has been shown to vary from 5-19 dB-A in large datasets of pediatric, adolescent, and adult human participants. However, variable EEA is an overlooked characteristic that likely plays a role in individual noise-induced hearing loss (NIHL) susceptibility. A noise exposure varying 5-19 dB-A translates to high-EEA individuals theoretically experiencing 3-4 times greater NIHL risk than low-EEA individuals.
OBJECTIVE: The purpose of this preliminary analysis was to test the hypothesis that higher EEA is correlated with increased noise-induced threshold shift susceptibility.
METHODS: Nine chinchillas were exposed to 4-kHz octave-band noise at 89 dB-SPL for 24 h. Auditory brainstem response thresholds were obtained pre-exposure, 24-h post-exposure, and 4-week post-exposure. Relationships between EEA and threshold shift were analyzed.
RESULTS: Open-ear EEA ranged 11-19 dB-SPL, and occluded-ear EEA ranged 10-21 dB-SPL. Higher occluded-ear EEA was correlated with increased NIHL susceptibility (p = 0.04), as was lower body weight (p = 0.01). Male animals exhibited more threshold shift than female animals (p = 0.02), lower body weight than female animals (p = 0.02), and higher occluded-ear EEA (male mean = 18 dB; female mean = 15 dB).
CONCLUSIONS: Taken together, increased threshold shift susceptibility was observed in the smallest animals, animals with the highest occluded-ear EEA, and in male animals (which tended to have higher occluded-ear EEA). Given the established relationship between smaller body size and higher occluded-ear EEA, these preliminary results suggest that body size (and occluded-ear EEA; a function of body size) could be a potential, underlying driver of NIHL susceptibility differences, rather than true sex differences.