Auditory outcomes after implantation and electrical stimulation of the lateral ampullar nerve in guinea pig.

OBJECTIVE: To determine in a guinea pig model the factors of invasiveness of a bipolar electrode implanted in the horizontal semicircular canal (HSC) and to evaluate the consequences on hearing of electrical stimulation of the ampullary nerve. DESIGN: Sixteen guinea pigs divided into four groups underwent surgical opening of the HSC of one ear as follows: control (group 1), cyanoacrylate glue application on the HSC opening (group 2), electrode implantation with cyanoacrylate glue on the HSC opening (group 3), and electrode implantation with electrical stimulation (1 hr/day) for 9 days (group 4). Auditory brainstem responses were recorded before and after surgery and after electrical stimulation. The effectiveness of electrical stimulation in producing a horizontal vestibulo-ocular reflex was evaluated by recording eye movement with video-oculography. RESULTS: Group 1 animals showed hearing loss, and in group 2, sealing the HSC opening with cyanoacrylate glue preserved the hearing thresholds. After electrode implantation, seven of the eight animals showed hearing loss compared with preoperative values. Electrical stimulation did not induce additional hearing loss. CONCLUSION: Electrode implantation at the canal level entailed a risk of hearing loss in an animal model, but electrical stimulation of the horizontal ampullary nerve did not further alter hearing function.

An animal model of central auditory pathway imaging in the rat brain by high resolution small animal positron emission tomography.

CONCLUSIONS: Our study demonstrated that high resolution animal positron emission tomography (PET) can non-invasively assess the change in glucose metabolism of the central auditory pathway including the inferior colliculus and auditory cortex in the rat. OBJECTIVES: The traditional in vitro approach with immunohistochemical staining or autoradiography to assess chronological changes or topographic arrangement of central auditory pathway required sacrificing a large number of animals. Inter-individual difference is also a major concern. Therefore, development of an in vivo animal model using PET imaging would be a rational method to overcome these shortcomings. MATERIALS AND METHODS: Small animal PET scan using (18)F-fluorodeoxyglucose (FDG) as a functional marker was performed in rats. Each animal was serially scanned before and after unilateral cochlear ablation, with and without acoustic stimulation. The images were analyzed by the region of interest (ROI) method. Ratios of radioactivity at the inferior colliculus and auditory cortex and a referenced cerebral cortex between bilateral hemispheres were measured. RESULTS: These scans demonstrated several brain structures including the inferior colliculus (IC) and cortex (B). Moreover, unilateral cochlear ablation decreased the radioactivity at contralateral IC and auditory cortex (C) areas. Differences may reach 33% in IC and 27% in C, and average radioactivity ratios were 1.24+/-0.08 and 1.18+/-0.07 in selected adjacent sections, respectively.