Perilymph sampling in Mongolian gerbil, technical note and procedure evaluation.

Abstract

Objective

The aim of this study is to detail and evaluate the surgical procedure for perilymph sampling from the cochlear apex in the Mongolian gerbil.

Design

Perilymph sampling from the cochlear apex was performed one to three time in 12 male gerbils aged 8 to 12 months via the submandibular route. 11 of them were previously implanted with intracochlear implants loaded with dexamethasone and placed in the scala tympani, the 12th was used to collect control samples. The procedure was performed under general gas anesthesia, with head support, by a submandibular approach. After opening the bulla and sacrificing the external and middle ears, the cochlea was exposed and perilymph sampled. Macroscopic features of perilymph samples were reported before an HPLC-MS/MS assay to detect and quantify dexamethasone. Some cochleae were then harvested, immunostained and cleared to study fibrosis formation along the labyrinth and evaluate the consequences of multiple sampling procedures.

Results

The perilymph sampling procedure was technically difficult and required experimenter training. The procedure was well tolerated by the animals. One drawback of this technique in our gerbil model was the need to sacrifice the external ear, eardrum and ossicular chain to allow sufficient exposure for a quality procedure. Our technique enabled the collection of perilymph samples of the desired volume. Most of our samples were contaminated by bleeding from the otic capsule bone secondary to the cochleostomy. Nevertheless, HPLC-MS/MS analyses which successfully found dexamethasone in the perilymph of implanted gerbils, confirmed that our method was suitable for pharmacokinetic analyses. The occurrence of areas of fibrosis in the labyrinth after a sampling procedure compromises the quality and reliability of subsequent samples from the same animal.

Conclusion

The Mongolian gerbil is an animal model that can be used to collect perilymph from the cochlear apex to perform pharmacokinetic studies. The number of samples taken from a single animal must be limited to one.