The Subject
Planning or setting up your ABR experiment must begin with an understanding of the subject's normal hearing range and factors that might have an effect on its response or recording. ABRs have been measured for many species. In this guide, we'll focus on the three most common species used in ABR experiments and screening protocols: mice, rats, and guinea pigs.
Expected Hearing Range
ABR tests are typically focused on the range in which the species is commonly known to hear well.
Note
The hearing range of laboratory subjects may vary across different strains or colonies and can be affected by age, the environment, and anesthesia.
Age-Related Effects on Hearing
Many lab subjects experience hearing loss due to age. The rate of loss varies across species and strains. This effect has been observed as early as 12 weeks in mice.
Anesthesia Considerations
Two types of anesthesia protocols are typically used for ABR testing. Each has benefits and limitations. Check your IRB approved guidelines for dosages and protocol.
Xylazine(XYL) + Ketamine to start, Ketamine to Boost
This aesthetic protocol uses an injectable combination of muscle relaxer and sedative. Typically, the subject is unconscious in a few minutes, begins to wake ~45 minutes and is completely awake at ~90 minutes after initial sedation. If a subject wakes early or a test runs longer than ~45 minutes, a booster of ketamine can be used to keep the subject anesthetized. Be sure to follow your approved IRB protocol.
Isoflurane (ISO)
This aesthetic protocol uses a fast-acting inhalant with a short duration. The subject is typically fully sedated within 4-5 minutes and wakes very quickly when the gas is removed.