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All procedures involving animal models have been reviewed by the local institutional animal care committee and the JoVE veterinary review board.
1. Auditory Brainstem Response (ABR) Recording
- Anesthetize Sprague Dawley (SD) rats (1-14 day old pups and 2-month-old adults, both sexes) with a single injection of 1.5% sodium pentobarbital (22 mg/kg for pups and 30 mg/kg for adults, intraperitoneal (i.p.).
- Place the anesthetized animal in a polyethylene-foam mold to immobilize the animal's body. Place the animal on an anti-vibration table in a sound-attenuating room. Keep the animal's body temperature at 37.5 °C with a heating pad.
- Wipe the head area with 70% (vol/vol) ethanol. By using a fine scissors, make a 1-2 mm incision ventrolateral to the external pinna to place the reference electrode or ground. A subdermal needle electrode (recording electrode) is located over the skull vertex (Figure 1A).
- Using the function generator, generate calibrated tone bursts (1 ms rise/fall, 3 ms plateau) of various frequencies (2, 4, 8, 16, 24, and 32 kHz) and intensities (decreased from 85 to 10 dB SPL in 5 dB step). Vary the frequency and amplitude manually or using a computer. Deliver sound stimuli through an electrostatic speaker located 10 cm away toward the head of the animal.
- Filter (100-1,000 Hz), amplify, and average (256 times) the sound elicited potential using a multi-function processor to get the ABRs. The ABR traces are monitored online and stored for offline analysis. It takes about 40 min to complete the ABR recording from one animal.
NOTE: Usually, three to seven peaks (wave I to wave VII) with latencies less than 15 ms can be identified (Figure 1B). The ABR threshold is defined as the minimum sound level at which wave I and II could be detected.
- Euthanize before the animals awake from anesthesia (with an intraperitoneal injection of 0.3 mL 1.5% sodium pentobarbital).
