Recording Auditory Brainstem Responses in a Rat Pup

Immobilize an anesthetized rat pup in a foam mold.

Position the pup on an anti-vibration table within a soundproof room to minimize vibration and noise-related artifacts. Place a heating pad underneath to maintain body temperature.

Sterilize the head.

Make incisions near the outer ears to place the reference and ground electrodes.

Next, insert the recording electrode beneath the skin at the skull vertex.

Using a speaker connected to a sound generator, deliver sound pulses of varying frequencies and intensities.

The mechanical vibrations from the sound pulses deflect the hair cell projections in the rat's inner ear.

This deflection opens mechanically-gated ion channels, inducing a positive ion influx and hair cell depolarization.

The depolarized hair cells release neurotransmitters, which bind to the inner ear neuronal receptors, generating action potentials.

The action potentials propagate through the auditory nerve to the brainstem.

The recording electrode detects the signal, which a processor converts into the auditory brainstem response.

To begin this procedure, place the anesthetized animal in a polyethylene foam mold to immobilize the animal's body. Then, place the animal on an anti-vibration table in a sound-attenuating room. Keep the animal's body temperature at 37.5 degrees Celsius with a heating pad.

Next, wipe the head area with 70% ethanol. Make a 1 to 2-millimeter incision ventrolaterally to the external pinna, to place the reference electrode or ground electrode. Then, place a subdermal recording electrode over the skull vertex.

Using the function generator, generate calibrated tone bursts of various frequencies and intensities. Deliver the sound stimuli through an electrostatic speaker located 10 centimeters away from the head of the animal.

To obtain the auditory brainstem responses, the sound elicited potentials are filtered, amplified, and averaged using a multifunction processor. The 40-minute ABR recording is monitored online and stored for offline analysis.