Intracellular recording

Intracellular recordings were performed using quartz microelectrodes (1.0-mm-diam with filament, Sutter Instruments, Novato, CA) filled with 1 M potassium acetate. The electrodes were pulled using a Flaming-Brown micropipette puller (P2000, Sutter Instrument) and had impedances ranging from 100 and 300 MΩ. The electrode was advanced into the IC in 2-μm steps using a precision microdrive (Model 660, KOPF Instrument). The intracellular responses of IC neurons were amplified (Model IR183A, Cygnus Technology) and monitored on a digital oscilloscope (DLM 3024, Yokogawa). The waveforms were digitized at a sampling rate of 100 kHz by a data acquisition system (EPC-10, Heka) and stored on a computer hard drive.

Recordings were conducted from both the ipsilateral and contralateral IC relative to the side of sound exposure in unanesthetized mice inside a single-walled sound attenuating booth (Industrial Acoustics Company, Inc.). Throughout the 3–5 h recording session, the animal was periodically offered water and monitored for any signs of discomfort. After each recording session, the exposed skull was covered with a Kwik-Sil silicone elastomer plug (World Precision Instruments) and the animal was returned to its holding cage. Experiments were conducted at least 2 months post-exposure in the SE group and recordings were performed every other day for up to 2 weeks. At the end of the experiment, the animal was sacrificed with an IP injection of Fatal-Plus. No sedative drugs were used during the recording sessions. If the animal showed any signs of discomfort, the recording session was terminated, and the mouse was returned to its cage.