Histology and Retention of Implanted Carbon Fiber Thread Electrodes in Fixed Tissue

Rats were deeply anesthetized with Euthasol (pentobarbital sodium and phenytoin sodium from Virbac AH Inc.), then transcardially perfused with 0.9% saline solution followed by 4% paraformaldehyde in 0.1 M phosphate buffer (PB).

The implanted electrodes were cut just above the skull and below the copper wire bundle component of the device with a rotary saw (Dremel) to retain the flexible Py-CF portion of the device in the fixed brain tissue.

Brains were removed from the skull, post-fixed for 24 hours in the same fixative solution and stored in 25% glycerol with 0.075% sodium azide in 0.1 M PB overnight or until cutting.

To prepare sections, brains were frozen on dry ice then cut in the transverse plane on a freezing microtome with a microtome knife (C. L. Sturkey, Inc. #K185A).

Sections were cut sequentially, with four sections at 25-μm then one section at 100-μm, repeated until the end of the frozen block of brain.

The 100-μm sections were immediately mounted onto glass slides and air dried, whereas the 25-μm sections were stored in 0.1% sodium azide in 0.1 M PB at 4°C until use.