Nerve Growth Factor Dependent Changes in Electrophysiology Measured in a Neurotrophic Electrode

We describe here a neurotrophic electrode designed to improve long-term reliability and signal-tonoise in a brain-device interface. Our electrode consists of a fine microwire inside a polyimide tube. The polyimide tube is filled with nerve growth factor (NGF) incorporated into a fibrin matrix. Our goal is to have a neurite grow into the tube. The close apposition between neurite and the recording wire should enhance signal-to-noise. The physical connection between device and tissue should improve reliability. We have implanted complete devices in 4 rats. Each rat gets a four-electrode device implanted in the barrel cortex of each hemisphere. Each electrode is filled with a different test substance. One control tube contains only saline, and another contains only the fibrin matrix. The other two electrodes in each array are filled with different concentrations of NGF. Once weekly following the implant, each rat is sedated, and electrical activity in each of the electrodes recorded. Electrodes in 5 of the 8 implants exhibited multi-unit spindling activity. A direct comparison of the amplitude of action potentials over time in each of the types of implants shows that the presence of NGF within the polyimide tube leads to an increase in action potential amplitude.