Dorsal root ganglia neurite outgrowth measured as a function of changes in microelectrode array resistance.

Current research in prosthetic device design aims to mimic natural movements using a feedback system that connects to the patient's own nerves to control the device. The first step in using neurons to control motion is to make and maintain contact between neurons and the feedback sensors. Therefore, the goal of this project was to determine if changes in electrode resistance could be detected when a neuron extended a neurite to contact a sensor. Dorsal root ganglia (DRG) were harvested from chick embryos and cultured on a collagen-coated carbon nanotube microelectrode array for two days. The DRG were seeded along one side of the array so the processes extended across the array, contacting about half of the electrodes. Electrode resistance was measured both prior to culture and after the two day culture period. Phase contrast images of the microelectrode array were taken after two days to visually determine which electrodes were in contact with one or more DRG neurite or tissue. Electrodes in contact with DRG neurites had an average change in resistance of 0.15 MΩ compared with the electrodes without DRG neurites. Using this method, we determined that resistance values can be used as a criterion for identifying electrodes in contact with a DRG neurite. These data are the foundation for future development of an autonomous feedback resistance measurement system to continuously monitor DRG neurite outgrowth at specific spatial locations

High resolution phase contrast photomicrograph of DRG tissue seeded on a microelectrode array after a 2 day culture.

<p>(A). 59 extracellular electrodes were visually classified as having contact with a DRG soma (B) or a DRG neurite (C). For some electrodes it was unclear if there was DRG neurite contact (D) and electrodes devoid of contact with DRG tissue were classified as CLEAN (E). The majority of electrodes classified as CLEAN were located on the opposite side of the array from where the DRG tissue was located (left side of A; scale bar = 200 μm).</p

The average change in resistance (MΩ) of each classified electrode after background subtraction for all six experiments (SEM in brackets).

<p>The average change in resistance (MΩ) of each classified electrode after background subtraction for all six experiments (SEM in brackets).</p

Electrode resistance values can reflect DRG neurite contact with electrode.

<p>In a single experiment resistance values from electrodes were averaged by classification (DRG neurite, UNCLEAR, or CLEAN). The soma in this experiment was not placed in contact with any electrodes. (A) The change in resistance for electrodes in contact with a DRG neurite (-0.24 ± 0.02 MΩ; n = 16; p < 0.001; F = 69.685) were significantly less than for electrodes classified as UNCLEAR (-0.42 ± 0.02 MΩ; n = 19; p < 0.001) or CLEAN (-0.53 ± 0.01 MΩ; n = 31 electrodes). (B) The distribution of the change in electrode resistances for CLEAN electrodes, UNCLEAR electrodes and electrodes contacted by a DRG neurite were plotted in a frequency curve (0.5 MΩ bins). (C) The average change in resistance of UNCLEAR electrodes was background subtracted across all electrodes in a single experiment. This did not change the relationship between resistance values of electrodes contacted by DRG neurites and CLEAN electrodes. However it allowed for a comparison of resistance values across experiments.</p