This protocol is the second installment of a two part protocol: “Micro-drive array for chronic in-vivo recording.” The combination of the micro-drive array and tetrode is a powerful tool for obtaining simultaneous recordings of many neurons in an awake, behaving animal preparation. Hopefully, we have provided you with all the necessary information for you will need to begin or improve electrophysiological recordings in your own laboratory.
The motorized tetrode twister device was custom designed and fabricated. We have provided a vendor and part number that will allow you to order a device with similar functionality. Alternatively, a motorized turning device may be constructed in-house simply by combining a motorized rotating bar magnet with a magnetized stirring rod that is attached to an alligator clip; this configuration would most likely require manual counting of rotations, manual reversal of rotation direction, and manual starting/stopping.
Some electrode interface boards do not have pin-and-hole mechanisms for connecting the electrode wire. Instead, you may have obtained an interface board that has metal pins that extend out from the connector board; such metal pins are similar to those often found on standard electronic components. We briefly outline a methodology for connecting the tetrode channels to metal pins. First, remove the insulation on the tips of the four electrode wires of each tetrode. This is accomplished by applying a flame to the tip of each electrode as briefly as possible using a handheld butane torch. Obtain shrink wrap that will fit easily over the metal pin, and will squeeze the pin tightly after the shrink wrap has been heated. Cut the shrink wrap tubing to the length of the metal pin. Use capillary action to fill the shrink wrap with silver paint. Insert the exposed tip of one electrode wire into the shrink wrap. Gently slide the shrink wrap over the metal pin such that the electrode wire is between the pin and the wall of the shrink wrap. Repeat these steps for the remaining three electrode channels of the tetrode. Finally, with a side-to-side motion of a heat gun, heat the four pins covered in shrink wrap (with the electrode wires inside the shrink wrap). At this point, you should have stable and reliable connections between the tetrode and connector board.
Throughout these fabrication procedures handle the electrode wires with care as very little force is required to damage them. There are many steps in the tetrode and micro-drive array procedure and each step is as crucial as the others for obtaining high quality data. The protocol described here has worked well for our laboratory considering the equipment available. The resources in your own laboratory may be different, therefore, consider each step carefully and do not hesitate to change the protocol to meet your own requirements and constraints in order to achieve optimal performance.