A gold-plated suction electrode for extracellular recording and dye infusion.

To record extracellular nerve activity, wires or polyethylene suction electrodes are commonly used, which are modified according to particular experimental requirements. For electrophysiological studies in a dissected animal, a length of the nerve under investigation may be lifted on to silver wires (Pearon, Stein & Malhotra, 1972), or a fine wire hook (Wilkens & Wolf, 1974), often under mineral oil. These methods produce good records but the mineral oil and the wires around the nerve and its associate muscle reduce the visibility of the preparation. This may cause difficulties when simultaneous records are required from other parts of a small preparation. Using drawn polyethylene suction electrodes, successful extracellular recordings can also be obtained from the cut ends of motor and sensory nerves. This is a simple electrode, but its major drawback is that it cannot be used to record from very fine nerves since it is difficult to construct very fine tips using polyethylene tubes. Other suction electrodes have also been used for en passant recording attached to the site of an intact nerve by slight negative pressure (Padst & Kennedy, 1967; Larimer & Eggleston, 1971), but it proved difficult to restrict the recording site to only a specific area of the fine nerve branches. Using extremely small diameter tips to localize the recording, new problems of tip clogging and high electrode resistance are encountered. To overcome these problems a gold-plated glass suction electrode has been developed. To construct this electrode a glass micropipette was pulled from a 1-1-5 m m diameter glass tube and rapidly tapered to reduce the internal resistance of the electrode. The outside surface of the micropipette was coated with a layer of gold about 100 nm thick, by vacuum deposition in a Polaron, Sputter Coater. The micro-pipette was mounted on the end of a stainless steel tube with a small piece of heat shrink sleeving (Fig. 1 A). One input of an a.c. differential amplifier was connected to the steel tube. The layer of gold around the pipette was connected to the other input of the amplifier by wrapping silver wire tightly around it and painting it with conductive silver paint. The main advantages of the gold-plated suction electrode are first, that it can be constructed very easily and, secondly, that it can be used to record from very fine fcrves. To achieve this, the tip of the micropipette is broken using a pair of …