Tools for physiology labs: an inexpensive high-performance amplifier and electrode for extracellular recording

The cost of electronic equipment can be a critical barrier to including neurophysiology exercises in biology teaching programs. We describe the construction of a simple and inexpensive AC preamplifier with performance comparable to that of commercial products. The amplifier consists of two integrated circuits in five stages: differential input, fixed gain, variable gain (100 or 1000), low-pass filter (5 or 20 kHz), and 50 or 60 Hz notch filter. We compared our amplifier with two commercial units, the A-M Systems Model 1700 and the Grass P15. The quality of extracellular recording from a typical student preparation (spontaneously active crayfish motor nerve) was the same for all three amplifiers, although our amplifier has slightly higher internal noise than the P15 and slightly lower common-mode rejection than the 1700 and P15. In addition, we describe a simple suction electrode for extracellular nerve recording. It is easily constructed from readily available materials and uses a disposable plastic pipette tip, instead of the traditional glass tip, to contact the nerve. This tip is easily replaced if broken or clogged, and can be adapted to different recording conditions by selecting a different tip size or stretching the plastic. Development of this equipment is part of an ongoing project to promote neuroscience education by expanding the neurophysiology options available to laboratory instructors.