Application of a spike sorting procedure to analyze recordings in the crayfish ventral superficial flexor preparation: A high resolution approach to the study of neuromodulators on axons and synapses.

The crayfish ventral superficial flexor (VSF) is innervated by the ventral branch of the third nerve. This nerve and muscle system is tonic, and is responsible for posture control of the animal. The easy accessibility of the third nerve and its muscle fibers, along with its display of tonic activity in vitro, make this preparation ideal for observing axonal action potentials and synaptic responses. As a result, this preparation has often been adopted for undergraduate electrophysiology laboratories. This report describes application of a spike sorting procedure to simultaneously recorded traces from the third nerve and associated muscle fiber. This procedure allows for isolation of action potentials arising from each of the six axons in the third nerve. Separation of action potentials and their corresponding synaptic responses from large data sets, with sample sizes in the thousands, enables us to perform averaging and to analyze waveforms of action potentials and synaptic responses with a high resolution. With this high resolution approach, we document variations in the shape of action potentials in the third nerve and in synaptic potential in muscle fibers. The approach described here can be used for detailed study of the effects mediated by neuromodulators and drugs. An example of such an application is illustrated using 50 μM GABA. Several possible student projects using this approach are outlined and discussed.