Electrophysiological recording system for the cervical vagus nerve. (A) (Top left) Surgical procedure used to place the cuff electrodes in the cervical vagus nerve of an anesthetized BALB/c mouse. (Top right) Enlargement indicating the cuff electrodes, the vagus nerve and neighboring structures. (Bottom left) Lab-made hook electrodes used to record compound action potentials (CAPs) from the vagus nerve. (Bottom right) Representative recording of the neural signals by three adjacent hook electrodes. (B) (Left) By using standard template matching and spike-sorting algorithms relying on principal component analysis, unit spikes are discriminated in the vagus nerve recordings. Most large-amplitude waveforms correspond to CAPs, but spikes in the 5–10 µV amplitude range are likely carried by single fibers. (Right) Putative single-fiber units identified by spike sorting. (C) (Left) Diagram of the axon-attached recordings triggered by a brief stimulating pulse (S1). (Right) Examples of superimposed single-fiber action potentials (shown as negative waves). Same scale as in B.