Methods of single unit recording from medullary neural substrates in awake, behaving guinea pigs

An electrophysiological procedure that permits extracellular single neuronal recording in the medulla of unanesthetized, freely behaving animals is described. System components consist of 1) a flexible, single-strand microwire as recording electrode; 2) a miniature, skull-mounted miniature microdrive used for isolation of single unit activity; and 3) a head-mounted voltage follower that conditions and stabilizes the neuronal signals prior to amplification and transmission for further processing. A unique advantage of this procedure is the latitude and provision for microwire replacement in the event that multiple penetrations are desired or the tip of the microwire recording electrode is insulated as a result of gliomatosis. With minor modification, this technique can be used for single unit recording virtually anywhere along the supra-segmental neuraxis. Technical aspects of this procedure, together with details of design and fabrication of implantable devices, chronic instrumentation procedure, and potentials for other chronic applications, are discussed.