Single-unit and polygraphic recordings associated with systemic or local pharmacology: a multi-purpose stereotaxic approach for the awake, anaesthetic-free, and head-restrained rat

In order to avoid any artifactual pharmacological interferences with anaesthetic agents, a procedure has been developed for working on the awake, anaesthetic-free rat in a head-restrained condition. It allows, on the same animal and over several consecutive days, single-unit recordings in combination with systemic or local pharmacology (microiontophoresis or micropressure ejections), as well as monitoring vigilance states via the electroencephalogram and the electromyogram. After the cementing of a special "U"-shaped device on its skull under general anaesthesia, the animal is progressively habituated to stay daily, for several hours, under a painless corresponding stereotaxic restraint. This system can be easily adapted to different stereotaxic frames and, because of its spatial flexibility for targetting the desired rostrocaudal or lateral positions, allows access to a large number of cerebral structures. Experiments performed on Globus Pallidus, Substantia Nigra, and Locus Coeruleus neurons, combining the different possibilities of this system, are reported. They demonstrate, on the awake anaesthetic-free head-restrained rat, and under suitable ethical conditions, the feasibility of single-unit recordings of identified neurons associated with the study of their pharmacological reactivity after systemic or local drug administrations without any other drug interferences, and in physiologically relevant conditions such as the spontaneous alternance of vigilance states.