ABSTRACT
In the mammalian central nervous system, main groups of noradrenergic and serotonergic neurons are found within the locus coeruleus (LC) and the dorsal raphe nucleus (DRN), respectively. By means of their widespread projections throughout the entire brain, these monoaminergic neurons are thought to play crucial roles in a great variety of physiological and behavioral functions including sleep and wakefulness. Extracellular electrophysiological recordings in freely moving rats and cats have shown that LC noradrenergic and DRN serotonergic neurons fire tonically during wakefulness (W), decrease their activity during slow-wave sleep (SWS), and are nearly quiescent during paradoxical sleep (PS). Iontophoretic applications during PS or SWS of bicuculline or strychnine induced a tonic firing in LC noradrenergic neurons. In addition, applications of bicuculline or strychnine during wakefulness induced a sustained increase in discharge rate. In addition to the lateral preoptic area, the lateral hypothalamic area, the periaqueductal gray, and the dorsal paragigantocellular nucleus provide substantial gamma-amino-butyric acid inputs to the DRN and LC.
