Serotonergic dorsal raphe neurons cease firing by disfacilitation during paradoxical sleep

Using in vivo extracellular unit recordings combined with microdialysis infusion in the cat, we found that the cessation of discharge of presumed serotonergic dorsal raphe neurons during paradoxical sleep (PS) was completely blocked by either histamine or phenylephrine, an alpha(1) adrenoceptor agonist, but not by bicuculline, a GABA receptor antagonist. In addition, application of mepyramine, a specific H-1 histamine receptor antagonist, or prazosin, a specific alpha(1) adrenoceptor antagonist, suppressed the spontaneous discharge of raphe neurons during both quiet waking and sleep. The present data suggest that this cessation of dorsal raphe unit activity is caused by the mechanism of disfacilitation resulting from the cessation of discharge of norepinephrine- or histamine-containing neurons during PS. NeuroReport 11:3237-3241 (C) 2000 Lippincott Williams & Wilkins.