Serotonergic mechanisms contributing to arousal and alerting

Abstract

Serotonin (5-HT) is implicated in the regulation of both behavioral arousal and a brainstem alerting system that operates in wakefulness and in rapid eye movement sleep (REM). Activation of the brainstem alerting system is marked by the presence of ponto-geniculooccipital (PGO) waves that occur in association with orienting in wakefulness and spontaneously in REM. Local application of serotonergic agents into REM and PGO wave regulatory regions can alter REM, but there is conflicting evidence as to whether 5-HT in the brainstem can independently influence PGO wave generation. A potential site of action of 5-HT outside the brainstem is the amygdala, which can influence arousal as well as neurobiological responses to novel and significant stimuli. The amygdala also modulates the occurrence and amplitude of PGO waves. We discuss the linkages between arousal and alerting systems and the role 5-HT may play in their regulation at brainstem and amygdalar sites. © 2008 Birkhäuser Verlag AG.