AMYGDALOID CONTROL OF ALERTING AND BEHAVIORAL AROUSAL IN RATS - INVOLVEMENT OF SEROTONERGIC MECHANISMS

The role of 5-HT mechanisms in the amygdala in the modulation of sleep and arousal states and PGO waves was examined. Studies of the amygdal a suggest that it provides a neural mechanism by which emotionally-rel evant or significant stimuli may influence behavioral state and alerti ng mechanisms. The amygdala projects massively (via the central nucleu s) into brainstem regions involved in alerting and in the generation o f REM and PGO waves. Serotonergic innervation of the amygdala comes fr om DRN and to a lesser degree MRN. Microinjections of 5-HT into the am ygdala produced short-latency changes of state from NREM and REM with the effect being relatively greater in REM. Microinjections of the 5-H T antagonist, methysergide, increased sleep efficiency and increased P GO wave frequency in waking and NREM. These results demonstrate an imp ortant role for the amygdala in the control of behavioral state and al erting mechanisms and suggest that 5-HT exerts some of its regulatory effects via an influence on forebrain regions.