Cardiovascular changes during arousal elicited by stimulation of amygdala, hypothalamus and locus coeruleus

Experiments were performed in chronically operated cats first awake and thereafter anesthetized with pentobarbitone, 16-20 mg/kg i.v. Stimulation of the central amygdala in awake cats elicited an arousal reaction seen in cortical and hippocampal EEG, and in muscle activity of dorsal neck muscles. Concomitantly therewith were autonomic system reactions resulting in a decrease in aortic blood flow distal to the renal arteries, an increase in arterial blood pressure, a tachycardia during, and a short-lasting bradycardia at the end of stimulation. In slightly anesthetized cats the cardiovascular reactions were found to be qualitatively similar. If the postero-lateral hypothalamus or the locus coeruleus complex were stimulated in cats first awake and thereafter anesthetized, similar arousal reactions and similar cardiovascular changes were obtained as with amygdaloid stimulations. However, the onset and magnitude of the response were more abrupt and more marked than those obtained by amygdaloid stimulations. Recordings of single unit activity within the central amygdala during spontaneously occurring changes in the level of arousal showed that amygdaloid units (n = 10) discharged at a rate of 7-14 impulses/sec during wakefulness whereas during slow wave sleep (n = 5) the discharge was only 2-9 impulses/sec. The hypothesis is put forward that the amygdala integrates behavioral and cardiovascular changes during arousal.