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Background and Purpose The beat-by-beat fluctuation (dynamics) of heart rate (HR) depends on centrally mediated control of the autonomic nervous system (ANS) reflecting the physiological state of an organism. 5-HT

The detailed knowledge of the neural substrates underlying cardiovascular adjustments, in particular to learned (conditioned) and innate (unconditioned) threatening conditions, is important for the understanding of the brain-heart interaction. Commonly, various aversive stimuli are used to investigate fear-induced autonomic adjustments. In general, the observed strong autonomic response to any stressor results in parasympathetic withdrawal and concomitant sympathetic activation, resulting in profound heart rate and blood pressure increase in many species. An improved knowledge of the functional role of specific molecular signals in defined brain areas of the central autonomic network will contribute to a better understanding of mechanisms contributing to central autonomic dysregulation. This is particularly important for various affective disorders that show high comorbidity with cardiovascular disease potentially due to autonomic dysregulation. Thereby, emotionally challenging conditions can induce pathological states increasing the risk for cardiac mortality including sudden cardiac death.