Origins of arousal: roles for medullary reticular neurons.

The existence of a primitive CNS function involved in the activation of all vertebrate behaviors, generalized arousal (GA), has been proposed. Here, we provide an overview of the neuroanatomical, neurophysiological and molecular properties of reticular neurons within the nucleus gigantocellularis (NGC) of the mammalian medulla, and propose that the properties of these neurons equip them to contribute powerfully to GA. We also explore the hypothesis that these neurons may have evolved from the Mauthner cell in the medulla of teleost fish, although NGC neurons have a wider range of action far beyond the specific escape network served by Mauthner cells. Understanding the neuronal circuits that control and regulate GA is central to understanding how motivated behaviors such as hunger, thirst and sexual behaviors arise.