Satiety controls behavior in Hydra through an interplay of pre-enteric and central nervous system-like neuron populations

Hunger and satiety can have an influence on decision-making, sensory processing, and motor behavior by altering the internal state of the brain. This process necessitates the integration of peripheral sensory stimuli into the central nervous system. Here, we show how animals without a central nervous system such as the cnidarian Hydra measure and integrate satiety into neuronal circuits and which specific neuronal populations are involved. We demonstrate that this simple nervous system, previously referred to as diffuse, has an endodermal subpopulation (N4) similar to the enteric nervous system (feeding-associated behavior) and an ectodermal population (N3) that performs central nervous system-like functions (physiology/motor). This view of a supposedly simple nervous system could open an important window into the origin of more complex nervous systems. [Display omitted] •Satiety controls behavior patterns in the ancestral metazoan Hydra•Two neuronal populations are responsible for behavioral changes•A pre-enteric-like population functions together with a central nervous-like subpopulation Giez et al. demonstrate that satiety in the ancestral metazoan Hydra is controlled by two distinct neuronal subpopulations and affects behavioral patterns. Both subpopulations show either pre-enteric- or central nervous system-like functions. The study contributes to our understanding of the evolution of the nervous system.