Neural Control and Modulation of Thirst, Sodium Appetite, and Hunger

Abstract

The function of central appetite neurons is instructing animals to ingest specific nutrient factors that the body needs. Emerging evidence suggests that individual appetite circuits for major nutrientswater, sodium, and food-operate on unique driving and quenching mechanisms. This review focuses on two aspects of appetite regulation. First, we describe the temporal relationship between appetite neuron activity and consumption behaviors. Second, we summarize ingestion-related satiation signals that differentially quench individual appetite circuits. We further discuss how distinct appetite and satiation systems for each factor may contribute to nutrient homeostasis from the functional and evolutional perspectives.

Neuromodulation Exerts Feedback and Feedforward Control of Action Selection

“…A salient feature of many survival circuits-first noted by Hess in his seminal studies of the mammalian hypothalamus (Hess, 1949)-is that their electrical stimulation evokes robust and rapid expression of consummatory behaviors. For homeostatic circuits, the sites stimulated to evoke such behavior are often interoceptive neurons that signal using neuromodulators (for review see Augustine et al, 2020). In the case of the BSEG, neuromodulatory signaling by Bursicon is required for behavioral induction , which, as we show here, is not time-locked to BSEG stimulation-typically starting only after a five minute stimulus-and is mimicked by acute elevation of the RK second messenger, cAMP, in RK neurons.…”

“…The search-or-expand decision of Drosophila lacks the complexity of decisions mediated by many survival circuits, such as those in mammals that regulate feeding, drinking, and salt appetite. These circuits are additionally regulated by learned cues, negative-feedback, and anticipatory-feedforward termination signals (Augustine et al, 2020;Sternson and Eiselt, 2017).…”

Feeding state functionally reconfigures a sensory circuit to drive thermosensory behavioral plasticity

“…Neuromodulation is a major mechanism driving satiety state-dependent behavioral plasticity. Modulation of interoceptive hypothalamic circuits by circulating hormones regulates appetitive behaviors in satiated and starved animals ( Andermann and Lowell, 2017 ; Augustine et al, 2020 ). In food-deprived Drosophila , increased attraction and decreased repulsion to appetitive and aversive stimuli, respectively, are mediated via parallel modulation of attractive and aversive chemosensory circuits by diverse neuromodulators [eg.…”

Feeding state functionally reconfigures a sensory circuit to drive thermosensory behavioral plasticity

“…A particularly well-studied internal state is that of satiety. Wellfed animals exhibit distinct responses to environmental cues compared to animals that have been food-deprived (Augustine et al, 2020;Kim et al, 2017). Starvation not only modulates responses to food-related chemical cues, but also generally and broadly regulates animal behaviors (Dietrich et al, 2015;Rengarajan et al, 2019;Sayin et al, 2019;Trent et al, 1983;Yang et al, 2015).…”

“…Neuromodulation is a major mechanism driving satiety statedependent behavioral plasticity. Modulation of interoceptive hypothalamic circuits by circulating hormones regulates appetitive behaviors in satiated and starved animals (Andermann and Lowell, 2017;Augustine et al, 2020). In food-deprived Drosophila, increased attraction and decreased repulsion to appetitive and aversive stimuli, respectively, are mediated via parallel modulation of attractive and aversive chemosensory circuits by diverse neuromodulators [eg.…”