Negative feedback control of hunger circuits by the taste of food.

The rewarding taste of food is critical for motivating animals to eat, but whether taste has a parallel function in promoting meal termination is not well understood. Here we show that hunger-promoting AgRP neurons are rapidly inhibited during each bout of ingestion by a signal linked to the taste of food. Blocking these transient dips in activity via closed-loop optogenetic stimulation increases food intake by selectively delaying the onset of satiety. We show that upstream leptin receptor-expressing neurons in the dorsomedial hypothalamus (DMHLepR) are tuned to respond to sweet or fatty tastes and exhibit time-locked activation during feeding that is the mirror image of downstream AgRP cells. These findings reveal an unexpected role for taste in the negative feedback control of ingestion. They also reveal a mechanism by which AgRP neurons, which are the primary cells that drive hunger, are able to influence the moment-by-moment dynamics of food consumption.

Dopamine subsystems that track internal states.

Food and water are rewarding in part because they satisfy our internal needs1,2. Dopaminergic neurons in the ventral tegmental area (VTA) are activated by gustatory rewards3-5, but how animals learn to associate these oral cues with the delayed physiological effects of ingestion is unknown. Here we show that individual dopaminergic neurons in the VTA respond to detection of nutrients or water at specific stages of ingestion. A major subset of dopaminergic neurons tracks changes in systemic hydration that occur tens of minutes after thirsty mice drink water, whereas different dopaminergic neurons respond to nutrients in the gastrointestinal tract. We show that information about fluid balance is transmitted to the VTA by a hypothalamic pathway and then re-routed to downstream circuits that track the oral, gastrointestinal and post-absorptive stages of ingestion. To investigate the function of these signals, we used a paradigm in which a fluid's oral and post-absorptive effects can be independently manipulated and temporally separated. We show that mice rapidly learn to prefer one fluid over another based solely on its rehydrating ability and that this post-ingestive learning is prevented if dopaminergic neurons in the VTA are selectively silenced after consumption. These findings reveal that the midbrain dopamine system contains subsystems that track different modalities and stages of ingestion, on timescales from seconds to tens of minutes, and that this information is used to drive learning about the consequences of ingestion.

Genetic Identification of Vagal Sensory Neurons That Control Feeding.

Energy homeostasis requires precise measurement of the quantity and quality of ingested food. The vagus nerve innervates the gut and can detect diverse interoceptive cues, but the identity of the key sensory neurons and corresponding signals that regulate food intake remains unknown. Here, we use an approach for target-specific, single-cell RNA sequencing to generate a map of the vagal cell types that innervate the gastrointestinal tract. We show that unique molecular markers identify vagal neurons with distinct innervation patterns, sensory endings, and function. Surprisingly, we find that food intake is most sensitive to stimulation of mechanoreceptors in the intestine, whereas nutrient-activated mucosal afferents have no effect. Peripheral manipulations combined with central recordings reveal that intestinal mechanoreceptors, but not other cell types, potently and durably inhibit hunger-promoting AgRP neurons in the hypothalamus. These findings identify a key role for intestinal mechanoreceptors in the regulation of feeding.