Data from: Dopamine subsystems that track internal states

Food and water are rewarding in part because they satisfy our internal
needs. Dopaminergic neurons in the ventral tegmental area (VTA)
are activated by gustatory rewards, 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 the 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 rerouted 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.