Context-Dependent Multiplexing by Individual VTA Dopamine Neurons.

Dopamine (DA) neurons of the VTA track cues and rewards to generate a reward prediction error signal during Pavlovian conditioning. Here we explored how these neurons respond to a self-paced, operant task in freely moving mice. The animal could trigger a reward-predicting cue by remaining in a specific location of an operant box for a brief time before moving to a spout for reward collection. VTA DA neurons were identified using DAT-Cre male mice that carried an optrode with minimal impact on the behavioral task. In vivo single-unit recordings revealed transient fast spiking responses to the cue and reward in correct trials, while for incorrect ones the activity paused, reflecting positive and negative error signals of a reward prediction. In parallel, a majority of VTA DA neurons simultaneously encoded multiple actions (e.g., movement velocity, acceleration, distance to goal, and licking) in sustained slow firing modulation. Applying a GLM, we show that such multiplexed encoding of rewarding and motor variables by individual DA neurons was only apparent while the mouse was engaged in the task. Downstream targets may exploit such goal-directed multiplexing of VTA DA neurons to adjust actions to optimize the task's outcome.SIGNIFICANCE STATEMENT VTA DA neurons code for multiple functions, including the reward prediction error but also motivation and locomotion. Here we show that about half of the recorded VTA DA neurons perform multiplexing: they exploit the phasic and tonic activity modes to encode, respectively, the cue/reward responses and motor parameters, most prominently when the mouse engages in a self-paced operand task. VTA non-DA neurons, by contrast, encode motor parameters regardless of task engagement.

Accumbal D1R Neurons Projecting to Lateral Hypothalamus Authorize Feeding.

Feeding satisfies metabolic need but is also controlled by external stimuli, like palatability or predator threat. Nucleus accumbens shell (NAcSh) projections to the lateral hypothalamus (LH) are implicated in mediating such feeding control, but the neurons involved and their mechanism of action remain elusive. We show that dopamine D1R-expressing NAcSh neurons (D1R-MSNs) provide the dominant source of accumbal inhibition to LH and provide rapid control over feeding via LH GABA neurons. In freely feeding mice, D1R-MSN activity reduced during consumption, while their optogenetic inhibition prolonged feeding, even in the face of distracting stimuli. Conversely, activation of D1R-MSN terminals in LH was sufficient to abruptly stop ongoing consumption, even during hunger. Direct inhibition of LH GABA neurons, which received input from D1R-MSNs, fully recapitulated these findings. Together, our study resolves a feeding circuit that overrides immediate metabolic need to allow rapid consumption control in response to changing external stimuli. VIDEO ABSTRACT.