Chronic augmentation of endocannabinoid levels persistently increases dopaminergic encoding of reward cost and motivation

Motivational deficits characterized by an unwillingness to overcome effortful costs are a common feature of neuropsychiatric and neurological disorders that are insufficiently understood and treated. Dopamine (DA) signaling in the nucleus accumbens (NAc) facilitates goal-seeking, but how NAc DA release encodes motivationally-salient stimuli to influence effortful investment is not clear. Using fast-scan cyclic voltammetry (FSCV) in male and female mice, we find that NAc DA release diametrically responds to cues signaling increasing cost of reward, while DA release to the reward itself is unaffected by its cost. Because endocannabinoid (eCB) signaling facilitates goal-seeking and NAc DA release, we further investigated whether repeated augmentation of the eCB 2-arachidonoylglycerol (2-AG) with a low dose of a monoacylglycerol lipase (MAGL) inhibitor facilitates motivation and DA signaling without the development of tolerance. We find that chronic MAGL treatment stably facilitates goal-seeking and DA encoding of prior reward cost, providing critical insight into the neurobiological mechanisms of a viable treatment for motivational deficits.

Significance StatementDecades of work has established a fundamental role for dopamine neurotransmission in motivated behavior and cue-reward learning, but how dopaminergic encoding of cues associates with motivated action has remained unclear. Specifically, how dopamine neurons signal future and prior reward cost, and whether this can be modified to influence motivational set points is not known. The current study provides important insight into how dopamine neurons encode motivationally-relevant stimuli to influence goal-directed action and supports cannabinoid-based therapies for treatment of motivational disorders.