The extensively abused recreational drug (±)3,4-methylenedioxymethamphetamine (MDMA) has shown promise as an adjunct to psychotherapy for treatment-resistant psychiatric disease. It is unknown, however, whether the mechanisms underlying its prosocial therapeutic effects and abuse potential are distinct. We modeled both the prosocial and nonsocial drug reward of MDMA in mice and investigated the mechanism of these processes using brain region–specific pharmacology, transgenic manipulations, electrophysiology, and in vivo calcium imaging. We demonstrate in mice that MDMA acting at the serotonin transporter within the nucleus accumbens is necessary and sufficient for MDMA’s prosocial effect. MDMA’s acute rewarding properties, in contrast, require dopaminergic signaling. MDMA’s prosocial effect requires 5-HT1b receptor activation and is mimicked by d-fenfluramine, a selective serotonin-releasing compound. By dissociating the mechanisms of MDMA’s prosocial effects from its addictive properties, we provide evidence for a conserved neuronal pathway, which can be leveraged to develop novel therapeutics with limited abuse liability.

The dorsal raphe (DR) is a heterogeneous nucleus containing dopamine (DA), serotonin (5HT), γ-aminobutyric acid (GABA) and glutamate neurons. Consequently, investigations of DR circuitry require Cre-driver lines that restrict transgene expression to precisely defined cell populations. Here, we present a systematic evaluation of mouse lines targeting neuromodulatory cells in the DR. We find substantial differences in specificity between lines targeting DA neurons, and in penetrance between lines targeting 5HT neurons. Using these tools to map DR circuits, we show that populations of neurochemically distinct DR neurons are arranged in a stereotyped topographical pattern, send divergent projections to amygdala subnuclei, and differ in their presynaptic inputs. Importantly, targeting DR DA neurons using different mouse lines yielded both structural and functional differences in the neural circuits accessed. These results provide a refined model of DR organization and support a comparative, case-by-case evaluation of the suitability of transgenic tools for any experimental application.

No abstract

Dopamine (DA) release in the ventral and dorsal striatum has been linked to reward processing and motivation, but there are longstanding controversies about whether DA release in these key target structures primarily reflects costs or benefits, and how these signals vary with motivation. Here we apply behavioral economic principles to generate demand curves for rewards while directly measuring DA release in the nucleus accumbens (NAc) and dorsolateral striatum (DLS) via a genetically-encoded sensor. By independently varying costs and benefits, we reveal that DA release in both structures incorporates reward magnitude and sunk cost. Surprisingly, motivation was inversely correlated with reward-evoked DA release; the higher the motivation for rewards the lower the reward-evoked DA release. These relationships between DA release, cost and motivation remained identical when we used optogenetic activation of striatal DA inputs as a reward. Our results reconcile previous disparate findings by demonstrating that during operant tasks, striatal DA release simultaneously encodes cost, benefit and motivation but in distinct manners over different time scales.