Reward effect of flubromazolam and its underlying neural circuit mechanism

Flubromazolam (Flub) is a novel psychoactive substance of benzodiazepines and the mechanism underlying its addiction still remains elusive. This study investigated the reward effect of Flub using conditioned place preference (CPP) mouse model. The neuronal activity was evaluated by c-Fos expression, and the neural circuit was tracked by virus tracing. This study also investigated the regulatory effect of neural circuits on Flub-induced reward effects through chemogenetic approach. The results showed that, at the dose of 3 mg/kg, Flub significantly increased CPP score and c-Fos expression in dopaminergic (DA) neurons of ventral tegmental area (VTA). Inhibition of VTA dopaminergic neuron activity dramatically decreased Flub-induced CPP score. Virus tracing verified GABAergic neuronal projection of medial rostrum tegmental nucleus (RMTg) to VTA dopaminergic neurons. Activation of RMTg^GABA→VTA^DA circuit or blockade of benzodiazepine receptors (BZR) in RMTg significantly decreased Flub-induced CPP score. These results indicate that Flub produced reward effect via BZR-mediated RMTg^GABA→VTA^DA circuit.