The Raphe Dopamine System: Roles in Salience Encoding, Memory Expression, and Addiction

Dopamine (DA) neurons of the dorsal raphe nucleus (DRN) were traditionally viewed as an extension of the ventral tegmental area (VTA) DA population. While the VTA DA population is known to play important roles in reward processing, emerging evidence now supports the view that DRN DA neurons are a specialized midbrain DA subsystem that performs distinct functions in parallel to the VTA DA population. Recent studies have shed new light on the roles of DRN DA neurons in encoding incentive salience and in regulating memory expression and arousal. Here, we review recent findings using mouse models about the physiology and behavioral functions of DRN DA neurons, highlight the engagement of DRN DA neurons and their upstream circuits in opioid addiction, and discuss emerging lines of investigation that reveal multifaceted heterogeneity among DRN DA neurons.