Excitatory SST neurons in the medial paralemniscal nucleus control repetitive self-grooming and encode reward.

The use of body-focused repetitive behaviors (BFRBs) is conceptualized as a means of coping with stress. However, the neurological mechanism by which repetitive behaviors affect anxiety regulation is unclear. Here, we identify that the excitatory somatostatin-positive neurons in the medial paralemniscal nucleus (MPL neurons) in mice promote self-grooming and encode reward. MPL neurons display prominent grooming-related neuronal activity. Loss of function of MPL neurons impairs both self-grooming and post-stress anxiety alleviation. Activation of MPL neurons is rewarding and sufficient to drive reinforcement by activating dopamine (DA) neurons in the ventral tegmental area (VTA) and eliciting dopamine release. The neuropeptide SST facilitates the rewarding impact of MPL neurons. MPL neuron-mediated self-grooming is triggered by the input from the central amygdala (CeA). Our study reveals a dual role of CeA-MPL-VTA circuit in self-grooming and post-stress anxiety regulation and conceptualizes MPL neurons as an interface linking the stress and reward systems in mice.