Distinct nucleus accumbens neural pathways underlie separate behavioral features of chronic pain and comorbid depression.

The comorbidity of depressive symptoms in chronic pain has been recognized as a key health issue. However, whether discrete circuits underlie behavioral subsets of chronic pain and comorbid depression has not been addressed. Here, we report that dopamine 2 (D2) receptor-expressing medium spiny neurons in the nucleus accumbens medial shell (mNAcSh) mediate pain hypersensitivity and depression-like behaviors in mice after nerve injury. Two separate neural pathways mediate different symptoms. The glutamatergic inputs from the anteromedial thalamic nucleus to mNAcSh D2 neurons that innervated orexin-expressing neurons in the lateral hypothalamic area contributed to pain regulation. In contrast, the lateral septum GABAergic inputs to mNAcSh D2 neurons that disinhibit the ventral pallidum glutamatergic neurons mediated depression-like behaviors. These findings indicate the functional significance of heterogeneous mNAcSh D2 neurons and their neural pathways, providing a perspective for symptom-specific treatments of chronic pain and comorbid depression.