A Central Amygdala Input to the Parafascicular Nucleus Controls Comorbid Pain in Depression

While comorbid pain in depression (CP) occurs at a high rate worldwide, the neural connections underlying the core symptoms of CP have yet to be elucidated. Here, we define a pathway whereby GABAergic neurons from the central nucleus of the amygdala (GABA(CeA)) project to glutamatergic neurons in the parafascicular nucleus (Glu(PF)). These Glu(PF) neurons relay directly to neurons in the second somatosensory cortex (S2), a well-known area involved in pain signal processing. Enhanced inhibition of the GABA(CeA) -> Glu(PF) -> S2 pathway is found in mice exhibiting CP symptoms. Reversing this pathway using chemogenetic or optogenetic approaches alleviates CP symptoms. Together, the current study demonstrates the putative importance of the GABA(CeA) -> Glu(PF )-> S2 pathway in controlling at least some aspects of CP.