Distinct thalamocortical circuits underlie allodynia induced by tissue injury and by depression-like states.

In humans, tissue injury and depression can both cause pain hypersensitivity, but whether this involves distinct circuits remains unknown. Here, we identify two discrete glutamatergic neuronal circuits in male mice: a projection from the posterior thalamic nucleus (POGlu) to primary somatosensory cortex glutamatergic neurons (S1Glu) mediates allodynia from tissue injury, whereas a pathway from the parafascicular thalamic nucleus (PFGlu) to anterior cingulate cortex GABA-containing neurons to glutamatergic neurons (ACCGABA→Glu) mediates allodynia associated with a depression-like state. In vivo calcium imaging and multi-tetrode electrophysiological recordings reveal that POGlu and PFGlu populations undergo different adaptations in the two conditions. Artificial manipulation of each circuit affects allodynia resulting from either tissue injury or depression-like states, but not both. Our study demonstrates that the distinct thalamocortical circuits POGlu→S1Glu and PFGlu→ACCGABA→Glu subserve allodynia associated with tissue injury and depression-like states, respectively, thus providing insights into the circuit basis of pathological pain resulting from different etiologies.

A somatosensory cortex input to the caudal dorsolateral striatum controls comorbid anxiety in persistent pain.

Chronic pain and anxiety symptoms are frequently encountered clinically, but the neural circuit mechanisms underlying the comorbid anxiety symptoms in pain (CASP) in context of chronic pain remain unclear. Using viral neuronal tracing in mice, we identified a previously unknown pathway whereby glutamatergic neurons from layer 5 of the hindlimb primary somatosensory cortex (S1) (Glu), a well-known brain region involved in pain processing, project to GABAergic neurons in the caudal dorsolateral striatum (GABA). In a persistent inflammatory pain model induced by complete Freund's adjuvant injection, enhanced excitation of the Glu→GABA pathway was found in mice exhibiting CASP. Reversing this pathway using chemogenetic or optogenetic approaches alleviated CASP. In addition, the optical activation of Glu terminals in the cDLS produced anxiety-like behaviors in naive mice. Overall, the current study demonstrates the putative importance of a novel Glu→GABA pathway in controlling at least some aspects of CASP.