Calretinin-Positive Neurons in Central Medial Thalamus Drive Nociception and Anxiety via Projections to Anterior Insular Cortex in male mice.

The central medial thalamic nucleus (CM), a key component of the thalamic intralaminar nuclei, receives nociceptive inputs from the lateral parabrachial nucleus and is implicated in pain processing. However, the specific neuronal subtypes and downstream pathways that mediate these functions remain poorly defined. Here, we combined tract tracing, immunofluorescence, in situ hybridization, chemogenetics, fiber photometry, and behavioral tests to investigate the role of calretinin-positive (CR+) neurons in the CM (CMCR+) and their projections to the anterior insular cortex (aIC) in nociceptive transmission. Our results demonstrated that activation of the CM promotes both pain and anxiety-like behaviors. The CM harbors a substantial population of excitatory CR+ neurons that are activated by nociceptive stimulati, as indicated by Fos expression and elevated calcium signals. Chemogenetic activation of CMCR+ neurons in control mice induced mechanical, cold, and thermal hypersensitivity, along with anxiety-like behaviors. Conversely, chemogenetic inhibition of these neurons in a CFA-induced model of chronic inflammatory pain markly alleviated pain hypersensitivity and comorbid anxiety. Anatomical tracing revealed that CMCR+ neurons send dense projections to the aIC. Functional manipulation of the CMCR+-aIC pathway confirmed its critical role in nociceptive transmission and pain-related affect behaviors. Together, our results identify a thalamocortical circuit that mediates nociceptive signaling and affective comorbidity in chronic pain, highlighting CMCR+  neurons as a potential therapeutic target for treating refractory pain and its emotional components.