CRHergic projections from the central amygdala to the parafascicular nucleus of the thalamus promote nociceptive hypersensitivity and anxiety-like behaviors in mice

Neuropathic pain is frequently accompanied by anxiety and other negative affective states, yet the neural mechanisms linking persistent sensory hypersensitivity to affective dysfunction remain incompletely understood. The parafascicular nucleus of the thalamus (PF) participates in nociceptive and affective processing, but the contribution of corticotropin-releasing hormone (CRH) signaling within the PF and the identity of its upstream CRHergic input remain unclear. We investigated whether CRH-expressing neurons in the central amygdala (CeA CRH neurons) regulate neuropathic pain and anxiety-like behaviors through projections to the PF and whether PF CRH receptor signaling contributes to this process. A spared nerve injury (SNI) mouse model was combined with in vivo fiber photometry, RNAscope, anatomical and monosynaptic tracing, local pharmacological manipulation, chemogenetic and optogenetic approaches, and behavioral assays. Mechanical, cold, and heat nociceptive responses and anxiety-like behaviors were assessed under baseline and neuropathic pain conditions. CeA CRH neurons were activated by nociceptive stimulation and were predominantly GABAergic. Manipulation of these neurons revealed a causal contribution to mechanical hypersensitivity, cold allodynia, and anxiety-like behaviors. Anatomical tracing further demonstrated that CeA CRH neurons project to the PF and provide monosynaptic input to vesicular glutamate transporter 2 (VGLUT2)-expressing PF neurons. Within the PF, CRHR1 transcripts were prominently detected and largely associated with VGLUT2-positive neurons, whereas CRHR2 expression was comparatively limited. Intra-PF administration of corticotropin-releasing factor (CRF) or a CRHR1 agonist enhanced mechanical and cold nociceptive responses without altering heat nociception. Consistently, selective activation of the CeA CRH -PF pathway under baseline conditions promoted mechanical hypersensitivity, cold allodynia, and anxiety-like behaviors, whereas pathway inhibition in SNI mice attenuated sensory hypersensitivity and anxiety-like behaviors. These findings identify a CeA CRH -PF circuit that contributes to both sensory and affective abnormalities associated with neuropathic pain. The convergence of anatomical and pharmacological evidence further suggests that CRHR1-related signaling in PF glutamatergic neurons represents a potential downstream receptor substrate for CRHergic modulation. This limbic-thalamic pathway provides a circuit framework for understanding the coupling of persistent pain with negative affect. Not applicable.