Excitatory paraventricular thalamus–posterior insular cortex circuit mediates pain–anxiety comorbidity in diabetic neuropathy

Painful diabetic neuropathy (PDN) is frequently accompanied by anxiety, yet the neural circuit mechanisms associated with nociceptive hypersensitivity to affective dysfunction remain unclear. Here we combined brain-wide c-Fos mapping, viral tracing, in vivo fiber photometry, whole-cell recordings, and projection-specific opto/chemogenetics in a mouse model of streptozotocin-induced PDN to define a thalamo–cortex circuit for pain–anxiety comorbidity. Within the posterior insular cortex (pIC), CaMKIIα⁺ excitatory neurons were recruited in PDN mice with comorbid anxiety, exhibiting heightened neuronal excitability and enhanced excitatory synaptic input. Bidirectional chemogenetic modulation of pICCaMKIIα neurons oppositely regulated anxiety-like behavior and mechanical hypersensitivity without locomotor or glycemic confounds. Circuit mapping identified a monosynaptic excitatory projection from the paraventricular thalamus (PVT) to the pIC; PVTCaMKIIα neurons were hyperactive in PDN, and projection-defined manipulation of the PVTCaMKIIα to pICCaMKIIα pathway bidirectionally controlled the behavioral phenotypes. Cacna1c was upregulated in the PVT of PDN mice; its knockdown in pIC-projecting PVTCaMKIIα neurons attenuated both pain and anxiety-like behaviors. Together, these results delineate a thalamo–cortex excitatory pathway that couples nociceptive and affective dimensions of PDN and suggest that selective targeting of the PVTCaMKIIα to pICCaMKIIα circuit may provide coordinated relief of pain and anxiety-related symptoms.