Distinct parafascicular neuronal ensembles mediate the sensory and affective dimensions of trigeminal neuralgia.

Trigeminal neuralgia (TN) is a severe orofacial pain disorder accompanied by anxiety, yet its central mechanisms remain elusive. Analysis of human functional MRI data identified the parafascicular nucleus (PF) as a candidate region. Using a TN mouse model, we uncovered 2 spatially and functionally distinct PF neuronal ensembles that separately encoded sensory and affective dimensions of pain. One population received inhibitory input from GABAergic neurons in the oral spinal trigeminal nucleus (Sp5O) and mediated nociception. The second population, driven by a glutamatergic Sp5O-lateral parabrachial nucleus (lPBN)-PF pathway, encoded pain-related anxiety. The engagement of the anxiety-encoding ensemble lagged behind that of the pain-encoding ensemble, with a shorter delay in females. Single-nucleus RNA sequencing identified Col25a1 and Syn2 as markers of the anxiety-encoding ensemble. Notably, this population, localized in the medial PF, formed a reciprocal lPBN-mPF-lPBN excitatory feedback loop that sustained affective pain. These findings positioned PF as a key node linking pain and emotion in TN.