A brainstem pathway underlying vagal modulation of somatic pain and affective states

Vagus nerve stimulation (VNS) alleviates pain, yet the underlying neural mechanisms remain elusive. Furthermore, the caudal nucleus of the solitary tract (cNTS) receives vagal and somatic inputs, but how it transforms pain signals into behavior and how VNS modulates this processing remain unclear. Here we identified a population of cNTS neurons projecting to the periaqueductal gray (PAG) (cNTS^PAG) as a critical node for VNS-dependent suppression of pain and negative affect in mice. Optogenetic activation of cNTS^PAG neurons recapitulated pain behavior. These neurons exhibited modality-specific encoding of pain and predictive signals after learning. Inhibition of spinal input-defined cNTS^PAG neurons reduced mechanical, but not thermal, nociception. Notably, VNS selectively dampened pain-evoked cNTS^PAG activity by recruiting local inhibition and attenuated pain-evoked dopamine reductions in the nucleus accumbens through cNTS^PAG. Our findings establish a brainstem pathway with a previously unrecognized role in VNS modulation of pain and negative affect, providing insights for targeted neuromodulation in pain management.