TRPV1-lineage somatosensory fibers communicate with taste neurons in the mouse parabrachial nucleus

Abstract

Trigeminal neurons supply somatosensation to craniofacial tissues. In mouse brain, ascending projections from medullary trigeminal neurons arrive at taste neurons in the autonomic parabrachial nucleus, suggesting taste neurons participate in somatosensory processing. However, the genetic cell types that support this convergence were undefined. Using Cre-directed optogenetics and in vivo neurophysiology in anesthetized mice of both sexes, here we studied whether TRPV1-lineage nociceptive and thermosensory fibers are primary neurons that drive trigeminal circuits reaching parabrachial taste cells. We monitored spiking activity in individual parabrachial neurons during photoexcitation of the terminals of TRPV1-lineage fibers that arrived at the dorsal spinal trigeminal nucleus pars caudalis, which relays orofacial somatosensory messages to the parabrachial area. Parabrachial neural responses to oral delivery of taste, chemesthetic, and thermal stimuli were also recorded. We found that optical excitation of TRPV1-lineage fibers frequently stimulated traditionally defined taste neurons in lateral parabrachial nuclei. The tuning of neurons across diverse tastes associated with their sensitivity to excitation of TRPV1-lineage fibers, which only sparingly engaged neurons oriented to preferred tastes like sucrose. Moreover, neurons that responded to photostimulation of TRPV1-lineage afferents showed strong responses to temperature including noxious heat, which predominantly excited parabrachial bitter taste cells. Multivariate analyses revealed the parabrachial confluence of TRPV1-lineage signals with taste captured sensory valence information shared across aversive gustatory, nociceptive, and thermal stimuli. Our results reveal that trigeminal fibers with defined roles in thermosensation and pain communicate with parabrachial taste neurons. This multisensory convergence supports dependencies between gustatory and somatosensory hedonic representations in the brain.