Spinal VGLUT3 lineage neurons drive visceral mechanical allodynia but not visceromotor reflexes

Abstract

Visceral pain is among the most prevalent and bothersome forms of chronic pain, but their transmission in the spinal cord is still poorly understood. Here we used a focal colorectal distention (fCRD) method to drive visceromotor responses (VMRs) plus affective pain-indicative aversive learning. We first found that spinal CCK neurons were necessary for noxious fCRD to drive both VMRs and aversion. We next showed that spinal VGLUT3 neurons mediate affective visceral allodynia, whose ablation caused loss of aversion evoked by low-intensity fCRD in mice with gastrointestinal (GI) inflammation or spinal circuit disinhibition. Importantly, these neurons are dispensable for driving VMRs. Anatomically, VGLUT3 neurons send projection to the parabrachial nuclei, whose photoactivation sufficiently generated aversion in mice with GI inflammation. Our studies suggest the presence of different spinal substrates that transmit nociceptive versus affective dimensions of visceral sensory information.