Descending GABAergic Neurons of the RVM That Mediate Widespread Bilateral Antinociception

Abstract

SummaryNeurons projecting from the rostral ventromedial medulla (RVM) to the spinal dorsal horn are critical elements of endogenous pain control systems. Here, we describe a GABA/glycinergic pathway that predominantly innervates the superficial dorsal horn. Anatomical and optogenetic tracing of these neurons from a single unilateral site of the lumbar spinal cord indicated that these neurons give rise to a dense bilateral innervation of the spinal cord along its entire rostrocaudal axis. Chemogenetic activation of these neurons caused a bilateral and widespread reduction in heat, cold, and mechanical sensitivity, while their silencing with tetanus toxin induced allodynia and spontaneous pain-like aversive behaviors. Consistent with a continuous role in the prevention of spontaneous pain, many descending RVM GABAergic neurons were found to be tonically active. This pathway may therefore be relevant for widespread conditioned analgesia, while its dysfunction may underlie chronic widespread pain syndromes.