Identification of Spinal Circuits Transmitting and Gating Mechanical Pain

Pain information processing in the spinal cord has been postulated to rely on nociceptive transmission (T) neurons receiving inputs from nociceptors and A beta mechanoreceptors, with A beta inputs gated through feed-forward activation of spinal inhibitory neurons (INs). Here, we used intersectional genetic manipulations to identify these critical components of pain transduction. Marking and ablating six populations of spinal excitatory and inhibitory neurons, coupled with behavioral and electrophysiological analysis, showed that excitatory neurons expressing somatostatin (SOM) include T-type cells, whose ablation causes loss of mechanical pain. Inhibitory neurons marked by the expression of dynorphin (Dyn) represent INs, which are necessary to gate A beta fibers from activating SOM+ neurons to evoke pain. Therefore, peripheral mechanical nociceptors and A beta mechanoreceptors, together with spinal SOM+ excitatory and Dyn(+) inhibitory neurons, form a microcircuit that transmits and gates mechanical pain.