It is known that stress powerfully alters pain, but its underlying mechanisms remain elusive. Here, we identified a circuit, locus coeruleus descending noradrenergic neurons projecting to the spinal dorsal horn (LC →SDH -NA neurons), that is activated by acute exposure to restraint stress and is required for stress-induced mechanical pain hypersensitivity in mice. Interestingly, the primary target of spinal NA released from descending LC →SDH -NAergic terminals causing the stress-induced pain hypersensitivity was α 1A -adrenaline receptors (α 1A Rs) in Hes5 -positive ( Hes5 + ) astrocytes located in the SDH, an astrocyte subset that has an ability to induce pain sensitization. Furthermore, activation of Hes5 + astrocytes reduced activity of SDH-inhibitory neurons (SDH-INs) that have an inhibitory role in pain processing. This astrocytic reduction of IN activity was canceled by an A 1 -adenosine receptor (A 1 R)-knockdown in SDH-INs, and the A 1 R-knockdown suppressed pain hypersensitivity caused by acute restraint stress. Therefore, our findings suggest that LC →SDH -NA neuronal signaling to Hes5 + SDH astrocytes and subsequent astrocytic reduction of SDH-IN activity are essential for mechanical pain facilitation caused by stress.
Kawanabe-Kobayashi et al. (Mon,) studied this question.