No abstract

Short-term central sensitization to pain temporarily increases the responsiveness of nociceptive pathways after peripheral injury. In dorsal horn neurons (DHNs), short-term sensitization can be monitored through the study of wind-up. Wind-up, a progressive increase in DHNs response following repetitive peripheral stimulations, depends on the post-synaptic L-type calcium channels. In the dorsal horn of the spinal cord, two L-type calcium channels are present, Cav1.2 and Cav1.3, each displaying specific kinetics and spatial distribution. In the present study, we used a mathematical model of DHNs in which we integrated the specific patterns of expression of each Cav subunits. This mathematical approach reveals that Cav1.3 is necessary for the onset of wind-up, whereas Cav1.2 is not and that synaptically triggered wind-up requires NMDA receptor activation. We then switched to a biological preparation in which we knocked down Cav subunits and confirmed the prominent role of Cav1.3 in both naive and spinal nerve ligation model of neuropathy (SNL). Interestingly, although a clear mechanical allodynia dependent on Cav1.2 expression was observed after SNL, the amplitude of wind-up was decreased. These results were confirmed with our model when adapting Cav1.3 conductance to the changes observed after SNL. Finally, our mathematical approach predicts that, although wind-up amplitude is decreased in SNL, plateau potentials are not altered, suggesting that plateau and wind-up are not fully equivalent. Wind-up and long-term hyperexcitability of DHNs are differentially controlled by Cav1.2 and Cav1.3, therefore confirming that short- and long-term sensitization are two different phenomena triggered by distinct mechanisms.