Abstract
Sensitization in spinal cord is believed to underlie the induction of abnormal pain sensitivity. Recently, purinergic receptors are shown to play important roles for hyperalgesia and allodynia. By optical recording of neuronal excitation in rat spinal cord slices with voltage dye, we analyzed actions of purinergic receptor agonists in the superficial dorsal horn. Excitation evoked by dorsal root stimulation of C fiber-activating strength was facilitated after the application of a P2X receptor agonist abmATP and a P2Y receptor agonist UTP. The long-term potentiation by abmATP was significantly inhibited by glial metabolism inhibitor monofluoro-acetic acid, evidence suggesting that abmATP acts via glial cells. In contrast, UTP facilitated presynaptic excitation recorded by anterograde labeling of primary afferent fibers with voltage dye. The facilitation was not observed in the presence of D-AP5 and CNQX, where excitatory synaptic transmission from afferents was blocked. UTP therefore acts on presynaptic elements via postsynaptic neurons. These results indicate that P2X and P2Y receptors sensitize pain pathway in the dorsal horn by acting two distinct mechanisms. Supported by the Grant-in-Aid from JSPS and a grant from Yazaki Memorial Foundation to KM. [Jpn J Physiol 55 Suppl:S171 (2005)]
