Spatiotemporal and anatomical analyses of P2X receptor-mediated neuronal and glial processing of sensory signals in the rat dorsal horn

Adenosine triphosphate in the dorsal horn acts on neuronal pre- and postsynaptic P2X receptors, especially in the deep layer, and astrocytes optimize the excitability, especially in the superficial layer. Extracellularly released adenosine triphosphate (ATP) modulates sensory signaling in the spinal cord. We analyzed the spatiotemporal profiles of P2X receptor-mediated neuronal and glial processing of sensory signals and the distribution of P2X receptor subunits in the rat dorsal horn. Voltage imaging of spinal cord slices revealed that extracellularly applied ATP (5–500 μM), which was degraded to adenosine and acting on P1 receptors, inhibited depolarizing signals and that it also enhanced long-lasting slow depolarization, which was potentiated after ATP was washed out. This post-ATP rebound potentiation was mediated by P2X receptors and was more prominent in the deep than in the superficial layer. Patch clamp recording of neurons in the superficial layer revealed long-lasting enhancement of depolarization by ATP through P2X receptors during the slow repolarization phase at a single neuron level. This depolarization pattern was different from that in voltage imaging, which reflects both neuronal and glial activities. By immunohistochemistry, P2X 1 and P2X 3 subunits were detected in neuropils in the superficial layer. The P2X 5 subunit was found in neuronal somata. The P2X 6 subunit was widely expressed in neuropils in the whole gray matter except for the dorsal superficial layer. Astrocytes expressed the P2X 7 subunit. These findings indicate that extracellular ATP is degraded into adenosine and prevents overexcitation of the sensory system, and that ATP acts on pre- and partly on postsynaptic neuronal P2X receptors and enhances synaptic transmission, predominantly in the deep layer. Astrocytes are involved in sensitization of sensory network activity more importantly in the superficial than in the deep layer.