Distinct Roles of P2X Receptors in Modulating Glutamate Release at Different Primary Sensory Synapses in Rat Spinal Cord

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Abstract
Using spinal cord slice preparations and patch-clamp recordings in lamina II and lamina V regions, we tested a hypothesis that P2X receptor subtypes differentially modulate glutamate release from primary afferent terminals innervating different sensory regions. We found that activation of P2X receptors by α,β-methylene-ATP increased glutamate release onto >80% of DH neurons in both lamina regions. However, two distinct types of modulation, a transient and a long-lasting enhancement of glutamate release were observed. In lamina II recordings, >70% of the modulation was transient. In contrast, P2X receptor-mediated modulation was always long-lasting in lamina V. Pharmacologically, both transient and long-lasting types of modulation were blocked by 10 μM pyridxal-phospahte-6-azophenyl-2′,4′-disulphonic acid tetrasodium, a broad-spectrum P2X receptor antagonist. Transient modulation was not observed in the presence of 1 μM trinitrophenyl-ATP (TNP-ATP), a subtype-selective P2X receptor antagonist, suggesting that homomeric P2X3receptors may be involved in the transient modulation in lamina II. The long-lasting modulation remained in the presence of 1 μM TNP-ATP. Selective removal of P2X3-expressing afferent terminals by the targeting toxin saporin-conjugated isolectin B4 or surgical removal of superficial DH did not affect P2X receptor-mediated long-lasting modulation in lamina V. Taken together, these results suggest that P2X receptor subtypes play distinct roles in sensory processing in functionally different sensory regions.