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Developmental changes in P2X purinoceptors on glycinergic presynaptic nerve terminals projecting to rat substantia gelatinosa neurones

Il-Sung Jang, Jeong Seop Rhee, Hisahiko Kubota, Norihiko Akaike * and Norio Akaike

1. In mechanically dissociated rat spinal cord substantia gelatinosa (SG) neurones attached with native presynaptic nerve endings, glycinergic miniature inhibitory postsynaptic currents (mIPSCs) were recorded using nystatin perforated patch recording mode under voltage-clamp conditions. Under these conditions, it was tested whether the changes in P2X receptor subtype on the glycinergic presynaptic nerve terminals occur during postnatal development.
2. ATP facilitated glycinergic mIPSC frequency in a concentration-dependent manner through all developmental stages tested, whereas -methylene-ATP (-me-ATP) was only effective at later developmental stages.
3. -me-ATP-elicited mIPSC frequency facilitation was completely occluded in the Ca²⁺-free external solution, but it was not affected by adding 10^-4 M Cd²⁺.
4. -me-ATP still facilitated mIPSC frequency even in the presence of 10^-6 M thapsigargin, a Ca²⁺ pump blocker.
5. In later developmental stages, ATP-elicited presynaptic or postsynaptic responses were reversibly blocked by 10^-5 M pyridoxal-5-phosphate-6-azophenyl-2',4'-disulfonic acid (PPADS), but only partially blocked by 10^-7 M 2',3'-O-(2,4,6-trinitrophenyl)-ATP (TNP-ATP). However, -me-ATP-elicited presynaptic or postsynaptic responses were completely and reversibly blocked by either 10^-5 M PPADS or 10^-7 M TNP-ATP.
6. -me-ATP significantly reduced the evoked glycinergic IPSC amplitude in postnatal 28-30 day neurones, whereas it had no effect in 10-12 day neurones.
7. It was concluded that -me-ATP-sensitive P2X receptors were functionally expressed on the glycinergic presynaptic nerve terminals projecting to SG neurones in later developmental stages. Such developmental changes of presynaptic P2X receptor subtypes might contribute to synaptic plasticity such as the regulation of neuronal excitability and the fine controlling of the pain signal in spinal dorsal horn neurones.

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