Purinergic P2X receptors presynaptically increase glutamatergic synaptic transmission in dorsolateral periaqueductal gray.

Purinergic P2X receptors have been reported to be present in regions of the midbrain periaqueductal gray (PAG). The purpose of this study was to determine the role of presynaptic P2X receptors in modulating excitatory and inhibitory synaptic inputs to the dorsolateral PAG (dl-PAG), which has abundant neuronal connections. First, whole cell voltage-clamp recording was performed to obtain excitatory and inhibitory postsynaptic currents (EPSCs and IPSCs) of the dl-PAG neurons. Our data show that alpha, beta-methylene ATP (a P2X receptor agonist), in the concentration of 50 microM, significantly increased the frequency of miniature EPSCs without altering the amplitude of miniature EPSCs in eight tested neurons. The effects were attenuated by PPADS, an antagonist to P2X receptors. Furthermore, alpha, beta-methylene ATP increased the amplitude of evoked EPSCs, and decreased the paired-pulse ratio of eEPSCs in ten neurons. In contrast, activation of P2X had no distinct effect on IPSCs. In addition, immunofluorescent methods demonstrate that P2X labeling was co-localized with a presynaptic marker, synaptophysin, in the dl-PAG. The results of the current study provide the first evidence indicating that P2X receptors facilitate glutamatergic synaptic transmission in the dl-PAG via presynaptic mechanisms.