With the exception of P2X7R that is only activated by high concentration of ATP (hundreds of μM), other P2X receptor subtypes are usually activated at high nM to low μM ATP concentration.10,11. In the CNS, P2XRs participate in modulation of neurotransmission, neuron-glia communication, inflammation, and apoptosis.136-139 Adenosine 5′-triphosphate released under physiological conditions modulate synaptic plasticity by acting on P2X receptors via Ca2+-dependent interaction with the NMDA receptors that facilitate LTP in the hippocampus.140 In general, overexpression of the P2X3, P2X4, and P2X7 receptors have been detected in CNS disorders and their antagonists could potentially be useful therapies for the treatment of CNS diseases including neurodegeneration and brain injuries.6,136,141 Among subtypes of the P2XRs, P2X7R has been the focus of many studies as a therapeutic target for treating brain disorders.142 Herein, we focus on 3, P2X3, P2X4 and P2X7, receptors and review their existing PET radioligands.
