ATP is a known mediator of inflammatory and neuropathic pain. However, the mechanisms by which specific purinergic receptors contribute to chronic pain states are still poorly characterized. Here, we demonstrate that in response to peripheral nerve injury, P2X 4 receptors (P2X 4 R) are expressed de novo by activated microglia in the spinal cord. Using in vitro and in vivo models, we provide direct evidence that P2X 4 R stimulation leads to the release of BDNF from activated microglia and, most likely phosphorylation of the NR1 subunit of NMDA receptors in dorsal horn neurons of the spinal cord. Consistent with these findings, P2X4-deficient mice lack mechanical hyperalgesia induced by peripheral nerve injury and display impaired BDNF signaling in the spinal cord. Furthermore, ATP stimulation is unable to stimulate BDNF release from P2X 4 -deficient mice microglia in primary cultures. These results indicate that P2X 4 R contribute to chronic pain through a central inflammatory pathway. P2X 4 R might thus represent a potential therapeutic target to limit microglia-mediated inflammatory responses associated with brain injury and neurodegenerative disorders.
P2X 4 purinergic receptors are calcium-permeable, ATP-activated ion channels. In the CA1 area of the hippocampus, they are located at the subsynaptic membrane somewhat peripherally to AMPA receptors. The possible role of P2X 4 receptors has been difficult to elucidate because of the lack of selective antagonists. Here we report the generation of a P2X 4 receptor knock-out mouse and show that long-term potentiation (LTP) at Schaffer collateral synapses is reduced relative to that in wild-type mice. Ivermectin, which selectively potentiates currents at P2X 4 , was found to increase LTP in wild-type mice but had no effect in P2X 4 knock-out mice. We suggest that calcium entry through subsynaptic P2X 4 receptors during high-frequency stimulation contributes to synaptic strengthening.
The nucleus accumbens (NAc) is an important cerebral area involved in reward and spatial memory (Pennartz et al., 1994), but little is known about synaptic plasticity in this region. Here, electron microscopy revealed that, in the NAc, metabotropic glutamate receptors 2/3 (mGlu2/3) immunostaining was essentially associated with axonal terminals and glial processes, whereas postsynaptic dendrites and neuronal cell bodies were unstained. Electrophysiological techniques in the NAc slice preparation demonstrated that activation of mGlu2/3 with synaptically released glutamate or specific exogenous agonist, such as LY354740 (200 nm, 10 min), induced long-term depression of excitatory synaptic transmission (mGlu2/3-LTD). Tetanic-LTD and pharmacological mGlu2/3-LTD occluded each other, suggesting common mechanisms. The mGlu2/3-LTD did not require synaptic activity but depended on the cAMP-protein kinase A cascade. Selective inhibition of P/Q-type Ca(2+) channels with omega-agatoxin-IVA occluded the expression of mGlu2/3-LTD, and, conversely, the inhibitory effects of omega-agatoxin-IVA were abolished during mGlu2/3-LTD. Thus, mGlu2/3 play an important role in the control of use-dependent synaptic plasticity at prelimbic cortex-NAc synapses: their activation causes a form of LTD mediated by the long-lasting reduction of P/Q-type Ca(2+)channels contribution to transmitter release.
It has been suggested that the auxiliary subunits of high voltage-activated (HVA) calcium channels modulate T-type, low voltage-activated (LVA) calcium channels. Such a regulation has yet to be documented, especially because there has been no biochemical characterization of T-channels. To monitor total protein levels and plasma membrane expression of T-channels in living cells, external epitopes (hemagglutinin, FLAG) were introduced into human recombinant Ca V 3 channels that were also N-terminally fused to green fluorescent protein. Utilizing Western blot techniques, fluorescence flow cytometry, immunofluorescence, luminometry, and electrophysiology, we describe here that  1b and ␣ 2 -␦ 1 subunits enhance the level of Ca V 3 proteins as well as their plasma membrane expression in various expression systems. We also report that, in both Xenopus oocytes and mammalian cells, the ␣ 2 -␦ 1 and  1b subunits increase by at least 2-fold the current density of Ca V 3 channels with no change in the electrophysiological properties. Altogether, these data indicate that HVA auxiliary subunits modulate Ca V 3 channel surface expression, suggesting that the membrane targeting of HVA and LVA ␣ 1 subunits is regulated dynamically through the expression of a common set of regulatory subunits.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.