CNQX

CNQX or cyanquixaline (6-cyano-7-nitroquinoxaline-2,3-dione) is a competitive AMPA/kainate receptor antagonist. Its chemical formula is C9H4N4O4. CNQX is often used in the retina to block the responses of OFF-bipolar cells for electrophysiology recordings.[1]

CNQX
Names
IUPAC name
7-nitro-2,3-dioxo-1,4- dihydroquinoxaline-6-carbonitrile
Identifiers
3D model (JSmol)
ChEMBL
ChemSpider
KEGG
UNII
Properties
C9H4N4O4
Molar mass 232.15 g/mol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

CNQX is an antagonist of α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptors (AMPARs).[2] A study of the effects of CNQX on vestibuloocular reflex adaptation was done on goldfish by injecting CNQX into the vestibulo-cerebullum.[3] The injection before adaptation significantly decreased and at the highest doses, completely inhibited the acquisition of adaptive reflex gain increases and decreases during a three-hour training period. Baseline performance was not affected by the CNQX injections. Injections of CNQX at the end of the training period shows a rapid loss of gained vestibuloocular reflex adaptation when the goldfish remained stationary in the dark. Instead of injecting CNQX immediately after training, injection made one to two hours after the initiation of the training period showed no signs of altering performance. CNQX injections did not have long-term permanent effects on the goldfish's ability to be retrained 48-hours later and was comparable to a control group that was not subjected to CNQX injections. CNQX did not inhibit adaptive changes while the injection was administered.

Research applications

Excitatory synaptic transmission can be mediated through changing the responsiveness of AMPA receptors.[4] One common method of altering responsiveness is changing the number of AMPA receptors in the postsynaptic membrane through endocytosis. Various stimuli, including CNQX, have diverse effects on AMPA receptor internalization. Known to be a competitive antagonist of the AMPA/kainate receptor, CNQX is used in studies investigating whether or not AMPA receptor endocytosis is ligand-dependent. In a culture of hippocampal neurons, CNQX partially inhibited AMPA receptor internalization that was stimulated by AMPA. However, when the hippocampal neurons were treated with CNQX alone, AMPA receptor internalization still took place in both the soma and dendrites. APV (NMDA receptor antagonist) or nimodipine (voltage gated calcium channel blocker) were also not able to block this internalization, suggesting that receptor activation is not a requirement for AMPA receptor endocytosis. The type of AMPA receptors endocytosed as a result of CNQX stimulation can also be identified using CNQX. In HEK cells tagged with GluR subunits, CNQX stimulates the internalization of GluR1 and GluR2 receptors. The intracellular region conserved in both GluR1 and GluR2 on the GluR2 C-terminal tail was identified and deleted. Deletion of this segment resulted in a decrease in constitutive endocytosis of the GluR2 receptor in HEK cells, pinpointing the sequence determining this effect.[5]

CNQX is known to be a selective competitive antagonist for both AMPA receptors, which have an IC50 value of 400 nM, and kainate receptors, which have an IC50 value of 4 µM.[6] It also noncompetitively inhibits NMDA receptors.[7] CNQX is thus used to isolate GABAA receptor mediated spontaneous inhibitory postsynaptic currents. The actions of CNQX on the frequency of spontaneous inhibitory postsynaptic currents are independent of their actions at ionotropic glutamate receptors. Although the EC50 value of CNQX on the frequency of spontaneous inhibitory postsynaptic currents is similar to the IC50 value on kainate receptors, the blockade of kainate receptors is not responsible for the actions of CNQX. NBQX is a quinoxaline derivative that is known to be more effective than CNQX in blocking kainate receptors, but there was not a large increase in the frequency of spontaneous inhibitory postsynaptic currents. Additionally, CNQX’s effects were not replicated by kynurenate (glutamate receptor antagonist) or NS-102 (selective kainate receptor blocker) since there was no increase in the frequency of spontaneous inhibitory postsynaptic currents. Furthermore, D-AP5 and 7-CIK did not affect the frequency of spontaneous inhibitory postsynaptic currents, proving that the action of NMDA receptors do not account for the effects of CNQX.[6]

See also

References
  1. Sasaki T, Kaneko A (March 1996). "L-Glutamate-induced responses in OFF-type bipolar cells of the cat retina". Vision Research. 36 (6): 787–95. doi:10.1016/0042-6989(95)00176-X. PMID 8736215.
  2. Attwell PJ, Rahman S, Ivarsson M, Yeo CH (December 1999). "Cerebellar cortical AMPA-kainate receptor blockade prevents performance of classically conditioned nictitating membrane responses". The Journal of Neuroscience. 19 (24): RC45. doi:10.1523/JNEUROSCI.19-24-j0003.1999. PMC 6784969. PMID 10594089.
  3. Carter TL, McElligott JG (October 2005). "Cerebellar AMPA/KA receptor antagonism by CNQX inhibits vestibuloocular reflex adaptation". Experimental Brain Research. 166 (2): 157–69. doi:10.1007/s00221-005-2349-z. PMID 16082536.
  4. Traynelis SF, Wollmuth LP, McBain CJ, Menniti FS, Vance KM, Ogden KK, et al. (September 2010). Sibley D (ed.). "Glutamate receptor ion channels: structure, regulation, and function". Pharmacological Reviews. 62 (3): 405–96. doi:10.1124/pr.109.002451. PMC 2964903. PMID 20716669.
  5. Lin JW, Ju W, Foster K, Lee SH, Ahmadian G, Wyszynski M, et al. (December 2000). "Distinct molecular mechanisms and divergent endocytotic pathways of AMPA receptor internalization". Nature Neuroscience. 3 (12): 1282–90. doi:10.1038/81814. PMID 11100149.
  6. Brickley SG, Farrant M, Swanson GT, Cull-Candy SG (November 2001). "CNQX increases GABA-mediated synaptic transmission in the cerebellum by an AMPA/kainate receptor-independent mechanism". Neuropharmacology. 41 (6): 730–6. doi:10.1016/S0028-3908(01)00135-6. PMID 11640927.
  7. Lester RA, Quarum ML, Parker JD, Weber E, Jahr CE (May 1989). "Interaction of 6-cyano-7-nitroquinoxaline-2,3-dione with the N-methyl-D-aspartate receptor-associated glycine binding site". Molecular Pharmacology. 35 (5): 565–70. PMID 2566902.

Further reading
  • Imamachi N, Saito Y, Hara K, Sakura S, Kosaka Y (August 1999). "The non-NMDA glutamate receptor antagonist CNQX augments lidocaine antinociception through a spinal action in rats". Anesthesia and Analgesia. 89 (2): 416–21. doi:10.1097/00000539-199908000-00031. PMID 10439758.
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