The novel antagonist 3-CBW discriminates between kainate receptors expressed on neonatal rat motoneurones and those on dorsal root C-fibres

The natural product willardiine is a selective AMPA receptor agonist. We report that an N3-substituted analogue of willardiine, (S)-3-(4-carboxybenzyl)willardiine (3-CBW), antagonizes AMPA and kainate receptors expressed on motoneurones and dorsal root C-fibres, respectively. Reduction of the fast component of the dorsal root-evoked ventral root potential (fDR-VRP) has been used as a novel method to compare AMPA receptor antagonists. 3-CBW, NBQX and GYKI53655 depressed the fDR-VRP with IC50 values of 10.3±2.4, 0.214±0.043 and 4.03±0.31 μM, respectively. That 3-CBW depressed the fDR-VRP by acting at AMPA and not metabotropic glutamate receptors was demonstrated by the lack of effect of LY341495 (100 μM). The Schild plot for antagonism of responses to (S)-5-fluorowillardiine on motoneurones by 3-CBW had a slope of 1.11±0.13 giving a pA2 value of 4.48. The Schild plot for antagonism of kainate responses on the dorsal root by 3-CBW had a slope of 1.05±0.05 giving a pA2 value of 4.96. On neonatal rat motoneurones 3-CBW (200 μM) almost completely abolished responses to AMPA while responses to NMDA, kainate and DHPG were 101.6±11.6%, 39.4±5.8% and 110.5±9.0% of control, respectively. 3-CBW can therefore be used to isolate kainate receptor responses from those mediated by AMPA receptors. 3-CBW antagonized kainate-induced responses on dorsal root C-fibres with a pA2 value of 4.96 whereas kainate receptor mediated responses (isolated by including GYKI53655 in the medium) on motoneurones were not completely blocked by 200 μM 3-CBW, substantiating evidence that kainate receptors on neonatal rat motoneurones differ from those on dorsal root C-fibres. British Journal of Pharmacology (2002) 137, 1125–1133. doi:10.1038/sj.bjp.0704957