Philanthotoxin blocks quisqualate-, AMPA- and kainate-, but not NMDA-, induced excitation of rat brainstem neurones in vivo.

1. The effect of electrophoretic ejection of philanthotoxin (the polyamine toxin, from the Egyptian digger wasp) was tested on responses of brainstem and spinal neurones in the pentobarbitone-anaesthetized rat to excitatory amino acids. 2. Philanthotoxin caused a dose-dependent reduction of responses to quisqualate, alpha-amino-3-hydroxy-5-phenyl-4-isoxazolepropionate (AMPA) and kainate with little effect on those to N-methyl-D-aspartate (NMDA). 3. The time-course of this antagonist action was slow. In particular the rate of recovery was dependent on frequency of ejection of the agonist. This agonist-dependent recovery suggests that philanthotoxin has a channel blocking mode of action on mammalian central neurones.