Effects of philanthotoxin-343 on CA1 pyramidal neurons of rat hippocampus in vitro.

A synthetic analog of philanthotoxin-433, philanthotoxin-343 (PhTX-343), was tested in hippocampal pyramidal neurons in vitro. PhTX-343 (2 microM) did not significantly change synaptic transmission mediated by AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid)/kainate receptors in the CA1 region of hippocampus. However, PhTX-343 significantly suppressed both the synaptic N-methyl-D-aspartate receptor-induced current (NMDA) obtained in the presence of CNQX(6-cyano-7-nitroquinoxaline-2,3-dione)/picrotoxin (10 microM) and the directly evoked NMDA receptor-induced current to pressure ejection of NMDA in the presence of tetrodotoxin (0.5 microM). A short transient facilitation of both types of NMDA response was seen immediately after the beginning of PhTX-343 application. Our results suggest that at high concentration (2 microM) PhTX-343 inhibits the NMDA-gated current, while the early facilitation occurred during an initial low concentration of the compound. Both facilitative and depressive actions of PhTX-343 are localized at the postsynaptic membrane.