Modulators of neurotransmitter release including substituted guanidines, N"-aminoguanidines, and N,N'N",N'"-tetrasubstituted hydrazinedicarboximidamides, and pharmaceutical compositions thereof are disclosed. Also disclosed are methods involving the use of such neurotransmitter release modulators for the treatment or prevention of pathophysiologic conditions characterized by the release of excessive or inappropriate levels of neurotransmitters. Also disclosed are screening assays for compounds which selectively inhibit glutamate release. Also disclosed are methods of blocking voltage sensitive sodium and calcium channels in mammalian nerve cells.