Spider toxins affecting glutamate receptors: polyamines in therapeutic neurochemistry

Polyamine amide toxins obtained from venous of spiders and wasps interact selectively with ionotropic glutamate receptors (GLU-R) of vertebrate central nervous systems. The sites and modes of action of these polyamine amide toxins are reviewed with particular reference to their structure-activity relationships. Qualitatively, their effects on GLU-R are identical to those exerted by polyamines such as spermine, but the polyamine amides are more potent. These compounds (a) potentiate and (b) antagonize GLU-R, the latter arising through open channel block. For the N-methyl-D-aspartate receptor this non-competitive antagonism probably arises through binding of toxin to the Mg2+ site(s) located in the channel gated by this receptor. Similarities and differences between GLU-R in vertebrates and in invertebrates with respect to their interactions with polyamines and polyamine amide toxins are discussed. In both groups the low specificity of these compounds is illustrated by their antagonism at nicotinic acetylcholine receptors in addition to GLU-R. Electrophysiological studies, including those employing Xenopus oocytes, are reviewed and future prospects for the use of polyamine amides in therapy are discussed.