The excitatory actions of a series of piperidine dicarboxylates on central neurons of the rat, snail, leech and horseshoe crab and on crab neuromuscular junction.

Abstract 1. 1. Intracellular recordings were made from Helix, Hirudo and Limulus central neurons and from Eupagurus leg muscle and extracellular recordings from rat lateral geniculate neurons. The actions of 2,3-, ,2,4-, 2,5- and 2,6-piperidine dicarboxylates were tested on those preparations for both direct effects and interactions with the response to L -glutamate. 2. 2. All four piperidine analogues were devoid of either reproducible direct or indirect effects on Helix and Limulus neurons save that the 2,5-analogue did mimic the action of L -glutamate on Limulus neurons which were inhibited by glutamate. 3. 3. On Hirudo and rat neurons and on Eupagurus muscle, all four piperidines mimicked the action of L -glutamate, all were weak agonists on rat neurones while on Hirudo neurons the 2,5-analogue was the most potent but on Eupagurus muscle, the 2,3- and 2,6-analogues were the most potent. 4. 4. All four piperidines potentiated the action of L -glutamate on rat and Hirudo neurons and on Eupagurus leg muscle and of muscle ejps. 5. 5. The piperidine analogues indicate that there are differences between the glutamate receptors used in the present study and provide some supportive evidence that the preferred conformation for glutamate on crab leg muscle is partially folded while for Hirudo neurons it is more extended.