Selective reduction of N-methyl-D-aspartate-evoked responses by 1,3-di(2-tolyl)guanidine in mouse and rat cultured hippocampal pyramidal neurones.
1. The effects of 1,3-di(2-tolyl)guanidine (DTG) were examined on the responses of cultured hippocampal neurones to the excitatory amino acid analogues N-methyl-D-aspartate (NMDA), kainate, quisqualate and (RS)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA). 2. In rat hippocampal neurones loaded with the Ca(2+)-sensitive dye Fura-2, DTG (10-100 microM) produced a concentration-dependent depression of the NMDA-evoked rises in intracellular free calcium ([Ca2+]i), an effect that was not modified by changes in the extracellular glycine concentration. DTG (at 50 and 100 microM) also attenuated, although to a lesser extent, the rises in [Ca2+]i evoked by naturally-derived quisqualate. In contrast, 50 and 100 microM DTG did not depress responses evoked by kainate, AMPA and synthetic, glutamate-free (+)-quisqualate although on occasions DTG enhanced kainate- and AMPA-evoked rises in [Ca2+]i. 3. DTG attenuated NMDA-evoked currents recorded from mouse hippocampal neurones under whole-cell voltage-clamp with an IC50 (mean +/- s.e. mean) of 37 +/- 5 microM at a holding potential of -60 mV. The DTG block of NMDA-evoked responses was not competitive in nature and was not dependent on the extracellular glycine or spermine concentration. The block did, however, exhibit both voltage-, and use-, dependency. The steady-state current evoked by naturally-derived quisqualate was also attenuated by DTG whereas those evoked by kainate and AMPA were not. 4. We conclude that DTG, applied at micromolar concentrations, is a selective NMDA antagonist in cultured hippocampal neurones, the block exhibiting both Mg(2+)- and phencyclidine-like characteristics. Given the nanomolar affinity of DTG for sigma binding sites it is unlikely that the antagonism observed here is mediated by sigma-receptors, but the data emphasize the potential danger of ascribing the functional consequences of DTG administration solely to sigma receptor-mediated events.
Fletcher
E J
EJ
Department of Physiology, University of Toronto, Ontario, Canada.
Church
J
J
Abdel-Hamid
K
K
MacDonald
J F
JF
D000596:Amino Acids / Q000037:antagonists & inhibitors / Q000494:pharmacology; D000818:Animals; D000927:Anticonvulsants / Q000494:pharmacology*; D001667:Binding, Competitive / Q000187:drug effects; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D004558:Electric Stimulation; D004594:Electrophysiology; D005071:Evoked Potentials / Q000187:drug effects; D005260:Female; D016257:Fura-2 / Q000494:pharmacology; D006146:Guanidines / Q000494:pharmacology*; D006624:Hippocampus / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D016202:N-Methylaspartate / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects*; D011247:Pregnancy; D011712:Pyramidal Tracts / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D017480:Receptors, sigma / Q000187:drug effects; D013050:Spectrometry, Fluorescence
D000596:Amino Acids; D000927:Anticonvulsants; D006146:Guanidines; D017480:Receptors, sigma; D016202:N-Methylaspartate; C050232:1,3-ditolylguanidine; D002118:Calcium; D016257:Fura-2