Brevetoxins cause acute excitotoxicity in primary cultures of rat cerebellar granule neurons.
Brevetoxins (designated PbTx-1 to -10) are potent lipid-soluble polyether compounds that are known to bind to and modulate voltage-gated sodium channel activity. To investigate whether brevetoxins produce direct central nervous system neurotoxic effects, cultured rat cerebellar granule neurons were exposed to brevetoxins in Locke's buffer for 2 h at 22 degrees C. Neuronal injury was quantified by assaying lactate dehydrogenase activity in the exposure buffer and in conditioned growth media collected at 22 h after brevetoxin exposure. Brevetoxins produced acute neuronal injury and death in neurons with a rank order potency of PbTx-1 (EC50 = 9.31 +/- 0.45 nM) > PbTx-3 (EC50 = 53.9 +/- 2.8 nM) > PbTx-2 (EC50 = 80.5 +/- 5.9 nM) > PbTx-6 (EC50 = 1417 +/- 32 nM), which is similar to their previously determined rank order potency for brevetoxin-induced icthyotoxicity and binding to [3H]PbTx-3-labeled sodium channels on synaptosomes. The neurotoxic response could be prevented by coapplication of the sodium channel antagonist tetrodotoxin or by the competitive or noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonists D-AP5 and MK-801, ketamine, dextromethorphan, and dextrorphan, respectively. NMDA receptor antagonists afforded neuroprotection with rank order potencies comparable to those measured previously for protection against glutamate-induced excitotoxic responses. Further analysis revealed that brevetoxins induced a concentration-dependent release of L-glutamate and L-aspartate into the exposure buffer. These data indicate that brevetoxin-induced injury in cultured rat cerebellar granule neurons is mediated by NMDA receptors that are activated indirectly as a consequence of PbTx-induced sodium channel activation and attendant excitatory amino acid release.
Berman
F W
FW
Department of Physiology and Pharmacology, College of Veterinary Medicine, The University of Georgia, Athens, Georgia, USA.
Murray
T F
TF
D000818:Animals; D001224:Aspartic Acid / Q000378:metabolism*; D016923:Cell Death / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology* / Q000187:drug effects; D018698:Glutamic Acid / Q000378:metabolism*; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008387:Marine Toxins / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism; D009498:Neurotoxins / Q000494:pharmacology*; D035964:Oxocins; D051381:Rats; D017207:Rats, Sprague-Dawley; D016194:Receptors, N-Methyl-D-Aspartate / Q000187:drug effects / Q000502:physiology; D000095702:Polyether Toxins
D001224:Aspartic Acid; D018698:Glutamic Acid; D007770:L-Lactate Dehydrogenase; D008387:Marine Toxins; D009498:Neurotoxins; D035964:Oxocins; D016194:Receptors, N-Methyl-D-Aspartate; C053342:brevetoxin; D000095702:Polyether Toxins