New insights into the mechanism of neurolathyrism: L-β-ODAP triggers [Ca2+]i accumulation and cell death in primary motor neurons through transient receptor potential channels and metabotropic glutamate receptors

Neurolathyrism is a motor neuron (MN) disease caused by β-N-oxalyl-L-α,β-diaminopropionic acid (L-β-ODAP), an AMPA receptor agonist. L-β-ODAP caused a prolonged rise of intracellular Ca2+ ([Ca2+]i) in rat spinal cord MNs, and the [Ca2+]i accumulation was inversely proportional to the MN’s life span. The [Ca2+]i rise induced by L-β-ODAP or (S)-AMPA was antagonized completely by NBQX, an AMPA-receptor blocker. However, blocking the L-type Ca2+ channel with nifedipine significantly lowered [Ca2+]i induced by (S)-AMPA, but not that by L-β-ODAP. Tetrodotoxin completely extinguished the [Ca2+]i rise induced by (S)-AMPA or kainic acid, whereas that induced by L-β-ODAP was only attenuated by 65.6 ± 6% indicating the prominent involvement of voltage-independent Ca2+ entry. The tetrodotoxin-resistant [Ca2+]i induced by L-β-ODAP was blocked by 2-APB, Gd3+, La3+, 1-(β-[3-(4-methoxy-phenyl)propoxy]-4-methoxyphenethyl)-1H-imidazole hydrochloride (SKF-96365) and flufenamic acid, which all are blockers of the transient receptor potential (TRP) channels. Blockers of group I metabotropic glutamate receptors (mGluR I), 7-(hydroxyiminocyclopropan[b]chromen-1α-carboxylate ethyl ester (CPCCPEt) and 2-methyl-6-(phenylethynyl)-pyridine (MPEP) also lowered the [Ca2+]i rise by L-β-ODAP. MN cell death induced by L-β-ODAP was prolonged significantly with SKF-96365 as well as NBQX. The results show the involvement of TRPs and mGluR I in L-β-ODAP-induced MN toxicity through prolonged [Ca2+]i mobilization, a unique characteristic of this neurotoxin.