[Nitric oxide-induced neurotoxicity versus neuroprotection; relationship with selective motor neuronal death]

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by selective motor neuronal death. In addition to elucidate the "cell death mechanism", we think it is also important to clarify the "cell survival mechanism", to understand the pathogenesis of this intractable disease. Glutamate (Glu) is an excitatory neurotransmitter in the central nervous system, and is implicated in the pathogenesis of ALS. In this report, we presented our current research, investigating the mechanism of Glu-induced selective motor neuronal death, derived from the study of primary culture of rat embryonic spinal cord. In brief, 1) motor neurons are selectively injured by long-term exposure to low-dose Glu through the activation of nNOS to generate NO and ONOO-: 2) nonmotor neurons are protected by cGMP which is formed by NONdependent guanylyl cyclase: 3) chronic exposure of spinal neurons to Glu increases nNOS positive neurons only in nonmotor neurons. These results indicate the cascade of Glu-calcium influx-NO generation is toxic to motor neurons and protective to nonmotor neurons. The different effect of cGMP on motor neurons and nonmotor neurons against Glu-induced excitotoxicity may explain the selective motor neuronal death of ALS. Further investigation might advance the possibility of new therapy against ALS.