POSSIBLE ROLE OF NITRIC-OXIDE IN THE DEVELOPMENT OF L-2-CHLOROPROPIONIC ACID-INDUCED CEREBELLAR GRANULE CELL NECROSIS

1 L-2-Chloropropionic acid (L-CPA) produces selective neuronal cell ne crosis in rat cerebellum when administered orally at 750 mg kg(-1) tha t is mediated in part through activation of N-methyl-D-aspartate (NMDA ) receptors. Cerebellar granule cell death occurs between 30 and 36 h following L-CPA administration exhibiting a number of features in comm on with excitatory amino acid-induced cell death. We have used this in vivo model to examine the neurochemical processes following L-CPA-ind uced activation of NMDA receptors leading to neuronal cell death in th e rat cerebellum. 2 The effects of a number of compounds which potentl y block nitric oxide synthase in vitro were examined on L-CPA-induced neurotoxicity 48 h following L-CPA dosing, to discover whether the neu ronal cell death is mediated in part by excessive nitric oxide generat ion. Four inhibitors were studied, N-G-nitro-L-arginine (L-NOARG), N-G -nitro-L-arginine methyl ester (L-NAME), N-G-iminoethyl-L-ornithine (L -NIO) and 3-bromo-7-nitroindazole (BrNI). 3 L-NAME (50 mg kg(-1), i.p. twice daily) and BrIN (50 mg kg(-1), i.p. twice daily) administration prevented the L-CPA-induced loss of granule cells which can reach up to 80-90% of the total cell number in rats treated with L-CPA alone. L -NOARG (50 mg kg(-1), i.p. twice daily) and L-NIO administered at eith er 25 or 100 mg kg(-1), twice daily did not produce any significant pr otection against L-CPA-induced neurotoxicity. 4 Both L-NAME and BrIN a lso prevented the L-CPA-induced increase in cerebellar water content a nd sodium concentrations. L-NIO when administered at the highest doses prevented the increase in cerebellar sodium concentration but not wat er content. L-NIO and L-NOARG were ineffective in preventing the L-CPA -induced increases in cerebellar water and sodium concentrations. 5 L- CPA-induced reductions in cerebellar aspartate and glutamate concentra tions and increases in glutamine and GABA concentrations were prevente d by L-NAME and BrIN, but not by L-NIO or L-NOARG. Also reductions in L-[H-3]-glutamate binding to glutamate ionotrophic and metabotrophic r eceptors in the granule cell layer of rat cerebellum was prevented by L-NAME and BrIN, but not L-NIO or L-NOARG. 6 In conclusion, the neurop rotection offered by L-NAME and BrIN suggests that L-CPA-induced cereb ellar granule cell necrosis is possibly mediated by or associated with excessive generation of nitric oxide. The inability of nitric oxide s ynthase inhibitors, L-NOARG and L-NIO to afford protection may result from their limited penetration into the brain (L-NIO) or rapid dissoci ation from the enzyme.