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 necrosis in rat cerebellum when administered orally at 750 mg kg-1 that 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 common with excitatory amino acid-induced cell death. We have used this in vivo model to examine the neurochemical processes following L-CPA-induced activation of NMDA receptors leading to neuronal cell death in the rat cerebellum. 2. The effects of a number of compounds which potently block nitric oxide synthase in vitro were examined on L-CPA-induced neurotoxicity 48 h following L-CPA dosing, to discover whether the neuronal cell death is mediated in part by excessive nitric oxide generation. Four inhibitors were studied, NG-nitro-L-arginine (L-NOARG), NG-nitro-L-arginine methyl ester (L-NAME), NG-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 either 25 or 100 mg kg-1, twice daily did not produce any significant protection against L-CPA-induced neurotoxicity. 4. Both L-NAME and BrIN also prevented the L-CPA-induced increase in cerebellar water content and sodium concentrations. L-NIO when administered at the highest doses prevented the increase in cerebellar sodium concentration but not water 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 concentrations and increases in glutamine and GABA concentrations were prevented by L-NAME and BrIn, but not by L-NIO or L-NOARG. Also reductions in L-[3H]-glutamate binding to glutamate ionotrophic and metabotrophic receptors 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 neuroprotection offered by L-NAME and BrIN suggests that L-CPA-induced cerebellar granule cell necrosis is possibly mediated by or associated with excessive generation of nitric oxide. The inability of nitric oxide synthase inhibitors, L-NOARG and L-NIO to afford protection may result from their limited penetration into the brain (L-NIO) or rapid dissociation from the enzyme.
Widdowson
P S
PS
Neurotoxicology Research Group, ZENECA Central Toxicology Laboratory.
Gyte
A
A
Simpson
M G
MG
Farnworth
M
M
Dunn
D
D
Moore
R B
RB
Wyatt
I
I
Lock
E A
EA
D000818:Animals; D001224:Aspartic Acid / Q000737:chemistry; D002531:Cerebellum / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D018698:Glutamic Acid / Q000737:chemistry; D005973:Glutamine / Q000737:chemistry; D006843:Hydrocarbons, Chlorinated; D066298:In Vitro Techniques; D007191:Indazoles / Q000494:pharmacology*; D008297:Male; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology*; D009336:Necrosis; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D019335:Nitroarginine / Q000494:pharmacology*; D009952:Ornithine / Q000031:analogs & derivatives* / Q000494:pharmacology; D011422:Propionates / Q000494:pharmacology* / Q000633:toxicity*; D051381:Rats; D005680:gamma-Aminobutyric Acid / Q000737:chemistry
D006843:Hydrocarbons, Chlorinated; D007191:Indazoles; D011422:Propionates; D005973:Glutamine; D019335:Nitroarginine; D001224:Aspartic Acid; C065027:N(G)-iminoethylornithine; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; C021974:2-chloropropionic acid; D009952:Ornithine; D019001:Nitric Oxide Synthase; C029658:propionic acid; D019331:NG-Nitroarginine Methyl Ester