Mechanisms of reduced striatal NMDA excitotoxicity in type I nitric oxide synthase knock-out mice.
We investigated the role of neuronal (type I) nitric oxide synthase (nNOS) in NMDA-mediated excitotoxicity in wild-type (SV129 and C57BL/6J) and type I NOS knock-out (nNOS-/-) mice and examined its relationship to apoptosis. Excitotoxic lesions were produced by intrastriatal stereotactic NMDA microinjections (10-20 nmol). Lesion size was dose- and time-dependent, completely blocked by MK-801 pretreatment, and smaller in nNOS knock-out mice compared with wild-type littermates (nNOS+/+, 11.7 +/- 1.7 mm3; n = 8; nNOS-/-, 6. 4 +/- 1.8 mm3; n = 7). The density and distribution of striatal NMDA binding sites, determined by NMDA receptor autoradiography, did not differ between strains. Pharmacological inhibition of nNOS by 7-nitroindazole (50 mg/kg, i.p.) decreased NMDA lesion size by 32% in wild-type mice (n = 7). Neurochemical and immunohistochemical measurements of brain nitrotyrosine, a product of peroxynitrite formation, were increased markedly in wild-type but not in the nNOS-/- mice. Moreover, elevations in 2,3- and 2,5-dihydroxybenzoic acid levels were significantly reduced in the mutant striatum, as a measure of hydroxyl radical production. The importance of apoptosis to NMDA receptor-mediated toxicity was evaluated by DNA laddering and by quantitative histochemistry [terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick end-labeling (TUNEL) staining]. DNA laddering was first detected within lesioned tissue after 12-24 hr. TUNEL-positive cells were first observed at 12 hr, increased in number at 48 hr and 7 d, and were located predominantly in proximity to the lesion border. The density was significantly lower in nNOS-/- mice. Hence, oligonucleosomal DNA breakdown suggesting apoptosis develops as a late consequence of NMDA microinjection and is reduced in nNOS mutants. The mechanism of protection in nNOS-/- mice may relate to decreased oxygen free radical production and related NO reaction products and, in part, involves mechanisms of neuronal death associated with the delayed appearance of apoptosis.
Ayata
C
C
Department of Medicine, Massachusetts General Hospital, Harvard Medical School, Charlestown, Massachusetts, 02129, USA.
Ayata
G
G
Hara
H
H
Matthews
R T
RT
Beal
M F
MF
Ferrante
R J
RJ
Endres
M
M
Kim
A
A
Christie
R H
RH
Waeber
C
C
Huang
P L
PL
Hyman
B T
BT
Moskowitz
M A
MA
D000818:Animals; D017209:Apoptosis; D001665:Binding Sites; D003342:Corpus Striatum / Q000187:drug effects* / Q000378:metabolism; D053938:DNA Fragmentation; D016291:Dizocilpine Maleate / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D017665:Hydroxyl Radical / Q000378:metabolism; D007608:Kainic Acid / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D016202:N-Methylaspartate / Q000633:toxicity*; D019001:Nitric Oxide Synthase / Q000235:genetics / Q000502:physiology*; D017470:Receptors, Glutamate / Q000378:metabolism; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism; D014443:Tyrosine / Q000031:analogs & derivatives / Q000096:biosynthesis; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid / Q000378:metabolism
D018691:Excitatory Amino Acid Antagonists; D017470:Receptors, Glutamate; D016194:Receptors, N-Methyl-D-Aspartate; D017665:Hydroxyl Radical; C002744:3-nitrotyrosine; D014443:Tyrosine; D016202:N-Methylaspartate; D016291:Dizocilpine Maleate; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; D019001:Nitric Oxide Synthase; D007608:Kainic Acid