The mechanisms underlying cognitive and neurobehavioral abnormalities associated with childhood exposure to manganese (Mn) are not well understood but may be influenced by neuroinflammatory activation of microglia and astrocytes that results in nitrosative stress due to expression of inducible nitric oxide synthase (iNOS/NOS2). We therefore postulated that gene deletion of NOS2 would protect against the neurotoxic effects of Mn in vivo and in vitro. Juvenile NOS2 knockout (NOS2(-/-)) mice were orally exposed to 50 mg/kg of MnCl₂ by intragastric gavage from days 21 to 34 postnatal. Results indicate that NOS2(-/-) mice exposed to Mn were protected against neurobehavioral alterations, despite histopathological activation of astrocytes and microglia in Mn-treated mice in both genotypes. NOS2(-/-) mice had decreased Mn-induced formation of 3-nitrotyrosine protein adducts within neurons in the basal ganglia that correlated with protection against Mn-induced neurobehavioral defects. Primary striatal astrocytes from wildtype mice caused apoptosis in cocultured striatal neurons following treatment with MnCl₂ and tumor necrosis factor-α, whereas NOS2(-/-) astrocytes failed to cause any increase in markers of apoptosis in striatal neurons. Additionally, scavenging nitric oxide (NO) with 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO) prevented the ability of Mn- and cytokine-treated wildtype astrocytes to cause apoptosis in cocultured striatal neurons. These data demonstrate that NO plays a crucial role in Mn-induced neurological dysfunction in juvenile mice and that NOS2 expression in activated glia is an important mediator of neuroinflammatory injury during Mn exposure.