Traumatic injury to rat brain upregulates neuronal nitric oxide synthase expression and L-[H-3]nitroarginine binding

Overstimulation of N-methyl-D-aspartate (NMDA) receptors is felt to precipi tate the neuronal damage following traumatic brain injury (TBI). NMDA recep tor-mediated, glutamate-induced excitotoxicity is thought to be mediated vi a nitric oxide (NO) formed by neuronal nitric oxide synthase (nNOS), The pr esent study examined the mRNA and protein levels of nNOS in the ipsilateral and contralateral cortex of rats as a function of time (5 minutes to 1 wee k) after controlled cortical impact (CCI) brain injury, Sham-operated rats served as controls. TBI resulted in a significant increase in the levels of nNOS mRNA (1.5- to 2.8-fold, p <.05) between 2 and 4 hours after the injur y, There was also a significant increase in the levels of nNOS protein (by 55% to 90%,p <.05) and binding densities of the nNOS-specific ligand L-[H-3 ]nitroarginine (L-[H-3]NOARG) (by 35% to 59%,p <.05) between 2 and 12 hours after the injury, Increased nNOS expression and function may contribute to the concomitant excitotoxic neuronal death after TBI.