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BACKGROUND: Inducible nitric oxide synthase (iNOS) cannot be detected in the neurons and glial cells of normal rats, but iNOS can be found in some neurons and glial cells of rats following ischemic, traumatic, neurotoxic or inflammatory damage.OBJECTIVE: To investigate iNOS expression and iNOS-positive cell types at various time points following damage to the rat frontal lobe using a sharp instrument.DESIGN: A nerve molecular biology, randomized, controlled study.TIME AND SETTING: This experiment was performed at the Department of Human Anatomy, Institute of Neurobiology, Medical School of Nantong University, between April 2006 and December 2007.MATERIALS: Rabbit anti-iNOS antibody (Santa Cruz, USA), biotin labeled goat anti-rabbit antibody (Sigma, USA), reverse transcription kit (Biouniquer, Hong Kong, China) and horseradish peroxidase labeled goat anti-rabbit antibody (Pierce, USA) were used for this study.METHODS: A total of 112 healthy rats aged 3 months were randomly assigned into a sham operation group (n = 28) and a damage group (n = 84). Rat models of frontal lobe damage were induced in the damage group using a sharp instrument to make an incision in the frontal lobe cortex. In the sham operation group, the rat bone window was opened but brain tissues were left intact.MAIN OUTCOME MEASURES: Parameters were measured at 3, 6, 12, 24, 72, 120 and 168 hours following damage in both groups. Pathological changes were observed using Nissl staining and hematoxylin-eosin staining. Expression of iNOS mRNA, iNOS protein and iNOS-positive cells were examined by RT-PCR, West blot analysis and immunohistochemistry, respectively.RESULTS: A large number of inflammatory cells infiltrated the damaged region 12 and 24 hours following damage, iNOS mRNA and iNOS protein expression increased in and around the damaged region 3 hours following damage, reached a peak at 24 hours, and then gradually decreased. The changes in iNOS-positive cell number reflected the changes in iNOS mRNA and iNOS protein expression after damage, iNOS was mainly found in neural cells at 3 and 6 hours, in macrophages at 12 and 24 hours, and in glial cells at 72 and 120 hours after damage. iNOS-positive cells were few in and surrounding the damaged region at 168 hours. There were a few iNOS-positive neural cells in the rat frontal lobe cortex in the sham operation group.CONCLUSION: Neurons, macrophages and glial cells can express iNOS following rat frontal lobe damage caused by a sharp instrument. The levels of iNOS expression, and the cell types expressing iNOS, change with time.