Neuroprotection by aminoguanidine after lateral fluid-percussive brain injury in rats: a combined magnetic resonance imaging, histopathologic and functional study.

The present study examined the effects of a selective inducible nitric oxide synthase (iNOS) inhibitor, aminoguanidine (AG), on neuronal cell survival and post-traumatic recovery in rats following a lateral fluid percussive brain injury. Daily treatment of AG at the dosage of 100 mg/kg or normal saline was given intraperitoneally into rats starting 2 h before or 30 min after brain injury. Treatment with AG significantly reduced lesion volumes in the brains of rats after injury, as evaluated by high-resolution magnetic resonance imaging (MRI). Immunohistochemical analysis showed a marked induction of iNOS expression in brain macrophages ipsilateral to the injury. Apoptotic neurons were observed in the ipsilateral cerebral cortex by in situ terminal transferase d-UTP nick-end labelling (TUNEL) and caspase-3 immunohistochemistry. In rats receiving prophylactic or post-injury treatment of AG, the number of degenerating neurons was markedly reduced in the cerebrum compared to those receiving saline injection. The location and extent of these pathologic changes correlated with MRI findings. Neurobehavioral studies showed that rotametric performance, grip-strength score, total and ambulatory locomotor responses and acoustic startle response were reduced in rats subjected to the injury but were significantly improved in AG-treated rats. It is suggested that inhibition of iNOS by AG may represent a potential therapeutic strategy for the treatment of traumatic brain injury.

Nitric oxide induces macrophage apoptosis following traumatic brain injury in rats.

This study examined the apoptotic mechanisms of macrophages following a lateral fluid percussive brain injury. A marked induction of inducible NO synthase (iNOS) immunoexpression was observed in brain macrophages in the subarachnoid space and lateral ventricles ipsilateral to the injury. Numerous apoptotic macrophages occurred in the same region 7 days after the injury as shown by in situ terminal transferase d-UTP nick-end labeling (TUNEL) and caspase-3 immunohistochemistry. Double immunofluorescence staining showed that only a small number of TUNEL positive cells were iNOS positive; many TUNEL positive cells, however, were observed in the vicinity of iNOS positive cells. Administration of aminoguanidine resulted in a marked reduction of apoptotic cells in the lesioned area suggesting that overproduction of NO is linked to diminution of brain macrophages by apoptosis.

Effects of aminoguanidine and L-arginine methyl ester resuscitation following induction of fluid-percussion injury and severe controlled hemorrhagic shock in the rat brain.

OBJECT: In this study the authors compared the effects of both a selective inducible nitric oxide synthase (iNOS) inhibitor and a nonselective inhibitor on posttraumatic recovery and neuron survival by using a combined model of lateral fluid-percussion injury (FPI) and hemorrhagic shock (HS). METHODS: Male Sprague-Dawley rats weighing 300 to 350 g underwent FPI to the brain (3.5 atm) and hemorrhage to a mean arterial blood pressure (MABP) of 40 mm Hg for 1 hour. Rats were then resuscitated during 1 hour with bolus infusions of aminoguanidine (AG) or nitro-L-arginine methyl ester (L-NAME). Neuronal apoptosis was determined by performing Nissl staining and in situ terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling technique. Rats infused with AG showed a significant increase in mean survival time and cerebral tissue perfusion, although the MABP and nitrate/nitrite levels did not significantly change compared with those in L-NAME-treated rats even though both animal groups had been subjected to combined FPI and HS, FPI alone, or HS alone. Furthermore, infusion of AG also significantly decreased the number of apoptotic neurons when compared with the number in rats treated with L-NAME. CONCLUSIONS: The authors asserted that treatment with AG, which causes the inhibition of iNOS, might contribute to improved physiological parameters and neuronal cell survival following FPI and HS.