Enhanced locomotor activity in adult rats with neonatal administration ofN-omega-nitro-L-arginine

Chronic inhibition of nitric oxide synthase activity by NG-nitro-L-arginine induces nitric oxide synthase expression in the developing rat cerebellum

Studies on chronic inhibition of nitric oxide synthase (NOS) in the CNS suggest a plastic change in nitric oxide (NO) synthesis in areas related to motor control, which might protect the animal from the functional and behavioral consequences of NO deficiency. In the present study, the acute and chronic effect of the substrate analogue inhibitor N(G)-nitro-l-arginine (l-NNA) was examined on NO production, NO-sensitive cyclic guanosine monophosphate (cGMP) levels and the expression of NOS isoforms in the developing rat cerebellum. Acute intraperitoneal administration of the inhibitor (5-200mg/kg) to 21-day-old rats reduced NOS activity and NO concentration dose dependently by 70-90% and the tissue cGMP level by 60-80%. By contrast, chronic application of l-NNA between postnatal days 4-21 diminished the total NOS activity and NO concentration only by 30%, and the tissue cGMP level by 10-50%. Chronic treatment of 10mg/kg l-NNA induced neuronal (n)NOS expression in granule cells, as revealed by in situ hybridization, NADPH-diaphorase histochemistry and Western-blot, but it had no significant influence on tissue cGMP level or on layer formation of the cerebellum. However, a higher concentration (50mg/kg) of l-NNA decreased the intensity of the NADPH-diaphorase reaction in granule cells, significantly reduced cGMP production, and retarded layer formation and induced inducible (i)NOS expression & activity in glial cells. Treatments did not affect endothelial (e)NOS expression. The administration of the biologically inactive isomer D-NNA (50mg/kg) or saline was ineffective. The present findings suggest the existence of a concentration-dependent compensatory mechanism against experimentally-induced cronich inhibition of NOS, including nNOS or iNOS up-regulation, which might maintain a steady-state NO level in the developing cerebellum.

Selective protection against oxidative damage in brain of mice with a targeted disruption of the neuronal nitric oxide synthase gene

Nitric oxide (NO) is an essential messenger molecule in brain, where it is produced in neurons mostly by the activity of the neuronal isoform of nitric oxide synthase (nNOS). To understand the participation of the different isoforms of NOS in physiological functioning and in pathological processes, mice with null mutations for each of the NOS isoforms have been generated. In the present paper, we report that there is a selective protection from oxidative damage in the brain of mice with a targeted disruption of the nNOS gene. The cerebellum of these mice shows reduced levels of lipid peroxidation (LP) at the different ages tested, compared with wild-type mice, and also a reduction in the formation of reactive oxygen species (ROS). We observed a decrease of LP in cortex, and no effect on either LP or ROS formation was observed in striatum of knockout mice compared with wild type. We also report increased spontaneous motor activity of knockout mice. The expression and activity of nNOS are crucial to maintain redox status in brain, and we consider that the alteration in oxidative damage may help us to explain the phenotypical characteristics of nNOS knockout mice and their differential susceptibility to brain insults.

Alterations in dendritic morphology of hippocampal neurons in adult rats after neonatal administration ofN-omega-nitro-L-arginine

The dendritic length and dendritic-spine density of the pyramidal neurons of the prefrontal cortex and the CA1 hippocampus of rats using the nonselective nitric oxide synthase inhibitor N-omega-nitro-L-arginine (L-NNA) at different postnatal day (P) periods of the brain development (P1-P3, P4-P6, and P7-P9) were assessed using Golgi-Cox staining after puberty (P60). At P4-P6, the L-NNA treatment produced a significant decrease of the dendritic length and dendritic-spine density of the pyramidal cells of the CA1 hippocampus. In addition, the dendritic length of the pyramidal neurons of the CA1 hippocampus decreased because of the L-NNA treatment at P1-P3. These data suggest that during a specific step in the development of the brain, the nitric oxide levels may play a critical role in the morphological modifications of the pyramidal neurons of the CA1 hippocampus at postpubertal age.