Presence of nitric oxide synthase activity in the neurons of the rat embryonal cerebrum.

Nitric oxide (NO), apparently identical to endothelium-derived relaxing factor (EDRF) in blood vessels, has been reported to be formed in adult brain tissue, and the possible physiological significance of NO in neuron functions has been suggested. The present study was undertaken to demonstrate the biochemical evidence of the presence of NO synthase activity in intact neurons. In this report, we will demonstrate first that NO synthase is also present in fetal brain where neurons can easily be isolated from and can be cultured in vitro and then we will present the evidence that the cultured neurons are responsible for NO production. We will also show that the distribution pattern of NO synthase in adult brain detected by our biochemical method is well consistent with the immunohistochemical data reported so far. NO synthase activity, which was measured as the formation of [3H]citrulline from [3H]arginine in the presence of Ca2+ and reduced nicotinamide adenine dinucleotide phosphate (NADPH), existed in the homogenate of adult rat cerebrum, olfactory bulb and cerebellum. The cerebellum showed the strongest NO synthase activity and the cerebrum showed the least but significant activity. It was also revealed that NO synthase activity also existed in the homogenate of cerebra of rat embryos, the activity, however, was about half of that in adult cerebrum. Furthermore, the homogenate of the cultured neurons prepared from the rat embryonal cerebra has also shown NO synthase activity. These results suggest that NO has some important roles in the development of the neuron system.