Species differences in the distribution of nitric oxide synthase in brain stem regions that regulate sympathetic activity.

The distribution of nitric oxide synthases (NOS) in the lower brain stem was studied by NADPH-diaphorase staining with emphasis on the nucleus of the solitary tract and the ventrolateral medulla. The order of NOS density was hamster > rabbit = rat > mouse > guinea-pig > cat with little variation within species or between regions. This heterogeneity may partly explain qualitatively and quantitatively variable effects of NO on sympathetic activity in different species.