NO-generating neurons in the medullary cardiovascular centers of rodents and carnivores.

The aim of the study was to characterize the species-related differences in the distribution of nitric oxide synthase (NOS)-containing neurons in rodents and carnivores medullary cardiovascular centers that take part in regulation of the sympathetic or parasympathetic drives. The order of the mean number of NOS-containing neurons in the dorsomedial and ventrolateral medulla (per section) in different animals was as follows: dog>cat>rat. Although the density of the positive cells in the both regions was changed in the following sequence: rat=cat>dog. Within the dorsal motor nucleus of vagus significant exceeding of the mean number and density of positive cells (preganglionic vagal neurons) in dog were found. Differences in the distribution of NO-generating neurons in the medullary cardiovascular centers and the heterogeneity in the basal level of NO release may contribute to the distinctive alterations of the hemodynamic reactions in the studied species after administration of NOS inhibitors.