Apposition of neuronal elements containing nitric oxide synthase and glutamate in the nucleus tractus solitarii of rat: A confocal microscopic analysis

The distribution of glutamate and neuronal nitric oxide synthase in the rat nucleus tractus solitarii was investigated by double fluorescent immunohis tochemistry combined with confocal laser scanning microscopy. Cells and fib ers that exhibited neuronal nitric oxide synthase immunoreactivity alone, g lutamate immunoreactivity alone or both immunolabels were present in all su bnuclei of the nucleus tractus solitarii, but staining intensities differed between the subnuclei. The percentages of double-labeled glutamate-immunor eactive cells also differed between the subnuclei. The central subnucleus c ontained the highest percentage of double-labeled glutamate-immunoreactive cells and the medial subnucleus contained the lowest. The percentages of do uble-labeled neuronal nitric oxide synthase-immunoreactive neurons likewise differed between the subnuclei. The central subnucleus contained the highe st percentage of double-labeled neuronal nitric oxide synthase-immunoreacti ve neurons and the commissural subnucleus contained the lowest. Because of our interest in cardiovascular regulation, the anatomical relationship betw een glutamate-immunoreactive and neuronal nitric oxide synthase-immunoreact ive fibers in the dorsolateral and commissural subnuclei was further examin ed at higher magnification. Close appositions were observed between neurona l nitric oxide synthase immunoreactive and glutamate-immunoreactive fibers, between double-labeled and glutamate-immunoreactive fibers, and between ne uronal nitric oxide synthase-immunoreactive and double-labeled fibers. We r ecognized that a single visual perspective might cause labeled fibers that pass in close proximity to appear to make contact. Therefore, we constructe d three-dimensional images from serial optical sections obtained from the d orsolateral and commissural subnuclei by means of a confocal scanning micro scope. Rotation of the three-dimensional images caused some fibers that had seemed to be in close apposition to other structures to separate from thos e structures. In contrast, some glutamate-immunoreactive and some neuronal nitric oxide synthase-immunoreactive fibers remained in close apposition re gardless of the angle at which they were viewed. This study supports there being an anatomical link between glutamatergic an d nitroxidergic systems in the nucleus tractus solitarii. Recognized physio logical interactions between the two systems could occur through such a lin k. Published by Elsevier Science Ltd.