Evidence for a pathway that facilitates nitric oxide diffusion in the brain

Nitric oxide (No-center dot) is a diffusible messenger that conveys information based on its concentration dynamics, which is dictated by the interplay between its synthesis, inactivation and diffusion. Here, we characterized (NO)-N-center dot diffusion in the rat brain in vivo. By direct sub-second measurement of (NO)-N-center dot, we determined the diffusion coefficient of (NO)-N-center dot in the rat brain cortex. The value of 2.2 x 10(-5) cm(2)/s obtained in vivo was only 14% lower than that obtained in agarose gel (used to evaluate (NO)-N-center dot free diffusion). These results reinforce the view of (NO)-N-center dot as a fast diffusing messenger but, noticeably, the data indicates that neither (NO)-N-center dot diffusion through the brain extracellular space nor homogeneous diffusion in the tissue through brain cells can account for the similarity between (NO)-N-center dot free diffusion coefficient and that obtained in the brain. Overall, the results support that (NO)-N-center dot diffusion in brain tissue is heterogeneous, pointing to the existence of a pathway that facilitates (NO)-N-center dot diffusion, such as cell membranes and other hydrophobic structures. (C) 2011 Elsevier B.V. All rights reserved,