Real-time in vivo simultaneous measurements of nitric oxide and oxygen using an amperometric dual microsensor

This paper reports a real-time study of the codynamical changes in the release of endogenous nitric oxide (NO) and oxygen (O₂) consumption in a rat neocortex in vivo upon electrical stimulation using an amperometric NO/O₂ dual microsensor. Electrical stimulation induced transient cerebral hypoxia due to the increased metabolic demands that were not met by the blood volume inside the stimulated cortical region. A NO/O₂ dual microsensor was successfully used to monitor the pair of real-time dynamic changes in the tissue NO and O₂ contents. At the onset of electrical stimulation, there was an immediate decrease in the cortical tissue O ₂ followed by a subsequent increase in the cortical tissue NO content. The averages of the maximum normalized concentration changes induced by the stimulation were a 0.41 (±0.04)-fold decrease in the O₂ and a 3.6 (±0.9)-fold increase in the NO concentrations when compared with the corresponding normalized basal levels. The peak increase in NO was always preceded by the peak decrease in O₂ in all animals (n = 11). The delay between the maximum decrease in O₂ and the maximum increase in NO varied from 3.1 to 54.8 s. This rather wide variation in the temporal associations was presumably attributed to the sparse distribution of NOS-containing neurons and the individual animal's differences in brain vasculatures, which suggests that a sensor with fine spatial resolution is needed to measure the location-specific real-time NO and O₂ contents. In summary, the developed NO/O₂ dual microsensor is effective for measuring the NO and O₂ contents in vivo. This study provides direct support for the dynamic role of NO in regulating the cerebral hemodynamics, particularly related to the tissue oxygenation.