Fiftieth anniversary of fiber optic-based fluorometry of brain mitochondrial NADH redox state monitored in vivo

Significance: It is well known and accepted that the normal mitochondrial function in all cells in any organism is critical for the maintenance of cellular homeostasis. The development of in vivo technology to monitor mitochondrial function using nicotine-amide adenine dinucleotide (NADH) fluorescence started in the early 1950s. Until the early 1970s, the technology used for the light transfer between the light source and the monitored tissue as well as the detection system was very rigid and complicated. Monitoring of mitochondrial NADH redox states in vivo using the fluorescence approach could use a few techniques to transmit the light between the fluorometer and the monitored tissue. Aim: I describe the introduction of optical fibers as a tool to illuminate the monitored tissue as well as the light emitted from the tissue. I also present the advantages of using optical fibers. Approach: I describe in detail the introduction of ultraviolet (UV) transmitting optical fibers into the NADH monitoring system using various experimental protocols. The contact between the fiber optic probe and the monitored brain tissue was done by a special cannula cemented to the skull after removing a disk of bone in the parietal bone of the skull. In the same brain cannula, stainless steel electrodes, for electrocortical activity monitoring, were embedded in the wall of the light guide holder. The light guide holder was cemented to the skull by dental acrylic cement. Results: Using the fiber optic probe to monitor NADH fluorescence together with microcirculatory blood flow measured by laser Doppler flowmeter provided the new very unique types of results not published before. Conclusions: The introduction of UV-transmitting optical fibers, 50 years ago, to monitor tissue mitochondrial redox state opened up a new era in understanding the energy metabolism of tissues under in vivo conditions and in real time.