Engelhardt, MD, PhD, FRCA, T., C. Zaarour, MD, and M. W. Crawford, MBBS, FRCPC. “Plasma Cyclic Guanosine 3′,5′-Monophosphate Levels: A Marker of Glutamate-Nitric Oxide-Guanyl Cyclase Activity?”. Journal of Opioid Management, vol. 7, no. 6, Nov. 2017, pp. 462-6, doi:10.5055/jom.2011.0087.