A chemist’s view of inflammation in contusion injured spinal cord in a rat model: noninvasive, noncontact, in vivo Raman spectroscopy minutes to hours after injury

The initial biological response to spinal cord injury is initiated by intra- and extracellular chemical signals. We compare Raman spectra of injured spinal cord obtained minutes after injury to those of uninjured spinal cord to obtain chemical information that precedes the biological response. We studied 29 rats including both Injured and Control using Raman spectra of spinal cords in vivo. Principal Component Analysis (PCA) indicates that <99% of the variation of these spectra across both Injured and Control groups is accounted for with 3 components. The first component does not vary significantly representing structural materials. The second and third components reflect the variation in the chemistry of the cerebrospinal fluid. We demonstrate the first noninvasive in vivo measurement of pH in the CSF using only Raman spectra. We hypothesize that the earliest inflammatory response to mild contusive injury reflects the chemistry of inorganic phosphate present at abnormally high concentrations, likely due to physical disruption of the blood-brain barrier in the choroid plexus and/or mitochondrial release of phosphate, reacting with CSF water.