Tissue oxygen partial pressure as a viability metric for ex vivo brain tissue slices

Despite the prevalent use of the ex vivo brain slice preparation in neurophysiology research, a reliable method for judging tissue viability - and thus suitability of a slice for inclusion in an experiment - is lacking. The utility of indirect electrophysiological measures of tissue health is model-specific and needs to be used cautiously. In this study, we verify a more direct test of slice viability, based on tissue oxygen consumption rate.

We hypothesised that the minimum intra-slice partial pressure of oxygen (pO₂^min) would correlate with tissue oxygen consumption rate, providing an accessible method for reliably assessing tissue viability status. Using mouse brain cortex slices, we measured tissue oxygen consumption rate using a Fick's law diffusion-consumption model applied to full intra-tissue pO₂ profiles and compared this to pO₂^min and 2,3,5-triphenol tetrazolium chloride (TTC) viability staining.

Tissue pO₂^min correlated strongly with oxygen consumption rate in both neurophysiological active and quiescent tissue (in "no-magnesium" and "normal" artificial cerebrospinal fluid, respectively) (R² =49.7% and 42.1%, respectively). Both correlated with TTC viability stain. Oxygen consumption rate was positively related to the frequency of seizure-like event activity in no-magnesium artificial cerebrospinal fluid (R² = 44.8%).

While measurement of tissue oxygen levels and oxygen consumption is not new, intra-tissue pO₂^min is a novel approach to assess brain slice viability.

The results confirm that tissue oxygen minimum pO₂^min is a robust metric for estimating tissue viability status - the lower the pO₂^min, the healthier the tissue.