Nuclear Spin Attenuates the Anesthetic Potency of Xenon Isotopes in Mice: Implications for the Mechanisms of Anesthesia and Consciousness

Abstract

What We Already Know about This Topic: What This Article Tells Us That Is New: Background: Xenon is an elemental anesthetic with nine stable isotopes. Nuclear spin is a quantum property which may differ among isotopes. Xenon 131 (131 Xe) has nuclear spin of 3/2, xenon 129 (129 Xe) a nuclear spin of 1/2, and the other seven isotopes have no nuclear spin. This study was aimed to explore the effect of nuclear spin on xenon anesthetic potency. Methods: Eighty C57BL/6 male mice (7 weeks old) were randomly divided into four groups, xenon 132 (132 Xe), xenon 134 (134 Xe),131 Xe, and 129 Xe groups. Due to xenon’s low potency, loss of righting reflex ED50 for mice to xenon was determined with 0.50% isoflurane. Loss of righting reflex ED50 of isoflurane was also measured, and the loss of righting reflex ED50 values of the four xenon isotopes were then calculated. The exact polarizabilities of the isotopes were calculated. Results: Combined with 0.50% isoflurane, the loss of righting reflex ED50 values were 15 ± 4%, 16 ± 5%, 22 ± 5%, and 23 ± 7% for 132 Xe,134 Xe,131 Xe, and 129 Xe, respectively. For xenon alone, the loss of righting reflex ED50 values of 132 Xe,134 Xe,131 Xe, and 129 Xe were 70 ± 4%, 72 ± 5%, 99 ± 5%, and 105 ± 7%, respectively. Four isotopes had a same exact polarizability of 3.60 Å 3. Conclusions: Xenon isotopes with nuclear spin are less potent than those without, and polarizability cannot account for the difference. The lower anesthetic potency of 129 Xe may be the result of it participating in conscious processing and therefore partially antagonizing its own anesthetic potency. Nuclear spin is a quantum property, and our results are consistent with theories that implicate quantum mechanisms in consciousness.