Nitric Oxide
Nitric oxide is recognized as a neuromodulator and has been hypothesized
to play a role in mediating consciousness. Although the short half-life (milliseconds
to seconds) of nitric oxide makes it a difficult compound to study, administration
of nitric oxide synthase inhibitors decreases (by about 30% to 50%) the MAC and righting-reflex
ED50
of halothane and isoflurane in rodents.[84]
[85]
However, sparing of anesthetic requirement
by nitric oxide synthase inhibitors is not found in all experiments.[86]
Nitric oxide is involved in cellular communication processes through production
of cGMP and various neurotransmitter pathways, processes that may be important to
the anesthetic state.[75]
In summary, the predominant effects of inhaled anesthetics are
not explained by the depletion, production, or release of a single neuromodulator
in the CNS. In all likelihood, the anesthetic state involves a balance between many
different neuromodulator systems.
