Volatile anaesthetics as central nervous system excitants

Area of Science:

• Neuroscience
• Anesthesiology
• Pharmacology

Background:

• Volatile anesthetics (VAs) are primarily known as central nervous system (CNS) depressants.
• Emerging evidence suggests VAs also exhibit CNS excitatory actions.

Purpose of the Study:

• To review behavioral evidence supporting the CNS excitatory actions of VAs.
• To investigate the mechanisms and correlates of VA-induced CNS excitation.

Main Methods:

• Observation of anesthetic-induced opisthotonus (OP) in mice.
• Correlation analysis of OP incidence with anesthetic properties (e.g., blood/gas partition coefficient).
• Assessment of receptor mediation (NMDA, glycine, GABAA) and neurochemical changes (methionine-enkephalin) in enflurane-induced OP.
• Evaluation of open-field activity and active avoidance learning post-anesthesia.

Main Results:

• The incidence of VA-induced opisthotonus (OP) in mice correlates inversely with the blood/gas partition coefficient, suggesting shorter induction times lead to higher OP incidence.
• Isoflurane induced higher OP incidence than enflurane in mice, contrasting with human clinical observations.
• Enflurane-induced OP appears mediated by NMDA and glycine receptors, not GABAA receptors.
• Methionine-enkephalin immunoreactivity in the hippocampus correlates with OP incidence across mouse strains.
• Open-field activity increased post-anesthesia with enflurane and isoflurane.

Conclusions:

• Volatile anesthetics exhibit significant CNS excitatory properties, evidenced by behaviors like opisthotonus in mice.
• The incidence and mechanisms of VA-induced CNS excitation vary between anesthetic agents and species.
• Further research is needed to fully elucidate the excitatory pathways of VAs and their clinical implications.