1. Introduction:
- Volatile anesthetics, including cyclopropane, have been studied for their neuroprotective properties.
- Initially, it was believed that these effects were primarily due to the suppression of cerebral metabolism.
- Recent research indicates that other protective factors, including interactions with receptors and channels, are involved.
2. Neuroprotective Impact During Ischemia:
- Research has primarily involved animal experiments to study the neuroprotective effects of volatile anesthetics.
- These anesthetics demonstrate protective effects against short-term ischemia.
- They can also delay neuronal cell death during long-term ischemia, particularly in mild ischemic conditions.
- The effectiveness of volatile anesthetics can be influenced by factors such as patient sex and the dose of the anesthetic.
- Isoflurane, sevoflurane, and desflurane exhibit similar neuroprotective effects, with isoflurane being extensively studied.
- Clinical studies suggest advantages for isoflurane in terms of maintaining cerebral blood flow and oxygen saturation during anesthesia.
3. Preconditioning Effects:
- Volatile anesthetics are explored as a means of achieving ischemic tolerance due to their safety profile.
- Preconditioning with volatile anesthetics has been effective against various forms of brain ischemia, including focal and global brain ischemia, as well as spinal ischemia models.
- Receptor and channel interactions play a crucial role in preconditioning effects.
- Initially, mitochondrial ATP-dependent potassium channels were thought to mediate these effects, but now mitochondrial permeability transition pores (mPTPs) are considered the primary mediators.
- Isoflurane, sevoflurane, and desflurane interact with specific receptors and channels to induce preconditioning.
4. Postconditioning Effects:
- Some studies suggest that volatile anesthetics may reduce the extent of neuronal injuries induced by ischemia.
- Mitochondrial structures and functions, including mitoKATP channels and mPTPs, are likely involved in the neuroprotective mechanisms of volatile anesthetics.
- However, conclusive evidence for postconditioning effects is currently lacking.
Title: Neuroprotective Mechanisms of Volatile Anesthetics
Introduction:
- Volatile anesthetics were initially perceived as suppressing cerebral metabolism for neuroprotection.
- Recent research highlights interactions with receptors and channels as the primary mechanisms.
- Introduction of key receptors and channels involved.
Introduction to Mechanisms:
Modulation of Cerebral Metabolic Rate (CMR):
Modulation of Cerebral Metabolic Rate (CMR):
- Volatile anesthetics reduce energy consumption during ischemia.
- Maintenance of high ATP and phosphocreatine levels, and reduction in lactic acid accumulation.
- Concentration-dependent suppression of EEG activity and its impact on CMR.
- Discussion on the fixed range of CMR and its relationship with histological damage and neurological function.
Inhibition of Glutamate Release:
- Volatile anesthetics modulate glutamate excitotoxicity.
- Prevention of excessive calcium influx into neurons by inhibiting glutamate release.
- The limitation of glutamate release inhibition as a sole approach to improving ischemic prognosis.
Antagonization of NMDA and AMPA Receptors:
- Volatile anesthetics, particularly isoflurane, suppress NMDA and AMPA receptors.
- Their contribution to neuroprotection by preventing neuronal cell damage.
Effects on Intracellular Calcium and Calcium-Dependent Processes:
- Suppression of NMDA receptor-mediated Ca2+ influx and its role in reducing ischemia-induced cell death.
- Prevention of intracellular Ca2+ overload in ischemic/hypoxic neurons.
- Discussion on how these effects contribute to the inhibition of apoptosis.
Antioxidant Mechanisms:
- Volatile anesthetics suppress extracellular glutamate accumulation and excessive Ca2+ loading, reducing free radical production and lipid peroxidation.
- Mention of isoflurane’s role in increasing heme oxygenase-1 production as part of the antioxidative mechanism.
Mechanisms of Neuroprotection:
GABA Receptors:
GABA Receptors:
- Insights into the neuroprotective effects of isoflurane mediated by GABAA receptors.
- The distinction between GABAA and GABAB receptor antagonists.
Two-Pore-Domain Potassium Channels (TREK-1):
- Significance of TREK-1 activation by volatile anesthetics, PUFAs, and LPLs.
- Closure of voltage-dependent calcium channels and its effect on glutamate release.
- Hyperpolarization at postsynaptic neurons and its role in reducing neurotransmission and glutamate toxicity.
Catecholamine Release:
- Implication of cerebral and circulating catecholamines, particularly dopamine, in exacerbating ischemic brain injuries.
- How volatile anesthetics contribute to neuroprotection by suppressing catecholamine release.
In summary, the neuroprotective effects of volatile anesthetics are mediated through complex mechanisms involving receptor and channel interactions, mitochondrial function, and preconditioning. Understanding these mechanisms is crucial for potential clinical applications in safeguarding neurological function during surgical procedures.