Modulation of Cerebral Function by Muscle Afferent Activity, with Reference to Intravenous Succinylcholine.

Area of Science:

• Anesthesiology
• Neuroscience
• Physiology

Background:

• The precise mechanism by which intravenous succinylcholine affects intracranial pressure (ICP) was debated.
• A prevailing hypothesis linked succinylcholine-induced ICP increases to fasciculations causing elevated intrathoracic and central venous pressures.
• An alternative explanation, the afferentation theory, proposed that stimulation of muscle stretch receptors influences brain activity.

Purpose of the Study:

• To investigate the mechanism of cerebral effects of intravenous succinylcholine.
• To determine if succinylcholine-induced cerebral changes are mediated by muscle afferent activity or by fasciculations and associated pressure changes.
• To assess the role of afferentation theory in cerebral arousal during anesthesia.

Main Methods:

• Experiments were conducted on tracheally intubated, lightly anesthetized dogs.
• Cerebral blood flow, electroencephalogram (EEG) activity, and intracranial pressure were monitored.
• Muscle afferent nerve traffic from muscle stretch receptors was simultaneously assessed.
• The effects of intravenous succinylcholine, with and without pancuronium pretreatment, were evaluated.

Main Results:

• Intravenous succinylcholine doubled cerebral blood flow for 30 minutes, increased EEG activity, and elevated ICP.
• These cerebral effects were directly correlated with increased muscle afferent nerve traffic.
• The observed cerebral responses were independent of fasciculations and changes in intrathoracic or central venous pressures.
• Pretreatment with pancuronium blocked fasciculations but did not abolish the cerebral effects of succinylcholine.

Conclusions:

• The cerebral arousal response to intravenous succinylcholine is primarily driven by muscle afferent activity, supporting the afferentation theory.
• Fasciculations and associated hemodynamic changes are not the primary drivers of succinylcholine's effects on the brain.
• Afferent stimulation from muscle stretch receptors plays a significant role in modulating cerebral state and physiology during anesthesia.