Asynchronous action potential discharge in human muscle sympathetic nerve activity.

Area of Science:

• Neuroscience
• Physiology

Background:

• Muscle sympathetic nerve activity (MSNA) has been traditionally viewed as synchronous action potential (AP) bursts.
• The existence and role of asynchronous AP firing between these bursts in human MSNA remain largely unexplored.

Purpose of the Study:

• To investigate the presence and characteristics of asynchronous AP discharge in human MSNA.
• To determine the influence of ganglionic mechanisms on this asynchronous activity.

Main Methods:

• Utilized multiunit microneurography and continuous wavelet transform to analyze AP synchronicity within human MSNA.
• Quantified asynchronous APs during baseline, lower body negative pressure, and apnea.
• Examined the effect of nicotinic blockade (trimethaphan) on AP synchronicity.

Main Results:

• Approximately 33% of total AP activity in human MSNA occurred asynchronously at baseline.
• Asynchronous discharge remained consistent across various physiological stress conditions.
• Nicotinic blockade partially reduced asynchronous APs, indicating a role for nonnicotinic ganglionic mechanisms in some asynchronous firing.

Conclusions:

• Human MSNA fundamentally includes asynchronous AP discharge between bursts, accounting for a significant portion of baseline activity.
• Nonnicotinic ganglionic pathways contribute to, but do not fully explain, the observed asynchronous sympathetic nerve activity.