Noradrenaline modifies sympathetic preganglionic neuron spike and afterpotential

Area of Science:

• Neuroscience
• Neurophysiology
• Autonomic Nervous System Research

Background:

• Sympathetic preganglionic neurons (SPNs) are crucial for regulating autonomic functions.
• Understanding the electrophysiological properties of SPNs is key to deciphering autonomic control.
• Action potential characteristics and afterpotentials influence neuronal excitability and firing patterns.

Purpose of the Study:

• To investigate the effects of norepinephrine on the electrophysiological properties of sympathetic preganglionic neurons.
• To characterize the changes in action potential shape and afterpotentials induced by norepinephrine.
• To determine the functional consequences of these changes on neuronal excitability.

Main Methods:

• Antidromic identification of sympathetic preganglionic neurons in adult cat upper thoracic spinal cord slices.
• In vitro electrophysiological recordings using intracellular stimulation.
• Application of norepinephrine (10-50 µM) in Krebs solution to superfuse the slices.
• Analysis of action potential waveform, afterhyperpolarization, and afterpotentials.

Main Results:

• Norepinephrine reversibly abolished the 'hump' on the action potential repolarization phase.
• The late component of the long afterhyperpolarization (2.8 s, 16.6 mV) was abolished by norepinephrine.
• Norepinephrine induced a reversible depolarizing afterpotential (100-600 ms), potentially leading to repetitive firing from a single stimulus.

Conclusions:

• Norepinephrine significantly alters the excitability of sympathetic preganglionic neurons.
• The observed changes in action potential and afterpotentials suggest a mechanism for modulating sympathetic outflow.
• Norepinephrine-induced depolarization may enhance sympathetic nervous system activity under certain physiological conditions.