Electrotonic coupling between rat sympathetic preganglionic neurones in vitro

Area of Science:

• Neuroscience
• Autonomic Nervous System Physiology
• Computational Neuroscience

Background:

• Sympathetic preganglionic neurons (SPNs) are crucial for regulating sympathetic outflow.
• Understanding the intrinsic electrical properties and network interactions of SPNs is vital for comprehending sympathetic control.
• Previous research has not fully elucidated the mechanisms underlying spontaneous activity and synchronization in SPNs.

Purpose of the Study:

• To investigate the phenomenon of spontaneous membrane potential oscillations in rat sympathetic preganglionic neurons (SPNs).
• To determine the underlying mechanisms responsible for these oscillations and their synchronization.
• To explore the functional implications of electrotonic coupling among SPNs for sympathetic information processing.

Main Methods:

• Whole-cell recording technique in rat spinal cord slices.
• Stimulation of ventral roots to induce short-latency depolarizations (SLDs).
• Intracellular application of drugs (QX-314) and extracellular application of tetrodotoxin (TTX) and alpha-chloralose.
• Current injection to induce and record neuronal activity.
• Simultaneous whole-cell recordings from pairs of SPNs.

Main Results:

• 26% of SPNs displayed spontaneous membrane potential oscillations, termed spikelets.
• Spikelets were inhibited by TTX and alpha-chloralose, but not by intracellular QX-314, suggesting a non-synaptic origin.
• Short-latency depolarizations (SLDs) in oscillating neurons mimicked spikelets and overrode their frequency, indicating electrotonic coupling.
• Quiescent SPNs also exhibited SLDs and could be induced to oscillate via current injection, suggesting gap-junction coupling.
• Simultaneous recordings confirmed electrotonic coupling, with synchronized oscillations and action potentials observed in some SPN pairs.

Conclusions:

• Spontaneous spikelets in SPNs result from electrotonic coupling mediated by gap junctions.
• Electrotonic coupling allows for the synchronization of activity among groups of SPNs.
• This network property provides a novel mechanism for integrating and synchronizing information within the sympathetic nervous system.