Multiple axonal spike initiation zones in a motor neuron: serotonin activation

Area of Science:

• Neuroscience
• Crustacean neurobiology
• Motor control

Background:

• The lateral gastric (LG) motor neuron in the crab stomatogastric nervous system (STNS) is crucial for gastric mill movements.
• This neuron has a soma in the stomatogastric ganglion (STG) and projects to peripheral muscles controlling lateral teeth.
• Understanding its signaling properties is key to deciphering motor pattern generation.

Purpose of the Study:

• To investigate the phenomenon of peripheral spike initiation in the LG motor neuron.
• To characterize the conditions and mechanisms underlying peripheral spike generation.
• To determine the functional consequences of peripherally initiated spikes on muscle activity and central network interactions.

Main Methods:

• Electrophysiological recordings from the LG neuron in the crab Cancer borealis.
• Experimental manipulations including nerve ligation, muscle removal, and pharmacological application (5-HT).
• Somatic current injection to modulate peripheral spike initiation and propagation.

Main Results:

• The LG neuron can initiate spikes at peripheral axonal sites (0.5-2.0 cm from STG) under specific conditions, such as when muscles are attached or with 5-HT application.
• Peripherally initiated spikes propagate both antidromically into the STG and orthodromically to the muscles.
• Antidromic spikes modulate muscle contraction duration but do not affect central neuronal targets, indicating differential signaling.

Conclusions:

• The LG neuron exhibits distinct spike initiation zones, allowing for context-dependent signaling to central and peripheral targets.
• Peripheral spike initiation, modulated by factors like 5-HT and axonal properties, contributes to fine-tuning muscle activity.
• This plasticity in spike initiation provides a mechanism for complex motor output modulation within the STNS.