A specific synaptic pathway activates a conditional plateau potential underlying protraction phase in the Aplysia...

Area of Science:

• Neuroscience
• Computational Neuroscience
• Systems Neuroscience

Background:

• Neuronal networks exhibit extensive synaptic connectivity, often with seemingly redundant inputs using the same neurotransmitter.
• The functional roles of these convergent inputs are not always equivalent, influencing network activity patterns.
• The feeding central pattern generator (CPG) in Aplysia provides a model to study differential roles of synaptic inputs.

Purpose of the Study:

• To investigate the functional distinctness of synaptic inputs converging on a single neuron within a neuronal network.
• To determine the specific role of indirect versus direct synaptic pathways in initiating a motor program.
• To elucidate the mechanisms underlying the conditional nature of neuronal plateau potentials.

Main Methods:

• Analysis of synaptic connectivity in the Aplysia feeding CPG.
• Pharmacological dissection using muscarinic cholinergic antagonist pirenzepine and agonist oxotremorine.
• Electrophysiological recordings to assess excitatory postsynaptic potentials (EPSPs) and plateau potentials.

Main Results:

• The indirect synaptic input from neuron B63 to B31/B32 is essential for initiating the B31/B32 plateau potential and motor program, despite direct input from B50.
• Pirenzepine selectively blocked the slow component of the EPSP from B63 and the motor program, while sparing the direct EPSP from B50.
• Oxotremorine restored the plateau potential and bypassed the requirement for the B63 input.

Conclusions:

• The plateau potential in neuron B31/B32 is conditional, not endogenous, and critically depends on the B63 synaptic input.
• Synaptic inputs using the same neurotransmitter (acetylcholine) can exhibit distinct functional roles.
• The B63 input is functionally specialized, providing preferential access to the plateau potential necessary for motor program initiation.