Synaptic Dynamics Convey Differential Sensitivity to Input Pattern Changes in Two Muscles Innervated by the Same...

Area of Science:

• Neuroscience
• Computational Neuroscience
• Synaptic Plasticity

Background:

• Postsynaptic responses are shaped by input patterns, short-term synaptic plasticity, summation, and postsynaptic membrane properties.
• The interplay between these dynamics and realistic neural input patterns remains incompletely understood.
• Understanding these interactions is crucial for deciphering neural circuit function.

Purpose of the Study:

• To investigate and compare the short-term synaptic plasticity and response dynamics of two pyloric dilator (PD) muscles, cpv2a and cpv2b, in the lobster Homarus americanus.
• To analyze how these muscles respond to identical periodic bursting input from the same motor neurons.
• To elucidate the differential readout of neuromodulatory signals at distinct synapses.

Main Methods:

• Electrophysiological recordings of cpv2a and cpv2b muscle responses.
• Application of identical periodic bursting input patterns from identified motor neurons.
• Analysis of short-term synaptic plasticity, including facilitation and depression, across various timescales and input frequencies.
• Characterization of steady-state responses to bursting input, examining frequency and temporal sensitivity.

Main Results:

• cpv2a and cpv2b muscles exhibited quantitative differences in membrane nonlinearities and synaptic summation.
• Short-timescale responses were dominated by facilitation, with distinct frequency and time dependencies for each muscle.
• Under realistic burst stimulation, cpv2a showed transient depression, while cpv2b displayed transient facilitation.
• Steady-state responses differed significantly: cpv2b exhibited pronounced bandpass filtering, whereas cpv2a was sensitive to burst and intra-burst spike frequency.
• cpv2b showed unique sensitivity to the initial intervals within bursts, a parameter modulated by dopamine (DA).

Conclusions:

• The study reveals significant differences in synaptic integration and plasticity between cpv2a and cpv2b muscles despite receiving identical input.
• These findings demonstrate how subtle changes in neural circuit output, mediated by neuromodulation, can be interpreted distinctly by postsynaptic targets.
• The differential responses highlight the complex mechanisms underlying neural computation and motor control.