Synaptic current at the rat ganglionic synapse and its interactions with the neuronal voltage-dependent currents

Area of Science:

• Neuroscience
• Cellular Electrophysiology

Background:

• Fast nicotinic excitation in sympathetic neurons is critical for physiological responses.
• Understanding the kinetics and voltage dependence of synaptic currents is essential for modeling neuronal behavior.

Purpose of the Study:

• To characterize the membrane current activated by fast nicotinic excitation in rat sympathetic neurons.
• To investigate the role of voltage-dependent currents, specifically IA, in shaping synaptic potentials and action potential firing.

Main Methods:

• Two-microelectrode voltage-clamp technique at 37°C.
• Modeling of excitatory postsynaptic current (EPSC) using double exponentials.
• Deconvolution procedures to analyze quantal secretion.
• Mathematical modeling of sympathetic neuron incorporating voltage-dependent currents.

Main Results:

• EPSC rise and decay kinetics were characterized, with fast rise (0.57 ms) and slower decay (5.2-6.8 ms).
• Miniature EPSCs exhibited similar time constants to compound EPSCs.
• IA channels were activated by subthreshold synaptic potentials under specific voltage conditions.
• IA significantly increased synaptic threshold conductance and distorted excitatory postsynaptic potential (EPSP) time course.

Conclusions:

• The IA current acts as a shunting conductance, delaying or preventing action potential firing in sympathetic neurons.
• IA speeds up spike repolarization and modulates neuronal excitability in response to synaptic input.
• The kinetic properties of IA are crucial for accurately modeling sympathetic neuron responses.