Miniature excitatory synaptic currents corrected for dendritic cable properties reveal quantal size and variance

Area of Science:

• Neuroscience
• Cellular Neuroscience
• Synaptic Physiology

Background:

• Miniature excitatory postsynaptic currents (mEPSCs) are crucial for understanding synaptic transmission.
• Motoneurons in the embryonic rat spinal cord are a key model for studying neuronal excitability.

Purpose of the Study:

• To investigate the quantal size and variance of non-NMDA receptor mediated mEPSCs in rat spinal cord motoneurons.
• To determine the influence of neuronal cable properties on the measurement of mEPSC amplitude.

Main Methods:

• Recording of mEPSCs from organotypic cultures of embryonic rat spinal cord motoneurons.
• Estimation of passive cable parameters (membrane time constant and electrotonic length) using voltage clamp techniques.
• Correction of mEPSC amplitudes for space and voltage clamp errors.

Main Results:

• Unimodal and skewed amplitude histograms of mEPSCs were observed, with a mean mode of -18 pA.
• After correction for cable properties, mEPSC amplitude histograms fitted a sum of two Gaussian curves, indicating a mean quantal size of -48 pA (cv=0.28).
• Neuronal cable properties significantly influenced the observed mEPSC amplitude and variance.

Conclusions:

• Quantal size and its variance are masked by the passive cable properties of motoneurons.
• Simultaneous release of multiple elementary quanta is suggested to occur occasionally.
• Accurate estimation of synaptic transmission parameters requires accounting for neuronal morphology and electrotonic structure.