Initial synaptic efficacy influences induction and expression of long-term changes in transmission

Area of Science:

• Neuroscience
• Synaptic Plasticity
• Cellular Electrophysiology

Background:

• Mixed synapses between eighth nerve fibers and goldfish Mauthner cells exhibit complex plasticity.
• Long-term depression (LTD) and long-term potentiation (LTP) are key forms of synaptic plasticity.
• Understanding the regulation of synaptic strength is crucial for comprehending neural circuit function.

Purpose of the Study:

• To investigate the induction and reversal of long-term depression (LTD) at mixed synapses.
• To determine the influence of prior synaptic efficacy on the induction of LTD and potentiation.
• To explore the role of synaptic history in modulating synaptic plasticity.

Main Methods:

• In vivo electrophysiological recordings from goldfish Mauthner cells.
• Induction of LTD by pairing presynaptic tetani with postsynaptic inhibition.
• Induction of LTP using stronger tetanization protocols.
• Manipulation of initial synaptic efficacy through prior potentiation.

Main Results:

• LTD of glutamatergic and electrotonic transmission was induced and reversed by LTP.
• Depression was more likely and longer-lasting when initial synaptic efficacy was high.
• Elevated synaptic efficacy altered the outcome of tetanization, preventing potentiation and causing depression of electrotonic coupling.

Conclusions:

• Synaptic modifications are dependent on the history of synaptic efficacy.
• The history-dependent nature of synaptic plasticity provides a basis for theoretical models.
• This study elucidates pre- and postsynaptic contributions to synaptic plasticity regulation.