Net interaction between different forms of short-term synaptic plasticity and slow-IPSPs in the hippocampus and...

Area of Science:

• Neuroscience
• Synaptic Plasticity
• Computational Neuroscience

Background:

• Paired-pulse plasticity studies synaptic transmission mechanisms.
• Opposing synaptic properties can lead to net facilitation or depression.
• Gamma-aminobutyric acid-B (GABAB) receptors mediate opposing processes: slow inhibitory postsynaptic potentials (IPSPs) and paired-pulse depression (PPD) of fast IPSPs.

Purpose of the Study:

• To investigate how time-dependent synaptic properties interact under physiological conditions.
• To determine the contribution of GABAB receptors to short-term synaptic plasticity.
• To examine whether net synaptic effects are facilitatory or depressive.

Main Methods:

• Intracellular recordings from rat CA3 hippocampal and auditory cortex L-II/III neurons.
• Paired-pulse stimulation with intervals of 50–400 ms.
• Analysis of excitatory postsynaptic potential (EPSP) amplitude, time-to-peak (TTP), and slope before and after GABAB antagonist (CGP-55845) application.

Main Results:

• At longer intervals, EPSPs showed depression in peak amplitude but broadening with longer TTP, potentially enhancing temporal summation.
• CA3 neurons exhibited short-interval facilitation, while auditory cortex neurons did not.
• GABAB antagonist CGP-55845 largely abolished short-term plasticity, equalizing responses.

Conclusions:

• Considering all time-dependent properties is essential for predicting net synaptic facilitation or depression.
• GABAB-dependent mechanisms appear to be major contributors to short-term plasticity on the scale of hundreds of milliseconds.
• The balance of synaptic processes modulates neural network states and temporally sensitive neural responses.