Long-term depression of synaptic inhibition is expressed postsynaptically in the developing auditory system

Area of Science:

• Neuroscience
• Synaptic Plasticity
• Auditory System Development

Background:

• Inhibitory transmission is crucial for neural circuit maturation.
• Mechanisms of inhibitory plasticity and development are not well understood.
• Long-term depression (LTD) decreases inhibitory synaptic gain and may cause synapse elimination.

Purpose of the Study:

• Determine the site of induction and expression of LTD at inhibitory synapses in the developing auditory brain stem.
• Investigate the roles of glycine and GABAA receptors in LTD.
• Clarify the involvement of GABA in LTD.

Main Methods:

• Whole-cell recordings from lateral superior olivary (LSO) neurons.
• Stimulation of the medial nucleus of the trapezoid body (MNTB) to evoke inhibitory potentials.
• Pharmacological isolation of glycine and GABAA receptors.
• Focal application of GABA and glycine.
• Use of GABAB receptor antagonist.
• Assessment of miniature inhibitory synaptic events using ruthenium red.

Main Results:

• Both postsynaptic glycine and GABAA receptors can independently exhibit LTD.
• Focal GABA application on LSO neurons induced depression, blocked by a GABAB antagonist.
• LTD decreased the mean amplitude of miniature inhibitory events without altering frequency.
• No changes were observed in paired-pulse ratio or release kinetics.

Conclusions:

• Activity-dependent LTD of inhibition has a postsynaptic locus of induction and alteration.
• GABA, not glycine, plays a pivotal role in this LTD.
• Findings provide direct evidence for postsynaptic mechanisms in inhibitory synaptic plasticity.