Metabotropic glutamate receptors and visual cortical synaptic plasticity

Area of Science:

• Neuroscience
• Synaptic Plasticity
• Receptor Pharmacology

Background:

• Use-dependent synaptic plasticity, including long-term potentiation (LTP) and long-term depression (LTD), is fundamental to learning and memory.
• Metabotropic excitatory amino acid receptors have been hypothesized to be critical for inducing LTP and LTD, particularly in the hippocampus.
• The selective metabotropic receptor antagonist (+/-)-alpha-methyl-4-carboxyphenylglycine (MCPG) has recently become available for experimental testing.

Purpose of the Study:

• To investigate the role of metabotropic receptors in synaptic plasticity in the rat visual cortex.
• To determine if MCPG selectively antagonizes metabotropic receptors and affects LTP and LTD.

Main Methods:

• Electrophysiological recordings from slices of adult rat visual cortex.
• Application of MCPG to assess its effect on synaptic plasticity.
• Differential stimulation paradigms to induce LTP and LTD.

Main Results:

• MCPG was found to block the activation of metabotropic receptors in the visual cortex.
• MCPG selectively interfered with the induction of LTD.
• MCPG did not affect the induction of LTP.

Conclusions:

• The metabotropic receptor subtype antagonized by MCPG is essential for the expression of LTD in the adult rat visual cortex.
• This specific metabotropic receptor is not required for the expression of LTP in the same brain region.
• These findings provide direct evidence for a differential role of metabotropic receptors in distinct forms of synaptic plasticity.