Presynaptic mGlu7 receptors control GABA release in mouse hippocampus

Area of Science:

• Neuroscience
• Molecular Biology
• Pharmacology

Background:

• Metabotropic glutamate receptors (mGluRs) modulate neurotransmitter release.
• The specific role of mGlu7 receptors in hippocampal GABAergic terminals remains to be fully elucidated.
• Understanding presynaptic receptor function is crucial for deciphering hippocampal circuitry.

Purpose of the Study:

• To investigate the functional role of presynaptic mGlu7 receptors in hippocampal GABA release.
• To determine the signaling pathways and interactions of mGlu7 receptors in GABAergic terminals.
• To examine the colocalization and functional cross-talk between mGlu7 receptors and GABA(B) autoreceptors.

Main Methods:

• Utilized mouse hippocampal synaptosomes preloaded with [(3)H]GABA.
• Measured K(+)-evoked [(3)H]GABA and endogenous GABA release under various agonist and antagonist conditions.
• Employed confocal microscopy to analyze the colocalization of mGlu7 receptors with key synaptic proteins.

Main Results:

• mGlu7 receptor activation by AMN082 and group III mGlu receptor agonist (l)-AP4 inhibited [(3)H]GABA release.
• mGlu7 receptor-mediated inhibition was sensitive to adenylyl cyclase (AC) inhibition and forskolin, indicating AC-dependent signaling.
• mGlu7 receptors colocalized with syntaxin-1A, VGAT, and GABA(B) receptor subunits but exhibited independent functional regulation.

Conclusions:

• Presynaptic inhibitory mGlu7 heteroreceptors are present in mouse hippocampal GABAergic terminals.
• These mGlu7 receptors are negatively coupled to an AC-dependent intraterminal pathway.
• mGlu7 receptors function independently of GABA(B) autoreceptors, despite their colocalization.