Adenosine decreases neurotransmitter release at central synapses

Area of Science:

• Neuroscience
• Synaptic Transmission
• Neuropharmacology

Background:

• Adenosine is a neuromodulator present in the brain.
• Perforant path synapses on dentate granule cells are crucial for memory formation.
• The precise mechanism of adenosine's action on these synapses is not fully understood.

Purpose of the Study:

• To elucidate the mechanism by which adenosine reduces synaptic efficacy at perforant path-dentate granule cell synapses.
• To investigate the role of endogenous adenosine in modulating synaptic strength.
• To determine if adenosine affects excitatory and inhibitory transmission differentially.

Main Methods:

• Whole-cell recordings from dentate granule cells in brain slices.
• Measurement of miniature excitatory postsynaptic currents (mEPSCs).
• Quantal analysis to assess neurotransmitter release probability and postsynaptic sensitivity.
• Application of adenosine and 3-isobutyl-1-methylxanthine (IBMX).

Main Results:

• Adenosine (5-100 microM) decreased synaptic strength without altering mEPSC amplitude, indicating no change in postsynaptic sensitivity.
• Quantal analysis revealed that adenosine significantly reduced neurotransmitter release.
• IBMX, an adenosine antagonist, increased synaptic strength by enhancing neurotransmitter release, suggesting tonic inhibition by endogenous adenosine.
• Adenosine selectively reduced excitatory transmission, leaving inhibitory transmission unaffected.

Conclusions:

• Adenosine attenuates perforant path synaptic transmission primarily by reducing presynaptic neurotransmitter release.
• Endogenous adenosine tonically suppresses excitatory neurotransmission at these synapses.
• Adenosine's action is specific to excitatory synapses, highlighting its role in regulating neural circuit activity.