Fast neurotransmitter release triggered by Ca influx through AMPA-type glutamate receptors

Andrés E. Chávez, Joshua H. Singer and Jeffrey S. Diamond ()
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Andrés E. Chávez: National Institute of Neurological Disorders and Stroke, National Institutes of Health
Joshua H. Singer: National Institute of Neurological Disorders and Stroke, National Institutes of Health
Jeffrey S. Diamond: National Institute of Neurological Disorders and Stroke, National Institutes of Health

Nature, 2006, vol. 443, issue 7112, 705-708

Abstract: Abstract Feedback inhibition at reciprocal synapses between A17 amacrine cells and rod bipolar cells (RBCs) shapes light-evoked responses in the retina1,2,3. Glutamate-mediated excitation of A17 cells elicits GABA (γ-aminobutyric acid)-mediated inhibitory feedback onto RBCs4,5,6, but the mechanisms that underlie GABA release from the dendrites of A17 cells are unknown. If, as observed at all other synapses studied, voltage-gated calcium channels (VGCCs) couple membrane depolarization to neurotransmitter release7, feedforward excitatory postsynaptic potentials could spread through A17 dendrites to elicit ‘surround’ feedback inhibitory transmission at neighbouring synapses. Here we show, however, that GABA release from A17 cells in the rat retina does not depend on VGCCs or membrane depolarization. Instead, calcium-permeable AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid) receptors (AMPARs), activated by glutamate released from RBCs, provide the calcium influx necessary to trigger GABA release from A17 cells. The AMPAR-mediated calcium signal is amplified by calcium-induced calcium release (CICR) from intracellular calcium stores. These results describe a fast synapse that operates independently of VGCCs and membrane depolarization and reveal a previously unknown form of feedback inhibition within a neural circuit.

Date: 2006
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DOI: 10.1038/nature05123

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