Timing of quantal release from the retinal bipolar terminal is regulated by a feedback circuit.
In isolation, a presynaptic terminal generally releases quanta according to Poisson statistics, but in a circuit its release statistics might be shaped by synaptic interactions. We monitored quantal glutamate release from retinal bipolar cell terminals (which receive GABA-ergic feedback from amacrine cells) by recording spontaneous EPSCs (sEPSCs) in their postsynaptic amacrine and ganglion cells. In about one-third of these cells, sEPSCs were temporally correlated, arriving in brief bursts (10-55 ms) more often than expected from a Poisson process. Correlations were suppressed by antagonizing the GABA(C) receptor (expressed on bipolar terminals), and correlations were induced by raising extracellular calcium or osmolarity. Simulations of the feedback circuit produced "bursty" release when the bipolar cell escaped intermittently from inhibition. Correlations of similar duration were present in the light-evoked sEPSCs and spike trains of sluggish-type ganglion cells. These correlations were suppressed by antagonizing GABA(C) receptors, indicating that glutamate bursts from bipolar terminals induce spike bursts in ganglion cells.
Freed
Michael A
MA
Department of Neuroscience, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA. michael@retina.anatomy.upenn.edu
Smith
Robert G
RG
Sterling
Peter
P
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D017660:Autoreceptors / Q000502:physiology; D002118:Calcium / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D025461:Feedback, Physiological / Q000502:physiology; D018756:GABA Antagonists / Q000494:pharmacology; D006168:Guinea Pigs; D009994:Osmolar Concentration; D010721:Phosphinic Acids / Q000494:pharmacology; D010775:Photic Stimulation; D011725:Pyridines / Q000494:pharmacology; D018079:Receptors, GABA / Q000378:metabolism; D012160:Retina / Q000166:cytology* / Q000502:physiology*; D012165:Retinal Ganglion Cells / Q000166:cytology / Q000502:physiology; D009435:Synaptic Transmission / Q000502:physiology*
C101879:(1,2,5,6-tetrahydropyridin-4-yl)methylphosphinic acid; D017660:Autoreceptors; D018691:Excitatory Amino Acid Antagonists; D018756:GABA Antagonists; D010721:Phosphinic Acids; D011725:Pyridines; D018079:Receptors, GABA; D002118:Calcium