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This Article Full Text Full Text (PDF) All Versions of this Article: 580/2/397    most recent jphysiol.2006.120790v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Pang, J.-J. Articles by Wu, S. M. Search for Related Content PubMed PubMed Citation Articles by Pang, J.-J. Articles by Wu, S. M. Related Collections Neuroscience

Departments of
¹ Ophthalmology
² Neuroscience, Baylor College of Medicine, Houston, TX 77030, USA
³ Biology Department, University of St Thomas, Houston, TX 77006, USA
⁴ Department of Neurobiology, Harvard Medical School, Boston, MA 02135, USA

AII amacrine cells (AIIACs) are crucial relay stations for rod-mediated signals in the mammalian retina and they receive synaptic inputs from depolarizing and hyperpolarizing bipolar cells (DBCs and HBCs) as well as from other amacrine cells. Using whole-cell voltage-clamp technique in conjunction with pharmacological tools, we found that the light-evoked current response of AIIACs in the mouse retina is almost completely mediated by two DBC synaptic inputs: a 6,7-dinitro-quinoxaline-2,3-dione (DNQX)-resistant component mediated by cone DBCs (DBC_Cs) through an electrical synapse, and a DNQX-sensitive component mediated by rod DBCs (DBC_Rs). This scheme is supported by AIIAC current responses recorded from two knockout mice. The dynamic range of the AIIAC light response in the Bhlhb4–/– mouse (which lacks DBC_Rs) resembles that of the DNQX-resistant component, and that of the connexin36 (Cx36)–/– mouse resembles the DNQX-sensitive component. By comparing the light responses of the DBC_Cs with the DNQX-resistant AIIAC component, and light responses of the DBC_Rs with the DNQX-sensitive AIIAC component, we obtained the input–output relations of the DBC_CAIIAC electrical synapse and the DBC_RAIIAC chemical synapse. Similar to other glutamatergic chemical synapses in the retina, the DBC_RAIIAC synapse is non-linear. Its highest voltage gain (approximately 5) is found near the dark membrane potential, and it saturates for presynaptic signals larger than 5.5 mV. The DBC_CAIIAC electrical synapse is approximately linear (voltage gain of 0.92), consistent with the linear junctional conductance found in retinal electrical synapses. Moreover, relative DBC_R and DBC_C contributions to the AIIAC response at various light intensity levels are determined.

(Received 8 September 2006; accepted after revision 22 January 2007; first published online 25 January 2007)
Corresponding author S. M. Wu: Cullen Eye Institute, Baylor College of Medicine, One Baylor Plaza, NC-205, Houston, TX 77030, USA.  Email: swu{at}bcm.tmc.edu

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