@article {6895,
	title = {Excitatory synaptic inputs to mouse on-off direction-selective retinal ganglion cells lack direction tuning.},
	journal = {The Journal of Neuroscience : the Official Journal of the Society for Neuroscience},
	volume = {34},
	year = {2014},
	month = {2014 Mar 12},
	pages = {3976-81},
	abstract = {<p>Direction selectivity represents a fundamental visual computation. In mammalian retina, On-Off direction-selective ganglion cells (DSGCs) respond strongly to motion in a preferred direction and weakly to motion in the opposite, null direction. Electrical recordings suggested three direction-selective (DS) synaptic mechanisms: DS GABA release during null-direction motion from starburst amacrine cells (SACs) and DS acetylcholine and glutamate release during preferred direction motion from SACs and bipolar cells. However, evidence for DS acetylcholine and glutamate release has been inconsistent and at least one bipolar cell type that contacts another DSGC (On-type) lacks DS release. Here, whole-cell recordings in mouse retina showed that cholinergic input to On-Off DSGCs lacked DS, whereas the remaining (glutamatergic) input showed apparent DS. Fluorescence measurements with the glutamate biosensor intensity-based glutamate-sensing fluorescent reporter (iGluSnFR) conditionally expressed in On-Off DSGCs showed that glutamate release in both On- and Off-layer dendrites lacked DS, whereas simultaneously recorded excitatory currents showed apparent DS. With GABA-A receptors blocked, both iGluSnFR signals and excitatory currents lacked DS. Our measurements rule out DS release from bipolar cells onto On-Off DSGCs and support a theoretical model suggesting that apparent DS excitation in voltage-clamp recordings results from inadequate voltage control of DSGC dendrites during null-direction inhibition. SAC GABA release is the apparent sole source of DS input onto On-Off DSGCs.</p>
},
	issn = {1529-2401},
	doi = {10.1523/JNEUROSCI.5017-13.2014},
	author = {Park, Silvia J H and Kim, In-Jung and Looger, Loren L and Demb, Jonathan B and Borghuis, Bart G}
}
@article {45045,
	title = {Receptive field properties of bipolar cell axon terminals in the direction-selective sublaminas of the mouse retina.},
	journal = {Journal of Neurophysiology},
	volume = {112},
	year = {2014},
	month = {2014 Jul 16},
	pages = {1950-62},
	abstract = {<p>Retinal bipolar cells (BCs) transmit visual signals in parallel channels from the outer to the inner retina, where they provide glutamatergic inputs to specific networks of amacrine and ganglion cells. Intricate network computation at BC axon terminals has been proposed as a mechanism for complex network computation, such as direction selectivity, but direct knowledge of the receptive field property and the synaptic connectivity of the axon terminals of various BC types is required in order to understand the role of axonal computation by BCs. The present study tested the essential assumptions of the presynaptic model of direction selectivity at axon terminals of three functionally distinct BC types that ramify in the direction-selective strata of the mouse retina. Results from two-photon Ca2+ imaging, optogenetic stimulation, and dual patch-clamp recording demonstrated that (1) CB5 cells do not receive fast GABAergic synaptic feedback from starburst amacrine cells (SACs), (2) light-evoked and spontaneous Ca2+ responses are well coordinated among various local regions of CB5 axon terminals, (3) CB5 axon terminals are not directionally selective, (4) CB5 cells consist of two novel functional subtypes with distinct receptive field structures, (5) CB7 cells provide direct excitatory synaptic inputs to, but receive no direct GABAergic synaptic feedback from SACs, and (6) CB7 axon terminals are not directionally selective either. These findings help to simplify models of direction selectivity by ruling out complex computation at BC terminals. They also show that CB5 comprises two functional subclasses of BCs.</p>
},
	issn = {1522-1598},
	doi = {10.1152/jn.00283.2014},
	author = {Chen, Minggang and Lee, Seunghoon and Park, Silvia J H and Looger, Loren L and Zhou, Z Jimmy}
}
