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Tomomi Ichinose, Jesse Cohn; Temporal Filtering in Cone Bipolar Cells in the Mouse Retina is Partially Subtype Specific. Invest. Ophthalmol. Vis. Sci. 2013;54(15):6153.
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© ARVO (1962-2015); The Authors (2016-present)
Retinal bipolar cells (BCs) are second-order neurons with 10 morphological subtypes. BCs are thought to encode particular aspects of visual signaling to start parallel processing. Transient and sustained responses in distinct BC subtypes might be the origin of temporal processing. However, how each BC subtype tunes to a particular temporal signaling is poorly understood. We have recorded light-evoked excitatory responses from many subtypes of BCs to test if the temporal filtering is subtype-specific.
Whole-cell recordings were made from cone BCs in dark-adapted mouse retinal slices. Light-evoked excitatory postsynaptic potentials (L-EPSPs) were elicited either with a step light or sinusoidal light (0.3-30 Hz) in the receptive field center. L-EPSPs were isolated by blocking glycinergic and GABAergic inhibition. BC subtypes were identified by sulforhodamine B and neurobiotin in the pipette together with calretinin staining in the inner plexiform layer (IPL).
L-EPSPs were recorded from more than 40 CBCs. Four ON BC subtypes and 4 OFF BC subtypes were identified. A step light-evoked EPSP was either transient or sustained, or a mixture of both. To examine whether the transient/ sustained dichotomy corresponds to temporal filtering, we used sinusoidal light stimuli. We found that transient cells behaved like band-pass filters, specifically tuned to a particular frequency. By contrast, sustained cells showed low-pass filtering features. We analyzed subtype specificity. ON BCs with terminals in the mid-IPL (S3; subtype 5) were sustained/ low-pass cells, whereas two ON BC subtypes ramifying in the inner IPL (S4; subtypes 6 & 7) were transient/ band-pass filtering. However, ON BCs with long umbrella-type terminals (also subtype 6) were either low-pass or band-pass filtering. Also, 2 OFF BC subtypes (subtypes 1 & 4) were tuned to a particular temporal feature, whereas 2 other subtypes were mixture of band-pass and low-pass temporal filtering cells.
We found that some ON and OFF BCs tune to a specific temporal visual signaling in a subtype-specific manner, but not other BCs. Temporal processing pathways might not be simply formed in morphologically characterized BC subtypes.
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