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M. Manookin, J.B. Demb; Spiking Is Not Sufficient to Evoke Slow Contrast Adaptation in Mammalian Retinal Ganglion Cells . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2237.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Following a period of high contrast stimulation, cells in the retina and visual cortex show decreased responsiveness that recovers slowly over seconds (slow contrast adaptation). In cortical cells, this decreased responsiveness corresponds to an after–hyperpolarization that can be induced following a period of either visual stimulation or direct current injection. Therefore, for cortical cells, the adaptive mechanism represents an intrinsic cellular property. We asked whether retinal ganglion cells express a similar mechanism for slow contrast adaptation. Methods: We made whole–cell voltage recordings from OFF Y ganglion cells in the intact, in vitro guinea pig retina (n = 6). A cell was stimulated with a 4–s drifting, high–contrast grating (spatial frequency, 6.7 cyc/mm; temporal frequency, 6 Hz; photopic mean luminance). The same cell was stimulated with a 4–s pulse of direct current (250 pA). Results: The grating stimulus and the current pulse evoked similar levels of depolarization (grating: 7.0 +/– 0.8 mV; current: 7.5 +/– 0.6 mV) (mean +/– sem) and spike rates (grating: 19.9 +/–2.3 Hz; current: 18.0 +/– 2.1 Hz). At the offset of the grating or current pulse, a cell showed an after–hyperpolarization (AHP). The AHP was larger following the grating (4.3 +/– 0.6 mV) relative to the current pulse (1.4 +/– 0.2 mV). We measured the recovery from the AHP as the time to return 63% of the way back to the resting potential. This recovery time was longer following the grating (2.5 +/– 0.2 seconds) relative to the current pulse (0.7 +/– 0.2 seconds). Conclusions: Based on the response to the current pulse, we conclude that spiking in ganglion cells is not sufficient to generate a large, long–lasting AHP. Instead, the AHP appears to depend on a previous period of synaptic input. Therefore, the retinal mechanism for slow contrast adaptation differs from the cortical mechanism.
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