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Paul Bonezzi, Jordan M Renna; Outer retinal photoreceptors in the postnatal mouse retina are electrically photoresponsive prior to eye opening. Invest. Ophthalmol. Vis. Sci. 2017;58(8):5351.
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Photoreceptors in the mouse retina express much of the molecular machinery necessary for phototransduction and glutamate release prior to eye opening at postnatal day 12 (P12; Regus-Leidig et al., 2009 and Sherry et al., 2003). Light responses can be observed from photoreceptors via electroretinogram (ERG) recordings after eye opening and as early as P13 (He et al., 2013). However, it is not known if photoreceptors are electrically active or photoresponsive prior to eye opening. Previous studies suggest that light reaches the retina prior to P12. For example, light has been shown to modulate critical developmental processes such as retinal wave activity and regression of the embryonic hyaloid vasculature through inner-retina photoreceptors (Renna et al., 2011 and Rao et al., 2013). However, the impact of light on outer retinal photoreceptors prior to eye opening is not known. We hypothesize that outer retinal photoreceptors are physiologically active and electrically responsive to light prior to eye-opening.
We recorded responses from developing wild-type mouse retinae at P8, P10 and P12 using ex-vivo ERG. Dark-adapted retinae were isolated and mounted on a custom-made ERG chamber. Oxygenated Ames solution was perfused at 37oC and barium chloride and D-LAP4 were used to isolate the a-wave (photoreceptor responses) after exposure to a 20ms flash. A paired t-test was used to calculate statistical significance between the baseline and the peak amplitude of the a-wave.
At P8 there was no detectable response to light (n=2; p>0.05). At P10 we found a small (on the order of 10-20 microvolts) a-wave in response to light that was statistically significant relative to baseline prior to light flash (n=4; p≤0.05). In p12 retinas the responses were significantly larger in amplitude with the same stimulus (n=4; p≤0.05).
Photoreceptors are electrically functional and photoresponsive prior to eye opening, earlier than previously thought. During postnatal development melanopsin ganglion cells extend dendrites to the outer-retina and are closely opposed to cone photoreceptor terminals. These outer retinal dendrites appear to express postsynaptic glutamate receptors and are in position to receive inputs from photoreceptors between P8 and P12. This appears to coincide with the time in which photoreceptors become electrically responsive to light.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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