The Development of Mid-Wavelength Photoresponsivity in the Mouse Retina

ABSTRACT

Purpose: Photoreceptors in the mouse retina express much of the molecular machinery necessary for phototransduction and glutamatergic transmission prior to eye opening at postnatal day 13 (P13). Light responses have been observed collectively from rod and cone photoreceptors via electroretinogram recordings as early as P13 in mouse, and the responses are known to become more robust with maturation, reaching a mature state by P30. Photocurrents from single rod outer segments have been recorded at P12, but no earlier, and similar studies on cone photoreceptors have been done, but only in the adult mouse retina. In this study, we wanted to document the earliest time point in which outer retinal photoreceptors in the mouse retina begin to respond to mid-wavelength light.

Methods: Ex-vivo electroretinogram recordings were made from isolated mouse retinae at P7, P8, P9, P10, and P30 at seven different flash energies (561 nm). The a-wave was pharmacologically isolated and measured at each developmental time point across all flash energies.

Results: Outer-retinal photoreceptors generated a detectable response to mid-wavelength light as early as P8, but only at photopic flash energies. a-wave intensity response curves and kinetic response properties are similar to the mature retina as early as P10.

Conclusion: These data represent the earliest recorded outer retinal light responses in the rodent. Photoreceptors are electrically functional and photoresponsive prior to eye opening, and much earlier than previously thought. Prior to eye opening, critical developmental processes occur that have been thought to be independent of outer retinal photic modulation. However, these data suggest light acting through outer-retinal photoreceptors has the potential to shape these critical developmental processes.

KEYWORDS:

• Ex-vivo electroretinogram
• photoreceptor
• a-wave
• postnatal
• outer retinal dendrite
• melanopsin

Acknowledgments

We would like to thank Brittany Day and Michael Weaver at the University of Akron for technical support. We would like to thank Matt Van Hook, PhD (University of Nebraska Medical School) for advice with ERG recordings and technical guidance, and Ricardo Vargas (Gamma Scientific) for assistance with the calibration of light measurement equipment. We would like to thank Matt Tarchick for help with data analysis. We thank Soile Nymark, PhD from Tampere University of Technology for advice and guidance with modeling functions for intensity response relationships.

Declaration of Interests

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

Additional information

Funding

This work was supported by the Karl Kirchgessner Foundation [grant number NIH R15EY026255-01].