ipRGC light response characteristics change from post-natal to adult primarily between P8 and P15 in mice

Abstract

Purpose: The extent and timing of development of intrinsic light sensitivity in ganglion cells has not been well described. Here, we compare light response dynamics and bleaching/adaptation of intrinsically photosensitive retinal ganglion cells (ipRGC) for three developmental time points in the mouse: P8, P15, and P30

Methods: Isolated retinas from mice at or near P8, P15 and P30, were recorded ganglion cell-side down on a multi-electrode array (MEA) while perfused with carbogen-bubbled Ames buffer at 3 ml/min with nicotinic and glutamatergic blockers (10 nM epibatidine, 10 μM DNQX, 20 μM AP-4, 50 μM AP-5) for P8-P10 retinas and glutamatergic blockers (80 μM CNQX, 100 μM AP-4, 200 μM AP-5) for all others. ipRGCs were illuminated with a xenon light filtered through a 480 nm bandpass filter at 3.98 x 10¹³ photon cm^-2 s^-1. For short-term bleaching/adaptation, retinas were exposed to a 1-min light stimulus followed by a 1-min light test with time intervals of 1-10 minutes between. Response dynamics were assessed from the initial light exposure of each retina from these experiments. For long-term bleaching/adaptation, retinas were exposed to a 1-hr continuous light, allowed to recover 10-min, and then assessed for light response every 10-min for 1-hr.

Results: Response dynamics to a 1-min light stimulus changed with increasing age. On-latency increased (medians of P8=7 sec, P15=10 sec, P30=10.5 sec). Maximal firing rate decreased (medians of P8=20 Hz, P15=16 Hz, P30=12 Hz). Off-latency decreased substantially (medians of P8=62 sec, P15=11 sec, P30=9.5 sec). The extent of adaptation/bleaching from a 1-min light stimulus also changed. ipRGCs from P8 animals showed a decreased response of ~10% after a 1-min recovery period, which took 6-min to return to pre-exposure levels. A larger decrease of ~40% was seen in both P15 and P30 ipRGCs after a 1-min recovery, which took up to 10-min to recover to pre-exposure levels. Similarly, the two older age groups had faster and more complete declines in firing over the course of a 1-hr continuous light exposure than the P8 group and then recovered to lower levels (P8 ipRGCs recovered to ~80% of pre-exposure activity, while P15 and P30 ipRGCs recovered to only ~40%.)

Conclusions: We show a generalized decrease in light responses and recovery from light exposure in ipRGCs over the first month of development. These changes occur primarily between days P8 and P15.

Keywords: 698 retinal development • 648 photoreceptors • 458 circadian rhythms