Influence of ipRGC activation on retinal physiology

Abstract

The intrinsically photosensitive retinal ganglion cells (ipRGCs) are photoreceptors in the mammalian retina expressing the photopigment melanopsin. Upon light activation ipRGCs signal light information to the brain either via an intrinsic light response or acting as conduits for rod and cone light responses. However, they also signal feedback information via intraretinal signalling to modulate the circuitry and output of the retina itself. The underlying mechanisms of this intraretinal signalling, and the impact of these pathways is yet to be fully understood. The work undertaken in this doctoral thesis focuses on studying the influence of activation of ipRGCs on retinal circuitry within the retina and, in addition, the influence of ipRGC signalling in one eye on the contralateral eye using dark-adapted dual-eye electroretinogram (ERG) and chemogenetic tools. The chemogenetic tools used for the selective activation of ipRGCs in the dark were characterised using immunohistochemistry and fluorescent and confocal microscopy. An optimum concentration of virus to achieve a uniform ipRGC viral transduction in the retina was determined. Using the dark-adapted electroretinogram (ERG) as a measure of retinal function, the impact of selective activation of ipRGCs on both rod and cone pathways was assessed. DREADDs receptor hM3Dq was selectively expressed in ipRGCs in Opn4cre/+ animals unilaterally via viral gene delivery (AAV2) and activated via intraperitoneal injection of 5 mg/kg Clozapine-N-oxide (CNO). Dark-adapted dual-eye ERG recordings showed a suppression of ERG a- and b-wave amplitudes in the ipRGC activated eye. Surprisingly, a comparable suppression was also observed in the contralateral eye with no DREADDs expression or ipRGC activation, suggesting that ipRGC activation in one eye is impacting the retinal function of the other. The suppression of the a- and b-wave ERG amplitude of the contralateral eye was blocked by TTX administration in the DREADDs injected eye prior to CNO injection. Further, TTX administration in the contralateral eye prior to the CNO activation of DREADDs injected eye also reverses the suppression of a- and b-wave amplitudes. This suggests that the ipRGC output of the activated eye is relayed to the contralateral eye via a neuronal pathway that requires spiking both as it leaves the activated retina, and once the signal has reached the contralateral eye. However, these melanopsin mediated signalling pathways did not cause release of dopamine in the retina or a noticeable change in the light adaptation state of the retina.

Date of Award	2023
Original language	English
Awarding Institution	Western Sydney University
Supervisor	Morven Cameron (Supervisor)