Abstract
Purpose :
Retinal ganglion cells (RGCs) encode different modalities of the visual field and their responses are shaped by various neurotransmitters and neuromodulators. Often, RGCs are grouped together when studying the effects of neurotransmitters on the retinal code. We developed a new approach that allows studying the effect of pharmacological manipulations on distinct RGC types.
Methods :
We used a two-photon calcium imaging setup to record the responses of RGCs that express GCaMP6f while projecting visual stimuli in the UV range onto the isolated retina. The visual stimuli included full-field illuminations, moving bars and gratings in eight directions and steps of varying contrasts. Responses were studied without and with pharmacological agents to elucidate the role of retinal neurotransmitters, e.g. dopamine (DA) and acetylcholine (ACh). We used the DA agonist Apomorphine (10μM), D1 and D2 receptor antagonists SCH23390 (5μM) and Raclopride (5μM), respectively, and ACh antagonist DHβE (4μM). Representative RGCs were filled at the end of the experiment to reveal their morphology.
Results :
We show that we can record for up to 5 hours from ~100 RGCs in a field of view of 250x250μm. We identified characteristic responses of RGCs based on the various visual stimuli, before and after the pharmacological manipulation. Distinct RGC types changed their responses with different pharmacological agents, while others maintained their response properties. These alterations included changes in the core encoding features of the cells, such as response polarity (e.g. OFF to ON response) and changes in response kinetics (e.g. sustained to transient response).
Conclusions :
Our approach opens up new opportunities to study the effect of neurotransmitters on visual processing of distinct RGC types and their implications in diseases, such as Parkinson’s disease. Here, understanding the effect of dopamine depletion could ultimately lead to the identification of pre-motor markers in the retina that may be used to improve diagnosis in early stages.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.