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Tareq Yousef, William H Baldridge; Melanopsin-immunoreactive neurons in the fish retina. Invest. Ophthalmol. Vis. Sci. 2019;60(9):5257.
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© ARVO (1962-2015); The Authors (2016-present)
Little is known about melanopsin expression in lower vertebrate retinas. In zebrafish melanopsin was shown to be expressed by virtually every class of retinal neuron (Davies et al., Cell Mol Life Sci 68:4115-32, 2011). Here we report on our efforts to determine which retinal neuron subtypes are melanopsin-immunoreactive (IR) in the goldfish and zebrafish.
Adult goldfish and zebrafish eyes were enucleated and retinas were prepared as wholemounts or eyecups for sectioning and fixed using a 2% paraformaldehyde solution. For melanopsin immunohistochemistry, tissue was labelled with: 1) pas350, raised against a 13-amino acid conserved region of opn4m-1, 2 and 3 or, 2) opn4a, multiple monoclonal antibodies raised against 3 regions of opn4m-1. To determine if melanopsin-IR is associated with dopamine-, γ-aminobutyric acid (GABA)- or cholinergic neurons, tissue was double-labelled with antibodies for tyrosine hydroxylase (TOH), GABA or choline acetyltransferase (ChAT), respectively. Imaging was performed using confocal microscopy.
Pas350 and opn4a labelled somas and processes in all layers of goldfish and zebrafish retinas, including presumptive horizontal (HC), bipolar, amacrine (AC) and ganglion cells. We examined 131 TOH-IR dopaminergic interplexiform cells (DICs) finding no melanopsin-IR. However, TOH-IR puncta were found opposed to melanopsin-IR somas, and vice versa, suggesting potential reciprocal contacts between dopaminergic and melanopsin neurons.GABA and opn4a co-labelling in zebrafish and goldfish retina was found in HCs. A key finding in the goldfish retina was melanopsin-IR of HC axon terminals (HATs). Melanopsin-IR of zebrafish HC axon terminals was not evident. A subset of GABAergic ACs, both in the goldfish inner nuclear (20%) and ganglion cell layers (70%) showed opn4a-IR. Finally, almost all zebrafish (87%) and goldfish ChAT-IR somas were melanopsin-IR.
Our work is consistent with the known ubiquity of melanopsin-IR in the zebrafish retina, but with some differences between zebrafish and goldfish. DICs are not melanopsin-IR but melanopsin-IR cells may contact DICs, and vice versa. Melanopsin-IR was found in presumptive GABAergic HCs, ACs, and cholinergic ACs. The significance of melanopsin-IR of goldfish HATs is unclear.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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