Abstract
Purpose :
This study has focused on defining and characterizing the vasoactive intestinal peptide (VIP) type 1 amacrine cell type in the mouse retina using a VIP-Cre recombinase mouse line. VIP-1 amacrine cells are bistratified cells that ramify in strata 1, 4, and 5.
Methods :
VIP-tdTomato was generated by crossing a VIP-Cre transgenic mouse line (JAX #10908) with a Cre-dependent tdTomato (JAX #7914) reporter mouse line. Fluorescent cell bodies in retinal whole-mounts were imaged and reconstructed using a Zeiss LSM 880 confocal microscope. VIP-tdTomato fluorescent cell bodies in the inner nuclear layer (INL) were injected with Neurobiotin in retinal whole-mounts to define their general morphology, stratification patterns and to test their gap junction connectivity with other cells in the presence and absence of dopamine.
Results :
Tracer injections revealed that VIP-1 amacrine cells are homologously coupled to other VIP-1 amacrine and heterologously to non-VIP amacrine cells in the INL. VIP-1 cells also exhibited coupling in the ganglion cell layer (GCL). Based on RBPMS immunostaining, coupled cells were defined as ganglion cells and displaced amacrine cells.
In order to identify the connexin forming the gap junctions, VIP-1 cells were immunostained against Cx36, the main connexin in the retina. Our data showed that the dendritic field in the ON layer expressed the majority of Cx36 when compared to the OFF layer (t-test ; p<0.05), suggesting that the majority of coupling occurs in the ON layer.
The number of coupled cells was significantly reduced in the presence of dopamine in the INL as well as in the GCL, indicating that dopamine modulates the permeability of the gap junctions to other VIP-1 cells and non-VIP cells.
Conclusions :
VIP-1 amacrine cells are homologously and heterologously coupled to cells in the INL and GCL. Electrical synapses/Gap junctions are made up of Cx36, mainly located in the ON layer. The extent of tracer coupling is modulated by dopamine, suggesting that endogenous dopamine might uncoupled VIP circuitry during light adaptation.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.