Abstract
Purpose :
Neuropeptides constitute a diverse class of secreted signaling molecules that can act over long timescales. While the retinal expression of several neuropeptides has been reported, their cellular targets and functions remain poorly understood. Here, we combine immunohistochemistry, confocal microscopy, and electrophysiology to identify specific cell types that express corticotropin-releasing hormone receptor 1 (CRHR1), the primary target of CRH, in the mouse retina.
Methods :
Retinas were obtained from CRHR1-GFP mice aged P14 to P60 (for histological experiments) or P30 to P90 (for physiological experiments). Additional cell populations were labeled immunohistochemically, using antibodies against CRH or melanopsin. Fluorescently-labeled cells were targeted for whole-cell voltage-clamp recording using two-photon fluorescence excitation. Recordings of intrinsic, melanopsin-dependent photoresponses in retinal ganglion cells (RGCs) were performed in the presence of ACET (2 mM), L-AP4 (20 mM), D-AP5 (50 mM), and DNQX (50 mM) to block rod- and cone-mediated inputs.
Results :
In CRHR1-GFP retinas, we observed GFP+ somata in both the inner nuclear and ganglion cell layers (INL and GCL). Fluorescence was present in the inner, but not the outer, plexiform layer, where it separated into three bands. Cells with intense GFP labeling in the GCL were identified as CRH+ ACs, based on immunocytochemistry. Cells with dim GFP labeling in the GCL included intrinsically-photosensitive RGCs (ipRGCs), based on staining against melanopsin. Voltage-clamp recording and dye-filling of GFP+ RGCs confirmed intrinsic photoresponses and dendritic morphologies characteristic of non-M1 ipRGCs. ACs recorded and filled in the INL included several narrow-field types, indicative of glycinergic ACs.
Conclusions :
CRHR1+ neurons include several populations of distinct AC and RGC types, facilitating future studies of CRH function. CRHR1+ cells include CRH+ ACs, suggesting a potential autocrine action of CRH. CRH apparently could play additional roles in modulating responses of specific AC and RGC types, including non-M1 ipRGCs.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.