Purchase this article with an account.
Ji-Jie Pang, Samuel M Wu; Contacts between axon terminals of rod bipolar cells and somas of ganglion cells in the mouse retina. Invest. Ophthalmol. Vis. Sci. 2019;60(9):556.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Axon terminals of mammalian retinal rod bipolar cells (RBCs) make membrane contacts with somas of retinal ganglion cells (RGCs), which were observed in Golgi studies a century ago by Ramón y Cajal and confirmed by observations at the ultrastructure level. Later studies, however, did not find chemical synapses between RBC axon terminals and RGC somas. Thus, the functional significance of these contacts has been unclear. The purpose of this project is to characterize the structure of these contacts and expression of neurotransmitter receptors and connexins associated with them to assess their possible function.
Confocal microscopy, RGC retrograde-labeling, whole-cell voltage-clamp recording with dye-labeling, and immunocytochemical techniques were used in this study.
Most axon terminals of RBCs that reached the RGC layer were found to contact RGC somas. Each RBC axon terminal branched into 2-5 globules, and each globule had one side contacting RGC somas. Most somas and some primary dendrites of ON RGCs showed such contacts. One RGC soma usually contacted 5-7 globules from 2-3 RBCs with a total contact area of 28-43 µm2, which accounted for 9-3% of the surface area of RGC somas between 10-20 μm in diameter. These closely opposed membrane areas may act as a capacitor between the two cells. Furthermore, GluR4, GluR1, NMDA R2, SV2, PSD-95, Cx45, and Cx36 were localized in RGCs and Cx36 in RBCs near the contacts. In retinas where RGCs were retrograde-labeled with gap-junction permeable dye neurobiotin (NB) and gap-junction less permeable dye Lucifer yellow (LY), NB-positive RBCs were not observed. In retinal slices, we recorded an RBC and filled it with NB and LY, and we found one NB-positive and LY-negative RGC soma adjacent to the axonal terminal of the recorded RBC.
Several types of glutamate receptors and gap junction proteins are found near the contact areas between RBC axon terminals and RGC somas, though electron microscopic studies show no conventional chemical and electrical synapses between them. There is no dye coupling in the RGC→RBC direction, but possibly in the RBC→RGC direction. These results open the possibility that contacts between RBC axon terminals and RGC somas are functional under certain conditions, mediating an RBC→RGC signal via the electrical coupling, non-conventional glutamatergic synapse, and/or capacitive coupling.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
This PDF is available to Subscribers Only