Abstract
Purpose::
Glycine and GABA are the major inhibitory neurotransmitters of the mammalian retina. Retinal ganglion cells receive glycinergic inputs from various narrow field amacrine cells. In this study, we have evaluated the spontaneous glycinergic inputs to the B-type ganglion cells of the mouse retina (Sun et al., 2002. J. Comp. Neurol. 451:115-126.).
Methods::
Patch-clamp recordings were performed on whole mounts of wildtype, Glra1(-/-), Glra3(-/-) and Glra2(-/-) mice. Glycinergic spontaneous inhibitory postsynaptic currents (sIPSCs) were recorded in the presence of GABA receptor blockers and the decay time constants (τs) of sIPSCs of wildtype and knockout mice were compared. The postsynaptic localization of glycine receptor (GlyR) was also studied in retinal whole mounts of GFP-O mice using specific antibodies against GlyR α1, α2, α3 and α4 subunits.
Results::
There are four classes of small field B-type ganglion cells in the mouse retina. B1 cells have glycinergic sIPSCs with very fast τs, B4 cells were found to have GlyRs preferably with slow τs. In GlyR deficient mice specific changes were observed. B1 cells of Glra1(-/-) mice showed a substantial reduction of the frequency of sIPSCs. In contrast, no such difference was present in B4 cells. B1 cells of Glra3(-/-) mice showed no difference in glycine evoked currents or sIPSCs compared to wildtype mice. However, in B4 cells of Glra3(-/-) mice, slow glycinergic sIPSCs were missing. Hence, GlyRs of B1 cells seem to be dominated by the α1 subunit, while in B4 cells the α3 subunit plays an important role. B2 and B3 cells express a more balanced mixture of fast (α1) and slow (α2, α3, α4) GlyR subunits. Immunocytochemical analyses supported these results.
Conclusions::
B-type cells of the retina are probably involved with sustained neurotransmission. They are also believed to perform complex tasks like local edge detection. However, the specific roles of different B-type cells in the mouse retina are not yet clearly understood. We demonstrate here that there is substantial heterogeneity with respect to GlyR expression in these cell types.
Keywords: ganglion cells • inhibitory receptors • electrophysiology: non-clinical