Abstract
Purpose::
Cholinergic or starburst amacrine cells appear mirror symmetrically in every vertebrate retina. The OFF-type stratifies in the outer portion of the inner plexiform layer (IPL) and has its soma in the amacrine cell layer; the ON-type stratifies in the inner IPL and has its soma in the ganglion cell layer (GCL). Cholinergic amacrine cells are involved in the generation of direction selectivity and their dendrites co-fasciculate with the dendritic branches of ON/OFF direction-selective ganglion cells and ON- and OFF parasol ganglion cells. We now discovered an additional pair of mirror symmetric amacrine cells in the macaque retina and studied them in relation to the cholinergic cells.
Methods::
The amacrine cells were labelled with an antiserum against glycogen phosphorylase (glypho). They were studied in sections and wholemounts of the macaque monkey retina immunostained for different bipolar and amacrine cell markers (CaBP, CaB5, ChAT, vGlut3, GABA) and synaptic markers (CtBP2, GlyRα1, 2 and 3).
Results::
Glypho-immunoreactive amacrine cells are similar to the cholinergic amacrine cells. Their dendrites stratify just below the OFF and above the ON cholinergic dendrites. They are GABAergic and their density in the GCL is comparable to that of the cholinergic cells in the GCL. However, their dendritic plexus is much denser in comparision to the cholinergic plexus. The glypho-OFF cells get input from DB3 and the glypho-ON cells from DB4 bipolar cells. In addition, glypho amacrine cells are extensively associated to vGluT3-immunoreactive amacrine cells - most likely via the GlyRα2 subunit.
Conclusions::
The glypho amacrine cells are good candidates to be involved in the generation of direction selectivity and/or modulating parasol ganglion cells and, therefore, a more detailed investigation of the synaptic circuitry of these cells is needed.
Keywords: amacrine cells • retinal connections, networks, circuitry • microscopy: light/fluorescence/immunohistochemistry