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P.R. Jusuf, S.C. Lee, U. Grunert; Synaptic Connectivity of a Diffuse Bipolar Cell Type in the Inner Primate Retina . Invest. Ophthalmol. Vis. Sci. 2003;44(13):5163.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To investigate the synaptic connectivity of diffuse bipolar (DB6) axon terminals in the retina of marmoset (Callithrix jacchus) and macaque (Macaca fascicularis) monkeys. Methods: Vertical cryostat sections of retinae were processed for double label immunohistochemistry using antibodies against CD15 (DB6 cells), calretinin (putative AII amacrine cells) and PKCα (rod bipolar cells). Immunoreactivity was visualised with secondary antibodies coupled to Alexa 488 or Alexa 594. Sections were analysed using a Leica confocal microscope and a Zeiss microscope in combination with deconvolution software. Cell process stratification in the inner plexiform layer (IPL) was quantified and spatial colocalisation between processes investigated qualitatively. Vertical vibratome sections of marmoset retina were processed for pre-embedding EM-immunocytochemistry with antibodies against CD15. Immunoreactivity was visualised using the avidin biotin complex method. Results: Light microscopy showed that the axon terminals of DB6 and rod bipolar cells stratify at the same depth in stratum 5 of the IPL, but occupy distinct regions with little overlap. As described previously, rod bipolar axon terminals are closely associated with calretinin stained AII cells at their site of synaptic output (Strettoi et al., 1992). Some calretinin labelled processes were closely associated with DB6 axon terminals. Electron microscopy of CD15 labelled marmoset retina showed that the axon terminals of DB6 cells receive input from amacrine cells at conventional synapses. The synaptic output of DB6 cells occurs via bipolar dyads. The majority of postsynaptic profiles were from amacrine cells (84%), with only a few processes originating from ganglion cells (16%). Conclusion: The major synaptic output of the DB6 cells is onto amacrine cell processes, some of which might be AII amacrine cells.
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