The retina contributes to visual submodalities by anatomically and functionally distinct parallel pathways. In this thesis, the synaptic connectivity of cell types in parallel visual pathways in marmoset (New World primate) and macaque (Old World primate) retinas are studied. / In Chapter 1 the main anatomical and physiological properties of parallel pathways in the primate retina are described. / Diffuse bipolar (DB) cells receive synaptic input from multiple cones and provide output to ganglion cells, but their synaptic connectivity in the inner plexiform layer is not well understood. In Chapter 2, the stratification and synaptic connectivity of DB6 axon terminals are described. It is shown that the axons of DB6 cells stratify in the same region as rod bipolar cells and blue-OFF/yellow-ON ganglion cells. The majority (86%) of their synaptic output is onto amacrine cells; only 14% goes to ganglion cells. The DB6 cells may synapse with amacrine cells in the rod pathway and the blue-OFF/yellow-ON ganglion cells. / The inhibitory neurotransmitter glycine is used by about half of all amacrine cells. Using immunohistochemical methods, the experiments in Chapter 3 investigated whether different bipolar and amacrine cell types differ with respect to the expression of glycine receptor (GlyR) subtypes. Postembedding electron microscopy showed the postsynaptic location of the a1, a2 and a3 subunits of the GlyR. Double immunofluorescence demonstrated that firstly, the three a subunits are clustered at different postsynaptic sites, and secondly that OFF bipolar types are predominantly associated with the a1 subunit, whereas ON bipolar types are predominantly associated with the a2 subunit. This shows that different amacrine cell types at synapses express different types of glycine receptors. / The midget pathway is involved in processing red-green colour vision and high spatial acuity. In Chapter 4, the synaptic connectivity of OFF midget bipolar cells was investigated in the central retina of marmosets and macaque. The OFF midget bipolar cells and their synapses were identified immunohistochemically. Midget ganglion cells in marmosets were retrogradely labelled from the parvocellular layers of the dorsal lateral geniculate nucleus. Consistent with previous studies of Old World primates, it is shown that in marmoset the midget bipolar cells contact midget ganglion cells at a ratio of 1:1. The number of output synapses was quantified for 330 OFF midget bipolar cells (n = 104, dichromatic marmoset; n = 108, trichromatic marmoset; n = 118, macaque). The average number of output synapses per axon terminal was comparable for all animal phenotypes. In all animals the number of output synapses per axon terminal showed a unimodal distribution. Our results suggest that the midget circuitry in central retina is comparable in dichromatic and trichromatic animals. / The midget pathway in mid-peripheral retina has been suggested to involve colour selective wiring of midget bipolar to midget ganglion cells. The question whether there is anatomical evidence for colour selective wiring was addressed in Chapter 5, in double labelled preparations of marmoset retina where OFF midget bipolar and OFF midget ganglion cells were identified. The relationship of the bipolar axon terminal mosaic and the dendritic fields of midget ganglion cells was analysed. No anatomical evidence for colour-selective connectivity in the inner retina of marmosets was found.
| Identifer | oai:union.ndltd.org:ADTP/245180 |
| Date | January 2005 |
| Creators | Jusuf, Patricia Regina |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
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