Novel processes invaginate the pre-synaptic terminal of retinal bipolar cells

Abstract

Mixed-rod cone bipolar (Mb) cells of goldfish retina have large synaptic terminals (10 microm in diameter) that make 60-90 ribbon synapses mostly onto amacrine cells and rarely onto ganglion cells and, in return, receive 300-400 synapses from gamma-aminobutyric acid (GABA)-ergic amacrine cells. Tissue viewed by electron microscopy revealed the presence of double-membrane-bound processes deep within Mb terminals. No membrane specializations were apparent on these invaginating processes, although rare vesicular fusion was observed. These invaginating dendrites were termed "InDents". Mb bipolar cells were identified by their immunoreactivity for protein kinase C. Double-label immunofluorescence with other cell-type-specific labels eliminated Müller cells, efferent fibers, other Mb bipolar cells, dopaminergic interplexiform cells, and somatostatin amacrine cells as a source of the InDents. Confocal analysis of double-labeled tissue clearly showed dendrites of GABA amacrine cells, backfilled ganglion cells, and dendrites containing PanNa immunoreactivity extending into and passing through Mb terminals. Nearly all Mb terminals showed evidence for the presence of InDents, indicating their common presence in goldfish retina. No PanNa immunoreactivity was found on GABA or ganglion cell InDents, suggesting that a subtype of glycine amacrine cell contained voltage-gated Na channels. Thus, potassium and calcium voltage-gated channels might be present on the InDents and on the Mb terminal membrane opposed to the InDents. In addition to synaptic signaling at ribbon and conventional synapses, Mb bipolar cells may exchange information with InDents by an alternative signaling mechanism.

Topographic mapping of retinal neurons in the european anchovy by nuclear staining and immunohistochemistry

“…The PKC‐positive bipolar cells make up a distinctive subpopulation, with dendrites reaching the rod spherules and with axon terminals in the ON‐layer of the IPL. They are either pure rod bipolars like those of mice (Haverkamp and Wässle,2000) or instead mixed rod‐cone bipolars, as described for different teleost species (Caminos et al,2001; Mack,2007; Zimov and Yazulla,2008). Their topography differs from that of most other interneurons.…”

The morphological characterization of orientation‐biased displaced large‐field ganglion cells in the central part of goldfish retina

“…Here, we defined these two TH‐positive neurons as dopaminergic neurons in the goldfish retina. Generally, the processes of dopaminergic amacrine cells in mice and primate ramify in stratum 1 of the IPL (Marshak, ; Contini & Raviola, ), while the processes of all dopaminergic neurons ramify in strata 1, 3, and 5 of the IPL in most vertebrates, including goldfish (Figure a middle, Figure e; Zimov & Yazulla, ; Hoshi & Mills, ; Hoshi et al, ).…”

“…The immunostaining of this antibody was detected in dopaminergic neurons of the goldfish retina (Braisted & Raymond, ). The immunostaining pattern of this antibody was also similar to the immunostaining result described in Zimov and Yazulla (), which used a different TH antibody.…”

Postsynaptic Plasticity Triggered by Ca2+-Permeable AMPA Receptor Activation in Retinal Amacrine Cells

“…The ACs in our paired recordings exhibited elaborate dendritic arborizations and contacted the Mb terminal at one or several locations (insets of Figure 1C–F). Some AC dendrites appeared to extensively invaginate the Mb terminal (Zimov and Yazulla, 2008; Figure 1E). We obtained recordings from ACs whose dendrites stratified exclusively in sublamina b of the inner plexiform layer (IPL; ON-type AC; Figure 1B–D) and also from bi-stratified ACs whose dendrites stratified in both sublamina a and b of the IPL (ON-OFF type AC; Figure 1E–F).…”