Adaptation-dependent changes of bipolar cell terminals in fish retina: Effects on overall morphology and spinule formation in Ma and Mb cells

Abstract

We have investigated the effects of light and dark adaptation on the overall morphology of bipolar cell (BC) terminals in sublaminae a and b of the inner plexiform layer after labelling with Lucifer Yellow (LY) and PKC immunostaining using confocal laser scanning microscopy and serially sectioned material for electron microscopy. Three-dimensional reconstructed terminals showed marked adaptation-dependent changes of their morphology. Terminals of mixed rod-cone BCs in sublamina a (Ma BC) were irregular and scalloped in light adapted, but smooth and regular in dark-adapted specimens. Terminals from mixed rod-cone BCs in sublamina b (Mb BCs) exhibited an opposite behaviour. At the ultrastructural level, bipolar terminals in both sublaminae showed fingerlike extensions (spinules) invaginating presynaptic amacrine cell (AC) processes. Sixty-two percent of the dark-adapted Mb terminals in sublamina b showed spinules, whereas 21% of the light-adapted terminals had spinules. By contrast, 50.6% of the light-adapted Ma terminals in sublamina a formed spinules, compared to 17.8% of the dark-adapted Ma terminals in this sublamina. These observations reflect the functional subdivision of the inner plexiform layer in an inner ON-and an outer OFF-centre lamina. Our findings suggest that the synaptic plasticity of BC axon terminals may be due to differences of BC membrane potential, or the activity of AC input onto bipolar terminals. They may contribute to processes of fine tuning regulating the efficiency of AC-BC interaction under varying adaptation conditions.

Daily rhythmic changes of cell size and shape in the first optic neuropil inDrosophila melanogaster

“…The generality of this finding is, moreover, strengthened by the report that retinal bipolar cell terminals in the goldfish swell during light adaptation and shrink during the night (Behrens and Wagner, 1996), indicating that size changes among visual interneurons might in fact be widespread.…”

Circadian rhythms in the morphology of neurons in Drosophila

“…Circadian changes in cell morphology have been documented for a wide range of cell types and organisms including photoreceptors in vertebrates (Basinger et al 1976;La Vail 1976;Behrens and Wagner 1996) and invertebrates (Barlow 2001), pinealocytes (Vollrath and Spiwoks-Becker 1996), and even the single cell organism Euglena gracilis (Lonergan 1983). We propose the term "circadian plasticity" for circadian changes in the morphology of neurons.…”

Distribution of phosphorylated protein kinase C alpha in goldfish retinal bipolar synaptic terminals: control by state of adaptation and pharmacological treatment

“…Whole-mount preparations of light-and dark-adapted goldfish retinae were stained with antibodies in accordance with standard protocols (Behrens and Wagner 1996).…”

“…Immunohistochemical studies have demonstrated that the axon terminals of Mb bipolar cells show adaptation-dependent changes in their morphology (Yazulla and Studholme 1992;Behrens and Wagner 1996).…”

“…The distribution of PKC immunoreactivity in Mb bipolar cells has been shown, by immunohistochemistry, to be affected by light and dark adaptation (Behrens and Wagner 1996;Vaquero et al 1996;Job and Lagnado 1998). The functional significance of the changes of PKC immunoreactivity in bipolar cells is not readily understood.…”