Adaptation-dependent plasticity of rod bipolar cell axon terminal morphology in the rat retina

Abstract

We chose synaptic terminals of rat rod bipolar cells as a model system to study activity-related changes in the overall morphology and the fine structure of synaptic sites. Using confocal laser scanning microscopy in conjunction with three-dimensional reconstruction and electron microscopy, we examined the effect of light and dark adaptation on axon terminals identified by protein kinase C (PKC) immunoreactivity. Rod bipolar cell axon terminals consisted of 2-3 polymorphic boutons situated close to the ganglion cell layer and a single ovoid swelling located more distally. Both components of the terminal complex showed adaptation-dependent differences in the distribution of PKC immunoreactivity and in their morphology. In light-adapted rod bipolar cell axon terminals, PKC immunoreactivity was homogeneously distributed throughout the cytoplasm, whereas terminals from dark-adapted animals showed PKC immunoreactivity preferentially localised in the submembrane compartment and a reduced staining of the more central cytoplasm. In three-dimensional reconstructions of optical sections and at the ultrastructural level, the shape of light-adapted axon terminals was round and smooth and exhibited more convexly curved synaptic membranes. In contrast, dark-adapted terminals had irregular contours, numerous dimples and a concave synaptic curvature. No spinules of bipolar cell terminals were observed in dark-adapted material. These observations are discussed in the context of activity-related morphological plasticity of central nervous system synapses and of the functions of PKC in the cycle of vesicle fusion and retrieval at the tonically active ribbon synapses of the rod bipolar axon terminal.

Localization of alpha integrin subunits in the neural retina of the tiger salamander

“…Integrin receptors containing α1 or α3 subunits are candidates to regulate neuritic sprouting by horizontal and bipolar cell processes in the OPL associated with retinal detachment [22]. Integrins also might have important roles in regulating normal plasticity such as light-and dark-induced changes reported in the ultrastructure of photoreceptor and bipolar cell terminals [1,45,47].…”

Patch-Clamp Investigations and Compartmental Modeling of Rod Bipolar Axon Terminals in an In Vitro Thin-Slice Preparation of the Mammalian Retina

“…In the absence of accurate morphological reconstructions, our simplified models of rod bipolar cells were based on approximate morphological parameters from several different sources, including Lucifer yellow-filled cells (Billups and Attwell 2002;Hartveit 1996), electron microscopic images and reconstructions of axon terminals (Chun et al 1993), and light microscopic and confocal images of immunolabeled cells (Behrens et al 1998;Chun et al 1993). The axonal length can vary between ϳ50 and ϳ70 m and the axonal diameter can vary between ϳ0.5 and ϳ1 m. The size of axon terminal swellings was measured as the distance along the longest diameter and perpendicular to this and ranged from 2.7 ϫ 1.5 m (Chun et al 1993;their Fig.…”

“…The axonal length can vary between ϳ50 and ϳ70 m and the axonal diameter can vary between ϳ0.5 and ϳ1 m. The size of axon terminal swellings was measured as the distance along the longest diameter and perpendicular to this and ranged from 2.7 ϫ 1.5 m (Chun et al 1993;their Fig. 6) to 10 ϫ 4 m (Behrens et al 1998; their Fig. 2A).…”

A Comparative Study of Protein Kinase C-Like Immunoreactive Cells in the Retina

“…For studying morphological and physiological features of rod bipolar cells, the protein kinase C (PKC) has been employed [Vaquero et al, 1996;Behrens et al, 1998;Caminos et al, 1999b;Pan, 2000;Pinzón-Duarte et al, 2000]. This enzyme has been found to be widely distributed in the central nervous system, where at least seven isoforms have been described [Minakuchi et al, 1981;Huang and Huang, 1986;Nishizuka, 1988].…”