The Fine Structure of the Rod-Bipolar Cell Synapse in the Retina of the Albino Rat

Abstract

The fine structure of the rod-bipolar synapse is described and illustrated. Each rod spherule possesses a large, single, oval or elongate mitochondrion approximately 0.5 X 2.0 microns. Surrounding the mitochondrion are elements of agranular endoplasmic reticulum. The bipolar dendrite projects into the lower pole of the spherule and usually terminates in two lobes separated by a cleft. The plasma membranes appear dense and thicker in the region of the synapse. In the rod spherule cytoplasm, contiguous with the plasma membrane is a dense, slightly concave arciform structure, the rod ardform density, extending from the base of the bipolar bifid process through the cleft to an equivalent point on the opposite side. Also within the spherule, and external (towards the sclera) to the rod arciform density, is a parallel, dense, thin lamella, the rod synaptic lamdla. This is approximately 25 m# in thickness and 400 m# in width at its widest extent. This halfmoon-shaped plate straddles the cleft between the two lobes of the bipolar process. The lamella appears to consist of short regular rodlets or cylinders 5 to 7 m# in diameter, oriented with their long axes perpendicular to the plane of the lamella. Minute cytoplasmic vesicles found in the cytoplasm of both the rod spherule and the bipolar terminal are most abundant near the rod synaptic lamella.

The primary visual system of the rat: A primer of its anatomy

“…In general terms, the rod synaptic base, that is the rod spherical, is one of the largest synapses in the central nervous system and may be characterized as a bulbar ending containing a bilobular invagination resembling two juxtaposed footballs. Ladman (1958) has further described the rod spherical as containing a single large mitochondria located above the bilobular invagination, although other authors have not specifically confirmed this observation. Other elements within the cytoplasm of the spherical are granular and innerplasmic reticulum and, of course, synaptic vesicles.…”

“…Following the elegant descriptions of De Roberts and Franchi (1956), Gray and Pease (1971), Ladman (1958), and Leure-duPree (1974), the present report will concentrate upon the synaptic base of the rod receptor. This concentration is not necessarily a denial of cone receptors within the rat's retina, but simply a concession to available data.…”

Glucose metabolism in mammalian photoreceptor inner and outer segments

“…Mitochondria are distributed throughout the inner segment and synaptic terminal. 6,9,11,35 The different architectures of rod and cone outer segments represent a major distinctive feature of the two photoreceptor cell types. Cones are conical shaped cells and their outer segments are generally shorter than rods.…”

The ZebrafishnrcMutant Reveals a Role for the Polyphosphoinositide Phosphatase Synaptojanin 1 in Cone Photoreceptor Ribbon Anchoring

“…The arciform density, which is thought to anchor ribbons to the presynaptic membrane (Ladman, 1958), is absent in the majority of nrc photoreceptor terminals (Allwardt et al, 2001). The nrc synaptic malformities are associated with blindness and defective synaptic transmission between cones and bipolar cells characterized by pronounced asynchronous oscillations in the electroretinogram response (Allwardt et al, 2001;Van Epps et al, 2001).…”