The pattern of cone pedicles and horizontal cells in the retina of the European anchovy, Engraulis encrasicolus L. (Engraulididae, Clupeiformes).
We have studied the architecture of polycone pedicles and their postsynaptic horizontal cells in the European anchovy using serial reconstruction by means of thin-sections from the cone outer segments to the outer plexiform layer. Within this layer there is a tesselated arrangement of pedicles in two strata, one made by the long-cone pedicles and one by those of the short-cones. The two pedicle types differ in the architecture of their synaptic sites. The long-cones possess two ribbon clusters corresponding to two bunches of subsynaptic dendrites, while the short-cones have only a single ribbon cluster innervated by a single group of dendrites. In addition, telodendria specifically connect the cone pedicles of neighbouring rows. Among the horizontal cells three classes arranged in separate levels can be distinguished. Serial reconstruction results suggest that first level horizontal cells contact long-cones preferentially. Among bipolar cells with an oval shaped dendritic field another type is found with a rectangular field of polycone-parallel dendritic combs. These findings indicate that the uncommon cone structures of engraulidids, which probably subserve polarization contrast vision, are correlated with a peculiar geometry of the outer plexiform layer.
Hess
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M
BioImaging Centre, Ludwig-Maximilians University, Munich, Germany. hess@biz.uni-muenchen.de
Melzer
R R
RR
Smola
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U
D000818:Animals; D005399:Fishes / Q000033:anatomy & histology*; D021621:Imaging, Three-Dimensional; D008854:Microscopy, Electron; D012160:Retina / Q000166:cytology*; D017949:Retinal Cone Photoreceptor Cells / Q000648:ultrastructure*