Displaced small amacrine cells in the retina of the marine teleost Callionymus lyra L.

The displaced small amacrine cells (DSA cells) in the dorsal pure cone part of the retina of the marine teleost Callionymus lyra have been analysed in a combined light and electron microcopical study. These unistratified cells have their dendritic arborization at 70% of the depth of the inner plexiform layer (P5 level). The DSA cells constitute a dense population and have variable dendritic field sizes. The bipolar input occurs in the P5,1 and the P5,2 pattern layer. The short, central DSA dendrites make ribbon synapses with midget mixed di-cone bipolar cells and with two types of pure cone bipolar cells. The amacrine input and output occurs in the fibrous layer that separates both pattern layers. The dendritic arborization is most extensive and the dendrites of neighbouring DSA cells are interconnected. The thick, central DSA dendrites are presynaptic to adjacent DSA cells and possibly to large bistratified and diffuse ganglion cells. The fine, peripheral DSA dendrites receive input from neighbouring DSA cells and probably from large uni- and bistratified and diffuse amacrine cells. A matching population of regularly placed small amacrine cells (RSA cells) has been observed. Their unistratified dendritic arborization is situated at 20% of the depth of the inner plexiform layer. The synaptic relations of RSA cells have not yet been completely analysed in detail. However, results up till now indicate that they most probably receive input from two bipolar cell types, one of which may be a pure cone type. In addition, the large bistratified amacrine and ganglion cells may be synaptically connected to the RSA cells as well as to the DSA cells.