Synaptic contacts of the horizontal cells in the retina of the marine teleost, Callionymus lyra L.

The horizontal cell system in the retina of the fish Callionymus lyra L. was investigated light microscopically and electron microscopically. One type of rod horizontal cells, which are only found in the mixed ventral part, exclusively contacts spherules with lateral endknobs in the triads. Three types of cone horizontal cells occur. The first type, c-H1, contacts pedicles of pale and dark double cones and single cones. The processes always have a lateral position in the triads. This type has a constant contact pattern with the photoreceptor cells. The second type, c-H2, selectively contacts pedicles of pale double cones and the endbuds occupy a central position in the triads. In the single cone pedicles in the dendritic field of the c-H2 horizontal cell, the endbuds never seem to reach the triads. The third type, c-H3, only sends processes to pedicles of single cones where the endbuds occupy a central position in the triads. The synaptic connections of the horizontal cells of Callionymus differ from those observed in Nannacara anomala and Carassius auratus. The difference from the results obtained from Carassius is such that the information transfer model proposed for Carassius cannot apply to Callionymus.