Dynamics of gap junctions between horizontal cells in the goldfish retina.

Experimental alterations of gap junctions between outer horizontal cells have been demonstrated in freeze-fracture replicas of goldfish retina. The alterations consisted predominantly of an increase of connexon densities and a decrease in the variability of the arrangement of connexons. They were observed i. in dark adapted retinae, ii. in animals with crushed optic nerves, iii. in picrotoxin- and bicuculline-treated animals. Since experiment i. is characterized by a depolarization of the horizontal cell, and experiment iii. was shown by others to result in uncoupling of horizontal cells, we conclude that the functional connectivity of horizontal cells might be correlated with the structure of gap junctions. An interesting detail is the differentiated reaction of axonal and perikaryal gap junctions on dark adaptation or blindness: whereas normally the axonal gap junctions are less densely packed, they increase their connexon density in darkness or blindness much more than the perikaryal gap junctions.