Developmental dynamic in synaptic ribbons of retinal receptor cells (Tilapia, Xenopus).

In the cichlid teleost Tilapia leucosticta, the origin and linear development of synaptic ribbons in retinal receptor cells have been studied. First ribbons are invariably found close to their future synaptic sites between two dendritic invaginations. They are then clearly shorter than at later stages and appear bifurcate, or of bulb or drop shape. From these precursors typical ribbons rapidly develop, and these vary considerably in length. From a shift in length distribution, a main growth phase can be ddetected which takes place at the time when the retina first becomes functional. Similar observations were made in Xenopus. Placing Tilapia larvae in conditions of 24 h continuous light had no effect on ribbon growth, while 24 h of continuous darkness resulted in a prevalence of shorter ribbons. Thus the growth of synaptic ribbons in the course of retinal development appears to be subject to modification by environmental light conditions.