Synaptic development in semi-dissociated cultures of rat retina

Cultured neurons provide a simpler and more accessible environment to study the synaptic physiology. However, it is not clear if development of synaps es in Culture is similar to that in the in vivo condition. We studied the d evelopmental sequence and morphological differentiation of chemical synapse s in semi-dissociated rat retinal cultures that consisted of dissociated ne urons as well as undissociated retinal aggregates. Synapses were quantified by synaptophysin immunoreactive puncta. During second week of in vitro dev elopment the average number of chemical synapses on the cell body decreased while that on the neurites increased significantly. Conventional synapses appeared both in aggregate and in dissociated neurons, with the development al profile similar to that reported for in vivo retina. In contrast, the de velopment of ribbon synapses was adversely affected by the in vitro microen vironment as suggested by following observations. The ribbon synapses were more frequently found in aggregate than in dissociated neurons, and were no t associated with dyadic or triadic synaptic arrangement. The photoreceptor ribbons did not contact a postsynaptic process while bipolar ribbons made single (monadic) synapses. Further, photoreceptor ribbons in dissociated ne urons were late to form and took more time to mature as compared to those i n the aggregate cultures. Most of the rod bipolar cells, identified by thei r immunoreactivity to protein kinase C (PKC), had three or more neurites. U nlike in the in vivo retina, the dissociated rod bipolar cells did not show any PKC immunoreactive varicosities, suggesting that they failed to develo p a well-differentiated synaptic terminal. Interestingly, we did not find a ny parvalbumin positive All amacrine cells that are normally postsynaptic t o rod bipolar cells. These results show that the conventional synapses of r etina, which are similar to chemical synapses in other parts of the brain, develop normally both in aggregate and dissociated neurons. However, the hi ghly specialized ribbon synapses have more stringent developmental requirem ents, and their normal development may require the presence of postsynaptic neurons in their close vicinity. (C) 2001 ISDN. Published by Elsevier Scie nce Ltd. All rights reserved.