Computer reconstruction of all the neurons in the optic ganglion of Daphnia magna.

The cellular architecture of the Daphnia compound eye visual system was studied by using computer-aided techniques. All the neurons in one half of the bilaterally symmetric optic ganglion (OG) were reconstructed in three dimensions from serial electron micrographs. The techniques employed were those developed by Levinthal and collaborators (Macagno, Levinthal, and Sobel, Ann. Rev. Biophys. Bioeng. 8:323-351, 1979). The approximately 200 neurons reconstructed were classified according to where they branch in the OG (the lamina and/or the medulla) and whether they send processes to the supraesophageal ganglion and/or across the midplane. Within each class, neurons were further characterized according to cell body location and size and location of their branching fields. Centrifugal processes from neurons with cell bodies not in the OG were also identified. These results provide the bases for a detailed examination of the synaptic connectivity of the identified neurons and for hypotheses concerning their functional roles in visually evoked behaviors.