The neural organization of the lamina ganglionaris in the crayfish: A Golgi and EM study

The lamina ganglionaris in the crayfish is composed of two cell layers and three acellular fibrous zones. The cells composing the layers above the acellular synaptic region (SR) show two distinct nuclear types in light microscopy and two cytoplasmic types with EM. Golgi impregnations of the lamina revealed three groups of elements which contribute processes to the SR; retinula axons from the retina, monopolar elements from the cell layers above the SR and horizontal elements whose perikaryal location is uncertain. Retinula elements terminate at various levels within the SR forming large irregular baglike terminals. Monopolar cells have a single axial fiber with numerous lateral processes which extend across the SR in a veriety of patterns. Horizontal elements have a more extensive lateral spead within the SR than monopolar processes. Electron microscopic data show the retinula terminal bags and monopolar processes to be organized into cartridge units at the superficial levels of the SR. Each cartridge consists of four enlarged terminals, three retinula axons and four to six central moncpolar processes. At deeper levels of the SR, the cartridge arrangement is not evident and the large terminals appear arranged in rows. Specialized synaptic contacts are found along the central borders of the retinula terminals.