Morphology of retinal ganglion cells in the flying fox (Pteropus scapulatus): A lucifer yellow investigation

The morphology of retinal ganglion cells was determined in megachiroptera, commonly known as flying foxes. Retinal ganglion cells were intracellularly injected with the fluorescent dye Lucifer yellow in fixed retinae from adult little red flying foxes (Pteropus scapulatus) captured in their natural habitat. Ganglion cells closely resembled the three main classes of cat retinal ganglion cells, and therefore were classified into alpha-, beta-, and gamma-type cells. The size of the alpha- and beta-type somas and dendritic fields increased with increasing distance from the area centralis. However, this eccentricity dependence was not as pronounced as in the cat. The gamma-type cells were sub-divided into mono-, bi-, and diffusely stratified, in accordance with the ramification of their dendrites within the inner plexiform layer. The alpha- and beta-type cells were uni-stratified in either the sublamina of the inner plexiform layer closest to the ganglion cell layer or in that closest to the inner nuclear layer. These laminae correspond to those in the cat retina which contain the dendritic ramifications of ganglion cells whose central receptive fields respond best to onset of light (the "on-centre" cells), or to ganglion cells whose centres respond optimally to light being extinguished (the "off-centre" cells). Thus the flying fox retina contains a morphological correlate of the "on"/"off" dichotomy of alpha and beta cells in the cat retina. In general the flying fox retinal ganglion cells exhibit a degree of morphological complexity reminiscent of cat retinal cells and this may reflect similar functional properties.