A study on the projection patterns of aberrant retinal ganglion cells in the albino rat

Injecting the retrograde fluorescent neuronal tracer fluoro-gold into the dorsal nucleus of the lateral geniculate body (dLGN), the olivary pretectal nucleus (OPN), and the superior colliculus (SC) revealed the existence of some ganglion cells (RGCs) scattered outside the temporoventral crescent of the ipsilateral retina in the adult albino rats. We studied the projection patterns, topographic distribution, number, and the soma size of these aberrant RGCs in 12 adult albino rats. We estimated a mean of 50 aberrant cells projecting to the dLGN. Their soma size ranged from 40.6 to 211.0 microns2, with an average of 108.6 microns2. The soma size of the 45.5 aberrant cells projecting to the OPN ranged from 41.5 to 312.5 microns2, with an average of 147.2 microns2. The SC received projection from 38.3 aberrant cells whose soma size ranged from 42.0 to 315.1 microns2, with an average of 120.7 microns2. These cells were almost equally distributed between the central and peripheral portions of the ipsilateral nasal retina. The mean cell count of the SC-projecting population was significantly lower than those of the other 2 groups. The mean soma size of the OPN-projecting aberrant cells was larger, and their soma size histogram was significantly different from those of the other 2 groups, whose histograms were almost alike. Though their physiological role in processing visual information is not fully understood, the aberrant RGCs might project their axons to--in addition to the dLGN, OPN, and SC--other visual centers.