A Study on the Projection Patterns of Aberrant Retinal Ganglion Cells in the Albino Rat

Abstract

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.

Retinal Input Induces Three Firing Patterns in Neurons of the Superficial Superior Colliculus of Neonatal Rats

“…During the refinement process, side branches and arbors from topographically inappropriate positions retract, and those at topographically correct positions increase. This remodeling of axon arbors leads to an adult-like topographic ordering of axonal arborization by P11-12 (O'Leary 1986;Simon and O'Leary 1992a,b;Simon et al 1994), although even in the adult there are still some aberrant ganglion cells that project to topographically inappropriate regions of the SC (Rahman and Yamadori 1994).…”