Abstract
Purpose:
During the first postnatal weeks of the developing rodent retina, rhodopsin can be detected in a number of neuron-like cells in the inner retina. In the present study we aimed to characterize the morphology, number and staining characteristics of this peculiar population.
Methods:
Misplaced rhodopsin-positive cells (MRCs) were analyzed on the retinas of four rodent species, labeled with various rhodopsin-specific antibodies. To investigate their possible relation with non-photoreceptor cells, sections were double-stained against distinct retinal cell types, while the possibility of photoreception was assessed by counter staining with cone- and melanopsin specific antibodies and proteins of the phototransduction cascade. The possibility of synapse formation and apoptosis were also investigated.
Results:
In all species studied, misplaced cells comprised a few percent of all rhodopsin-positive elements. Their ratio was relatively constant with a decline from the end of the second week, and MRCs disappeared near completely from the retina by P24. MRCs resembled resident neurons of the inner retina; outer segment-like processes were seen only rarely. MRCs expressed no other photopigment types and showed no colocalization with any of the bipolar, horizontal, amacrine and ganglion cell markers used. While all MRCs colabeled for arrestin and recoverin, other proteins of the phototransduction cascade were only detectable in a minority of the population. Only a few MRCs were shown to form synaptic-like endings.
Conclusions:
Our results showed that during development a significant percentage of the hodopsin-expressing cells are displaced to the inner retinal layers. Although most MRCs lack morphological features of photoreceptors, they contain some, but not all elements of the phototransduction cascade, indicating that they are most probably misplaced rods that failed to complete differentiation and integrate into the photoreceptor mosaic.
Keywords: 698 retinal development •
648 photoreceptors