Cone and rod cells have different target preferences in vitro as revealed by optical tweezers.
OBJECTIVE
When neural circuits are damaged in adulthood, regenerating and sprouting processes must distinguish appropriate targets to recreate the normal circuitry. We tested the ability of adult nerve cells to target specific cells in culture using the retina as a model system.


METHODS
Under sterile culture conditions, retinal cells, isolated from tiger salamander retina, were micromanipulated with optical tweezers to create pairs of first-order photoreceptor cells with second- or third-order retinal neurons. The development of cell contact and presynaptic varicosities, the direction and amount of neuritic growth, and nerve cell polarity were assessed after seven days in vitro. Cultures were labeled for rod opsin to distinguish rod from cone cells and for the alpha subunit of the trimeric G protein Go (Go alpha) to identify cone-dominated and mixed rod-cone ON bipolar cells.


RESULTS
Quantitative analysis of growth demonstrated that target preferences were cell-specific: Cone cells preferred second-order bipolar cells, whereas rod cells grew toward third-order neurons, which include amacrine and ganglion cells. In addition, when rod cells grew toward bipolar cells, they chose an abnormally high number of Go alpha-positive bipolar cells. These growth patterns were not affected by tweezers manipulation or the amount of growth. Cell orientation of the photoreceptor also did not affect preferences: Cells oriented away from dendritic processes could reorient their axonal pole toward the target cell.


CONCLUSIONS
Cone cells preferred normal partners, and rod cells preferred novel partners. These intrinsic preferences indicate that adult nerve cells can have differing capacities for targeting even if they come from the same cell class. Further,these differences may help explain the patterns of photoreceptor sprouting seen in retinal degeneration in which rod, but not cone, cells invade the inner retinal layers where third-order neurons are located.
Clarke
Robert J
RJ
Department of Neurology and Neuroscience, New Jersey Medical School, University of Medicine and Dentistry of New Jersey, Newark, NJ 07103, USA.
Högnason
Kormákur
K
Brimacombe
Michael
M
Townes-Anderson
Ellen
E
D000818:Animals; D002450:Cell Communication; D002465:Cell Movement; D016764:Cell Polarity; D002478:Cells, Cultured; D052898:Optical Tweezers; D020419:Photoreceptor Cells, Vertebrate / Q000166:cytology; D051245:Retinal Bipolar Cells / Q000166:cytology; D017949:Retinal Cone Photoreceptor Cells / Q000166:cytology* / Q000502:physiology*; D017948:Retinal Rod Photoreceptor Cells / Q000166:cytology* / Q000502:physiology*; D014562:Caudata