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R.J. Clarke, K. Hognason, R. Chawla, E. Townes–Anderson; Photoreceptor interactions with second– and third–order retinal neurons after optical tweezer micromanipulation . Invest. Ophthalmol. Vis. Sci. 2004;45(13):5368.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Transplanted photoreceptors fail to form appropriate connections with second order neurons. Previous work, examining random groupings of retinal neurons, suggested that synaptic contact at 2 weeks was more frequent between photoreceptors and multipolar (amacrine and ganglion cells) than other cell types (Sherry et al. J. Comp. Neurol.1996; 376:476). The purpose of the present study was to re–examine the apparent attraction between novel partners using a newly developed system where cell pairing could be carefully controlled. Methods: Adult, tiger salamander retinas were dissociated and plated, and a single photoreceptor was paired with either a bipolar or a multipolar neuron by micromanipulation of the photoreceptor using optical tweezers. Bipolar and multipolar cells were identified at plating by their distinct morphologies. Cell pairs were followed for 7 days, then fixed and immunostained for rod opsin to distinguish rods from cones. Photoreceptors were classified as attracted to, or inhibited by, or neither attracted nor inhibited by its paired neuron. This was quantified according to total neurite growth, toward or away from the target neuron, or movement or merging of the pair. In addition, the number of presynaptic varicosities formed by the photoreceptor toward and away from the neuron was examined. Results: Of 10 rods paired with bipolar cells, neurite growth of 6 cells was attracted to the 2nd order neuron. However, varicosities were more prevalent on processes growing away from the target suggesting antagonism to bipolar cells. Of 13 rods paired with multipolar cells, neuritic growth of 8 cells was attracted to the 3rd order neuron. Varicosities were also more prevalent towards the paired neuron. Of 7 cones paired with bipolar cells, 4 cells were attracted. Varicosities were also more numerous toward the bipolar cell. Of 6 cones paired with multipolar cells, only 2 cells showed attraction and varicosities were predominantly away from the target neuron. Conclusions: Partially confirming previous work, bipolar cells had limited attraction for both rods and cones, whereas multipolar cells were more strongly attractive to rods. Unexpectedly, multipolar cells were inhibitory to cone cells. These results are reminiscent of the rod neurite growth into inner nuclear and plexiform layers and the lack of growth of cones into these layers observed in certain retinal diseases.
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