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A microtubule 'roadway' in the retina helps provide energy for vision

Rockefeller University Press

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IMAGE: Fluorescently labeled microtubules extend from the tips of the dendrites (top) into the axon and down into the giant synaptic terminal (bottom) of a single isolated goldfish retinal bipolar cell.... view more

Credit: Graffe et al., 2015

Researchers have discovered a thick band of microtubules in certain neurons in the retina that they believe acts as a transport road for mitochondria that help provide energy required for visual processing. The findings appear in the July issue of The Journal of General Physiology.

The retina is a layer of tissue in the back of the eye that converts light into nerve impulses. The retina contains small, specialized neurons called bipolar cells that transmit information from light-sensitive photoreceptor cells to ganglion neurons, which send information to the brain for interpretation as images.

Bipolar cells are continuously active, a characteristic few other neurons share. They require a constant supply of energy to mediate the sustained release of the contents of an enormous number of synaptic vesicles, which store the transmitters that convey information between neurons. An intriguing new study of their subcellular structure could help explain how bipolar synaptic terminals meet such excessive energy demands.

Using cutting-edge 3D microscopy, researchers from the National Heart, Lung, and Blood Institute and Yale University examined the subcellular architecture of presynaptic terminals in retinal bipolar cells of live goldfish. Goldfish retinal bipolar cells have giant presynaptic terminals that make them especially amenable for investigation. Unexpectedly, the team discovered a thick band of microtubules, a component of the cell's cytoskeleton, that extended from the axon of the neuron into the synaptic terminal and then looped around the interior periphery of the terminal.

The microtubule band appeared to associate with mitochondria--organelles known for providing energy to cells--in the synaptic terminal. When the researchers administered drugs to inhibit the movement of certain "motor" proteins that transport mitochondria and other cargo within the cell by traveling along microtubules, the mitochondria accumulated in the axon of the neuron and never made it to the synaptic terminal.

The findings suggest that these previously unknown microtubule structures provide a "roadway" for the transport of mitochondria crucial to maintain energy supplies into the synaptic terminals of these highly active neurons associated with vision.

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Graffe, M., et al. 2015. J. Gen. Physiol.doi:10.1085/jgp.201511396

About The Journal of General Physiology

Founded in 1918, The Journal of General Physiology (JGP) is published by The Rockefeller University Press. All editorial decisions on manuscripts submitted are made by leading, research-active scientists in conjunction with our in-house scientific editor. JGP content is posted to PubMed Central, where it is available to the public for free six months after publication. Authors retain copyright of their published works and third parties may reuse the content for non-commercial purposes under a creative commons license. For more information, please visit http://www.jgp.org.

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