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 research is in Journal of General Physiology. (full access paywall)
Research: “A marginal band of microtubules transports and organizes mitochondria in retinal bipolar synaptic terminals” by Malkolm Graffe, David Zenisek, and Justin W. Taraska in Journal of General Physiology doi:10.1085/jgp.201511396
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. A loop of microtubules encircles the inner plasma membrane of the terminal and anchors mitochondria. Image credit: Graffe et al.