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G. Zeck, A. Lambacher, P. Fromherz; Electrical Image of the Nerve Fibre Layer of the Rabbit Retina. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1406.
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© ARVO (1962-2015); The Authors (2016-present)
The mammalian retina processes and transmits visual information through more than a dozen channels embodied in different types of ganglion cells. Recent studies established that coincident activity of ganglion cells facilitates the transmission from the retina to higher brain areas and facilitates the encoding of visual stimulus information. An implicit assumption for the coincident arrival of afferent input signals at the postsynaptic target cell constitutes the preservation of the temporal activity structure. However, it is unknown if the temporal relation between individual neuronal signals is preserved from the site of initiation along the unmyelinated axons in the retinal nerve fibre layer. Here we electrically image the propagation of action potentials in the nerve fibre layer of the rabbit retina.
Action potentials were elicited by visual stimuli in the whole mount rabbit retina and detected by a multi-transistor array comprising 16000 extracellular sensor sites. We followed the signal propagation of individual action potentials at very high spatial (7.8 µm) and temporal (0.1 msec) resolution. This high spatial sampling was necessary to measure the conduction velocity in axonal populations that curve and cross each other.
The temporal action potential patterns in one axon are unchanged during the transmission in individual axons and bundles thereof. We also recorded misrouted axons with signals propagating away from the optic nerve. These signals were unaffected as well by parallel axons.Our measurements on more than hundred axons at different retinal positions prove that the mean conduction velocity is uniform throughout the rabbit retina. This means that intraretinal unmyelinated axons act as delay lines.The intraretinal conduction velocity varies among cell types. Transient cells have a high intraretinal conduction velocity of ~ 1.5 m/sec. The value decreases for direction selective cells and is smallest for cells wit long inter-spike intervals in their spike train (~1 m/sec).
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