Form and Function of on-off Amacrine Cells in the Amphibian Retina

Abstract

Miller, Robert F., Nathan P. Staff, and Toby J. Velte. Form and function of ON-OFF amacrine cells in the amphibian retina. J Neurophysiol 95: 3171-3190, 2006. First published February 15, 2006 doi:10.1152/jn.00090.2005. ON-OFF amacrine cells were studied with whole cell recording techniques and intracellular staining methods using intact retina-eyecup preparations of the tiger salamander (Ambystoma tigrinum) and the mudpuppy (Necturus maculosus). Morphological characterization of these cells included three-dimensional reconstruction methods based on serial optical sections obtained with a confocal microscope. Some cells had their detailed morphology digitized with a computer-assisted tracing system and converted to compartmental models for computer simulations. The dendrites of ON-OFF amacrine cells have spines and numerous varicosities. Physiological recordings confirmed that ON-OFF amacrine cells generate both large-and small-amplitude impulses attributed, respectively, to somatic and dendritic generation sites. Using a multichannel model for impulse generation, computer simulations were carried out to evaluate how impulses are likely to propagate throughout these structures. We conclude that the ON-OFF amacrine cell is organized with multifocal dendritic impulse generating sites and that both dendritic and somatic impulse activity contribute to the functional repertoire of these interneurons: locally generated dendritic impulses can provide regional activation, while somatic impulse activity results in rapid activation of the entire dendritic tree.

Mechanisms Underlying Lateral GABAergic Feedback onto Rod Bipolar Cells in Rat Retina

“…Although it is possible that these GABAergic inputs to RBCs are mediated by amacrine cells that are activated purely by ON or OFF channels, combinations of ON and OFF inputs cannot be ruled out (Werblin and Dowling, 1969; Dacheux and Raviola, 1995; Bloomfield and Volgyi, 2007). Previous work on amacrine cells that respond to both light increments and decrements has shown that these cells can mediate feedforward inhibition to ganglion cells (Cook and Werblin, 1994; Taylor, 1999) or feedback inhibition onto bipolar cells (Shields and Lukasiewicz, 2003) and possess a similar sensitivity to TTX (Miller and Dacheux, 1976; Werblin, 1977; Cook and Werblin, 1994; Miller et al, 2006; Bloomfield and Volgyi, 2007), as observed here (Figure 3). …”

Narrow and wide field amacrine cells fire action potentials in response to depolarization and light stimulation

“…This finding is consistent with previous modeling papers showing that a single-spiking cell could be caused to fire repetitively by increasing the number of sodium channels or I NaṼ Eliasof et al, 1987;Fohlmeister & Miller, 1997b;Miller et al, 2006!. Repetitive-spiking cells had a larger peak I NaV , lower action potential threshold and larger action potentials than single-spiking cells.…”

Mapping a Complete Neural Population in the Retina

“…However, this possibility is made very unlikely by the size of the spikes of amacrine cells. These spikes are small (~20 mV), even in intracellular recordings (Barnes and Werblin, 1986, Sakai et al, 1997, Miller et al, 2006). If the amacrine cell’s spike is 5 times smaller than that of the ganglion cell, then it often will not exceed our spike threshold in the pre-processing step.…”