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

Abstract

Action potentials in amacrine cells are important for lateral propagation of signals across the inner retina, but it is unclear how many subclasses of amacrine cells contain voltage-gated sodium channels or can fire action potentials. This study investigated the ability of amacrine cells with narrow ( <200 microm) and wide (>200 microm) dendritic fields to fire action potentials in response to depolarizing current injections and light stimulation. The pattern of action potentials evoked by current injections revealed two distinct classes of amacrine cells; those that responded with a single action potential (single-spiking cells) and those that responded with repetitive action potentials (repetitive-spiking cells). Repetitive-spiking cells differed from single-spiking cells in several regards: Repetitive-spiking cells were more often wide field cells, while single-spiking cells were more often narrow field cells. Repetitive-spiking cells had larger action potential amplitudes, larger peak voltage-gated NaV currents lower action potential thresholds, and needed less current to induce action potentials. However, there was no difference in the input resistance, holding current or time constant of these two classes of cells. The intrinsic capacity to fire action potentials was mirrored in responses to light stimulation; single-spiking amacrine cells infrequently fired action potentials to light steps, while repetitive-spiking amacrine cells frequently fired numerous action potentials. These results indicate that there are two physiologically distinct classes of amacrine cells based on the intrinsic capacity to fire action potentials.

All Spiking, Sustained ON Displaced Amacrine Cells Receive Gap-Junction Input from Melanopsin Ganglion Cells

“…TTX did reduce these responses, however, indicating ipRGC signaling is facilitated by voltage-gated Na + channels, and indeed wide-field amacrines often use active conductances to boost long-range propagation [21, 39, 40]. Such partial reliance on voltage gating suggests that ipRGCs’ light responses might travel fairly far to reach the coupled amacrine cells.…”

Expression and localisation of two-pore domain (K2P) background leak potassium ion channels in the mouse retina

“…This pattern of expression is potentially in keeping the nature of electrical activity observed within the retina. With the exception of RGCs (and a few specialised subtypes of bipolar cells82 and amacrine cells8384), the majority of retinal cell types do not classically encode light signals as patterns of action potential firing but instead show graded changes in membrane potential28586. It is therefore possible that these cell types show less functional reliance on K + leak currents than typical spike firing neurones, such as RGCs.…”

Light adaptation alters inner retinal inhibition to shape OFF retinal pathway signaling

“…4E). Many GABAergic amacrine cells mediate wide inhibitory surrounds (Dacey et al 2000;Ichinose and Lukasiewicz 2005;Sinclair et al 2004;Zhang and Wu 2009) and can be coupled and/or fire action potentials to further extend their spatial signaling (Cook and Werblin 1994;Heflin and Cook 2007;Volgyi et al 2009). Isolated GABAergic input was wider than total input (Figs.…”