Erika D Eggers
Associate Professor, BIO5 Institute
Associate Professor, Biomedical Engineering
Associate Professor, Neuroscience - GIDP
Associate Professor, Physiological Sciences - GIDP
Associate Professor, Physiology
Primary Department
Department Affiliations
(520) 626-7137
Work Summary
My laboratory studies how the retina takes visual information about the world and transmits it to the brain. We are trying to understand how this signaling responds to changing amounts of background light and becomes dysfunctional in diabetes.
Research Interest
The broad goal of research in our laboratory is to understand how inhibitory inputs influence neuronal signaling and sensory signal processing in the healthy and diabetic retina. Neurons in the brain receive inputs that are both excitatory, increasing neural activity, and inhibitory, decreasing neural activity. Inhibitory and excitatory inputs to neurons must be properly balanced and timed for correct neural signaling to occur. To study sensory inhibition we use the retina, a unique preparation which can be removed intact and can be activated physiologically, with light, in vitro. Thus using the retina as a model system, we can study how inhibitory synaptic physiology influences inhibition in visual processing. This intact system also allows us to determine the mechanisms of retinal damage in early diabetes. Keywords: neuroscience, diabetes, vision, electrophysiology, light

Publications

Moore-Dotson, J. M., Beckman, J. J., Mazade, R. E., Hoon, M., Bernstein, A. S., Romero-Aleshire, M. J., Brooks, H. L., & Eggers, E. D. (2016). Early Retinal Neuronal Dysfunction in Diabetic Mice: Reduced Light-Evoked Inhibition Increases Rod Pathway Signaling. Investigative ophthalmology & visual science, 57(3), 1418-30.
BIO5 Collaborators
Heddwen L Brooks, Erika D Eggers

Recent studies suggest that the neural retinal response to light is compromised in diabetes. Electroretinogram studies suggest that the dim light retinal rod pathway is especially susceptible to diabetic damage. The purpose of this study was to determine whether diabetes alters rod pathway signaling.

Schubert, T., Kerschensteiner, D., Eggers, E. D., Misgeld, T., Kerschensteiner, M., Lichtman, J. W., Lukasiewicz, P. D., & Wong, R. O. (2008). Development of presynaptic inhibition onto retinal bipolar cell axon terminals is subclass-specific. Journal of neurophysiology, 100(1), 304-16.

Synaptic integration is modulated by inhibition onto the dendrites of postsynaptic cells. However, presynaptic inhibition at axonal terminals also plays a critical role in the regulation of neurotransmission. In contrast to the development of inhibitory synapses onto dendrites, GABAergic/glycinergic synaptogenesis onto axon terminals has not been widely studied. Because retinal bipolar cells receive subclass-specific patterns of GABAergic and glycinergic presynaptic inhibition, they are a good model for studying the development of inhibition at axon terminals. Here, using whole cell recording methods and transgenic mice in which subclasses of retinal bipolar cells are labeled, we determined the temporal sequence and patterning of functional GABAergic and glycinergic input onto the major subclasses of bipolar cells. We found that the maturation of GABAergic and glycinergic synapses onto the axons of rod bipolar cells (RBCs), on-cone bipolar cells (ON-CBCs) and off-cone bipolar cells (OFF-CBCs) were temporally distinct: spontaneous chloride-mediated currents are present in RBCs earlier in development compared with ON- and OFF-CBC, and RBCs receive GABAergic and glycinergic input simultaneously, whereas in OFF-CBCs, glycinergic transmission emerges before GABAergic transmission. Because on-CBCs show little inhibitory activity, GABAergic and glycinergic events could not be pharmacologically distinguished for these bipolar cells. The balance of GABAergic and glycinergic input that is unique to RBCs and OFF-CBCs is established shortly after the onset of synapse formation and precedes visual experience. Our data suggest that presynaptic modulation of glutamate transmission from bipolar cells matures rapidly and is differentially coordinated for GABAergic and glycinergic synapses onto distinct bipolar cell subclasses.

Eggers, E. D., Klein, J. S., & Moore-Dotson, J. M. (2013). Slow changes in Ca2(+) cause prolonged release from GABAergic retinal amacrine cells. Journal of neurophysiology, 110(3), 709-19.

The timing of neurotransmitter release from neurons can be modulated by many presynaptic mechanisms. The retina uses synaptic ribbons to mediate slow graded glutamate release from bipolar cells that carry photoreceptor inputs. However, many inhibitory amacrine cells, which modulate bipolar cell output, spike and do not have ribbons for graded release. Despite this, slow glutamate release from bipolar cells is modulated by slow GABAergic inputs that shorten the output of bipolar cells, changing the timing of visual signaling. The time course of light-evoked inhibition is slow due to a combination of receptor properties and prolonged neurotransmitter release. However, the light-evoked release of GABA requires activation of neurons upstream from the amacrine cells, so it is possible that prolonged release is due to slow amacrine cell activation, rather than slow inherent release properties of the amacrine cells. To test this idea, we directly activated primarily action potential-dependent amacrine cell inputs to bipolar cells with electrical stimulation. We found that the decay of GABAC receptor-mediated electrically evoked inhibitory currents was significantly longer than would be predicted by GABAC receptor kinetics, and GABA release, estimated by deconvolution analysis, was inherently slow. Release became more transient after increasing slow Ca(2+) buffering or blocking prolonged L-type Ca(2+) channels and Ca(2+) release from intracellular stores. Our results suggest that GABAergic amacrine cells have a prolonged buildup of Ca(2+) in their terminals that causes slow, asynchronous release. This could be a mechanism of matching the time course of amacrine cell inhibition to bipolar cell glutamate release.

Lukasiewicz, P. D., Eggers, E. D., Sagdullaev, B. T., & McCall, M. A. (2004). GABAC receptor-mediated inhibition in the retina. Vision research, 44(28), 3289-96.

Inhibition at bipolar cell axon terminals regulates excitatory signaling to ganglion cells and is mediated, in part, by GABAC receptors. We investigated GABAC receptor-mediated inhibition using pharmacological approaches and genetically altered mice that lack GABAC receptors. Responses to applied GABA showed distinct time courses in various bipolar cell classes, attributable to different proportions of GABAA and GABAC receptors. The elimination of GABAC receptors in GABAC null mice reduced and shortened GABA-activated currents and light-evoked inhibitory synaptic currents (L-IPSCs) in rod bipolar cells. ERG measurements and recordings from the optic nerve showed that inner retinal function was altered in GABAC null mice. These data suggest that GABAC receptors determine the time course and extent of inhibition at bipolar cell terminals that, in turn, modulates the magnitude of excitatory transmission from bipolar cells to ganglion cells.

Flood, M. D., Wellington, A., & Eggers, E. D. (2017). Dopamine modulation of the inner retina in early diabetes. TBD.