Biology subjects

Eggers, E. D.

Publications and source records attributed to Eggers, E. D..

4 recordsLinked to original sources

bioRxiv2025

Early Diabetic Ca2+ Handling Impairments in the Rod Bipolar Pathway

BackgroundPrevious work showed that electrically-evoked inhibition to Rod Bipolar Cells (RBC) is reduced in a mouse model of early diabetes. It is hypothesized that this is due to impaired Ca2+ handling in the presynaptic amacrine cell, either through increased Ca2+ buffering or decreased influx. To test this hypothesis and develop a mechanism for this effect, a model where direct optogenetic activation of inhibitory amacrine cells that expressed the light-activated channel ChR2 was used to isolate amacrine cell inputs to RBCs. Application of selective Ca2+ channel blockers could then assess potential locations of amacrine Ca2+ disruption. Using whole cell patch clamp electrophysiology, recordings were made from a 6 week diabetic population (DM) and vehicle injected non-DM animals. ResultsRobust GABAC receptor inhibitory currents were recorded from RBCs after ChR2 stimulus that were significantly diminished by the application of nifedipine to block L-type Ca2+ channels in both DM and non-DM conditions. There were significant differences in the peak amplitude of these responses between DM and non-DM groups (p = 0.0146). However, in the non-DM group the decay tau of the response to the 50ms stimulus was significantly diminished by nifedipine ({tau} p =0.0498, n = 5), but this was not seen in the DM group ({tau} p = 0.9498, n=7). A 1s nifedipine-reduced response saw its decay tau increase in the DM group but not the non-DM. Ca2+ - induced Ca2+ release (CICR) blockade with ryanodine decreased responsivity equally between groups in the 1s stimulus but showed no significant kinetic changes. CICR blockade for a 50ms stimulus response showed significant kinetic changes in diabetes but otherwise reduced the response equally between DM and non-DM. Blockade of the mitochondrial Ca2+ uniporter (MCU) had little effect on the optogenetic response. ConclusionThis study presents evidence that diabetes alters amacrine cell output to the RBC unmasked through blockade of the L-type calcium channel, and the Endoplasmic Reticulum (ER). An apparent explanation for our results is that DM calcium buffering is dysregulated, leading to prolonged responses. The underlying mechanism for this alteration is complex and not yet clearly elucidated.

neuroscience↗

bioRxiv2025

Dopamine D1 Receptors Modulate glycinergic Inhibitory Inputs to OFF cone bipolar cells elicited by Optogenetic Activation of Amacrine Cells

PurposeLight evoked inhibition of OFF cone bipolar cells (OFF BCs) is modulated both by background light levels and the action of dopamine through the dopamine D1 receptor (R). Since D1Rs are localized throughout the mouse retina, it is not known where in the light signaling pathway dopamine is modulating signals to OFF BCs. Here we tested a technique that allowed for the isolation of the amacrine cell (AC) to OFF BC circuit to determine if there are local D1R-induced changes in inhibition from presynaptic ACs onto OFF BCs. MethodsWe utilized the B6.Cg-Tg(Slc32al-COP4*H134R/EYFP) mouse line that expresses ChR2 in all the inhibitory cells in the retina. ACs expressing ChR2 were directly activated by light, while blocking photoreceptor mediated inputs. Inhibitory synaptic currents or ChR2-evoked excitatory currents were recorded using whole-cell patch clamp electrophysiology. ResultsOptogenetically activated inhibition from ACs elicited inhibitory currents that had slow kinetics similar to light-evoked inhibition, suggesting that they are using native synaptic mechanisms. We recorded optogenetically activated inputs to OFF BCs from pharmacologically isolated GABAergic and glycinergic input while photoreceptor inputs were blocked. D1R activation reduced glycinergic inputs to OFF BCs while leaving GABAergic inputs intact. ConclusionsD1R modulation of isolated optogenetic activation of AC-OFF BC synapses showed similar changes to previous experiments with light-evoked inhibition to OFF BCs. Together, this suggests optogenetic activation of ACs can be used to understand how dopamine differentially shapes inhibitory changes in the inner retina.

neuroscience↗

bioRxiv2023

Parallel Neurodegenerative Phenotypes in Sporadic Parkinsons Disease Fibroblasts and Midbrain Dopamine Neurons

Understanding the mechanisms causing Parkinsons disease (PD) is vital to the development of much needed early diagnostics and therapeutics for this debilitating condition. Here, we report cellular and molecular alterations in skin fibroblasts of late-onset sporadic PD subjects, that were recapitulated in matched induced pluripotent stem cell (iPSC)-derived midbrain dopamine (DA) neurons, reprogrammed from the same fibroblasts. Specific changes in growth, morphology, reactive oxygen species levels, mitochondrial function, and autophagy, were seen in both the PD fibroblasts and DA neurons, as compared to their respective controls. Additionally, significant alterations in alpha synuclein expression and electrical activity were also noted in the PD DA neurons. Interestingly, although the fibroblast and neuronal phenotypes were similar to each other, they also differed in their nature and scale. Furthermore, statistical analysis revealed novel associations between various clinical measures of the PD subjects and the different fibroblast and neuronal data. In essence, these findings encapsulate spontaneous, in-tandem, disease-related phenotypes in both sporadic PD fibroblasts and iPSC-based DA neurons, from the same patient, and generates an innovative model to investigate PD mechanisms with a view towards rational disease stratification and precision treatments.

neuroscience↗

bioRxiv2020

Dopamine D1 and D4 receptors contribute to light adaptation in ON-sustained retinal ganglion cells

The adaptation of ganglion cells to increasing light levels is a crucial property of the retina. The retina must respond to light intensities that vary by 10-12 orders of magnitude, but the dynamic range of ganglion cell responses covers only [~]3 orders of magnitude. Dopamine is a crucial neuromodulator for light adaptation and activates receptors in the D1 and D2 families. D1Rs are expressed on horizontal cells and some bipolar, amacrine and ganglion cells. In the D2 family D2Rs are expressed on dopaminergic amacrine cells and D4Rs are primarily expressed on photoreceptors. However, the roles of activating these receptors to modulate the synaptic properties of the inputs to ganglion cells are not yet clear. Here we used single cell retinal patch-clamp recordings from the mouse retina to determine how activating D1Rs and D4Rs changed the light-evoked and spontaneous excitatory inputs to ON-sustained (ON-s) ganglion cells. We found that both D1R and D4R activation decrease the light-evoked excitatory inputs to ON-s ganglion cells, but that only the sum of the peak response decrease due to activating the two receptors was similar to the effect of light adaptation to a rod-saturating background. The largest effects on spontaneous excitatory activity of both D1R and D4R agonists was on the frequency of events, suggesting that both D1Rs and D4Rs are acting upstream of the ganglion cells. New and NoteworthyDopamine by bright light conditions allows retinal neurons to reduce sensitivity to adapt to bright light conditions. It is not clear how and why dopamine receptors modulate retinal ganglion cell signaling. We found that both D1 and D4 dopamine receptors in photoreceptors and inner retinal neurons contribute significantly to the reduction in sensitivity of ganglion cells with light adaptation. However, light adaptation also requires dopamine independent mechanisms that could reflect inherent sensitivity changes in photoreceptors.

neuroscience↗