Biology subjects

Murphy-Baum, B. L.

Publications and source records attributed to Murphy-Baum, B. L..

2 recordsLinked to original sources

bioRxiv2022

Spatiotemporal properties of glutamate input support direction selectivity in the dendrites of retinal starburst amacrine cells

AO_SCPLOWBSTRACTC_SCPLOWThe asymmetric summation of kinetically distinct glutamate inputs across the dendrites of retinal "starburst" amacrine cells is proposed to underlie their direction selective properties, but experimentally verifying input kinetics has been a challenge. Here, we used two-photon glutamate sensor (iGluSnFR) imaging to directly measure the input kinetics across individual starburst dendrites. We found that signals measured from proximal dendrites were relatively sustained compared to those measured from distal dendrites. These differences were observed across a range of stimulus sizes and appeared to be shaped mainly by excitatory rather than inhibitory network interactions. Temporal deconvolution analysis suggests that the steady-state vesicle release rate was [~] 3 times larger at proximal sites compared to distal sites. Using a connectomics-inspired computational model, we demonstrate that input kinetics play an important role in shaping direction selectivity at low stimulus velocities. Together, these results provide direct support for the space-time wiring model for direction selectivity.

neuroscience↗

bioRxiv2019

Precise subcellular functional organization of excitation and inhibition in the direction-selective ganglion cell circuit

Recent studies indicate that the precise timing and location of excitation and inhibition (E/I) within active dendritic trees can significantly impact neuronal function. How excitatory and inhibitory inputs are functionally organized at the subcellular level in intact circuits remains unclear. To address this issue, we took advantage of the retinal direction-selective ganglion cell circuit, in which directionally tuned inhibitory GABAergic input arising from starburst amacrine cells shape direction-selective dendritic responses. We combined two-photon Ca2+ imaging with genetic, pharmacological, and single-cell ablation methods to examine local E/I. We demonstrate that when active dendritic conductances are blocked, direction selectivity emerges semi-independently within unusually small dendritic segments (<10 {micro}m). Impressively, the direction encoded by each segment is relatively homogenous throughout the ganglion cells dendritic tree. Together the results demonstrate a precise subcellular functional organization of excitatory and inhibitory input, which suggests that the parallel processing scheme proposed for direction encoding could be more fine-grained than previously envisioned.

neuroscience↗