Rod and cone signals in the on-center bipolar cell: Their different ionic mechanisms

Simultaneous intracellular recordings were made from a bipolar cell and a horizontal cell in the carp retina. The properties of the bipolar cell were studied while injecting current into the horizontal cell. Hyperpolarization of horizontal cells, irrespective of their type, elicited a hyperpolarizing response in on-center bipolar cells and a depolarizing response in off-center bipolar cells. Analyses of the ionic mechanisms of bipolar cell responses revealed that depolarization of horizontal cells simulated and hyperpolarization opposed the effect of central illumination. The effect of polarization was exerted in such a manner that each type of horizontal cells modified the transmission from those photoreceptors from which they receive main inputs. In on-center bipolar cells, for example, the L-type horizontal cells receiving inputs mainly from red cones modified the cone-bipolar transmission accompanied by a conductance change of K+ and/or Cl- channels, and the intermediate horizontal cells receiving inputs from rods modified the rod-bipolar transmission accompanied by a conductance change of Na+ channels. In off-center bipolar cells, the effect of polarization of any type of horizontal cells was mediated mainly by conductance changes of Na+ channels. Feedback mechanisms from horizontal cells to photoreceptors could explain these results reasonably well.

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Hydrostibination of Alkynes: A Radical Mechanism

10.26434/chemrxiv.12497834 ◽

2020 ◽

Author(s):

Josh MacMillan ◽

Katherine Marczenko ◽

Erin Johnson ◽

Saurabh Chitnis

Keyword(s):

Density Functional ◽

Activation Barrier ◽

Closed Shell ◽

Reaction Rates ◽

Radical Mechanism ◽

Neutral Radical ◽

Kinetic Isotope ◽

Rate Limiting Step ◽

Ionic Mechanisms ◽

Terminal Acetylenes

The addition of Sb-H bonds to alkynes was reported recently as a new hydroelementation reaction that exclusively yields anti-Markovnikov Z-olefins from terminal acetylenes. We examine four possible mechanisms that are consistent with the observed stereochemical and regiochemical outcomes. A comprehensive analysis of solvent, substituent, isotope, additive, and temperature effects on hydrostibination reaction rates definitively refutes three ionic mechanisms involving closed-shell charged intermediates. Instead the data support a fourth pathway featuring neutral radical SbII and SbIII intermediates. Density Functional Theory (DFT) calculations are consistent this model, predicting an activation barrier that is within 1 kcal mol-1 of the experimental value (Eyring analysis) and a rate limiting step that is congruent with experimental kinetic isotope effect. We therefore conclude that hydrostibination of arylacetylenes is initiated by the generation of stibinyl radicals, which then participate in a cycle featuring SbII and SbIII intermediates to yield the observed Z-olefins as products. This mechanistic understanding will enable rational evolution of hydrostibination as a methodology for accessing challenging products such as E-olefins.

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Faculty Opinions recommendation of Development of presynaptic inhibition onto retinal bipolar cell axon terminals is subclass-specific.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.1124541.581747 ◽

2008 ◽

Author(s):

Marla Feller

Keyword(s):

Bipolar Cell ◽

Presynaptic Inhibition ◽

Cell Axon ◽

Axon Terminals

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Faculty Opinions recommendation of TRPM1 is a component of the retinal ON bipolar cell transduction channel in the mGluR6 cascade.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.4390960.4227055 ◽

2010 ◽

Author(s):

David Zenisek ◽

Christina Joselevitch

Keyword(s):

Bipolar Cell

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A model of on/off transitions in neurons of the deep cerebellar nuclei: deciphering the underlying ionic mechanisms

The Journal of Mathematical Neuroscience ◽

10.1186/s13408-021-00105-3 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Hugues Berry ◽

Stéphane Genet

Keyword(s):

Cerebellar Nuclei ◽

Biophysical Model ◽

High Threshold ◽

Deep Cerebellar Nuclei ◽

Functional Link ◽

Electrophysiological Properties ◽

Voltage Dependent ◽

Ionic Mechanisms ◽

The Central Nervous System ◽

Overall Functioning

AbstractThe neurons of the deep cerebellar nuclei (DCNn) represent the main functional link between the cerebellar cortex and the rest of the central nervous system. Therefore, understanding the electrophysiological properties of DCNn is of fundamental importance to understand the overall functioning of the cerebellum. Experimental data suggest that DCNn can reversibly switch between two states: the firing of spikes (F state) and a stable depolarized state (SD state). We introduce a new biophysical model of the DCNn membrane electro-responsiveness to investigate how the interplay between the documented conductances identified in DCNn give rise to these states. In the model, the F state emerges as an isola of limit cycles, i.e. a closed loop of periodic solutions disconnected from the branch of SD fixed points. This bifurcation structure endows the model with the ability to reproduce the $\text{F}\to \text{SD}$ F → SD transition triggered by hyperpolarizing current pulses. The model also reproduces the $\text{F}\to \text{SD}$ F → SD transition induced by blocking Ca currents and ascribes this transition to the blocking of the high-threshold Ca current. The model suggests that intracellular current injections can trigger fully reversible $\text{F}\leftrightarrow \text{SD}$ F ↔ SD transitions. Investigation of low-dimension reduced models suggests that the voltage-dependent Na current is prominent for these dynamical features. Finally, simulations of the model suggest that physiological synaptic inputs may trigger $\text{F}\leftrightarrow \text{SD}$ F ↔ SD transitions. These transitions could explain the puzzling observation of positively correlated activities of connected Purkinje cells and DCNn despite the former inhibit the latter.

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