Biology subjects

Jackson, M. B.

Publications and source records attributed to Jackson, M. B..

6 recordsLinked to original sources

bioRxiv2025

Biased inter-columnar communication and short-term plasticity in mouse barrel cortex

The barrel cortex (BC) processes complex direction-, frequency-, and phase-dependent input from whiskers to analyze objects in the immediate environment. Little is known about how BC microcircuits process this information and integrate input from multiple whiskers. To investigate these circuits we targeted a hybrid voltage sensor (hVOS) to Scnn1a excitatory neurons in cortical layer 4 (L4), and imaged population responses to electrical stimulation. BC in coronal and sagittal slices presented the laminar structure of the cortex with barrels aligned along stereotyped whisking directions. Voltage imaging tracked activity along an L4[->]L2/3[->]L4 relay during inter-barrel communication. AMPA receptor blockade demonstrated that this relay depends on excitatory synaptic transmission, and revealed intra- and inter-barrel feedforward inhibition. Communication between barrels was isotropic in response amplitude, half-width, and conduction velocity, but latency was longer for communication to caudal barrels. Furthermore, paired-pulse depression was weakest and recovery slowest for protraction-related directions, especially to caudally adjacent barrels. Such biases will preferentially enhance repetitive inputs in this direction. These results identify direction-dependent synaptic circuitry that shapes inter-barrel communication. Anisotropy in short-term plasticity aligns with whisker motion kinematics, suggesting that BC microcircuits are tuned to preserve temporal fidelity and selectively filter inputs according to whisking phase and direction.

neuroscience↗

bioRxiv2025

Plasma membrane-endoplasmic reticulum coupling probed with genetically-encoded voltage sensors

The endoplasmic reticulum (ER) forms an elaborate contiguous network extending through the cytoplasm of eukaryotic cells. The ER is surrounded by a membrane that separates its lumen from the cytoplasm. The ER membrane harbors channels and pumps capable of controlling ion flux and creating a voltage gradient. Because the ER membrane potential is difficult to study experimentally little is known about how voltage influences its many vital functions. Here we introduce optical probes of ER membrane potential derived from the hybrid voltage sensor (hVoS) family of genetically-encoded voltage sensors. Probes were targeted to the ER using motifs from three ER proteins, Sec61{beta}, cytochrome P450, and cytochrome b5 type A. As shown recently with other types of ER voltage sensors, patch-clamp fluorometry recording with our new probes demonstrated that voltage steps applied to the plasma membrane elicit a voltage change at the ER membrane. These probes exhibited subtle differences in their responses suggesting they target different ER compartments. The steeper voltage dependence of Sec61{beta}-hVoS (mCerulean3-Sec61{beta}) signals suggested that this probe targets an ER compartment rich in voltage-gated ion channels. The ER voltage change is slow, but its onset is virtually synchronous with the plasma membrane voltage step. This suggests a direct electrical coupling into the ER lumen through plasma membrane-ER contacts. Analysis with the aid of an equivalent circuit provided an estimate of the resistance of these contacts. The rapid, direct transmission of voltage changes from the plasma membrane to the ER provides a mechanism for regulating ER function that could be especially important in excitable cells. The sensors introduced here provide researchers with powerful tools for imaging ER voltage and assessing its impact on cellular function. SignificanceThe ER is encompassed by a membrane, and the voltage across this membrane is likely to play important roles in many cellular functions. It is difficult to study this voltage due to the inaccessibility of organelle membranes. We introduced new hybrid genetically-encoded optical voltage sensors that target the ER. These probes showed that a voltage step applied to the plasma membrane changes the voltage at the ER membrane in a manner consistent with direct electrical coupling to the cell surface through contacts. This coupling will enable voltage changes at the plasma membrane to influence ER function. The probes introduced here will enable researchers to image ER voltage and probe plasma membrane-ER signaling.

biophysics↗

bioRxiv2023

Inter and Intralaminar Excitation of Parvalbumin Interneurons in Mouse Barrel Cortex

Parvalbumin (PV) interneurons are inhibitory fast-spiking cells with essential roles in directing the flow of information through cortical circuits. These neurons set the balance between excitation and inhibition, control rhythmic activity, and have been linked to disorders including autism spectrum and schizophrenia. PV interneurons differ between cortical layers in their morphology, circuitry, and function, but how their electrophysiological properties vary has received little attention. Here we investigate responses of PV interneurons in different layers of primary somatosensory barrel cortex (BC) to different excitatory inputs. With the genetically-encoded hybrid voltage sensor, hVOS, we recorded voltage changes simultaneously in many L2/3 and L4 PV interneurons to stimulation in either L2/3 or L4. Decay-times were consistent across L2/3 and L4. Amplitude, half-width, and rise-time were greater for PV interneurons residing in L2/3 compared to L4. Stimulation in L2/3 elicited responses in both L2/3 and L4 with longer latency compared to stimulation in L4. These differences in latency between layers could influence their windows for temporal integration. Thus PV interneurons in different cortical layers of BC show differences in response properties with potential roles in cortical computations. Key points summaryO_LIExcitatory synaptic responses were imaged in parvalbumin (PV) interneurons in slices of mouse barrel cortex using a targeted genetically-encoded voltage sensor. This approach revealed simultaneous voltage changes in approximately 20 neurons pre slice in response to stimulation. C_LIO_LIPV interneurons residing in layer 2/3 had larger amplitudes, longer half-widths, and longer rise-times than PV interneurons residing in layer 4. C_LIO_LIResponses of PV interneurons residing in either layer 2/3 or layer 4 had shorter latencies to stimulation of layer 4 compared to stimulation of layer 2/3. C_LIO_LIExcitatory synaptic transmission to PV interneurons varies with layer of residence and source of excitation. C_LI

neuroscience↗

bioRxiv2022

Conduction Velocities of Excitatory Axons Innervating Parvalbumin Interneurons in Primary Somatosensory Cortex

Inhibitory interneurons that express parvalbumin (PV) play critical roles throughout the brain. Their rapid-spiking characteristics enable them to control the dynamics of neural circuits across a range of time scales, but the timing of their activation by different cortical pathways remains unclear. Here, we use a genetically encoded hybrid voltage sensor, hVOS, to image PV interneuron voltage changes with sub-millisecond precision in primary somatosensory barrel cortex (BC) of adult male and female mice. Electrical stimulation evoked depolarizing responses with a latency that increased with distance from the stimulating electrode, allowing us to determine conduction velocity. By focusing on conduction between cortical layers or between barrel columns we were able to measure interlaminar or intralaminar conduction velocity, respectively. Velocities ranged from 74 to 473 m/msec depending on trajectory, and we found that interlaminar conduction velocity was about 71% faster than intralaminar conduction velocity. This suggests that computations within columns can be processed more rapidly than between columns. BC circuitry integrates thalamic and intracortical input for a variety of functions including texture discrimination and sensory tuning. The difference in timing between intra- and interlaminar activation of PV interneurons could impact these functions. This study illustrates how hVOS imaging of PV interneuron electrical activity can reveal differences in the dynamics of signaling within different elements of cortical circuitry, and this approach offers a unique opportunity to investigate conduction in populations of axons based on their targeting specificity.

neuroscience↗

bioRxiv2022

The Third Transmembrane Domain of Synaptophysin Regulates Initial Fusion Pore Dynamics during Ca2+ -Triggered Exocytosis in Chromaffin cells

Synaptophysin (syp) is a major secretory vesicle protein comprising four transmembrane domains (TMDs) and a large cytoplasmic C-terminus. The C-terminus of syp has been shown to regulate exocytosis, vesicle cycling, and synaptic plasticity, but the roles of its TMDs remain unclear. SNARE TMDs line initial fusion pores, and structural work along with sequence analysis suggest that TMD III of syp may play a similar role. To test this hypothesis, we expressed TMD III tryptophan mutants in chromaffin cells from mice lacking both syp and its homolog synaptogyrin, and used amperometry to evaluate fusion pores. In contrast to SNARE TMDs, tryptophan substitutions in syp TMD III had no effect on the flux through initial fusion pores. However, these mutants increased the fraction of kiss-and-run events and decreased the initial fusion pore lifetime. Thus, syp TMD III does not line the initial fusion pore, but interacts with it to influence its stability and choice of release mode.

biophysics↗

bioRxiv2020

Fusion pore expansion and contraction during catecholamine release from endocrine cells

Amperometry recording reveals the exocytosis of catecholamine from individual vesicles as a sequential process, typically beginning slowly with a pre-spike foot, accelerating sharply to initiate a spike, reaching a peak, and then decaying. This complex sequence reflects the interplay between diffusion, flux through a fusion pore, and possibly dissociation from a vesicles densecore. In an effort to evaluate the impacts of these factors, a model was developed that combines diffusion with flux through a static pore. This model recapitulated the rapid phases of a spike, but generated relations between spike shape parameters that differed from experimental results. To explore the possibility of fusion pore dynamics, a transformation of amperometry current was introduced that yields fusion pore permeability divided by vesicle volume (g/V). Applying this transform to individual fusion events yielded a highly characteristic time course. g/V initially tracks the pre-spike foot and the start of the spike, increasing [~]15-fold to the peak. However, after the spike peaks, g/V unexpectedly declines and settles to a constant value that indicates the presence of a stable post-spike pore. g/V of the post-spike pore varies greatly between events, and has an average that is [~]3.5-fold below the peak value and [~]4.5-fold above the pre-spike value. The post-spike pore persists and g/V remains flat for tens of milliseconds, as long as catecholamine flux can be detected. Applying the g/V transform to rare events with two peaks revealed a stepwise increase in g/V during the second peak. The g/V transform offers an interpretation of amperometric current in terms of fusion pore dynamics and provides a new framework for analyzing the actions of proteins that alter spike shape. The stable post-spike pore conforms with predictions from lipid bilayer elasticity, and offers an explanation for previous reports of prolonged hormone retention within fusing vesicles. STATEMENT OF SIGNIFICANCEAmperometry recordings of catecholamine release from single vesicles reveal a complex waveform with distinct phases. The role of the fusion pore in this waveform is poorly understood. A model based on a static fusion pore fails to recapitulate important aspects of the waveform. A new transform of amperometric current introduced here renders fusion pore permeability in real time. This transform reveals rich dynamic behavior of the fusion pore as catecholamine leaves a vesicle. This analysis shows that fusion pore permeability rapidly increases and then decreases before settling into a stable post-spike configuration.

biophysics↗