Biology subjects

Kushner, J. K.

Publications and source records attributed to Kushner, J. K..

4 recordsLinked to original sources

bioRxiv2026

Synaptotagmin isoforms differentially regulate glutamate and GABA release in the lateral habenula

Neurotransmitter co-transmission contributes to diverse physiological processes throughout the mammalian brain, including sensory integration, motivational control, and social behaviors. Projections from the globus pallidus internus (GPi; the entopeduncular nucleus, EPN, in rodents) to the lateral habenula (LHb) are well-characterized by the co-transmission of both GABA and glutamate. These dual-release inputs modulate behavioral states in chronically learned helpless (cLH) rats, influencing both the onset and recovery of pathological phenotypes. Here, we employed confocal 3D reconstructions that confirmed the presence of both vesicular transporters VGAT and VGLUT2 in EPN axon terminals within the LHb. Further investigation revealed that GABA and glutamate are packaged in distinct vesicle populations within individual presynaptic terminals. Notably, the calcium (Ca{superscript 2}) sensors Synaptotagmin-2 (Syt2) and Synaptotagmin-3 (Syt3) are highly expressed in the EPN whereas expression of the canonical Ca{superscript 2} sensor, Synaptotagmin 1 (Syt1), is downregulated. Additionally, using confocal microscopy, we observed selective spatial correlations of Syt2 and VGLUT2 and between Syt3 and VGAT in LHb axon terminals. These observations strongly suggested that Syt2 serves as the predominant Ca{superscript 2} sensor for glutamatergic vesicle fusion, and Syt3 serves as the predominant Ca{superscript 2} sensor for GABAergic vesicle fusion in the LHb. To test this hypothesis, we employed targeted antisense oligonucleotide (ASO) knockdown of Syt2 and Syt3 in EPN neurons and measured LHb glutamatergic and GABAergic currents. Syt2 knockdown resulted in an increase in mEPSC frequency, amplitude, half-width and decay, suggesting increased glutamate vesicle release probability and increased glutamate vesicle packing. However, Syt2 knockdown had no influence on mIPSCs amplitude or frequency. On the other hand, Syt3 knockdown had no apparent effect on glutamate release but caused an increase in mIPSC frequency suggesting increased quantal release probability of GABA. Together, these findings identify a molecular mechanism by which synaptotagmin isoforms govern differential glutamate and GABA release at EPN dual-transmitter terminals in the LHb. These results provide evidence for presynaptic mechanisms regulating excitatory-inhibitory balance within this brain structure and importantly provide molecular targets for pharmacological intervention.

neuroscience↗

bioRxiv2023

Developmental Characterization of Neuronal Migration Anomalies and Axon Proliferation in mTOR pathway-associated Malformations of Cortical Development

Drug-resistant epilepsy (DRE) is a prevalent problem in children that can lead to abnormal development and various psychiatric comorbidities. Malformations of cortical development (MCD) include focal cortical dysplasia, tuberous sclerosis complex and hemimegalencephaly, which are the most common pathologies among children who undergo surgical resection for treatment of DRE. These disorders share many histopathological features, including dyslamination of the cerebral cortex and enlarged neuronal somata. Recently, genetic mutations in the mammalian target of rapamycin (mTOR) signaling cascade have been shown to underpin most MCDs. Rodent models, including the RhebCA model, recapitulate histologic and physiologic aspects of human DRE. However, there have been few studies characterizing the developmental time point of the histological changes seen in MCDs. In this study, we use in utero electroporation to upregulate the Rheb protein (directly upstream of mTOR) in a focal area of the neocortex. We demonstrate that mTOR dysregulation leads to focal dyslamination and increased neuronal size that is histologically similar to MCD, which correlates to spontaneous recurrent seizures. We used immunohistochemistry to investigate neuronal lamination at several time points during development between E18 and P21 and show early differences in lamination that persisted through development. Furthermore, the increased axonal length associated with mTOR upregulation occurs early in development. Our study provides a time frame for the initial development of abnormal neuronal migration and cellular growth that occurs in MCDs, and our data supports that these anatomical changes may contribute to the formation of epileptic networks.

neuroscience↗

bioRxiv2022

Characterizing the diversity of L2/3 human neocortical neurons in epilepsy

In the current study, we performed whole-cell current clamp recordings from human cortical neurons in layer 2/3 of the human neocortex in order to characterize the diversity of L2/3 human neocortical neurons in epileptic foci with various etiologies in order to begin to elucidate the underlying mechanisms of hyperexcitability which are still mostly unknown. We differentiated neuronal subtypes based on their firing patterns and AHP kinetics or epilepsy subtype (malformation of cortical development (MCD) vs. other (non-MCD)). We found that L2/3 pyramidal neurons have diverse firing properties and action potential kinetics, with some neurons looking remarkably similar to LTS interneurons. We also saw that L2/3 pyramidal neurons could be split into those with fast AHPs and those without, medium AHPs (mAHPs). Based on these parameters, we were unable to significantly differentiate neurons based on firing properties indicating that AHP component kinetics alone do not dictate L2/3 pyramidal neuron firing in human epileptic cortical slices. We also report significant differences in intrinsic properties between MCD and non-MCD and control L2/3 pyramidal neurons and are the first to characterize that wash on of the proconvulsant drug, 4-aminopyridine (4-AP), leads to increased AP duration, less firing rate (FR) accommodation, and slowed down AHPs. Overall, the present study is the first to characterize the large variability of L2/3 human neocortical pyramidal neurons, to compare between L2/3 pyramidal neurons within the epileptic foci between MCD and non-MCD cases, to use control tissue from tumor patients without incidence of seizure, and to determine the influence of 4-AP on L2/3 pyramidal neuron intrinsic properties.

neuroscience↗

bioRxiv2020

Hyperexcitability and loss of feedforward inhibition in the Fmr1KO lateral amygdala.

Fragile X Syndrome (FXS) is a neurodevelopmental disorder characterized by intellectual disability, autism spectrum disorders (ASDs), and anxiety disorders. The disruption in the function of the FMR1 gene results in a range of alterations in cellular and synaptic function. Previous studies have identified dynamic alterations in inhibitory neurotransmission in early postnatal development in the amygdala of the mouse model of FXS. Yet little is known how these changes alter microcircuit development and plasticity in the lateral amygdala (LA). Using whole-cell patch clamp electrophysiology, we demonstrate that principal neurons (PNs) in the LA exhibit hyperexcitability with a concomitant increase in the synaptic strength of excitatory synapses in the BLA. Further, reduced feed-forward inhibition appears to enhance synaptic plasticity in the FXS amygdala. These results demonstrate that plasticity is enhanced in the amygdala of the juvenile Fmr1 KO mouse and that E/I imbalance may underpin anxiety disorders commonly seen in FXS and ASDs.

neuroscience↗