Biology subjects

Augustine, G. J.

Publications and source records attributed to Augustine, G. J..

6 recordsLinked to original sources

bioRxiv2024

Low intensity pulsed ultrasound activates excitatory synaptic networks in cultured hippocampal neurons

Ultrasound can non-invasively penetrate deep into brain for neuromodulation and has demonstrated good potential for clinical application. Excitation or inhibition of neurons by ultrasound has been reported, but the underlying mechanisms are largely unknown. So far most in vitro studies have focused on the activation of individual neurons by ultrasound with calcium imaging. As the focal region of ultrasound is typically millimeter or submillimeter size, it is important to investigate yet so far unclear how the mechanical effects of ultrasound would influence on the synaptic circuit activity of neurons. MethodsLow-intensity pulsed ultrasound (LIPUS) (25 MHz, 5% duty cycle, 5 Hz pulse repetition frequency, 0.4 - 1.6 W/cm2) was used to stimulate cultured hippocampal neurons. Action potentials and excitatory postsynaptic currents were recorded in individual cells with the whole-cell patch-clamp technique. We also simultaneously imaged intracellular calcium, along with neuronal electrical signals, to resolve neuronal network dynamics during LIPUS. ResultsExcitatory postsynaptic currents (EPSCs) were evoked by LIPUS in high-density neuronal cultures. Both the frequency and amplitude of EPSCs increased, indicating enhanced glutamatergic synaptic transmission. The probability of evoking responses, as well as the total charge of EPSCs evoked by ultrasound, increased with ultrasound intensity. Mechanistic analysis reveals that extracellular calcium influx, action potential (AP) firing and synaptic transmission are necessary for the responses to ultrasound in the high-density culture. In contrast, EPSCs were not enhanced in cultures with low densities of neurons. Simultaneous calcium imaging of neuronal network activity indicated that recurrent excitatory network activity is recruited during ultrasound stimulation in high-density cultures. ConclusionUltrasound can activate recurrent neuronal network activity, caused by excitatory synaptic transmission, over tens to hundreds of seconds. Our study provides insights into the mechanisms involved in the response of the brain to ultrasound and illuminates the potential to use ultrasound to regulate synaptic function in neurological disorders that involve synaptic dysfunction, such as Parkinsons disease and Alzheimers disease. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=146 SRC="FIGDIR/small/614451v1_ufig1.gif" ALT="Figure 1"> View larger version (25K): org.highwire.dtl.DTLVardef@bd419org.highwire.dtl.DTLVardef@91d93corg.highwire.dtl.DTLVardef@14d0c14org.highwire.dtl.DTLVardef@153f7c4_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2023

Presynaptic and Postsynaptic Determinants of the Functional Connectivity Between the Claustrum and Anterior Cingulate Cortex.

The claustrum (CLA) is a brain nucleus located between the insula and lateral striatum, implicated in a wide range of behaviors. Underpinning the different behavioral phenotypes is the connectivity between the claustrum and various cortical regions, including the anterior cingulate cortex (ACC). CLA projection neurons are glutamatergic neurons, however, the impact of CLA on its cortical targets has been shown in some studies to be inhibitory. Such inhibition is likely to arise from claustral activation of cortical interneurons, however, the intricate synaptic connectivity between different CLA and cortical cell types is not known. Here, we combine in vivo and ex vivo electrophysiology and optogenetics to reveal the functional organization of the CLA-ACC pathway according to the identity of its pre- and postsynaptic populations. Optogenetic stimulation of CLA neurons in awake mice resulted in multiphasic excitatory and inhibitory responses in ACC cells, which depended on the layer, cell type, and stimulated CLA population. Using ex vivo paired recordings in ACC, monosynaptic responses were recorded in pyramidal cells and different types of interneurons following photostimulation of CLA-ACC synaptic terminals. CLA axons formed monosynaptic connections in all ACC cortical layers, but the probability and strength of synaptic responses depended on the type of CLA projection, target layer in ACC, and the type of postsynaptic neuron. This intricate organization of the CLA-ACC pathway may explain the complex impact of CLA on ACC and other cortical regions, thus resolving some of the discrepancies in the field and shedding light on the functional role CLA plays in cortical function.

neuroscience↗

bioRxiv2023

Different mechanisms of synapsin-induced vesicle clustering at inhibitory and excitatory synapses

Synapsins cluster synaptic vesicles (SVs) to provide a reserve pool (RP) of SVs that maintains synaptic transmission during sustained activity. However, it is unknown how synapsins cluster SVs. Here we show that either liquid-liquid phase separation (LLPS) or tetramerization-dependent cross-linking can cluster SVs, depending upon whether a synapse is excitatory or inhibitory. Cell-free reconstitution revealed that both mechanisms can cluster SVs, with tetramerization bring more effective. At inhibitory synapses, perturbing synapsin-dependent LLPS impairs SV clustering and synchronization of GABA release, while perturbing synapsin tetramerization does not. At glutamatergic synapses, the opposite is true: synapsin tetramerization enhances clustering of glutamatergic SVs and mobilization of these SVs from the RP, while synapsin LLPS does not. Comparison of inhibitory and excitatory transmission during prolonged synaptic activity revealed that synapsin LLPS serves as a brake to limit GABA release, while synapsin tetramerization enables rapid mobilization of SVs from the RP to sustain glutamate release.

neuroscience↗

bioRxiv2022

Feedback Inhibition Underlies New Computational Functions of Cerebellar Interneurons

The function of a feedback inhibitory circuit between cerebellar Purkinje cells and molecular layer interneurons (MLIs) was defined by combining optogenetics, neuronal activity recordings both in cerebellar slices and in vivo, and computational modeling. Purkinje cells inhibit a subset of MLIs in the inner third of the molecular layer. This inhibition is non-reciprocal, short-range (less than 200 m) and is based on convergence of 1-2 Purkinje cells onto MLIs. During learning-related eyelid movements in vivo, the activity of a subset of MLIs progressively increases at the same time that Purkinje cell activity decreases, with Purkinje cells usually leading the MLIs. Computer simulations indicate that these relationships are best explained by the feedback circuit from Purkinje cells to MLIs and that this feedback circuit plays a central role in making cerebellar learning efficient.

neuroscience↗

bioRxiv2021

A functional logic for neurotransmitter co-release in the cholinergic forebrain pathway

The forebrain cholinergic system has recently been shown to co-release both acetylcholine and GABA. We have discovered that such co-release by cholinergic inputs to the claustrum differentially affects neurons that project to cortical versus subcortical targets. The resulting changes in neuronal gain toggles network efficiency and discriminability of output between two different projection subcircuits. Our results provide a potential logic for neurotransmitter co-release in cholinergic systems.

neuroscience↗

bioRxiv2020

Heterogeneous somatostatin-expressing neuron population in mouse ventral tegmental area

The cellular architecture of the ventral tegmental area (VTA), the main hub of the brain reward system, remains only partially characterized. To extend the characterization to inhibitory neurons, we have identified three distinct subtypes of somatostatin (Sst)-expressing neurons in the mouse VTA. These neurons differ in their electrophysiological and morphological properties, anatomical localization, as well as mRNA expression profiles. Importantly, similar to cortical Sst-containing interneurons, most VTA Sst neurons express GABAergic inhibitory markers, but some of them also express glutamatergic excitatory markers and a subpopulation even express dopaminergic markers. Furthermore, only some of the proposed marker genes for cortical Sst neurons were expressed in the VTA Sst neurons. Physiologically, one of the VTA Sst neuron subtypes locally inhibited neighboring dopamine neurons. Overall, our results demonstrate the remarkable complexity and heterogeneity of VTA Sst neurons and suggest that these cells are multifunctional players in the midbrain reward circuitry.

neuroscience↗