A Metabolic Mechanism for Anaesthetic Suppression of Cortical Synaptic Function in Mouse Brain Slices—A Pilot Investigation

Regulation of synaptically located ionotropic receptors is thought to be the main mechanism by which anaesthetics cause unconsciousness. An alternative explanation, which has received much less attention, is that of primary anaesthetic disruption of brain metabolism via suppression of mitochondrial proteins. In this pilot study in mouse cortical slices, we investigated the effect of disrupting cellular metabolism on tissue oxygen handling and cortical population seizure-like event (SLE) activity, using the mitochondrial complex I inhibitor rotenone, and compared this to the effects of the general anaesthetics sevoflurane, propofol and ketamine. Rotenone caused an increase in tissue oxygen (98 mmHg to 157 mmHg (p < 0.01)) before any measurable change in SLE activity. Thereafter, tissue oxygen continued to increase and was accompanied by a significant and prolonged reduction in SLE root mean square (RMS) activity (baseline RMS of 1.7 to 0.7 µV, p < 0.001) and SLE frequency (baseline 4.2 to 0.4 events/min, p = 0.001). This temporal sequence of effects was replicated by all three anaesthetic drugs. In conclusion, anaesthetics with differing synaptic receptor mechanisms all effect changes in tissue oxygen handling and cortical network activity, consistent with a common inhibitory effect on mitochondrial function. The temporal sequence suggests that the observed synaptic depression—as seen in anaesthesia—may be secondary to a reduction in cellular metabolic capacity.

Download Full-text

Altered network properties in C9ORF72 repeat expansion cortical neurons are due to synaptic dysfunction

Molecular Neurodegeneration ◽

10.1186/s13024-021-00433-8 ◽

2021 ◽

Vol 16 (1) ◽

Author(s):

Emma M. Perkins ◽

Karen Burr ◽

Poulomi Banerjee ◽

Arpan R. Mehta ◽

Owen Dando ◽

...

Keyword(s):

Synaptic Plasticity ◽

Synaptic Vesicle ◽

Cortical Neurons ◽

Electrode Array ◽

Repeat Expansion ◽

Cortical Network ◽

Synaptic Function ◽

Network Activity ◽

Cortical Function ◽

Network Function

Abstract Background Physiological disturbances in cortical network excitability and plasticity are established and widespread in amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) patients, including those harbouring the C9ORF72 repeat expansion (C9ORF72RE) mutation – the most common genetic impairment causal to ALS and FTD. Noting that perturbations in cortical function are evidenced pre-symptomatically, and that the cortex is associated with widespread pathology, cortical dysfunction is thought to be an early driver of neurodegenerative disease progression. However, our understanding of how altered network function manifests at the cellular and molecular level is not clear. Methods To address this we have generated cortical neurons from patient-derived iPSCs harbouring C9ORF72RE mutations, as well as from their isogenic expansion-corrected controls. We have established a model of network activity in these neurons using multi-electrode array electrophysiology. We have then mechanistically examined the physiological processes underpinning network dysfunction using a combination of patch-clamp electrophysiology, immunocytochemistry, pharmacology and transcriptomic profiling. Results We find that C9ORF72RE causes elevated network burst activity, associated with enhanced synaptic input, yet lower burst duration, attributable to impaired pre-synaptic vesicle dynamics. We also show that the C9ORF72RE is associated with impaired synaptic plasticity. Moreover, RNA-seq analysis revealed dysregulated molecular pathways impacting on synaptic function. All molecular, cellular and network deficits are rescued by CRISPR/Cas9 correction of C9ORF72RE. Our study provides a mechanistic view of the early dysregulated processes that underpin cortical network dysfunction in ALS-FTD. Conclusion These findings suggest synaptic pathophysiology is widespread in ALS-FTD and has an early and fundamental role in driving altered network function that is thought to contribute to neurodegenerative processes in these patients. The overall importance is the identification of previously unidentified defects in pre and postsynaptic compartments affecting synaptic plasticity, synaptic vesicle stores, and network propagation, which directly impact upon cortical function.

Download Full-text

Long-term depression of excitatory transmission in the lateral septum

Journal of Neurophysiology ◽

10.1152/jn.00657.2019 ◽

2021 ◽

Author(s):

Chanchanok Chaichim ◽

Madeleine Jessica Radnan ◽

Gadiel Dumlao ◽

John M. Power

Keyword(s):

Sex Differences ◽

Drugs Of Abuse ◽

Brain Slices ◽

Lateral Septum ◽

Network Activity ◽

Excitatory Postsynaptic Potential ◽

Glutamatergic Transmission ◽

Long Term Depression

Neurons in the lateral septum (LS) integrate glutamatergic synaptic inputs, primarily from hippocampus, and send inhibitory projections to brain regions involved in reward and the generation of motivated behavior. Motivated learning and drugs of abuse have been shown to induce long-term changes in the strength of glutamatergic synapses in the LS, but the cellular mechanisms underlying long-term synaptic modification in the LS are poorly understood. Here we examined synaptic transmission and long-term depression (LTD) in brain slices prepared from male and female C57BL/6 mice. No sex differences were observed in whole-cell patch-clamp recordings of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPA-R) and N-methyl-D-aspartate receptor (NMDA-R) mediated currents. Low frequency stimulation of the fimbria fibre bundle (1 Hz 15 min) induced LTD of the LS field excitatory postsynaptic potential (fEPSP). Induction of LTD was blocked by the NMDA-R antagonist APV, but not the selective antagonist of GluN2B-containing NMDA-R ifenprodil. These results demonstrate the NMDA-R dependence of LTD in the LS. The LS is a sexually dimorphic structure and sex differences in glutamatergic transmission have been reported in vivo; our results suggest sex differences observed in vivo result from network activity rather than intrinsic differences in glutamatergic transmission.

Download Full-text

Understanding the Effects of General Anesthetics on Cortical Network Activity Using Ex Vivo Preparations

Anesthesiology ◽

10.1097/aln.0000000000002554 ◽

2019 ◽

Vol 130 (6) ◽

pp. 1049-1063 ◽

Cited By ~ 10

Author(s):

Logan J. Voss ◽

Paul S. García ◽

Harald Hentschke ◽

Matthew I. Banks

Keyword(s):

Molecular Mechanisms ◽

Ex Vivo ◽

Brain Slices ◽

Brain Regions ◽

Cortical Network ◽

Network Activity ◽

Common Mechanism ◽

General Anesthetics ◽

Neural Basis

Abstract General anesthetics have been used to ablate consciousness during surgery for more than 150 yr. Despite significant advances in our understanding of their molecular-level pharmacologic effects, comparatively little is known about how anesthetics alter brain dynamics to cause unconsciousness. Consequently, while anesthesia practice is now routine and safe, there are many vagaries that remain unexplained. In this paper, the authors review the evidence that cortical network activity is particularly sensitive to general anesthetics, and suggest that disruption to communication in, and/or among, cortical brain regions is a common mechanism of anesthesia that ultimately produces loss of consciousness. The authors review data from acute brain slices and organotypic cultures showing that anesthetics with differing molecular mechanisms of action share in common the ability to impair neurophysiologic communication. While many questions remain, together, ex vivo and in vivo investigations suggest that a unified understanding of both clinical anesthesia and the neural basis of consciousness is attainable.

Download Full-text

L-type voltage-gated calcium channel regulation of in vitro human cortical neuronal networks

Scientific Reports ◽

10.1038/s41598-019-50226-9 ◽

2019 ◽

Vol 9 (1) ◽

Cited By ~ 2

Author(s):

William Plumbly ◽

Nick Brandon ◽

Tarek Z. Deeb ◽

Jeremy Hall ◽

Adrian J. Harwood

Keyword(s):

Calcium Channel ◽

Neuronal Networks ◽

Gene Mutations ◽

Synaptic Function ◽

Neuronal Firing ◽

Network Activity ◽

Electrode Arrays ◽

Voltage Gated ◽

Voltage Gated Calcium Channel

Abstract The combination of in vitro multi-electrode arrays (MEAs) and the neuronal differentiation of stem cells offers the capability to study human neuronal networks from patient or engineered human cell lines. Here, we use MEA-based assays to probe synaptic function and network interactions of hiPSC-derived neurons. Neuronal network behaviour first emerges at approximately 30 days of culture and is driven by glutamate neurotransmission. Over a further 30 days, inhibitory GABAergic signalling shapes network behaviour into a synchronous regular pattern of burst firing activity and low activity periods. Gene mutations in L-type voltage gated calcium channel subunit genes are strongly implicated as genetic risk factors for the development of schizophrenia and bipolar disorder. We find that, although basal neuronal firing rate is unaffected, there is a dose-dependent effect of L-type voltage gated calcium channel inhibitors on synchronous firing patterns of our hiPSC-derived neural networks. This demonstrates that MEA assays have sufficient sensitivity to detect changes in patterns of neuronal interaction that may arise from hypo-function of psychiatric risk genes. Our study highlights the utility of in vitro MEA based platforms for the study of hiPSC neural network activity and their potential use in novel compound screening.

Download Full-text

Neuropeptide S: a novel regulator of pain-related amygdala plasticity and behaviors

Journal of Neurophysiology ◽

10.1152/jn.00874.2012 ◽

2013 ◽

Vol 110 (8) ◽

pp. 1765-1781 ◽

Cited By ~ 32

Author(s):

Wenjie Ren ◽

Takaki Kiritoshi ◽

Stéphanie Grégoire ◽

Guangchen Ji ◽

Remo Guerrini ◽

...

Keyword(s):

Basolateral Amygdala ◽

Direct Action ◽

Brain Slices ◽

Inhibitory Effect ◽

Central Nucleus ◽

High Frequency Stimulation ◽

Synaptic Inhibition ◽

Neuropeptide S ◽

Cellular Mechanisms ◽

Postsynaptic Action

Amygdala plasticity is an important contributor to the emotional-affective dimension of pain. Recently discovered neuropeptide S (NPS) has anxiolytic properties through actions in the amygdala. Behavioral data also suggest antinociceptive effects of centrally acting NPS, but site and mechanism of action remain to be determined. This is the first electrophysiological analysis of pain-related NPS effects in the brain. We combined whole cell patch-clamp recordings in brain slices and behavioral assays to test the hypothesis that NPS activates synaptic inhibition of amygdala output to suppress pain behavior in an arthritis pain model. Recordings of neurons in the laterocapsular division of the central nucleus (CeLC), which serves pain-related amygdala output functions, show that NPS inhibited the enhanced excitatory drive [monosynaptic excitatory postsynaptic currents (EPSCs)] from the basolateral amygdala (BLA) in the pain state. As shown by miniature EPSC analysis, the inhibitory effect of NPS did not involve direct postsynaptic action on CeLC neurons but rather a presynaptic, action potential-dependent network mechanism. Indeed, NPS increased external capsule (EC)-driven synaptic inhibition of CeLC neurons through PKA-dependent facilitatory postsynaptic action on a cluster of inhibitory intercalated (ITC) cells. NPS had no effect on BLA neurons. High-frequency stimulation (HFS) of excitatory EC inputs to ITC cells also inhibited synaptic activation of CeLC neurons, providing further evidence that ITC activation can control amygdala output. The cellular mechanisms by which EC-driven synaptic inhibition controls CeLC output remain to be determined. Administration of NPS into ITC, but not CeLC, also inhibited vocalizations and anxiety-like behavior in arthritic rats. A selective NPS receptor antagonist ([d-Cys(tBu)5]NPS) blocked electrophysiological and behavioral effects of NPS. Thus NPS is a novel tool to control amygdala output and pain-related affective behaviors through a direct action on inhibitory ITC cells.

Download Full-text

Effects of Electrical Stimulation of NAc Afferents on VP Neurons’ Tonic Firing

Frontiers in Cellular Neuroscience ◽

10.3389/fncel.2020.599920 ◽

2020 ◽

Vol 14 ◽

Author(s):

Martin Clark

Keyword(s):

Brain Slices ◽

Electrode Array ◽

Inhibitory Effect ◽

Pause Duration ◽

Firing Frequency ◽

Ventral Pallidum ◽

Cellular Mechanisms ◽

Tonic Firing ◽

Afferent Stimulation ◽

Stimulation Of

Afferents from the nucleus accumbens (NAc) are a major source of input into the ventral pallidum (VP). Research reveals that these afferents are GABAergic, however, stimulation of these afferents induces both excitatory and inhibitory responses within the VP. These are likely to be partially mediated by enkephalin and substance P (SP), which are also released by these afferents, and are known to modulate VP neurons. However, less is known about the potentially differential effects stimulation of these afferents has on subpopulations of neurons within the VP and the cellular mechanisms by which they exert their effects. The current study aimed to research this further using brain slices containing the VP, stimulation of the NAc afferents, and multi-electrode array (MEA) recordings of their VP targets. Stimulation of the NAc afferents induced a pause in the tonic firing in 58% of the neurons studied in the VP, while 42% were not affected. Measures used to reveal the electrophysiological difference between these groups found no significant differences in firing frequency, coefficient of variation, and spike half-width. There were however significant differences in the pause duration between neurons in the dorsal and ventral VP, with stimulation of NAc afferents producing a significantly longer pause (0.48 ± 0.06 s) in tonic firing in dorsal VP neurons, compared to neurons in the ventral VP (0.21 ± 0.09 s). Pauses in the tonic firing of VP neurons, as a result of NAc afferent stimulation, were found to be largely mediated by GABAA receptors, as the application of picrotoxin significantly reduced their duration. Opioid agonists and antagonists were found to have no significant effects on the pause in tonic activity induced by NAc afferent stimulation. However, NK-1 receptor antagonists caused significant decreases in the pause duration, suggesting that SP may contribute to the inhibitory effect of NAc afferent stimulation via activation of NK-1 receptors.

Download Full-text

Dopaminergic Modulation of Local Network Activity in Rat Prefrontal Cortex

Journal of Neurophysiology ◽

10.1152/jn.00898.2006 ◽

2007 ◽

Vol 97 (6) ◽

pp. 4120-4128 ◽

Cited By ~ 31

Author(s):

Susanta Bandyopadhyay ◽

John J. Hablitz

Keyword(s):

Prefrontal Cortex ◽

Synaptic Transmission ◽

Receptor Agonist ◽

Neuronal Networks ◽

Brain Slices ◽

Pyramidal Cells ◽

Network Activity ◽

Lateral Spread ◽

Local Network ◽

Evoked Activity

Dopamine modulates prefrontal cortex excitability in complex ways. Dopamine's net effect on local neuronal networks is therefore difficult to predict based on studies on pharmacologically isolated excitatory or inhibitory connections. In the present work, we have studied the effects of dopamine on evoked activity in acute rat brain slices when both excitation and inhibition are intact. Whole cell recordings from layer II/III pyramidal cells under conditions of normal synaptic transmission showed that bath-applied dopamine (30 μM) increased the outward inhibitory component of composite postsynaptic currents, whereas inward excitatory currents were not significantly affected. Optical imaging with the voltage-sensitive dye N-(3-(triethylammonium)propyl)-4-(4-(p-diethylaminophenyl)buta-dienyl)pyridinium dibromide revealed that bath application of dopamine significantly decreased the amplitude, duration, and lateral spread of activity in local cortical networks. This effect of dopamine was observed both with single and train (5 at 20 Hz) stimuli. The effect was mimicked by the D1-like receptor agonist R(+)-6-chloro-7,8-dihydroxy-1-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrobromide (1 μM) and was blocked by R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride (10 μM), a selective antagonist for D1-like receptors. The D2-like receptor agonist quinpirole (10 μM) had no significant effect on evoked dye signals. Our results suggest that dopamine's effect on inhibition dominates over that on excitation under conditions of normal synaptic transmission. Such neuromodulation by dopamine may be important for maintenance of stability in local neuronal networks in the prefrontal cortex.

Download Full-text