Number Of Excitatory Neurons Research Articles

On the physiological and structural contributors to the overall balance of excitation and inhibition in local cortical networks

Overall balance of excitation and inhibition in cortical networks is central to their functionality and normal operation. Such orchestrated co-evolution of excitation and inhibition is established through convoluted local interactions between neurons, which are organized by specific network connectivity structures and are dynamically controlled by modulating synaptic activities. Therefore, identifying how such structural and physiological factors contribute to establishment of overall balance of excitation and inhibition is crucial in understanding the homeostatic plasticity mechanisms that regulate the balance. We use biologically plausible mathematical models to extensively study the effects of multiple key factors on overall balance of a network. We characterize a network’s baseline balanced state by certain functional properties, and demonstrate how variations in physiological and structural parameters of the network deviate this balance and, in particular, result in transitions in spontaneous activity of the network to high-amplitude slow oscillatory regimes. We show that deviations from the reference balanced state can be continuously quantified by measuring the ratio of mean excitatory to mean inhibitory synaptic conductances in the network. Our results suggest that the commonly observed ratio of the number of inhibitory to the number of excitatory neurons in local cortical networks is almost optimal for their stability and excitability. Moreover, the values of inhibitory synaptic decay time constants and density of inhibitory-to-inhibitory network connectivity are critical to overall balance and stability of cortical networks. However, network stability in our results is sufficiently robust against modulations of synaptic quantal conductances, as required by their role in learning and memory. Our study based on extensive bifurcation analyses thus reveal the functional optimality and criticality of structural and physiological parameters in establishing the baseline operating state of local cortical networks.

Androgens increase excitatory neurogenic potential in human brain organoids.

The biological basis of male-female brain differences has been difficult to elucidate in humans. The most notable morphological difference is size, with male individuals having on average a larger brain than female individuals1,2, but a mechanistic understanding of how this difference arises remains unknown. Here we use brain organoids3 to show that although sex chromosomal complement has no observable effect on neurogenesis, sex steroids-namely androgens-lead to increased proliferation of cortical progenitors and an increased neurogenic pool. Transcriptomic analysis and functional studies demonstrate downstream effects on histone deacetylase activity and the mTOR pathway. Finally, we show that androgens specifically increase the neurogenic output of excitatory neuronal progenitors, whereas inhibitory neuronal progenitors are not increased. These findings reveal a role for androgens in regulating the number of excitatory neurons and represent a step towards understanding the origin of sex-related brain differences in humans.

Emergence of Neuronal Synchronisation in Coupled Areas.

One of the most fundamental questions in the field of neuroscience is the emergence of synchronous behaviour in the brain, such as phase, anti-phase, and shift-phase synchronisation. In this work, we investigate how the connectivity between brain areas can influence the phase angle and the neuronal synchronisation. To do this, we consider brain areas connected by means of excitatory and inhibitory synapses, in which the neuron dynamics is given by the adaptive exponential integrate-and-fire model. Our simulations suggest that excitatory and inhibitory connections from one area to another play a crucial role in the emergence of these types of synchronisation. Thus, in the case of unidirectional interaction, we observe that the phase angles of the neurons in the receiver area depend on the excitatory and inhibitory synapses which arrive from the sender area. Moreover, when the neurons in the sender area are synchronised, the phase angle variability of the receiver area can be reduced for some conductance values between the areas. For bidirectional interactions, we find that phase and anti-phase synchronisation can emerge due to excitatory and inhibitory connections. We also verify, for a strong inhibitory-to-excitatory interaction, the existence of silent neuronal activities, namely a large number of excitatory neurons that remain in silence for a long time.

High-throughput screening of human induced pluripotent stem cell-derived brain organoids

BackgroundThe need for scalable high-throughput screening (HTS) approaches for 3D human stem cell platforms remains a central challenge for disease modeling and drug discovery. We have developed a workflow to screen cortical organoids across platforms. New methodWe used serum-free embryoid bodies (SFEBs) derived from human induced pluripotent stem cells (hiPSCs) and employed high-content imaging (HCI) to assess neurite outgrowth and cellular composition within SFEBs. We multiplexed this screening assay with both multi-electrode arrays (MEAs) and single-cell calcium imaging. ResultsHCI was used to assess the number of excitatory neurons (VGlut+) in experimental replicates of hiPSC-derived SFEBs, demonstrating experiment-to-experiment consistency. Neurite detection using HCI was applied to assess neurite morphology. MEA analysis showed that firing and burst rates in SFEBs decreased with blockade of NMDARs and AMPARs and increased with GABAR blockade. We also demonstrate effective combination of both MEA and HCI to analyze VGlut+ populations surrounding electrodes within MEAs. HCI-based (Ca2+) transient analysis revealed firing in individual cells surrounding active MEA electrodes. Comparison with existing methodsCurrent methods to generate neural organoids show high degrees of variability, and often require sectioning or special handling for analysis. The protocol outlined in this manuscript generates SFEBs with high degree of consistency making them amenable to complex assays combining HTS and electrophysiology allowing for an in-depth, unbiased analysis. ConclusionsSFEBs can be used in combination with HTS to compensate for experimental variability common in 3D cultures, while significantly decreasing processing speed, making this an efficient starting point for phenotypic drug screening.

Optogenetic stimulation of the pre‐Bötzinger Complex and the control of breathing in a mouse model of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder well known for its progressive loss of dopaminergic neurons in the substantia nigra compacta (SNpc). Much less known, yet clinically very important, are the detrimental effects on breathing associated with this disease. Studies in the 6‐hydroxydopamine (6‐OHDA) rat model of PD revealed reductions of respiratory frequency (fR) and NK1r‐immunoreactivity in the pre‐Bötzinger complex (preBötC), a medullary region critical for generating inspiration. To unravel mechanisms that underlie breathing disturbances in PD, we used a transgenic approach to specifically label or stimulate different excitatory (Dbx1‐ERT2Cre, Vglut2‐Cre) and inhibitory (Vgat‐Cre) neural populations in the preBötC. Homozygous Cre mice were bred with homozygous Ai6 (ZsGreen) or Ai32 (ChR2) mice. Adult offspring then received bilateral injections of vehicle or 6‐OHDA (10 μg/μl) into the striatum (CPu) to induce PD; and Ai32 mice also received preBötC fiber optic cannulation. 10–12 days later, whole body plethysmography was used to measure ventilation at rest and during optogenetic photo‐stimulation of the preBötC in unanaesthetized and unrestrained mice. As expected, fR at rest was reduced by 24.9% in PD mice (154.6 ± 6.0 vs. vehicle: 205.9 ± 3.7 bpm, p<0.05). Dbx1 photo‐stimulation during the inspiratory phase did not affect the rhythm in control animals, but increased fR by 17% in PD animals. Similarly, Vglut2 photo‐stimulation in control animals did not change the rhythm, but increased fR by 30% in PD animals. No changes were elicited by photo‐stimulation during expiration. Photo‐stimulation of preBötC inhibitory Vgat neurons during inspiration increased fR by 21%, but only in vehicle‐injected mice; no changes were observed in PD mice. Histology confirmed that 6‐OHDA injections reduced the number of catecholaminergic neurons in the SNpc by 69% (150.4 ± 4.9 vs. vehicle: 494.7 ± 14.5 cells). Surprisingly, the number of Dbx1 and Vglut2 neurons in the preBötC and the adjacent ventral respiratory column (VRC) were also reduced by 47.6 and 17.3%, respectively (p<0.05), whereas the number of Vgat neurons did not change. In conclusion, our study reveals that the 6‐OHDA model of PD is associated with a specific reduction in the number of excitatory neurons within the preBötC, which includes rhythmogenic Dbx1 neurons. Photo‐stimulating specifically these neurons can restore breathing in this PD mouse model.Support or Funding InformationNIH and FAPESP.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Parvalbumin fast-spiking interneurons are selectively altered by paediatric traumatic brain injury.

Traumatic brain injury (TBI) in children remains a leading cause of death and disability and it remains poorly understood why children have worse outcomes and longer recover times. TBI has shown to alter cortical excitability and inhibitory drive onto excitatory neurons, yet few studies have directly examined changes to cortical interneurons. This is addressed in the present study using a clinically relevant model of severe TBI (controlled cortical impact) in interneuron cell type specific Cre-dependent mice. Mice subjected to controlled cortical impact exhibit specific loss of parvalbumin (PV) but not somatostatin immunoreactivity and cell density in the peri-injury zone. PV interneurons are primarily of a fast-spiking (FS) phenotype that persisted in the peri-injury zone but received less frequent inhibitory and stronger excitatory post-synaptic currents. The targeted loss of PV-FS interneurons appears to be distinct from previous reports in adult mice suggesting that TBI-induced pathophysiology is dependent on the age at time of impact. Paediatric traumatic brain injury (TBI) is a leading cause of death and disability in children. Traditionally, ongoing neurodevelopment and neuroplasticity have been considered to confer children with an advantage following TBI. However, recent findings indicate that the paediatric brain may be more sensitive to brain injury. Inhibitory interneurons are essential for proper cortical function and are implicated in the pathophysiology of TBI, yet few studies have directly investigated TBI-induced changes to interneurons themselves. Accordingly, in the present study, we examine how inhibitory neurons are altered following controlled cortical impact (CCI) in juvenile mice with targeted Cre-dependent fluorescence labelling of interneurons (Vgat:Cre/Ai9 and PV:Cre/Ai6). Although CCI failed to alter the number of excitatory neurons or somatostatin-expressing interneurons in the peri-injury zone, it significantly decreased the density of parvalbumin (PV) immunoreactive cells by 71%. However, PV:Cre/Ai6 mice subjected to CCI showed a lower extent of fluorescence labelled cell loss. PV interneurons are predominantly of a fast-spiking (FS) phenotype and, when recorded electrophysiologically from the peri-injury zone, exhibited intrinsic properties similar to those of control neurons. Synaptically, CCI induced a decrease in inhibitory drive onto FS interneurons combined with an increase in the strength of excitatory events. The results of the present study indicate that CCI induced both a loss of PV interneurons and an even greater loss of PV expression. This suggests caution is required when interpreting changes in PV immunoreactivity alone as direct evidence of interneuronal loss. Furthermore, in contrast to reports in adults, TBI in the paediatric brain selectively alters PV-FS interneurons, primarily resulting in a loss of interneuronal inhibition.

The Increase of the Functional Entropy of the Human Brain with Age

We use entropy to characterize intrinsic ageing properties of the human brain. Analysis of fMRI data from a large dataset of individuals, using resting state BOLD signals, demonstrated that a functional entropy associated with brain activity increases with age. During an average lifespan, the entropy, which was calculated from a population of individuals, increased by approximately 0.1 bits, due to correlations in BOLD activity becoming more widely distributed. We attribute this to the number of excitatory neurons and the excitatory conductance decreasing with age. Incorporating these properties into a computational model leads to quantitatively similar results to the fMRI data. Our dataset involved males and females and we found significant differences between them. The entropy of males at birth was lower than that of females. However, the entropies of the two sexes increase at different rates, and intersect at approximately 50 years; after this age, males have a larger entropy.

Fgfr2Is Required for the Development of the Medial Prefrontal Cortex and Its Connections with Limbic Circuits

To understand the role of specific fibroblast growth factor receptors (FGFRs) in cortical development, we conditionally inactivated Fgfr2 or both Fgfr1 and Fgfr2 [Fgfr2 conditional knock-out (cKO) or double knock-out mice, respectively] in radial glial cells of the dorsal telencephalon. Fgfr1 and Fgfr2 are necessary for the attainment of a normal number of excitatory neurons in the cerebral cortex. The action of FGF receptors appears to be through increasing self-renewal of neuronal precursors within the ventricular zone. Volume measurements, assessments of excitatory neuron number, and areal marker expression suggested that the proper formation of the medial prefrontal cortex (mPFC) depends on the function of Fgfr2, whereas Fgfr1 together with Fgfr2 control excitatory cortical neuron development within the entire cerebral cortex. Fgfr2 cKO mice had fewer and smaller glutamate synaptic terminals in the bed nuclei of the stria terminalis (BST), a projection area for mPFC cortical neurons. Furthermore, Fgfr2 cKO mice showed secondary decreases in GABAergic neurons in the BST and septum. These data demonstrate that FGFR2 signaling expands the number of excitatory neurons in the mPFC and secondarily influences target neurons in subcortical stations of the limbic system.

A cellular automaton model for collective neural dynamics

A stochastic epidemic model for the collective behaviour of a large set of Boolean automata placed upon the sites of a complete graph is revisited. In this paper we study the generalisation of the model to take into account inhibitory neurons. The resulting stochastic cellular automata are completely defined by five parameters: the number of excitatory neurons, N , the number of inhibitory neurons, M , the probabilities of excitation, α , and inhibition, γ , among neurons and the spontaneous transition rate from the firing to the quiescent state, β . We propose that the background of the electroencephalographic signals could be mimicked by the fluctuations in the total number of firing neurons in the excitatory subnetwork. These fluctuations are Gaussian and the mean-square displacement from an initial state displays a strongly subdiffusive behaviour approximately given by σ 2 ( t ) = A ( 1 − e − t / τ ) , where N A = β / ( β + M γ ) , τ = 2 ( N α − β ) . Comparison with real EEG records exhibits good agreement with these predictions.

Basic fibroblast growth factor increases the number of excitatory neurons containing glutamate in the cerebral cortex.

Stem cells isolated from the ventricular zone of embryonic day 12.5 rat telencephalon progressively proliferate and differentiate in vitro into three major classes of amino acid-containing neurons, glutamate, aspartate, and GABA. We quantitatively examined the effect of basic fibroblast growth factor (bFGF) and nerve growth factor (NGF) on amino acid-containing neurons. bFGF caused a threefold increase in glutamate-containing neurons, while the number of GABA- and aspartate-containing neurons was not significantly changed. In contrast, NGF did not alter the number of amino acid-containing neurons. The ratio of glutamate- to GABA-containing neurons in untreated or NGF-treated cultures was 0.6:1. In the bFGF-treated cultures, this ratio was 1.4:1, which closely approximates the ratio in the cerebral cortex in vivo. Treatment with antisense oligonucleotides targeted to bFGF mRNA provoked a 50% decrease in the number of glutamate-containing neurons but had no significant effect on the GABA-containing neurons. Thus, diffusible factors such as bFGF may play an important role in determining the relative proportion of excitatory versus inhibitory neurons in the cerebral cortex by selectively regulating the proliferation of stem cells committed to different neurotransmitter phenotypes.