Pyramidal Neurons Research Articles

Cytoplasmic vacuolization and ectopic formation of perineuronal nets are characteristic pathologies of cytomegalic neurons in tuberous sclerosis.

Cytomegalic neurons, characterized by increased size and a hyperactive mechanistic target of rapamycin complex 1 (mTORC1), are pathognomonic for tuberous sclerosis complex (TSC). To model these neurons, we recently generated a murine Tsc1 conditional knockout model in which Tsc1 deletion in late embryonic radial glia results in neuronal hypertrophy of a subset of isocortical pyramidal neurons. In the current study, we compared the cellular pathology of these cytomegalic neurons to those of the enlarged neurons in human cortical tubers. Neurons from the mice showed unique features, such as cytoplasmic vacuoles associated with Golgi complexes and the ectopic formation of perineuronal nets (PNNs), a feature of inhibitory neurons, rarely present in excitatory cortical neurons. The membranes of these vacuoles were enriched for the plasma membrane proteins CD44, KCC2, and Na+/K+ ATPase, suggesting deficits in Golgi membrane trafficking. These aberrant features in the mouse appeared only after the onset of seizures, probably due to the prolonged seizure activity in the context of constitutive mTORC1 activation. Similar PNNs and cytoplasmic vacuoles were present in the cytomegalic neurons of human cortical tubers. Our findings reveal novel pathological features of Golgi complexes and PNNs in the cytomegalic neurons in TSC.

Primary auditory thalamus relays directly to cortical layer 1 interneurons.

Inhibitory interneurons within cortical layer 1 (L1-INs) integrate inputs from diverse brain regions to modulate sensory processing and plasticity, but the sensory inputs that recruit these interneurons have not been identified. Here we used monosynaptic retrograde tracing and whole-cell electrophysiology to characterize the thalamic inputs onto two major subpopulations of L1-INs in the mouse auditory cortex. We find that the vast majority of auditory thalamic inputs to these L1-INs unexpectedly arise from the ventral subdivision of the medial geniculate body (MGBv), the tonotopically-organized primary auditory thalamus. Moreover, these interneurons receive robust functional monosynaptic MGBv inputs that are comparable to those recorded in the L4 excitatory pyramidal neurons. Our findings identify a direct pathway from the primary auditory thalamus to the L1-INs, suggesting that these interneurons are uniquely positioned to integrate thalamic inputs conveying precise sensory information with top-down inputs carrying information about brain states and learned associations.

Recovery of Learning and Memory Deficits Despite Persistent Pyknosis of the Hippocampal Pyramidal Neurons of Adult Hydrocephalic Mice.

The hippocampal alterations resulting from hydrocephalus are associated with various cognitive dysfunctions. Reduced learning and memory are early functional deficits that recover with time in experimental hydrocephalus. This study investigated the recovery processes of learning and memory loss in relation to the morphology of hippocampal pyramidal neurons and the degree of expansion of the ventricles. Hydrocephalus was induced in adult mice by intracisternal injection of sterile kaolin while controls received sham operation. Neurobehavioral tests for memory and learning were conducted, after which the animals were sacrificed in batches: 7 (acute) and 28 (subacute) days postinduction. After sacrifice, mice were categorized into mild and moderate hydrocephalus, and their fixed brain samples were processed for hematoxylin, eosin, and Nissl stains. In moderate acute hydrocephalus, the indices of learning and memory were reduced escape latency (67.20 ± 12.83 s), number of platform crossing (4.000 ± 1.658), duration in platform quadrant (4.000 ± 1.658), and percent of total investigation (44.857% ± 3.981%) but not in the subacute stage. Pyknotic indices (PI) were significantly higher in the cornu ammonis (CA)1 and 3 regions in all hydrocephalic groups than in controls. However, within groups, PI was significantly higher only in the CA1 of moderate acute (28.149% ± 1.875%) compared to moderate subacute hydrocephalic group (12.903% ± 3.23%). Hydrocephalus caused cellular injury to the hippocampus associated with spatial learning and memory deficits. However, these functional deficits were partially reversed in moderate subacute hydrocephalus despite the persistence of the structural alterations in the CA1 and CA3 subregions.

Dendritic Morphology of Developing Hippocampal Neurons in Cyp11a1 Null Mice.

Neurosteroids have a variety of neurological functions, such as neurite growth, neuroprotection, myelination, and neurogenesis. P450scc, encoded by CYP11A1 gene, is the cholesterol side chain cleavage enzyme that catalyzes the first and rate-limiting step in steroidogenesis. In this study, we examine the dendritic morphology in developing hippocampal neurons of Cyp11a1 null mice at P15, a critical period for synapse formation and maturation. Knockout mice were maintained until P15 with hormone administration. The Golgi-Cox method stained CA1 and CA3 pyramidal neurons in the hippocampus to reveal dendritic morphology. We demonstrated that Cyp11a1 null mice usually die within 7 days after birth and thus collected brain samples at postnatal day 5 (P5) for examination. There was significant shrinkage of dendrite size and diminishment of dendritic branching in CA1 and CA3 pyramidal neurons in the hippocampus of Cyp11a1 null mice, suggesting a developmental delay. We wonder if this delay may catch up later in life. Since the age of P15 is a critical period for synapse formation and maturation, the Cyp11a1 null mice were rescued by receiving hormone administration until P15 that the dendritic morphology in the developing hippocampal neurons could be examined. The results indicated that the total dendritic length, the number of dendritic branches, as well as dendritic arborization in the CA1 and CA3 pyramidal neurons are significantly decreased in P15 knockout mice when compared to the wild type. The spine densities were also significantly decreased. In addition, the Western blot analysis revealed decreased PSD-95 expression levels in the knockout mice compared to the wild type at P15. These results suggested that Cyp11a1 deficiency impairs the dendritic structures in the developing hippocampal pyramidal neurons.

Expression of activity-regulated transcripts in pyramidal neurons across the cortical visuospatial working memory network in unaffected comparison individuals and individuals with schizophrenia

Visuospatial working memory (vsWM), which is impaired in schizophrenia (SZ), is mediated by multiple cortical regions including the primary (V1) and association (V2) visual, posterior parietal (PPC) and dorsolateral prefrontal (DLPFC) cortices. In these regions, parvalbumin (PV) or somatostatin (SST) GABA neurons are altered in SZ as reflected in lower levels of activity-regulated transcripts. As PV and SST neurons receive excitatory inputs from neighboring pyramidal neurons, we hypothesized that levels of activity-regulated transcripts are also lower in pyramidal neurons in these regions. Thus, we quantified levels of four activity-regulated, pyramidal neuron-selective transcripts, namely adenylate cyclase-activating polypeptide-1 (ADCYAP1), brain-derived neurotrophic factor (BDNF), neuronal pentraxin-2 (NPTX2) and neuritin-1 (NRN1) mRNAs, in V1, V2, PPC and DLPFC from unaffected comparison and SZ individuals. In SZ, BDNF and NPTX2 mRNA levels were lower across all four regions, whereas ADCYAP1 and NRN1 mRNA levels were lower in V1 and V2. The regional pattern of deficits in BDNF and NPTX2 mRNAs was similar to that in transcripts in PV and SST neurons in SZ. These findings suggest that lower activity of pyramidal neurons expressing BDNF and/or NPTX2 mRNAs might contribute to alterations in PV and SST neurons across the vsWM network in SZ.

Skimmianine Showed Neuroprotection against Cerebral Ischemia/Reperfusion Injury.

The aim of this study was to investigate the antioxidant and anti-inflammatory effects of skimmianine on cerebral ischemia-reperfusion (IR) injury. Twenty-four female Wistar albino rats were randomly divided into three groups: Sham, Ischemia-Reperfusion (IR), and IR + Skimmianine (40 mg/kg Skimmianine). Cerebral ischemia was induced using a monofilament nylon suture to occlude the middle cerebral artery for 60 min. Following 23 h of reperfusion, the animals were sacrificed 14 days later. The effects of skimmianine on brain tissue post-IR injury were examined through biochemical and immunochemical analyses. In silico analysis using the Enrichr platform explored skimmianine's potential biological processes involving IBA-1, IL-6, and NF-κB proteins. In the IR group, MDA levels increased, while SOD and CAT antioxidant enzyme activities decreased. In the IR + Skimmianine group, skimmianine treatment resulted in decreased MDA levels and increased SOD and CAT activities. Significant increases in IBA-1 expression were observed in the IR group, which skimmianine treatment significantly reduced, modulating microglial activation. High levels of IL-6 expression were noted in pyramidal neurons, vascular structures, and neuroglial cells in the IR group; skimmianine treatment reduced IL-6 expression, demonstrating anti-inflammatory effects. Increased NF-κB expression was observed in neurons and blood vessels in the gray and white matter in the IR group; skimmianine treatment reduced NF-κB expression. Gene Ontology results suggest skimmianine impacts immune and inflammatory responses via IBA-1 and IL-6, with potential effects on estrogen mechanisms mediated by NF-κB. Skimmianine may be a potential therapeutic strategy due to its antioxidant and anti-inflammatory effects on cerebral IR injury.

Astrocytes enhance plasticity response during reversal learning

Astrocytes play a key role in the regulation of synaptic strength and are thought to orchestrate synaptic plasticity and memory. Yet, how specifically astrocytes and their neuroactive transmitters control learning and memory is currently an open question. Recent experiments have uncovered an astrocyte-mediated feedback loop in CA1 pyramidal neurons which is started by the release of endocannabinoids by active neurons and closed by astrocytic regulation of the D-serine levels at the dendrites. D-serine is a co-agonist for the NMDA receptor regulating the strength and direction of synaptic plasticity. Activity-dependent D-serine release mediated by astrocytes is therefore a candidate for mediating between long-term synaptic depression (LTD) and potentiation (LTP) during learning. Here, we show that the mathematical description of this mechanism leads to a biophysical model of synaptic plasticity consistent with the phenomenological model known as the BCM model. The resulting mathematical framework can explain the learning deficit observed in mice upon disruption of the D-serine regulatory mechanism. It shows that D-serine enhances plasticity during reversal learning, ensuring fast responses to changes in the external environment. The model provides new testable predictions about the learning process, driving our understanding of the functional role of neuron-glia interaction in learning.

Cerebroprotective Potential of Andrographolide Nanoparticles: In silico and In vivo Investigations.

Ischemic stroke remains the leading cause of death and disability, while the main mechanisms of dominant neurological damage in stroke contain oxidative stress and inflammation. Docking studies revealed a binding energy of - 6.1 kcal/mol for AG, while the co-crystallized ligand (CCl) exhibited a binding energy of - 7.3 kcal/mol with NOS. AG demonstrated favourable hydrogen bond interactions with amino acids ASN A:354 and ARG A:388 and hydrophobic interactions with GLU A:377. Molecular dynamics simulations throughout 100 ns indicated a binding affinity of - 27.65±2.88 kcal/mol for AG, compared to - 18.01±4.02 kcal/mol for CCl. These findings suggest that AG possesses a superior binding affinity for NOS compared to CCl, thus complementing the stability of NOS at the docked site.AG has limited applications owing to its low bioavailability, poor water solubility, and high chemical and metabolic instability.The fabrication method was employed in the preparation of AGNP, SEM analysis confirmed spherical shape with size in 19.4±5 nm and investigated the neuroprotective effect in cerebral stroke rats induced by 30 min of carotid artery occlusion followed by 4 hr reperfusion, evaluated by infarction size, ROS/RNS via GSH, MPO, NO estimationand AchE activity, and monitoring EEG function. Cortex and hippocampal histology were compared between groups. AGNP treatment significantly decreased Infarction size and increased GSH levels (p<0.01**), decreased MPO (p<0.01**), NO (p<0.01**), AchE (p<0.01**), restored to normal EEG amplitude, minimizing unsynchronized polyspikes and histological data revealed that increased pyramidal cell layer thickness and decreased apoptotic neurons in hippocampus, cortex appeared normal neurons with central large vesicular nuclei, containing one or more nucleoli in compared to AG treatment. Based on brain biochemical, histopathology reports AGNP exhibited significant cerebroprotective activity compared to AG on ischemic rats.

Sex-specific GABAergic microcircuits that switch vulnerability into resilience to stress and reverse the effects of chronic stress exposure.

Clinical and preclinical studies have identified somatostatin (SST)-positive interneurons as key elements that regulate the vulnerability to stress-related psychiatric disorders. Conversely, disinhibition of SST neurons in mice results in resilience to the behavioral effects of chronic stress. Here we established a low-dose chronic chemogenetic protocol to map these changes in positively and negatively motivated behaviors to specific brain regions. AAV-hM3Dq mediated chronic activation of SST neurons in the prelimbic cortex (PLC) had antidepressant drug-like effects on anxiety- and anhedonia-related motivated behaviors in male but not female mice. Analogous manipulation of the ventral hippocampus (vHPC) had such effects in female but not male mice. Moreover, activation of SST neurons in the PLC of male and the vHPC of female mice resulted in stress resilience. Activation of SST neurons in the PLC reversed prior chronic stress-induced defects in motivated behavior in males but was ineffective in females. Conversely, activation of SST neurons in the vHPC reversed chronic stress-induced behavioral alterations in females but not males. Quantitation of c-Fos+ and FosB+ neurons in chronic stress-exposed mice revealed that chronic activation of SST neurons leads to a paradoxical increase in pyramidal cell activity. Collectively, these data demonstrate that GABAergic microcircuits driven by dendrite targeting interneurons enable sex- and brain-region-specific neural plasticity that promotes stress resilience and reverses stress-induced anxiety- and anhedonia-like motivated behavior. Our studies provide a mechanistic rationale for antidepressant efficacy of dendrite-targeting, low-potency GABAA receptor agonists, independent of sex and despite striking sex differences in the relevant brain substrates.

Morphological and Functional Alterations in the CA1 Pyramidal Neurons of the Rat Hippocampus in the Chronic Phase of the Lithium-Pilocarpine Model of Epilepsy.

Epilepsy is known to cause alterations in neural networks. However, many details of these changes remain poorly understood. The objective of this study was to investigate changes in the properties of hippocampal CA1 pyramidal neurons and their synaptic inputs in a rat lithium-pilocarpine model of epilepsy. In the chronic phase of the model, we found a marked loss of pyramidal neurons in the CA1 area. However, the membrane properties of the neurons remained essentially unaltered. The results of the electrophysiological and morphological studies indicate that the direct pathway from the entorhinal cortex to CA1 neurons is reinforced in epileptic animals, whereas the inputs to them from CA3 are either unaltered or even diminished. In particular, the dendritic spine density in the str. lacunosum moleculare, where the direct pathway from the entorhinal cortex terminates, was found to be 2.5 times higher in epileptic rats than in control rats. Furthermore, the summation of responses upon stimulation of the temporoammonic pathway was enhanced by approximately twofold in epileptic rats. This enhancement is believed to be a significant contributing factor to the heightened epileptic activity observed in the entorhinal cortex of epileptic rats using an ex vivo 4-aminopyridine model.

Withdrawal from chronic alcohol impairs the serotonin-mediated modulation of GABAergic transmission in the infralimbic cortex in male rats

The infralimbic cortex (IL) is part of the medial prefrontal cortex (mPFC), exerting top-down control over structures that are critically involved in the development of alcohol use disorder (AUD). Activity of the IL is tightly controlled by γ-aminobutyric acid (GABA) transmission, which is susceptible to chronic alcohol exposure and withdrawal. This inhibitory control is regulated by various neuromodulators, including 5-hydroxytryptamine (5-HT; serotonin). We used chronic intermittent ethanol vapor inhalation exposure, a model of AUD, in male Sprague-Dawley rats to induce alcohol dependence (Dep) followed by protracted withdrawal (WD; 2 weeks) and performed ex vivo electrophysiology using whole-cell patch clamp to study GABAergic transmission in layer V of IL pyramidal neurons. We found that WD increased frequencies of spontaneous inhibitory postsynaptic currents (sIPSCs), whereas miniature IPSCs (mIPSCs; recorded in the presence of tetrodotoxin) were unaffected by either Dep or WD. The application of 5-HT (50 μM) increased sIPSC frequencies and amplitudes in naive and Dep rats but reduced sIPSC frequencies in WD rats. Additionally, 5-HT2A receptor antagonist M100907 and 5-HT2C receptor antagonist SB242084 reduced basal GABA release in all groups to a similar extent. The blockage of either 5-HT2A or 5-HT2C receptors in WD rats restored the impaired response to 5-HT, which then resembled responses in naive rats. Our findings expand our understanding of synaptic inhibition in the IL in AUD, indicating that antagonism of 5-HT2A and 5-HT2C receptors may restore GABAergic control over IL pyramidal neurons. Significance statementImpairment in the serotonergic modulation of GABAergic inhibition in the medial prefrontal cortex contributes to alcohol use disorder (AUD). We used a well-established rat model of AUD and ex vivo whole-cell patch-clamp electrophysiology to characterize the serotonin modulation of GABAergic transmission in layer V infralimbic (IL) pyramidal neurons in ethanol-naive, ethanol-dependent (Dep), and ethanol-withdrawn (WD) male rats. We found increased basal inhibition following WD from chronic alcohol and altered serotonin modulation. Exogenous serotonin enhanced GABAergic transmission in naive and Dep rats but reduced it in WD rats. 5-HT2A and 5-HT2C receptor blockage in WD rats restored the typical serotonin-mediated enhancement of GABAergic inhibition. Our findings expand our understanding of synaptic inhibition in the infralimbic neurons in AUD.

Neurocognitive, Clinical and Reelin Activity in Rehabilitation Using Neurofeedback Therapy in Patients with Schizophrenia.

Introduction: Reelin is a neuropeptide responsible for the migration and positioning of pyramidal neurons, interneurons, and Purkinje cells. In adulthood, it still supports neuroplasticity, especially dendritic spines formation and glutamatergic neurotransmission. Genetic studies have confirmed the involvement of reelin system failure in the etiopathogenesis of mental diseases, including schizophrenia. Given the role of reelin in brain cytoarchitectonics and the regularly observed reduction in its activity in prefrontal areas in cases of schizophrenia, dysfunction of the reelin pathway fits the neurodevelopmental hypothesis of schizophrenia, both as a biochemical predisposition and/or the ultimate trigger of psychosis and as a biosocial factor determining the clinical course, and finally, as a potential target for disease monitoring and treatment. Aim: The purpose of this study was to examine associations of the reelin blood level with clinical and neurocognitive parameters during an intensive, structured neurofeedback therapy of patients with schizophrenia. Methods: Thirty-seven male patients with paranoid schizophrenia were randomly divided into two groups: a group with 3-month neurofeedback as an add-on to ongoing antipsychotic treatment (NF, N18), and a control group with standard social support and antipsychotic treatment (CON, N19). The reelin serum concentration, clinical and neurocognitive tests were compared between the groups. Results: After 3-month trial (T2), the reelin serum level increased in the NF group vs. the CON group. The negative and general symptoms of PANSS (Positive and Negative Syndrome Scale) were reduced significantly more in the NF group at T2, and the d2 (d2 Sustained Attention Test) and BCIS (Beck Cognitive Insight Scale) scores improved only in the NF group. The AIS scores improved more dynamically in the NF group, but not enough to differentiate them from the CON group at T2. Conclusions: The clinical and neurocognitive improvement within the 3-month NF add-on therapy trial was associated with a significant increase of reelin serum level in schizophrenia patients.

Anti-CRMP2 antibody induces anxiety-like behavior and increases pyramidal neuron excitability in mice

BackgroundWe have previously identified auto-antibody (Ab) to collapsin response mediator protein 2 (CRMP2) in patients with encephalitis. The present study aims to evaluate the pathogenic effects of anti-CRMP2 Ab. MethodsRecombinant CRMP2 protein was injected subcutaneously into mice to establish an active immune mouse model with anti-CRMP2 Ab. Behavioral assessments, histopathological staining, and electrophysiological testing were performed to identify any pathogenic changes. ResultsThe mice exhibited signs of impaired motor coordination four weeks post-immunization of CRMP2 protein. Moreover, CRMP2 immunized mice for eight weeks showed anxiety-like behaviors indicating by tests of open field and the elevated plus maze. After incubating the CA1 region of hippocampal brain section with the sera from CRMP2 immunized mice, the whole-cell path-clamp recordings showed increased excitability of pyramidal neurons. However, no obvious inflammation and infiltration of immune cells were observed by histopathological analysis. Western blot showed that the phosphorylation levels of CRMP2-Thr514 and -Ser522 were not affected. ConclusionIn an active immunization model with CRMP2 protein, impaired coordination and anxiety-like behaviors were observed. Also, anti-CRMP2 Abs containing sera heightened the excitability of hippocampal pyramidal neurons in vitro, which imply the pathogenic effects of anti-CRMP2 Ab.

Kv7/M channel dysfunction produces hyperexcitability in hippocampal CA1 pyramidal cells of Fmr1 knockout mice.

Fragile X syndrome (FXS), the most frequent monogenic form of intellectual disability, is caused by transcriptional silencing of the FMR1 gene that could render neuronal hyperexcitability. Here we show that pyramidal cells (PCs) in the dorsal CA1 region of the hippocampus elicited a larger action potential (AP) number in response to suprathreshold stimulation in juvenile Fmr1 knockout (KO) than wild-type (WT) mice. Because Kv7/M channels modulate CA1 PC excitability in rats, we investigated if their dysfunction produces neuronal hyperexcitability in Fmr1 KO mice. Immunohistochemical and western blot analyses showed no differences in the expression of Kv7.2 and Kv7.3 channel subunits between genotypes; however, the current mediated by Kv7/M channels was reduced in Fmr1 KO mice. In both genotypes, bath application of XE991 (10μM), a blocker of Kv7/M channels: produced an increased AP number, produced an increased input resistance, produced a decreased AP voltage threshold and shaped AP medium afterhyperpolarization by increasing mean velocities. Retigabine (10μM), an opener of Kv7/M channels, produced opposite effects to XE991. Both XE991 and retigabine abolished differences in all these parameters found in control conditions between genotypes. Furthermore, a low concentration of retigabine (2.5μM) normalized CA1 PC excitability of Fmr1 KO mice. Finally, ex vivo seizure-like events evoked by 4-aminopyiridine (200μM) in the dorsal CA1 region were more frequent in Fmr1 KO mice, and were abolished by retigabine (5-10μM). We conclude that CA1 PCs of Fmr1 KO mice exhibit hyperexcitability, caused by Kv7/M channel dysfunction, and increased epileptiform activity, which were abolished by retigabine. KEY POINTS: Dorsal pyramidal cells of the hippocampal CA1 region of Fmr1 knockout mice exhibit hyperexcitability. Kv7/M channel activity, but not expression, is reduced in pyramidal cells of the hippocampal CA1 region of Fmr1 knockout mice. Kv7/M channel dysfunction causes hyperexcitability in pyramidal cells of the hippocampal CA1 region of Fmr1 knockout mice by increasing input resistance, decreasing AP voltage threshold and shaping medium afterhyperpolarization. A Kv7/M channel opener normalizes neuronal excitability in pyramidal cells of the hippocampal CA1 region of Fmr1 knockout mice. Ex vivo seizure-like events evoked in the dorsal CA1 region were more frequent in Fmr1 KO mice, and such an epileptiform activity was abolished by a Kv7/M channel opener depending on drug concentration. Kv7/M channels may represent a therapeutic target for treating symptoms associated with hippocampal alterations in fragile X syndrome.

Neonatal Diazepam Exposure Decreases Dendritic Arborization and Spine Density of Cortical Pyramidal Neurons in Rats.

Benzodiazepines are extensively utilized in pediatric anesthesia and critical care for their anxiolytic and sedative properties. However, preclinical studies indicate that neonatal exposure to GABAergic drugs, including benzodiazepines, leads to long-term cognitive deficits, potentially mediated by altered GABAergic signaling during brain development. This preclinical study investigated the impact of early-life diazepam exposure on cortical neuronal morphology, specifically exploring dendritic arborization and spine density, crucial factors in synaptogenesis. Male and female Sprague Dawley rat pups were exposed to a single neonatal dose of diazepam (30mg/kg) or vehicle on postnatal day (PND) 7. Golgi-Cox staining was used to assess cortical pyramidal neuron development at 4 developmental stages: neonatal (PND8), infantile (PND15), juvenile (PND30), and adolescence (PND42). Animals were randomized equally to 4 groups: male-vehicle, male-diazepam, female-vehicle, and female-diazepam. Neuronal morphology was evaluated after reconstruction in neurolucida, and dendritic spine density was analyzed through high-power photomicrographs using ImageJ. Diazepam exposure resulted in decreased dendritic complexity in both sexes, with reduced arborization and spine density observed in cortical pyramidal neurons. Significant differences were found at each developmental stage, indicating a persistent impact. Dendritic length increased with age but was attenuated by diazepam exposure. Branching length analysis revealed decreased complexity after diazepam treatment. Spine density at PND42 was significantly reduced in both apical and basal dendrites after diazepam exposure. Neonatal diazepam exposure adversely affected cortical pyramidal neuron development, leading to persistent alterations in dendritic arborization and spine density. These structural changes suggest potential risks associated with early-life diazepam exposure. Further research is needed to unravel the functional consequences of these anatomic alterations.

Sex differences in motor learning flexibility are accompanied by sex differences in mushroom spine pruning of the mouse primary motor cortex during adolescence.

Although males excel at motor tasks requiring strength, females exhibit greater motor learning flexibility. Cognitive flexibility is associated with low baseline mushroom spine densities achieved by pruning which can be triggered by α4βδ GABAA receptors (GABARs); defective synaptic pruning impairs this process. We investigated sex differences in adolescent pruning of mushroom spine pruning of layer 5 pyramidal cells of primary motor cortex (L5M1), a site essential for motor learning, using microscopic evaluation of Golgi stained sections. We assessed α4GABAR expression using immunohistochemical and electrophysiological techniques (whole cell patch clamp responses to 100 nM gaboxadol, selective for α4βδ GABARs). We then compared performance of groups with different post-pubertal mushroom spine densities on motor learning (constant speed) and learning flexibility (accelerating speed following constant speed) rotarod tasks. Mushroom spines in proximal L5M1 of female mice decreased >60% from PND35 (puberty onset) to PND56 (Pubertal: 2.23 ± 0.21 spines/10 μm; post-pubertal: 0.81 ± 0.14 spines/10 μm, P < 0.001); male mushroom spine density was unchanged. This was due to greater α4βδ GABAR expression in the female (P < 0.0001) because α4 -/- mice did not exhibit mushroom spine pruning. Although motor learning was similar for all groups, only female wild-type mice (low mushroom spine density) learned the accelerating rotarod task after the constant speed task (P = 0.006), a measure of motor learning flexibility. These results suggest that optimal motor learning flexibility of female mice is associated with low baseline levels of post-pubertal mushroom spine density in L5M1 compared to male and female α4 -/- mice.

Multi-scale modelling of location- and frequency-dependent synaptic plasticity induced by transcranial magnetic stimulation in the dendrites of pyramidal neurons.

Repetitive transcranial magnetic stimulation (rTMS) induces long-term changes of synapses, but the mechanisms behind these modifications are not fully understood. Although there has been progress in the development of multi-scale modeling tools, no comprehensive module for simulating rTMS-induced synaptic plasticity in biophysically realistic neurons exists.. We developed a modelling framework that allows the replication and detailed prediction of long-term changes of excitatory synapses in neurons stimulated by rTMS. We implemented a voltage-dependent plasticity model that has been previously established for simulating frequency-, time-, and compartment-dependent spatio-temporal changes of excitatory synapses in neuronal dendrites. The plasticity model can be incorporated into biophysical neuronal models and coupled to electrical field simulations. We show that the plasticity modelling framework replicates long-term potentiation (LTP)-like plasticity in hippocampal CA1 pyramidal cells evoked by 10-Hz repetitive magnetic stimulation (rMS). This plasticity was strongly distance dependent and concentrated at the proximal synapses of the neuron. We predicted a decrease in the plasticity amplitude for 5 Hz and 1 Hz protocols with decreasing frequency. Finally, we successfully modelled plasticity in distal synapses upon local electrical theta-burst stimulation (TBS) and predicted proximal and distal plasticity for rMS TBS. Notably, the rMS TBS-evoked synaptic plasticity exhibited robust facilitation by dendritic spikes and low sensitivity to inhibitory suppression. The plasticity modelling framework enables precise simulations of LTP-like cellular effects with high spatio-temporal resolution, enhancing the efficiency of parameter screening and the development of plasticity-inducing rTMS protocols.

Modeling the impact of neuromorphological alterations in Down syndrome on fast neural oscillations.

Cognitive disorders, including Down syndrome (DS), present significant morphological alterations in neuron architectural complexity. However, the relationship between neuromorphological alterations and impaired brain function is not fully understood. To address this gap, we propose a novel computational model that accounts for the observed cell deformations in DS. The model consists of a cross-sectional layer of the mouse motor cortex, composed of 3000 neurons. The network connectivity is obtained by accounting explicitly for two single-neuron morphological parameters: the mean dendritic tree radius and the spine density in excitatory pyramidal cells. We obtained these values by fitting reconstructed neuron data corresponding to three mouse models: wild-type (WT), transgenic (TgDyrk1A), and trisomic (Ts65Dn). Our findings reveal a dynamic interplay between pyramidal and fast-spiking interneurons leading to the emergence of gamma activity (∼40 Hz). In the DS models this gamma activity is diminished, corroborating experimental observations and validating our computational methodology. We further explore the impact of disrupted excitation-inhibition balance by mimicking the reduction recurrent inhibition present in DS. In this case, gamma power exhibits variable responses as a function of the external input to the network. Finally, we perform a numerical exploration of the morphological parameter space, unveiling the direct influence of each structural parameter on gamma frequency and power. Our research demonstrates a clear link between changes in morphology and the disruption of gamma oscillations in DS. This work underscores the potential of computational modeling to elucidate the relationship between neuron architecture and brain function, and ultimately improve our understanding of cognitive disorders.

A pH-sensitive closed-loop nanomachine to control hyperexcitability at the single neuron level

Epilepsy affects 1% of the general population and 30% of patients are resistant to antiepileptic drugs. Although optogenetics is an efficient antiepileptic strategy, the difficulty of illuminating deep brain areas poses translational challenges. Thus, the search of alternative light sources is strongly needed. Here, we develop pH-sensitive inhibitory luminopsin (pHIL), a closed-loop chemo-optogenetic nanomachine composed of a luciferase-based light generator, a fluorescent sensor of intracellular pH (E2GFP), and an optogenetic actuator (halorhodopsin) for silencing neuronal activity. Stimulated by coelenterazine, pHIL experiences bioluminescence resonance energy transfer between luciferase and E2GFP which, under conditions of acidic pH, activates halorhodopsin. In primary neurons, pHIL senses the intracellular pH drop associated with hyperactivity and optogenetically aborts paroxysmal activity elicited by the administration of convulsants. The expression of pHIL in hippocampal pyramidal neurons is effective in decreasing duration and increasing latency of pilocarpine-induced tonic-clonic seizures upon in vivo coelenterazine administration, without affecting higher brain functions. The same treatment is effective in markedly decreasing seizure manifestations in a murine model of genetic epilepsy. The results indicate that pHIL represents a potentially promising closed-loop chemo-optogenetic strategy to treat drug-refractory epilepsy.

The mechanics of correlated variability in segregated cortical excitatory subnetworks

Understanding the genesis of shared trial-to-trial variability in neuronal population activity within the sensory cortex is critical to uncovering the biological basis of information processing in the brain. Shared variability is often a reflection of the structure of cortical connectivity since it likely arises, in part, from local circuit inputs. A series of experiments from segregated networks of (excitatory) pyramidal neurons in the mouse primary visual cortex challenge this view. Specifically, the across-network correlations were found to be larger than predicted given the known weak cross-network connectivity. We aim to uncover the circuit mechanisms responsible for these enhanced correlations through biologically motivated cortical circuit models. Our central finding is that coupling each excitatory subpopulation with a specific inhibitory subpopulation provides the most robust network-intrinsic solution in shaping these enhanced correlations. This result argues for the existence of excitatory-inhibitory functional assemblies in early sensory areas which mirror not just response properties but also connectivity between pyramidal cells. Furthermore, our findings provide theoretical support for recent experimental observations showing that cortical inhibition forms structural and functional subnetworks with excitatory cells, in contrast to the classical view that inhibition is a nonspecific blanket suppression of local excitation.