Excitatory Projections Research Articles

Quantitative, real-time imaging of spreading depolarization-associated neuronal ROS production.

Spreading depolarization (SD) causes a massive neuronal/glial depolarization, disturbs ionic homeostasis and deranges neuronal network function. The metabolic burden imposed by SD may also generate marked amounts of reactive oxygen species (ROS). Yet, proper optical tools are required to study this aspect with spatiotemporal detail. Therefore, we earlier generated transgenic redox indicator mice. They express in excitatory projection neurons the cytosolic redox-sensor roGFP, a reduction/oxidation sensitive green fluorescent protein which is ratiometric by excitation and responds reversibly to redox alterations. Using adult male roGFPc mice, we analyzed SD-related ROS production in CA1 stratum pyramidale of submerged slices. SD was induced by K+ microinjection, O2 withdrawal or mitochondrial uncoupling (FCCP). The extracellular DC potential deflection was accompanied by a spreading wavefront of roGFP oxidation, confirming marked neuronal ROS generation. Hypoxia-induced SD was preceded by a moderate oxidation, which became intensified as the DC potential deflection occurred. Upon K+-induced SD, roGFP oxidation slowly recovered within 10-15 min in some slices. Upon FCCP-or hypoxia-induced SD, recovery was limited. Withdrawing extracellular Ca2+ markedly dampened the SD-related roGFP oxidation and improved its reversibility, confirming a key-role of neuronal Ca2+ load in SD-related ROS generation. Neither mitochondrial uncoupling, nor inhibition of NADPH oxidase or xanthine oxidase abolished the SD-related roGFP oxidation. Therefore, ROS generation during SD involves mitochondria as well as non-mitochondrial sources. This first-time analysis of SD-related ROS dynamics became possible based on quantitative redox imaging in roGFP mice, an advanced approach, which will contribute to further decipher the molecular understanding of SD in brain pathophysiology.

Activity in the dorsal hippocampus-mPFC circuit modulates stress-coping strategies during inescapable stress

Anatomical connectivity and lesion-deficit studies have shown that the dorsal and ventral hippocampi contribute to cognitive and emotional processes, respectively. However, the role of the dorsal hippocampus (dHP) in emotional or stress-related behaviors remains unclear. Here, we showed that neuronal activity in the dHP affects stress-coping behaviors in mice via excitatory projections to the medial prefrontal cortex (mPFC). The antidepressant ketamine rapidly induced c-Fos expression in both the dorsal and ventral hippocampi. The suppression of GABAergic transmission in the dHP-induced molecular changes similar to those induced by ketamine administration, including eukaryotic elongation factor 2 (eEF2) dephosphorylation, brain-derived neurotrophic factor (BDNF) elevation, and extracellular signal-regulated kinase (ERK) phosphorylation. These synaptic and molecular changes in the dHP induced a reduction in the immobility time of the mice in the tail-suspension and forced swim tests without affecting anxiety-related behavior. Conversely, pharmacological and chemogenetic potentiation of inhibitory neurotransmission in the dHP CA1 region induced passive coping behaviors during the tests. Transneuronal tracing and electrophysiology revealed monosynaptic excitatory connections between dHP CA1 neurons and mPFC neurons. Optogenetic stimulation of dHP CA1 neurons in freely behaving mice produced c-Fos induction and spike firing in the mPFC neurons. Chemogenetic activation of the dHP-recipient mPFC neurons reversed the passive coping behaviors induced by suppression of dHP CA1 neuronal activity. Collectively, these results indicate that neuronal activity in the dHP modulates stress-coping strategies to inescapable stress and contributes to the antidepressant effects of ketamine via the dHP-mPFC circuit.

Morphine-responsive neurons that regulate mechanical antinociception.

Opioids are widely used, effective analgesics to manage severe acute and chronic pain, although they have recently come under scrutiny because of epidemic levels of abuse. While these compounds act on numerous central and peripheral pain pathways, the neuroanatomical substrate for opioid analgesia is not fully understood. By means of single-cell transcriptomics and manipulation of morphine-responsive neurons, we have identified an ensemble of neurons in the rostral ventromedial medulla (RVM) that regulates mechanical nociception in mice. Among these, forced activation or silencing of excitatory RVMBDNF projection neurons mimicked or completely reversed morphine-induced mechanical antinociception, respectively, via a brain-derived neurotrophic factor (BDNF)/tropomyosin receptor kinase B (TrkB)-dependent mechanism and activation of inhibitory spinal galanin-positive neurons. Our results reveal a specific RVM-spinal circuit that scales mechanical nociception whose function confers the antinociceptive properties of morphine.

GAP43 Located on Corticostriatal Terminals Restrains Novelty-Induced Hyperactivity in Mice.

Growth-associated protein of 43 kDa (GAP43) is a key cytoskeleton-associated component of the presynaptic terminal that facilitates neuroplasticity. Downregulation of GAP43 expression has been associated to various psychiatric conditions in humans and evokes hippocampus-dependent memory impairments in mice. Despite the extensive studies conducted on hippocampal GAP43 in past decades, however, very little is known about its roles in modulating the excitatory versus inhibitory balance in other brain regions. We recently generated conditional knock-out mice in which the Gap43 gene was selectively inactivated in either telencephalic glutamatergic neurons (Gap43fl/fl ;Nex1Cre mice, hereafter Glu-GAP43-/- mice) or forebrain GABAergic neurons (Gap43fl/fl ;Dlx5/6Cre mice, hereafter GABA-GAP43-/- mice). Here, we show that Glu-GAP43-/- but not GABA-GAP43-/- mice of either sex show a striking hyperactive phenotype when exposed to a novel environment. This behavioral alteration of Glu-GAP43-/- mice was linked to a selective activation of dorsal-striatum neurons, as well as to an enhanced corticostriatal glutamatergic transmission and an abrogation of corticostriatal endocannabinoid-mediated long-term depression. In line with these observations, GAP43 was abundantly expressed in corticostriatal glutamatergic terminals of wild-type mice. The novelty-induced hyperactive phenotype of Glu-GAP43-/- mice was abrogated by chemogenetically inhibiting corticostriatal afferences with a Gi-coupled "designer receptor exclusively activated by designer drugs" (DREADDs), thus further supporting that novelty-induced activity is controlled by GAP43 at corticostriatal excitatory projections. Taken together, these findings show an unprecedented regulatory role of GAP43 in the corticostriatal circuitry and provide a new mouse model with a delimited neuronal-circuit alteration for studying novelty-induced hyperactivity, a phenotypic shortfall that occurs in diverse psychiatric diseases.

Oligodendrocytes produce amyloid-β and contribute to plaque formation alongside neurons in Alzheimer’s disease model mice

Amyloid-β (Aβ) is thought to be neuronally derived in Alzheimer’s disease (AD). However, transcripts of amyloid precursor protein (APP) and amyloidogenic enzymes are equally abundant in oligodendrocytes (OLs). By cell-type-specific deletion of Bace1 in a humanized knock-in AD model, APPNLGF, we demonstrate that OLs and neurons contribute to Aβ plaque burden. For rapid plaque seeding, excitatory projection neurons must provide a threshold level of Aβ. Ultimately, our findings are relevant for AD prevention and therapeutic strategies.

Neuronal network dynamics in the posterodorsal amygdala: shaping reproductive hormone pulsatility.

Normal reproductive function and fertility rely on the rhythmic secretion of gonadotropin-releasing hormone (GnRH), which is driven by the hypothalamic GnRH pulse generator. A key regulator of the GnRH pulse generator is the posterodorsal subnucleus of the medial amygdala (MePD), a brain region that is involved in processing external environmental cues, including the effect of stress. However, the neuronal pathways enabling the dynamic, stress-triggered modulation of GnRH secretion remain largely unknown. Here, we employ in silico modelling in order to explore the impact of dynamic inputs on GnRH pulse generator activity. We introduce and analyse a mathematical model representing MePD neuronal circuits composed of GABAergic and glutamatergic neuronal populations, integrating it with our GnRH pulse generator model. Our analysis dissects the influence of excitatory and inhibitory MePD projections' outputs on the GnRH pulse generator's activity and reveals a functionally relevant MePD glutamatergic projection to the GnRH pulse generator, which we probe with in vivo optogenetics. Our study sheds light on how MePD neuronal dynamics affect the GnRH pulse generator activity and offers insights into stress-related dysregulation.

A hypothalamic-amygdala circuit underlying sexually dimorphic aggression

Male animals often display higher levels of aggression than females. However, the neural circuitry mechanisms underlying this sexually dimorphic aggression remain elusive. Here, we identify a hypothalamic-amygdala circuit that mediates male-biased aggression in mice. Specifically, the ventrolateral part of the ventromedial hypothalamus (VMHvl), a sexually dimorphic region associated with eliciting male-biased aggression, projects densely to the posterior substantia innominata (pSI), an area that promotes similar levels of attack in both sexes of mice. Although the VMHvl innervates the pSI unidirectionally through both excitatory and inhibitory connections, it is the excitatory VMHvl-pSI projections that are strengthened in males to promote aggression, whereas the inhibitory connections that reduce aggressive behavior are strengthened in females. Consequently, the convergent hypothalamic input onto the pSI leads to heightened pSI activity in males, resulting in male-biased aggression. Our findings reveal a sexually distinct excitation-inhibition balance of a hypothalamic-amygdala circuit that underlies sexually dimorphic aggression.

Excitatory Projections of Wide Field Collicular Neurons to the Nucleus of the Optic Tract in the Rat.

The superficial layers of the mammalian superior colliculus (SC) contain neurons that are generally responsive to visual stimuli but can differ considerably in morphology and response properties. To elucidate the structure and function of these neurons, we combined extracellular recording and juxtacellular labeling, detailed anatomical reconstruction, and ultrastructural analysis of the synaptic contacts of labeled neurons, using transmission electron microscopy. Our labeled neurons project to different brainstem nuclei. Of particular importance are neurons that fit the morphological criteria of the wide field (WF) neurons and whose dendrites are horizontally oriented. They display a rather characteristic axonal projection pattern to the nucleus of optic tract (NOT); thus, we call them superior collicular WF projecting to the NOT (SCWFNOT) neurons. We corroborated the morphological characterization of this neuronal type as a distinct neuronal class with the help of unsupervised hierarchical cluster analysis. Our ultrastructural data demonstrate that SCWFNOT neurons establish excitatory connections with their targets in the NOT. Although, in rodents, the literature about the WF neurons has focused on their extensive projection to the lateral posterior nucleus of the thalamus, as a conduit for information to reach the visual association areas of the cortex, our data suggest that this subclass of WF neurons may participate in the optokinetic nystagmus.

Making Ramón y Cajal proud: Development of cell identity and diversity in the cerebral cortex.

Since the beautiful images of Santiago Ramón y Cajal provided a first glimpse into the immense diversity and complexity of cell types found in the cerebral cortex, neuroscience has been challenged and inspired to understand how these diverse cells are generated and how they interact with each other to orchestrate the development of this remarkable tissue. Some fundamental questions drive the field's quest to understand cortical development: what are the mechanistic principles that govern the emergence of neuronal diversity? How do extrinsic and intrinsic signals integrate with physical forces and activity to shape cell identity? How do the diverse populations of neurons and glia influence each other during development to guarantee proper integration and function? The advent of powerful new technologies to profile and perturb cortical development at unprecedented resolution and across a variety of modalities has offered a new opportunity to integrate past knowledge with brand new data. Here, we review some of this progress using cortical excitatory projection neurons as a system to draw out general principles of cell diversification and the role of cell-cell interactions during cortical development.

The stabilized supralinear network accounts for the contrast dependence of visual cortical gamma oscillations.

When stimulated, neural populations in the visual cortex exhibit fast rhythmic activity with frequencies in the gamma band (30-80 Hz). The gamma rhythm manifests as a broad resonance peak in the power-spectrum of recorded local field potentials, which exhibits various stimulus dependencies. In particular, in macaque primary visual cortex (V1), the gamma peak frequency increases with increasing stimulus contrast. Moreover, this contrast dependence is local: when contrast varies smoothly over visual space, the gamma peak frequency in each cortical column is controlled by the local contrast in that column's receptive field. No parsimonious mechanistic explanation for these contrast dependencies of V1 gamma oscillations has been proposed. The stabilized supralinear network (SSN) is a mechanistic model of cortical circuits that has accounted for a range of visual cortical response nonlinearities and contextual modulations, as well as their contrast dependence. Here, we begin by showing that a reduced SSN model without retinotopy robustly captures the contrast dependence of gamma peak frequency, and provides a mechanistic explanation for this effect based on the observed non-saturating and supralinear input-output function of V1 neurons. Given this result, the local dependence on contrast can trivially be captured in a retinotopic SSN which however lacks horizontal synaptic connections between its cortical columns. However, long-range horizontal connections in V1 are in fact strong, and underlie contextual modulation effects such as surround suppression. We thus explored whether a retinotopically organized SSN model of V1 with strong excitatory horizontal connections can exhibit both surround suppression and the local contrast dependence of gamma peak frequency. We found that retinotopic SSNs can account for both effects, but only when the horizontal excitatory projections are composed of two components with different patterns of spatial fall-off with distance: a short-range component that only targets the source column, combined with a long-range component that targets columns neighboring the source column. We thus make a specific qualitative prediction for the spatial structure of horizontal connections in macaque V1, consistent with the columnar structure of cortex.

Arid1b haploinsufficiency in cortical inhibitory interneurons causes cell-type-dependent changes in cellular and synaptic development.

Autism spectrum disorder (ASD) presents with diverse cognitive and behavioral abnormalities beginning during early development. Although the neural circuit mechanisms remain unclear, recent work suggests pathology in cortical inhibitory interneurons (INs) plays a crucial role. However, we lack fundamental information regarding changes in the physiology of synapses to and from INs in ASD. Here, we used transgenic mice to conditionally knockout one copy of the high confidence ASD risk gene Arid1b from the progenitors of parvalbumin-expressing fast-spiking (PV-FS) INs and somatostatin-expressing non-fast-spiking (SST-NFS) INs. In brain slices, we performed paired whole-cell recordings between INs and excitatory projection neurons (PNs) to investigate changes in synaptic physiology. In neonates, we found reduced synaptic input to INs but not PNs, with a concomitant reduction in the frequency of spontaneous network events, which are driven by INs in immature circuits. In mature mice, we found a reduction in the number of PV-FS INs in cortical layers 2/3 and 5. However, changes in PV-FS IN synaptic physiology were cortical layer and PN cell-type dependent. In layer 5, synapses from PV-FS INs to subcortical-projecting PNs were weakened. In contrast, in layer 2/3, synapses to and from PV-FS INs and corticocortical-projecting PNs were strengthened, leading to enhanced feedforward inhibition of input from layer 4. Finally, we found a novel synaptic deficit among SST-NFS INs, in which excitatory synapses from layer 2/3 PNs failed to facilitate. Our data highlight that changes in unitary synaptic dynamics among INs in ASD depend on neuronal cell-type.

A specific olfactory bulb interneuron subtype Tpbg/5T4 generated at embryonic and neonatal stages.

Various mammals have shown that sensory stimulation plays a crucial role in regulating the development of diverse structures, such as the olfactory bulb (OB), cerebral cortex, hippocampus, and retina. In the OB, the dendritic development of excitatory projection neurons like mitral/tufted cells is influenced by olfactory experiences. Odor stimulation is also essential for the dendritic development of inhibitory OB interneurons, such as granule and periglomerular cells, which are continuously produced in the ventricular-subventricular zone throughout life. Based on the morphological and molecular features, OB interneurons are classified into several subtypes. The role for each interneuron subtype in the control of olfactory behavior remains poorly understood due to lack of each specific marker. Among the several OB interneuron subtypes, a specific granule cell subtype, which expresses the oncofetal trophoblast glycoprotein (Tpbg or 5T4) gene, has been reported to be required for odor detection and discrimination behavior. This review will primarily focus on elucidating the contribution of different granule cell subtypes, including the Tpbg/5T4 subtype, to olfactory processing and behavior during the embryonic and adult stages.

Arid1b haploinsufficiency in pyramidal neurons causes cellular and circuit changes in neocortex but is not sufficient to produce behavioral or seizure phenotypes.

Arid1b is a high confidence risk gene for autism spectrum disorder that encodes a subunit of a chromatin remodeling complex expressed in neuronal progenitors. Haploinsufficiency causes a broad range of social, behavioral, and intellectual disability phenotypes, including Coffin-Siris syndrome. Recent work using transgenic mouse models suggests pathology is due to deficits in proliferation, survival, and synaptic development of cortical neurons. However, there is conflicting evidence regarding the relative roles of excitatory projection neurons and inhibitory interneurons in generating abnormal cognitive and behavioral phenotypes. Here, we conditionally knocked out either one or both copies of Arid1b from excitatory projection neuron progenitors and systematically investigated the effects on intrinsic membrane properties, synaptic physiology, social behavior, and seizure susceptibility. We found that disrupting Arid1b expression in excitatory neurons alters their membrane properties, including hyperpolarizing action potential threshold; however, these changes depend on neuronal subtype. Using paired whole-cell recordings, we found increased synaptic connectivity rate between projection neurons. Furthermore, we found reduced strength of excitatory synapses to parvalbumin (PV)-expression inhibitory interneurons. These data suggest an increase in the ratio of excitation to inhibition. However, the strength of inhibitory synapses from PV interneurons to excitatory neurons was enhanced, which may rebalance this ratio. Indeed, Arid1b haploinsufficiency in projection neurons was insufficient to cause social deficits and seizure phenotypes observed in a preclinical germline haploinsufficient mouse model. Our data suggest that while excitatory projection neurons likely contribute to autistic phenotypes, pathology in these cells is not the primary cause.

A multi-omic single-cell landscape of cellular diversification in the developing human cerebral cortex

The vast neuronal diversity in the human neocortex is vital for high-order brain functions, necessitating elucidation of the regulatory mechanisms underlying such unparalleled diversity. However, recent studies have yet to comprehensively reveal the diversity of neurons and the molecular logic of neocortical origin in humans at single-cell resolution through profiling transcriptomic or epigenomic landscapes, owing to the application of unimodal data alone to depict exceedingly heterogeneous populations of neurons. In this study, we generated a comprehensive compendium of the developing human neocortex by simultaneously profiling gene expression and open chromatin from the same cell. We computationally reconstructed the differentiation trajectories of excitatory projection neurons of cortical origin and inferred the regulatory logic governing lineage bifurcation decisions for neuronal diversification. We demonstrated that neuronal diversity arises from progenitor cell lineage specificity and postmitotic differentiation at distinct stages. Our data paves the way for understanding the primarily coordinated regulatory logic for neuronal diversification in the neocortex.

Mapping inhibitory and excitatory projections to the preBӧtzinger complex

Breathing relies on rhythmic activity generated by the preBӧtzinger complex (preBӧtC), a small brainstem region. Because breathing is influenced by many different physiological, behavioral, and emotional contexts, the preBӧtC is not only highly connected with nearby respiratory related regions in the hindbrain, but also has widespread connections with other mid-and forebrain regions not generally implicated in the regulation of breathing. The specific functions for many of these preBӧtC inputs remain unclear. Although afferent pathways indiscriminately target excitatory and inhibitory neurons in the preBӧtC, we hypothesized that inputs to the preBӧtC would map to distinct brain regions based on the inhibitory or excitatory phenotype of the projecting neurons. To test this, mice that express tdTomato only when both Cre and FlpO recombinases are present (Ai65) were bred with mice that express Cre in inhibitory neurons ( VgatCre). Adult offspring ( VgatCre; Ai65) received a unilateral preBӧtC injection of a retrograde AAV that expresses FlpO recombinase (AAVrg-Flpo), thereby specifically activating tdTomato expression in any inhibitory neurons that project directly to the preBӧtC. Whole-brain imaging revealed many labeled neurons along the ipsilateral ventral respiratory column (VRC), far rostral and caudal of the injection site, extending along the intermediate reticular zone (IRt) from the VII nucleus through the caudal end of the ventral respiratory group (VRG). Interestingly, this well-defined and continuous column of labeled neurons was confined to the ventral IRt at its caudal end but moved dorsally at its rostral end. Only a small number of neurons were labeled along the contralateral VRC. Sparse labeling was present in the medial parabrachial, Kolliker-Fuse, and reticular regions of the pons. Many projecting neurons were observed across subregions of the amygdala, which were almost exclusively ipsilateral. The hypothalamus contained diffuse projecting neurons along its rostral-caudal extent that were also mostly ipsilateral. However, denser labeling was present in a distinctly curved cluster of the lateral hypothalamus, which was observed on both the ipsilateral and contralateral side. Consistent with the preBӧtC having distinct inhibitory and excitatory input pathways, we did not observe significant labelling in other regions with known projections to the preBotC identified previously using non-cell-type specific tracing strategies. These included cortex, lateral parabrachial, NTS, and RVM. This will be tested further by replicating this experiment with targeting of glutamatergic ( Vglut2) neurons. Defining these cell-type-specific inputs to the preBӧtC will provide an essential foundation for future functional studies to determine how these circuits may regulate breathing. R01 HL1660317 (Baertsch) R00 HL145004 (Baertsch). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Disynaptic Inhibitory Cerebellar Control Over Caudal Medial Accessory Olive.

The olivocerebellar system, which is critical for sensorimotor performance and learning, functions through modules with feedback loops. The main feedback to the inferior olive comes from the cerebellar nuclei (CN), which are predominantly GABAergic and contralateral. However, for the subnucleus d of the caudomedial accessory olive (cdMAO), a crucial region for oculomotor and upper body movements, the source of GABAergic input has yet to be identified. Here, we demonstrate the existence of a disynaptic inhibitory projection from the medial CN (MCN) to the cdMAO via the superior colliculus (SC) by exploiting retrograde, anterograde, and transsynaptic viral tracing at the light microscopic level as well as anterograde classical and viral tracing combined with immunocytochemistry at the electron microscopic level. Retrograde tracing in Gad2-Cre mice reveals that the cdMAO receives GABAergic input from the contralateral SC. Anterograde transsynaptic tracing uncovered that the SC neurons receiving input from the contralateral MCN provide predominantly inhibitory projections to contralateral cdMAO, ipsilateral to the MCN. Following ultrastructural analysis of the monosynaptic projection about half of the SC terminals within the contralateral cdMAO are GABAergic. The disynaptic GABAergic projection from the MCN to the ipsilateral cdMAO mirrors that of the monosynaptic excitatory projection from the MCN to the contralateral cdMAO. Thus, while completing the map of inhibitory inputs to the olivary subnuclei, we established that the MCN inhibits the cdMAO via the contralateral SC, highlighting a potential push-pull mechanism in directional gaze control that appears unique in terms of laterality and polarity among olivocerebellar modules.

Bilateral and symmetric glycinergic and glutamatergic projections from the LSO to the IC in the CBA/CaH mouse.

Auditory space has been conceptualized as a matrix of systematically arranged combinations of binaural disparity cues that arise in the superior olivary complex (SOC). The computational code for interaural time and intensity differences utilizes excitatory and inhibitory projections that converge in the inferior colliculus (IC). The challenge is to determine the neural circuits underlying this convergence and to model how the binaural cues encode location. It has been shown that midbrain neurons are largely excited by sound from the contralateral ear and inhibited by sound leading at the ipsilateral ear. In this context, ascending projections from the lateral superior olive (LSO) to the IC have been reported to be ipsilaterally glycinergic and contralaterally glutamatergic. This study used CBA/CaH mice (3-6 months old) and applied unilateral retrograde tracing techniques into the IC in conjunction with immunocytochemical methods with glycine and glutamate transporters (GlyT2 and vGLUT2, respectively) to analyze the projection patterns from the LSO to the IC. Glycinergic and glutamatergic neurons were spatially intermixed within the LSO, and both types projected to the IC. For GlyT2 and vGLUT2 neurons, the average percentage of ipsilaterally and contralaterally projecting cells was similar (ANOVA, p = 0.48). A roughly equal number of GlyT2 and vGLUT2 neurons did not project to the IC. The somatic size and shape of these neurons match the descriptions of LSO principal cells. A minor but distinct population of small (< 40 μm2) neurons that labeled for GlyT2 did not project to the IC; these cells emerge as candidates for inhibitory local circuit neurons. Our findings indicate a symmetric and bilateral projection of glycine and glutamate neurons from the LSO to the IC. The differences between our results and those from previous studies suggest that species and habitat differences have a significant role in mechanisms of binaural processing and highlight the importance of research methods and comparative neuroscience. These data will be important for modeling how excitatory and inhibitory systems converge to create auditory space in the CBA/CaH mouse.

Fractal Neurodynamics.

The neuronal ongoing electrical activity in the brain network, the neurodynamics, reflects the structure and functionality of generating neuronal pools. The activity of neurons due to their excitatory and inhibitory projections is associated with specific brain functions. Here, the purpose was to investigate if the local ongoing electrical activity exhibits its characteristic spectral and fractal features in wakefulness and sleep across and within subjects. Moreover, we aimed to show that measures typical of complex systems catch physiological features missed by linear spectral analyses. For this study, we concentrated on the evaluation of the power spectral density (PSD) and Higuchi fractal dimension (HFD) measures. Relevant clinical impact of the specific features of neurodynamics identification stands primarily in the potential of classifying cortical parcels according to their neurodynamics as well as enhancing the effectiveness of neuromodulation interventions to cure symptoms secondary to neuronal activity unbalances.

Chronic Pb exposure impairs learning and memory abilities by inhibiting excitatory projection neuro-circuit of the hippocampus in mice

Lead (Pb) is an environmental neurotoxic metal. Chronic Pb exposure causes behavioral changes in humans and rodents, such as dysfunctional learning and memory. Nevertheless, it is not clear whether Pb exposure disrupts the neural circuit. Thus, here we aim at investigating the effects the chronic Pb exposure on neural-behavioral and neural circuits in mice from prenatal to postnatal day (PND) 63. Pregnant mice and their male offspring were treated with Pb (150 ppm) until postnatal day 63. In this study, several behavior tests and Golgi-Cox staining methods were used to assess spatial memory ability and synaptogenesis. Virus-based tracing systems and immunohistochemistry assays were used to test the relevance of chronic Pb exposure with disrupted neural circuits. The behavioral experiments and Golgi-Cox staining results showed that Pb exposure impaired spatial memory and spine density in mice. The virus tracing results revealed that the Entorhinal cortex (EC) neurons could be directly projected to Cornuammonis 1 (CA1) and Dentate gyrus (DG), forming a critical circuit inhibited, in either a direct or indirect way, by Pb invasion. In addition, excitatory neural input from EC（labeled with CaMKII）to CA1 and DG was significantly attenuated by Pb exposure. In conclusion, our data indicated that Pb significantly impaired the excitatory connections from EC to the hippocampus (CA1 and DG), providing a novel neuro-circuitry basis for Pb neurotoxicity.

The delta opioid receptor agonist KNT-127 relieves innate anxiety-like behavior in mice by suppressing transmission from the prelimbic cortex to basolateral amygdala.

Excitatory projections from the prelimbic cortex (PL) to the basolateral nucleus of the amygdala (BLA) are implicated in the regulation of anxiety-like behaviors, and we previously demonstrated that anxiolytic-like effects of the selective delta-opioid receptor (DOP) agonist KNT-127 is involved in suppressing glutamate neurotransmission in the PL. Here, we investigated the mechanisms underlying the anxiolytic-like effect of KNT-127 in mice by combining optogenetic stimulation of the PL-BLA pathway with behavioral analyses. Four-week-old male C57BL/6J mice received bilateral administration of adeno-associated virus (AAV)2-CaMKIIa-hChR2(H134R)-enhanced yellow fluorescent protein (EYFP) into the PL to induce expression of the light-activated excitatory ionic channel ChR2. Subsequently, an optic fiber cannula connected to a wireless photo-stimulator was implanted into the BLA for optogenetic PL-BLA pathway stimulation. We evaluated innate anxiety using the elevated plus maze (EPM) and open field (OF) tests as well as learned anxiety using the contextual fear conditioning (CFC) test. Optogenetic activation of the PL-BLA pathway enhanced anxiety-like behaviors in the EPM and OF, while prior subcutaneous administration of KNT-127 (10 mg/kg) reduced this anxiogenic effect. In contrast, optogenetic activation of the PL-BLA pathway had no significant effect on conditioned fear. Our findings indicate that the PL-BLA circuit contributes to innate anxiety and that the anxiolytic-like effects of KNT-127 are mediated at least in part by suppression of PL-BLA transmission. The PL delta-opioid receptor may thus be an effective therapeutic target for anxiety disorders.