Highly unstable heterogeneous representations in VIP interneurons of the anterior cingulate cortex.

A hallmark of the anterior cingulate cortex (ACC) is its functional heterogeneity. Functional and imaging studies revealed its importance in the encoding of anxiety-related and social stimuli, but it is unknown how microcircuits within the ACC encode these distinct stimuli. One type of inhibitory interneuron, which is positive for vasoactive intestinal peptide (VIP), is known to modulate the activity of pyramidal cells in local microcircuits, but it is unknown whether VIP cells in the ACC (VIPACC) are engaged by particular contexts or stimuli. Additionally, recent studies demonstrated that neuronal representations in other cortical areas can change over time at the level of the individual neuron. However, it is not known whether stimulus representations in the ACC remain stable over time. Using in vivo Ca2+ imaging and miniscopes in freely behaving mice to monitor neuronal activity with cellular resolution, we identified individual VIPACC that preferentially activated to distinct stimuli across diverse tasks. Importantly, although the population-level activity of the VIPACC remained stable across trials, the stimulus-selectivity of individual interneurons changed rapidly. These findings demonstrate marked functional heterogeneity and instability within interneuron populations in the ACC. This work contributes to our understanding of how the cortex encodes information across diverse contexts and provides insight into the complexity of neural processes involved in anxiety and social behavior.

Increased expression of schizophrenia-associated gene C4 leads to hypoconnectivity of prefrontal cortex and reduced social interaction.

Schizophrenia is a severe mental disorder with an unclear pathophysiology. Increased expression of the immune gene C4 has been linked to a greater risk of developing schizophrenia; however, it is not known whether C4 plays a causative role in this brain disorder. Using confocal imaging and whole-cell electrophysiology, we demonstrate that overexpression of C4 in mouse prefrontal cortex neurons leads to perturbations in dendritic spine development and hypoconnectivity, which mirror neuropathologies found in schizophrenia patients. We find evidence that microglia-mediated synaptic engulfment is enhanced with increased expression of C4. We also show that C4-dependent circuit dysfunction in the frontal cortex leads to decreased social interactions in juvenile and adult mice. These results demonstrate that increased expression of the schizophrenia-associated gene C4 causes aberrant circuit wiring in the developing prefrontal cortex and leads to deficits in juvenile and adult social behavior, suggesting that altered C4 expression contributes directly to schizophrenia pathogenesis.

Depth resolution in multifocus laser speckle contrast imaging.

Laser speckle contrast imaging (LSCI) can be used to evaluate blood flow based on spatial or temporal speckle statistics, but its accuracy is undermined by out-of-focus image blur. In this Letter, we show how the fraction of dynamic versus static light scattering is dependent on focus, and describe a deconvolution strategy to correct for out-of-focus blur. With the aid of a z-splitter, which enables instantaneous multifocus imaging, we demonstrate depth-resolved LSCI that can robustly extract multi-plane structural and flow-speed information simultaneously. This method is applied to in vivo imaging of blood vessels in a mouse cortex and provides improved estimates of blood flow speed throughout a depth range of 300µm.

A Sparse Probabilistic Code Underlies the Limits of Behavioral Discrimination.

The cortical code that underlies perception must enable subjects to perceive the world at time scales relevant for behavior. We find that mice can integrate visual stimuli very quickly (<100 ms) to reach plateau performance in an orientation discrimination task. To define features of cortical activity that underlie performance at these time scales, we measured single-unit responses in the mouse visual cortex at time scales relevant to this task. In contrast to high-contrast stimuli of longer duration, which elicit reliable activity in individual neurons, stimuli at the threshold of perception elicit extremely sparse and unreliable responses in the primary visual cortex such that the activity of individual neurons does not reliably report orientation. Integrating information across neurons, however, quickly improves performance. Using a linear decoding model, we estimate that integrating information over 50-100 neurons is sufficient to account for behavioral performance. Thus, at the limits of visual perception, the visual system integrates information encoded in the probabilistic firing of unreliable single units to generate reliable behavior.

A dedicated circuit links direction-selective retinal ganglion cells to the primary visual cortex.

How specific features in the environment are represented within the brain is an important unanswered question in neuroscience. A subset of retinal neurons, called direction-selective ganglion cells (DSGCs), are specialized for detecting motion along specific axes of the visual field. Despite extensive study of the retinal circuitry that endows DSGCs with their unique tuning properties, their downstream circuitry in the brain and thus their contribution to visual processing has remained unclear. In mice, several different types of DSGCs connect to the dorsal lateral geniculate nucleus (dLGN), the visual thalamic structure that harbours cortical relay neurons. Whether direction-selective information computed at the level of the retina is routed to cortical circuits and integrated with other visual channels, however, is unknown. Here we show that there is a di-synaptic circuit linking DSGCs with the superficial layers of the primary visual cortex (V1) by using viral trans-synaptic circuit mapping and functional imaging of visually driven calcium signals in thalamocortical axons. This circuit pools information from several types of DSGCs, converges in a specialized subdivision of the dLGN, and delivers direction-tuned and orientation-tuned signals to superficial V1. Notably, this circuit is anatomically segregated from the retino-geniculo-cortical pathway carrying non-direction-tuned visual information to deeper layers of V1, such as layer 4. Thus, the mouse harbours several functionally specialized, parallel retino-geniculo-cortical pathways, one of which originates with retinal DSGCs and delivers direction- and orientation-tuned information specifically to the superficial layers of the primary visual cortex. These data provide evidence that direction and orientation selectivity of some V1 neurons may be influenced by the activation of DSGCs.

Overexpression of the schizophrenia risk gene C4 in PV cells drives sex-dependent behavioral deficits and circuit dysfunction.

Fast-spiking parvalbumin (PV)-positive cells are key players in orchestrating pyramidal neuron activity, and their dysfunction is consistently observed in myriad brain diseases. To understand how immune complement dysregulation - a prevalent locus of brain disease etiology - in PV cells may drive disease pathogenesis, we have developed a transgenic mouse line that permits cell-type specific overexpression of the schizophrenia-associated complement component 4 (C4) gene. We found that overexpression of mouse C4 (mC4) in PV cells causes sex-specific behavioral alterations and concomitant deficits in synaptic connectivity and excitability of PV cells of the prefrontal cortex. Using a computational network, we demonstrated that these microcircuit deficits led to hyperactivity and disrupted neural communication. Finally, pan-neuronal overexpression of mC4 failed to evoke the same deficits in behavior as PV-specific mC4 overexpression, suggesting that C4 perturbations in fast-spiking neurons are more harmful to brain function than pan-neuronal alterations. Together, these results provide a causative link between C4 and the vulnerability of PV cells in brain disease.

A pipeline for STED super-resolution imaging and Imaris analysis of nanoscale synapse organization in mouse cortical brain slices.

Advances in super-resolution imaging enable us to delve into its intricate structural and functional complexities with unprecedented detail. Here, we present a pipeline to visualize and analyze the nanoscale organization of cortical layer 1 apical dendritic spines in the mouse prefrontal cortex. We describe steps for brain slice preparation, immunostaining, stimulated emission depletion super-resolution microscopy, and data analysis using the Imaris software package. This protocol allows the study of physiologically relevant brain circuits implicated in neuropsychiatric disorders.

REVEALS: An Open Source Multi Camera GUI For Rodent Behavior Acquisition.

Understanding the rich behavioral data generated by mice is essential for deciphering the function of the healthy and diseased brain. However, the current landscape lacks effective, affordable, and accessible methods for acquiring such data, especially when employing multiple cameras simultaneously. We have developed REVEALS (Rodent BEhaVior Multi-camErA Laboratory AcquiSition), a graphical user interface (GUI) written in python for acquiring rodent behavioral data via commonly used USB3 cameras. REVEALS allows for user-friendly control of recording from one or multiple cameras simultaneously while streamlining the data acquisition process, enabling researchers to collect and analyze large datasets efficiently. We release this software package as a stand-alone, open-source framework for researchers to use and modify according to their needs. We describe the details of the GUI implementation, including the camera control software and the video recording functionality. We validate results demonstrating the GUI's stability, reliability, and accuracy for capturing and analyzing rodent behavior using DeepLabCut pose estimation in both an object and social interaction assay. REVEALS can also be incorporated into other custom pipelines to analyze complex behavior, such as MoSeq. In summary, REVEALS provides an interface for collecting behavioral data from one or multiple perspectives that, combined with deep learning algorithms, will allow the scientific community to discover and characterize complex behavioral phenotypes to understand brain function better.

C4 induces pathological synaptic loss by impairing AMPAR trafficking.

During development, activation of the complement pathway, an extracellular proteolytic cascade, results in microglia-dependent synaptic elimination via complement receptor 3 (CR3). Here, we report that decreased connectivity caused by overexpression of C4 (C4-OE), a schizophrenia-associated gene, is CR3 independent. Instead, C4-OE triggers GluR1 degradation through an intracellular mechanism involving endosomal trafficking protein SNX27, resulting in pathological synaptic loss. Moreover, the connectivity deficits associated with C4-OE were rescued by increasing levels of SNX27, linking excessive complement activity to an intracellular endolysosomal recycling pathway affecting synapses.

Delayed stabilization of dendritic spines in fragile X mice.

Fragile X syndrome (FXS) causes mental impairment and autism through transcriptional silencing of the Fmr1 gene, resulting in the loss of the RNA-binding protein fragile X mental retardation protein (FMRP). Cortical pyramidal neurons in affected individuals and Fmr1 knock-out (KO) mice have an increased density of dendritic spines. The mutant mice also show defects in synaptic and experience-dependent circuit plasticity, which are known to be mediated in part by dendritic spine dynamics. We used in vivo time-lapse imaging with two-photon microscopy through cranial windows in male and female neonatal mice to test the hypothesis that dynamics of dendritic protrusions are altered in KO mice during early postnatal development. We find that layer 2/3 neurons from wild-type mice exhibit a rapid decrease in dendritic spine dynamics during the first 2 postnatal weeks, as immature filopodia are replaced by mushroom spines. In contrast, KO mice show a developmental delay in the downregulation of spine turnover and in the transition from immature to mature spine subtypes. Blockade of metabotropic glutamate receptor (mGluR) signaling, which reverses some adult phenotypes of KO mice, accentuated this immature protrusion phenotype in KO mice. Thus, absence of FMRP delays spine stabilization and dysregulated mGluR signaling in FXS may partially normalize this early synaptic defect.

Sex Differences in Behavioral and Brainstem Transcriptomic Neuroadaptations following Neonatal Opioid Exposure in Outbred Mice.

The opioid epidemic led to an increase in the number of neonatal opioid withdrawal syndrome (NOWS) cases in infants born to opioid-dependent mothers. Hallmark features of NOWS include weight loss, severe irritability, respiratory problems, and sleep fragmentation. Mouse models provide an opportunity to identify brain mechanisms that contribute to NOWS. Neonatal outbred Swiss Webster Cartworth Farms White (CFW) mice were administered morphine (15 mg/kg, s.c.) twice daily from postnatal day 1 (P1) to P14, an approximation of the third trimester of human gestation. Female and male mice underwent behavioral testing on P7 and P14 to determine the impact of opioid exposure on anxiety and pain sensitivity. Ultrasonic vocalizations (USVs) and daily body weights were also recorded. Brainstems containing pons and medulla were collected during morphine withdrawal on P14 for RNA sequencing. Morphine induced weight loss from P2 to P14, which persisted during adolescence (P21) and adulthood (P50). USVs markedly increased at P7 in females, emerging earlier than males. On P7 and P14, both morphine-exposed female and male mice displayed hyperalgesia on the hot plate and tail-flick assays, with females showing greater hyperalgesia than males. Morphine-exposed mice exhibited increased anxiety-like behavior in the open-field arena on P21. Transcriptome analysis of the brainstem, an area implicated in opioid withdrawal and NOWS, identified pathways enriched for noradrenergic signaling in females and males. We also found sex-specific pathways related to mitochondrial function and neurodevelopment in females and circadian entrainment in males. Sex-specific transcriptomic neuroadaptations implicate unique neurobiological mechanisms underlying NOWS-like behaviors.

The Inflamed Brain in Schizophrenia: The Convergence of Genetic and Environmental Risk Factors That Lead to Uncontrolled Neuroinflammation.

Schizophrenia is a disorder with a heterogeneous etiology involving complex interplay between genetic and environmental risk factors. The immune system is now known to play vital roles in nervous system function and pathology through regulating neuronal and glial development, synaptic plasticity, and behavior. In this regard, the immune system is positioned as a common link between the seemingly diverse genetic and environmental risk factors for schizophrenia. Synthesizing information about how the immune-brain axis is affected by multiple factors and how these factors might interact in schizophrenia is necessary to better understand the pathogenesis of this disease. Such knowledge will aid in the development of more translatable animal models that may lead to effective therapeutic interventions. Here, we provide an overview of the genetic risk factors for schizophrenia that modulate immune function. We also explore environmental factors for schizophrenia including exposure to pollution, gut dysbiosis, maternal immune activation and early-life stress, and how the consequences of these risk factors are linked to microglial function and dysfunction. We also propose that morphological and signaling deficits of the blood-brain barrier, as observed in some individuals with schizophrenia, can act as a gateway between peripheral and central nervous system inflammation, thus affecting microglia in their essential functions. Finally, we describe the diverse roles that microglia play in response to neuroinflammation and their impact on brain development and homeostasis, as well as schizophrenia pathophysiology.

A Pipeline using Bilateral In Utero Electroporation to Interrogate Genetic Influences on Rodent Behavior.

As genome-wide association studies shed light on the heterogeneous genetic underpinnings of many neurological diseases, the need to study the contribution of specific genes to brain development and function increases. Relying on mouse models to study the role of specific genetic manipulations is not always feasible since transgenic mouse lines are quite costly and many novel disease-associated genes do not yet have commercially available genetic lines. Additionally, it can take years of development and validation to create a mouse line. In utero electroporation offers a relatively quick and easy method to manipulate gene expression in a cell-type specific manner in vivo that only requires developing a DNA plasmid to achieve a particular genetic manipulation. Bilateral in utero electroporation can be used to target large populations of frontal cortex pyramidal neurons. Combining this gene transfer method with behavioral approaches allows one to study the effects of genetic manipulations on the function of prefrontal cortex networks and the social behavior of juvenile and adult mice.

Imbalance between excitation and inhibition among synaptic connections of CA3 pyramidal neurons in cultured hippocampal slices.

A fundamental property of small neuronal ensembles is their ability to be selectively activated by distinct stimuli. One cellular mechanism by which neurons achieve this input selectivity is by modulating the temporal dynamics of excitation and inhibition. We explored the interplay of excitation and inhibition in synapses between pyramidal neurons of cornu ammonis field 3 of the hippocampal formation (CA3) in cultured rat hippocampal slices, where activation of a single excitatory cell can readily recruit local interneurons. Simultaneous whole-cell recordings from pairs of CA3 pyramidal neurons revealed that the strength of connections was neither uniform nor balanced. Rather, stimulation of presynaptic neurons elicited distinct combinations of excitatory postsynaptic current-inhibitory postsynaptic current (EPSC-IPSC) amplitudes in the postsynaptic neurons. EPSC-IPSC sequences with small EPSCs had large IPSCs and sequences that contained large EPSCs had small IPSCs. In addition to differences in the amplitudes of the responses, the kinetics of the EPSCs were also different, creating distinct temporal dynamics of excitation and inhibition. Weaker EPSCs had significantly slower kinetics and were efficiently occluded by IPSCs, thereby further limiting their contribution to depolarizing the postsynaptic membrane. Our data suggest that hippocampal pyramidal cells may use an imbalance between excitation and inhibition as a filter to enhance selectivity toward preferential excitatory connections.

Acute changes in short-term plasticity at synapses with elevated levels of neuronal calcium sensor-1.

Short-term synaptic plasticity is a defining feature of neuronal activity, but the underlying molecular mechanisms are poorly understood. Depression of synaptic activity might be due to limited vesicle availability, whereas facilitation is thought to result from elevated calcium levels. However, it is unclear whether the strength and direction (facilitation versus depression) of plasticity at a given synapse result from preexisting synaptic strength or whether they are regulated by separate mechanisms. Here we show, in rat hippocampal cell cultures, that increases in the calcium binding protein neuronal calcium sensor-1 (NCS-1) can switch paired-pulse depression to facilitation without altering basal synaptic transmission or initial neurotransmitter release probability. Facilitation persisted during high-frequency trains of stimulation, indicating that NCS-1 can recruit 'dormant' vesicles. Our results suggest that NCS-1 acts as a calcium sensor for short-term plasticity by facilitating neurotransmitter output independent of initial release. We conclude that separate mechanisms are responsible for determining basal synaptic strength and short-term plasticity.

In vivo imaging of axonal and dendritic structures in neonatal mouse cortex.

Time-lapse in vivo imaging of neuronal structures is critical for understanding the assembly of neural circuits during development. Imaging developing neurons in vivo can be performed with relative ease in lower vertebrates, but ideally, one would also like to image the developing mammalian brain. In vivo chronic imaging of mice is particularly desirable because of the availability of transgenic lines that model human neuropsychiatric disease or those that allow cell- or region-specific expression of fluorescent proteins (e.g., green fluorescent protein [GFP], channelrhodopsins, and genetically encoded calcium indicators). Unfortunately, although chronic imaging of neural structures in adult mice that express GFP is now commonplace, similar approaches in neonatal mice face several additional challenges. First, the small size of the animal complicates the cranial window surgery. Second, there is a tendency for dams to cannibalize pups with head caps. Third, the head cap can impede the normal growth of the skull in neonates, which can limit the duration of imaging. Here, we describe a method for implanting chronic glass-covered cranial windows in the skulls of early postnatal mice through which axonal and dendritic structures can be imaged in vivo over a period of hours or even days.

Visual cognition: rats compare shapes among the crowd.

Rats can discriminate simple shapes visually, even if they are moved around, made smaller, or partially covered up; the strategy they use may help shed light on human brain mechanisms for discriminating complex features, such as faces.

Glutamate induces the elongation of early dendritic protrusions via mGluRs in wild type mice, but not in fragile X mice.

Fragile X syndrome (FXS), the most common inherited from of autism and mental impairment, is caused by transcriptional silencing of the Fmr1 gene, resulting in the loss of the RNA-binding protein FMRP. Dendritic spines of cortical pyramidal neurons in affected individuals are abnormally immature and in Fmr1 knockout (KO) mice they are also abnormally unstable. This could result in defects in synaptogenesis, because spine dynamics are critical for synapse formation. We have previously shown that the earliest dendritic protrusions, which are highly dynamic and might serve an exploratory role to reach out for axons, elongate in response to glutamate. Here, we tested the hypothesis that this process is mediated by metabotropic glutamate receptors (mGluRs) and that it is defective in Fmr1 KO mice. Using time-lapse imaging with two-photon microscopy in acute brain slices from early postnatal mice, we find that early dendritic protrusions in layer 2/3 neurons become longer in response to application of glutamate or DHPG, a Group 1 mGluR agonist. Blockade of mGluR5 signaling, which reverses some adult phenotypes of KO mice, prevented the glutamate-mediated elongation of early protrusions. In contrast, dendritic protrusions from KO mice failed to respond to glutamate. Thus, absence of FMRP may impair the ability of cortical pyramidal neurons to respond to glutamate released from nearby pre-synaptic terminals, which may be a critical step to initiate synaptogenesis and stabilize spines.

Fate of cajal-retzius neurons in the postnatal mouse neocortex.

Cajal-Retzius (CR) neurons play a critical role in cortical neuronal migration, but their exact fate after the completion of neocortical lamination remains a mystery. Histological evidence has been unable to unequivocally determine whether these cells die or undergo a phenotypic transformation to become resident interneurons of Layer 1 in the adult neocortex. To determine their ultimate fate, we performed chronic in vivo two-photon imaging of identified CR neurons during postnatal development in mice that express the green fluorescent protein (GFP) under the control of the early B-cell factor 2 (Ebf2) promoter. We find that, after birth, virtually all CR neurons in mouse neocortex express Ebf2. Although postnatal CR neurons undergo dramatic morphological transformations, they do not migrate to deeper layers. Instead, their gradual disappearance from the cortex is due to apoptotic death during the second postnatal week. A small fraction of CR neurons present at birth survive into adulthood. We conclude that, in addition to orchestrating cortical layering, a subset of CR neurons must play other roles beyond the third postnatal week.

Acerca del denominado problema ecológico / Talking about the so-called \"Efcological problem\"

El análisis de los problemas globales en sus diferentes aspectos, constituye actualmente una preocupación de primer orden. Entre estos problemas, ocupa un lugar destacado el denominado "problema ecológico". Es propósito fundamental del trabajo, analizar sus aspectos socio-clasistas y filosóficos en general, particularizando en la crítica del Club de Roma, por cuanto esta institución reune a los máximos representante del pensamiento burgués en esta dirección. Por otra parte el trabajo se propone demostrar la supremacía del socialismo con respecto al capitalismo en la solución de la problemática ecológica. La revisión de bibliografía especializada de autores soviéticos y del campo socialista, así como los materiales del II Congreso del PCC, constituyen el procedimiento fundamental utilizado