Obesity and the cerebral cortex: Underlying neurobiology in mice and humans.

Obesity is a major modifiable risk factor for Alzheimer's disease (AD), characterized by progressive atrophy of the cerebral cortex. The neurobiology of obesity contributions to AD is poorly understood. Here we show with in vivo MRI that diet-induced obesity decreases cortical volume in mice, and that higher body adiposity associates with lower cortical volume in humans. Single-nuclei transcriptomics of the mouse cortex reveals that dietary obesity promotes an array of neuron-adverse transcriptional dysregulations, which are mediated by an interplay of excitatory neurons and glial cells, and which involve microglial activation and lowered neuronal capacity for neuritogenesis and maintenance of membrane potential. The transcriptional dysregulations of microglia more than of other cell types are like those in AD, as assessed with single-nuclei cortical transcriptomics in a mouse model of AD and two sets of human donors with the disease. Serial two-photon tomography of microglia demonstrates microgliosis throughout the mouse cortex. The spatial pattern of adiposity-cortical volume associations in human cohorts interrogated together with in silico bulk and single-nucleus transcriptomic data from the human cortex implicated microglia (along with other glial cells and subtypes of excitatory neurons), and it correlated positively with the spatial profile of cortical atrophy in patients with mild cognitive impairment and AD. Thus, multi-cell neuron-adverse dysregulations likely contribute to the loss of cortical tissue in obesity. The dysregulations of microglia may be pivotal to the obesity-related risk of AD at a population level.

Histological characterization and development of mesial surface sulci in the human brain at 13-15 gestational weeks through high-resolution histology.

Cellular-level anatomical data from early fetal brain are sparse yet critical to the understanding of neurodevelopmental disorders. We characterize the organization of the human cerebral cortex between 13 and 15 gestational weeks using high-resolution whole-brain histological data sets complimented with multimodal imaging. We observed the heretofore underrecognized, reproducible presence of infolds on the mesial surface of the cerebral hemispheres. Of note at this stage, when most of the cerebrum is occupied by lateral ventricles and the corpus callosum is incompletely developed, we postulate that these mesial infolds represent the primordial stage of cingulate, callosal, and calcarine sulci, features of mesial cortical development. Our observations are based on the multimodal approach and further include histological three-dimensional reconstruction that highlights the importance of the plane of sectioning. We describe the laminar organization of the developing cortical mantle, including these infolds from the marginal to ventricular zone, with Nissl, hematoxylin and eosin, and glial fibrillary acidic protein (GFAP) immunohistochemistry. Despite the absence of major sulci on the dorsal surface, the boundaries among the orbital, frontal, parietal, and occipital cortex were very well demarcated, primarily by the cytoarchitecture differences in the organization of the subplate (SP) and intermediate zone (IZ) in these locations. The parietal region has the thickest cortical plate (CP), SP, and IZ, whereas the orbital region shows the thinnest CP and reveals an extra cell-sparse layer above the bilaminar SP. The subcortical structures show intensely GFAP-immunolabeled soma, absent in the cerebral mantle. Our findings establish a normative neurodevelopment baseline at the early stage.

Expression characteristics and potential function of non-coding RNA in mouse cortical cells.

Non-coding RNAs (ncRNAs) play essential regulatory functions in various physiological and pathological processes in the brain. To systematically characterize the ncRNA profile in cortical cells, we downloaded single-cell SMART-Seq v4 data of mouse cerebral cortex. Our results revealed that the ncRNAs alone are sufficient to define the identity of most cortical cell types. We identified 1,600 ncRNAs that exhibited cell type specificity, even yielding to distinguish microglia from perivascular macrophages with ncRNA. Moreover, we characterized cortical layer and region specific ncRNAs, in line with the results by spatial transcriptome (ST) data. By constructing a co-expression network of ncRNAs and protein-coding genes, we predicted the function of ncRNAs. By integrating with genome-wide association studies data, we established associations between cell type-specific ncRNAs and traits related to neurological disorders. Collectively, our study identified differentially expressed ncRNAs at multiple levels and provided the valuable resource to explore the functions and dysfunctions of ncRNAs in cortical cells.

Unambiguous identification of asymmetric and symmetric synapses using volume electron microscopy.

The brain contains thousands of millions of synapses, exhibiting diverse structural, molecular, and functional characteristics. However, synapses can be classified into two primary morphological types: Gray's type I and type II, corresponding to Colonnier's asymmetric (AS) and symmetric (SS) synapses, respectively. AS and SS have a thick and thin postsynaptic density, respectively. In the cerebral cortex, since most AS are excitatory (glutamatergic), and SS are inhibitory (GABAergic), determining the distribution, size, density, and proportion of the two major cortical types of synapses is critical, not only to better understand synaptic organization in terms of connectivity, but also from a functional perspective. However, several technical challenges complicate the study of synapses. Potassium ferrocyanide has been utilized in recent volume electron microscope studies to enhance electron density in cellular membranes. However, identifying synaptic junctions, especially SS, becomes more challenging as the postsynaptic densities become thinner with increasing concentrations of potassium ferrocyanide. Here we describe a protocol employing Focused Ion Beam Milling and Scanning Electron Microscopy for studying brain tissue. The focus is on the unequivocal identification of AS and SS types. To validate SS observed using this protocol as GABAergic, experiments with immunocytochemistry for the vesicular GABA transporter were conducted on fixed mouse brain tissue sections. This material was processed with different concentrations of potassium ferrocyanide, aiming to determine its optimal concentration. We demonstrate that using a low concentration of potassium ferrocyanide (0.1%) improves membrane visualization while allowing unequivocal identification of synapses as AS or SS.

Functional lateralization in the medial prefrontal cortex control of contextual conditioned emotional responses in rats.

A functional lateralization has been reported in control of emotional responses by the medial prefrontal cortex (mPFC). However, a hemisphere asymmetry in involvement of the mPFC in expression of fear conditioning responses has never been reported. Therefore, we investigated whether control by mPFC of freezing and cardiovascular responses during re-exposure to an aversively conditioned context is lateralized. For this, rats had guide cannulas directed to the mPFC implanted bilaterally or unilaterally in the right or left hemispheres. Vehicle or the non-selective synaptic inhibitor CoCl2 was microinjected into the mPFC 10 min before re-exposure to a chamber where the animals had previously received footshocks. A catheter was implanted into the femoral artery before the fear retrieval test for cardiovascular recordings. We observed that bilateral microinjection of CoCl2 into the mPFC reduced both the freezing behavior (enhancing locomotion and rearing) and arterial pressure and heart rate increases during re-exposure to the aversively conditioned context. Unilateral microinjection of CoCl2 into the right hemisphere of the mPFC also decreased the freezing behavior (enhancing locomotion and rearing), but without affecting the cardiovascular changes. Conversely, unilateral synaptic inhibition in the left mPFC did not affect either behavioral or cardiovascular responses during fear retrieval test. Taken together, these results suggest that the right hemisphere of the mPFC is necessary and sufficient for expression of freezing behavior to contextual fear conditioning. However, the control of cardiovascular responses and freezing behavior during fear retrieval test is somehow dissociated in the mPFC, being the former bilaterally processed.

Association cortical areas in the mouse contain a large population of fast-spiking GABAergic neurons that do not express parvalbumin.

GABAergic neurons represent 10-15% of the neuronal population of the cortex but exert a powerful control over information flow in cortical circuits. The largest GABAergic class in the neocortex is represented by the parvalbumin-expressing fast-spiking neurons, which provide powerful somatic inhibition to their postsynaptic targets. Recently, the density of parvalbumin interneurons has been shown to be lower in associative areas of the mouse cortex as compared with sensory and motor areas. Modelling work based on these quantifications linked the low-density of parvalbumin interneurons with specific computations of associative cortices. However, it is still unknown whether the total GABAergic population of association cortices is smaller or whether another GABAergic type can compensate for the low density of parvalbumin interneurons. In the present study, we investigated these hypotheses using a combination of neuroanatomy, mouse genetics and neurophysiology. We found that the GABAergic population of association areas is comparable with that of primary sensory areas, and it is enriched of fast-spiking neurons that do not express parvalbumin and were not accounted for by previous quantifications. We developed an intersectional viral strategy to demonstrate that the population of fast-spiking neurons is comparable across cortical regions. Our results provide quantifications of the density of fast-spiking GABAergic neurons and offers new biological constrains to refine current models of cortical computations.

Tcf4 dysfunction alters dorsal and ventral cortical neurogenesis in Pitt-Hopkins syndrome mouse model showing sexual dimorphism.

Pitt-Hopkins syndrome (PTHS) is a neurodevelopmental disorder caused by haploinsufficiency of transcription factor 4 (TCF4). In this work, we focused on the cerebral cortex and investigated in detail the progenitor cell dynamics and the outcome of neurogenesis in a PTHS mouse model. Labeling and quantification of progenitors and newly generated neurons at various time points during embryonic development revealed alterations affecting the dynamic of cortical progenitors since the earliest stages of cortex formation in PTHS mice. Consequently, establishment of neuronal populations and layering of the cortex were found to be altered in heterozygotes subjects at birth. Interestingly, defective layering process of pyramidal neurons was partially rescued by reintroducing TCF4 expression using focal in utero electroporation in the cerebral cortex. Coincidentally with a defective dorsal neurogenesis, we found that ventral generation of interneurons was also defective in this model, which may lead to an excitation/inhibition imbalance in PTHS. Overall, sex-dependent differences were detected with more marked effects evidenced in males compared with females. All of this contributes to expand our understanding of PTHS, paralleling the advances of research in autism spectrum disorder and further validating the PTHS mouse model as an important tool to advance preclinical studies.

Effect of transcranial direct current stimulation on postoperative sleep disturbance in older patients undergoing lower limb major arthroplasty: a prospective, double-blind, pilot, randomised controlled trial.

Background: Postoperative sleep disturbance (PSD) is a common and serious postoperative complication and is associated with poor postoperative outcomes. Aims: This study aimed to investigate the effect of transcranial direct current stimulation (tDCS) on PSD in older patients undergoing lower limb major arthroplasty. Methods: In this prospective, double-blind, pilot, randomised, sham-controlled trial, patients 65 years and over undergoing lower limb major arthroplasty were randomly assigned to receive active tDCS (a-tDCS) or sham tDCS (s-tDCS). The primary outcomes were the objective sleep measures on postoperative nights (N) 1 and N2. Results: 116 inpatients were assessed for eligibility, and a total of 92 patients were enrolled; 47 received a-tDCS and 45 received s-tDCS. tDCS improved PSD by altering the following sleep measures in the a-tDCS and s-tDCS groups; the respective comparisons were as follows: the promotion of rapid eye movement (REM) sleep time on N1 (64.5 (33.5-105.5) vs 19.0 (0.0, 45.0) min, F=20.10, p<0.001) and N2 (75.0 (36.0-120.8) vs 30.0 (1.3-59.3) min, F=12.55, p<0.001); the total sleep time on N1 (506.0 (408.0-561.0) vs 392.0 (243.0-483.5) min, F=14.13, p<0.001) and N2 (488.5 (455.5-548.5) vs 346.0 (286.5-517.5) min, F=7.36, p=0.007); the deep sleep time on N1 (130.0 (103.3-177.0) vs 42.5 (9.8-100.8) min, F=24.4, p<0.001) and N2 (103.5 (46.0-154.8) vs 57.5 (23.3-106.5) min, F=8.4, p=0.004); and the percentages of light sleep and REM sleep on N1 and N2 (p<0.05 for each). The postoperative depression and anxiety scores did not differ significantly between the two groups. No significant adverse events were reported. Conclusion: In older patients undergoing lower limb major arthroplasty, a single session of anodal tDCS over the left dorsolateral prefrontal cortex showed a potentially prophylactic effect in improving postoperative short-term objective sleep measures. However, this benefit was temporary and was not maintained over time.

Neuroligin-2 shapes individual slow waves during slow-wave sleep and the response to sleep deprivation in mice.

BACKGROUND: Sleep disturbances are a common comorbidity to most neurodevelopmental disorders and tend to worsen disease symptomatology. It is thus crucial to understand mechanisms underlying sleep disturbances to improve patients' quality of life. Neuroligin-2 (NLGN2) is a synaptic adhesion protein regulating GABAergic transmission. It has been linked to autism spectrum disorders and schizophrenia in humans, and deregulations of its expression were shown to cause epileptic-like hypersynchronized cerebral activity in rodents. Importantly, the absence of Nlgn2 (knockout: KO) was previously shown to alter sleep-wake duration and quality in mice, notably increasing slow-wave sleep (SWS) delta activity (1-4 Hz) and altering its 24-h dynamics. This type of brain oscillation is involved in memory consolidation, and is also a marker of homeostatic sleep pressure. Sleep deprivation (SD) is notably known to impair cognition and the physiological response to sleep loss involves GABAergic transmission. METHODS: Using electrocorticographic (ECoG) recordings, we here first aimed to verify how individual slow wave (SW; 0.5-4 Hz) density and properties (e.g., amplitude, slope, frequency) contribute to the higher SWS delta activity and altered 24-h dynamics observed in Nlgn2 KO mice. We further investigated the response of these animals to SD. Finally, we tested whether sleep loss affects the gene expression of Nlgn2 and related GABAergic transcripts in the cerebral cortex of wild-type mice using RNA sequencing. RESULTS: Our results show that Nlgn2 KO mice have both greater SW amplitude and density, and that SW density is the main property contributing to the altered 24-h dynamics. We also found the absence of Nlgn2 to accelerate paradoxical sleep recovery following SD, together with profound alterations in ECoG activity across vigilance states. Sleep loss, however, did not modify the 24-h distribution of the hypersynchronized ECoG events observed in these mice. Finally, RNA sequencing confirmed an overall decrease in cortical expression of Nlgn2 and related GABAergic transcripts following SD in wild-type mice. CONCLUSIONS: This work brings further insight into potential mechanisms of sleep duration and quality deregulation in neurodevelopmental disorders, notably involving NLGN2 and GABAergic neurotransmission.

Assessing regional intracortical myelination in schizophrenia spectrum and bipolar disorders using the optimized T1w/T2w-ratio.

BACKGROUND: Dysmyelination could be part of the pathophysiology of schizophrenia spectrum (SCZ) and bipolar disorders (BPD), yet few studies have examined myelination of the cerebral cortex. The ratio of T1- and T2-weighted magnetic resonance images (MRI) correlates with intracortical myelin. We investigated the T1w/T2w-ratio and its age trajectories in patients and healthy controls (CTR) and explored associations with antipsychotic medication use and psychotic symptoms. METHODS: Patients with SCZ (n = 64; mean age = 30.4 years, s.d. = 9.8), BPD (n = 91; mean age 31.0 years, s.d. = 10.2), and CTR (n = 155; mean age = 31.9 years, s.d. = 9.1) who participated in the TOP study (NORMENT, University of Oslo, Norway) were clinically assessed and scanned using a General Electric 3 T MRI system. T1w/T2w-ratio images were computed using an optimized pipeline with intensity normalization and field inhomogeneity correction. Vertex-wise regression models were used to compare groups and examine group × age interactions. In regions showing significant differences, we explored associations with antipsychotic medication use and psychotic symptoms. RESULTS: No main effect of diagnosis was found. However, age slopes of the T1w/T2w-ratio differed significantly between SCZ and CTR, predominantly in frontal and temporal lobe regions: Lower T1w/T2w-ratio values with higher age were found in CTR, but not in SCZ. Follow-up analyses revealed a more positive age slope in patients who were using antipsychotics and patients using higher chlorpromazine-equivalent doses. CONCLUSIONS: While we found no evidence of reduced intracortical myelin in SCZ or BPD relative to CTR, different regional age trajectories in SCZ may suggest a promyelinating effect of antipsychotic medication.

Heart failure potentially affects the cortical structure of the brain.

BACKGROUND: Heart failure (HF) has been reported to affect cerebral cortex structure, but the underlying cause has not been determined. This study used Mendelian randomization (MR) to reveal the causal relationship between HF and structural changes in the cerebral cortex. METHODS: HF was defined as the exposure variable, and cerebral cortex structure was defined as the outcome variable. Inverse-variance weighted (IVW), MR-Egger regression and weighted median (WME) were performed for MR analysis; MR-PRESSO and Egger's intercept was used to test horizontal pleiotropy; and "leave-one-out" was used for sensitivity analysis. RESULTS: Fifty-two single nucleotide polymorphisms (SNPs) were defined as instrumental variables (IVs), and there was no horizontal pleiotropy in the IVs. According to the IVW analysis, the OR and 95% CI of cerebral cortex thickness were 0.9932 (0.9868-1.00) (P=0.0402), and the MR-Egger intercept was -15.6× 10-5 (P = 0.7974) and the Global test pval was 0.078. The P-value of the cerebral cortex surface was 0.2205, and the MR-Egger intercept was -34.69052 (P= 0.6984) and the Global Test pval was 0.045. HF had a causal effect on the surface area of the caudal middle frontal lobule (P=0.009), insula lobule (P=0.01), precuneus lobule (P=0.049) and superior parietal lobule (P=0.044). CONCLUSIONS: HF was potentially associated with changes in cortical thickness and in the surface area of the caudal middle frontal lobule, insula lobule, precuneus lobule and superior parietal lobule.

Overview: Research on the Genetic Architecture of the Developing Cerebral Cortex in Norms and Diseases.

The human brain is characterized by high cell numbers, diverse cell types with diverse functions, and intricate connectivity with an exceedingly broad surface of the cortex. Human-specific brain development was accomplished by a long timeline for maturation from the prenatal period to the third decade of life. The long timeline makes complicated architecture and circuits of human cerebral cortex possible, and it makes human brain vulnerable to intrinsic and extrinsic insults resulting in the development of variety of neuropsychiatric disorders. Unraveling the molecular and cellular processes underlying human brain development under the elaborate regulation of gene expression in a spatiotemporally specific manner, especially that of the cortex will provide a biological understanding of human cognition and behavior in health and diseases. Global research consortia and the advancing technologies in brain science including functional genomics equipped with emergent neuroinformatics such as single-cell multiomics, novel human models, and high-volume databases with high-throughput computation facilitate the biological understanding of the development of the human brain cortex. Knowing the process of interplay of the genome and the environment in cortex development will lead us to understand the human-specific cognitive function and its individual diversity. Thus, it is worthwhile to overview the recent progress in neurotechnology to foresee further understanding of the human brain and norms and diseases.

Live Imaging of Migrating Neurons and Glial Progenitors Visualized by in Utero Electroporation.

During cortical development, both neurons and glial cells are generated in the germinal zone near the lateral ventricle, migrate in the correct direction, and settle in their appropriate locations. This developmental process can be clearly visualized by introducing fluorescent protein-expression vectors via in utero electroporation. In this chapter, we describe labeling methods for migrating neurons and glial progenitors, as well as methods for slice culture, and time-lapse imaging.

Primary Culture of Dissociated Neurons from the Embryonic Cerebral Cortex.

Primary neuronal culture is a valuable in vitro model for analyzing the molecular mechanisms underlying the development and function of neural circuits. In contrast to neurons in vivo, primary cultured neurons can easily be transfected with genes of interest or treated with chemicals such as agonists and inhibitors of a specific target molecule. Furthermore, time-dependent morphological changes, such as the acquisition of neuronal polarity, axon elongation, and dendrite branch formation, can be analyzed by using primary neuronal cultures. Here, we describe a method for preparing a primary culture of neurons from the developing cerebral cortex, together with a method for gene transfer to primary cultured cortical neurons.

Immunocytochemistry of Primary Cultured Cerebral Cortical Neurons.

Immunocytochemistry combined with confocal or superresolution microscopy allows us to observe molecular localization and intracellular structures. However, it is challenging to analyze individual neurons in brain tissue, where neurons are densely packed. In contrast, we can easily observe structures such as the axonal growth cone and dendritic spines in dissociated individual neurons. Thus, the immunocytochemistry of primary cultured neurons is often used because it reflects the in vivo condition at least in part. Here, we describe a method for indirect fluorescence immunocytochemistry of primary cultured neurons from the embryonic cerebral cortex. This involves multiple steps including fixation, permeabilization, and antibody reaction, and in particular, we introduce an optimized protocol for permeabilization to enable the precise localization of target molecules.

Morphological correlates of pyramidal cell axonal myelination in mouse and human neocortex.

The axons of neocortical pyramidal neurons are frequently myelinated. Heterogeneity in the topography of axonal myelination in the cerebral cortex has been attributed to a combination of electrophysiological activity, axonal morphology, and neuronal-glial interactions. Previously, we showed that axonal segment length and caliber are critical local determinants of fast-spiking interneuron myelination. However, the factors that determine the myelination of individual axonal segments along neocortical pyramidal neurons remain largely unexplored. Here, we used structured illumination microscopy to examine the extent to which axonal morphology is predictive of the topography of myelination along neocortical pyramidal neurons. We identified critical thresholds for axonal caliber and interbranch distance that are necessary, but not sufficient, for myelination of pyramidal cell axons in mouse primary somatosensory cortex (S1). Specifically, we found that pyramidal neuron axonal segments with a caliber < 0.24 µm or interbranch distance < 18.10 µm are rarely myelinated. Moreover, we further confirmed that these findings in mice are similar for human neocortical pyramidal cell myelination (caliber < 0.25 µm, interbranch distance < 19.00 µm), suggesting that this mechanism is evolutionarily conserved. Taken together, our findings suggest that axonal morphology is a critical correlate of the topography and cell-type specificity of neocortical myelination.

Foxg1 bimodally tunes L1-mRNA and -DNA dynamics in the developing murine neocortex.

Foxg1 masters telencephalic development via a pleiotropic control over its progression. Expressed within the central nervous system (CNS), L1 retrotransposons are implicated in progression of its histogenesis and tuning of its genomic plasticity. Foxg1 represses gene transcription, and L1 elements share putative Foxg1 binding motifs, suggesting the former might limit telencephalic expression (and activity) of the latter. We tested such prediction, in vivo as well as in engineered primary neural cultures, by loss- and gain-of-function approaches. We showed that Foxg1-dependent, transcriptional L1 repression specifically occurs in neopallial neuronogenic progenitors and post-mitotic neurons, where it is supported by specific changes in the L1 epigenetic landscape. Unexpectedly, we discovered that Foxg1 physically interacts with L1-mRNA and positively regulates neonatal neopallium L1-DNA content, antagonizing the retrotranscription-suppressing activity exerted by Mov10 and Ddx39a helicases. To the best of our knowledge, Foxg1 represents the first CNS patterning gene acting as a bimodal retrotransposon modulator, limiting transcription of L1 elements and promoting their amplification, within a specific domain of the developing mouse brain.

GABA Administration Ameliorates the Toxicity of Doxorubicin on CSF and the Brain of Albino Rats.

Background: Gamma-aminobutyric acid (GABA) is the main inhibitory neurotransmitter in the mammalian brain and is a non-proteinogenic amino acid. Doxorubcin (DOX) or adriamycin is one of the most potent chemotherapy drugs for breast cancer. Purpose: This study focused on diminishing the brain injury and neurotoxicity of doxorubicin (DOX) by GABA administration. Methods: Rats were randomly divided into four groups (8 rats each), which were the control group, DOX group (3 mg/kg for 4 weeks, then 2 mg/kg for 2 weeks), GABA group (2 mg/kg for 21 days), and DOX + GABA group (treated as the second and third groups). Neurotoxicity and brain injury were assessed by determining CSF biomarkers, serum inflammatory markers, and histopathological evaluation of the cerebral cortex. Results: DOX treatment significantly increased the levels of all CSF biomarkers (S100B, IL-1ß, ubiquitin carboxy-terminal hydrolase L1 (UCH-L1), glial fibrillary acidic protein (GFAP), spectrin breakdown products (SBDP145), and C-C motif chemokine ligand 2 (CCL2) and all inflammatory markers (IL-6, TNF-α, and IFN-γ), causing extensive neutrophilic infiltration and great alteration in the cerebral cortex architecture as evidence of neurotoxicity. The oral administration of GABA significantly reduced the levels of all CSF biomarkers and inflammatory markers and restored the normal architecture of the cerebral cortex, with observed ameliorations in neutrophilic infiltration. Conclusion: GABA administration can ameliorate neurotoxicity and protect the brain against the negative effects of DOX treatment.

Somatostatin interneurons control the timing of developmental desynchronization in cortical networks.

Synchronous neuronal activity is a hallmark of the developing brain. In the mouse cerebral cortex, activity decorrelates during the second week of postnatal development, progressively acquiring the characteristic sparse pattern underlying the integration of sensory information. The maturation of inhibition seems critical for this process, but the interneurons involved in this crucial transition of network activity in the developing cortex remain unknown. Using in vivo longitudinal two-photon calcium imaging during the period that precedes the change from highly synchronous to decorrelated activity, we identify somatostatin-expressing (SST+) interneurons as critical modulators of this switch in mice. Modulation of the activity of SST+ cells accelerates or delays the decorrelation of cortical network activity, a process that involves regulating the maturation of parvalbumin-expressing (PV+) interneurons. SST+ cells critically link sensory inputs with local circuits, controlling the neural dynamics in the developing cortex while modulating the integration of other interneurons into nascent cortical circuits.

Depth-Specific Hypoxic Responses to Spreading Depolarizations in Gyrencephalic Swine Cortex Unveiled by Photoacoustic Imaging.

Spreading depolarizations (SDs) are a marker of brain injury and have a causative effect on ischemic lesion progression. The hemodynamic responses elicited by SDs are contingent upon the metabolic integrity of the affected tissue, with vasoconstrictive reactions leading to pronounced hypoxia often indicating poor outcomes. The stratification of hemodynamic responses within different cortical layers remains poorly characterized. This pilot study sought to elucidate the depth-specific hemodynamic changes in response to SDs within the gray matter of the gyrencephalic swine brain. Employing a potassium chloride-induced SD model, we utilized multispectral photoacoustic imaging (PAI) to estimate regional cerebral oxygen saturation (rcSO2%) changes consequent to potassium chloride-induced SDs. Regions of interest were demarcated at three cortical depths covering up to 4 mm. Electrocorticography (ECoG) strips were placed to validate the presence of SDs. Through PAI, we detected 12 distinct rcSO2% responses, which corresponded with SDs detected in ECoG. Notably, a higher frequency of hypoxic responses was observed in the deeper cortical layers compared to superficial layers, where hyperoxic and mixed responses predominated (p < 0.001). This data provides novel insights into the differential oxygenation patterns across cortical layers in response to SDs, underlining the complexity of cerebral hemodynamics post-injury.