This Special Issue, "GABA Signaling: Therapeutic Targets for Neurodegenerative and Neurodevelopmental Disorders", focuses on a fundamental property of the neurotransmitter γ-aminobutyric acid (GABA), namely its capacity to shift, in particular conditions, from the hyperpolarizing to the depolarizing direction [...].

The specific NKCC1 cotransporter antagonist, bumetanide, attenuates the severity of Autism Spectrum Disorders (ASD), and many neurodevelopmental or neurodegenerative disorders in animal models and clinical trials. However, the pervasive expression of NKCC1 in many cell types throughout the body is thought to challenge the therapeutic efficacy of bumetanide. However, many peripheral functions, including intestinal, metabolic, or vascular, etc., are perturbed in brain disorders contributing to the neurological sequels. Alterations of these functions also increase the incidence of the disorder suggesting complex bidirectional links with the clinical manifestations. We suggest that a more holistic view of ASD and other disorders is warranted to account for the multiple sites impacted by the original intra-uterine insult. From this perspective, large-spectrum active repositioned drugs that act centrally and peripherally might constitute a useful approach to treating these disorders.

Les troubles du spectre de l’autisme (TSA) « naissent » in utero à la suite d’évènements pathologiques génétiques ou environnementaux. Le diagnostic des TSA n’est cependant effectué que vers l’âge de 3-5 ans en Europe et aux États-Unis. Un pronostic précoce permettrait pourtant d’atténuer la sévérité des atteintes cognitives, grâce à des approches psycho-éducatives. Une large panoplie d’approches a été suggérée pour établir un pronostic précoce des TSA, se fondant sur l’imagerie cérébrale, sur des enregistrements EEG, sur des biomarqueurs sanguins ou sur l’analyse des contacts visuels. Nous avons développé une approche fondée sur l’analyse par machine learning des données biologiques et échographiques recueillies en routine, du début de la grossesse au lendemain de la naissance, dans les maternités françaises. Ce programme qui permet d’identifier la presque totalité des bébés neurotypiques et la moitié des bébés qui auront un diagnostic de TSA quelques années plus tard, permet aussi d’identifier les paramètres ayant un impact sur le pronostic. Si quelques-uns d’entre eux étaient attendus, d’autres n’ont aucun lien avec les TSA. L’étude sans a priori des données de maternité devrait ainsi permettre un pronostic des TSA dès la naissance, ainsi que de mieux comprendre la pathogenèse de ces syndromes et de les traiter plus tôt.

Although several observations suggest that the constitutive biological, genetic or physiological changes leading to autism spectrum disorders (ASD) start in utero, their early impact on the number and density of neurons in the brain remains unknown. Using genetic fate mapping associated with the immunollabeling-enabled three-dimensional imaging of solvent-cleared organs (iDISCO) clearing method we identified and counted a selective population of neocortical and hippocampal pyramidal neurons in the in utero valproate (VPA) mouse model of autism. We report that 1 day before birth, the number of pyramidal neurons born at E14.5 in the neocortex and hippocampus of VPA mice is smaller than in age-matched controls. VPA also induced a reduction of the neocortical-but not hippocampal-volume 1 day before birth. Interestingly, VPA mice present an increase in both neocortical and hippocampal volumes 2 days after birth compared with controls. These results suggest that the VPA-exposed hippocampus and neocortex differ substantially from controls during the highly complex perinatal period, and specially 1 day before birth, reflecting the early pathogenesis of ASD.

The complex organization of brain regions during development requires a three-dimensional approach to facilitate the visualization and quantification of dynamic changes taking place throughout this important period. Using the tissue clearing method combined with immunohistochemistry, three-dimensional (3D) lightsheet microscopy and a multiresolution registration technique, we provide the first 3D atlases of the main cholinergic (CH) and catecholaminergic (CA) systems in the mouse brain from embryonic day 12 (E12) to post-natal day 8 (P8). We report that in several brain structures, there is a logarithmic scale increase of choline acetyltransferase and tyrosine hydroxylase positive neurons from E18 to P8. In addition, a detailed voxel-wise analysis revealed abrupt modifications in the developmental trajectory of many brain structures during the transition from E18 to P0. Our atlases will not only facilitate developmental studies aimed at quantitatively determining the fate of CH or CA neurons in utero but also be used as an anatomical reference to quantify other neuronal populations present in the annotated regions. In the future, these maps will be a reliable tool to study developmental malformations associated with neurological and psychiatric disorders.

GABA depolarizes and often excites immature neurons in all animal species and brain structures investigated due to a developmentally regulated reduction in intracellular chloride concentration ([Cl−]i) levels. The control of [Cl−]i levels is mediated by the chloride cotransporters NKCC1 and KCC2, the former usually importing chloride and the latter exporting it. The GABA polarity shift has been extensively validated in several experimental conditions using often the NKCC1 chloride importer antagonist bumetanide. In spite of an intrinsic heterogeneity, this shift is abolished in many experimental conditions associated with developmental disorders including autism, Rett syndrome, fragile X syndrome, or maternal immune activation. Using bumetanide, an EMA- and FDA-approved agent, many clinical trials have shown promising results with the expected side effects. Kaila et al. have repeatedly challenged these experimental and clinical observations. Here, we reply to the recent reviews by Kaila et al. stressing that the GABA polarity shift is solidly accepted by the scientific community as a major discovery to understand brain development and that bumetanide has shown promising effects in clinical trials.

Autism Spectrum Disorders (ASD) are born in the womb generated by intrauterine genetic or environmental insult. ASD diagnostic is made at the age of 3-5 years in Europe and in the US. Relying on this, we have tested the hypothesis of identifying already at birth babies who might be diagnosed later with ASD, thereby facilitating an early use of psychoeducative techniques to attenuate the severity of the symptoms. Here, we discuss the various approaches that have been used to enable an early diagnosis. We have ourselves used an approach based on a "without a priori" machine learning analysis of all maternity biological and ultrasound data available in French maternities (around 116) in utero and after birth. This program made it possible to identify at birth almost all (96%) of babies who will be later neurotypical and around half of those who will be diagnosed with ASD. Some of the parameters allowing this identification were largely unexpected with no known links with ASD. This approach will enable an early identification of babies at risk, but also might be used to diagnose ASD later on, and perhaps could help to get a better understanding of the heterogeneity of ASD.

After over seven decades of neuroscience research, it is now well established that γ-aminobutyric acid (GABA) is the main inhibitory neurotransmitter in the brain. In this paper dedicated to Krešimir Krnjević (1927-2021), a pioneer and leader in neuroscience, we briefly highlight the fundamental contributions he made in identifying GABA as an inhibitory neurotransmitter in the brain and our personal interactions with him. Of note, between 1972 and 1978 Dr. Krnjević was a highly reputed Chief Editor of the Canadian Journal of Physiology and Pharmacology.

Benzodiazepines (BZDs) such as Zolpidem can produce a temporary revival of patients who have been akinetic and apathic for years. The mechanisms underlying this “awakening” reaction are suggested globally to be related to an activation of gamma-aminobutyric acid (GABA) inhibitory systems. However, brain trauma or cerebro-vascular infarcts, like many other pathological insults, are associated with a shift of the polarity of GABA from inhibition to excitation consequently to an increase of intracellular chloride concentration ([Cl − ] i ) levels. Experimental and clinical observations suggest that BZDs generate paradoxical reactions in these conditions, hence the transient “awakening”. The NKCC1 (Na-K-2Cl co-transporter isoform 1) chloride importer antagonist Bumetanide restores low [Cl − ] i levels and an efficient inhibitory drive. It is therefore suggested that the administration of Bumetanide might provide a persistent “awakening” by shifting GABAergic actions from excitation to inhibition and attenuating the mechanism underlying the apathic/akinetic state.

The rate of cesarean section (CS) delivery has steadily increased over the past decades despite epidemiological studies reporting higher risks of neonatal morbidity and neurodevelopmental disorders. Yet, little is known about the immediate impact of CS birth on the brain, hence the need of experimental studies to evaluate brain parameters following this mode of delivery. Using the solvent clearing method iDISCO and 3D imaging technique, we report that on the day of birth, whole-brain, hippocampus, and striatum volumes are reduced in CS-delivered as compared to vaginally-born mice, with a stronger effect observed in preterm CS pups. These results stress the impact of CS delivery, at term or preterm, during parturition and at birth. In contrast, cellular activity and apoptosis are reduced in mice born by CS preterm but not term, suggesting that these early-life processes are only impacted by the combination of preterm birth and CS delivery.

Kaila, Löscher, and colleagues report that phenobarbital (PHB) and midazolam (MDZ) attenuate neonatal seizures following birth asphyxia, but the former only when applied before asphyxia and the latter before or after the triggering insult. In contrast, the NKCC1 chloride importer antagonist bumetanide (BUM) had no effect whether applied alone or with PHB. The observations are compelling and in accord with earlier studies. However, there are several general issues that deserve discussion. What is the clinical relevance of these data and the validity of animal models of encephalopathic seizures? Why is it that although they act on similar targets, these agents have different efficacy? Are both PHB and MDZ actions restricted to γ-aminobutyric acidergic (GABAergic) mechanisms? Why is BUM inefficient in attenuating seizures but capable of reducing the severity of other brain disorders? We suggest that the relative failure of antiepileptic drugs (AEDs) to treat this severe life-threatening condition is in part explicable by the recurrent seizures that shift the polarity of GABA, thereby counteracting their effects on their target. AEDs might be efficient after a few seizures but not recurrent ones. In addition, PHB and MDZ actions are not limited to GABA signals. BUM efficiently attenuates autism symptomatology notably in patients with tuberous sclerosis but does not reduce the recurrent seizures, illustrating the uniqueness of epilepsies. Therefore, the efficacy of AEDs to treat babies with encephalopathic seizures will depend on the history and severity of the seizures prior to their administration, challenging a universal common underlying mechanism.

To identify newborns at risk of developing ASD and to detect ASD biomarkers early after birth, we compared retrospectively ultrasound and biological measurements of babies diagnosed later with ASD or neurotypical (NT) that are collected routinely during pregnancy and birth. We used a supervised machine learning algorithm with a cross-validation technique to classify NT and ASD babies and performed various statistical tests. With a minimization of the false positive rate, 96% of NT and 41% of ASD babies were identified with a positive predictive value of 77%. We identified the following biomarkers related to ASD: sex, maternal familial history of auto-immune diseases, maternal immunization to CMV, IgG CMV level, timing of fetal rotation on head, femur length in the 3rd trimester, white blood cell count in the 3rd trimester, fetal heart rate during labor, newborn feeding and temperature difference between birth and one day after. Furthermore, statistical models revealed that a subpopulation of 38% of babies at risk of ASD had significantly larger fetal head circumference than age-matched NT ones, suggesting an in utero origin of the reported bigger brains of toddlers with ASD. Our results suggest that pregnancy follow-up measurements might provide an early prognosis of ASD enabling pre-symptomatic behavioral interventions to attenuate efficiently ASD developmental sequels.

Importance: The global prevalence of autism spectrum disorder (ASD) has been reported to be between 1% and 2% of the population, with little research in Black, Asian, and other racial/ethnic minority groups. Accurate estimates of ASD prevalence are vital to planning diagnostic, educational, health, and social care services and may detect possible access barriers to diagnostic pathways and services and inequalities based on social determinants of health.Objective: To evaluate whether socioeconomic disadvantage is associated with ASD prevalence and the likelihood of accessing ASD services in racial/ethnic minority and disadvantaged groups in England.Design, Setting, and Participants: This case-control prevalence cohort study used the Spring School Census 2017 from the Pupil Level Annual Schools Census of the National Pupil Database, which is a total population sample that includes all English children, adolescents, and young adults aged 2 to 21 years in state-funded education. Data were collected on January 17, 2017, and analyzed from August 2, 2018, to January 28, 2020.Exposures: Age and sex were treated as a priori confounders while assessing correlates of ASD status according to (1) race/ethnicity, (2) social disadvantage, (3) first language spoken, (4) Education, Health and Care Plan or ASD Special Educational Needs and Disability support status, and (5) mediation analysis to assess how social disadvantage and language might affect ASD status.Main Outcomes and Measures: Sex- and age-standardized ASD prevalence by race/ethnicity and 326 English local authority districts in pupils aged 5 to 19 years.Results: The final population sample consisted of 7 047 238 pupils (50.99% male; mean [SD] age, 10.18 [3.47] years) and included 119 821 pupils with ASD, of whom 21 660 also had learning difficulties (18.08%). The standardized prevalence of ASD was 1.76% (95% CI, 1.75%-1.77%), with male pupils showing a prevalence of 2.81% (95% CI, 2.79%-2.83%) and female pupils a prevalence of 0.65% (95% CI, 0.64%-0.66%), for a male-to-female ratio (MFR) of 4.32:1. Standardized prevalence was highest in Black pupils (2.11% [95% CI, 2.06%-2.16%]; MFR, 4.68:1) and lowest in Roma/Irish Travelers (0.85% [95% CI, 0.67%-1.03%]; MFR, 2.84:1). Pupils with ASD were more likely to face social disadvantage (adjusted prevalence ratio, 1.61; 95% CI, 1.59-1.63) and to speak English as an additional language (adjusted prevalence ratio, 0.64; 95% CI, 0.63-0.65). The effect of race/ethnicity on ASD status was mediated mostly through social disadvantage, with Black pupils having the largest effect (standardized mediation coefficient, 0.018; P < .001) and 12.41% of indirect effects through this way.Conclusions and Relevance: These findings suggest that significant differences in ASD prevalence exist across racial/ethnic groups and geographic areas and local authority districts, indicating possible differential phenotypic prevalence or differences in detection or referral for racial/ethnic minority groups. PMID: 33779707