Calcium-stimulated adenylyl cyclases modulate ethanol-induced neurodegeneration in the neonatal brain

Arthropods to Eutherians: A Historical and Contemporary Comparison of Sparse Prenatal Microbial Communities Among Animalia Species

Since the advent of next-generation sequencing, investigators worldwide have sought to discern whether a functional and biologically or clinically relevant prenatal microbiome exists. One line of research has led to the hypothesis that microbial DNA detected in utero/in ovo or prior to birth/hatching is a result of contamination and does not belong to viable and functional microbes. Many of these preliminary evaluations have been conducted in humans, mice, and nonhuman primates due to sample and specimen availability. However, a comprehensive review of the literature across animal species suggests organisms that maintain an obligate relationship with microbes may act as better models for interrogating the selective pressures placed on vertical microbial transfer over traditional laboratory species. To date, studies in humans and viviparous laboratory species have failed to illustrate the clear presence and transfer of functional microbes in utero. Until a ground truth regarding the status and relevance of prenatal microbes can be ascertained, it is salient to conduct parallel investigations into the prevalence of a functional prenatal microbiome across the developmental lifespan of multiple organisms in the kingdom Animalia. This comprehensive understanding is necessary not only to determine the role of vertically transmitted microbes and their products in early human health but also to understand their full One Health impact. This review is among the first to compile such comprehensive primary conclusions from the original investigator's conclusions, and hence collectively illustrates that prenatal microbial transfer is supported by experimental evidence arising from over a long and rigorous scientific history encompassing a breadth of species from kingdom Animalia.

GABA system as the cause and effect in early development

GABA is the primary inhibitory neurotransmitter in the adult brain and through its actions on GABAARs, it protects against excitotoxicity and seizure activity, ensures temporal fidelity of neurotransmission, and regulates concerted rhythmic activity of neuronal populations. In the developing brain, the development of GABAergic neurons precedes that of glutamatergic neurons and the GABA system serves as a guide and framework for the development of other brain systems. Despite this early start, the maturation of the GABA system also continues well into the early postnatal period. In this review, we organize evidence around two scenarios based on the essential and protracted nature of GABA system development: 1) disruptions in the development of the GABA system can lead to large scale disruptions in other developmental processes (i.e., GABA as the cause), 2) protracted maturation of this system makes it vulnerable to the effects of developmental insults (i.e., GABA as the effect). While ample evidence supports the importance of GABA/GABAAR system in both scenarios, large gaps in existing knowledge prevent strong mechanistic conclusions.

Dose-Related Reduction in Hippocampal Neuronal Populations in Fetal Alcohol Exposed Vervet Monkeys

Fetal alcohol spectrum disorder (FASD) is a chronic debilitating condition resulting in behavioral and intellectual impairments and is considered the most prevalent form of preventable mental retardation in the industrialized world. We previously reported that 2-year-old offspring of vervet monkey (Chlorocebus sabeus) dams drinking, on average, 2.3 ± 0.49 g ethanol per Kg maternal body weight 4 days per week during the last third of pregnancy had significantly lower numbers of CA1 (-51.6%), CA2 (-51.2%) and CA3 (-42.8%) hippocampal neurons, as compared to age-matched sucrose controls. Fetal alcohol-exposed (FAE) offspring also showed significantly lower volumes for these structures at 2 years of age. In the present study, we examined these same parameters in 12 FAE offspring with a similar average but a larger range of ethanol exposures (1.01-2.98 g/Kg/day; total ethanol exposure 24-158 g/Kg). Design-based stereology was performed on cresyl violet-stained and doublecortin (DCX)-immunostained sections of the hippocampus. We report here significant neuronal deficits in the hippocampus with a significant negative correlation between daily dose and neuronal population in CA1 (r2 = 0.486), CA2 (r2 = 0.492), and CA3 (r2 = 0.469). There were also significant correlations between DCX population in the dentate gyrus and daily dose (r2 = 0.560). Both correlations were consistent with linear dose-response models. This study illustrates that neuroanatomical sequelae of fetal ethanol exposure are dose-responsive and suggests that there may be a threshold for this effect.

Discovery of a potent and selective adenylyl cyclase type 8 agonist by docking-based virtual screening

Adenylyl cyclases (ACs), which are responsible for catalyzing the conversion of adenosine triphosphate (ATP) into the second messenger cyclic adenosine monophosphate (cAMP), play a critical role in cell signal transduction. In this study, a combined approach involving docking-based virtual screening, with the combination of homology modeling followed by an in-vitro, and cell-based biological assay have been performed for discovering a class of novel potent and selective isoform adenylyl cyclase type 8 (AC8) agonist. The computer-aided virtual screening was used to identify fourteen virtual cluster compounds as potential hits which were further subjected to rigorous bioassays. A novel hit compound VHC-7 (ethyl 3-(2,4-dichlorobenzyl)-2-oxoindoline-3-carboxylate) was identified as a highly potent selective AC8 agonist with EC₅₀ value of 0.1052 ± 0.038 µM. Remarkably, the molecule herein reported can be explored further to discover greater number of hit compounds with better pharmacokinetic properties as well as to serve as a promising novel hit agonist of AC8 for the treatment of various central nervous system disorders and its associated diseases.

Neonatal alcohol exposure augments voluntary ethanol intake in the absence of potentiated anxiety-like behavior induced by chronic intermittent ethanol vapor exposure

Individuals fetally exposed to alcohol have a disproportionate risk for developing lifetime alcohol dependence, an association that may be confounded by the presence of comorbid conditions, such as anxiety. Anxiety is also observed following fetal alcohol exposure and is known to exacerbate ethanol consumption, highlighting the utility of animal models to assess this relationship. The present study evaluated the impact of third-trimester equivalent ethanol exposure on ethanol consumption and anxiety-like, marble burying behavior in adult, male C57BL/6 mice following exposure to chronic intermittent ethanol vapor, proposed to model dependence. Neonatal mice (P5-6, 2.5-3.0 g) were administered one injection of saline or ethanol (2.5 g/kg, subcutaneously [s.c.]). Pre-vapor marble burying and limited-access two-bottle choice ethanol intake (15% v/v, 2 h) were comparable in adults (8 weeks of age) across neonatal treatment groups. Five consecutive drinking sessions were repeated 72 h after each weekly ethanol vapor exposure procedure for a total of five vapor/drinking cycles. Consistent with prior research, an increase in voluntary ethanol drinking was observed in vapor-exposed, neonatal saline-treated mice throughout the study starting after the second vapor cycle compared to both air-exposed control groups. In neonatal ethanol-treated mice, this increase in ethanol intake and preference following vapor exposure was accelerated, being observed after the first vapor cycle, and observed at an augmented level compared to vapor-exposed, neonatal saline-treated mice and air controls for both neonatal conditions. Conversely, marble burying was enhanced equivalently in vapor-exposed mice from either neonatal treatment group relative to their respective air-exposed controls. These data recapitulate clinical observations of enhanced sensitivity for alcohol dependence following developmental alcohol exposure, which may reflect enhanced motivational drive rather than potentiated negative affect. The present model will facilitate the future exploration of mechanisms that underlie increased risk for alcohol use after early developmental exposure.

Calcium/calmodulin-stimulated adenylyl cyclases 1 and 8 regulate reward-related brain activity and ethanol consumption

Evidence suggests a predictive link between elevated basal activity within reward-related networks (e.g., cortico-basal ganglia-thalamic networks) and vulnerability for alcoholism. Both calcium channel function and cyclic adenosine monophosphate (cAMP)/protein kinase A-mediated signaling are critical modulators of reward neurocircuitry and reward-related behaviors. Calcium/calmodulin-stimulated adenylyl cyclases (AC) 1 and 8 are sensitive to activity-dependent increases in intracellular calcium and catalyze cAMP production. Therefore, we hypothesized AC1 and 8 regulate brain activity in reward regions of the cortico-basal ganglia-thalamic circuit and that this regulatory influence predicts voluntary ethanol drinking responses. This hypothesis was evaluated by manganese-enhanced magnetic resonance imaging and chronic, intermittent ethanol access procedures. Ethanol-naïve mice with genetic deletion of both AC1 and 8 (DKO mice) exhibited bilateral reductions in baseline activity within cortico-basal ganglia-thalamic regions associated with reward processing compared to wild-type controls (WT, C57BL/6 mice). Significant activity changes were not evident in regions either outside of the cortico-basal ganglia-thalamic network or within the network that are not associated with reward processing. Parallel studies demonstrated that reward network hypoactivity in DKO mice predicted a significant attenuation in consumption and preference levels to escalating ethanol concentrations (12, 20 and 30%) compared to WT mice, an effect that was maintained over extended access (14 sessions) to 20% ethanol. Summarizing, these data support a contribution of AC1 and 8 in cortico-basal ganglia-thalamic activity and the predictive value of this regulatory influence on ethanol drinking behavior, which merits the future evaluation of calcium-stimulated ACs in the neural processes that engender vulnerability to maladaptive alcohol drinking.

Inheritance and Establishment of Gut Microbiota in Chickens

In mammals, the microbiota can be transmitted from the placenta, uterus, and vagina of the mother to the infant. Unlike mammals, development of the avian embryo is a process isolated from the mother and thus in the avian embryo the gut microbial developmental process remains elusive. To explore the establishment and inheritance of the gut microbiome in the avian embryo, we used the chicken as the model organism to investigate the gut microbial composition in embryos, chicks, and maternal hens. We observed: (1) 28 phyla and 162 genera of microbes in embryos where the dominated genus was Halomonas (79%). (2) 65 genera were core microbiota in all stages with 42% and 62% gut microbial genera of embryo were found in maternal hen and chick, respectively. There was a moderate correlation (0.40) between the embryo and maternal, and 0.52 between the embryo and chick at the family level. (3) Gut microbes that are involved in substance metabolism, infectious disease, and environmental adaptation are enriched in embryos, chicks, and maternal hens, respectively. (4) 94% genera of gut microbial composition were similar among three different chicken breeds which were maintained under similar conditions. Our findings provide evidence to support the hypothesis that part of the microbial colonizers harbored in early embryos were inherited from maternal hens, and the gut microbial abundance and diversity were influenced by environmental factors and host genetic variation during development.

Ethanol Stimulates Locomotion via a Gαs-Signaling Pathway in IL2 Neurons in Caenorhabditis elegans

Alcohol abuse is among the top causes of preventable death, generating considerable financial, health, and societal burdens. Paradoxically, alcohol...

Alcohol is a potent pharmacological agent when consumed acutely at sufficient quantities and repeated overuse can lead to addiction and deleterious effects on health. Alcohol is thought to modulate neuronal function through low-affinity interactions with proteins, in particular with membrane channels and receptors. Paradoxically, alcohol acts as both a stimulant and a sedative. The exact molecular mechanisms for the acute effects of ethanol on neurons, as either a stimulant or a sedative, however remain unclear. We investigated the role that the heat shock transcription factor HSF-1 played in determining a stimulatory phenotype of Caenorhabditis elegans in response to physiologically relevant concentrations of ethanol (17 mM; 0.1% v/v). Using genetic techniques, we demonstrate that either RNA interference of hsf-1 or use of an hsf-1(sy441) mutant lacked the enhancement of locomotion in response to acute ethanol exposure evident in wild-type animals. We identify that the requirement for HSF-1 in this phenotype was IL2 neuron-specific and required the downstream expression of the α-crystallin ortholog HSP-16.48. Using a combination of pharmacology, optogenetics, and phenotypic analyses we determine that ethanol activates a G_αs-cAMP-protein kinase A signaling pathway in IL2 neurons to stimulate nematode locomotion. We further implicate the phosphorylation of a specific serine residue (Ser322) on the synaptic protein UNC-18 as an end point for the G_αs-dependent signaling pathway. These findings establish and characterize a distinct neurosensory cell signaling pathway that determines the stimulatory action of ethanol and identifies HSP-16.48 and HSF-1 as novel regulators of this pathway.

International Union of Basic and Clinical Pharmacology. CI. Structures and Small Molecule Modulators of Mammalian Adenylyl Cyclases

Adenylyl cyclases (ACs) generate the second messenger cAMP from ATP. Mammalian cells express nine transmembrane AC (mAC) isoforms (AC1-9) and a soluble AC (sAC, also referred to as AC10). This review will largely focus on mACs. mACs are activated by the G-protein Gαs and regulated by multiple mechanisms. mACs are differentially expressed in tissues and regulate numerous and diverse cell functions. mACs localize in distinct membrane compartments and form signaling complexes. sAC is activated by bicarbonate with physiologic roles first described in testis. Crystal structures of the catalytic core of a hybrid mAC and sAC are available. These structures provide detailed insights into the catalytic mechanism and constitute the basis for the development of isoform-selective activators and inhibitors. Although potent competitive and noncompetitive mAC inhibitors are available, it is challenging to obtain compounds with high isoform selectivity due to the conservation of the catalytic core. Accordingly, caution must be exerted with the interpretation of intact-cell studies. The development of isoform-selective activators, the plant diterpene forskolin being the starting compound, has been equally challenging. There is no known endogenous ligand for the forskolin binding site. Recently, development of selective sAC inhibitors was reported. An emerging field is the association of AC gene polymorphisms with human diseases. For example, mutations in the AC5 gene (ADCY5) cause hyperkinetic extrapyramidal motor disorders. Overall, in contrast to the guanylyl cyclase field, our understanding of the (patho)physiology of AC isoforms and the development of clinically useful drugs targeting ACs is still in its infancy.

Dysregulation of TrkB phosphorylation and proBDNF protein in adenylyl cyclase 1 and 8 knockout mice in a model of fetal alcohol spectrum disorder

Brain-derived neurotrophic factor (BDNF) mediates neuron growth and is regulated by adenylyl cyclases (ACs). Mice lacking AC1/8 (DKO) have a basal reduction in the dendritic complexity of medium spiny neurons in the caudate putamen and demonstrate increased neurotoxicity in the striatum following acute neonatal ethanol exposure compared to wild type (WT) controls, suggesting a compromise in BDNF regulation under varying conditions. Although neonatal ethanol exposure can negatively impact BDNF expression, little is known about the effect on BDNF receptor activation and its downstream signaling, including Akt activation, an established neuroprotective pathway. Therefore, here we determined the effects of AC1/8 deletion and neonatal ethanol administration on BDNF and proBDNF protein expression, and activation of tropomyosin-related kinase B (TrkB), Akt, ERK1/2, and PLCγ. WT and DKO mice were treated with a single dose of 2.5 g/kg ethanol or saline at postnatal days 5-7 to model late-gestational alcohol exposure. Striatal and cortical tissues were analyzed using a BDNF enzyme-linked immunosorbent assay or immunoblotting for proBDNF, phosphorylated and total TrkB, Akt, ERK1/2, and PLCɣ1. Neither postnatal ethanol exposure nor AC1/8 deletion affected total BDNF protein expression at any time point in either region examined. Neonatal ethanol increased the expression of proBDNF protein in the striatum of WT mice 6, 24, and 48 h after exposure, with DKO mice demonstrating a reduction in proBDNF expression 6 h after exposure. Six and 24 h after ethanol administration, phosphorylation of full-length TrkB in the striatum was significantly reduced in WT mice, but was significantly increased in DKO mice only at 24 h. Interestingly, 48 h after ethanol, both WT and DKO mice demonstrated a reduction in phosphorylated full-length TrkB. In addition, Akt and PLCɣ1 phosphorylation was also decreased in ethanol-treated DKO mice 48 h after injection. These data demonstrate dysregulation of a potential survival pathway in the AC1/8 knockout mice following early-life ethanol exposure.

Phosphodiesterase regulation of alcohol drinking in rodents

Alcohol use disorders are chronically relapsing conditions characterized by persistent drinking despite the negative impact on one's life. The difficulty of achieving and maintaining sobriety suggests that current treatments fail to fully address the underlying causes of alcohol use disorders. Identifying additional pathways controlling alcohol consumption may uncover novel targets for medication development to improve treatment options. One family of proteins recently implicated in the regulation of alcohol consumption is the cyclic nucleotide phosphodiesterases (PDEs). As an integral component in the regulation of the second messengers cyclic AMP and cyclic GMP, and thus their cognate signaling pathways, PDEs present intriguing targets for pharmacotherapies to combat alcohol use disorders. As activation of cAMP/cGMP-dependent signaling cascades can dampen alcohol intake, PDE inhibitors may provide a novel target for reducing excessive alcohol consumption, as has been proposed for PDE4 and PDE10A. This review highlights preclinical literature demonstrating the involvement of cyclic nucleotide-dependent signaling in neuronal and behavioral responses to alcohol, as well as detailing the capacity of various PDE inhibitors to modulate alcohol intake. Together these data provide a framework for evaluating the potential utility of PDE inhibitors as novel treatments for alcohol use disorders.

Adenylyl cylases 1 and 8 mediate select striatal-dependent behaviors and sensitivity to ethanol stimulation in the adolescent period following acute neonatal ethanol exposure

Neonatal alcohol exposure in rodents causes dramatic neurodegenerative effects throughout the developing nervous system, particularly in the striatum, acutely after exposure. These acute neurodegenerative effects are augmented in mice lacking adenylyl cyclases 1 and 8 (AC1/8) as neonatal mice with a genetic deletion of both AC isoforms (DKO) have increased vulnerability to ethanol-induced striatal neurotoxicity compared to wild type (WT) controls. While neonatal ethanol exposure is known to negatively impact cognitive behaviors, such as executive functioning and working memory in adolescent and adult animals, the threshold of ethanol exposure required to impinge upon developmental behaviors in mice has not been extensively examined. Therefore, the purpose of this study was to determine the behavioral effects of neonatal ethanol exposure using various striatal-dependent developmental benchmarks and to assess the impact of AC1/8 deletion on this developmental progression. WT and DKO mice were treated with 2.5 g/kg ethanol or saline on postnatal day (P)6 and later subjected to the wire suspension, negative geotaxis, postural reflex, grid hang, tail suspension and accelerating rotarod tests at various time points. At P30, mice were evaluated for their hypnotic responses to 4.0 g/kg ethanol by using the loss of righting reflex assay and ethanol-induced stimulation of locomotor activity after 2.0 g/kg ethanol. Ethanol exposure significantly impaired DKO performance in the negative geotaxis test while genetic deletion of AC1/8 alone increased grid hang time and decreased immobility time in the tail suspension test with a concomitant increase in hindlimb clasping behavior. Locomotor stimulation was significantly increased in animals that received ethanol as neonates, peaking significantly in ethanol-treated DKO mice compared to ethanol-treated WT controls, while sedation duration following high-dose ethanol challenge was unaffected. These data indicate that the maturational parameters examined in the current study may not be sensitive enough to detect effects of a single ethanol exposure during the brain growth spurt period. Genetic deletion of AC1/8 reveals a role for these cylases in attenuating ethanol-induced behavioral effects in the neonatally-exposed adolescent.

Postnatal ethanol exposure simplifies the dendritic morphology of medium spiny neurons independently of adenylyl cyclase 1 and 8 activity in mice

BACKGROUND

Fetal exposure to alcohol can have multiple deleterious effects, including learning disorders and behavioral and executive functioning abnormalities, collectively termed fetal alcohol spectrum disorders. Neonatal mice lacking both calcium-/calmodulin-stimulated adenylyl cyclases (ACs) 1 and 8 demonstrate increased vulnerability to ethanol (EtOH)-induced neurotoxicity in the striatum compared with wild-type (WT) controls. However, the developmental impact on surviving neurons is still unclear.

METHODS

WT and AC1/8 double knockout (DKO) mice were administered 1 dose of EtOH (2.5 g/kg) between postnatal days 5 to 7 (P5-7). At P30, brains were removed and processed for Golgi-Cox staining. Medium spiny neurons (MSNs) from the caudate putamen were analyzed for changes in dendritic complexity; number of branches, branch points and terminals, total and average dendritic length; spine density and soma size.

RESULTS

EtOH significantly reduced the dendritic complexity and soma size in surviving MSNs regardless of genotype without affecting spine density. In the absence of EtOH, genetic deletion of AC1/8 reduced the dendritic complexity, number of branch points, spine density, and soma size of MSNs compared with WT controls.

CONCLUSIONS

These data indicate that neonatal exposure to a single dose of EtOH is sufficient to cause long-term alterations in the dendritic complexity of MSNs and that this outcome is not altered by the functional status of AC1 and AC8. Therefore, although deletion of AC1/8 demonstrates a role for the ACs in normal morphologic development and EtOH-induced neurodegeneration, loss of AC1/8 activity does not exacerbate the effects of EtOH on dendritic morphology or spine density.

Dantrolene blockade of ryanodine receptor impairs ethanol-induced behavioral stimulation, ethanol intake and loss of righting reflex

Calcium has been characterized as one of the most ubiquitous, universal and versatile intracellular signals. Among other substances with the ability to alter intracellular calcium levels, ethanol has been described as particularly relevant because of its social and economic impact. Ethanol effects on calcium distribution and flux in vitro have been widely studied, showing that acute ethanol administration can modulate intracellular calcium concentrations in a dose dependent manner. Intracellular calcium released from the endoplasmic reticulum plays a determinant role in several cellular processes. In this study, we aim to assess the effect of dantrolene, a ryanodine receptor antagonist, on three different ethanol-elicited behaviors: locomotor activity, loss of righting reflex and ethanol intake. Mice were challenged with an injection of dantrolene (0-5 mg/kg, i.p.) 30 min before ethanol (0-4 g/kg, i.p.) administration. Animals were immediately placed in an open field cylinder to monitor distance travelled horizontally or in a V-shaped trough to measure righting reflex recovery time. For ethanol intake, dantrolene (0-5mg/kg, i.p.) was administered 30 min before ethanol (20%, v/v) exposure, following a drinking in the dark paradigm. Our results showed that dantrolene selectively reduces ethanol-induced stimulation, loss of righting reflex, and ethanol intake in a dose dependent manner. Together, these data suggest that intracellular calcium released from the endoplasmic reticulum may play a critical role in behavioral effects caused by ethanol, and point to a calcium-dependent pathway as a possible cellular mechanism of action for ethanol.

Acute administration of vinpocetine, a phosphodiesterase type 1 inhibitor, ameliorates hyperactivity in a mice model of fetal alcohol spectrum disorder

BACKGROUND

Maternal alcohol use during pregnancy causes a continuum of long-lasting disabilities in the offspring, commonly referred to as fetal alcohol spectrum disorder (FASD). Attention-deficit/hyperactivity disorder (ADHD) is possibly the most common behavioral problem in children with FASD and devising strategies that ameliorate this condition has great clinical relevance. Studies in rodent models of ADHD and FASD suggest that impairments in the cAMP signaling cascade contribute to the hyperactivity phenotype. In this work, we investigated whether the cAMP levels are affected in a long-lasting manner by ethanol exposure during the third trimester equivalent period of human gestation and whether the acute administration of the PDE1 inhibitor vinpocetine ameliorates the ethanol-induced hyperactivity.

METHODS

From postnatal day (P) 2 to P8, Swiss mice either received ethanol (5g/kg i.p.) or saline every other day. At P30, the animals either received vinpocetine (20mg/kg or 10mg/kg i.p.) or vehicle 4h before being tested in the open field. After the test, frontal cerebral cortices and hippocampi were dissected and collected for assessment of cAMP levels.

RESULTS

Early alcohol exposure significantly increased locomotor activity in the open field and reduced cAMP levels in the hippocampus. The acute treatment of ethanol-exposed animals with 20mg/kg of vinpocetine restored both their locomotor activity and cAMP levels to control levels.

CONCLUSIONS

These data lend support to the idea that cAMP signaling system contribute to the hyperactivity induced by developmental alcohol exposure and provide evidence for the potential therapeutic use of vinpocetine in FASD.

Recommended Neuroanatomical Sampling Practices for Comprehensive Brain Evaluation in Nonclinical Safety Studies

Adequate tissue sampling is known to reduce the likelihood that the toxicity of novel biomolecules, chemicals, and drugs might go undetected. Each organ, and often specific structurally and functionally distinct regions within it, must be assessed to detect potential site-specific toxicity. Adequate sampling of the brain requires particular consideration because of the many major substructures and more than 600 subpopulations of generally irreplaceable cells with unique functions and vulnerabilities. All known neurotoxicants affect specific subpopulations (usually neurons) rather than damaging a certain percentage of cells throughout the brain; thus, all populations should be independently assessed for lesions. Historically, the affected neural cell subpopulation has not been predictable, but it is now clear that sampling selected populations (e.g., cerebral cortex, hippocampus, cerebellar folia) cannot forecast the health of other populations. This article reviews the neuroanatomical domains affected by several model neurotoxicants to illustrate the need for more comprehensive neurohistological evaluation during nonclinical development of novel compounds. The article also describes an easily executed, cost-effective method that uses a set number of evenly spaced coronal (cross) sections to accomplish this comprehensive brain assessment during nonclinical safety studies performed in rodents, dogs, and nonhuman primates.

[Effects of general anaesthetics on the developing brain]

OBJECTIVE

To expose the current knowledge about the anaesthetic effects on the developing brain.

DATA SOURCES

Publications (original articles and reviews) in English and in French language from 1980 were obtained from the Medline database using alone or in combination following keywords: anaesthetics, developing brain, neurodevelopment, neurogenesis, synaptogenesis, neurotoxicity, apoptosis.

DATA SYNTHESIS

Several lines of evidence resulting from animal experiments conducted in rodents and non-human primates have suggested that exposing the developing brain to anaesthetic drugs may elicit an increase a physiological programmed neuronal death (i.e. apoptosis). This neuronal death is not only seen at the cellular level but also results in alterations in some behavioural abilities in the adult animal. However, the vast majority of experiments reported have been conducted in animals not exposed to any surgical or painful stimulation. Moreover, the literature raises contradictory results, some authors not confirming this neurotoxic effect of anaesthetic drugs. Last, available clinical data are scarce and do not allow to claim that exposure to general anaesthesia definitely alters the cognitive development of children.

CONCLUSION

This review raises the question of the innocuity of anaesthetic agents on the developing brain; further clinical trials are required in order to test this effect on human babies.

Phosphodiesterase type 1 inhibition improves learning in rats exposed to alcohol during the third trimester equivalent of human gestation

Deficits in learning and memory have been extensively observed in animal models of fetal alcohol spectrum disorders (FASD). Here we use the Morris maze to test whether vinpocetine, a phosphodiesterase type 1 inhibitor, restores learning performance in rats exposed to alcohol during the third trimester equivalent of human gestation. Long Evans rats received ethanol (5g/kg i.p.) or saline on alternate days from postnatal day (P) 4 to P10. Two weeks later (P25), the latency to find a hidden platform was evaluated (2 trials per day spaced at 40-min inter-trial intervals) during 4 consecutive days. Vinpocetine treatment started on the first day of behavioral testing: animals received vinpocetine (20mg/kg i.p.) or vehicle solution every other day until the end of behavioral procedures. Early alcohol exposure significantly affected the performance to find the hidden platform. The average latency of ethanol-exposed animals was significantly higher than that observed for the control group. Treatment of alcohol-exposed animals with vinpocetine restored their performance to control levels. Our results show that inhibition of PDE1 improves learning and memory deficits in rats early exposed to alcohol and provide evidence for the potential therapeutic use of vinpocetine in FASD.

Effects of straight chain alcohols on specific isoforms of adenylyl cyclase

BACKGROUND

Our previous studies showed that the activity of adenylyl cyclase (AC) was enhanced by pharmacologically relevant concentrations of ethanol, that this enhancing effect of ethanol on AC activity was AC isoform specific, and that the alcohol cutoff effect for n-alkanol potentiation of AC activity was also AC isoform specific. Therefore, we hypothesized that within the cyclic AMP-generating system, AC is the target of ethanol's action and that alcohols interact directly with the AC molecules. To characterize the interaction between alcohols and AC proteins, the effects of a series of straight chain alcohols would be very valuable in understanding alcohol action at the molecular level. To our knowledge, straight chain alcohols other than n-alkanols and 1,Omega-diols have not been used extensively to study alcohol effects on the activity of AC or other proteins important in the alcohol research field.

METHODS

The effects of a series of straight chain alcohols on D1A dopamine receptor-stimulated activity of AC isoforms type 6, 7, and 9 (AC6, AC7, and AC9) were examined in transfected Hela cells by a cAMP accumulation assay.

RESULTS

In general, all 3 AC isoforms responded to a series of straight chain alcohols in a similar manner. The order of responsiveness is as follows: monoalcohol > diol > triol and tetraol. Within monoalcohols, 1-alcohols had larger effects than 2-alcohols. Two of 3 stereoisomers of 2,3-butanediol, [D-(-)-2,3-butanediol and meso-2,3-butanediol] showed similar enhancing effects on all 3 AC isoforms. However, the third stereoisomer, L-(+)-2,3-butanediol, inhibited AC7 activity, while it stimulated AC6 and AC9.

CONCLUSION

The number and the position of hydroxyl groups in straight chain alcohols play an important role in the magnitude of the enhancement on AC activity. Regardless of AC isoforms, the most effective of the straight chain alcohols seems to be the 1-alcohol (n-alkanol) for a given chain length. We found that one of the stereoisomers of 2,3-butanediol had opposite effects on AC activity depending on the AC isoform. Overall, the results are consistent with the hypotheses and demonstrate that a series of straight chain alcohols can be a valuable tool to study AC-alcohol interactions.

Phosphodiesterase type 4 inhibition does not restore ocular dominance plasticity in a ferret model of fetal alcohol spectrum disorders

BACKGROUND

There is growing evidence that deficits in neuronal plasticity account for some of the neurological problems observed in fetal alcohol spectrum disorders (FASD). Recently, we showed that early alcohol exposure results in a permanent impairment in visual cortex ocular dominance (OD) plasticity in a ferret model of FASD. This disruption can be reversed, however, by treating animals with a Phosphodiesterase (PDE) type 1 inhibitor long after the period of alcohol exposure.

AIM

Because the mammalian brain presents different types of PDE isoforms we tested here whether inhibition of PDE type 4 also ameliorates the effects of alcohol on OD plasticity.

MATERIAL AND METHODS

Ferrets received 3.5 g/Kg alcohol i.p. (25% in saline) or saline as control every other day between postnatal day (P) 10 to P30, which is roughly equivalent to the third trimester equivalent of human gestation. Following a prolonged alcohol-free period (10 to 15 days), ferrets had the lid of the right eye sutured closed for 4 days and were examined for ocular dominance changes at the end of the period of deprivation.

RESULTS

Using in vivo electrophysiology we show that inhibition of PDE4 by rolipram does not restore OD plasticity in alcohol-treated ferrets.

CONCLUSION

This result suggests that contrary to PDE1, PDE4 inhibition does not play a role in the restoration of OD plasticity in the ferret model of FASD.

Capturing adenylyl cyclases as potential drug targets

Cyclic AMP (cAMP) is an important intracellular signalling mediator. It is generated in mammals by nine membrane-bound and one soluble adenylyl cyclases (ACs), each with distinct regulation and expression patterns. Although many drugs inhibit or stimulate AC activity through the respective upstream G-protein coupled receptors (for example, opioid or beta-adrenergic receptors), ACs themselves have not been major drug targets. Over the past decade studies on the physiological functions of the different mammalian AC isoforms as well as advances in the development of isoform-selective AC inhibitors and activators suggest that ACs could be useful drug targets. Here we discuss the therapeutic potential of isoform-selective compounds in various clinical settings, including neuropathic pain, neurodegenerative disorders, congestive heart failure, asthma and male contraception.

Effect of gestational ethanol exposure on parvalbumin and calretinin expressing hippocampal neurons in a chick model of fetal alcohol syndrome

Fetal alcohol syndrome (FAS), a condition occurring in some children of mothers who have consumed alcohol during pregnancy, is characterized by physical deformities and learning and memory deficits. The chick hippocampus, whose functions are controlled by interneurons expressing calcium-binding proteins parvalbumin (PV) and calretinin (CR), is involved in learning and memory mechanisms. Effects on growth and development and hippocampal morphology were studied in chick embryos exposed to 5% and 10% ethanol volume/volume (vol/vol) for 2 or 8 days of gestation. There was a significant dose-dependent reduction (P<.05) in body weight and mean number per section of PV and CR expressing hippocampal neurons in ethanol-exposed chicks, without alterations in neuronal nuclear size or hippocampal volume, compared appropriate controls. Moreover, when chicks exposed to 5% ethanol for 2 and 8 days of gestation were compared, no significant differences were found in body parameters or neuronal counts. Similarly, exposure to 10% ethanol did not induce any significant changes in chicks exposed for 2 or 8 gestational days. Thus, these results suggest that gestational ethanol exposure induces a reduction in the mean number per section of PV and CR expressing hippocampal neurons, and could be a possible mechanism responsible for learning and memory disorders in FAS.

Adenylyl cyclases types 1 and 8 promote pro-survival pathways after ethanol exposure in the neonatal brain

Although a wide range of developmental disabilities following fetal alcohol exposure are observed clinically, the molecular factors that determine the severity of these sequelae remain undefined. In mice exposed to ethanol, deletion of adenylyl cyclases (ACs) 1 and 8 exacerbates the neuroapoptosis that occurs in a prolonged post-treatment period; however, it remains unclear whether AC1 and AC8 are critical to the primary or secondary mechanisms underlying ethanol-induced neurodegeneration. Here we demonstrate that mice lacking AC1 and AC8 (DKO) display significantly increased apoptosis in the striatum, a region sensitive to neuroapoptosis in the acute post-treatment period, compared to WT controls. The enhanced neuroapoptotic response observed in the striatum of DKO mice is accompanied by significant reductions in phosphorylation of known pro-survival proteins, insulin receptor substrate-1 (IRS-1), Akt and extracellular signal-regulated kinases (ERKs). These data suggest that AC1/AC8 are crucial activators of cell survival signaling pathways acutely following ethanol exposure and represent molecular factors that may directly modulate the severity of symptoms associated with Fetal Alcohol Syndrome.

Physiological roles for G protein-regulated adenylyl cyclase isoforms: insights from knockout and overexpression studies

Cyclic AMP is a universal second messenger, produced by a family of adenylyl cyclase (AC) enzymes. The last three decades have brought a wealth of new information about the regulation of cyclic AMP production by ACs. Nine hormone-sensitive, membrane-bound AC isoforms have been identified in addition to a tenth isoform that lacks membrane spans and more closely resembles the cyanobacterial AC enzymes. New model systems for purifying and characterizing the catalytic domains of AC have led to the crystal structure of these domains and the mapping of numerous interaction sites. However, big hurdles remain in unraveling the roles of individual AC isoforms and their regulation in physiological systems. In this review we explore the latest on AC knockout and overexpression studies to better understand the roles of G protein regulation of ACs in the brain, olfactory bulb, and heart.

Genetic evidence for adenylyl cyclase 1 as a target for preventing neuronal excitotoxicity mediated by N-methyl-D-aspartate receptors

The excessive activation of N-methyl-D-aspartate (NMDA) receptors by glutamate results in neuronal excitotoxicity. cAMP is a key second messenger and contributes to NMDA receptor-dependent synaptic plasticity. Adenylyl cyclases 1 (AC1) and 8 (AC8) are the two major calcium-stimulated ACs in the central nervous system. Previous studies demonstrate AC1 and AC8 play important roles in synaptic plasticity, memory, and persistent pain. However, little is known about the possible roles of these two ACs in glutamate-induced neuronal excitotoxicity. Here, we report that genetic deletion of AC1 significantly attenuated neuronal death induced by glutamate in primary cultures of cortical neurons, whereas AC8 deletion did not produce a significant effect. AC1, but not AC8, contributes to intracellular cAMP production following NMDA receptor activation by glutamate in cultured cortical neurons. AC1 is involved in the dynamic modulation of cAMP-response element-binding protein activity in neuronal excitotoxicity. To explore the possible roles of AC1 in cell death in vivo, we studied neuronal excitotoxicity induced by an intracortical injection of NMDA. Cortical lesions induced by NMDA were significantly reduced in AC1 but not in AC8 knock-out mice. Our findings provide direct evidence that AC1 plays an important role in neuronal excitotoxicity and may serve as a therapeutic target for preventing excitotoxicity in stroke and neurodegenerative diseases.

Developmental changes in Ca2+-regulated functions of early postnatal Purkinje neurons

Ca(2+) influx through L-type Ca(2+) channels regulates several different cellular processes in developing Purkinje neurons, including activation of transcription factors and expression of cellular proteins. In the current studies, we examined the age dependence of these actions of Ca(2+) during the early developmental period. Purkinje neurons acutely isolated from postnatal day 4-8 rat pups were studied. We also examined the sensitivity of the Ca(2+)-regulated processes to a toxic environmental factor (ethanol) known to show age-dependent actions on developing Purkinje neurons. Results show that Ca(2+) activation of the transcription factor cAMP-responsive element binding protein (CREB) and Ca(2+)-induced alterations in the level of the apoptotic enzyme caspase 3 show both dose and age dependence in the early-developing Purkinje neurons. Interestingly, the age dependence was opposite for the two proteins. Ca(2+) regulation of calbindin, a Ca(2+) binding protein, was dose dependent but showed little age dependence. Exposure to ethanol altered Ca(2+) activation of pCREB in an age-dependent manner but did not alter Ca(2+) regulation of caspase 3 or calbindin levels. Taken together, these results show that the downstream effects of Ca(2+) signaling have age-dependent components during early Purkinje neuron development. This age dependence may play an important role in the normal developmental program and could contribute to the critical window of sensitivity observed for certain toxic agents during early development.

The importance of alcohol misuse, malnutrition and genetic susceptibility on brain growth and plasticity

The "dyad: alcoholic mother and foetus" is a very complex entity in which several elements such as genes, metabolism, diet, drugs and social habits play a role at different stages in the development of the fetal brain damage. The literature on the effects of alcohol consumption on the developing brain is extensive but very few evidences have been reported regarding the combined neurotoxic effects of poor nutrition and alcohol consumption. The consequences of ethanol intake alone or combined with poor maternal nutrition appear to be severe and life-long. Alcohol exerts its neurotoxic effects on the developing brain directly by acting on fetal brain tissues, and indirectly either by interfering with placental physiology or by impairing the mother's physiology. Alcohol misuse in pregnancy is also frequently associated with other conditions that can potentially increase the brain damage such as poor nutrition and smoking. This article reviews the effects of poor nutrition and alcohol misuse during pregnancy on the development of the fetal brain and discusses the cumulative effects of these two environmental factors and their interaction with maternal and fetal genetic make-ups.

Widespread Neonatal Brain Damage following Calcium Channel Blockade

An abundance of evidence exists that shows calcium channel blockade promotes injury in cultured neurons. However, few studies have addressed the in vivo toxicity of such agents. We now show that the L-type calcium channel antagonist nimodipine promotes widespread and robust injury throughout the neonatal rat brain, in an age-dependent manner. Using both isolated neuronal as well as brain slice approaches, we address mechanisms behind such injury. These expanded studies show a consistent pattern of injury using a variety of agents that lower intracellular calcium. Collectively, these observations indicate that postnatal brain development represents a transitional period for still developing neurons, from being highly sensitive to reductions in intracellular calcium to being less vulnerable to such changes. These observations directly relate to current therapeutic strategies targeting neonatal brain injury.

Inhibition of ethanol-induced toxicity by tanshinone IIA in PC12 cells

AIM

To observe the effects of tanshinone IIA (Tan IIA) on the neurotoxicity induced by ethanol in PC12 cells and to explore its protective role.

METHODS

PC12 cell survival was measured by MTT assay. The formation of reactive oxygen species (ROS) and lactate dehydrogenase (LDH) release were detected by 2',7'-dichlorofluorescin (DCF) fluorescence and calorimetric method, respectively. The percentage of cell apoptosis was monitored by flow cytometry. The expression of p53 was detected by immuno-fluorescence and flow cytometry.

RESULTS

Ethanol significantly impaired the survival of PC12 cells as demonstrated by MTT assay. Ethanol also induced significant ROS formation and increased LDH release. Pre-incubation with Tan IIA in the culture medium significantly reversed these changes. Ethanol caused cell apoptosis and the upregulation of p53 protein. The anti-apoptosis effects of Tan IIA on ethanol-induced toxicity were accompanied by the downregulation of pro-apoptotic p53 protein expression.

CONCLUSION

Tan IIA can protect neurons from apoptosis and might serve as a potential therapeutic drug for neurological disorders induced by ethanol.

Ethanol induces apoptotic death of developing beta-endorphin neurons via suppression of cyclic adenosine monophosphate production and activation of transforming growth factor-beta1-linked apoptotic signaling

The mechanism by which ethanol induces beta-endorphin (beta-EP) neuronal death during the developmental period was determined using fetal rat hypothalamic cells in primary cultures. The addition of ethanol to hypothalamic cell cultures stimulated apoptotic cell death of beta-EP neurons by increasing caspase-3 activity. Ethanol lowered the levels of adenylyl cyclase (AC)7 mRNA, AC8 mRNA, and/or cAMP in hypothalamic cells, whereas a cAMP analog blocked the apoptotic action of ethanol on beta-EP neurons. The AC inhibitor dideoxyadenosine (DDA) increased cell apoptosis and reduced the number of beta-EP neurons, and it potentiated the apoptotic action of ethanol on these neurons. beta-EP neurons in hypothalamic cultures showed immunoreactivity to transforming growth factor-beta1 (TGF-beta1) protein. Ethanol and DDA increased TGF-beta1 production and/or release from hypothalamic cells. A cAMP analog blocked the activation by ethanol of TGF-beta1 in these cells. TGF-beta1 increased apoptosis of beta-EP neurons, but it did not potentiate the action of ethanol or DDA actions on these neurons. TGF-beta1 neutralizing antibody blocked the apoptotic action of ethanol on beta-EP neurons. Determination of TGF-beta1-controlled cell apoptosis regulatory gene levels in hypothalamic cell cultures and in isolated beta-EP neurons indicated that ethanol, TGF-beta1, and DDA similarly alter the expression of these genes in these cells. These data suggest that ethanol increases beta-EP neuronal death during the developmental period by cellular mechanisms involving, at least partly, the suppression of cAMP production and activation of TGF-beta1-linked apoptotic signaling.

Restoration of neuronal plasticity by a phosphodiesterase type 1 inhibitor in a model of fetal alcohol exposure

Although some studies showed the efficacy of phosphodiesterase (PDE) inhibitors as neuronal plasticity enhancers, little is known about the effectiveness of these drugs to improve plasticity in cases of mental retardation. Fetal alcohol syndrome (FAS) is the leading cause of mental retardation in the western world. Using a combination of electrophysiological and optical imaging techniques, we show here that vinpocetine, a PDE type I inhibitor, restores ocular dominance plasticity in the ferret model of fetal alcohol exposure. Our finding should contribute to a better understanding and treatment of cognitive deficits associated with mental disorders, such as FAS.

Caspase-3 deficiency during development increases vulnerability to hypoxic-ischemic injury through caspase-3-independent pathways

Neonatal hypoxia-ischemia (H-I) is a common cause of perinatal morbidity and mortality leading to prominent activation of caspase-3 in the brain. Previous studies have shown that acute inhibition of caspase-3 can protect against neonatal H-I in rats. In this study, we investigated brain injury following neonatal H-I in mice deficient in caspase-3. Wild-type, caspase-3+/- and caspase-3-/- mice underwent unilateral carotid ligation at postnatal day (P) 7, followed by 45 min of exposure to 8% oxygen. Surprisingly, tissue loss at P14 was significantly higher in caspase-3-/- mice when compared to wild-type littermates. As in rats, we found that acute inhibition of caspase-3 in mice leads to decrease in tissue loss at P14. There was no difference in nuclear morphology, DNA laddering or calpain activation between caspase-3-/-caspase-3+/- and wild-type mice subjected to H-I, and there was no evidence for compensatory activation of other caspases in caspase-3-/- mice. Also, all genotypes showed evidence of mitochondrial dysfunction after H-I, suggesting that this is a critical point in regulation of neuronal cell death following neonatal H-I. Our results suggest that long-term inhibition of caspase-3 during development, unlike acute inhibition, leads to upregulation of caspase-3-independent cell death pathways and increases the vulnerability of the developing brain to neonatal H-I injury.