GABAA receptors, anesthetics and anticonvulsants in brain development

Stroke and Translational Research - Review of Experimental Models with a Focus on Awake Ischaemic Induction and Anaesthesia

Animal models are an indispensable tool in the study of ischaemic stroke with hundreds of drugs emerging from the preclinical pipeline. However, all of these drugs have failed to translate into successful treatments in the clinic. This has brought into focus the need to enhance preclinical studies to improve translation. The confounding effects of anaesthesia on preclinical stroke modelling has been raised as an important consideration. Various volatile and injectable anaesthetics are used in preclinical models during stroke induction and for outcome measurements such as imaging or electrophysiology. However, anaesthetics modulate several pathways essential in the pathophysiology of stroke in a dose and drug dependent manner. Most notably, anaesthesia has significant modulatory effects on cerebral blood flow, metabolism, spreading depolarizations, and neurovascular coupling. To minimise anaesthetic complications and improve translational relevance, awake stroke induction has been attempted in limited models. This review outlines anaesthetic strategies employed in preclinical ischaemic rodent models and their reported cerebral effects. Stroke related complications are also addressed with a focus on infarct volume, neurological deficits, and thrombolysis efficacy. We also summarise routinely used focal ischaemic stroke rodent models and discuss the attempts to induce some of these models in awake rodents.

Ligand-gated ion channels as potential biomarkers for ADT-mediated cognitive decline in prostate cancer patients

Men with prostate cancer are at increased risk of developing cognitive decline by the use of second-generation androgen signaling inhibitors. To date, reliable and sensitive biomarkers that could distinguish men at high risk of cognitive dysfunction under androgen deprivation therapy (ADT) have not been characterized. We used high-throughput transcriptional profiling utilizing human prostate cancer cell culture models mimicking ADT, biomarker selection using minimal common oncology data elements-cytoscape, and bioinformatic analyses employing Advaita® iPathwayGuide and DisGeNET for identification of disease-related gene associations. Validation analysis of genes was performed on brain neuronal and glial cells by quantitative real-time polymerase chain reaction assay. Our systematic analysis of androgen deprivation-associated genes involved multiple biological processes, including neuroactive ligand-receptor interaction, axon guidance, cytokine-cytokine receptor interaction, and metabolic and cancer signaling pathways. Genes associated with neuroreceptor ligand interaction, including gamma-aminobutyric acid (GABA) A and B receptors and nuclear core proteins, were identified as top upstream regulators. Functional enrichment and protein-protein interaction network analysis highlighted the role of ligand-gated ion channels (LGICs) and their receptors in cognitive dysfunction. Gene-disease association assigned forgetfulness, intellectual disability, visuospatial deficit, bipolar disorder, and other neurocognitive impairment with upregulation of type-1 angiotensin II receptor, brain-derived neurotrophic factor, GABA type B receptor subunit 2 (GABBR2), GABRA3, GABRA5, GABRB1, glycine receptor beta, glutamate ionotropic receptor N-methyl-D-aspartate receptor (NMDA) type subunit 1, glutamate ionotropic receptor NMDA type subunit 2D, 5-hydroxytryptamine receptor 1D, interferon beta 1, and nuclear receptor subfamily 3 group C member 1 as top differentially expressed genes. Validation studies of brain glial cells, neurons, and patients on ADT demonstrated the association of these genes with cognitive decline. Our findings highlight LGICs as potential biomarkers for ADT-mediated cognitive decline. Further validation of these biomarkers may lead to future practical clinical use.

Efficacy and safety of ketamine for neonatal refractory status epilepticus: case report and systematic review

Background

Evidence-based data on treatment of neonatal status epilepticus (SE) are scarce. We aimed to collect data on the efficacy and safety of ketamine for the treatment of neonatal SE and to assess its possible role in the treatment of neonatal SE.

Methods

We described a novel case and conducted a systematic literature review on neonatal SE treated with ketamine. The search was carried out in Pubmed, Cochrane, Clinical Trial Gov, Scopus and Web of Science.

Results

Seven published cases of neonatal SE treated with ketamine were identified and analyzed together with our novel case. Seizures typically presented during the first 24 h of life (6/8). Seizures were resistant to a mean of five antiseizure medications. Ketamine, a NMDA receptor antagonist, appeared to be safe and effective in all neonates treated. Neurologic sequelae including hypotonia and spasticity were reported for 4/5 of the surviving children (5/8). 3/5 of them were seizure free at 1-17 months of life.

Discussion

Neonatal brain is more susceptible to seizures due to a shift towards increased excitation because of a paradoxical excitatory effect of GABA, a greater density of NMDA receptors and higher extracellular concentrations of glutamate. Status epilepticus and neonatal encephalopathy could further enhance these mechanisms, providing a rationale for the use of ketamine in this setting.

Conclusions

Ketamine in the treatment of neonatal SE showed a promising efficacy and safety profile. However, further in-depth studies and clinical trials on larger populations are needed.

Exploring the role of nanomedicines for the therapeutic approach of central nervous system dysfunction: At a glance

In recent decades, research scientists, molecular biologists, and pharmacologists have placed a strong emphasis on cutting-edge nanostructured materials technologies to increase medicine delivery to the central nervous system (CNS). The application of nanoscience for the treatment of neurodegenerative diseases (NDs) such as Alzheimer’s disease (AD), Parkinson’s disease (PD), multiple sclerosis (MS), Huntington’s disease (HD), brain cancer, and hemorrhage has the potential to transform care. Multiple studies have indicated that nanomaterials can be used to successfully treat CNS disorders in the case of neurodegeneration. Nanomedicine development for the cure of degenerative and inflammatory diseases of the nervous system is critical. Nanoparticles may act as a drug transporter that can precisely target sick brain sub-regions, boosting therapy success. It is important to develop strategies that can penetrate the blood–brain barrier (BBB) and improve the effectiveness of medications. One of the probable tactics is the use of different nanoscale materials. These nano-based pharmaceuticals offer low toxicity, tailored delivery, high stability, and drug loading capacity. They may also increase therapeutic effectiveness. A few examples of the many different kinds and forms of nanomaterials that have been widely employed to treat neurological diseases include quantum dots, dendrimers, metallic nanoparticles, polymeric nanoparticles, carbon nanotubes, liposomes, and micelles. These unique qualities, including sensitivity, selectivity, and ability to traverse the BBB when employed in nano-sized particles, make these nanoparticles useful for imaging studies and treatment of NDs. Multifunctional nanoparticles carrying pharmacological medications serve two purposes: they improve medication distribution while also enabling cell dynamics imaging and pharmacokinetic study. However, because of the potential for wide-ranging clinical implications, safety concerns persist, limiting any potential for translation. The evidence for using nanotechnology to create drug delivery systems that could pass across the BBB and deliver therapeutic chemicals to CNS was examined in this study.

GABAA receptors: structure, function, pharmacology, and related disorders

Background

γ-Aminobutyric acid sub-type A receptors (GABA_ARs) are the most prominent inhibitory neurotransmitter receptors in the CNS. They are a family of ligand-gated ion channel with significant physiological and therapeutic implications.

Main body

GABA_ARs are heteropentamers formed from a selection of 19 subunits: six α (alpha1-6), three β (beta1-3), three γ (gamma1-3), three ρ (rho1-3), and one each of the δ (delta), ε (epsilon), π (pi), and θ (theta) which result in the production of a considerable number of receptor isoforms. Each isoform exhibits distinct pharmacological and physiological properties. However, the majority of GABA_ARs are composed of two α subunits, two β subunits, and one γ subunit arranged as γ2β2α1β2α1 counterclockwise around the center. The mature receptor has a central chloride ion channel gated by GABA neurotransmitter and modulated by a variety of different drugs. Changes in GABA synthesis or release may have a significant effect on normal brain function. Furthermore, The molecular interactions and pharmacological effects caused by drugs are extremely complex. This is due to the structural heterogeneity of the receptors, and the existence of multiple allosteric binding sites as well as a wide range of ligands that can bind to them. Notably, dysfunction of the GABAergic system contributes to the development of several diseases. Therefore, understanding the relationship between GABA_A receptor deficits and CNS disorders thus has a significant impact on the discovery of disease pathogenesis and drug development.

Conclusion

To date, few reviews have discussed GABA_A receptors in detail. Accordingly, this review aims to summarize the current understanding of the structural, physiological, and pharmacological properties of GABA_ARs, as well as shedding light on the most common associated disorders.

Effects of new antiseizure drugs on seizure activity and anxiety-like behavior in adult zebrafish

Several studies with larvae and adult zebrafish have shown that old and new antiseizure drugs (ASDs) produce discrepant results in seizure tests, locomotor activity or anxiety models. In this study, the pentylenetetrazole seizure test (PTZ) was performed to assess the effectiveness of four new ASDs: lamotrigine (LTG), topiramate (TPM), felbamate (FBM), and levetiracetam (LEV) in the subsequent stages of seizures in adult fish. All ASDs were administered intraperitoneally (i.p.). The time of maximal anticonvulsant effect and the dose-response relationship of the drugs were assessed. The effects of studied ASDs on the locomotor activity and the anxiety-like behavior in the color preference test were also investigated. Furthermore, drug concentrations in zebrafish homogenates were determined. LTG, TPM, and LEV significantly increased the seizure latency at three subsequent stages of seizures (SI-SIII), while FBM was effective only at SI. Locomotor activity decreased after TPM treatment. TPM and FBM exhibited a strong anxiolytic-like effect in the color preference test. LEV at the highest dose tested had a weak anxiolytic-like effect. The HPLC analysis showed average concentrations of the studied ASDs in the fish body during their maximum anticonvulsant activity. The present study shows that FBM cannot inhibit all subsequent PTZ seizure stages in the adult fish. Except for LTG, the studied drugs affected the anxiety-like behavior of treated animals. Furthermore, only TPM significantly changed locomotion parameters. Our findings support the need to accurately characterize the efficacy of new ASDs at different stages of the PTZ-induced seizures in adult zebrafish.

Melanin-concentrating hormone does not modulate serotonin release in primary cultures of fetal raphe nucleus neurons

Melanin-concentrating hormone (MCH) is a neuropeptide present in neurons located in the hypothalamus that densely innervate serotonergic cells in the dorsal raphe nucleus (DRN). MCH administration into the DRN induces a depressive-like effect through a serotonergic mechanism. To further understand the interaction between MCH and serotonin, we used primary cultured serotonergic neurons to evaluate the effect of MCH on serotonergic release and metabolism by HPLC-ED measurement of serotonin (5-HT) and 5-hydroxyindolacetic acid (5-HIAA) levels. We confirmed the presence of serotonergic neurons in the E14 rat rhombencephalon by immunohistochemistry and showed for the first time evidence of MCHergic fibers reaching the area. Cultures obtained from rhombencephalic tissue presented 2.2 ± 0.7% of serotonergic and 48.9 ± 5.4% of GABAergic neurons. Despite the low concentration of serotonergic neurons, we were able to measure basal cellular and extracellular levels of 5-HT and 5-HIAA without the addition of any serotonergic-enhancer drug. As expected, 5-HT release was calcium-dependent and induced by depolarization. 5-HT extracellular levels were significantly increased by incubation with serotonin reuptake inhibitors (citalopram and nortriptyline) and a monoamine-oxidase inhibitor (clorgyline), and were not significantly modified by a 5-HT1A autoreceptor agonist (8-OHDPAT). Even though serotonergic cells responded as expected to these pharmacological treatments, MCH did not induce significant modifications of 5-HT and 5-HIAA extracellular levels in the cultures. Despite this unexpected result, we consider that assessment of 5-HT and 5-HIAA levels in primary serotonergic cultures may be an adequate approach to study the effect of other drugs and modulators on serotonin release, uptake and turnover.

GABA inhibits proliferation and self-renewal of mouse retinal progenitor cell

Gamma-amino butyric acid (GABA) is the main inhibitory neurotransmitter in the central nervous system, including the retina, and play an important role in both regulating neurogenesis and neural stem cell proliferation. GABAa receptor has been identified in the retina, however, the function of GABAa receptor on retinal progenitor cell (RPC) is unclear. RPCs were cultured to analyze changes in cell proliferation and cell cycle distribution after GABAa receptor activation. The activation of GABAa receptor significantly inhibits RPCs proliferation, cell cycle progress, and self-renewal. Moreover, the activation of GABAa receptor leads to the up-expression of p21 and p27 and down-expression of Nestin, Pax6, Sox2, and Chx10. These results suggest that GABA acts as a negative regulator of RPCs proliferation and self-renewal.

Traditional uses, phytochemistry and pharmacological properties of Neolamarckia cadamba: A review

ETHNOPHARMACOLOGICAL RELEVANCE

There are more than 3000 officially documented plants in the Indian subcontinent that hold great medicinal potential. One such under-explored plant is an evergreen tropical tree Neolamarckia cadamba (Roxb.) Bosser (Rubiaceae). It is widely distributed in tropical and subtropical regions of the world and has therapeutic potential against many diseases such as diabetes, anaemia, stomatitis, leprosy, cancer and infectious diseases. Neolamarckia cadamba has historical existence in India and it is mentioned in mythical stories. There are several reports on medicinal values of root, bark and leaves of N. cadamba; but the literature on its fruits is scanty. Therefore, the present review aims to provide updated comprehensive information on the phytochemistry and pharmacological properties of different parts of N. cadamba tree with special reference to its fruit, in order to open new perspectives for future food and pharmacological research.

MATERIALS AND METHODS

A literature search was performed on N. cadamba using ethnobotanical textbooks, published articles in peer-reviewed journals, unpublished materials, government survey reports and scientific databases such as Pubmed, Scopus, Web of Science, Science Direct, Google Scholar and other web search engines (Google, Yahoo). The Plant List, International Plant Name Index and Kew Botanical Garden Plant name databases were used to validate the scientific names.

RESULTS AND DISCUSSION

Neolamarckia cadamba is one of the economically important trees, which is being exploited for paper, pulp and wood industry. In folk medicine, various parts of N. cadamba are used in the treatment of various ailments such as fever, uterine complaints, blood diseases, skin diseases, tumour, anaemia, eye inflammation and diarrhoea. Other reported uses of N. cadamba include antihepatotoxic, antimalarial, analgesic, anti-inflammatory, antipyretic, diuretic and laxative. Various phytochemicals such as cadambine and its derivatives (dihydrocadambine and isodihydrocadambine) and indole alkaloids (Neolamarckines) were isolated from the leaves; whereas the presence of quinovic acid derivatives have been reported in the bark of N. cadamba.

CONCLUSION

The present review compiles information on an ethnopharmacologically useful plant N. cadamba. Bioactive compounds responsible for its various medicinal properties and their effects at the molecular level need to be investigated in more detail. Furthermore, the detailed study of toxicity and pharmacological properties of extracts as well as molecules in N. cadamba is required to confirm the ethnomedicinal claims of N. cadamba for food and pharmaceutical applications.

Effects of gaboxadol on the expression of cocaine sensitization in rats

Behavioral sensitization to psychostimulants is associated with changes in dopamine (DA), glutamate, and GABA within the mesocorticolimbic and nigrostriatal DA systems. Because GABAA receptors are highly expressed within these systems, we examined the role of these receptors containing a δ subunit in cocaine behavioral sensitization. Experiment 1 examined the effects of Gaboxadol (GBX, also known as THIP [4,5,6,7-tetrahydro-isoxazolo[5,4-c]pyridin-3-ol]), a selective δ-GABAA receptor agonist, on the locomotor responses to acute cocaine. GBX at 1.25 mg/kg produced locomotor depression in female rats alone. We then examined the effects of GBX on the expression of cocaine-induced locomotion and stereotypy in female and male rats treated with 5 days of cocaine (15 mg/kg) followed by cocaine challenge 7 days later. We administered systemic (Experiment 2) or intranucleus accumbens (intra-NAC; Experiment 3) injections of GBX (0, 1.25, 2.5, 5, or 10 mg/kg subcutaneously, or 1 μmol/L or 1 mM intra-NAC, respectively) prior to cocaine challenge (10 mg/kg). In our experiments females were robustly sensitized to cocaine at low dose whereas males did not show such sensitization-limiting comparisons between the 2 sexes. Sensitized females showed a biphasic response to low (1.25 mg/kg and 1 μmol/L) and high (10 mg/kg and 1 mM) dose GBX whereas nonsensitized males showed this pattern only following intra-NAC injection. Immunohistochemical analysis of the NAC revealed that females have more δ-containing GABAA receptors than do males and that following chronic cocaine injections this difference persisted (Experiment 4). Together, our results support the notion of the key role of extrasynaptic GABAA δ-subunit containing receptors in cocaine sensitization.

Involvement of the GABAA Receptor in Age-Dependent Differences in Binge-Like Ethanol Intake

BACKGROUND

Binge alcohol (ethanol [EtOH]) drinking is common during adolescence, a time characterized by many behavioral and neurobiological changes. Among them, the GABAA receptor system undergoes substantial modifications, including changes in the density, distribution, and subunit composition of the receptor. Based on its demonstrated role in EtOH consumption, this study aimed to investigate the effects of 2 different GABAA receptor agonists on binge-like EtOH intake in adolescent and adult mice using the Drinking-in-the-Dark model.

METHODS

Three hours into their dark cycle, adolescent (postnatal day 28 [P28]) and adult (P63) male C57BL/6J mice were given daily access to 20% EtOH for 2 hours during 8 consecutive days. Immediately before the access on day 8, mice (P35 and P70) were systemically injected with 1 of 2 different GABAergic drugs. The effects of muscimol, a full GABAA agonist, were assessed in a first experiment. The second experiment tested for the more specific involvement of δ-containing extrasynaptic GABAA receptors through the administration of THIP (4,5,6,7-tetrahydroisoxazolo(5,4-c)pyridin-3-ol).

RESULTS

Adolescent mice consumed more EtOH than their adult counterparts. Following the administration of GABAA agonists, levels of EtOH intake were reduced at both ages. However, age-dependent differences were revealed following the administration of THIP, with adolescents exhibiting greater sensitivity to its suppressant effects, especially during the first 30 minutes of binge EtOH access.

CONCLUSIONS

This study adds to the existing literature demonstrating the crucial role of the GABAA receptor in alcohol consumption. In addition, it suggests that age differences in the GABAA receptor modulation of binge alcohol drinking might be more dependent on extrasynaptic GABAA receptors.

Tranexamic acid-associated seizures: Causes and treatment

Antifibrinolytic drugs are routinely used worldwide to reduce the bleeding that results from a wide range of hemorrhagic conditions. The most commonly used antifibrinolytic drug, tranexamic acid, is associated with an increased incidence of postoperative seizures. The reported increase in the frequency of seizures is alarming, as these events are associated with adverse neurological outcomes, longer hospital stays, and increased in‐hospital mortality. However, many clinicians are unaware that tranexamic acid causes seizures. The goal of this review is to summarize the incidence, risk factors, and clinical features of these seizures. This review also highlights several clinical and preclinical studies that offer mechanistic insights into the potential causes of and treatments for tranexamic acid–associated seizures. This review will aid the medical community by increasing awareness about tranexamic acid–associated seizures and by translating scientific findings into therapeutic interventions for patients. ANN NEUROL 2016;79:18–26

Sevoflurane-induced changes in infants' quantifiable electroencephalogram parameters

BACKGROUND

Electroencephalogram (EEG) based depth of anesthesia algorithms developed in the adult population have not demonstrated the same reliability when applied to infants. This may be due to frequency changes occurring in the EEG during development. Amplitude-integrated EEG (aEEG) is based primarily in the time domain and hence may have greater utility in infants.

OBJECTIVE

To investigate the relationship between age adjusted Minimal Alveolar Concentration (MAC) multiples and aEEG in children under 2 years of age.

METHODS

The aEEG, Spectral Edge Frequency 90% (SEF90) and Bispectral Index™ (BIS) were investigated in a prospective study of children <2 years of age. After anesthetic induction, and caudal block administration, EEG data were collected simultaneously with BrainZ BRM2™ and BIS™ monitors. Using a randomized crossover design, children received up to three age adjusted concentrations of sevoflurane: 0.75, 1 and 1.25 MAC. After 15 min of stable anesthetic delivery EEG readings were obtained. Prediction Probability (Pk ) and correlation coefficients were calculated for each EEG parameter.

RESULTS

From 51 children 102 stable anesthetics concentrations were obtained. For all age groups Pk of aEEG to multiple of age adjusted MAC was <0.72 indicating a poor predictive power for aEEG. In contrast for the SEF90 and BIS there was evidence for better predictive properties in children aged between 6 months and 2 years, with a Pk >0.81.

CONCLUSION

The aEEG is unlikely to be a useful measure of anesthesia depth in young children.

GABAergic contributions to alcohol responsivity during adolescence: insights from preclinical and clinical studies

There is a considerable body of literature demonstrating that adolescence is a unique age period, which includes rapid and dramatic maturation of behavioral, cognitive, hormonal and neurobiological systems. Most notably, adolescence is also a period of unique responsiveness to alcohol effects, with both hyposensitivity and hypersensitivity observed to the various effects of alcohol. Multiple neurotransmitter systems are undergoing fine-tuning during this critical period of brain development, including those that contribute to the rewarding effects of drugs of abuse. The role of developmental maturation of the γ-amino-butyric acid (GABA) system, however, has received less attention in contributing to age-specific alcohol sensitivities. This review integrates GABA findings from human magnetic resonance spectroscopy studies as they may translate to understanding adolescent-specific responsiveness to alcohol effects. Better understanding of the vulnerability of the GABA system both during adolescent development, and in psychiatric conditions that include alcohol dependence, could point to a putative mechanism, boosting brain GABA, that may have increased effectiveness for treating alcohol use disorders.

Time-dependent modulation of GABA(A)-ergic synaptic transmission by allopregnanolone in locus coeruleus neurons of Mecp2-null mice

Rett syndrome (RTT) is a neurodevelopmental disorder with symptoms starting 6-18 mo after birth, while what underlies the delayed onset is unclear. Allopregnanolone (Allop) is a metabolite of progesterone and a potent modulator of GABAA-ergic currents whose defects are seen in RTT. Allop changes its concentration during the perinatal period, which may affect central neurons via the GABAA-ergic synaptic transmission, contributing to the onset of the disease. To determine whether Mecp2 disruption affects Allop modulation, we performed studies in brain slices obtained from wild-type (WT) and Mecp2(-/Y) mice. Allop dose dependently suppressed locus coeruleus (LC) neuronal excitability in WT mice, while Mecp2-null neurons showed significant defects. Using optogenetic approaches, channelrhodopsin was specifically expressed in GABA-ergic neurons in which optical stimulation evoked action potentials. In LC neurons of WT mice, Allop exposure increased the amplitude of GABAA-ergic inhibitory postsynaptic currents (IPSCs) evoked by optical stimulation and prolonged the IPSC decay time. Consistently, Allop augmented both frequency and amplitude of GABAA-ergic spontaneous IPSCs (sIPSCs) and extended the decay time of sIPSCs. The Allop-induced potentiation of sIPSCs was deficient in Mecp2(-/Y) mice. Surprisingly, the impairment occurred at 3 wk postnatal age, while no significant difference in Allop modulation was observed in 1-2 wk between WT and Mecp2(-/Y) mice. These results indicate that the modulation of GABAA-ergic synaptic transmission by Allop is impaired in LC neurons of Mecp2-null mice at a time when RTT-like symptoms manifest, suggesting a potential mechanism for the delayed onset of the disease.

GABA(A) receptor characterization and subunit localization in the human sub-ventricular zone

It is now well established that the human brain continuously produces new stem cells until well into old age. One of these stem-cell rich areas in the human brain is the sub-ventricular zone (SVZ). The human SVZ is organized in four distinctive layers containing type A, B and C cells. To date, no studies have investigated the distribution of inhibitory neurotransmitters such as γ-aminobutyric acid (GABA) and their respective receptors on the different cell types in the human SVZ. GABA(A) receptors (GABA(A)R) are ubiquitously expressed, inhibitory heteropentameric chloride ion channels comprised of a variety of subunits that are targeted by many prescribed drugs. In this study we present detailed immunohistochemical data on the regional and cellular localization of α₁, α₂, α3, β₂,₃ and γ₂ subunits of GABA(A)R in the human SVZ. The results from our double and triple labeling studies demonstrate that the cell types and subunit composition throughout the SVZ is heterogeneous; the thickness of the SVZ and GABA(A)R α₂ and γ₂ expression is increased especially in the vicinity of large SVZ blood vessels. GABA(A)R γ₂ is the most specific to the SVZ and present on various cells that express, either glial fibrillary acidic protein (GFAPδ) or polysialic acid-neural cell adhesion molecule (PSA-NCAM) separately, or together in a respective ratio of 7:6:2. Proliferating (type C) cells in the SVZ express GAD65/67, GFAPδ and GABA(A)R β₂,₃ receptor subunits. Within the SVZ the majority of cells have an unexpected nuclear GABA(A)R β₂,₃ expression that is inversely proportional to that of PCNA (proliferating cell nuclear antigen marker), which is a very different pattern of expression compared with underlying caudate nucleus cells. Taken together our results provide a detailed description of the chemo-architecture of the adult human SVZ demonstrating the importance of GABA and GABA(A) receptors on the various cell types in the SVZ.

Effect of propofol in the immature rat brain on short- and long-term neurodevelopmental outcome

Background

Propofol is commonly used as sedative in newborns and children. Recent experimental studies led to contradictory results, revealing neurodegenerative or neuroprotective properties of propofol on the developing brain. We investigated neurodevelopmental short- and long-term effects of neonatal propofol treatment.

Methods

6-day-old Wistar rats (P6), randomised in two groups, received repeated intraperitoneal injections (0, 90, 180 min) of 30 mg/kg propofol or normal saline and sacrificed 6, 12 and 24 hrs following the first injection. Cortical and thalamic areas were analysed by Western blot and quantitative real-time PCR (qRT-PCR) for expression of apoptotic and neurotrophin-dependent signalling pathways. Long-term effects were assessed by Open-field and Novel-Object-Recognition at P30 and P120.

Results

Western blot analyses revealed a transient increase of activated caspase-3 in cortical, and a reduction of active mitogen-activated protein kinases (ERK1/2, AKT) in cortical and thalamic areas. qRT-PCR analyses showed a down-regulation of neurotrophic factors (BDNF, NGF, NT-3) in cortical and thalamic regions. Minor impairment in locomotive activity was observed in propofol treated adolescent animals at P30. Memory or anxiety were not impaired at any time point.

Conclusion

Exposing the neonatal rat brain to propofol induces acute neurotrophic imbalance and neuroapoptosis in a region- and time-specific manner and minor behavioural changes in adolescent animals.

Anxiolytic effects of the GABA(A) receptor partial agonist, L-838,417: impact of age, test context familiarity, and stress

The partial α2,3,5 GABA(A) receptor agonist, L-838,417 has been reported to have anxiolytic effects in adult rodents. Although maturational differences exist for the GABA(A) receptor subunits, the anxiolytic effects of L-838,417 have not been tested in younger animals. The goal of the present experiments was to determine whether L-838,417 reverses anxiety-like behavior induced by either an unfamiliar environment (Experiment 1) or repeated restraint stress (Experiment 2) differentially in adolescent and adult, male and female Sprague-Dawley rats using a modified social interaction test. In Experiment 1, rats were injected with 0, 0.5, 1.0, 2.0, or 4.0 mg/kg L-838,417, i.p. and tested 30 min later in an unfamiliar test context for 10 min. In Experiment 2, rats were exposed to restraint stress (90 min daily for 5 days). Immediately after the last restraint session, animals were injected with L-838,417 and placed alone for 30 min in the test apparatus to familiarize them to this context prior to the 10 min social interaction test. In Experiment 1, L-838,417 produced anxiolytic effects in adults at 1.0 mg/kg, as indexed by a transformation of social avoidance into preference and an increase in social investigation. In adolescents, a dose of 2.0 mg/kg eliminated social avoidance, but had no anxiolytic effects on social investigation. Testing under familiar circumstances (Experiment 2) after repeated restraint stress eliminated age differences in sensitivity to L-838,417, with 0.5 mg/kg reversing the anxiogenic effects of prior stress regardless of age, but with doses ≥ 1 mg/kg decreasing social investigation, an effect possibly due in part to locomotor-impairing effects of this compound. Although locomotor activity was suppressed in both experiments, higher doses of L-838,417 were necessary to suppress locomotor activity in Experiment 1. Thus, anxiolytic effects of L-838,417 were found to be context-, age-, and stress-dependent.

AMPA and GABA(A/B) receptor subunit expression in the cortex of adult squirrel monkeys during peripheral nerve regeneration

The primate somatosensory neuroaxis provides a highly translational model system with which to investigate adult neural plasticity. Here, we report immunohistochemical staining data for AMPA and GABAA/B receptor subunits in the area 3b cortex of adult squirrel monkeys one and five months after median nerve compression. This method of nerve injury was selected because it allows unique insight into how receptor expression changes during the regeneration of the peripheral nerve. One month after nerve compression, the pattern of subunit staining provides evidence that the cortex enters a state of reorganization. GABA α1 receptor subunits are significantly down-regulated in layer IV, V, and VI. Glur2/3 AMPA receptor subunits and postsynaptic GABABR1b receptor subunits are up and down regulated respectively across all layers of cortex. After five months of recovery from nerve compression, the pattern of AMPA and GABAA/B receptor subunits remain significantly altered in a layer specific manner. In layer II/III, GluR1, GluR2/3, and GABA α1 subunit expression is significantly up-regulated while post synaptic GABABR1b receptor subunits are significantly down regulated. In layer VI, V, and VI the GluR2/3 and presynaptic GABABR1a receptor subunits are significantly up-regulated, while the postsynaptic GABABR1b receptor subunits remain significantly down-regulated. Taken together, these results suggest that following nerve injury the cortex enters a state of reorganization that has persistent effects on cortical plasticity even after partial or total reinnervation of the peripheral nerve.

Characterization and quantification of isoflurane-induced developmental apoptotic cell death in mouse cerebral cortex

BACKGROUND

Accumulating evidence indicates that isoflurane and other, similarly acting anesthetics exert neurotoxic effects in neonatal animals. However, neither the identity of dying cortical cells nor the extent of cortical cell loss has been sufficiently characterized. We conducted the present study to immunohistochemically identify the dying cells and to quantify the fraction of cells undergoing apoptotic death in neonatal mouse cortex, a substantially affected brain region.

METHODS

Seven-day-old littermates (n = 36) were randomly assigned to a 6-hour exposure to either 1.5% isoflurane or fasting in room air. Animals were euthanized immediately after exposure and brain sections were double-stained for activated caspase 3 and one of the following cellular markers: Neuronal Nuclei (NeuN) for neurons, glutamic acid decarboxylase (GAD)65 and GAD67 for GABAergic cells, as well as GFAP (glial fibrillary acidic protein) and S100β for astrocytes.

RESULTS

In 7-day-old mice, isoflurane exposure led to widespread increases in apoptotic cell death relative to controls, as measured by activated caspase 3 immunolabeling. Confocal analyses of caspase 3-labeled cells in cortical layers II and III revealed that the overwhelming majority of cells were postmitotic neurons, but some were astrocytes. We then quantified isoflurane-induced neuronal apoptosis in visual cortex, an area of substantial injury. In unanesthetized control animals, 0.08% ± 0.001% of NeuN-positive layer II/III cortical neurons were immunoreactive for caspase 3. By contrast, the rate of apoptotic NeuN-positive neurons increased at least 11-fold (lower end of the 95% confidence interval [CI]) to 2.0% ± 0.004% of neurons immediately after isoflurane exposure (P = 0.0017 isoflurane versus control). In isoflurane-treated animals, 2.9% ± 0.02% of all caspase 3-positive neurons in superficial cortex also coexpressed GAD67, indicating that inhibitory neurons may also be affected. Analysis of GABAergic neurons, however, proved unexpectedly complex. In addition to inducing apoptosis among some GAD67-immunoreactive neurons, anesthesia also coincided with a dramatic decrease in both GAD67 (0.98 vs 1.84 ng/mg protein, P < 0.00001, anesthesia versus control) and GAD65 (2.25 ± 0.74 vs 23.03 ± 8.47 ng/mg protein, P = 0.0008, anesthesia versus control) protein levels.

CONCLUSIONS

Prolonged exposure to isoflurane increased neuronal apoptotic cell death in 7-day-old mice, eliminating approximately 2% of cortical neurons, of which some were identified as GABAergic interneurons. Moreover, isoflurane exposure interfered with the inhibitory nervous system by downregulating the central enzymes GAD65 and GAD67. Conversely, at this age, only a minority of degenerating cells were identified as astrocytes. The clinical relevance of these findings in animals remains to be determined.

GABAergic synaptic inputs of locus coeruleus neurons in wild-type and Mecp2-null mice

Rett syndrome is an autism spectrum disorder resulting from defects in the gene encoding the methyl-CpG-binding protein 2 (MeCP2). Deficiency of the Mecp2 gene causes abnormalities in several systems in the brain, especially the norepinephrinergic and GABAergic systems. The norepinephrinergic neurons in the locus coeruleus (LC) modulate a variety of neurons and play an important role in multiple functions in the central nervous system. In Mecp2(-/Y) mice, defects in the intrinsic membrane properties of LC neurons have been identified, while how their synaptic inputs are affected remains unclear. Therefore, we performed these brain slice studies to demonstrate how LC neurons are regulated by GABAergic inputs and how such synaptic inputs are affected by Mecp2 knockout. In whole cell current clamp, the firing activity of LC neurons was strongly inhibited by the GABAA receptor agonist muscimol, accompanied by hyperpolarization and a decrease in input resistance. Such a postsynaptic inhibition was significantly reduced (by ~30%) in Mecp2(-/Y) mice. Post- and presynaptic GABABergic inputs were found in LC neurons, which were likely mediated by the G protein-coupled, Ba(2+)-sensitive K(+) channels. The postsynaptic GABABergic inhibition was deficient by ~50% in Mecp2 knockout mice. Although the presynaptic GABABergic modulation appeared normal, both frequency and amplitude of the GABAAergic mIPSCs were drastically decreased (by 30-40%) in Mecp2-null mice. These results suggest that the Mecp2 disruption causes defects in both post- and presynaptic GABAergic systems in LC neurons, impairing GABAAergic and GABABergic postsynaptic inhibition and decreasing the GABA release from presynaptic terminals.

NKCC1 knockdown decreases neuron production through GABA(A)-regulated neural progenitor proliferation and delays dendrite development

Signaling through GABA(A) receptors controls neural progenitor cell (NPC) development in vitro and is altered in schizophrenic and autistic individuals. However, the in vivo function of GABA(A) signaling on neural stem cell proliferation, and ultimately neurogenesis, remains unknown. To examine GABA(A) function in vivo, we electroporated plasmids encoding short-hairpin (sh) RNA against the Na-K-2Cl cotransporter NKCC1 (shNKCC1) in NPCs of the neonatal subventricular zone in mice to reduce GABA(A)-induced depolarization. Reduced GABA(A) depolarization identified by a loss of GABA(A)-induced calcium responses in most electroporated NPCs led to a 70% decrease in the number of proliferative Ki67(+) NPCs and a 60% reduction in newborn neuron density. Premature loss of GABA(A) depolarization in newborn neurons resulted in truncated dendritic arborization at the time of synaptic integration. However, by 6 weeks the dendritic tree had partially recovered and displayed a small, albeit significant, decrease in dendritic complexity but not total dendritic length. To further examine GABA(A) function on NPCs, we treated animals with a GABA(A) allosteric agonist, pentobarbital. Enhancement of GABA(A) activity in NPCs increased the number of proliferative NPCs by 60%. Combining shNKCC1 and pentobarbital prevented the shNKCC1 and the pentobarbital effects on NPC proliferation, suggesting that these manipulations affected NPCs through GABA(A) receptors. Thus, dysregulation in GABA(A) depolarizing activity delayed dendritic development and reduced NPC proliferation resulting in decreased neuronal density.

Hippocampal extracellular signal-regulated kinase signaling has a role in passive avoidance memory retrieval induced by GABAA Receptor modulation in mice

Available evidence strongly suggests that the γ-aminobutyric acid type A (GABA(A)) receptor has a crucial role in memory retrieval. However, the signaling mechanisms underlying the role of GABA(A) receptor modulation in memory retrieval are unclear. We conducted one-trial passive avoidance task with pre-retention trial drug administration in the hippocampus to test the effects of GABA(A) receptor modulation on memory retrieval. We further tested the co-involvement of signaling molecules: extracellular signal-regulated kinase (ERK), Ca(2+)/calmodulin-dependent protein kinase II (CaMKII), and cAMP responsive element-binding protein (CREB). First, we observed that the phosphorylation of hippocampal ERK was required for memory retrieval during the task. Accordingly, to investigate whether GABA(A) receptor activation or inhibition induces ERK phosphorylation during memory retrieval, drugs that target the GABA(A) receptor were administered into the hippocampus before the retention trial. Muscimol, a GABA(A) receptor agonist, and diazepam, an agonist to benzodiazepine-binding site of GABA(A) receptor, blocked retention trial-induced ERK phosphorylation and impaired memory retrieval. Furthermore, co-treatment with sub-effective dose of U0126, a mitogen-activated protein kinase inhibitor, blocked the upregulation of ERK phosphorylation and impaired memory retrieval, and bicuculline methiodide (BMI), a GABA(A) receptor antagonist, increased ERK phosphorylation induced by the retention trial and facilitated memory retrieval. Finally, the effects of BMI were blocked by the co-application of a sub-effective dose of U0126. These results suggest that GABA(A) receptor-mediated memory retrieval is closely related to ERK activity.

Ontogenetic modifications of neuronal excitability during brain maturation: developmental changes of neurotransmitter receptors

The development of the human brain depends on a precisely orchestrated cascade of events, including proliferation, migration and maturation of neural progenitor cells. Different mechanisms coordinate these stages to reach a normal structural organization, producing appropriate excitatory and inhibitory networks. Here, we will briefly review the developmental changes of glutamate (Glu) and γ-aminobutyric acid (GABA) receptors, with particular attention to the development of the human brain. We will also briefly discuss recent evidence on the involvement of the endocannabinoid signaling in the regulation of neuronal excitability during early brain development..

Identifying developmental toxicity pathways for a subset of ToxCast chemicals using human embryonic stem cells and metabolomics

Metabolomics analysis was performed on the supernatant of human embryonic stem (hES) cell cultures exposed to a blinded subset of 11 chemicals selected from the chemical library of EPA's ToxCast™ chemical screening and prioritization research project. Metabolites from hES cultures were evaluated for known and novel signatures that may be indicative of developmental toxicity. Significant fold changes in endogenous metabolites were detected for 83 putatively annotated mass features in response to the subset of ToxCast chemicals. The annotations were mapped to specific human metabolic pathways. This revealed strong effects on pathways for nicotinate and nicotinamide metabolism, pantothenate and CoA biosynthesis, glutathione metabolism, and arginine and proline metabolism pathways. Predictivity for adverse outcomes in mammalian prenatal developmental toxicity studies used ToxRefDB and other sources of information, including Stemina Biomarker Discovery's predictive DevTox® model trained on 23 pharmaceutical agents of known developmental toxicity and differing potency. The model initially predicted developmental toxicity from the blinded ToxCast compounds in concordance with animal data with 73% accuracy. Retraining the model with data from the unblinded test compounds at one concentration level increased the predictive accuracy for the remaining concentrations to 83%. These preliminary results on a 11-chemical subset of the ToxCast chemical library indicate that metabolomics analysis of the hES secretome provides information valuable for predictive modeling and mechanistic understanding of mammalian developmental toxicity.

Sedative and antiepileptic effects of Anthocephalus cadamba Roxb. in mice and rats

OBJECTIVE

The aim of the present study was to evaluate the sedative and antiepileptic activities of ethanolic extract of Anthocephalus cadamba (ACE) bark in various experimental animal models.

MATERIALS AND METHODS

ACE was tested at three doses viz. 100, 200 and 400 mg/kg p.o. We used ketamine-induced sleeping time model to test the sedative property of the extract where, onset and duration of sleep were observed. A paradigm of anticonvulsant models (pentylenetetrazole, isoniazid and maximal electroshock-induced seizures) were used to evaluate its protective effect against absence and generalized types of seizures. Onset of clonic convulsions, tonic extension and time of death were observed in PTZ and INH-induced seizure models. In MES model, duration of tonic hind leg extension and onset of stupor were observed.

RESULTS

ACE showed significant increase in ketamine induced sleeping time. It also exhibited significant increase (P<0.05, 0.01 and 0.001) in latency to clonic convulsion, tonic extension and time of death in PTZ and INH models at all tested doses, whereas in the MES model, the lower dose was found to be effective when compared with the higher doses (200 and 400 mg/kg, p.o.).

CONCLUSION

The results of the present investigation demonstrated that ACE possesses sedative and antiepileptic activities.

Editing of neurotransmitter receptor and ion channel RNAs in the nervous system

The central dogma of molecular biology defines the major route for the transfer of genetic information from genomic DNA to messenger RNA to three-dimensional proteins that affect structure and function. Like alternative splicing, the post-transcriptional conversion of adenosine to inosine (A-to-I) by RNA editing can dramatically expand the diversity of the transcriptome to generate multiple, functionally distinct protein isoforms from a single genomic locus. While RNA editing has been identified in virtually all tissues, such post-transcriptional modifications have been best characterized in RNAs encoding both ligand- and voltage-gated ion channels and neurotransmitter receptors. These RNA processing events have been shown to play an important role in the function of the encoded protein products and, in several cases, have been shown to be critical for the normal development and function of the nervous system.

Allosteric Modulation of αβδ GABAA Receptors

GABA_A receptors mediate the majority of the fast inhibition in the mature brain and play an important role in the pathogenesis of many neurological and psychiatric disorders. The αβδ GABA_A receptor localizes extra- or perisynaptically and mediates GABAergic tonic inhibition. Compared with synaptically localized αβγ receptors, αβδ receptors are more sensitive to GABA, display relatively slower desensitization and exhibit lower efficacy to GABA agonism. Interestingly, αβδ receptors can be positively modulated by a variety of structurally different compounds, even at saturating GABA concentrations. This review focuses on allosteric modulation of recombinant αβδ receptor currents and αβδ receptor-mediated tonic currents by anesthetics and ethanol. The possible mechanisms for the positive modulation of αβδ receptors by these compounds will also be discussed.

The effect of sevoflurane on neuronal degeneration and GABAA subunit composition in a developing rat model of organotypic hippocampal slice cultures

OBJECTIVE

The GABA(A) receptor subunit composition undergoes a switch from a predominantly alpha2 to a predominantly alpha1 around postnatal day (PND) 7 in a rat pup. This developmental switch in the GABA(A) receptor subunit composition changes the kinetics and pharmacologic properties of the GABA(A) receptor. Using a developmental organotypic hippocampal slice model, we hypothesized that the developmental changes in the GABA(A) receptor subunit composition may promote neurodegeneration after exposure to sevoflurane.

DESIGN

Organotypic hippocampal slices (OHS) were prepared from rat pups on PND 4, 7, and 14 and exposed to 2.0% sevoflurane or air for 5 hours. Hippocampal CA1, CA3, and dentate gyrus neuronal survival and GABA(A) receptor subunit composition were assessed immediately, 24 and 72 hours after exposure and compared with air.

MEASUREMENTS AND RESULTS

Early cell death immediately after exposure to sevoflurane was statistically significant in the PND14 (P<0.001). At 24 hours, cell death was not significant for any PND age-examined OHS. However, at 72 hours, cell death was significant in the OHS prepared from the PND7 and 4 rat pups (P<0.001). In further analysis, either a decrease in the alpha1 and/or increase in the alpha2 subunit composition promoted cell survival in the PND 4 and 7 OHS. On PND14, cell survival was promoted by an increase in the alpha1 subunit composition.

CONCLUSIONS

This in vitro investigation supports an age-dependent and GABA(A) receptor subunit composition relationship between 2.0% sevoflurane exposure and cell death.

Regional and temporal profiles of calpain and caspase-3 activities in postnatal rat brain following repeated propofol administration

Exposure of newborn rats to a variety of anesthetics has been shown to induce apoptotic neurodegeneration in the developing brain. We investigated the effect of the general anesthetic propofol on the brain of 7-day-old (P7) Wistar rats during the peak of synaptic growth. Caspase and calpain protease families most likely participate in neuronal cell death. Our objective was to examine regional and temporal patterns of caspase-3 and calpain activity following repeated propofol administration (20 mg/kg). P7 rats were exposed for 2, 4 or 6 h to propofol and killed 0, 4, 16 and 24 h after exposure. Relative caspase-3 and calpain activities were estimated by Western blot analysis of the proteolytic cleavage products of α-II-spectrin, protein kinase C and poly(ADP-ribose) polymerase 1. Caspase-3 activity and expression displayed a biphasic pattern of activation. Calpain activity changed in a region- and time-specific manner that was distinct from that observed for caspase-3. The time profile of calpain activity exhibited substrate specificity. Fluoro-Jade B staining revealed an immediate neurodegenerative response that was in direct relationship to the duration of anesthesia in the cortex and inversely related to the duration of anesthesia in the thalamus. At later post-treatment intervals, dead neurons were detected only in the thalamus 24 h following the 6-hour propofol exposure. Strong caspase-3 expression that was detected at 24 h was not followed by cell death after 2- and 4-hour exposures to propofol. These results revealed complex patterns of caspase-3 and calpain activities following prolonged propofol anesthesia and suggest that both are a manifestation of propofol neurotoxicity at a critical developmental stage.

Early exposure to haloperidol or olanzapine induces long-term alterations of dendritic form

Exposure of the developing brain to a wide variety of drugs of abuse (e.g., stimulants, opioids, ethanol, etc.) can induce life-long changes in behavior and neural circuitry. However, the long-term effects of exposure to therapeutic, psychotropic drugs have only recently begun to be appreciated. Antipsychotic drugs are little studied in this regard. Here, we quantitatively analyzed dendritic architecture in adult mice treated with paradigmatic typical- (haloperidol) or atypical (olanzapine) antipsychotic drugs at developmental stages corresponding to fetal or fetal plus early childhood stages in humans. In layer 3 pyramidal cells of the medial and orbital prefrontal cortices and the parietal cortex and in spiny neurons of the core of the nucleus accumbens, both drugs induced significant changes (predominantly reductions) in the amount and complexity of dendritic arbor and the density of dendritic spines. The drug-induced plasticity of dendritic architecture suggests changes in patterns of neuronal connectivity in multiple brain regions that are likely to be functionally significant.

Neurotransmitter signaling in postnatal neurogenesis: The first leg

Like the liver or other peripheral organs, two regions of the adult brain possess the ability of self-renewal through a process called neurogenesis. This raises tremendous hope for repairing the damaged brain, and it has stimulated research on identifying signals controlling neurogenesis. Neurogenesis involves several stages from fate determination to synaptic integration via proliferation, migration, and maturation. While fate determination primarily depends on a genetic signature, other stages are controlled by the interplay between genes and microenvironmental signals. Here, we propose that neurotransmitters are master regulators of the different stages of neurogenesis. In favor of this idea, a description of selective neurotransmitter signaling and their functions in the largest neurogenic zone, the subventricular zone (SVZ), is provided. In particular, we emphasize the interactions between neuroblasts and astrocyte-like cells that release gamma-aminobutyric acid (GABA) and glutamate, respectively. However, we also raise several limitations to our knowledge on neurotransmitters in neurogenesis. The function of neurotransmitters in vivo remains largely unexplored. Neurotransmitter signaling has been viewed as uniform, which dramatically contrasts with the cellular and molecular mosaic nature of the SVZ. How neurotransmitters are integrated with other well-conserved molecules, such as sonic hedgehog, is poorly understood. In an effort to reconcile these differences, we discuss how specificity of neurotransmitter functions can be provided through their multitude of receptors and intracellular pathways in different cell types and their possible interactions with sonic hedgehog.

The role of GABA(A) receptors in the acute and chronic effects of ethanol: a decade of progress

The past decade has brought many advances in our understanding of GABA(A) receptor-mediated ethanol action in the central nervous system. We now know that specific GABA(A) receptor subtypes are sensitive to ethanol at doses attained during social drinking while other subtypes respond to ethanol at doses attained by severe intoxication. Furthermore, ethanol increases GABAergic neurotransmission through indirect effects, including the elevation of endogenous GABAergic neuroactive steroids, presynaptic release of GABA, and dephosphorylation of GABA(A) receptors promoting increases in GABA sensitivity. Ethanol's effects on intracellular signaling also influence GABAergic transmission in multiple ways that vary across brain regions and cell types. The effects of chronic ethanol administration are influenced by adaptations in GABA(A) receptor function, expression, trafficking, and subcellular localization that contribute to ethanol tolerance, dependence, and withdrawal hyperexcitability. Adolescents exhibit altered sensitivity to ethanol actions, the tendency for higher drinking and longer lasting GABAergic adaptations to chronic ethanol administration. The elucidation of the mechanisms that underlie adaptations to ethanol exposure are leading to a better understanding of the regulation of inhibitory transmission and new targets for therapies to support recovery from ethanol withdrawal and alcoholism.

GABA's control of stem and cancer cell proliferation in adult neural and peripheral niches

Aside from traditional neurotransmission and regulation of secretion, gamma-amino butyric acid (GABA) through GABA(A) receptors negatively regulates proliferation of pluripotent and neural stem cells in embryonic and adult tissue. There has also been evidence that GABAergic signaling and its control over proliferation is not only limited to the nervous system, but is widespread through peripheral organs containing adult stem cells. GABA has emerged as a tumor signaling molecule in the periphery that controls the proliferation of tumor cells and perhaps tumor stem cells. Here, we will discuss GABA's presence as a near-universal signal that may be altered in tumor cells resulting in modified mitotic activity.