Microglial Expression of the Wnt Signaling Modulator DKK2 Differs between Human Alzheimer's Disease Brains and Mouse Neurodegeneration Models.

Wnt signaling is crucial for synapse and cognitive function. Indeed, deficient Wnt signaling is causally related to increased expression of DKK1, an endogenous negative Wnt regulator, and synapse loss, both of which likely contribute to cognitive decline in Alzheimer's disease (AD). Increasingly, AD research efforts have probed the neuroinflammatory role of microglia, the resident immune cells of the CNS, which have furthermore been shown to be modulated by Wnt signaling. The DKK1 homolog DKK2 has been previously identified as an activated response and/or disease-associated microglia (DAM/ARM) gene in a mouse model of AD. Here, we performed a detailed analysis of DKK2 in mouse models of neurodegeneration, and in human AD brain. In APP/PS1 and APPNL-G-F AD mouse model brains as well as in SOD1G93A ALS mouse model spinal cords, but not in control littermates, we demonstrated significant microgliosis and microglial Dkk2 mRNA upregulation in a disease-stage-dependent manner. In the AD models, these DAM/ARM Dkk2+ microglia preferentially accumulated close to ßAmyloid plaques. Furthermore, recombinant DKK2 treatment of rat hippocampal primary neurons blocked WNT7a-induced dendritic spine and synapse formation, indicative of an anti-synaptic effect similar to that of DKK1. In stark contrast, no such microglial DKK2 upregulation was detected in the postmortem human frontal cortex from individuals diagnosed with AD or pathologic aging. In summary, the difference in microglial expression of the DAM/ARM gene DKK2 between mouse models and human AD brain highlights the increasingly recognized limitations of using mouse models to recapitulate facets of human neurodegenerative disease.

Regulation of mitophagy by the NSL complex underlies genetic risk for Parkinson's disease at 16q11.2 and MAPT H1 loci.

Parkinson's disease is a common incurable neurodegenerative disease. The identification of genetic variants via genome-wide association studies has considerably advanced our understanding of the Parkinson's disease genetic risk. Understanding the functional significance of the risk loci is now a critical step towards translating these genetic advances into an enhanced biological understanding of the disease. Impaired mitophagy is a key causative pathway in familial Parkinson's disease, but its relevance to idiopathic Parkinson's disease is unclear. We used a mitophagy screening assay to evaluate the functional significance of risk genes identified through genome-wide association studies. We identified two new regulators of PINK1-dependent mitophagy initiation, KAT8 and KANSL1, previously shown to modulate lysine acetylation. These findings suggest PINK1-mitophagy is a contributing factor to idiopathic Parkinson's disease. KANSL1 is located on chromosome 17q21 where the risk associated gene has long been considered to be MAPT. While our data do not exclude a possible association between the MAPT gene and Parkinson's disease, they provide strong evidence that KANSL1 plays a crucial role in the disease. Finally, these results enrich our understanding of physiological events regulating mitophagy and establish a novel pathway for drug targeting in neurodegeneration.

Dysregulated Wnt Signalling in the Alzheimer's Brain.

The Wnt signalling system is essential for both the developing and adult central nervous system. It regulates numerous cellular functions ranging from neurogenesis to blood brain barrier biology. Dysregulated Wnt signalling can thus have significant consequences for normal brain function, which is becoming increasingly clear in Alzheimer's disease (AD), an age-related neurodegenerative disorder that is the most prevalent form of dementia. AD exhibits a range of pathophysiological manifestations including aberrant amyloid precursor protein processing, tau pathology, synapse loss, neuroinflammation and blood brain barrier breakdown, which have been associated to a greater or lesser degree with abnormal Wnt signalling. Here we provide a comprehensive overview of the role of Wnt signalling in the CNS, and the research that implicates dysregulated Wnt signalling in the ageing brain and in AD pathogenesis. We also discuss the opportunities for therapeutic intervention in AD via modulation of the Wnt signalling pathway, and highlight some of the challenges and the gaps in our current understanding that need to be met to enable that goal.

Alzheimer's disease phospholipase C-gamma-2 (PLCG2) protective variant is a functional hypermorph.

BACKGROUND: Recent Genome Wide Association Studies (GWAS) have identified novel rare coding variants in immune genes associated with late onset Alzheimer's disease (LOAD). Amongst these, a polymorphism in phospholipase C-gamma 2 (PLCG2) P522R has been reported to be protective against LOAD. PLC enzymes are key elements in signal transmission networks and are potentially druggable targets. PLCG2 is highly expressed in the hematopoietic system. Hypermorphic mutations in PLCG2 in humans have been reported to cause autoinflammation and immune disorders, suggesting a key role for this enzyme in the regulation of immune cell function. METHODS: We assessed PLCG2 distribution in human and mouse brain tissue via immunohistochemistry and in situ hybridization. We transfected heterologous cell systems (COS7 and HEK293T cells) to determine the effect of the P522R AD-associated variant on enzymatic function using various orthogonal assays, including a radioactive assay, IP-One ELISA, and calcium assays. RESULTS: PLCG2 expression is restricted primarily to microglia and granule cells of the dentate gyrus. Plcg2 mRNA is maintained in plaque-associated microglia in the cerebral tissue of an AD mouse model. Functional analysis of the p.P522R variant demonstrated a small hypermorphic effect of the mutation on enzyme function. CONCLUSIONS: The PLCG2 P522R variant is protective against AD. We show that PLCG2 is expressed in brain microglia, and the p.P522R polymorphism weakly increases enzyme function. These data suggest that activation of PLCγ2 and not inhibition could be therapeutically beneficial in AD. PLCγ2 is therefore a potential target for modulating microglia function in AD, and a small molecule drug that weakly activates PLCγ2 may be one potential therapeutic approach.

Targeting the cAMP and Transforming Growth Factor-ß Pathway Increases Proliferation to Promote Re-Epithelialization of Human Stem Cell-Derived Retinal Pigment Epithelium.

UNLABELLED: Retinal pigment epithelium (RPE) cell integrity is critical to the maintenance of retinal function. Many retinopathies such as age-related macular degeneration (AMD) are caused by the degeneration or malfunction of the RPE cell layer. Replacement of diseased RPE with healthy, stem cell-derived RPE is a potential therapeutic strategy for treating AMD. Human embryonic stem cells (hESCs) differentiated into RPE progeny have the potential to provide an unlimited supply of cells for transplantation, but challenges around scalability and efficiency of the differentiation process still remain. Using hESC-derived RPE as a cellular model, we sought to understand mechanisms that could be modulated to increase RPE yield after differentiation. We show that RPE epithelialization is a density-dependent process, and cells seeded at low density fail to epithelialize. We demonstrate that activation of the cAMP pathway increases proliferation of dissociated RPE in culture, in part through inhibition of transforming growth factor-ß (TGF-ß) signaling. This results in enhanced uptake of epithelial identity, even in cultures seeded at low density. In line with these findings, targeted manipulation of the TGF-ß pathway with small molecules produces an increase in efficiency of RPE re-epithelialization. Taken together, these data highlight mechanisms that promote epithelial fate acquisition in stem cell-derived RPE. Modulation of these pathways has the potential to favorably impact scalability and clinical translation of hESC-derived RPE as a cell therapy. SIGNIFICANCE: Stem cell-derived retinal pigment epithelium (RPE) is currently being evaluated as a cell-replacement therapy for macular degeneration. This work shows that the process of generating RPE in vitro is regulated by the cAMP and transforming growth factor-ß signaling pathway. Modulation of these pathways by small molecules, as identified by phenotypic screening, leads to an increased efficiency of generating RPE cells with a higher yield. This can have a potential impact on manufacturing transplantation-ready cells at large scale and is advantageous for clinical studies using this approach in the future.

6-Sulphated chondroitins have a positive influence on axonal regeneration.

Chondroitin sulphate proteoglycans (CSPGs) upregulated in the glial scar inhibit axon regeneration via their sulphated glycosaminoglycans (GAGs). Chondroitin 6-sulphotransferase-1 (C6ST-1) is upregulated after injury leading to an increase in 6-sulphated GAG. In this study, we ask if this increase in 6-sulphated GAG is responsible for the increased inhibition within the glial scar, or whether it represents a partial reversion to the permissive embryonic state dominated by 6-sulphated glycosaminoglycans (GAGs). Using C6ST-1 knockout mice (KO), we studied post-injury changes in chondroitin sulphotransferase (CSST) expression and the effect of chondroitin 6-sulphates on both central and peripheral axon regeneration. After CNS injury, wild-type animals (WT) showed an increase in mRNA for C6ST-1, C6ST-2 and C4ST-1, but KO did not upregulate any CSSTs. After PNS injury, while WT upregulated C6ST-1, KO showed an upregulation of C6ST-2. We examined regeneration of nigrostriatal axons, which demonstrate mild spontaneous axon regeneration in the WT. KO showed many fewer regenerating axons and more axonal retraction than WT. However, in the PNS, repair of the median and ulnar nerves led to similar and normal levels of axon regeneration in both WT and KO. Functional tests on plasticity after the repair also showed no evidence of enhanced plasticity in the KO. Our results suggest that the upregulation of 6-sulphated GAG after injury makes the extracellular matrix more permissive for axon regeneration, and that the balance of different CSs in the microenvironment around the lesion site is an important factor in determining the outcome of nervous system injury.

Differential contribution of GABA(A) receptor subtypes to the anticonvulsant efficacy of benzodiazepine site ligands.

Non-selective benzodiazepines, such as diazepam, interact with equivalent affinity and agonist efficacy at GABA(A) receptors containing either an alpha1, alpha2, alpha3 or alpha5 subunit. However, which of these particular subtypes are responsible for the anticonvulsant effects of diazepam remains uncertain. In the present study, we examined the ability of diazepam to reduce pentylenetetrazoLe (PTZ)-induced and maximal electroshock (MES)-induced seizures in mice containing point mutations in single (alpha1H101R, alpha2H101R or alpha5H105R) or multiple (alpha125H-->R) alpha subunits that render the resulting GABA(A) receptors diazepam-insensitive. Furthermore, the anticonvulsant properties of diazepam, the alpha1- and alpha3-selective compounds zolpidem and TP003, respectively, and the alpha2/alpha3 preferring compound TP13 were studied against PTZ-induced seizures. In the transgenic mice, no single subtype was responsible for the anticonvulsant effects of diazepam in either the PTZ or MES assay and neither the alpha3 nor alpha5 subtypes appeared to confer anticonvulsant activity. Moreover, whereas the alpha1 and alpha2 subtypes played a modest role with respect to the PTZ assay, they had a negligible role in the MES assay. With respect to subtype-selective compounds, zolpidem and TP003 had much reduced anticonvulsant efficacy relative to diazepam in both the PTZ and MES assays whereas TP13 had high anticonvulsant efficacy in the PTZ but not the MES assay. Taken together, these data not only indicate a role for alpha2-containing GABA(A) receptors in mediating PTZ and MES anticonvulsant activity but also suggest that efficacy at more than one subtype is required and that these subtypes act synergistically.

A genetically modified mouse model probing the selective action of ifenprodil at the N-methyl-D-aspartate type 2B receptor.

Selective antagonism of N-methyl-d-aspartate (NMDA) 2B subunit containing receptors has been suggested to have potential therapeutic application for multiple CNS disorders. The amino terminal NR2B residues 1 to 282 were found to be both necessary and sufficient for the binding and function of highly NR2B subunit specific antagonists like ifenprodil and CP-101,606. Using a genetic approach in mice, we successfully replaced the murine NR2B gene function by "knocking-in" (KI) a chimeric human NR2A/B cDNA containing the minimal domain abolishing ifenprodil binding into the endogenous NR2B locus. Patch-clamp recording from hippocampal cultures of the NR2B KI mice demonstrated that their NMDA receptors have reduced sensitivity to both ifenprodil and CP-101,606, as predicted, but also have a lower affinity for glycine. The NR2B KI mice exhibited normal locomotor activity making this ifenprodil-insensitive mouse model a valuable tool to test the specificity of NR2B selective antagonists in vivo.

Mechanisms of anabolic androgenic steroid inhibition of mammalian epsilon-subunit-containing GABAA receptors.

GABAergic transmission regulates the activity of gonadotrophin-releasing hormone (GnRH) neurons in the preoptic area/hypothalamus that control the onset of puberty and the expression of reproductive behaviours. One of the hallmarks of illicit use of anabolic androgenic steroids (AAS) is disruption of behaviours under neuroendocrine control. GnRH neurons are among a limited population of cells that express high levels of the epsilon-subunit of the GABAA receptor. To better understand the actions of AAS on neuroendocrine mechanisms, we have characterized modulation of GABAA receptor-mediated currents in mouse native GnRH neurons and in heterologous cells expressing recombinant alpha2beta3epsilon-receptors. GnRH neurons exhibited robust currents in response to millimolar concentrations of GABA and a picrotoxin (PTX)-sensitive, bicuculline-insensitive current that probably arises from spontaneous openings of GABAA receptors. The AAS 17alpha-methyltestosterone (17alpha-MeT) inhibited spontaneous and GABA-evoked currents in GnRH neurons. For recombinant alpha2beta3epsilon-receptors, 17alpha-MeT inhibited phasic and tonic GABA-elicited responses, accelerated desensitization and slowed paired pulse response recovery. Single channel analysis indicated that GABA-evoked events could be described by three open dwell components and that 17alpha-MeT enhanced residence in the intermediate dwell state. This AAS also inhibited a PTX-sensitive, spontaneous current (open probability, approximately 0.15-0.2) in a concentration-dependent fashion (IC50 approximately 9 microm). Kinetic modelling indicated that the inhibition induced by 17alpha-MeT occurs by an allosteric block in which the AAS interacts preferentially with a closed state and promotes accumulation in that state. Finally, studies with a G302S mutant epsilon-subunit suggest that this residue within the transmembrane domain TM2 plays a role in mediating AAS binding and modulation. In sum, our results indicate that inclusion of the epsilon-subunit significantly alters the profile of AAS modulation and that this allosteric inhibition of native GnRH neurons should be considered with regard to AAS disruption of neuroendocrine control.

GABA-A receptors: a viable target for novel anxiolytics?

Benzodiazepine (BZ) anxiolytics mediate their clinical effects by enhancing the effect of gamma-aminobutyric acid (GABA) at the GABA-A receptor. Classical BZ full agonists such as diazepam, which maximally enhance the function of GABA-A receptors, are effective anxiolytics but carry unwanted side effects including sedation, dependence and abuse liability, limiting their utility. Although a second generation of 'partial agonist' BZs have been pursued, promising preclinical data, in terms of anxiolytic efficacy and decreased unwanted effects, have so far failed to translate to the clinic. Following the insights into GABA-A receptor subtypes mediating the effects of BZs, a third generation of 'receptor subtype-selective' BZ site ligands have been developed. However, it remains to be determined whether promising preclinical data are recapitulated in the clinic.

Evidence for a significant role of alpha 3-containing GABAA receptors in mediating the anxiolytic effects of benzodiazepines.

The GABA(A) receptor subtypes responsible for the anxiolytic effects of nonselective benzodiazepines (BZs) such as chlordiazepoxide (CDP) and diazepam remain controversial. Hence, molecular genetic data suggest that alpha2-rather than alpha3-containing GABA(A) receptors are responsible for the anxiolytic effects of diazepam, whereas the anxiogenic effects of an alpha3-selective inverse agonist suggest that an agonist selective for this subtype should be anxiolytic. We have extended this latter pharmacological approach to identify a compound, 4,2'-difluoro-5'-[8-fluoro-7-(1-hydroxy-1-methylethyl)imidazo[1,2-á]pyridin-3-yl]biphenyl-2-carbonitrile (TP003), that is an alpha3 subtype selective agonist that produced a robust anxiolytic-like effect in both rodent and non-human primate behavioral models of anxiety. Moreover, in mice containing a point mutation that renders alpha2-containing receptors BZ insensitive (alpha2H101R mice), TP003 as well as the nonselective agonist CDP retained efficacy in a stress-induced hyperthermia model. Together, these data show that potentiation of alpha3-containing GABA(A) receptors is sufficient to produce the anxiolytic effects of BZs and that alpha2 potentiation may not be necessary.

DISC1 and PDE4B are interacting genetic factors in schizophrenia that regulate cAMP signaling.

The disrupted in schizophrenia 1 (DISC1) gene is a candidate susceptibility factor for schizophrenia, but its mechanistic role in the disorder is unknown. Here we report that the gene encoding phosphodiesterase 4B (PDE4B) is disrupted by a balanced translocation in a subject diagnosed with schizophrenia and a relative with chronic psychiatric illness. The PDEs inactivate adenosine 3',5'-monophosphate (cAMP), a second messenger implicated in learning, memory, and mood. We show that DISC1 interacts with the UCR2 domain of PDE4B and that elevation of cellular cAMP leads to dissociation of PDE4B from DISC1 and an increase in PDE4B activity. We propose a mechanistic model whereby DISC1 sequesters PDE4B in resting cells and releases it in an activated state in response to elevated cAMP.

Inhibition of NUDEL (nuclear distribution element-like)-oligopeptidase activity by disrupted-in-schizophrenia 1.

Recently, nuclear distribution element-like (NUDEL) has been implicated to play a role in lissencephaly and schizophrenia through interactions with the lissencephaly gene 1 (Lis1) and disrupted-in-schizophrenia 1 (DISC1) products, respectively. Interestingly, NUDEL is the same protein as endooligopeptidase A (EOPA), a thiol-activated peptidase involved in conversion and inactivation of a number of bioactive peptides. In this study, we have cloned EOPA from the human brain and have confirmed that it is equivalent to NUDEL, leading us to suggest a single name, NUDEL-oligopeptidase. In the brain, the monomeric form of NUDEL-oligopeptidase is responsible for the peptidase activity whose catalytic mechanism is likely to involve a reactive cysteine, because mutation of Cys-273 fully abolished NUDEL-oligopeptidase activity without disrupting the protein's secondary structure. Cys-273 is very close to the DISC1-binding site on NUDEL-oligopeptidase. Intriguingly, DISC1 inhibits NUDEL-oligopeptidase activity in a competitive fashion. We suggest that the activity of NUDEL-oligopeptidase is under tight regulation through protein-protein interactions and that disruption of these interactions, as postulated in a Scottish DISC1 translocation schizophrenia cohort, may lead to aberrant regulation of NUDEL-oligopeptidase, perhaps providing a substrate for the pathology of schizophrenia.

gamma-Aminobutyric acid A receptor subunit mutant mice: new perspectives on alcohol actions.

gamma-Aminobutyric acid A (GABA(A)) receptors are believed to mediate a number of alcohol's behavioral actions. Because the subunit composition of GABA(A) receptors determines receptor pharmacology, behavioral sensitivity to alcohol (ethanol) may depend on which subunits are present (or absent). A number of knock-out and/or transgenic mouse models have been developed (alpha1, alpha2, alpha5, alpha6, beta2, beta3, gamma2S, gamma2L, delta) and tested for behavioral sensitivity to ethanol. Here we review the current GABA(A) receptor subunit knock-out and transgenic literature for ethanol sensitivity, and integrate these results into those obtained using quantitative trait loci (QTL) analysis and gene expression assays. Converging evidence from these three approaches support the notion that different behavioral actions of ethanol are mediated by specific subunits, and suggest that new drugs that target specific GABA(A) subunits may selectively alter some behavioral actions of ethanol, without altering others. Current data sets provide strongest evidence for a role of alpha1-subunits in ethanol-induced loss of righting reflex, and alpha5-subunits in ethanol-stimulated locomotion. However, three-way validation is hampered by the incomplete behavioral characterization of many of the mutant mice, and additional subunits are likely to be linked to alcohol actions as behavioral testing progresses.

Activity of chlormethiazole at human recombinant GABA(A) and NMDA receptors.

1. Investigation into the modulatory effects of chlormethiazole at human recombinant gamma-aminobutyric acid A receptor (GABAA) and N-methyl-d-aspartate (NMDA) receptors was undertaken to gain insight into its mechanism of action and determine if the drug exhibited any subtype-selective activity. 2. Despite a structural similarity to the beta-subunit-selective compound loreclezole, chlormethiazole did not show any difference in maximum efficacy and only a slight difference in EC50 in its potentiating action at alpha1beta1gamma2 and alpha1beta2gamma2 GABAA receptor subtypes with preference for alpha1beta1gamma2. 3. Similar to the previously reported subtype-dependent activity of pentobarbital, chlormethiazole elicited a significantly greater degree of maximum potentiation on receptors lacking a gamma2 subunit, and also those receptors containing an alpha4 or alpha6 subunit. This also demonstrates that chlormethiazole does not act via the benzodiazepine binding site. 4. Unlike pentobarbital and propofol, chlormethiazole elicited only a slight direct GABAA receptor activation at concentrations up to 1 mm. In addition, the drug did not potentiate anaesthetic-mediated currents elicited by pentobarbital or propofol, suggesting that chlormethiazole may be acting via an anaesthetic binding site. 5. Chlormethiazole produced weak nonselective inhibition of human NMDA NR1a+NR2A and NR1a+NR2B receptors. IC50's were approximately 500 microm that likely exceed the therapeutic dose range for chlormethiazole, indicating that the primary mechanism of the compounds in vivo activity is via GABAA receptors.

The GABAA receptor gene family: new opportunities for drug development.

gamma-Aminobutyric acid (GABA), which is the main inhibitory neurotransmitter in the mammalian brain, exerts its effects through the activation of a ligand-gated ion channel, the GABAA receptor, leading to the inhibition of the activity of neurons. A family of GABAA receptors has been identified, some of which are targets for therapeutic agents such as benzodiazepines, barbiturates and general anesthetics. Recently, novel transgenic approaches have been used to understand the function of receptor subtypes and, thereby, their therapeutic utility. Additionally, progress has been made in the development of novel receptor subtype-selective compounds. In this review, we will primarily focus on progress achieved in the understanding of the function of this receptor family, and potential exploitation for drug development.

Sedation and anesthesia mediated by distinct GABA(A) receptor isoforms.

The specific mechanisms underlying general anesthesia are primarily unknown. The intravenous general anesthetic etomidate acts by potentiating GABA(A) receptors, with selectivity for beta2 and beta3 subunit-containing receptors determined by a single asparagine residue. We generated a genetically modified mouse containing an etomidate-insensitive beta2 subunit (beta2 N265S) to determine the role of beta2 and beta3 subunits in etomidate-induced anesthesia. Loss of pedal withdrawal reflex and burst suppression in the electroencephalogram were still observed in the mutant mouse, indicating that loss of consciousness can be mediated purely through beta3-containing receptors. The sedation produced by subanesthetic doses of etomidate and during recovery from anesthesia was present only in wild-type mice, indicating that the beta2 subunit mediates the sedative properties of anesthetics. These findings show that anesthesia and sedation are mediated by distinct GABA(A) receptor subtypes.

GABA-A receptor subtypes in the brain: a paradigm for CNS drug discovery?

The clinical importance of benzodiazepines, barbiturates and general anesthetics, all of which act through the gamma-aminobutyric acid (GABA)-A neurotransmitter receptor, is testament to its significance as a CNS drug target. These drugs were all developed before there was any understanding of the diversity of this receptor gene family. Recent studies using genetically modified mice and GABA-A receptor-subtype-selective compounds have helped to delineate the function of some of these subtypes, and have revealed that it might be possible to develop a new generation of selective drugs with improved profiles or novel applications.

Effects of ginsenosides on GABA(A) receptor channels expressed in Xenopus oocytes.

Ginsenosides, major active ingredients of Panax ginseng, are known to regulate excitatory ligand-gated ion channel activity such as nicotinic acetylcholine and NMDA receptor channel activity. However, it is not known whether ginsenosides affect inhibitory ligand-gated ion channel activity. We investigated the effect of ginsenosides on human recombinant GABA(A) receptor (alpha1beta1gamma2S) channel activity expressed in Xenopus oocytes using a two-electrode voltage-clamp technique. Among the eight individual ginsenosides examined, namely, Rb1, Rb2, Rc, Rd, Re, Rf, Rg1 and Rg2, we found that Rc most potently enhanced the GABA-induced inward peak current (I(GABA)). Ginsenoside Rc alone induced an inward membrane current in certain batches of oocytes expressing the GABA(A) receptor. The effect of ginsenoside Rc on I(GABA) was both dose-dependent and reversible. The half-stimulatory concentration (EC50) of ginsenoside Rc was 53.2 +/- 12.3 microM. Both bicuculline, a GABA(A) receptor antagonist, and picrotoxin, a GABA(A) channel blocker, blocked the stimulatory effect of ginsenoside Rc on I(GABA). Niflumic acid (NFA) and 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), both Cl- channel blockers, attenuated the effect of ginsenoside Rc on I(GABA). This study suggests that ginsenosides regulated GABA(A) receptor expressed in Xenopus oocytes and implies that this regulation might be one of the pharmacological actions of Panax ginseng.

Enhanced learning and memory and altered GABAergic synaptic transmission in mice lacking the alpha 5 subunit of the GABAA receptor.

The alpha5 subunit of the GABA(A) receptor is localized mainly to the hippocampus of the mammalian brain. The significance of this rather distinct localization and the function of alpha5-containing GABA(A) receptors has been explored by targeted disruption of the alpha5 gene in mice. The alpha5 -/- mice showed a significantly improved performance in a water maze model of spatial learning, whereas the performance in non-hippocampal-dependent learning and in anxiety tasks were unaltered in comparison with wild-type controls. In the CA1 region of hippocampal brain slices from alpha5 -/- mice, the amplitude of the IPSCs was decreased, and paired-pulse facilitation of field EPSP (fEPSP) amplitudes was enhanced. These data suggest that alpha5-containing GABA(A) receptors play a key role in cognitive processes by controlling a component of synaptic transmission in the CA1 region of the hippocampus.