Cancer and hepatic steatosis

Non-alcoholic fatty liver disease (NAFLD) is a highly prevalent and increasing liver disease, which encompasses a variety of liver diseases of different severity. NAFLD can lead to liver cirrhosis with all its complications as well as hepatocellular carcinoma (HCC). Steatosis of the liver is not only related to obesity and other metabolic risk factors, but can also be caused by several drugs, including certain cytotoxic chemotherapeutic agents. In patients undergoing liver surgery, hepatic steatosis is associated with an increased risk of post-operative morbidity and mortality. This review paper summarizes implications of hepatic steatosis on the management of patients with cancer. Specifically, we discuss the epidemiological trends, pathophysiological mechanisms, and management of NAFLD, and its role as a leading cause of liver cancer. We elaborate on factors promoting immunosuppression in patients with NAFLD-related HCC and how this may affect the efficacy of immunotherapy. We also summarize the mechanisms and clinical course of chemotherapy-induced acute steatohepatitis (CASH) and its implications on cancer treatment, especially in patients undergoing liver resection.

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Non-alcoholic fatty liver disease can lead to cirrhosis with all its complications, including hepatocellular carcinoma.

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Chemotherapy-associated acute steatohepatitis is a side-effect of chemotherapeutic agents and may limit treatment options.

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In this review we summarize current clinical concepts of NAFLD and CASH that help clinicians in their clinical practice.

The parvalbumin-positive interneurons in the mouse dentate gyrus express GABAA receptor subunits α1, β2, and δ along their extrasynaptic cell membrane

Neuronal circuitries in the hippocampus are involved in navigation and memory and are controlled by major networks of GABAergic interneurons. Parvalbumin (PV)-expressing interneurons in the dentate gyrus (DG) are identified as fast-spiking cells, playing a crucial role in network oscillation and synchrony. The inhibitory modulation of these interneurons is thought to be mediated mainly through GABAA receptors, the major inhibitory neurotransmitter receptors in the brain. Here we show that all PV-positive interneurons in the granular/subgranular layer (GL/SGL) of the mouse DG express high levels of the GABAA receptor δ subunit. PV-containing interneurons in the hilus and the molecular layer, however, express the δ subunit to a lower extent. Only 8% of the somatostatin-containing interneurons express the δ subunit, whereas calbindin- or calretinin-containing interneurons in the DG seem not to express the GABAA receptor δ subunit at all. Hence, these cells receive a GABAergic control different from that of PV-containing interneurons in the GL/SGL. Experiments investigating a possible co-expression of GABAA receptor α1, α2, α3, α4, α5, β1, β2, β3, or γ2 subunits with PV and δ subunits indicated that α1 and β2 subunits are co-expressed with δ subunits along the extrasynaptic membranes of PV-interneurons. These results suggest a robust tonic GABAergic control of PV-containing interneurons in the GL/SGL of the DG via δ subunit-containing receptors. Our data are important for better understanding of the neuronal circuitries in the DG and the role of specific cell types under pathological conditions.

Patterns of mRNA and protein expression for 12 GABAA receptor subunits in the mouse brain

The GABA_A receptor is the main inhibitory receptor in the brain and its subunits originate from different genes or gene families (α1–α6, β1–β3, γ1–γ3, δ, ε, θ, π, or ρ1–3). In the mouse brain the anatomical distribution of GABA_A receptor subunit mRNAs so far investigated is restricted to subunits forming benzodiazepine-sensitive receptor complexes (α1–α3, α5, β2, β3 and γ2) in the forebrain and midbrain as assessed by in situ hybridization (ISH). In the present study the anatomical distribution of the GABA_A receptor subunits α1–α6, β1–β3, γ1–γ2 and δ was analyzed in the mouse brain (excluding brain stem) by ISH and immunohistochemistry (IHC). In several brain areas such as hippocampus, cerebellum, bulbus olfactorius and habenula we observed that mRNA levels did not reflect protein levels, indicating that the protein is located far distantly from the cell body. We also compared the distribution of these 12 subunit mRNAs and proteins with that reported in the rat brain. Although in general there is a considerable correspondence in the distribution between mouse and rat brains, several species-specific differences were observed.

The effects of sorafenib on the portal hypertensive syndrome in patients with liver cirrhosis and hepatocellular carcinoma--a pilot study

BACKGROUND

Increased intrahepatic vascular resistance and hyperperfusion in the splanchnic circulation are the principal mechanisms leading to portal hypertension in cirrhosis. Several preclinical studies have demonstrated a beneficial effect of the multikinase inhibitor sorafenib on the portal hypertensive syndrome.

AIM

To investigate the effect of sorafenib on hepatic venous pressure gradient (HVPG), systemic hemodynamics and intrahepatic mRNA expression of proangiogenic, profibrogenic and proinflammatory genes.

METHODS

Patients with liver fibrosis/cirrhosis and hepatocellular carcinoma were treated with sorafenib 400 mg b.d. HVPG measurement and transjugular liver biopsy were performed at baseline and at week 2. Changes in HVPG and intrahepatic mRNA expression of vascular endothelial growth factor (VEGF), platelet-derived growth factor (PDGF), RhoA, tumour necrosis factor-alpha (TNF-α) and placental growth factor (PlGF) were evaluated.

RESULTS

Thirteen patients (m/f = 12/1; Child-Pugh class A/B = 10/3) were included. The most common aetiology of liver disease was alcohol consumption (n = 7). Eleven patients had an elevated portal pressure, including eight patients with clinically significant portal hypertension. A significant decrease of HVPG (≥ 20% from baseline) was observed in four subjects. In HVPG responders, we observed mRNA downregulation of VEGF, PDGF, PlGF, RhoA kinase and TNF-α, while no substantial mRNA decrease was found in nonresponders in any of the five genes. In two of the four HVPG responders we observed a dramatic (43-85%) mRNA decrease of all five investigated genes.

CONCLUSION

Larger controlled clinical trials are needed to demonstrate any potential beneficial effect of sorafenib on portal hypertension in patients with cirrhosis.

Spatio-temporal expression analysis of the calcium-binding protein calumenin in the rodent brain

Calumenin is a Ca²⁺-binding protein that belongs to the CREC superfamily. It contains six EF-hand domains that exhibit a low affinity for Ca²⁺ as well as an endoplasmic reticulum retention signal. Calumenin exhibits a broad and relatively high expression in various brain regions during development as demonstrated by in situ hybridization. Signal intensity of calumenin is highest during the early development and then declines over time to reach a relatively low expression in adult animals. Immunohistochemistry indicates that at the P0 stage, calumenin expression is most abundant in migrating neurons in the zones around the lateral ventricle. In the brain of adult animals, it is expressed in various glial and neuronal cell types, including immature neurons in subgranular zone of hippocampal dentate gyrus. At the subcellular level, calumenin is identified in punctuate and diffuse distribution mostly in somatic regions where it co-localizes with endoplasmic reticulum (ER) and partially Golgi apparatus. Upon subcellular fractionation, calumenin is enriched in fractions containing membranes and is only weakly present in soluble fractions. This study points to a possible important role of calumenin in migration and differentiation of neurons, and/or in Ca²⁺ signaling between glial cells and neurons.

Prognostic factors in patients with advanced hepatocellular carcinoma treated with sorafenib

BACKGROUND

Sorafenib is the new reference standard for patients with advanced hepatocellular carcinoma (HCC).

AIM

To identify prognostic factors in sorafenib-treated HCC patients and to evaluate outcomes with respect to liver function.

METHODS

In this retrospective study, 148 HCC patients received sorafenib 400 mg b.d. across 11 Austrian institutions. Seventy-eight HCC patients who received best supportive care (BSC) in the pre-sorafenib era served as a control.

RESULTS

In sorafenib-treated patients, low baseline α-fetoprotein, low Child-Pugh (CP) score, compensated cirrhosis, and low baseline aspartate aminotransferase (AST) were associated with significantly longer overall survival (OS) on univariate analysis. CP score and baseline AST remained independent prognostic factors on multivariate analysis. In patients with Barcelona Clinic liver Cancer (BCLC) stage B or C HCC (sorafenib: n = 139; BSC: n = 39), CP-A patients had a median OS of 11.3 (sorafenib [n = 76]) vs. 6.4 (BSC [n = 17]) months (P = 0.010), and CP-B patients had a median OS of 5.5 (sorafenib [n = 55]) vs. 1.9 (BSC [n = 22]) months (P = 0.021). In the sorafenib group, median OS according to baseline AST was 11.8 (<100 U/L [n = 58]) vs. 3.9 (≥100 U/L [n = 15]) months for CP-A patients (P = 0.127), and 6.5 (<100 U/L [n = 33]) vs. 2.1 (≥100 U/L [n = 21]) months for CP-B patients (P = 0.011). There was no survival difference between sorafenib and BSC in patients with BCLC stage D HCC (1.5 vs. 1.4 months; P = 0.116).

CONCLUSIONS

Sorafenib was associated with improved survival in both CP-A and CP-B patients. In CP-B patients, baseline AST may be helpful in determining which patients are most likely to benefit from sorafenib.

Differential localization of GABA(A) receptor subunits in relation to rat striatopallidal and pallidopallidal synapses

As a central integrator of basal ganglia function, the external segment of the globus pallidus (GP) plays a critical role in the control of voluntary movement. The GP is composed of a network of inhibitory GABA-containing projection neurons which receive GABAergic input from axons of the striatum (Str) and local collaterals of GP neurons. Here, using electrophysiological techniques and immunofluorescent labeling we have investigated the differential cellular distribution of α1, α2 and α3 GABA(A) receptor subunits in relation to striatopallidal (Str-GP) and pallidopallidal (GP-GP) synapses. Electrophysiological investigations showed that zolpidem (100 nm; selective for the α1 subunit) increased the amplitude and the decay time of both Str-GP and GP-GP IPSCs, indicating the presence of the α1 subunits at both synapses. However, the application of drugs selective for the α2, α3 and α5 subunits (zolpidem at 400 nm, L-838,417 and TP003) revealed differential effects on amplitude and decay time of IPSCs, suggesting the nonuniform distribution of non-α1 subunits. Immunofluorescence revealed widespread distribution of the α1 subunit at both soma and dendrites, while double- and triple-immunofluorescent labeling for parvalbumin, enkephalin, gephyrin and the γ2 subunit indicated strong immunoreactivity for GABA(A) α3 subunits in perisomatic synapses, a region mainly targeted by local axon collaterals. In contrast, immunoreactivity for synaptic GABA(A) α2 subunits was observed in dendritic compartments where striatal synapses are preferentially located. Due to the kinetic properties which each GABA(A) α subunit confers, this distribution is likely to contribute differentially to both physiological and pathological patterns of activity.

Dual inhibition of EGFR and mTOR pathways in small cell lung cancer

Background:

In this report we investigated the combination of epidermal growth factor receptor (EGFR) and mammalian target of rapamycin (mTOR) pathway inhibition as a possible new therapeutic strategy for small cell lung cancer (SCLC).

Methods:

EGFR, p-AKT, p-ERK, p-mTOR and p-p70s6K protein expressions were studied by immunohistochemistry in 107 small cell lung carcinomas and correlated with clinicopathological parameters. Cells of SCLC were treated with erlotinib±RAD001 and analysed for cell viability, proliferation, autophagy, and pathway regulation.

Results:

Epidermal growth factor receptor, p-AKT, p-ERK, p-mTOR, and p-p70s6K were expressed in 37, 24, 13, 55 and 91% of the tumour specimens of all SCLC patients, respectively, and were not associated with disease-free or overall survival. The expression of EGFR was lower in neoadjuvant-treated patients (P=0.038); mTOR pathway activation was higher in the early stages of disease (P=0.048). Coexpression of EGFR/p-mTOR/p-p70s6K was observed in 28% of all patients . EGFR immunoreactivity was associated with p-ERK and p-mTOR expression (P=0.02 and P=0.0001); p-mTOR immunoreactivity was associated with p-p70s6K expression (P=0.001). Tumour cells comprised a functional EGFR, no activating mutations in exons 18–21, and resistance to RAD001 monotherapy. We found synergistic effects of erlotinib and RAD001 combination therapy on the molecular level, cell viability, proliferation and autophagy.

Conclusions:

The combined inhibition of EGFR/mTOR pathways could be a promising approach to treat SCLC.

HIV-HCV co-infected patients with low CD4+ cell nadirs are at risk for faster fibrosis progression and portal hypertension

Patients co-infected with the human immunodeficiency virus (HIV) and the hepatitis C virus (HCV) are fraught with a rapid fibrosis progression rate and with complications of portal hypertension (PHT) We aimed to assess the influence of immune function [Centers of Disease Control and Prevention (CDC) stage] on development of PHT and disease progression in HIV-HCV co-infection. Data of 74 interferon-naïve HIV-HCV co-infected patients undergoing liver biopsy, measurement of portal pressure and of liver stiffness and routine laboratory tests (including CD4+ cell count, HIV and HCV viral load) were analysed. Time of initial exposure (risk behaviour) was used to assess fibrosis progression. Fibrosis progression, time to cirrhosis and portal pressure were correlated with HIV status (CDC stage). HIV-HCV patients had rapid progression of fibrosis [0.201 +/- 0.088 METAVIR fibrosis units/year (FU/y)] and accelerated time to cirrhosis (24 +/- 13 years), high HCV viral loads (4.83 x 10(6) IU/mL) and a mean HVPG at the upper limit of normal (5 mmHg). With moderate or severe immunodeficiency, fibrosis progression was even higher (CDC-2 = 0.177 FU/y; CDC-3 = 0.248 FU/y) compared with patients with higher CD4+ nadirs (CDC-1 = 0.120 FU/y; P = 0.0001). An indirect correlation between CD4+ cell count and rate of fibrosis progression (R = -0.6654; P < 0.001) could be demonstrated. Hepatic venous pressure gradient (HVPG) showed early elevation of portal pressure with median values of 4, 8 and 12 mmHg after 10, 15 and 20 years of HCV infection for CDC-3 patients. Patients treated with highly active anti-retroviral therapy (HAART) had similar rates of progression and portal pressure values than patients without HAART. Progression of HCV disease is accelerated in HIV-HCV co-infection, being more pronounced in patients with low CD4+ cell count. A history of a CD4+ cell nadir <200/microL is a risk factor for rapid development of cirrhosis and PHT. Thus, HCV treatment should be considered early in patients with HIV-HCV co-infection and largely preserved CD4+ cell counts.

Differential role of circulating endothelial progenitor cells in cirrhotic patients with or without hepatocellular carcinoma

BACKGROUND AND AIMS

Circulating endothelial progenitor cells have a negative prognostic impact in patients with hepatocellular carcinoma, but may play a different role in portal hypertension according to preclinical data. Here, we address this issue for the first time in cirrhotic patients+/-hepatocellular carcinoma.

METHODS

Portal hypertension in cirrhotic and hepatocellular carcinoma patients was determined by hepatic venous pressure gradient. Blood cells staining positive for CD34/KDR/AC133 using flow cytometry were characterised as endothelial progenitor cells. Vascular endothelial growth factor levels were determined by ELISA.

RESULTS

Endothelial progenitor cells levels in peripheral blood were elevated in cirrhotic (n=23) (mean: 0.12+/-0.06% S.D.) and in hepatocellular carcinoma patients (n=24) (0.14+/-0.09% S.D.) relative to healthy controls (H-group, n=15) (0.06+/-0.04% S.D.) (P=0.056 and P=0.02, respectively). There were higher vascular endothelial growth factor levels in hepatocellular carcinoma patients compared to cirrhotics (P=0.047) and HC (P=0.037). Notably, hepatic venous pressure gradient was positively correlated with vascular endothelial growth factor (r=0.5, P=0.046) but negatively with endothelial progenitor cells levels (r=-0.51, P=0.02) in cirrhotics, but not hepatocellular carcinoma patients.

CONCLUSION

Circulating endothelial progenitor cells are increased in patients with portal hypertension+/-hepatocellular carcinoma. The negative correlation of endothelial progenitor cells with hepatic venous pressure gradient suggests a protective role of endothelial progenitor cells in liver cirrhosis whilst vascular endothelial growth factor is associated with high hepatic venous pressure gradient. In contrast, increased endothelial progenitor cells in hepatocellular carcinoma rather reflect tumour specific endothelial progenitor cells mobilisation.

New insights on the role of gephyrin in regulating both phasic and tonic GABAergic inhibition in rat hippocampal neurons in culture

Gephyrin is a tubulin-binding protein that acts as a scaffold for clustering glycine and GABA(A) receptors at postsynaptic sites. In this study, the role of gephyrin on GABA(A) receptor function was assessed at the post-translational level, using gephyrin-specific single chain antibody fragments (scFv-gephyrin). When expressed in cultured rat hippocampal neurons as a fusion protein containing a nuclear localization signal, scFv-gephyrin were able to remove endogenous gephyrin from GABA(A) receptor clusters. Immunocytochemical experiments revealed a significant reduction in the number of synaptic gamma2-subunit containing GABA(A) receptors and a significant decrease in the density of the GABAergic presynaptic marker vesicular GABA transporter (VGAT). These effects were associated with a slow down of the onset kinetics, a reduction in the amplitude and in the frequency of miniature inhibitory postsynaptic currents (mIPSCs). The quantitative analysis of current responses to ultrafast application of GABA suggested that changes in onset kinetics resulted from modifications in the microscopic gating of GABA(A) receptors and in particular from a reduced entry into the desensitized state. In addition, hampering gephyrin function with scFv-gephyrin induced a significant reduction in GABA(A) receptor-mediated tonic conductance. This effect was probably dependent on the decrease in GABAergic innervation and in GABA release from presynaptic nerve terminals. These results indicate that gephyrin is essential not only for maintaining synaptic GABA(A) receptor clusters in the right position but also for regulating both phasic and tonic inhibition.

Estimating the efficiency of benzodiazepines on GABA(A) receptors comprising gamma1 or gamma2 subunits

Background and purpose:

Heterologous expression of α1, β2 and γ2S(γ1) subunits produces a mixed population of GABA_A receptors containing α1β2 or α1β2γ2S(γ1) subunits. GABA sensitivity (lower in receptors containing γ1 or γ2S subunits) and the potentiation of GABA-activated chloride currents (I_GABA) by benzodiazepines (BZDs) are dependent on γ2S(γ1) incorporation. A variable γ subunit incorporation may affect the estimation of I_GABA potentiation by BZDs. We propose an approach for estimation of BZD efficiency that accounts for mixed population of α1β2 and α1β2γ2S(γ1) receptors.

Experimental approach:

We investigated the relation between GABA sensitivity (EC₅₀) and BZD modulation by analysing triazolam-, clotiazepam- and midazolam-induced potentiation of I_GABA in Xenopus oocytes under two-microelectrode voltage clamp.

Key results:

Plotting EC₅₀ versus BZD-induced shifts of GABA concentration-response curves (ΔEC₅₀(BZD)) of oocytes injected with different amounts of α1, β2 and γ2S(γ1) cRNA (1:1:1–1:1:10) revealed a linear regression between γ2S(γ1)-mediated reduction of GABA sensitivity (EC₅₀) and ΔEC₅₀(BZD). The slope factors of the regression were always higher for oocytes expressing α1β2γ1 subunit receptors (1.8±0.1 (triazolam), 1.6±0.1 (clotiazepam), 2.3±0.2 (midazolam)) than for oocytes expressing α1β2γ2S receptors (1.4±0.1 (triazolam), 1.4±0.1 (clotiazepam), 1.3±0.1 (midazolam)). Mutant GABA_A receptors (α1β2-R207Cγ2S) with lower GABA sensitivity showed higher drug efficiencies (slope factors=1.1±0.1 (triazolam), 1.1±0.1 (clotiazepam), 1.2±0.1 (midazolam)).

Conclusions and implications:

Regression analysis enabled the estimation of BZD efficiency when variable mixtures of α1β2 and α1β2γ2S(γ1) receptors are expressed and provided new insights into the γ2S(γ1) dependency of BZD action.

An updated unified pharmacophore model of the benzodiazepine binding site on gamma-aminobutyric acid(a) receptors: correlation with comparative models

A successful unified pharmacophore/receptor model which has guided the synthesis of subtype selective compounds is reviewed in light of recent developments both in ligand synthesis and structural studies of the binding site itself. The evaluation of experimental data in combination with a comparative model of the alpha1beta2gamma2 GABA(A) receptor leads to an orientation of the pharmacophore model within the Bz BS. Results not only are important for the rational design of selective ligands, but also for the identification and evaluation of possible roles which specific residues may have within the benzodiazepine binding pocket.

Effects of low dose endotoxemia on endothelial progenitor cells in humans

BACKGROUND

Endothelial progenitor cells (EPCs) are a specific subtype of hematopoietic stem cells that migrate from the bone marrow to the peripheral circulation where they contribute to the repair of injured endothelium and to the formation of new blood vessels. Levels of circulating EPCs have been investigated in different inflammatory disease states. However, data on circulating EPC levels and systemic inflammation remain scarce and contradictory.

OBJECTIVE

We investigated a putative relationship of low grade experimental endotoxemia to changes in circulating EPC levels.

METHODS

Randomized, double-blind, placebo-controlled parallel group trial in 36 healthy male volunteers. Thirty-two volunteers received 2 ng/kg LPS intravenously, the remaining four an equal volume of physiologic saline solution as placebo.

RESULTS

Endothelial progenitor cells showed a significant decrease over the observation period among the 32 subjects challenged with LPS (P<0.0001) and reached their nadir at 6 h, with a median decrease of 62% (interquartile range: 48-81%) compared with baseline levels. Circulating EPCs returned to values comparable to baseline 24 h after LPS challenge.

CONCLUSION

Infusion of 2 ng/kg LPS led to a significant decrease in peripheral EPCs. These results suggest that the early phase of acute inflammation is associated with a decrease in peripheral EPCs.

Pharmacological properties of GABAA receptors containing gamma1 subunits

GABA(A) receptors composed of alpha(1), beta(2), gamma(1) subunits are expressed in only a few areas of the brain and thus represent interesting drug targets. The pharmacological properties of this receptor subtype, however, are largely unknown. In the present study, we expressed alpha(1)beta(2)gamma(1)-GABA(A) receptors in Xenopus laevis oocytes and analyzed their modulation by 21 ligands from 12 structural classes making use of the two-microelectrode voltage-clamp method and a fast perfusion system. Modulation of GABA-induced chloride currents (I(GABA)) was studied at GABA concentrations eliciting 5 to 10% of the maximal response. Triazolam, clotiazepam, midazolam, 2-(4-methoxyphenyl)-2,3,5,6,7,8,9,10-octahydro-cyclohepta-(b)pyrazolo[4,3-d]pyridin-3-one (CGS 20625), 2-(4-chlorophenyl)-pyrazolo[4,3-c]quinolin-3-one (CGS 9896), diazepam, zolpidem, and bretazenil at 1 microM concentrations were able to significantly (>20%) enhance I(GABA) in alpha(1)beta(2)gamma(1) receptors. Methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate, 3-methyl-6-[3-trifluoromethyl-phenyl]-1,2,4-triazolo[4,3-b]pyridazine (Cl 218,872), clobazam, flumazenil, 5-(6-ethyl-7-methoxy-5-methylimidazo[1,2-a]pyrimidin-2-yl)-3-methyl-[1,2,4]-oxadiazole (Ru 33203), 2-phenyl-4-(3-ethyl-piperidinyl)-quinoline (PK 9084), flurazepam, ethyl-7-methoxy-11,12,13,13a-tetrahydro-9-oxo-9H-imidazo[1,5-a]pyrrolo[2,1-c] [1,4]benzodiazepine-1-carboxylate (l-655,708), 2-(6-ethyl-7-methoxy-5-methylimidazo[1,2-a]pyrimidin-2-yl)-4-methyl-thiazole (Ru 33356), and 6-ethyl-7-methoxy-5-methylimidazo[1,2-a]pyrimidin-2-yl)phenylmethanone (Ru 32698) (1 microM each) had no significant effect, and flunitrazepam and 2-phenyl-4-(4-ethyl-piperidinyl)-quinoline (PK 8165) inhibited I(GABA). The most potent compounds triazolam, clotiazepam, midazolam, and CGS 20625 were investigated in more detail on alpha(1)beta(2)gamma(1) and alpha(1)beta(2)gamma(2S) receptors. The potency and efficiency of these compounds for modulating I(GABA) was smaller for alpha(1)beta(2)gamma(1) than for alpha(1)beta(2)gamma(2S) receptors, and their effects on alpha(1)beta(2)gamma(1) could not be blocked by flumazenil. CGS 20625 displayed the highest efficiency by enhancing at 100 microM I(GABA) (alpha(1)beta(2)gamma(2)) by 775 +/- 17% versus 526 +/- 14% I(GABA) (alpha(1)beta(2)gamma(1)) and 157 +/- 17% I(GABA) (alpha(1)beta(2)) (p < 0.05). These data provide new insight into the pharmacological properties of GABA(A) receptors containing gamma(1) subunits and may aid in the design of specific ligands for this receptor subtype.

Loss of zolpidem efficacy in the hippocampus of mice with the GABAA receptor gamma2 F77I point mutation

Zolpidem is a hypnotic benzodiazepine site agonist with some gamma-aminobutyric acid (GABA)(A) receptor subtype selectivity. Here, we have tested the effects of zolpidem on the hippocampus of gamma2 subunit (gamma2F77I) point mutant mice. Analysis of forebrain GABA(A) receptor expression with immunocytochemistry, quantitative [(3)H]muscimol and [(35)S] t-butylbicyclophosphorothionate (TBPS) autoradiography, membrane binding with [(3)H]flunitrazepam and [(3)H]muscimol, and comparison of miniature inhibitory postsynaptic current (mIPSC) parameters did not reveal any differences between homozygous gamma2I77/I77 and gamma2F77/F77 mice. However, quantitative immunoblot analysis of gamma2I77/I77 hippocampi showed some increased levels of gamma2, alpha1, alpha4 and delta subunits, suggesting that differences between strains may exist in unassembled subunit levels, but not in assembled receptors. Zolpidem (1 microm) enhanced the decay of mIPSCs in CA1 pyramidal cells of control (C57BL/6J, gamma2F77/F77) mice by approximately 60%, and peak amplitude by approximately 20% at 33-34 degrees C in vitro. The actions of zolpidem (100 nm or 1 microm) were substantially reduced in gamma2I77/I77 mice, although residual effects included a 9% increase in decay and 5% decrease in peak amplitude. Similar results were observed in CA1 stratum oriens/alveus interneurons. At network level, the effect of zolpidem (10 microm) on carbachol-induced oscillations in the CA3 area of gamma2I77/I77 mice was significantly different compared with controls. Thus, the gamma2F77I point mutation virtually abolished the actions of zolpidem on GABA(A) receptors in the hippocampus. However, some residual effects of zolpidem may involve receptors that do not contain the gamma2 subunit.

No association of clock gene T3111C polymorphism and affective disorders

CLOCK was hypothesised to be related to susceptibility of affective disorders. To test subsamples of affectively disordered patients, we examined age of onset (AoO), numbers of episodes and melancholic type of clinical manifestation. Using PCR and RFLP, we investigated in patients with unipolar depression and bipolar disorder (BP) whether the CLOCK T3111C SNP is associated with affective disorders (n=102) compared to healthy controls (n=103). No differences were found either in genotype or allele frequency distributions of T3111C polymorphism between patients compared to healthy controls (p>0.2). No deviations from Hardy-Weinberg Equilibrium (HWE) were detected either in patients, or healthy controls. Results suggest that there is no association between the T3111C SNP and affective disorders in general. Data of our sample replicate prior findings of Desan et al. [Am. J. Med. Genet. 12 (2000) 418]. Subsamples of patients with high numbers of affective episodes did show some deviations in genotypes (p=0.0585).

Abolition of zolpidem sensitivity in mice with a point mutation in the GABAA receptor gamma2 subunit

Agonists of the allosteric benzodiazepine site of GABAA receptors bind at the interface of the alpha and gamma subunits. Here, we tested the in vivo contribution of the gamma2 subunit to the actions of zolpidem, an alpha1 subunit selective benzodiazepine agonist, by generating mice with a phenylalanine (F) to isoleucine (I) substitution at position 77 in the gamma2 subunit. The gamma2F77I mutation has no major effect on the expression of GABAA receptor subunits in the cerebellum. The potency of zolpidem, but not that of flurazepam, for the inhibition of [3H]flunitrazepam binding to cerebellar membranes is greatly reduced in gamma2I77/I77 mice. Zolpidem (1 microM) increased both the amplitude and decay of miniature inhibitory postsynaptic currents (mIPSCs) in Purkinje cells of control C57BL/6 (34% and 92%, respectively) and gamma2F77/F77 (20% and 84%) mice, but not in those of gamma2F77I mice. Zolpidem tartrate had no effect on exploratory activity (staircase test) or motor performance (rotarod test) in gamma2I77/I77 mice at doses up to 30 mg/kg (i.p.) that strongly sedated or impaired the control mice. Flurazepam was equally effective in enhancing mIPSCs and disrupting performance in the rotarod test in control and gamma2I77/I77 mice. These results show that the effect of zolpidem, but not flurazepam, is selectively eliminated in the brain by the gamma2F77I point mutation.

A polymorphism (5-HTTLPR) in the serotonin transporter promoter gene is associated with DSM-IV depression subtypes in seasonal affective disorder

Serotonergic mechanisms are thought to play an important role in the pathogenesis of seasonal affective disorder (SAD). The expression of the serotonin transporter (5-HTT) is regulated in part by an insertion/deletion polymorphism in the serotonin transporter gene promoter region (5-HTTLPR). The 5-HTTLPR short allele (s) has been associated with anxiety-related personality traits and depression, and one study observed an association between the 5-HTTLPR s-allele and SAD and the trait of seasonality. We genotyped 138 SAD patients and 146 healthy volunteers with low seasonality for 5-HTTLPR. No difference between patients and controls was found for genotype distribution and s-allele frequency. However, genotype distribution and allele frequencies were strongly associated with DSM-IV depression subtypes. Melancholic depression was associated with the 5-HTTLPR long (l) allele and atypical depression with the 5-HTTLPR s-allele (two-sided Fisher's exact test: genotype distribution: P=0.0038; allele frequencies: P=0.007). Our data are compatible with the hypothesis of a disease process that is not causally related to 5-HTTLPR, but involves 5-HT neurotransmission and 5-HTTLPR somewhere on its way to phenotypic disease expression.

Comparative modeling of GABA(A) receptors: limits, insights, future developments

GABA(A) receptors are chloride ion channels that mediate fast synaptic transmission and belong to a superfamily of pentameric ligand-gated ion channels. The recently published crystal structure of the acetylcholine binding protein can be used as a template for comparative modeling of the extracellular domain of GABA(A) receptors. In this commentary, difficulties with comparative modeling at low sequence identity are discussed, the degree of structural conservation to be expected within the superfamily is analyzed and numerical estimates of model uncertainties in functional regions are provided. Topography of the binding sites at subunit-interfaces is examined and possible targets for rational mutagenesis studies are suggested. Allosteric motions are considered and a mechanism for mediation of positive cooperativity at the benzodiazepine site is proposed.

Ectopic expression of the GABA(A) receptor alpha6 subunit in hippocampal pyramidal neurons produces extrasynaptic receptors and an increased tonic inhibition

We generated transgenic (Thy1alpha6) mice in which the GABA(A) receptor alpha6 subunit, whose expression is usually confined to granule cells of cerebellum and cochlear nuclei, is ectopically expressed under the control of the pan-neuronal Thy-1.2 promoter. Strong Thy1alpha6 subunit expression occurs, for example, in deep cerebellar nuclei, layer V iscocortical and hippocampal pyramidal cells and dentate granule cells. Ligand binding and protein biochemistry show that most forebrain alpha6 subunits assemble as alpha6betagamma2-type receptors, and some as alpha1alpha6betagamma2 and alpha3alpha6betagamma2 receptors. Electron microscopic immunogold labeling shows that most Thy1-derived alpha6 immunoreactivity is in the extrasynaptic plasma membrane of dendrites and spines in both layer V isocortical and CA1pyramidal cells. Synaptic immunolabeling is rare. Consistent with the alpha6 subunits' extrasynaptic localization, Thy1alpha6 CA1 pyramidal neurons have a five-fold increased tonic GABA(A) receptor-mediated current compared with wild-type cells; however, the spontaneous IPSC frequency and the mIPSC amplitude in Thy1alpha6 mice decrease 37 and 30%, respectively compared with wild-type. Our results strengthen the idea that GABA(A) receptors containing alpha6 subunits can function as extrasynaptic receptors responsible for tonic inhibition and further suggest that a homeostatic mechanism might operate, whereby increased tonic inhibition causes a compensatory decrease in synaptic GABA(A) receptor responses.

Homologous sites of GABA(A) receptor alpha(1), beta(3) and gamma(2) subunits are important for assembly

GABA(A) receptors are the major inhibitory transmitter receptors in the central nervous system. The majority of these receptors is composed of two alpha, two beta and one gamma subunit that assemble around an aqueous pore and form an intrinsic chloride ion channel. Using full-length or truncated chimeric subunits it was demonstrated that homologous sequences from different subunit classes, alpha(1)(54-68), beta(3)(52-66), and gamma(2)(67-81), are important for assembly of GABA(A) receptors composed of alpha(1), beta(3), and gamma(2) subunits. In addition, evidence was provided that these sequences all are located in topologically homologous regions of the different subunits. Finally, it was demonstrated that the sequences investigated cause a selective assembly with certain subunits only and thus influence subunit arrangement within GABA(A) receptors.

Subunit composition, distribution and function of GABA(A) receptor subtypes

GABA(A) receptors are the major inhibitory neurotransmitter receptors in the brain and are the site of action of many clinically important drugs. These receptors are composed of five subunits that can belong to eight different subunit classes. Depending on their subunit composition, these receptors exhibit distinct pharmacological and electrophysiological properties. Recent studies on recombinant and native GABA(A) receptors suggest the existence of far more receptor subtypes than previously assumed. Thus, receptors composed of one, two, three, four, or five different subunits might exist in the brain. Studies on the regional, cellular and subcellular distribution of GABA(A) receptor subunits, and on the co-localization of these subunits at the light and electron microscopic level for the first time provide information on the distribution of GABA(A) receptor subtypes in the brain. These studies will have to be complemented by electrophysiological and pharmacological studies on the respective recombinant and native receptors to finally identify the receptor subtypes present in the brain. The distinct cellular and subcellular location of individual receptor subtypes suggests that they exhibit specific functions in the brain that can be selectively modulated by subtype specific drugs. This conclusion is supported by the recent demonstration that different GABA(A) receptor subtypes mediate different effects of benzodiazepines. Together, these results should cause a revival of GABA(A) receptor research and strongly stimulate the development of drugs with a higher selectivity for alpha2-, alpha3-, or alpha5-subunit-containing receptor subtypes. Such drugs might exhibit quite selective clinical effects.

Altered receptor subtypes in the forebrain of GABA(A) receptor delta subunit-deficient mice: recruitment of gamma 2 subunits

A GABA(A) receptor delta subunit-deficient mouse line was created by homologous recombination in embryonic stem cells to investigate the role of the subunit in the brain GABA(A) receptors. High-affinity [(3)H]muscimol binding to GABA sites as studied by ligand autoradiography was reduced in various brain regions of delta(-/-) animals. [(3)H]Ro 15-4513 binding to benzodiazepine sites was increased in delta(-/-) animals, partly due to an increment of diazepam-insensitive receptors, indicating an augmented forebrain assembly of gamma 2 subunits with alpha 4 subunits. In the western blots of forebrain membranes of delta(-/-) animals, the level of gamma 2 subunit was increased and that of alpha 4 decreased, while the level of alpha1 subunits remained unchanged. In the delta(-/-) forebrains, the remaining alpha 4 subunits were associated more often with gamma 2 subunits, since there was an increase in the alpha 4 subunit level immunoprecipitated by the gamma 2 subunit antibody. The pharmacological properties of t-butylbicyclophosphoro[(35)S]thionate binding to the integral ion-channel sites were slightly altered in the forebrain and cerebellum, consistent with elevated levels of alpha 4 gamma 2 and alpha 6 gamma 2 subunit-containing receptors, respectively.The altered pharmacology of forebrain GABA(A) receptors and the decrease of the alpha 4 subunit level in delta subunit-deficient mice suggest that the delta subunit preferentially assembles with the alpha 4 subunit. The delta subunit seems to interfere with the co-assembly of alpha 4 and gamma 2 subunits and, therefore, in its absence, the gamma 2 subunit is recruited into a larger population of alpha 4 subunit-containing functional receptors. These results support the idea of subunit competition during the assembly of native GABA(A) receptors.

Alternate use of distinct intersubunit contacts controls GABAA receptor assembly and stoichiometry

GABA(A) receptors are the major inhibitory transmitter receptors in the CNS. Recombinant GABA(A) receptors composed of alpha(1)beta(3)gamma(2) subunits have been demonstrated to assemble as pentamers consisting of two alpha(1), two beta(3), and one gamma(2) subunit. Using truncated and chimeric alpha(1) subunits, we identified the alpha(1)(80-100) sequence as a major binding site for gamma(2) subunits. In addition, we demonstrated its direct interaction with gamma(2)(91-104), a sequence that previously has been identified to form the contact to alpha(1) subunits. The observation that the amino acid residues alpha(1)P96 and alpha(1)H101, which can be photolabeled by [(3)H]flunitrazepam, are located within or adjacent to the alpha(1)(80-100) sequence, indicates that the benzodiazepine binding site of GABA(A) receptors is located close to this intersubunit contact. The observation that alpha(1)(80-100) interacts with gamma(2) but not with beta(3) subunits indicates the existence of an additional beta(3) binding site on alpha(1) subunits. The preferred alternate use of the gamma(2) and beta(3) binding sites in two different alpha(1) subunits of the same receptor ensures the incorporation of only a single gamma(2) subunit and thus, determines subunit stoichiometry of alpha(1)beta(3)gamma(2) receptors. Distinct binding sites and their alternate use can therefore explain how subunits of hetero-oligomeric transmembrane proteins assemble into a defined protein complex.

GABA influences the development of the ventromedial nucleus of the hypothalamus

The region that becomes the ventromedial nucleus of the hypothalamus (VMH) is surrounded by cells and fibers containing immunoreactive gamma-aminobutyric acid (GABA) by embryonic day 13 (E13), several days before the nucleus emerges in Nissl stains. As GABA plays many roles during neural development, we hypothesized that it influences VMH development, perhaps by providing boundary information for migrating neurons. To test this hypothesis we examined the VMH in embryonic mice in which the beta3 subunit of the GABA(A)-receptor, a receptor subunit that is normally highly expressed in this nucleus, was disrupted by gene targeting. In beta3 -/- embryos the VMH was significantly larger, and the distribution of cells containing immunoreactive estrogen receptor-alpha was expanded compared to controls. Using in vitro brain slices from wild-type C57BL/6J mice killed at E15 we found that treatment with the GABA(A) antagonist bicuculline increased the number of cells migrating per video field analyzed in the VMH. In addition, treatment with either bicuculline or the GABA(A) agonist muscimol altered the orientation of cell migration in particular regions of this nucleus. These data suggest that GABA is important for the organization of cells during VMH formation.

No evidence for in vivo regulation of midbrain serotonin transporter availability by serotonin transporter promoter gene polymorphism

BACKGROUND

A polymorphism in the serotonin transporter promoter gene region (5-HTTLPR) has been shown to influence the quantity of serotonin transporter expressed in human cell lines: the 5-HTTLPR short allele (s) has been associated with reduced 5-HTT expression when compared to cells carrying the 5-HTTLPR long allele (l). We performed a single photon emission computed tomography (SPECT) study using the ligand [(123)I]-2-beta-carbomethoxy-3-beta-(4-iodophenyl)tropane ([(123)I]-beta-CIT) to measure 5-HTT availability in 16 healthy subjects genotyped for 5-HTTLPR.

METHODS

SPECT scans were performed 24 hours after tracer injection, regions of interest anatomically corresponding to the thalamus-hypothalamus and mesencephalon-pons areas were compared to the binding in the cerebellum, representing the nondisplaceable [(123)I]-beta-CIT-binding (results expressed as target activity minus cerebellum activity/cerebellum activity). DNA from peripheral nuclear blood cells was genotyped for 5-HTTLPR using standard polymerase chain reaction methods.

RESULTS

Specific binding ratios in the thalamus-hypothalamus were 2.65 +/- 0.4 in subjects with the l/l genotype (n = 3), 2.76 +/- 0.5 in subjects with the l/s genotype (n = 9), and 2.77 +/- 0.4 in subjects with the s/s genotype (n = 4). Binding ratios in the mesencephalon-pons were 1.43 +/- 0.3 (l/l; n = 3), 1.37 +/- 0.3 (l/s; n = 9), and 1.28 +/- 0.3 (s/s; n = 4). None of these differences was statistically significant.

CONCLUSIONS

Our data provide no evidence for in vivo functional regulation of 5-HTT availability by 5-HTTLPR in the thalamus-hypothalamus and mesencephalon-pons of healthy subjects.

Differential Cross Talk of ROD Compounds with the Benzodiazepine Binding Site

We have recently identified a novel class of allosteric modulators of GABA(A) receptors, the ROD compounds that are structurally related to bicuculline. Here, the relationship of their site of action relative to other known modulatory sites of this receptor was investigated. Two types of ROD compounds, R1 (ROD164A, ROD185) and R2 (ROD222 and ROD259) could be differentiated. R1 compounds competitively inhibited binding of benzodiazepines in alpha1beta2gamma2 receptors, and their functional effects were partially inhibited by the benzodiazepine antagonist Ro15-1788 in a noncompetitive manner. The enhancement by an R1 compound was not additive with that by diazepam. R2 compounds in contrast failed to inhibit binding of benzodiazepines; the R2 compounds' functional effects were not inhibited by the benzodiazepine antagonist. The enhancement by an R2 compound was additive with that by diazepam. In contrast to benzodiazepines, both R1 and R2 type compounds were still able to enhance alpha1beta2 receptors. ROD164A in alpha1beta2gamma2 receptors was found to be partially antagonized by Ro15-1788 in a noncompetitive way. ROD178B did not affect gamma-aminobutyric acid induced currents, but was able to inhibit both enhancement by R1 and R2 type compounds as well as enhancement by diazepam. R1 and R2 type compounds as well as diazepam enhanced pentobarbital-induced currents in a Ro15-1788-sensitive way. We conclude that R1 type compounds act at the benzodiazepine binding site and additionally at a different R1 site, and that the R1, but not the R2 site is allosterically coupled to the benzodiazepine binding site. ROD178B is a competitive antagonist at the R1 site in that it shows allosteric interaction with the benzodiazepine binding site and displacement of benzodiazepines, and a negative allosteric modulator at the R2 site.

Distribution of the major gamma-aminobutyric acid(A) receptor subunits in the basal ganglia and associated limbic brain areas of the adult rat

Within the basal ganglia, gamma-aminobutyric acid (GABA) exerts a fundamental role as neurotransmitter of local circuit and projection neurons. Its fast hyperpolarizing action is mediated through GABA(A) receptors. These ligand-gated chloride channels are assembled from five subunits, which derive from multiple genes. Using immunocytochemistry, we investigated the distribution of 12 major GABA(A) receptor subunits (alpha1-5, beta1-3, gamma1-3, and delta) in the basal ganglia and associated limbic brain areas of the rat. Immunoreactivity for an additional subunit (subunit alpha6) was not observed. The striatum, the nucleus accumbens, and the olfactory tubercle displayed strong, diffuse staining for the subunits alpha2, alpha4, beta3, and delta presumably located on dendrites of the principal medium spiny neurons. Subunit alpha1-, beta2-, and gamma2-immunoreactivities were apparently mostly restricted to interneurons of these areas. In contrast, the globus pallidus, the entopeduncular nucleus, the ventral pallidum, the subthalamic nucleus, and the substantia nigra pars reticulata revealed dense networks of presumable dendrites of resident projection neurons, which were darkly labeled for subunit alpha1-, beta2-, and gamma2-immunoreactivities. The globus pallidus, ventral pallidum, entopeduncular nucleus, and substantia nigra pars reticulata, all areas receiving innervations from the striatum, displayed strong subunit gamma1-immunoreactivity compared to other brain areas. In the substantia nigra pars compacta and in the ventral tegmental area, numerous presumptive dopaminergic neurons were labeled for subunits alpha3, gamma3, and/or delta. This highly heterogeneous distribution of individual GABA(A) receptor subunits suggests the existence of differently assembled, and presumably also functionally different, GABA(A) receptors within individual nuclei of the basal ganglia and associated limbic brain areas.

Detection and binding properties of GABA(A) receptor assembly intermediates

Density gradient centrifugation of native and recombinant gamma-aminobutyric acid, type A (GABA(A)) receptors was used to detect assembly intermediates. No such intermediates could be identified in extracts from adult rat brain or from human embryonic kidney (HEK) 293 cells transfected with alpha(1), beta(3), and gamma(2) subunits and cultured at 37 degrees C. However, subunit dimers, trimers, tetramers, and pentamers were found in extracts from the brain of 8-10-day-old rats and from alpha(1)beta(3)gamma(2) transfected HEK cells cultured at 25 degrees C. In both systems, alpha(1), beta(3), and gamma(2) subunits could be identified in subunit dimers, indicating that different subunit dimers are formed during GABA(A) receptor assembly. Co-transfection of HEK cells with various combinations of full-length and C-terminally truncated alpha(1) and beta(3) or alpha(1) and gamma(2) subunits and co-immunoprecipitation with subunit-specific antibodies indicated that even subunits containing no transmembrane domain can assemble with each other. Whereas alpha(1)gamma(2), alpha(1)Ngamma(2), alpha(1)gamma(2)N, and alpha(1)Ngamma(2)N, combinations exhibited specific [(3)H]Ro 15-1788 binding, specific [(3)H]muscimol binding could only be found in alpha(1)beta(3) and alpha(1)beta(3)N, but not in alpha(1)Nbeta(3) or alpha(1)Nbeta(3)N combinations. This seems to indicate that a full-length alpha(1) subunit is necessary for the formation of the muscimol-binding site and for the transduction of agonist binding into channel gating.

GABA expression dominates neuronal lineage progression in the embryonic rat neocortex and facilitates neurite outgrowth via GABA(A) autoreceptor/Cl- channels

GABA emerges as a trophic signal during rat neocortical development in which it modulates proliferation of neuronal progenitors in the ventricular/subventricular zone (VZ/SVZ) and mediates radial migration of neurons from the VZ/SVZ to the cortical plate/subplate (CP/SP) region. In this study we investigated the role of GABA in the earliest phases of neuronal differentiation in the CP/SP. GABAergic-signaling components emerging during neuronal lineage progression were comprehensively characterized using flow cytometry and immunophenotyping together with physiological indicator dyes. During migration from the VZ/SVZ to the CP/SP, differentiating cortical neurons became predominantly GABAergic, and their dominant GABA(A) receptor subunit expression pattern changed from alpha4beta1gamma1 to alpha3beta3gamma2gamma3 coincident with an increasing potency of GABA on GABA(A) receptor-mediated depolarization. GABA(A) autoreceptor/Cl(-) channel activity in cultured CP/SP neurons dominated their baseline potential and indirectly their cytosolic Ca(2+) (Ca(2+)c) levels via Ca(2+) entry through L-type Ca(2+) channels. Block of this autocrine circuit at the level of GABA synthesis, GABA(A) receptor activation, intracellular Cl(-) ion homeostasis, or L-type Ca(2+) channels attenuated neurite outgrowth in most GABAergic CP/SP neurons. In the absence of autocrine GABAergic signaling, neuritogenesis could be preserved by depolarizing cells and elevating Ca(2+)c. These results reveal a morphogenic role for GABA during embryonic neocortical neuron development that involves GABA(A) autoreceptors and L-type Ca(2+) channels.

Targeted disruption of the GABA(A) receptor delta subunit gene leads to an up-regulation of gamma 2 subunit-containing receptors in cerebellar granule cells

GABA(A) receptors are chloride channels composed of five subunits. Cerebellar granule cells express abundantly six subunits belonging to four subunit classes. These are assembled into a number of distinct receptors, but the regulation of their relative proportions is yet unknown. Here, we studied the composition of cerebellar GABA(A) receptors after targeted disruption of the delta subunit gene. In membranes and extracts of delta-/- cerebellum, [(3)H]muscimol binding was not significantly changed, whereas [(3)H]Ro15-4513 binding was increased by 52% due to an increase in diazepam-insensitive binding. Immunocytochemical and Western blot analysis revealed no change in alpha(6) subunits but an increased expression of gamma(2) subunits in delta-/- cerebellum. Immunoaffinity chromatography of cerebellar extracts indicated there was an increased coassembly of alpha(6) and gamma(2) subunits and that 24% of all receptors in delta-/- cerebellum did not contain a gamma subunit. Because 97% of delta subunits are coassembled with alpha(6) subunits in the cerebellum of wild-type mice, these results indicated that, in delta-/- mice, alpha(6)betagamma(2) and alphabeta receptors replaced delta subunit-containing receptors. The availability of the delta subunit, thus, influences the level of expression or the extent of assembly of the gamma(2) subunit, although these two subunits do not occur in the same receptor.

Two novel residues in M2 of the gamma-aminobutyric acid type A receptor affecting gating by GABA and picrotoxin affinity

An amino acid residue was found in M2 of gamma-aminobutyric acid (GABA) type A receptors that has profound effects on the binding of picrotoxin to the receptor and therefore may form part of its binding pocket. In addition, it strongly affects channel gating. The residue is located N-terminally to residues suggested so far to be important for channel gating. Point mutated alpha1beta(3) receptors were expressed in Xenopus oocytes and analyzed using the electrophysiological techniques. Coexpression of the alpha(1) subunit with the mutated beta(3) subunit beta(3)L253F led to spontaneous picrotoxin-sensitive currents in the absence of GABA. Nanomolar concentrations of GABA further promoted channel opening. Upon washout of picrotoxin, a huge transient inward current was observed. The reversal potential of the inward current was indicative of a chloride ion selectivity. The amplitude of the inward current was strongly dependent on the picrotoxin concentration and on the duration of its application. There was more than a 100-fold decrease in picrotoxin affinity. A kinetic model is presented that mimics the gating behavior of the mutant receptor. The point mutation in the neighboring residue beta(3)A252V resulted in receptors that displayed an about 6-fold increased apparent affinity to GABA and an about 10-fold reduced sensitivity to picrotoxin.

GABA(A) receptors: immunocytochemical distribution of 13 subunits in the adult rat brain

GABA(A) receptors are ligand-operated chloride channels assembled from five subunits in a heteropentameric manner. Using immunocytochemistry, we investigated the distribution of GABA(A) receptor subunits deriving from 13 different genes (alpha1-alpha6, beta1-beta3, gamma1-gamma3 and delta) in the adult rat brain. Subunit alpha1-, beta1-, beta2-, beta3- and gamma2-immunoreactivities were found throughout the brain, although differences in their distribution were observed. Subunit alpha2-, alpha3-, alpha4-, alpha5-, alpha6-, gamma1- and delta-immunoreactivities were more confined to certain brain areas. Thus, alpha2-subunit-immunoreactivity was preferentially located in forebrain areas and the cerebellum. Subunit alpha6-immunoreactivity was only present in granule cells of the cerebellum and the cochlear nucleus, and subunit gamma1-immunoreactivity was preferentially located in the central and medial amygdaloid nuclei, in pallidal areas, the substantia nigra pars reticulata and the inferior olive. The alpha5-subunit-immunoreactivity was strongest in Ammon's horn, the olfactory bulb and hypothalamus. In contrast, alpha4-subunit-immunoreactivity was detected in the thalamus, dentate gyrus, olfactory tubercle and basal ganglia. Subunit alpha3-immunoreactivity was observed in the glomerular and external plexiform layers of the olfactory bulb, in the inner layers of the cerebral cortex, the reticular thalamic nucleus, the zonal and superficial layers of the superior colliculus, the amygdala and cranial nerve nuclei. Only faint subunit gamma3-immunoreactivity was detected in most areas; it was darkest in midbrain and pontine nuclei. Subunit delta-immunoreactivity was frequently co-distributed with alpha4 subunit-immunoreactivity, e.g. in the thalamus, striatum, outer layers of the cortex and dentate molecular layer. Striking examples of complementary distribution of certain subunit-immunoreactivities were observed. Thus, subunit alpha2-, alpha4-, beta1-, beta3- and delta-immunoreactivities were considerably more concentrated in the neostriatum than in the pallidum and entopeduncular nucleus. In contrast, labeling for the alpha1-, beta2-, gamma1- and gamma2-subunits prevailed in the pallidum compared to the striatum. With the exception of the reticular thalamic nucleus, which was prominently stained for subunits alpha3, beta1, beta3 and gamma2, most thalamic nuclei were rich in alpha1-, alpha4-, beta2- and delta-immunoreactivities. Whereas the dorsal lateral geniculate nucleus was strongly immunoreactive for subunits alpha4, beta2 and delta, the ventral lateral geniculate nucleus was predominantly labeled for subunits alpha2, alpha3, beta1, beta3 and gamma2; subunit alpha1- and alpha5-immunoreactivities were about equally distributed in both areas. In most hypothalamic areas, immunoreactivities for subunits alpha1, alpha2, beta1, beta2 and beta3 were observed. In the supraoptic nucleus, staining of conspicuous dendritic networks with subunit alpha1, alpha2, beta2, and gamma2 antibodies was contrasted by perykarya labeled for alpha5-, beta1- and delta-immunoreactivities. Among all brain regions, the median emminence was most heavily labeled for subunit beta2-immunoreactivity. In most pontine and cranial nerve nuclei and in the medulla, only subunit alpha1-, beta2- and gamma2-immunoreactivities were strong, whereas the inferior olive was significantly labeled only for subunits beta1, gamma1 and gamma2. In this study, a highly heterogeneous distribution of 13 different GABA(A) receptor subunit-immunoreactivities was observed. This distribution and the apparently typical patterns of co-distribution of these GABA(A) receptor subunits support the assumption of multiple, differently assembled GABA(A) receptor subtypes and their heterogeneous distribution within the adult rat brain.

Genome scan for susceptibility loci for schizophrenia

OBJECTIVE

Schizophrenia is a relatively common, often chronic and debilitating mental illness. Evidence from various studies has clearly demonstrated that genetic factors contribute substantially to the etiology. The goal of this study was to identify chromosomal regions likely to contain schizophrenia susceptibility genes.

METHODS

A genome-wide map of 388 microsatellite DNA markers was genotyped in 5 schizophrenia families. Nonparametric linkage analysis (Genehunter) was used to assess the pattern of allele sharing at each marker locus relative to the presence of disease.

RESULTS

Nonparametric linkage scores did not reach a genome-wide level of statistical significance (p < 0.00002) or a p value suggestive of linkage (p < 0.007) for any marker; however, one p value suggested replicated linkage (p < 0.01) at chromosome 6p24 in region D6S309 (p = 0.0047). Furthermore, 11 markers resulted in p < 0.05 at chromosomes 6p, 6q, 10q, 12q and 14q.

CONCLUSIONS

Despite the differences in diagnostic schemes, in markers used and methods of analyses between studies published so far, we think that our result supports the notion that there is possibly some consistent evidence for replicated linkage of a schizophrenia susceptibility locus around the region of D6S309 at chromosome 6p24.

Association studies of candidate genes in bipolar disorders

The aim of the investigation was to test genes for predisposition to bipolar affective disorder. Therefore, we studied candidate genes in a sample of unrelated patients (n = 102) and healthy controls (n = 79) of Austrian origin, searching for a possible association between polymorphic DNA markers of 5 candidate genes (serotonin transporter, 5-HTT; serotonin 2a receptor, 5-HT2a; dopamine D2 receptor, DRD2; dopamine D3 receptor, DRD3; dopamine transporter, DAT1) and bipolar disorder. There was an association between allelic and genotypic frequencies of 5-HTT and affection status (p = 0.014 and p = 0.017, respectively). However, after correction for multiple comparisons (Bonferroni), these results did not remain significant. Nevertheless, the findings might suggest that alterations in the structure of 5-HTT are involved in the pathogenesis of bipolar disorder, which could have major implications in treatment. No association between 5-HT2a, DRD2, DRD3, DAT1 and bipolar disorder was found.

Gamma-aminobutyric acid receptor (GABA(A)) subunits in rat nucleus tractus solitarii (NTS) revealed by polymerase chain reaction (PCR) and immunohistochemistry

Expression of mRNAs encoding seven GABA(A) receptor subunits (alpha1, alpha2, alpha3, alpha5, beta2, beta3, gamma2) in the nucleus tractus solitarii (NTS) of rat medulla oblongata was examined by reverse transcription-polymerase chain reaction (RT-PCR). All subunit mRNAs, except alpha5, were clearly detected. Band densities produced by alpha1, alpha3, beta3, and gamma2 subunits were greater than those corresponding to beta2 and alpha2 transcripts. The localization of these subunits in tissue sections through NTS was examined by immunohistochemistry. The differential patterns of immunoreactivity in neuronal somata and dendrites of NTS neurons were generally in agreement with the PCR results, confirming that mRNA expression is correlated with receptor protein synthesis. At ultrastructural level, alpha1, alpha3, beta2/3, and gamma2 subunits were localized in both cytoplasmic and subsynaptic sites, the latter often apposed to GABA immunoreactive synapses. These results suggest that ionotropic receptors comprising the alpha1, alpha3, beta2/3, and gamma2 may mediate inhibitory GABA responses in the NTS.

GABAA receptor phosphorylation and functional modulation in cortical neurons by a protein kinase C-dependent pathway

GABA(A) receptors are critical mediators of fast synaptic inhibition in the brain, and the predominant receptor subtype in the central nervous system is believed to be a pentamer composed of alpha, beta, and gamma subunits. Previous studies on recombinant receptors have shown that protein kinase C (PKC) and PKA directly phosphorylate intracellular serine residues within the receptor beta subunit and modulate receptor function. However, the relevance of this regulation for neuronal receptors remains poorly characterized. To address this critical issue, we have studied phosphorylation and functional modulation of GABA(A) receptors in cultured cortical neurons. Here we show that the neuronal beta3 subunit is basally phosphorylated on serine residues by a PKC-dependent pathway. PKC inhibitors abolish basal phosphorylation, increasing receptor activity, whereas activators of PKC enhance beta3 phosphorylation with a concomitant decrease in receptor activity. PKA activators were shown to increase the phosphorylation of the beta3 subunit only in the presence of PKC inhibitors. We also show that the main sites of phosphorylation within the neuronal beta3 subunit are likely to include Ser-408 and Ser-409, residues that are important for the functional modulation of beta3-containing recombinant receptors. Furthermore, PKC activation did not change the total number of GABA(A) receptors in the plasma membrane, suggesting that the effects of PKC activation are on the gating or conductance of the channel. Together, these results illustrate that cell-signaling pathways that activate PKC may have profound effects on the efficacy of synaptic inhibition by directly modulating GABA(A) receptor function.

gamma-Aminobutyric acid, acting through gamma -aminobutyric acid type A receptors, inhibits the biosynthesis of neurosteroids in the frog hypothalamus

Most of the actions of neurosteroids on the central nervous system are mediated through allosteric modulation of the gamma-aminobutyric acid type A (GABA(A)) receptor, but a direct effect of GABA on the regulation of neurosteroid biosynthesis has never been investigated. In the present report, we have attempted to determine whether 3beta-hydroxysteroid dehydrogenase (3beta-HSD)-containing neurons, which secrete neurosteroids in the frog hypothalamus, also express the GABA(A) receptor, and we have investigated the effect of GABA on neurosteroid biosynthesis by frog hypothalamic explants. Double immunohistochemical labeling revealed that most 3beta-HSD-positive neurons also contain GABA(A) receptor alpha(3) and beta(2)/beta(3) subunit-like immunoreactivities. Pulse-chase experiments showed that GABA inhibited in a dose-dependent manner the conversion of tritiated pregnenolone into radioactive steroids, including 17-hydroxy-pregnenolone, progesterone, 17-hydroxy-progesterone, dehydroepiandrosterone, and dihydrotestosterone. The effect of GABA on neurosteroid biosynthesis was mimicked by the GABA(A) receptor agonist muscimol but was not affected by the GABA(B) receptor agonist baclofen. The selective GABA(A) receptor antagonists bicuculline and SR95531 reversed the inhibitory effect of GABA on neurosteroid formation. The present results indicate that steroid-producing neurons of the frog hypothalamus express the GABA(A) receptor alpha(3) and beta(2)/beta(3) subunits. Our data also demonstrate that GABA, acting on GABA(A) receptors at the hypothalamic level, inhibits the activity of several key steroidogenic enzymes, including 3beta-HSD and cytochrome P450(C17) (17alpha-hydroxylase).

Use of bicuculline, a GABA antagonist, as a template for the development of a new class of ligands showing positive allosteric modulation of the GABA(A) receptor

Analogues of bicuculline devoid of the benzo ring fused to the lactone moiety were prepared by reacting 2-(tert-butyl-dimethylsiloxy)furans with 3,4-dihydroisoquinolinium salts. Some of these compounds (e.g., ROD185, 8) acted as modulators of the GABAA receptor, displacing ligands of the benzodiazepine binding site. They also strongly stimulated GABA currents mediated by recombinant GABA(A) receptors expressed in Xenopus oocytes.

Association study of schizophrenia spectrum disorders and dopamine D3 receptor gene: is schizoaffective disorder special?

Alterations in dopamine neurotransmission have been hypothesized to play a role in the etiology of schizophrenia. We considered the dopamine D3 receptor gene on chromosome 3 as a candidate gene for an association analysis. We compared PCR-based genotype markers for healthy controls (n=120) and patients (n=95) with schizophrenia and schizophrenia spectrum disorders as diagnosed by consensus according to DSM-III-R. Our results possibly indicate an association of schizoaffective disorder with DRD3 homozygosity (P=0.056).

Role of the GABA(A) receptor gamma2 subunit in the development of gonadotropin-releasing hormone neurons in vivo

We have employed transgenic mouse models to examine the functional significance of the gamma2 subunit of the GABA(A) (gamma-aminobutyric acid) receptor to the correct development of gonadotropin-releasing hormone (GnRH) neurons in vivo. In the first experiment, the expression of gamma2 subunit protein by the GnRH phenotype was determined using transgenic mice in which GnRH gene sequences direct the expression of the LacZ reporter to the nucleus of the GnRH neurons. This greatly facilitates the immunocytochemical identification of non-nuclear-located antigens within GnRH neurons and revealed that approximately 25% of juvenile GnRH neurons were immunoreactive for the gamma2 subunit and that this increased to 40% in pubertal mice. In the second experiment, GnRH mRNA expression was examined in the brains of gamma2 subunit knockout mice (gamma2(0/0)) and their wild-type (gamma2+/+) littermates at embryonic day 15 and postnatal days (P) 0 and 11-16 using in situ hybridization. The distribution and numbers of cells expressing GnRH mRNA in gamma2+/+ and gamma2(0/0) mice were not found to differ at any age. However, the GnRH mRNA content of medial septal cells was significantly lower in gamma2(0/0) compared with gamma2+/+ mice at P11-16 (P<0.05) and the same trend was observed for preoptic area neurons. These results demonstrate that while the gamma2 subunit of the GABA(A) receptor is expressed by postnatal GnRH neurons, their embryonic development does not require a functional gamma2 subunit. In contrast, postnatal GnRH mRNA expression was found to be dependent upon signalling through the GABA(A) receptor.

Non-association of dopamine D4 and D2 receptor genes with personality in healthy individuals

Recently, different research groups reported conflicting results with regard to an association of dopamine 4 receptor (DRD4) genotypes and the personality dimension of novelty seeking (NS). High scores for NS seemed to be associated with long alleles of a DRD4 polymorphism. Furthermore, an association between personality traits and the dopamine 2 (DRD2) receptor gene was reported. NS and persistence (PS) high scores seemed to be associated with alleles of DRD2. We examined 109 (78 female and 31 male) normal healthy individuals using Cloninger's Temperament and Character Inventory (TCI) in order to replicate these findings. We genotyped a 48 base pair variable number of tandem repeats (from two to eight repeats) polymorphism in the third exon of DRD4 and a Cys311Ser polymorphism in exon 7 of DRD2. We tested alleles and genotypes of DRD4 (allele 7 absent or present; genotype 4,4 versus 4,7), and Ser/Cys and Cys/Cys genotypes of DRD2 for associations with TCI values. NS and the alleles and genotypes of DRD4 did not show any association. In associating the genotypes of DRD2 with TCI scales (NS, harm avoidance, reward dependence and PS), we also found no association. Recent findings associating NS with DRD4 could not be replicated. With regard to DRD2, we tested a different polymorphism as published recently and could not find an association of TCI scales with the gene. The present results therefore do not provide evidence that the DRD2 and DRD4 receptor genes contribute a common and relevant effect to personality traits.