Dendritic spine loss in the hippocampus of young PDAPP and Tg2576 mice and its prevention by the ApoE2 genotype.

Postmortem AD brains exhibit dendritic spine loss in the hippocampus. To determine whether this pathology may be associated with amyloid burden, the present study used the Golgi stain technique to assess age- and genotype-dependent changes in dendritic spine density in CA1 hippocampus of two transgenic mouse lines that produce high levels of Abeta. Tg2576 and PDAPP mice, as well as a group of Tg2576 mice crossed with human apoE2-expressing transgenic mice, were compared to respective transgene-negative controls. Since the time course of amyloid plaque deposition in the PDAPP and Tg2576 mice is well characterized, we examined changes in spine density at ages that corresponded to different levels of amyloid plaque load. The data show age- and genotype-dependent reductions in spine density in both Tg2576 and PDAPP mice, albeit at somewhat different time courses. The spine loss occurred prior to plaque deposition and was ameliorated by the overexpression of human apoE2. These results suggest that a soluble Abeta species may affect hippocampal synapses and thereby contribute to functional deficits evident in these animals.

Transgenic swine for biomedicine and agriculture.

Initial technologies for creating transgenic swine only permitted random integration of the construct. However, by combining the technology for homologous recombination in fetal somatic cells with that of nuclear transfer (NT), it is now possible to create specific modifications to the swine genome. The first such example is that of knocking out a gene that is responsible for hyperacute rejection (HAR) when organs from swine are transferred to primates. Because swine are widely used as models of human diseases, there are opportunities for genetic modification to alter these models or to create additional models of human disease. Unfortunately, some of the offspring resulting from NT have abnormal phenotypes. However, it appears that these abnormal phenotypes are a result of epigenetic modifications and, thus, are not transmitted to the offspring of the clones. Although the technique of producing animals with specific genetic modifications by NT has been achieved, improvements to the NT technique as well as improvements in the culture conditions for somatic cells and the techniques for genetic modification are still needed.

Mosaic gene expression in nuclear transfer-derived embryos and the production of cloned transgenic pigs from ear-derived fibroblasts.

Genetically modified domestic animals have many potential applications ranging from basic research to production agriculture. One of the goals in transgenic animal production schemes is to reliably predict the expression pattern of the foreign gene. Establishing a method to screen genetically modified embryos for transgene expression before transfer to surrogates may improve the likelihood of producing offspring with the desired expression pattern. In order to determine how transgene expression may be regulated in the early embryo, we generated porcine embryos from two distinct genetically modified cell lines by using the nuclear transfer (NT) technique. Both cell lines expressed the enhanced green fluorescent protein (eGFP); the first was a fibroblast cell line derived from the skin of a newborn pig that expressed eGFP, whereas the second was a fetal derived fibroblast cell line into which the eGFP gene was introduced by a retroviral vector. The reconstructed embryos were activated by electrical pulses and cultured in NCSU23. Although the in vitro developmental ability of each group of NT embryos was not different, the eGFP expression pattern was different. All embryos produced from the transduced fetal cell line fluoresced, but only 26% of the embryos generated from the newborn cell line fluoresced, and among those that did express eGFP, more than half had a mosaic expression pattern. This was unexpected because the fetal cell line was not clonally selected, and each cell had potentially different sites of integration. Embryos generated from the newborn cell line were surgically transferred to five surrogate gilts. One gilt delivered four female piglets, all of which expressed eGFP, and all had microsatellites identical to the donor. Here we demonstrate that transgene expression in all the blastomeres of an NT embryo is not uniform. In addition, transgene expression in a genetically manipulated embryo may not be an accurate indicator of expression in the resulting offspring.

Human apolipoprotein E4 accelerates beta-amyloid deposition in APPsw transgenic mouse brain.

The human apolipoprotein E4 (ApoE4) isoform is associated with genetic risk for Alzheimer's disease. To assess the effects of different ApoE isoforms on amyloid plaque formation, human ApoE3 and ApoE4 were expressed in the brains of transgenic mice under the control of the human transferrin promoter. Mice were crossed with transgenic mice expressing human amyloid precursor protein containing the Swedish mutation (APPsw), which facilitates amyloid beta peptide (A beta) production. The following progeny were selected for characterization: APPsw+/- x ApoE3+/- and APPsw+/-, APPsw+/- x ApoE4+/- and APPsw+/- littermates. All mice analyzed were wild type for the endogenous mouse APP and ApoE genes. Mice expressing ApoE4 in combination with APPsw have accelerated A beta deposition in the brain as assessed by enzyme immunoassay for A beta40 and A beta42 extractable in 70% formic acid, by assessment of amyloid plaque formation using thioflavin-S staining, and by immunohistochemical staining with antibodies specific for A beta40 or A beta42 and the 4G8 monoclonal or 162 polyclonal antibody. No difference in the rate of A beta deposition in the brain was seen in mice expressing ApoE3 in combination with APPsw. Thus, our data are consistent with the observation in Alzheimer's disease that ApoE4 is associated with increased accumulation of A beta in the brain relative to ApoE3.

Production of nuclear transfer-derived swine that express the enhanced green fluorescent protein.

The ability to add or delete specific genes in swine will likely provide considerable benefits not just to agriculture but also to medicine, where pigs have potential as models for human disease and as organ donors. Here we have transferred nuclei from a genetically modified fibroblast cell line to porcine oocytes, matured in vitro under defined culture conditions, to create piglets expressing enhanced green fluorescent protein. The nuclear transfer-derived piglets were of normal size, although some mild symptoms of "large offspring syndrome" were evident. These experiments represent a next step towards creating swine with more useful genetic modifications.

Endogenous brain cytokine mRNA and inflammatory responses to lipopolysaccharide are elevated in the Tg2576 transgenic mouse model of Alzheimer's disease.

Beta-amyloid (Abeta) plaques have been shown to induce inflammatory changes in Alzheimer's disease brains. Cortical, but not cerebellar tissue from 16-month-old Tg2576 (Tg+) mice showed significant increases in interleukin (IL)-1alpha (2.2-fold), IL-1beta (3.4-fold), tumor necrosis factor-alpha (3.9-fold), and monocyte chemoattractant protein-1 (2.5-fold) mRNA levels compared to controls (Tg-). These changes were not apparent in 6-month-old Tg+ mice except for TNF-alpha. mRNA levels of glial fibrillary acidic protein and complement components, C1qA and C3 were also elevated in aged mice. Lipopolysaccharide (LPS) (25 microg/mouse, i.v.) induced a significantly greater production of IL-1beta protein in the cortices and hippocampi of Tg+ vs. Tg- mice at 1, 2, 4, and 6 h. Experiments in 6-month-old mice showed that not only was there less cytokine produced compared to 16-month-old mice, but the exacerbated cytokine response to LPS in Tg+ mice was not apparent. Higher levels of Abeta1-40 were measured in the cortices of 6- and 16-month-old Tg+ mice at 4-6 h after LPS, which returned to baseline after 18 h. We demonstrate that Abeta plaques elicit inflammatory responses in Tg2576 mice that are further exacerbated when challenged by an exogenous inflammatory insult, which may serve to amplify degenerative processes.

Membrane-anchored aspartyl protease with Alzheimer's disease beta-secretase activity.

Mutations in the gene encoding the amyloid protein precursor (APP) cause autosomal dominant Alzheimer's disease. Cleavage of APP by unidentified proteases, referred to as beta- and gamma-secretases, generates the amyloid beta-peptide, the main component of the amyloid plaques found in Alzheimer's disease patients. The disease-causing mutations flank the protease cleavage sites in APP and facilitate its cleavage. Here we identify a new membrane-bound aspartyl protease (Asp2) with beta-secretase activity. The Asp2 gene is expressed widely in brain and other tissues. Decreasing the expression of Asp2 in cells reduces amyloid beta-peptide production and blocks the accumulation of the carboxy-terminal APP fragment that is created by beta-secretase cleavage. Solubilized Asp2 protein cleaves a synthetic APP peptide substrate at the beta-secretase site, and the rate of cleavage is increased tenfold by a mutation associated with early-onset Alzheimer's disease in Sweden. Thus, Asp2 is a new protein target for drugs that are designed to block the production of amyloid beta-peptide peptide and the consequent formation of amyloid plaque in Alzheimer's disease.

Piperazine imidazo[1,5-a]quinoxaline ureas as high-affinity GABAA ligands of dual functionality.

A series of imidazo[1,5-a]quinoxaline piperazine ureas appended with a tert-butyl ester side chain at the 3-position was developed. Analogues within this series have high affinity for the gamma-aminobutyric acid A (GABAA)/benzodiazepine receptor complex with efficacies ranging from inverse agonists to full agonists. Many analogues were found to be partial agonists as indicated by [35S]TBPS and Cl- current ratios. Uniquely, a number of these analogues were found to have a bell-shaped dose-response profile in the alpha1 beta2 gamma2 subtype as determined by whole cell patch-clamp technique, where in vitro efficacy was found to decrease with increasing drug concentration. Many of the compounds from this series were effective in antagonizing metrazole-induced seizures, consistent with anticonvulsant and possibly anxiolytic activity. Additionally, several analogues were also effective in lowering cGMP levels (to control values) after applied stress, also consistent with anxiolytic-like properties. The most effective compounds in these screens were also active in animal models of anxiety such as the Vogel and Geller assays. The use of the piperazine substituent allowed for excellent drug levels and a long duration of action in the central nervous system for many of the quinoxalines, as determined by ex vivo assay. Pharmacokinetic analysis of several compounds indicated excellent oral bioavailability and a reasonable half-life in rats. From this series emerged two partial agonists (55, 91) which had good activity in anxiolytic models, acceptable pharmacokinetics, and minimal benzodiazepine-type side effects.

Neuroprotective efficacy and mechanisms of novel pyrrolopyrimidine lipid peroxidation inhibitors in the gerbil forebrain ischemia model.

A brief period of bilateral carotid occlusion (BCO)-induced forebrain ischemia in gerbils triggers neuronal degeneration and the subsequent expression of amyloid precursor protein (APP), b-amyloid protein (b-AP), and apolipoprotein E (APO-E) in the selectively vulnerable CA1 region of the hippocampus. The increase in immunoreactivity is secondary to the postischemic degeneration of the CA1 neurons and is largely astrocyte-derived as evidenced by a simultaneous increase in glial fibrillary acidic protein (GFAP) staining. Oxygen radical-induced lipid peroxidation has been strongly suggested to play a role in postischemic neuronal damage and Alzheimer's disease. Recent literature suggests a possible link between early oxidative stress and APP overexpression. Therefore, the present investigation examined the effect of two novel brain-penetrating pyrrolopyrimidine lipid peroxidation inhibitors (PNU-101033E and PNU-104067F) on CA1 neurodegeneration and the subsequent increase in APP, b-AP, APO-E, and GFAP immunostaining at 4 days after a 5-minute episode of forebrain ischemia. Using an antibody for lipid peroxidation-derived malondialdehyde (MDA)-modified proteins, the authors also examined the effects of PNU-104067F on MDA immunostaining 2 days after ischemia, before completion of the neuronal loss. At 2 days, the authors also evaluated microglial activation using an antibody to surface major histocompatibility complex class II antigen expressed by activated microglia. Gerbils were treated at 30 mg/kg orally 30 minutes before the BCO and 2 hours after ischemia, followed by daily dosing for the next day (microglia and MDA) and the successive 3 days for APP, b-AP, APO-E, and GFAP immunostaining. APP and APO-E staining was significantly suppressed by 50% and 66%, respectively, with either compound. b-AP immunoreactivity was decreased 56% with both compounds, and GFAP expression was significantly decreased 53% (PNU-101033E) and 60.5% (PNU-104067F). There was a concomitant partial sparing of the CA1 hippocampal neurons by both PNU-101033E and PNU-104067F (P < .01) as determined by cresyl violet histochemistry. PNU-104067F significantly inhibited lipid peroxidation-derived MDA immunostaining and microglia activation (P < .05) at 48 hours after ischemia. Brain-penetrable lipid peroxidation inhibitors may provide attenuation of various glial response proteins after ischemic injury, probably secondary to neuronal protection.

A model for structure-dependent binding of Congo red to Alzheimer beta-amyloid fibrils.

The cytotoxic A beta fibril is a logical candidate for the entity causing the initiating damage to neurons in Alzheimer's disease and Down's syndrome. We have derived a model of binding for the dye molecule, Congo red (CR), to a beta-sheet structure of beta-amyloid (1-42). This model is based on the crystal coordinates of CR binding to porcine insulin fibrils from Turnell and Finch. Intact insulin is composed of protein dimers and X-ray diffraction studies show that CR intercalates between two insulin monomers at an interface formed by a pair of antiparallel beta-strands. The intercalation of CR has disrupted the four main-chain hydrogen bonds between the two beta-strands, but they are still tethered with each other through new hydrogen bonds with the CR nitrogen atoms. The CR molecule has been aligned along the homologous stretch of amino acids in Alzheimer beta peptide (two molecules in antiparallel distorted or pseudo beta-sheet conformation) using the crystal coordinates from the Turnell-Finch paper to arrive at a putative structure for CR binding to Alzheimer's amyloid fibrils.

Ibuprofen: effect on inducible nitric oxide synthase.

Treatment with ibuprofen and other non-steroidal anti-inflammatory drugs (NSAIDS) has been reported to decrease the incidence as well as slow down the progression of Alzheimer's disease. Understanding the mechanism of this therapeutic effect would provide a target for development of drugs which may be devoid of side effects observed with NSAIDs. In addition to inhibiting cyclooxygenase (COX), the NSAIDs have recently been shown to decrease inducible nitric oxide synthase (iNOS) activity. Ibuprofen and other NSAIDs had no direct effect on catalytic activity of iNOS, but decreased levels of iNOS mRNA. The mechanism of action of ibuprofen on reduction of iNOS activity has been further investigated in the present study using rat primary cerebellar glial cell cultures. In addition, the effect of ibuprofen on COX mRNA expression and prostaglandin formation was also studied. Glial cells treated with E. coli lipopolysaccharide (LPS) and interferony (INFgamma) for 16 h expressed iNOS and COX. Ibuprofen did not directly inhibit iNOS activity. However, when ibuprofen was incubated at the same time with LPS and INFgamma for 16 h, enzyme activity was reduced, with an IC50 of 0.76 mM. Ibuprofen concentration-dependently decreased iNOS mRNA levels, with an IC50 > 2 mM. Thus, there was no correlation between decrease in iNOS activity and reduction in iNOS mRNA levels. Ibuprofen decreased iNOS protein levels, as determined by Western blot, with an IC50 of 0.89 mM. The data suggest that the reduction in iNOS activity by ibuprofen is due to inhibition of post-transcriptional processing of this enzyme. Ibuprofen had no effect on constitutive COX (COX-1) or inducible COX (COX-2) mRNA expression. However, ibuprofen inhibited PGE2 formation with an IC50 of 0.86 mM. The anti-inflammatory actions of ibuprofen have been related to inhibition of COX and, subsequently, reducing prostaglandin formation. Since the potency of ibuprofen for inhibition of PGE2 formation and reduction in iNOS activity are similar, it is suggested that, at therapeutically effective doses, a decrease in iNOS activity may also occur in vivo. Therefore, reduction in iNOS protein levels in the brain may have a role in preserving the integrity of neurons in individuals susceptible to Alzheimer's disease.

The relationships among sex role orientation, egalitarianism, attitudes toward sexuality, and attitudes toward violence against women.

Relationships among U.S. college students' (N = 618) attitudes toward rape myths and their sex role orientation, affective responses to sexuality, sex role egalitarianism, and attitudes toward violence against women were investigated. Results indicated that men were more tolerant of rape, more likely to attribute blame for rape to the victim, and less negative in their views of rapists than women were. In addition, for men, but not for women, masculinity and femininity were predictive of rape attitudes and attributions of blame to rape victims. Positive attitudes toward sexuality were predictive of intolerance of rape for the total sample and for men, but not for women, and were predictive of perceptions of women as innocent victims of rape for both the total sample and the sexes separately. Attitudes toward pornography were unrelated to attitudes toward rape. Acceptance of violence against women and a lack of sexual egalitarianism were predictive of acceptance of rape myths. Androgynous, masculine, and feminine individuals were less tolerant of rape than undifferentiated persons were.

Neuroprotective properties of the benzodiazepine receptor, partial agonist PNU-101017 in the gerbil forebrain ischemia model.

PNU-101017 is a novel, imidazoquinoline amide and benzodiazepine receptor partial agonist that has high affinity for the GABAA receptor subtypes containing the alpha 1 and alpha 3 or alpha 5 subunits. At each of these receptors, the compound is a partial agonist with approximately 50% of the intrinsic activity of the full agonist diazepam. In view of the previously demonstrated anti-ischemic effects of some GABA agonists, the purpose of this study was to determine the ability of PNU-101017 to salvage selectively vulnerable neuronal populations in the gerbil forebrain ischemia model. In an initial set of experiments, male gerbils were pretreated 30 minutes before ischemia induction (5 minutes) with PNU-101017 (3, 10, or 30 mg/kg intraperitoneally) and again 2 hours after reperfusion. In vehicle (0.05 N HC1)-treated gerbils, the loss of hippocampal CA1 neurons at 5 days was 80%. PNU-101017 was shown to produce a dose-related increase in CA1 neuronal survival; at either 10 or 30 mg/kg, the loss of CA1 neurons was only 21% (P < 0.005 versus vehicle). A second experiment, examined the therapeutic window for PNU-101017 using the dose level of 30 mg/kg intraperitoneally. Administration of the first of two doses (2 hours apart) at the time of reperfusion resulted in an identical decrease in CA1 damage at 5 days to that seen with preischemic treatment (P < 0.003 versus vehicle). Even with a delay of the initial dosing until 4 hours after reperfusion, PNU-101017 reduced CA1 neuronal loss to only 32% (P < 0.01 versus vehicle). In a third experiment in which the duration of the ischemic insult was increased to 10 minutes and the brains were not analyzed until 28 days after ischemia, daily PNU-101017 dosing for the full 28 days still significantly preserved CA1 neurons, although less effectively than in the milder 5 minute-ischemia model. The loss of dopaminergic nigrostriatal neurons was also reduced. The neuroprotective effect of PNU-101017 was not associated with any overt CNS depression and it did not correlate with hypothermia. This benzodiazepine-receptor partial agonist may have potential for the treatment of global cerebral ischemia.

Anxiolytic-like effects of PNU-101017, a partial agonist at the benzodiazepine receptor.

PNU-101017 is a chemically novel ligand at the benzodiazepine recognition site of cloned GABAA receptors. It was reported to potentiate GABA-mediated chloride current in cultured cells with a moderate intrinsic activity and a biphasic dose-response relationship. In this study, we confirmed that PNU-101017 has a partial agonist-like effect in the antagonism of metrazole-induced seizures in mice. It produced no sedation or ataxia, but did antagonize diazepam-induced motor deficit of mice in the rotarod test. PNU-101017 was weakly active in anti-conflict anxiolytic tests, but attenuated the plasma corticosteroid response to mild stress in rats. It also antagonized stress-induced elevation of cerebellar cGMP levels in mice. Like chlordiazepoxide, it increased drinking of saline solution in thirsty rats. PNU-101017 did not potentiate the CNS-depressant effects of ethanol, and produced no evidence of physical dependence when administered repeatedly. Agonists with low intrinsic activity at the benzodiazepine receptor, such as PNU-101017, should be further explored for therapeutic uses.

Evaluating the effectiveness of workshop interventions on contraceptive use among first-year college students.

PIP: This study tested the effectiveness of 4 interventions designed to affect contraceptive knowledge, attitudes, and use among first-year Syracuse University students in New York State in the US. Pre- and post-tests obtained data on demographic characteristics, sexual behavior, contraceptive knowledge, sexual opinions, contraceptive attitudes, and contraceptive progress on a 5-step scale. Group 1 (79 students) received contraceptive information (CI) only. Group 2 (76) received CI and a cognitively oriented intervention. Group 3 (73) received CI and an experience-oriented intervention. Group 4 (77) received a combined cognitively and experience-oriented intervention with CI. The control group included 57 people. 78% on the pretest, and 84% on the post-test, had engaged in sexual intercourse for the first time in high school. 200 indicated previous intercourse in the past 3 months. Groups varied significantly in their knowledge, beliefs, and practices. All groups had greater contraceptive knowledge than control groups. Greater behavior beliefs about contraceptive use occurred in Groups 1 and 2. Groups 3 and 4 showed greater increases in positive attitudes toward use. All intervention students showed greater increases in positive attitudes toward a contraceptive process. Greater increases in the intention to use birth control occurred in Groups 3 and 4. Groups 2, 3, and 4 showed greater increases in reported use of birth control. Group 4 intervention was the most effective for males. Females were influenced by all interventions. Findings affirm the importance of including attitudinal components in sexuality and contraception workshops.^ieng

PNU-107484A with alpha isoform-dependent functional changes in alpha(x)beta2gamma2 subtypes of rat recombinant GABA(A) receptors.

1. We discovered a novel gamma-aminobutyric acidA (GABA(A)) receptor ligand displaying seemingly opposite functionalities, depending on the alpha isoform of the alpha(x)beta2gamma2 subtypes. PNU-107484A enhanced GABA-induced Cl- currents in the alpha1beta2gamma2 subtype, but inhibited the currents in the alpha3beta2gamma2 and alpha6beta2gamma2 subtypes, and its half-maximal concentrations in the subtypes were 3.1 +/- 0.5, 4.2 +/- 1, and 3.5 +/- 0.2 microM, respectively, without showing much dependency on alpha isoforms. 2. In the alpha1beta2 subtype, the drug at concentrations up to 40 microM showed no effect on GABA-induced Cl- currents, suggesting the requirement of the gamma subunit for its action. 3. PNU-107484A behaved like a positive allosteric modulator of the alpha1beta2gamma2 subtype with its binding site distinct from those for benzodiazepines, barbiturates and neurosteroids. With the alpha3beta2gamma2 subtype, the drug behaved like a non-competitive inhibitor of GABA, thus blocking Cl- currents by GABA alone or in the presence of pentobarbitone and neurosteroids. 4. It appears that PNU-107484A is a unique GABA(A) receptor ligand with alpha isoform-dependent functionalities, which may provide a basis for development of alpha isoform-selective ligands, and it could be useful as a probe to investigate the physiological roles of the various alpha isoform subtypes.

Chronic triazolam and its withdrawal alters GABAA receptor subunit mRNA levels: an in situ hybridization study.

The benzodiazepine (BZ), triazolam (TRZ), results in tolerance and physical dependence. We performed in situ hybridization (ISH) experiments to gain a more complete understanding of the processes involved in mediating the effects of chronic TRZ ISH allowed us to determine whether GABAA receptor subunit mRNAs are affected by 4 weeks of TRZ administration and its withdrawal and to localize the changes to discrete brain regions. Using oligonucleotide probes directed toward the alpha 1-6, beta 1-3, and delta subunit mRNAs, we analyzed message density in 63 brain regions of TRZ-treated and control rat brains, alpha 1-4, beta 1-3, and delta subunit mRNA levels were altered by 28 days of chronic TRZ. No changes were noted in alpha 5-6 mRNA levels. Many of the changes measured were localized to neural structures within the limbic circuit of Papez, or in close communication with this pathway. After a 24 h withdrawal period from 4 weeks of TRZ treatment, the changes noted on the 28th day of treatment were reversed. Moreover, brain regions that were unaffected by the 4-week treatment were altered by the 24 h withdrawal. Our results indicate that chronic treatment and withdrawal are associated with separate processes and that chronic TRZ is correlated with limbic alterations which may be responsible for some of its chronic effects.

High-affinity alpha-aminobutyric acid A/benzodiazepine ligands: synthesis and structure-activity relationship studies of a new series of tetracyclic imidazoquinoxalines.

A series of tetracyclic imidazoquinoxaline analogs was developed which constrain the carbonyl group of the partial agonist 3-(5-cyclopropyl-1,2,4-oxadiazol-3-yl)-5-[(dimethylamino)carbonyl] - 4,5-dihydroimidazo[1,5-alpha]quinoxaline (2, U-91571) away from the benzene ring. These analogs orient the carbonyl group in the opposite direction of the previously reported full agonist 1-(5- cyclopropyl-1,2,4-oxadiazol-3-yl)-12,12a-dihydroimidazo[1,5- alpha]pyrrolo [2,1-c]quinoxalin-10(11H)-one (3, U-89267). A number of approaches were utilized to form the "bottom" ring of this tetracyclic ring system including intramolecular cyclizations promoted by Lewis acids or base, as well as metal-carbenoid conditions. The size and substitution pattern of the additional ring was widely varied. Analogs within this series had high affinity for the benzodiazepine receptor on the alpha-aminobutyric acid A chloride ion channel complex. From TBPS shift and Cl- current assays, the in vitro efficacy of compounds within this class ranged from antagonists to partial agonists with only 18a identified as a full agonist. Additionally, several analogs were quite potent at antagonizing metrazole-induced seizures indicating possible anticonvulsant or anxiolytic activity. Unlike 3, analogs in this series did not have high affinity for the diazepam insensitive alpha 6 beta 2 delta 2 subtype. These results suggest that either constraining the carbonyl group away from the benzene ring or the greater planarity that results from the additional cyclic structure provides analogs with partial agonist properties and prevents effective interaction with the alpha 6 beta 2 delta 2 subtype.

Pharmacological modulation of the diazepam-insensitive recombinant gamma-aminobutyric acidA receptors alpha 4 beta 2 gamma 2 and alpha 6 beta 2 gamma 2.

We characterized modulation of the gamma-aminobutyric acid (GABA)-evoked responses of the diazepam-insensitive alpha 4 beta 2 gamma2 and alpha 6 beta 2 gamma 2 recombinant GABAA receptors. The partial agonist bretazenil potentiated the responses of both receptors with similar dose dependence but with a higher maximal enhancement at the alpha 4 beta 2 gamma 2 receptor. The bretazenil-induced potentiation was reduced by the benzodiazepine antagonist flumazenil. At a high concentration (10 microM), flumazenil was a weak potentiator of the GABA response. The partial agonist imidazenil was inactive. The imidazobenzodiazepine inverse agonist Ro 15-4513, which is known to bind with high affinity to the alpha 6 beta 2 gamma 2 receptor, potentiated the GABA responses of the alpha 4 beta 2 gamma 2 and alpha 6 beta 2 gamma 2 receptor subtypes with similar dose dependence over the concentration range of 0.1-10 microM. Methyl-6, 7-dimethoxy-4-ethyl-beta-carboline, a beta-carboline inverse agonist, had a similar potentiating effect when tested at a concentration of 10 microM. The alpha 4 beta 2 gamma 2 and alpha 6 beta 2 gamma 2 receptor-mediated currents had equal sensitivities to furosemide and Zn2+ ions, both of which reduced the GABA-evoked responses. The alpha 6 beta 2 gamma 2 receptor but not the alpha 4 beta 2 gamma 2 receptor exhibited a low level of spontaneous activity in the absence of GABA; this resting current could be directly potentiated by Ro 15-4513, methyl-6,7-dimethoxy-4-ethyl-beta-carboline, bretazenil and flumazenil and was blocked by picrotoxin. Thus, although the alpha 4 beta 2 gamma 2 receptors are insensitive to benzodiazepine binding site full agonists, such as diazepam, they can be modulated by certain ligands acting as partial and inverse agonists at diazepam-sensitive receptors and thereby contribute to the respective pharmacological profiles.

Differential effects of hexachlorocyclohexane isomers on the GABA receptor subunits expressed in human embryonic kidney cell line.

We have recently demonstrated by patch clamp experiments that the four isomers of hexachlorocyclohexane (HCH), alpha-, beta-, gamma- and delta-HCH insecticides, modulated the kinetics of the GABAA receptor-chloride channel complex of rat dorsal root ganglion neurons. The present paper reports the differential effects of HCH isomers of the GABA-induced chloride currents in three combinations of alpha, beta and gamma subunits of GABAA receptor expressed in human embryonic kidney cells. When co-applied with GABA, gamma-HCH strongly suppressed the peak amplitude of GABA-induced current, and delta-HCH strongly enhanced it in the alpha 1 beta 2 gamma 2s, alpha 1 beta 2, alpha 6 beta 2 gamma 2s combinations in a dose-dependent manner. There was little or no difference in the dose dependence of the effects between gamma- and delta-HCH in any of the three subunit combinations. However, alpha- and beta-HCH showed differential effects on GABA-induced chloride currents in the three subunit combinations tested. alpha-HCH showed enhancing effects on the peak current in alpha 1 beta 2 gamma 2s, small enhancing effects on alpha 1 beta 2, and biphasic effects on alpha 6 beta 2 gamma 2s subunit combinations. beta-HCH had little or no effect on the peak current in alpha 1 beta 2 gamma 2s and alpha 1 beta 2 combinations, but suppressed currents in the alpha 6 beta2 gamma 2s subunit combination in a dose-dependent manner. The differential actions of HCH isomers may produce variable effects on different regions of the nervous systems and in different species of animals.