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Biomedical subjects

Giovanni Biggio

Publications and source records attributed to Giovanni Biggio.

At least 37 records · Page 2Linked to original sources

Synthesis, structure-activity relationships at the GABA(A) receptor in rat brain, and differential electrophysiological profile at the recombinant human GABA(A) receptor of a series of substituted 1,2-diphenylimidazoles.

A series of new 1,2-diphenylimidazole derivatives (1a-x) were synthesized and evaluated for their ability to potentiate gamma-aminobutyric acid (GABA)-evoked currents in Xenopus laevis oocytes expressing recombinant human GABA(A) receptors. Many of these compounds enhanced GABA action with potencies (EC(50) = 0.19-19 muM) and efficacies (maximal efficacies of up to 640%) similar to or greater than those of anesthetics such as etomidate, propofol, and alphaxalone. Structure-activity relationship analysis revealed that the presence of an ester moiety in the imidazole ring was required for full agonist properties, while modifications made in the phenyl rings affected potency and efficacy, with ethyl 2-(4-bromophenyl)-1-(2,4-dichlorophenyl)-1H-4-imidazolecarboxylate showing the highest potency. These compounds potentiated the [(3)H]GABA binding to rat brain membranes, suggesting a site of interaction different from that of GABA. As for etomidate, mutation of asparagine-265 in the beta2 subunit of the GABA(A) receptor into serine reduced the ability of derivative 1i to modulate the GABA function.

Amino Acid Sequence↗

Chronic administration of the SSRI fluvoxamine markedly and selectively reduces the sensitivity of cortical serotonergic neurons to footshock stress.

We have evaluated, with the use of vertical microdialysis, the effects of fluvoxamine, a selective serotonin reuptake inhibitor (SSRI) on the increase in serotonin and norepinephrine output elicited in rats prefrontal cortex by exposure to footshock stress. Exposure to footshock stress induced a marked increase in the cortical extracellular concentration of both serotonin and norepinephrine (+70% and +100%, respectively) in control rats. Long term, but not acute administration of fluvoxamine (10 mg/kg, i.p. once a days for 21 days) completely antagonized the stress induced increase in cortical serotonin extracellular concentration, while failed to modify the sensitivity of cortical noradrenergic neurons to the same stressful stimulus. Our results have shown that it is possible to independently modulate the sensitivity of cortical serotonergic neurons to stressful stimuli without altering the responsiveness of noradrenergic neurons to the same stress. Given the different role played by serotonin and norepinephrine in the modulation of the stress response, the availability of drugs able to selectively modulate the plastic response of serotonergic neurons to stress in specific brain areas might be important for the pharmacotherapy of anxiety disorders.

Animals↗

Structure-activity relationships and effects on neuroactive steroid synthesis in a series of 2-phenylimidazo[1,2-a]pyridineacetamide peripheral benzodiazepine receptors ligands.

A series of 36 imidazopyridineacetamides (2-37) were designed and synthesized to evaluate the effects of structural changes on the amide nitrogen at both central (CBRs) and peripheral benzodiazepine receptors (PBRs). These changes include variations in the length and number of the alkyl groups as well as introduction of different aromatic, heteroaromatic, and conformationally constrained groups. The affinities of these compounds for CBRs and PBRs were determined, and the results indicate that bulkiness of the substituents, their branching, and length beyond an optimal value may cause hindrance to the ligand in its interaction with the receptor. The presence of aromatic or conformationally constrained substituents on the carboxamide nitrogen can be conducive to high affinity and selectivity. Furthermore, the ability of a subset of the most active ligands to stimulate synthesis of neuroactive steroids in plasma and brain was evaluated in vivo and in vitro. Compound 3 exhibited very marked effects on the peripheral and central synthesis of neuroactive steroids, while 36 (potent at subnanomolar level) showed a slight ability to affect neuroactive steroid content in the cerebral cortex.

Acetamides↗

Modulation of GABA(A) receptor gene expression by allopregnanolone and ethanol.

Expression of specific gamma-aminobutyric acid type A (GABA(A)) receptor subunit genes in neurons is affected by endogenous modulators of receptor function such as neuroactive steroids. This effect of steroids appears to be mediated through modulation of GABA(A) receptor signalling mechanisms that control the expression of specific receptor subunit genes. Furthermore, the specific outcomes of such signalling appear to differ among neurons in different regions of the brain. Neuroactive steroids such as the progesterone metabolite allopregnanolone might thus exert differential effects on GABA(A) receptor plasticity in distinct neuronal cell populations, likely accounting for some of the physiological actions of these compounds. Here we summarise experimental data obtained both in vivo and in vitro that show how fluctuations in the concentration of allopregnanolone regulate both the expression and function of GABA(A) receptors and consequently affect behaviour. Such regulation is operative both during physiological conditions such as pregnancy and lactation as well as in pharmacologically induced states such as pseudopregnancy and long-term treatment with steroid derivatives or anxiolytic-hypnotic drugs. Accordingly, long-lasting exposure of GABA(A) receptors to ethanol, as well as its withdrawal, induces marked effects on receptor structure and function. These results suggest the possible synergic action between endogenous steroids and ethanol in modulating the functional activity of specific neuronal populations.

Animals↗

Brain steroidogenesis mediates ethanol modulation of GABAA receptor activity in rat hippocampus.

An interaction with the GABA type A (GABA(A)) receptor has long been recognized as one of the main neurochemical mechanisms underlying many of the pharmacological actions of ethanol. However, more recent data have suggested that certain behavioral and electrophysiological actions of ethanol are mediated by an increase in brain concentration of neuroactive steroids that results from stimulation of the hypothalamic-pituitary-adrenal (HPA) axis. Neuroactive steroids such as 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-THP) are, in fact, potent and efficacious endogenous positive modulators of GABA(A) receptor function. Because neurosteroids can be synthesized de novo in the brain, we have investigated whether ethanol might affect both neurosteroid synthesis and GABA(A) receptor function in isolated rat hippocampal tissue. Here, we show that ethanol increases the concentration of 3alpha,5alpha-THP as well as the amplitude of GABA(A) receptor-mediated IPSCs recorded from CA1 pyramidal neurons in isolated hippocampal slices. These effects are shared by the neurosteroid precursor progesterone, the peripheral benzodiazepine receptor-selective agonist CB34, and gamma-hydroxybutyrate, all of which are known to increase the formation of neuroactive steroids in plasma and in the brain. The action of ethanol on GABA(A) receptor-mediated IPSC amplitude is biphasic, consisting of a rapid, direct effect on GABA(A) receptor activity and an indirect effect that appears to be mediated by neurosteroid synthesis. Furthermore, ethanol affects GABA(A) receptor activity through a presynaptic action, an effect that is not dependent on neurosteroid formation. These observations suggest that ethanol may modulate GABA(A) receptor function through an increase in de novo neurosteroid synthesis in the brain that is independent of the HPA axis. This novel mechanism may have a crucial role in mediating specific central effects of ethanol.

Animals↗

Inhibition by miltirone of up-regulation of GABAA receptor alpha4 subunit mRNA by ethanol withdrawal in hippocampal neurons.

Miltirone, a tanshinone isolated from the root of Salvia miltiorrhiza, has been characterized as a low-affinity ligand for central benzodiazepine receptors. We have now shown that this compound bound with low affinity (micromolar range) to central benzodiazepine recognition sites but did not interact with peripheral benzodiazepine receptors. It failed to potentiate Cl(-) currents induced by gamma-aminobutyric acid (GABA) both in Xenopus oocytes expressing recombinant human GABA(A) receptors and in cultured rat hippocampal pyramidal cells, but it inhibited the ability of diazepam to potentiate the effect of GABA in these systems. Miltirone (1-10 microM) also partially inhibited the increase in the abundance of the mRNA for the alpha(4) subunit of the GABA(A) receptor induced by ethanol withdrawal in cultured hippocampal neurons. These results suggest that miltirone might ameliorate the symptoms associated with discontinuation of long-term administration of ethanol or of other positive modulators of the GABA(A) receptor.

Animals↗

Failure of gamma-hydroxybutyric acid both to increase neuroactive steroid concentrations in adrenalectomized-orchiectomized rats and to induce tolerance to its steroidogenic effect in intact animals.

Gamma-Hydroxybutyric acid (GHB), a drug proposed in the treatment of alcohol withdrawal syndrome, increases the cerebrocortical and plasma concentrations of the neuroactive steroids allopregnanolone and allotetrahydrodeoxycorticosterone (THDOC). In the present study, we examined the role of hypothalamic-pituitary-adrenal (HPA) axis in the effect of GHB by measuring the concentrations of these steroids in the brain and plasma of adrenalectomized-orchiectomized (Adx-Orx) rats. The acute administration of GHB (500 mg/kg, i.p.) induced in 30 min an increase in the concentrations of allopregnanolone, THDOC and their precursors pregnenolone and progesterone in different brain areas (cerebral cortex, hypothalamus and cerebellum) and plasma of sham-operated rats but had no effect on the concentrations of these compounds in Adx-Orx rats, suggesting that activation of the HPA axis mediates the effect of GHB on brain and plasma concentrations of neuroactive steroids. Moreover, we evaluated whether repeated exposure of GHB induces tolerance to its steroidogenic effects. Chronic administration of GHB (500 mg/kg, i.p., twice a day for 10 days) to intact animals failed to affect the levels of progesterone, allopregnanolone, or THDOC measured 3 or 48 h after the last drug administration, whereas a challenge injection of GHB or ethanol was still able to increase the concentrations of these steroids in brain and plasma. These results indicate that repeated exposure to GHB fails to induce tolerance or cross-tolerance to the steroidogenic action of GHB or ethanol, respectively.

Adrenalectomy↗

Inhibition of stress-induced dopamine output in the rat prefrontal cortex by chronic treatment with olanzapine.

BACKGROUND: Chronic exposure to stressful events precipitates or exacerbates many neuropsychiatric disorders, including depression and schizophrenia. Evidence suggests that treatment with the atypical antipsychotic drugs olanzapine or clozapine results in a superior amelioration of the anxious and depressive symptoms that accompany schizophrenia relative to therapy with classical antipsychotics such as haloperidol. Moreover, olanzapine and clozapine, but not haloperidol, increase the brain content of neuroactive steroids. The effects of olanzapine and clozapine on the stress-induced increase in dopamine output in the rat cerebral cortex have now been compared with that of haloperidol. METHODS: Rats chronically treated (3 weeks, once a day) with each drug were exposed to foot-shock stress or injected with a single dose of the anxiogenic benzodiazepine receptor ligand FG7142, and dopamine release was then measured in the prefrontal cortex by vertical microdialysis. RESULTS: Long-term administration of olanzapine or clozapine prevented or markedly inhibited, respectively, the increase in the extracellular dopamine concentration induced by foot shock; haloperidol had no such effect. Chronic olanzapine treatment also blocked the effect of FG7142 on dopamine output. CONCLUSIONS: The reduction in the sensitivity of cortical dopaminergic neurons to stress shown to be elicited by treatment with olanzapine or clozapine may contribute to the anxiolytic actions of these drugs.

Analysis of Variance↗

Ethanol withdrawal-induced up-regulation of the alpha2 subunit of the GABAA receptor and its prevention by diazepam or gamma-hydroxybutyric acid.

The gamma-aminobutyric acid type A (GABA(A)) receptor is an important pharmacological target of ethanol. The effect of ethanol withdrawal on the expression of the alpha(2) subunit of this receptor was examined with rat cerebellar granule cells in primary culture. Long-term exposure of these cells to ethanol (100 mM, 5 days) did not affect the abundance of the mRNA for the alpha(2) subunit, as revealed by an RNase protection assay. In contrast, subsequent ethanol withdrawal for 3 h induced a marked increase in the amount of this mRNA (2.6-fold) as well as in that of the encoded polypeptide (2.2-fold), the latter revealed by immunoblot analysis. Exposure of the cells to gamma-hydroxybutyric acid (100 mM) during ethanol withdrawal prevented the increase in the amounts of both the alpha(2) mRNA and polypeptide, whereas similar treatment with diazepam (10 microM) blocked the increase in the abundance of the alpha(2) polypeptide but not that in the amount of the alpha(2) mRNA. The effect of gamma-hydroxybutyric acid was not blocked by the competitive GABA(B) receptor antagonist SCH 50911(10 microM). Given that the alpha(2) subunit of the GABA(A) receptor mediates the anxiolytic action of benzodiazepines, its up-regulation during discontinuation of long-term ethanol exposure might be relevant to the therapeutic efficacy of these drugs in the treatment of anxiety associated with ethanol withdrawal.

Animals↗

Psychological effect of the oral contraceptive formulation containing 3 mg of drospirenone plus 30 microg of ethinyl estradiol.

OBJECTIVE: To investigate in healthy eumenorrheic young women whether an oral contraceptive (OC) containing drospirenone (DRSP) (3 mg) + ethinyl estradiol (EE) (30 microg) (DRSP + EE) could modify psychological symptoms and whether it could modify steroids interfering with the gamma-aminobutyric acid (GABA)-A receptors. DESIGN: Clinical study of treated subjects and nontreated controls. SETTING: Healthy volunteers in the Department of Obstetrics and Gynecology at Cagliari University. PATIENT(S): Control group (n = 12) and OC group (n = 10) women with similar age, body mass index, and main outcome measures. INTERVENTION(S): The control group was studied during the first menstrual cycle at the follicular phase (FP) and at the luteal phase (LP) and during the third cycle at the LP; the OC group was studied during the first cycle, as described above, and on day 16-18 of the third cycle of treatment with DRSP + EE. MAIN OUTCOME MEASURE(S): Psychometric scale (SCL-90), DHEAS, P, allopregnanolone (AP), and allotetrahydrodeoxy-corticosterone (THDOC). RESULT(S): SCL-90 and DHEAS did not vary throughout the menstrual cycle. P, AP, and THDOC values were higher during the LP than the FP. At the third cycle, in the control group the main outcome measures were similar to those at LP. In the OC group, the SCL-90 global score, the intensity of anxiety and phobic anxiety, the levels of anxiolytic steroids (P, AP, THDOC) and the anxiety-inducing steroid DHEAS were reduced. CONCLUSION(S): The results suggest beneficial effects of DRSP + EE on psychological symptoms by decreasing DHEAS.

Adult↗

Social isolation increases the response of peripheral benzodiazepine receptors in the rat.

Social isolation of rats for 30 days immediately after weaning reduces the cerebrocortical and plasma concentrations of progesterone, 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-TH PROG), and 3alpha,5alpha-tetrahydrodeoxycorticosterone (3alpha,5alpha-TH DOC). The percentage increases in the brain and plasma concentrations of these neuroactive steroids apparent 30 min after intraperitoneal injection of the peripheral benzodiazepine receptor (PBR) ligand CB 34 (25 mg/kg) have now been shown to be markedly greater in isolated rats than in group-housed controls. The CB 34-induced increase in the abundance of 3alpha,5alpha-TH PROG was more pronounced in the brain than in the plasma of isolated rats. Analysis of [3H]PK 11195 binding to membranes prepared from the cerebral cortex, adrenals, or testis revealed no significant difference in either the maximal number of binding sites for this PBR ligand or its dissociation constant between isolated and group-housed animals. Social isolation also induced a small but significant decrease in the plasma concentration of adrenocorticotropic hormone. Moreover, CB 34 increased the plasma concentration of this hormone to a greater extent in isolated rats than in group-housed animals. The persistent decrease in the concentrations of neuroactive steroids induced by social isolation might thus be due to an adaptive decrease in the activity either of the hypothalamic-pituitary-adrenal axis or of PBRs during the prolonged stress, reflecting a defense mechanism to limit glucocorticoid production. The larger increase in neuroactive steroid concentrations induced by CB 34 and the enhanced pituitary response to this compound in isolated rats indicate that this mild stressor increases the response of PBRs.

Adrenocorticotropic Hormone↗

Long-term treatment with clozapine does not affect morning circulating levels of allopregnanolone and THDOC in patients with schizophrenia: a preliminary study.

Clozapine has been shown to acutely increase the rat brain and plasma concentrations of the neuroactive steroids 3alpha,5alpha-tetrahydroprogesterone (3alpha,5alpha-THP) or allopregnanolone and THDOC, 2 positive allosteric modulators of GABA-A receptors. Hence, it has been suggested that this effect could underlie the therapeutic efficacy of this drug, contributing to its atypical profile. So far, no study assessed whether the effects on neurosteroids reported in the experimental animal occur also in humans. Therefore, we measured plasma levels of 3alpha,5alpha-THP and THDOC in a sample of drug-resistant schizophrenic patients before and after 1, 2, 4, 6, 8, 12, and 24 weeks of clozapine administration (600 mg/d by the end of the 6th week). No significant changes in circulating concentrations of 3alpha,5alpha-THP and THDOC were observed in the course of clozapine administration in spite of the patients' good clinical response to the drug. These findings provide evidence, for the first time, that clozapine is not able to affect morning circulating levels of 3alpha,5alpha-THP and THDOC in humans. Therefore, although we cannot exclude that changes in neuroactive steroids could occur immediately after the daily administration of clozapine as in the experimental animal, our data support the view that the therapeutic efficacy of this atypical antipsychotic is not linked to changes in the baseline concentrations of peripheral 3alpha,5alpha-THP and THDOC.

Adult↗

Increased expression of the gene for the Y1 receptor of neuropeptide Y in the amygdala and paraventricular nucleus of Y1R/LacZ transgenic mice in response to restraint stress.

A sustained increase in the brain concentrations of neuroactive steroids was previously shown to induce Y1 receptor gene expression in the amygdala of Y1R/LacZ transgenic mice which harbour a construct comprising the murine Y1 receptor gene promoter and the lacZ reporter gene. We now investigated the effects of restraint stress on both the cerebrocortical concentrations of neuroactive steroids and Y1 receptor gene expression in the amygdala and hypothalamic paraventricular nucleus (PVN) of Y1R/LacZ transgenic mice. The cerebrocortical concentrations of allopregnanolone and allotetrahydrodeoxycorticosterone were significantly increased immediately after a 1-h exposure to restraint stress and had returned to control values within 30 min. Expression of Y1R/LacZ was increased in the amygdala and PVN 6 h after restraint. The 5alpha-reductase inhibitor finasteride, that prevented the increase in neuroactive steroid concentrations, did not block that in transgene expression induced by 1-h restraint. Daily exposure to restraint for 10 days also increased the cerebrocortical concentrations of neuroactive steroids but failed to affect transgene expression. Acute but not repeated restraint thus increases Y1 receptor gene expression in the amygdala and PVN, suggesting that tolerance develops towards this stressor. The effect of acute restraint is not mediated by the increase in the brain concentrations of neuroactive steroids but may rather reflect a ligand-induced increase in Y1 receptor gene transcription. Data support a role of Y1 receptors in the behavioural and neuroendocrine responses to stress.

Amygdala↗

Plasma concentrations of anxiolytic neurosteroids in men with normal anxiety scores: a correlation analysis.

Neurosteroids are physiological regulators of anxiety in experimental animals, but there are no data for humans about the modulatory effects of the hormones on normal aspects of this emotional parameter. Plasma concentrations of four neurosteroids, pregnenolone, progesterone (PROG), allopregnanolone and tetrahydrodeoxycorticosterone, suggested to be major anxiety regulators in experimental animals, were measured in a group of 58 physically and psychologically normal adult male subjects. In parallel, trait (genotypical) and state (phenotypical) anxiety scores were measured by the State-Trait Anxiety Inventory. The possible correlations between the hormonal secretions and the psychological parameters were statistically analyzed. The neurosteroid concentrations and the anxiety scores of the probands were within the ranges of normality according to data of the literature and our own. PROG concentrations correlated significantly with state anxiety scores. These data suggest that neurosteroids may physiologically modulate anxiety not only in experimental animals but also in humans.

Adult↗

Changes in GABA(A) receptor gene expression associated with selective alterations in receptor function and pharmacology after ethanol withdrawal.

Changes in the expression of subunits of the GABA type A (GABA(A)) receptor are implicated in the development of ethanol tolerance and dependence as well as in the central hyperexcitability associated with ethanol withdrawal. The impact of such changes on GABA(A) receptor function and pharmacological sensitivity was investigated with cultured rat hippocampal neurons exposed to ethanol for 5 d and then subjected to ethanol withdrawal. Both ethanol treatment and withdrawal were associated with a marked decrease in the maximal density of GABA-evoked Cl- currents, whereas the potency of GABA was unaffected. Ethanol exposure also reduced the modulatory efficacy of the benzodiazepine receptor agonists lorazepam, zolpidem, and zaleplon as well as that of the inverse agonists Ro 15-4513 and FG 7142, effects that were associated with a reduced abundance of mRNAs encoding the receptor subunits alpha1, alpha3, gamma2L, and gamma2S. Ethanol withdrawal restored the efficacy of lorazepam, but not that of low concentrations of zolpidem or zaleplon, to control values. Flumazenil, which was ineffective in control neurons, and Ro 15-4513 each potentiated the GABA response after ethanol withdrawal. These effects of withdrawal were accompanied by upregulation of the alpha2, alpha3, and alpha4 subunit mRNAs as well as of the alpha4 protein. Diazepam or gamma-hydroxybutyrate, but not baclofen, prevented the changes in both GABA(A) receptor pharmacology and subunit mRNA levels induced by ethanol withdrawal. Changes in GABA(A) receptor gene expression induced by prolonged exposure to and withdrawal of ethanol are thus associated with altered GABA(A) receptor function and pharmacological sensitivity.

Animals↗

High affinity central benzodiazepine receptor ligands. Part 3: insights into the pharmacophore and pattern recognition study of intrinsic activities of pyrazolo[4,3-c]quinolin-3-ones.

Novel 2-phenyl-2,5-dihydropyrazolo[4,3-c]quinolin-3-(3H)-ones (PQs) endowed with high affinity for central benzodiazepine receptor (BzR) were synthesized. In particular, 9-fluoro-2-(2-fluorophenyl)-2,5-dihydro-3H-pyrazolo[4,3-c]quinolin-3-one (2(2)) showed binding affinity in the subnanomolar concentration range and proved to be in vitro a potent antagonist. This finding allowed the nature of the hydrogen bonding receptor site H(2) to be established, as located between the N-1 nitrogen of the PQ nucleus and the ortho position of the N-2-aryl group. [35S]tert-Butylbicyclophosphorothionate ([35S]TBPS) binding assays and electrophysiological measurements of the effects on GABA-evoked Cl(-) currents at recombinant human alpha(1)beta(2)gamma(2)(L) GABA(A) receptors, expressed in Xenopus laevis oocytes, were used to assess the intrinsic activities of a large series of PQs. With the aim of extracting discriminant information and distinguishing BzR ligands with different profiles of efficacy, 51 PQ derivatives, including full and partial agonists, antagonists, and inverse agonists, were analyzed in a multidimensional chemical descriptor space, defined by the lipophilicity parameter CLOG P and 3-D molecular WHIM descriptors, by means of principal component analysis, k-nearest neighbors (k-NN) method, and linear discriminant analysis (LDA). The classification methods were applied to subsets of pairs of efficacy classes, and lipophilicity and 3-D size descriptors were detected as the discriminant variables by a stepwise linear discriminant analysis. LDA proved to be superior to k-NN, especially in classifying PQ ligands (60-84% of success in prediction ability) into categories of efficacies which were contiguous and quite overlapped in the hyperspace of variables.

Animals↗

Antagonism of the stress-induced increase in cortical norepinephrine output by the selective norepinephrine reuptake inhibitor reboxetine.

We have previously shown that long-term treatment of rats with antidepressant drugs that affect the activity of noradrenergic and serotonergic neurons by different mechanisms, inhibits the increase in cortical norepinephrine output induced by stress. With the use of microdialysis, we have now evaluated the effects of reboxetine, an antidepressant drug that selectively inhibits norepinephrine reuptake, on the increase in cortical norepinephrine output elicited in rats by exposure to foot-shock stress or by the acute administration of N-methyl-beta-carboline-3-carboxamide (FG 7142) (20 mg/kg, i.p.). Foot-shock stress and FG 7142 each induced a marked increase in the cortical extracellular concentration of norepinephrine (+200 and +90%, respectively) in control rats. Long-term treatment with reboxetine (10 mg/kg, i.p., once a day for 21 days) reduced the effect of foot-shock stress and completely antagonized the effect of FG 7142 on cortical norepinephrine output. Our results suggest that changes in the activity of noradrenergic neurons in the cortex might be relevant to the anxiolytic and antidepressant effects of reboxetine.

Adrenergic Uptake Inhibitors↗