SEED: An Operational Numerical Tool for Dosimetric Reconstruction in Case of External Radiological Overexposure.

ABSTRACT: In the event of a radiological accident involving external exposure of one or more victims and potential high doses, it is essential to know the dose distribution within the body in order to sort the victims according to the severity of the irradiation and then to take them to the most suitable medical facilities. However, there are currently few techniques that can be rapidly deployed on field and capable of characterizing an irradiation. Therefore, a numerical simulation tool has been designed. It can be implemented by a doctor/physicist pairing, projected within a limited time as close as possible to the irradiation accident and emergency response teams. Called SEED (Simulation of External Exposures & Dosimetry), this tool (dedicated to dose reconstruction in case of external exposure) allows a rapid modeling of the irradiation scene and a visual exchange with the victims and witnesses of the event. The user can navigate in three dimensions in the accident scene thanks to a graphical user interface including a "first person" camera. To validate the performance of the SEED tool, two dosimetric benchmarking exercises were performed. The first consisted in comparing the dose value provided by SEED to that given by a reference calculation code: MCNPX. The purpose of the second validation was to perform an experiment irradiating a physical dummy equipped with dosimeters and to reconstruct this irradiation using SEED. These two validation protocols have shown satisfactory results with mean difference less than 2% and 12% for the first and second exercises, respectively. They confirm that this new tool is able to provide useful information to medical teams in charge of dosimetric triage in case of a major external exposure event.

[Radiotherapy for HIV-infected patients]. / Spécificités de la prise en charge par radiothérapie chez les patients séropositifs pour le virus de l'immunodéficience humaine (VIH).

Since the advent of highly active antiretroviral therapy, cancer incidence is still 2 to 3-fold higher in patients infected by human immunodeficiency virus (HIV) than in the general population, with an increased incidence of malignancies not associated with acquired immunodeficiency syndrome (AIDS). HIV-infected patients cancer treatment does not differ from that in the general population. However, the management of those patients have some particularities due to preexisting comorbid conditions, including metabolic, cardiovascular, renal or hepatic complications and the risk for potential drug - drug interactions in HIV-infected patients. In this review, we described efficacy and tolerance of radiotherapy with or without chemotherapy in this frail population treated for cancer. Utilization of modern radiotherapy techniques such as intensity-modulated radiotherapy may improve the treatment tolerance.

EGFR-mediated macrophage activation promotes colitis-associated tumorigenesis.

Epidermal growth factor receptor (EGFR) signaling is a known mediator of colorectal carcinogenesis. Studies have focused on the role of EGFR signaling in epithelial cells, although the exact nature of the role of EGFR in colorectal carcinogenesis remains a topic of debate. Here, we present evidence that EGFR signaling in myeloid cells, specifically macrophages, is critical for colon tumorigenesis in the azoxymethane-dextran sodium sulfate (AOM-DSS) model of colitis-associated carcinogenesis (CAC). In a human tissue microarray, colonic macrophages demonstrated robust EGFR activation in the pre-cancerous stages of colitis and dysplasia. Utilizing the AOM-DSS model, mice with a myeloid-specific deletion of Egfr had significantly decreased tumor multiplicity and burden, protection from high-grade dysplasia and significantly reduced colitis. Intriguingly, mice with gastrointestinal epithelial cell-specific Egfr deletion demonstrated no differences in tumorigenesis in the AOM-DSS model. The alterations in tumorigenesis in myeloid-specific Egfr knockout mice were accompanied by decreased macrophage, neutrophil and T-cell infiltration. Pro-tumorigenic M2 macrophage activation was diminished in myeloid-specific Egfr-deficient mice, as marked by decreased Arg1 and Il10 mRNA expression and decreased interleukin (IL)-4, IL10 and IL-13 protein levels. Surprisingly, diminished M1 macrophage activation was also detectable, as marked by significantly reduced Nos2 and Il1b mRNA levels and decreased interferon (IFN)-γ, tumor necrosis factor (TNF)-α and IL-1ß protein levels. The alterations in M1 and M2 macrophage activation were confirmed in bone marrow-derived macrophages from mice with the myeloid-specific Egfr knockout. The combined effect of restrained M1 and M2 macrophage activation resulted in decreased production of pro-angiogenic factors, CXCL1 and vascular endothelial growth factor (VEGF), and reduced CD31+ blood vessels, which likely contributed to protection from tumorigenesis. These data reveal that EGFR signaling in macrophages, but not in colonic epithelial cells, has a significant role in CAC. EGFR signaling in macrophages may prove to be an effective biomarker of CAC or target for chemoprevention in patients with inflammatory bowel disease.

EGFR-independent mechanisms of acquired resistance to AZD9291 in EGFR T790M-positive NSCLC patients.

BACKGROUND: AZD9291 is an oral, irreversible, mutant-selective epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (EGFR-TKI), which specifically targets both sensitizing and resistant T790M mutations. This compound has shown outstanding activity, in a phase I/II (AURA) trial. However, despite impressive tumor responses in T790M-positive patients, acquired resistance to this drug limits the benefit of this compound. Mutations at the EGFR C797 codon, located within the kinase-binding site, were very recently reported to be a potential mechanism of resistance to AZD9291 in T790M-positive patients. PATIENTS AND METHODS: To identify potential mechanisms of resistance to AZD9291, we report here on two patients with resistant biopsy specimens that had been treated with AZD9291. RESULTS: We identified in two distinct cases, HER2 and MET amplification by FISH and CGH as a potential mechanism of acquired resistance to third-generation EGFR-TKI. Interestingly, this event occurred with complete loss of the T790M mutation. In one case, we observed a different molecular status at two biopsy sites (the T790M mutation at the primary site and wild-type T790M at the metastatic site with different pathways of acquired resistance to AZD9291). CONCLUSION: Our observations suggest that T790M-positive and wild-type T790M clones may coexist at baseline. AZD9291 efficiently suppresses the growth of T790M-positive cells, but a population of wild-type T790M cells at baseline will mediate the development of resistance, here via a by-pass pathway activating either HER2 or MET.

The novel melatonin agonist agomelatine (S20098) is an antagonist at 5-hydroxytryptamine2C receptors, blockade of which enhances the activity of frontocortical dopaminergic and adrenergic pathways.

Agomelatine (S20098) displayed pKi values of 6.4 and 6.2 at native (porcine) and cloned, human (h)5-hydroxytryptamine (5-HT)2C receptors, respectively. It also interacted with h5-HT2B receptors (6.6), whereas it showed low affinity at native (rat)/cloned, human 5-HT2A (<5.0/5.3) and 5-HT1A (<5.0/5.2) receptors, and negligible (<5.0) affinity for other 5-HT receptors. In antibody capture/scintillation proximity assays, agomelatine concentration dependently and competitively abolished h5-HT2C receptor-mediated activation of Gq/11 and Gi3 (pA2 values of 6.0 and 6.1). As measured by [3H]phosphatidylinositol depletion, agomelatine abolished activation of phospholipase C by h5-HT2C (pKB value of 6.1) and h5-HT2B (pKB value of 6.6) receptors. In vivo, it dose dependently blocked induction of penile erections by the 5-HT2C agonists (S)-2-(6-chloro-5-fluoroindol-1-yl)-1-methylethylamine (Ro60,0175) and 1-methyl-2-(5,8,8-trimethyl-8H-3-aza-cyclopenta[a]inden-3-yl) ethylamine (Ro60,0332). Furthermore, agomelatine dose dependently enhanced dialysis levels of dopamine in frontal cortex of freely moving rats, whereas they were unaffected in nucleus accumbens and striatum. Although the electrical activity of ventrotegmental dopaminergic neurons was unaffected agomelatine, it abolished their inhibition by Ro60,0175. Extracellular levels of noradrenaline in frontal cortex were also dose dependently enhanced by agomelatine in parallel with an acceleration in the firing rate of adrenergic cell bodies in the locus coeruleus. These increases in noradrenaline and dopamine levels were unaffected by the selective melatonin antagonist N-[2-(5-ethyl-benzo[b]thien-3-yl)ethyl] acetamide (S22153) and likely flect blockade of 5-HT2C receptors inhibitory to frontocortical dopaminergic and adrenergic pathways. Correspondingly, distinction to agomelatine, melatonin showed negligible activity 5-HT2C receptors and failed to modify the activity of adrenergic and dopaminergic pathways. In conclusion, in contrast to melatonin, agomelatine behaves as an antagonist at 5-HT2B and 5-HT2C receptors: blockade of the latter reinforces frontocortical adrenergic and dopaminergic transmission.

Piribedil enhances frontocortical and hippocampal release of acetylcholine in freely moving rats by blockade of alpha 2A-adrenoceptors: a dialysis comparison to talipexole and quinelorane in the absence of acetylcholinesterase inhibitors.

In a dialysis procedure not requiring perfusate addition of acetylcholinesterase inhibitors to "boost" basal levels of acetylcholine (ACh), the influence of the antiparkinson agent piribedil upon levels of ACh in frontal cortex and dorsal hippocampus of freely moving rats was compared with those of other antiparkinson drugs and selective ligands at alpha(2)-adrenoceptors (ARs). Suggesting a tonic, inhibitory influence of alpha(2A)-ARs upon cholinergic transmission, the alpha(2)-AR agonist 5-bromo-6-[2-imidazolin-2-yl-amino]-quinoxaline tartrate (UK14,304), and the preferential alpha(2A)-AR agonist guanabenz reduced levels of ACh. They were elevated by the antagonists 2(2-methoxy-1,4 benzodioxan-2-yl)-2-imidazoline HCl (RX821002) and atipamezole and by the preferential alpha(2A)-AR antagonist 2-(2H-(1-methyl-1,3-dihydroisoindole)methyl)-4,5-dihydroimidazole (BRL44008). In contrast, trans-2,3,9,13b-tetrahydro-1,2-dimethyl-1H-dibenz[c,f]imidazo[1,5-a]azepine (BRL41992) and prazosin, preferential alpha(2B/2C)-AR antagonists, were inactive. The dopaminergic agonist and antiparkinson agent piribedil, which behaves as an antagonist at alpha(2)-ARs, dose dependently increased extracellular levels of ACh. This action was absent upon pretreatment with a maximally effective dose of RX821002. On the other hand, a further dopaminergic agonist and antiparkinson agent, talipexole, which possesses agonist properties at alpha(2)-ARs, dose dependently reduced levels of ACh. This action was also blocked by RX821002. In contrast to piribedil and talipexole, quinelorane, which interacts with dopaminergic receptors but not alpha(2)-ARs, failed to affect ACh levels. Finally, in analogy to the frontal cortex, piribedil likewise elicited a dose-dependent increase in extracellular levels of ACh in the dorsal hippocampus. In conclusion, in distinction to talipexole and quinelorane, and reflecting its antagonist properties at alpha(2A)-ARs, piribedil reinforces cholinergic transmission in the frontal cortex and dorsal hippocampus of freely moving rats. These actions may be related to its facilitatory influence upon cognitive function.

Helicobacter pylori arginase inhibits nitric oxide production by eukaryotic cells: a strategy for bacterial survival.

The antimicrobial effect of nitric oxide (NO) is an essential part of innate immunity. The vigorous host response to the human gastric pathogen Helicobacter pylori fails to eradicate the organism, despite up-regulation of inducible NO synthase (iNOS) in the gastric mucosa. Here we report that wild-type strains of H. pylori inhibit NO production by activated macrophages at physiologic concentrations of l-arginine, the common substrate for iNOS and arginase. Inactivation of the gene rocF, encoding constitutively expressed arginase in H. pylori, restored high-output NO production by macrophages. By using HPLC analysis, we show that l-arginine is effectively consumed in the culture medium by wild-type but not arginase-deficient H. pylori. The substantially higher levels of NO generated by macrophages cocultured with rocF-deficient H. pylori resulted in efficient killing of the bacteria, whereas wild-type H. pylori exhibited no loss of survival under these conditions. Killing of the arginase-deficient H. pylori was NO-dependent, because peritoneal macrophages from iNOS(-/-) mice failed to affect the survival of the rocF mutant. Thus, bacterial arginase allows H. pylori to evade the immune response by down-regulating eukaryotic NO production.

Discriminative stimulus properties of the selective norepinephrine reuptake inhibitor, reboxetine, in rats.

RATIONALE: Although drug discrimination procedures have proven difficult to apply to antidepressant agents, we recently characterized discriminative stimulus properties of the selective serotonin (5-HT) reuptake inhibitor, citalopram, in rats. However, discriminative stimulus properties of selective norepinephrine (NE) reuptake inhibitors remain to be evaluated. OBJECTIVE: We determined the potential discriminative stimulus properties of the highly selective NE reuptake inhibitor and antidepressant, reboxetine. METHODS: Employing a two-lever discrimination procedure, rats were trained to discriminate reboxetine (2.5 mg/kg, IP) from saline. In parallel, the influence of reboxetine (2.5 mg/kg) upon dialysate levels of monoamines in frontal cortex and dorsal hippocampus of freely moving rats was determined. RESULTS: After 54+/-10 training sessions, reboxetine elicited robust stimulus recognition, fully generalizing to itself with an ED50 of 1.2 mg/kg. Two further NE reuptake inhibitors, desipramine (5.3) and maprotiline (1.8), as well as the 5-HT/NE reuptake inhibitor, venlafaxine (1.0), likewise generalized. In contrast, the 5-HT reuptake inhibitors, paroxetine, citalopram and sertraline, and the DA reuptake inhibitors, GBR12935 and bupropion, did not show significant generalization. Reboxetine markedly increased dialysate levels of NE, but not 5-HT, in frontal cortex and hippocampus. Dopamine (DA) levels were also (though less markedly) enhanced in frontal cortex. CONCLUSION: In parallel with an elevation in extracellular levels of NE, the selective NE reuptake inhibitor, reboxetine, elicits a specific discriminative stimulus in rats.

Anxiolytic properties of the selective, non-peptidergic CRF(1) antagonists, CP154,526 and DMP695: a comparison to other classes of anxiolytic agent.

The selective, non-peptidergic corticotropin-releasing factor (CRF)(1) receptor antagonists, CP154,526 and DMP695, dose-dependently increased punished responses of rats in a Vogel conflict test and enhanced social interaction (SI) of rats in an unfamiliar environment. They were, however, inactive in a plus-maze procedure and failed to reduce ultrasonic vocalizations (USV) associated with an aversive environment. In contrast, the benzodiazepine, chlordiazepoxide, was effective in all these procedures. Further, the serotonin (5-HT)(1A) agonist, flesinoxan, was active in each paradigm (except the plus-maze) while the 5-HT(2C) antagonist, SB242,084, was effective in the SI and Vogel but not the plus-maze and USV procedures. In contrast to chlordiazepoxide, flesinoxan and SB242,084, CP154,526 did not modify dialysate levels of 5-HT, norepinephrine (NE) and dopamine (DA) in the frontal cortex (FCX) of freely moving rats. In conclusion, CP154,526 and DMP695 possess a common and distinctive profile of anxiolytic action expressed in the absence of an intrinsic influence upon monoamine release.

S33005, a novel ligand at both serotonin and norepinephrine transporters: I. Receptor binding, electrophysiological, and neurochemical profile in comparison with venlafaxine, reboxetine, citalopram, and clomipramine.

S33005 displayed marked affinity for native, rat, and cloned human serotonin (5-HT) transporters (SERT) and less pronounced affinity for norepinephrine (NE) transporters (NET), while its affinity at dopamine (DA) transporters and >50 other sites was negligible. Reuptake of 5-HT and (less potently) NE into cerebral synaptosomes was inhibited by S33005, whereas DA reuptake was little affected. In vivo, S33005 prevented depletion of cerebral pools of 5-HT by parachloroamphetamine. Furthermore, it decreased electrical activity of raphe-localized serotonergic neurones, an action abolished by the 5-HT1A antagonist WAY100,635. At higher doses, S33005 blocked firing of locus ceruleus-localized adrenergic neurones, an action abolished by the alpha2-adrenergic antagonist idazoxan. In contrast, S33005 did not inhibit ventrotegmental dopaminergic neurones. In frontal cortex of freely moving rats, S33005 dose dependently elevated dialysate levels of 5-HT, NE, and DA. In hippocampus, levels of 5-HT and NE were similarly elevated, while in nucleus accumbens and striatum, levels of 5-HT were increased whereas DA was unaffected. Upon chronic (2 weeks) administration, basal levels of NE were elevated in frontal cortex and, therein, 5-HT2A receptor density was decreased. Comparative studies with clinically used antidepressants showed that venlafaxine possessed a profile similar to S33005 but was less potent. Clomipramine likewise interacted with SERTs and NETs but also with several other receptors types, while citalopram and reboxetine were preferential ligands of SERTs and NETs, respectively. In conclusion, S33005 interacts potently with SERTs and, less markedly, with NETs. It enhances extracellular levels of 5-HT and NE throughout corticolimbic structures and selectively elevates dialysis levels of DA in frontal cortex versus subcortical regions.

Generalization of serotonin (5-HT)1A agonists and the antipsychotics, clozapine, ziprasidone and S16924, but not haloperidol, to the discriminative stimuli elicited by PD128,907 and 7-OH-DPAT.

Rats were trained to recognize a discriminative stimulus (DS) elicited by the dopamine D(2)/D(3) receptor agonist, PD128,907 (0.16 mg/kg, i.p.), which suppressed frontocortical release of dopamine (DA) but not 5-HT. The selective 5-HT1A receptor agonists, 8-OH-DPAT and flesinoxan, dose-dependently generalized to PD128,907 with effective dose(50)s (ED50s) of 0.08 and 1.5mg/kg, s.c., respectively, and inhibited the release and synthesis of 5-HT but not of DA. The 'atypical' antipsychotic, clozapine, which displays weak partial agonist properties at 5-HT1A receptors, dose-dependently, though partially, generalized to PD128,907 (50%, 2.5mg/kg, s.c.). Further, S16924 and ziprasidone, which in a like manner, display partial agonist activity at 5-HT1A receptors, generalized with ED50s of 0.6 and 2.3mg/kg, s.c., respectively. In contrast, haloperidol, which is devoid of affinity at 5-HT1A sites, was inactive. At doses equivalent to those generalizing to PD128,907, clozapine, S16924 and ziprasidone reduced serotonergic (but not dopaminergic) transmission, whereas haloperidol was inactive. In rats trained to recognize a further D2/D3 agonist, 7-OH-DPAT (0.16 mg/kg, i.p.), generalization was obtained similarly with 8-OH-DPAT (ED50 = 0.07 mg/kg, s.c.), flesinoxan (3.4) and clozapine (0.6), but not with haloperidol. In conclusion, although PD128,907 and 7-OH-DPAT do not directly interact with 5-HT1A receptors or influence serotonergic transmission, their DS properties are mimicked by 5-HT1A receptor agonists at doses activating 5-HT1A but not D2/D3 (auto)receptors. These observations likely account for generalization of clozapine, S16924 and ziprasidone to PD128,907 and 7-OH-DPAT inasmuch as they behave as antagonists at D2/D3 receptors, yet agonists at 5-HT1A (auto)receptors.

Antiparkinsonian agent piribedil displays antagonist properties at native, rat, and cloned, human alpha(2)-adrenoceptors: cellular and functional characterization.

Compared with cloned, human (h)D(2) receptors (pK(i) = 6.9), the antiparkinsonian agent piribedil showed comparable affinity for halpha(2A)- (7.1) and halpha(2C)- (7.2) adrenoceptors (ARs), whereas its affinity for halpha(2B)-ARs was less marked (6.5). At halpha(2A)- and halpha(2C)-ARs, piribedil antagonized induction of [(35)S]guanosine-5'-O-(3-thio)triphosphate (GTPgammaS) binding by norepinephrine (NE) with pK(b) values of 6.5 and 6.9, respectively. Furthermore, Schild analysis of the actions of piribedil at halpha(2A)-ARs indicated competitive antagonism, yielding a pA(2) of 6.5. At a porcine alpha(2A)-AR-Gi1alpha-Cys351C (wild-type) fusion protein, piribedil competitively abolished (pA(2) = 6.5) GTPase activity induced by epinephrine. However, at a alpha(2A)-AR-Gi1alpha-Cys351I (mutant) fusion protein of amplified sensitivity, although still acting as a competitive antagonist (pA(2) = 6.2) of epinephrine, piribedil itself manifested weak partial agonist properties. Similarly, piribedil weakly induced mitogen-activated protein kinase phosphorylation via wild-type halpha(2A)-ARs, although attenuating its phosphorylation by NE. As demonstrated by functional [(35)S]GTPgammaS autoradiography in rats, piribedil antagonized activation by NE of alpha(2)-ARs in cortex, amygdala, and septum. Antagonist properties were also expressed in a dose-dependent enhancement of the firing rate of adrenergic neurons in locus ceruleus (0.125-4.0 mg/kg i.v.). Furthermore, piribedil (2.5-4.0 mg/kg s.c.) accelerated hippocampal NE synthesis, elevated dialysis levels of NE in hippocampus and frontal cortex, and blocked hypnotic-sedative properties of the alpha(2)-AR agonist xylazine. Finally, piribedil showed only modest affinity for rat alpha(1)-ARs (5.9) and weakly antagonized NE-induced activation of phospholipase C via halpha(1A)-ARs (pK(b) = 5.6). In conclusion, piribedil displays essentially antagonist properties at cloned, human and cerebral, rat alpha(2)-ARs. Blockade of alpha(2)-ARs may, thus, contribute to its clinical antiparkinsonian profile.

Selective blockade of neurokinin (NK)(1) receptors facilitates the activity of adrenergic pathways projecting to frontal cortex and dorsal hippocampus in rats.

The selective NK(1) receptor antagonist, GR205,171 (2.5-40.0 mg/kg, i.p.), dose-dependently elevated dialysate levels of noradrenaline (NA), but not serotonin (5-HT), in the frontal cortex of freely moving rats. This action was exerted stereospecifically inasmuch as its less active isomer, GR226,206, was ineffective. In the dorsal hippocampus, GR205,171 (but not GR226,206) also significantly increased dialysate levels of NA, whereas levels of 5-HT were unaffected. Further, in anaesthetized rats, GR205,171 dose-dependently (1.0-4.0 mg/kg, i.v.) increased the firing rate of adrenergic perikarya in the locus coeruleus. In contrast, their activity was not modified by GR226,206. These findings indicate that selective blockade of NK(1) receptors enhances the activity of ascending adrenergic pathways in rats. Adrenergic mechanisms may, thus, be involved in the potential antidepressant and other functional properties of NK(1) receptor antagonists.

S18616, a highly potent spiroimidazoline agonist at alpha(2)-adrenoceptors: II. Influence on monoaminergic transmission, motor function, and anxiety in comparison with dexmedetomidine and clonidine.

The alpha(2)-adrenoceptor (AR) agonist, S18616 ((S)-spiro[(1-oxa-2-amino-3-azacyclopent-2-ene)-4,2'-(8'-chloro-1' , 2',3',4'-tetrahydronaphthalene)] accompanying article), suppressed electrical activity of adrenergic neurons in the locus ceruleus, an action reversed by the alpha(2)-AR antagonist, idazoxan, which itself enhanced their firing rate. Electrical activity of serotonergic neurons in the dorsal raphe nucleus was similarly suppressed, an action likewise blocked by idazoxan, which did not, itself, influence firing. In freely moving rats, S18616 decreased extracellular levels of norepinephrine (NE), serotonin (5-HT), and dopamine (DA) in frontal cortex and hippocampus. The selective alpha(2)- versus alpha(1)-AR antagonists, atipamezole and BRL-44408 (a preferential alpha(2A)-AR antagonist), elevated levels of NE and DA but not 5-HT. In their presence, the influence of S18616 on frontocortical levels of NE, DA, and 5-HT was blocked. In contrast, prazosin, a selective alpha(1)- versus alpha(2)-AR antagonist (which also preferentially blocks alpha(2B/2C)-ARs) dose dependently decreased levels of 5-HT, but not NE and DA, and failed to modify the actions of S18616. Ultrasonic vocalizations elicited by rats in an aversive environment were inhibited by S18616, which also suppressed aggressive and marble-burying behaviors in mice. Furthermore, S18616 (biphasically) enhanced punished responses in the Vogel conflict test and active social interaction tests in rats. At higher doses, S18616 displayed sedative/hypnotic properties. Both anxiolytic and motor actions of S18616 were inhibited by atipamezole and BRL-44408 but not prazosin. Dexmedetomidine mimicked the actions of S18616 at higher doses except for more potent sedative/hypnotic properties. Clonidine also mimicked S18616, but only at markedly higher doses. In conclusion, via activation of alpha(2)-ARs, S18616 potently inhibits corticolimbic adrenergic, serotonergic, and (frontocortical) dopaminergic transmission in parallel with the expression of its anxiolytic and sedative properties.

The selective serotonin (5-HT)1A receptor ligand, S15535, displays anxiolytic-like effects in the social interaction and Vogel models and suppresses dialysate levels of 5-HT in the dorsal hippocampus of freely-moving rats. A comparison with other anxiolytic agents.

RATIONALE: The benzodioxane, S15535, possesses low intrinsic activity and marked selectivity at 5-HT1A receptors, hippocampal populations of which are implicated in anxious states. OBJECTIVE: Herein, we examined its potential anxiolytic actions in relation to its influence upon extracellular levels of 5-HT in the dorsal hippocampus of freely-moving rats. Its effects were compared with those of other anxiolytic agents: the 5-HT1A agonists, buspirone and 8-hydroxy-2-(di-n-propylamino)-tetralin HBr (8-OH-DPAT), the 5-HT2C antagonist, SB206,553 and the benzodiazepine, diazepam. METHODS: Potential anxiolytic actions were evaluated in the Vogel conflict paradigm (increase in punished responses) and the social interaction (SI) test (increase in active SI) in rats. Extracellular levels of 5-HT were determined by microdialysis. RESULTS: In analogy to diazepam. S15535 increased punished responses in the Vogel test. This action was dose dependently expressed over a broad (16-fold) dose range. Buspirone and 8-OH-DPAT were likewise active, but yielded highly biphasic dose-response curves. SB206,553 was dose dependently active in this model. In the SI test, S15535 similarly mimicked the anxiolytic-like effect of diazepam and was active over a broad dose range. Buspirone and 8-OH-DPAT again showed biphasic dose-response curves, as did SB206,553. In both the Vogel and SI tests, the anxiolytic-like effects of S15535 were abolished by the selective 5-HT1A receptor antagonist, WAY100,635, which was inactive alone. S15535 exerted its anxiolytic-like effects with a more pronounced separation to motor-disruptive doses than the other drugs. Finally, S15535 suppressed dialysate levels of 5-HT in the dorsal hippocampus, an action abolished by WAY100,635. Buspirone, 8-OH-DPAT and diazepam, but not SB206,553, also reduced 5-HT levels. CONCLUSION: Likely reflecting its distinctive ability to selectively and preferentially activate pre- versus postsynaptic 5-HT1A receptors, S15535 suppresses hippocampal 5-HT release and displays marked anxiolytic-like effects over a broad dose range in the relative absence of motor perturbation.

L-Arginine availability modulates local nitric oxide production and parasite killing in experimental trypanosomiasis.

Nitric oxide (NO) is an important effector molecule of the immune system in eliminating numerous pathogens. Peritoneal macrophages from Trypanosoma brucei brucei-infected mice express type II NO synthase (NOS-II), produce NO, and kill parasites in the presence of L-arginine in vitro. Nevertheless, parasites proliferate in the vicinity of these macrophages in vivo. The present study shows that L-arginine availability modulates NO production. Trypanosomes use L-arginine for polyamine synthesis, required for DNA and trypanothione synthesis. Moreover, arginase activity is up-regulated in macrophages from infected mice from the first days of infection. Arginase competes with NOS-II for their common substrate, L-arginine. In vitro, arginase inhibitors decreased urea production, increased macrophage nitrite production, and restored trypanosome killing. In vivo, a dramatic decrease in L-arginine concentration was observed in plasma from infected mice. In situ restoration of NO production and trypanosome killing were observed when excess L-arginine, but not D-arginine or L-arginine plus N(omega)-nitro-L-arginine (a NOS inhibitor), was injected into the peritoneum of infected mice. These data indicate the role of L-arginine depletion, induced by arginase and parasites, in modulating the L-arginine-NO pathway under pathophysiological conditions.

Reciprocal autoreceptor and heteroreceptor control of serotonergic, dopaminergic and noradrenergic transmission in the frontal cortex: relevance to the actions of antidepressant agents.

The frontal cortex (FCX) plays a key role in processes that control mood, cognition and motor behaviour, functions which are compromised in depression, schizophrenia and other psychiatric disorders. In this regard, there is considerable evidence that a perturbation of monoaminergic input to the FCX is involved in the pathogenesis of these states. Correspondingly, the modulation of monoaminergic transmission in the FCX and other corticolimbic structures plays an important role in the actions of antipsychotic and antidepressant agents. In order to further understand the significance of monoaminergic systems in psychiatric disorders and their treatment, it is essential to characterize mechanisms underlying their modulation. Within this framework, the present commentary focuses on our electrophysiological and dialysis analyses of the complex and reciprocal pattern of auto- and heteroreceptor mediated control of dopaminergic, noradrenergic and serotonergic transmission in the FCX. The delineation of such interactions provides a framework for an interpretation of the influence of diverse classes of antidepressant agent upon extracellular levels of dopamine, noradrenaline and serotonin in FCX. Moreover, it also generates important insights into strategies for the potential improvement in the therapeutic profiles of antidepressant agents.

The ability of WAY100,635 to potentiate the neurochemical and functional actions of fluoxetine is enhanced by co-administration of SB224,289, but not BRL15572.

The present study employed a combined neurochemical and behavioural approach to address the question of whether blockade of (presynaptic) 5-HT(1B) or 5-HT(1D) receptors enhances the facilitatory influence of 5-HT(1A) autoreceptor antagonism upon the actions of selective serotonin re-uptake inhibitors (SSRI). In the presence of the selective 5-HT(1A) antagonist, WAY100,635, the fluoxetine-induced increase in dialysate levels of 5-HT in the frontal cortex (FCX) of freely-moving rats was significantly potentiated. The selective 5-HT(1B) antagonist, SB224,289, likewise potentiated the increase in 5-HT levels evoked by fluoxetine. Further, administered together, WAY100,635 and SB224,289, at least additively, potentiated the influence of fluoxetine upon 5-HT levels. This effect was selective inasmuch as, either alone or together, WAY100,635 and SB224,289 did not modify the influence of fluoxetine upon FCX levels of dopamine (DA) or noradrenaline (NA) quantified in the same dialysis samples. Co-administration of SB224,289 also enhanced the ability of WAY100,635 to potentiate the induction of head-twitches (HTW) by fluoxetine. This response reflects activation of 5-HT(2A) sites in FCX and was abolished by the selective 5-HT(2A) antagonist, MDL100,907. In contrast to SB224,289, the 5-HT(1D) antagonist, BRL15572, failed to enhance the facilitatory influence of WAY100,635 upon the neurochemical or behavioural actions of fluoxetine. In conclusion, co-joint blockade of 5-HT(1B) - but not 5-HT(1D) - with 5-HT(1A) autoreceptors markedly potentiates the neurochemical and functional actions of the SSRI, fluoxetine.

S33084, a novel, potent, selective, and competitive antagonist at dopamine D(3)-receptors: I. Receptorial, electrophysiological and neurochemical profile compared with GR218,231 and L741,626.

The benzopyranopyrrole S33084 displayed pronounced affinity (pK(i) = 9.6) for cloned human hD(3)-receptors, and >100-fold lower affinity for hD(2) and all other receptors (>30) examined. S33084 concentration dependently, potently, and competitively (pA(2) = 9.7) antagonized dopamine (DA)-induced [(35)S]guanosine-5'- O-(3-thio)triphosphate (GTPgammaS) binding at hD(3)-receptors. It also concentration dependently abolished stimulation by DA of hD(3)-receptor-coupled mitogen-activated protein kinase. Administered alone, S33084 did not modify dialysate levels of DA in the frontal cortex, nucleus accumbens, or striatum of freely moving rats, nor the firing rate of ventrotegmental dopaminergic cell bodies. Furthermore, it had minimal effect on DA turnover in mesocortical, mesolimbic, and nigrostriatal projection regions. However, S33084 dose dependently blocked the suppressive influence of the preferential D(3)-agonist PD128,907 on frontocortical release of DA. Furthermore, it likewise antagonized the inhibitory influence of PD128,907 on the electrical activity of ventrotegmental dopaminergic neurons. Although less potent than S33084, GR218,231 likewise behaved as a selective hD(3)- versus hD(2)-receptor antagonist and its neurochemical and electrophysiological profiles were similar. In contrast, L741,626 was a preferential antagonist at hD(2) versus hD(3) sites. In vivo, on administration alone, L741,626 increased frontocortical, mesolimbic, and (more potently) striatal DA release, enhanced the firing rate of dopaminergic perikarya, and accelerated cerebral DA synthesis. It also blocked the actions of PD128,907. In conclusion, S33084 is a novel, potent, selective, and competitive antagonist at hD(3)-receptors. Although GR218,231 behaves similarly, L741,626 is a preferential D(2)-receptor antagonist. DA D(2)- but not D(3)-(auto) receptors tonically inhibit ascending dopaminergic pathways, although the latter may contribute to phasic suppression of DA release in frontal cortex.

Serotonin(2C) receptors tonically suppress the activity of mesocortical dopaminergic and adrenergic, but not serotonergic, pathways: a combined dialysis and electrophysiological analysis in the rat.

The present study evaluated, via a combined electrophysiological and dialysis approach, the potential influence of serotonin (5-HT)(2C) as compared to 5-HT(2A) and 5-HT(2B) receptors on dopaminergic, adrenergic, and serotonergic transmission in frontal cortex (FCX). Whereas the selective 5-HT(2A) antagonist MDL100,907 failed to modify extracellular levels of dopamine (DA), noradrenaline (NA) or 5-HT simultaneously quantified in single dialysate samples of freely-moving rats, the 5-HT(2B)/5-HT(2C) antagonist SB206,553 dose-dependently increased levels of DA and NA without affecting those of 5-HT. This action was attributable to 5-HT(2C) receptor blockade inasmuch as the selective 5-HT(2C) antagonist SB242,084 likewise increased FCX levels of DA and NA, whereas the selective 5-HT(2B) antagonist SB204,741 was ineffective. Further, the preferential 5-HT(2C) receptor agonist Ro60-0175 dose-dependently depressed FCX levels of DA. The suppressive influence of 5-HT(2C) receptors on DA release was also expressed on mesolimbic and nigrostriatal dopaminergic pathways, in that levels of DA in nucleus accumbens and striatum were likewise reduced by Ro60-0175 and elevated, though less markedly, by SB206,553. In line with the above findings, Ro60-0175 dose-dependently decreased the firing rate of ventrotegmental dopaminergic and locus coeruleus (LC) adrenergic perikarya, whereas their activity was dose-dependently enhanced by SB206,553. Furthermore, SB206,553 transformed the firing pattern of ventrotegmental dopaminergic neurons into a burst mode. In contrast to SB206,553, MDL100,907 had little affect on the firing rate of dopaminergic or adrenergic neurons. In conclusion, as compared to 5-HT(2A) and 5-HT(2B) receptors, 5-HT(2C) receptors exert a tonic, suppressive influence on the activity of mesocortical - as well as mesolimbic and nigrostriatal - dopaminergic pathways, likely via indirect actions expressed at the level of their cell bodies. Frontocortical adrenergic, but not serotonergic, transmission is also tonically suppressed by 5-HT(2C) receptors.