Biomedical subjects

L Virag

Publications and source records attributed to L Virag.

7 recordsLinked to original sources

PubMed1999

Reduction of cognitive and motor deficits after traumatic brain injury in mice deficient in poly(ADP-ribose) polymerase.

Poly(ADP-ribose) polymerase (PARP), or poly-(ADP-ribose) synthetase, is a nuclear enzyme that consumes NAD when activated by DNA damage. The role of PARP in the pathogenesis of traumatic brain injury (TBI) is unknown. Using a controlled cortical impact (CCI) model of TBI and mice deficient in PARP, the authors studied the effect of PARP on functional and histologic outcome after CCI using two protocols. In protocol 1, naive mice (n = 7 +/+, n = 6 -/-) were evaluated for motor and memory acquisition before CCI. Mice were then subjected to severe CCI and killed at 24 hours for immunohistochemical detection of nitrated tyrosine, an indicator of peroxynitrite formation. Motor and memory performance did not differ between naive PARP +/+ and -/- mice. Both groups showed nitrotyrosine staining in the contusion, suggest ing that peroxynitrite is produced in contused brain. In protoco 2, mice (PARP +/+, n = 8; PARP -/-, n = 10) subjected to CCI were tested for motor and memory function, and contusion volume was determined by image analysis. PARP -/- mice demonstrated improved motor and memory function after CC versus PARP +/+ mice (P < 0.05). However, contusion volume was not different between groups. The results suggest a detri mental effect of PARP on functional outcome after TBI.

Animals↗

PubMed1998

Interaction of the alpha-2 adrenergic- and opioid receptor with the cGMP system in the mouse cerebellum.

The alpha-2 adrenergic agonist dexmedetomidine (Dex), 3-300 microg/kg, i.p., decreased cerebellar cGMP in a dose-dependent manner. Fentanyl (F), an opioid agonist, increased cerebellar cGMP at 0.3 mg/kg, s.c., and decreased it at doses >/=1 mg/kg. The inhibitory effect was receptor specific, that of Dex being blocked by the alpha-2 adrenergic antagonist yohimbine, 5 mg/kg, i.p.; that of F by the opioid antagonist naloxone, 5 mg/kg, i.p. In contrast the stimulatory effect of F was blocked by both naloxone and yohimbine. Yohimbine also enhanced the inhibitory effect of F. In mice pretreated with pertussis toxin, 2 microgram/mouse, given i.c.v. 72 h before the agonists, the decrease in cGMP induced by Dex or F was not affected, while the stimulatory effect of F was reversed to an inhibitory effect. When inhibiting doses of F and Dex were administered together, the cGMP response was smaller than the sum of the individual responses. Dex attenuated in a dose-dependent manner the decrease in cGMP induced by F, and unmasked or enhanced the stimulatory effect of F. These results show that the alpha-2 adrenergic- and opioid-receptors are coupled to the cGMP effector system and suggest that the two pathways converge at a common post-receptor site in the cascade of events transducing the receptor signal to cGMP regulation.

Adrenergic alpha-Agonists↗

PubMed1998

NADPH diaphorase-positive dendritic profiles in rat thymus are discrete from autofluorescent cells, immunoreactive for inducible nitric oxide synthase, and show strain-specific abundance differences.

Predisposition to autoimmune disorder in Lewis rats has been associated with abnormal hypothalamic regulation of circulating steroids, leading to inadequate suppression of T helper 1 (Th1) cell-mediated inflammatory reactions. In addition, autoimmune syndromes can be triggered within formerly resistant animals, following damage to the negative selection process of the thymus. A contribution to the autoimmune-susceptible phenotype may therefore derive from the status of thymic tolerance. One mechanism of intrathymic negative selection may involve nitric oxide. Because inducible nitric oxide synthase (iNOS) is known to be inhibitable by steroids, its expression might be different within strains having neuroendocrine disturbance. We report on a study to compare intrathymic iNOS expression in autoimmune-prone Lewis rats with other resistant strains. Interdigitating cells (IDC), darkly stained for diaphorase, were confirmed as immunoreactive for iNOS. They were located towards the medullary side of an accumulation of unstained, but autofluorescent cells (presumed to be macrophages) that circumscribes the corticomedullary zone. The role of iNOS+ IDC in the apoptotic deletion of T cells has been suggested by other studies. Despite the blunted steroidal condition reported for Lewis, nitrergic cell abundance was shown, by quantitative analysis of histochemical stain, to be on average approximately twofold lower compared with resistant strains (Fischer and Sprague-Dawley). This trend was evident in males and females, and confirmed by independent observers. We hypothesize that an intrathymic, iNOS-dependent mechanism may be important for the suppression of potentially autoreactive T-cell clones.

Animals↗

PubMed1996

Determination of cocaine, norcocaine, benzoylecgonine and ecgonine methyl ester in rat plasma by high-performance liquid chromatography with ultraviolet detection.

An isocratic high-performance liquid chromatographic method with ultraviolet detection at 235 nm is described for the determination of cocaine and its metabolites benzoylecgonine, norcocaine and ecgonine methyl ester in rat plasma, collected during toxicity studies. Following simultaneous solid-phase extraction of all analytes and the internal standard tropacocaine, cocaine, benzoylecgonine and norcocaine were separated on a C18 column. Ecgonine methyl ester and cocaine were separated on coupled cyanopropyl and silica columns, following derivatization of ecgonine methyl ester to p-fluorococaine. The extraction efficiencies of these compounds from plasma ranged from 78 to 87%, while the limits of detection ranged from 35 to 90 ng/ml. The assay was linear from 300 to 5000 ng/ml, and the within-day precision 2 to 8% over this concentration range.

Animals↗

PubMed1996

Alpha-2 adrenoceptor agonists decrease cyclic guanosine 3',5'-monophosphate in the mouse brain.

BACKGROUND: In the central nervous system neurotransmitters, drugs or conditions that excite increase cyclic guanosine 3',5'-monophosphate (cGMP), an effect mediated by the neuromodulator nitric oxide, whereas those that sedate decrease cGMP. Volatile anesthetics were shown to decrease cerebellar cGMP, an effect that correlates with their anesthetic and anticonvulsant effect. Because alpha-2 adrenoceptor agonists have anesthetic properties, the role of the nitric oxide-cGMP pathway in the action of the alpha-2 adrenoceptor agonists clonidine and dexmedetomidine was investigated. METHODS: Groups of mice were given, intraperitoneally, one dose of either 30-600 micrograms/kg clonidine, or 3-300 micrograms/kg D-medetomidine (dexmedetomidine) or L-medetomidine. The alpha-2 adrenoceptor antagonists, 0.3-5 mg/kg yohimbine or 1 mg/kg atipamezole, 1 mg/kg of the alpha-1 antagonist prazosin, and 10-300 mg/kg of the nitric oxide synthase inhibitors, N omega-nitro-1-arginine methylester and N omega-nitro-1-arginine, were given 10-20 min before the agonist. The mice were killed by microwave radiation focused to the head. Cyclic GMP was measured by radioimmunoassay in deproteinized extracts from different brain areas. RESULTS: Clonidine and dexmedetomidine, at sedative doses, dose-dependently decreased cerebellar cGMP (ED50: 100 and 50 micrograms/kg for clonidine and dexmedetomidine, respectively). This effect was inhibited by yohimbine and atipamezole, but not by prazosin, confirming the alpha-2 nature of the response to the agonists. L-medetomidine, which has no sedative/hypnotic effect, did not decrease cGMP. Pretreatment of the mice with a maximum dose of 100 mg/kg of a nitric oxide synthase antagonist abolished the cGMP response to the agonists. Similar results were obtained in the cerebral cortex, hippocampus and caudate nucleus. CONCLUSIONS: The results suggest that the nitric oxide-cGMP pathway is an effector system coupled to the alpha-2 adrenoceptor mediating sedation.

Adrenergic alpha-2 Receptor Agonists↗

PubMed1995

Lethal toxicity from equimolar infusions of cocaine and cocaine metabolites in conscious and anesthetized rats.

We compared the lethal toxicity of cocaine with that of three of its metabolites to determine the contribution of these metabolites to the lethal potential from cocaine infusion. Equimolar quantities of cocaine, norcocaine, benzoylecgonine, and ecgonine methyl ester were infused in conscious rats to determine onset of convulsions and respiratory arrest. In addition, the convulsive and respiratory toxicity for cocaine and norcocaine were evaluated in anesthetized rats and their circulatory toxicity in anesthetized and ventilated rats. Norcocaine infusion resulted in earlier onset of convulsions and respiratory arrest in conscious rats than cocaine and earlier onset of circulatory arrest. Plasma concentrations of norcocaine and cocaine were not different at these times. Benzoylecgonine and ecgonine methyl ester were less potent convulsants and respiratory depressants than norcocaine and cocaine, with ecgonine methyl ester more respiratory depressant than benzoylecgonine. Pentobarbital anesthesia enhanced the respiratory depression and suppressed or delayed the onset of convulsions from norcocaine and cocaine infusion. Prolonged infusion of cocaine to circulatory arrest resulted in benzoylecgonine concentrations approximately 60%, and norcocaine concentrations approximately 5%, of the cocaine concentration, but no detectable ecgonine methyl ester formation. We conclude that although norcocaine, ecgonine methyl ester, and benzoylecgonine administered separately have lethal potential in massive dosages, death from cocaine overdose primarily results from the parent compound and not from metabolite formation.

Animals↗

PubMed1994

Sensitive assay for cocaine and benzoylecgonine using solid-phase extraction and gas chromatography.

An improved method for the simultaneous determination of cocaine and benzoylecgonine by means of gas chromatography with nitrogen-phosphorus detection is described. Following a solid-phase extraction and derivatization of benzoylecgonine to its butyl ester, chromatography was performed using a capillary column. The n-propylester of benzoylecgonine served as the internal standard. The assay was linear from 4 to 2000 ng/ml for both cocaine and benzoylecgonine, with a good precision over this concentration range. This method may be particularly useful for small volume samples since it requires only 250 microliters of plasma for analysis of both cocaine and benzoylecgonine.

Chromatography, Gas↗