Henry N Nguyen

George Washington University, Washington, D. C., DC, United States

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Publications (6)24.09 Total impact

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    Henry N Nguyen, Bruce A Rasmussen, David C Perry
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    ABSTRACT: Chronic nicotine exposure up-regulates neuronal nicotinic receptors, but the functional consequences for these receptors is less well understood. Following 2 weeks of nicotine or saline treatment by osmotic minipump, the functional activity of nicotinic receptors was measured by concentration-response curves for epibatidine-stimulated (86)Rb efflux. Nicotine-treated animals had a significantly higher maximal efflux in cerebral cortex and superior colliculus, but not in thalamus or interpeduncular nucleus plus medial habenula. This increase was confirmed in a separate experiment with stimulation by single concentrations of epibatidine (cortex, superior colliculus) or nicotine (cortex only). Chronic nicotine did not alter (86)Rb efflux stimulated by cytisine, an alpha3beta4-selective agonist, or by potassium chloride, in any region. Short-term (16 h) nicotine exposure caused no changes in either (86)Rb efflux or receptor binding measured with [(3)H]epibatidine. Binding was significantly increased after 2 weeks nicotine exposure in cortex, superior colliculus and thalamus, but not in interpeduncular nucleus plus medial habenula. The increases in epibatidine-stimulated (86)Rb efflux in the four regions tested was linearly correlated with the increases in [(3)H]epibatidine binding in these regions (R(2) = 0.91), suggesting that rat brain receptors up-regulated by chronic nicotine are active. These results have important consequences for understanding nicotinic receptor neurobiology in smokers and users of nicotine replacement therapy.
    Journal of Neurochemistry 08/2004; 90(1):40-9. · 3.97 Impact Factor
  • Henry N Nguyen, Bruce A Rasmussen, David C Perry
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    ABSTRACT: Subtypes of neuronal nicotinic acetylcholine receptors (nAChRs) are differentially sensitive to up-regulation by chronic nicotine exposure in vitro. To determine whether this occurs in animals, rats were implanted with minipumps containing saline +/- nicotine (6.0 mg/kg/rat/day) for 14 days. Autoradiography with [125I]epibatidine using 3-(2(S)-azetidinylmethoxy)pyridine dihydrochloride (A-85380) or cytisine as selective competitors allowed quantitative measurement in 33 regions of 3 families of nAChR binding, with properties of alpha4beta2, alpha3beta4, and alpha3/alpha6beta2. Chronic nicotine exposure caused increases of 20 to 100% for alpha4beta2-like binding in most regions surveyed. However, binding to this subtype was not increased in some regions, including habenulopeduncular structures, certain thalamic nuclei, and several brainstem regions. In 9 of 33 regions, including catecholaminergic areas and visual structures, alpha3/alpha6beta2-like binding represented >10% of total binding. Binding to this subtype was up-regulated by nicotine in only two of these nine regions: the nucleus accumbens and superior colliculus. alpha3beta4-Like binding represented >10% of total in 15 of the 33 regions surveyed. Binding to this subtype was increased by nicotine in only 1 of these 15 regions, and actually decreased in subiculum and cerebellum. These studies yielded two principal findings. First, chronic nicotine exposure selectively up-regulates alpha4beta2-like binding, with relatively little effect on alpha3/alpha6beta2-like and alpha3beta4-like binding in vivo. Second, up-regulation by chronic nicotine exposure shows considerable regional variation. Differential subtype sensitivity to chronic nicotine exposure may contribute to altered pharmacological response in individuals who smoke or use nicotine replacement therapy.
    Journal of Pharmacology and Experimental Therapeutics 12/2003; 307(3):1090-7. · 3.89 Impact Factor
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    ABSTRACT: Comparison of [125I]epibatidine and 5-[125I]iodo-3-(2-azetidinylmethoxy)pyridine ([125I]A-85380) autoradiography showed evidence for nicotinic receptor heterogeneity. To identify the receptor subtypes, we performed [125I]epibatidine autoradiography in the presence of cytisine or A-85380. By comparing these results with binding data from human embryonic kidney (HEK) 293 cells stably transfected with different combinations of rat nicotinic receptor subunits, we were able to quantify three distinct populations of [125I]epibatidine binding sites with characteristics of alpha4beta2, alpha3beta2 and alpha3beta4 receptors. Although the predominant subtype in rat brain was alpha4beta2, non-alpha4beta2 binding sites were prominent in many regions. In the habenulo-peduncular system, cerebellum, substantia gelatinosa, and many medullary nuclei, alpha3beta4-like binding accounted for more than 40% of [125I]epibatidine binding, and nearly all binding in superior cervical ganglion and pineal gland. Other regions enriched in alpha3beta4-like binding included locus ceruleus, dorsal tegmentum, subiculum and anteroventral thalamic nucleus. Regions enriched in alpha3beta2-like binding included the habenulo-peduncular system, many visual system structures, certain geniculate nuclei, and dopaminergic regions. The combination of autoradiography using a broad spectrum radioligand in the presence of selective competitors, and data from binding to defined receptor subtypes in expression systems, allowed us to quantify the relative populations of these three subtypes.
    Journal of Neurochemistry 09/2002; 82(3):468-81. · 3.97 Impact Factor
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    ABSTRACT: Comparison of [125I]epibatidine and 5-[125I]iodo-3-(2-azetidinylmethoxy)pyridine ([125I]A-85380) autoradiography showed evidence for nicotinic receptor heterogeneity. To identify the receptor subtypes, we performed [125I]epibatidine autoradiography in the presence of cytisine or A-85380. By comparing these results with binding data from human embryonic kidney (HEK) 293 cells stably transfected with different combinations of rat nicotinic receptor subunits, we were able to quantify three distinct populations of [125I]epibatidine binding sites with characteristics of α4β2, α3β2 and α3β4 receptors. Although the predominant subtype in rat brain was α4β2, non-α4β2 binding sites were prominent in many regions. In the habenulo-peduncular system, cerebellum, substantia gelatinosa, and many medullary nuclei, α3β4-like binding accounted for more than 40% of [125I]epibatidine binding, and nearly all binding in superior cervical ganglion and pineal gland. Other regions enriched in α3β4-like binding included locus ceruleus, dorsal tegmentum, subiculum and anteroventral thalamic nucleus. Regions enriched in α3β2-like binding included the habenulo-peduncular system, many visual system structures, certain geniculate nuclei, and dopaminergic regions. The combination of autoradiography using a broad spectrum radioligand in the presence of selectivecompetitors, and data from binding to defined receptor subtypes in expression systems, allowed us to quantify the relative populations of these three subtypes.
    Journal of Neurochemistry 07/2002; 82(3):468 - 481. · 3.97 Impact Factor
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    ABSTRACT: To determine the role of calcium homeostasis in ischemic neuronal death, the authors used an in vitro model of oxygen-glucose deprivation in neuronal cell lines. Exposure of human neuroblastoma SH-SY5Y cells to 10-to 16-hour oxygen-glucose deprivation decreased viability to 50% or less, and longer exposure times killed almost all cells. The death following 10-to 16-hour oxygen-glucose deprivation was not manifested until 24 to 72 hours after exposure. Deprivation of both glucose and oxygen together was required for expression of toxicity at these exposure times. Dantrolene, which blocks the release of endoplasmic reticulum Ca2+ stores, partially protected SH-SY5Y cells from oxygen-glucose deprivation toxicity. The addition of dantrolene during the deprivation phase alone produced the maximal drug effect; no further protection was obtained by continued drug exposure during the recovery phase. Prevention of Ca2+ influx by chelation or channel blockade or the chelation of cytosolic Ca2+ did not inhibit oxygen-glucose deprivation toxicity. In contrast, increasing extracellular Ca2+ or stimulating Ca2+ influx did inhibit toxicity. Calcium measurements with fura-2 acetoxymethylester revealed that oxygen-glucose deprivation caused a significant reduction in thapsigargin-releasable endoplasmic reticular stores of Ca2+. These studies suggest that an important component of the neuronal toxicity in cerebral ischemia is due to disruption of calcium homeostasis, particularly to the depletion of intracellular Ca2+ stores.
    Journal of Cerebral Blood Flow & Metabolism 03/2002; 22(2):206-14. · 5.40 Impact Factor
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    Henry N Nguyen, Chen Wang, David C Perry
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    ABSTRACT: Inhibiting Ca(2+) uptake by the sarcoendoplasmic reticular Ca(2+)-ATPase pump (SERCA) causes release of Ca(2+) from the endoplasmic reticulum (ER), increased cytosolic Ca(2+) ([Ca(2+)](cyt)) and depletion of ER Ca(2+) stores. These studies were designed to test the effects of SERCA inhibition on neuronal viability, using as a model the human neuroblastoma cell line, SH-SY5Y. Continuous exposure to the SERCA inhibitor thapsigargin (TG) decreased SH-SY5Y viability to <30% after 48 h exposure, and produced DNA laddering. Two other SERCA inhibitors, BHQ and cyclopiazonic acid CPA, were similarly toxic, although at 1000-fold higher concentrations. BHQ and CPA toxicity was prevented by removing drug within several hours, whereas TG toxicity was essentially irreversible. All three SERCA inhibitors caused an increase in [Ca(2+)](cyt) that was partially blocked by the ryanodine receptor inhibitors, dantrolene and DHBP. Pretreatment with 40 microM dantrolene gave substantial protection against TG- or BHQ-induced cell death but it did not inhibit death from staurosporine, which does not cause release of ER Ca(2+). DHBP (20-100 microM) also gave partial protection against TG toxicity, as did ruthenium red (2 microM), but not ryanodine (10 microM). Inhibition of capacitative Ca(2+) entry with EGTA or LaCl(3) or low extracellular Ca(2+), or chelation of [Ca(2+)](cyt) with BAPTA-AM, failed to inhibit TG toxicity, although they prevented increases in [Ca(2+)](cyt) caused by TG. Taken together, these data suggest that toxicity caused by SERCA inhibition in SH-SY5Y cells is caused by ER Ca(2+) depletion, which triggers an apparent apoptotic pathway.
    Brain Research 01/2002; 924(2):159-66. · 2.88 Impact Factor