Biomedical subjects

V L Dawson

Publications and source records attributed to V L Dawson.

At least 55 records · Page 3Linked to original sources

PubMed1999

Rate and severity of HIV-associated dementia (HAD): correlations with Gp41 and iNOS.

BACKGROUND: Fifteen to thirty percent of AIDS patients develop some type of neurologic disorder during the course of their illness and the vast majority of these neurologic disorders will be HIV-associated dementia (HAD). These patients can exhibit varying degrees of severity and rates of progression of HAD. Neuropathologic variables that are associated with the rate of progression of HAD are not known. MATERIALS AND METHODS: Tissue was collected at autopsy from the Johns Hopkins University HIV Neurology Program. Seventy-one AIDS patients of this prospectively characterized population were followed until death to obtain information on dementia severity and the rate of neurological progression. Immunoblot analysis of immunological nitric oxide synthase (iNOS), HAM56, gp41, p24, gp120, and beta-tubulin was performed and the levels of iNOS, HAM56, gp41, and p24 were normalized to beta-tubulin and analyzed for significance by means of the Kruskal-Wallis test for multiple groups. RESULTS: We have identified unique groups within this spectrum and designated them slow, moderate, and rapid progressors. Slow and moderate progressors' neurological progression occurs over a course of months to years, whereas the rapid progressors' disease shows rapid increases in severity over weeks to months. In the present study we demonstrate that the severity and rate of progression of HAD correlates significantly with levels of the HIV-1 coat protein, gp41, iNOS, and HAM56, a marker of microglial/macrophage activation. CONCLUSION: The severity and rate of progression of HAD correlates with indices of immune activation as well as levels of iNOS and gp41. There appears to be a threshold effect in which high levels of gp41, iNOS, and immune activation are particularly associated with severe (Memorial Sloan-Kettering score 3 to 4) and rapidly progressive HAD.

AIDS Dementia Complex↗

PubMed1998

Interaction between neuronal nitric oxide synthase and inhibitory G protein activity in heart rate regulation in conscious mice.

Nitric oxide (NO) synthesized within mammalian sinoatrial cells has been shown to participate in cholinergic control of heart rate (HR). However, it is not known whether NO synthesized within neurons plays a role in HR regulation. HR dynamics were measured in 24 wild-type (WT) mice and 24 mice in which the gene for neuronal NO synthase (nNOS) was absent (nNOS-/- mice). Mean HR and HR variability were compared in subsets of these animals at baseline, after parasympathetic blockade with atropine (0.5 mg/kg i.p.), after beta-adrenergic blockade with propranolol (1 mg/kg i.p.), and after combined autonomic blockade. Other animals underwent pressor challenge with phenylephrine (3 mg/kg i.p.) after beta-adrenergic blockade to test for a baroreflex-mediated cardioinhibitory response. The latter experiments were then repeated after inactivation of inhibitory G proteins with pertussis toxin (PTX) (30 microgram/kg i.p.). At baseline, nNOS-/- mice had higher mean HR (711+/-8 vs. 650+/-8 bpm, P = 0.0004) and lower HR variance (424+/-70 vs. 1,112+/-174 bpm2, P = 0.001) compared with WT mice. In nNOS-/- mice, atropine administration led to a much smaller change in mean HR (-2+/-9 vs. 49+/-5 bpm, P = 0.0008) and in HR variance (64+/-24 vs. -903+/-295 bpm2, P = 0.02) than in WT mice. In contrast, propranolol administration and combined autonomic blockade led to similar changes in mean HR between the two groups. After beta-adrenergic blockade, phenylephrine injection elicited a fall in mean HR and rise in HR variance in WT mice that was partially attenuated after treatment with PTX. The response to pressor challenge in nNOS-/- mice before PTX administration was similar to that in WT mice. However, PTX-treated nNOS-/- mice had a dramatically attenuated response to phenylephrine. These findings suggest that the absence of nNOS activity leads to reduced baseline parasympathetic tone, but does not prevent baroreflex-mediated cardioinhibition unless inhibitory G proteins are also inactivated. Thus, neuronally derived NO and cardiac inhibitory G protein activity serve as parallel pathways to mediate autonomic slowing of heart rate in the mouse.

Animals↗

PubMed1998

Nitric oxide mediates N-methyl-D-aspartate receptor-induced activation of p21ras.

N-methyl-D-aspartate (NMDA) glutamate receptor-mediated increases in intracellular calcium are thought to play a critical role in synaptic plasticity. The mechanisms by which changes in cytoplasmic calcium transmit the glutamate signal to the nucleus, which is ultimately important for long-lasting neuronal responses, are poorly understood. We show that NMDA receptor stimulation leads to activation of p21(ras) (Ras) through generation of nitric oxide (NO) via neuronal NO synthase. The competitive NO synthase inhibitor, L-nitroarginine methyl ester, prevents Ras activation elicited by NMDA and this effect is competitively reversed by the NO synthase substrate, L-arginine. NMDA receptor stimulation fails to activate Ras in neuronal cultures from mice lacking neuronal NO synthase. NMDA-induced Ras activation occurs through a cGMP-independent pathway as 1H-[1,2,4]oxadiazolo[4,3-alpha]quinoxalin-1-one (ODQ), a potent and selective inhibitor of guanylyl cyclase, has no effect on NMDA receptor-induced activation of Ras, and the cell-permeable cGMP analog, 8Br-cGMP, does not activate Ras. Furthermore, NO directly activates immunoprecipitated Ras from neurons. NMDA also elicits tyrosine phosphorylation of extracellular signal-regulated kinases, a downstream effector pathway of Ras, through a NO/non-cGMP dependent mechanism, thus supporting the physiologic relevance of endogenous NO regulation of Ras. These results suggest that Ras is a physiologic target of endogenously produced NO and indicates a signaling pathway for NMDA receptor activation that may be important for long-lasting neuronal responses.

Animals↗

PubMed1998

Manganese superoxide dismutase protects nNOS neurons from NMDA and nitric oxide-mediated neurotoxicity.

Neuronal nitric oxide synthase (nNOS) neurons kill adjacent neurons through the action of NMDA-glutamate receptor activation, although they remain relatively resistant to the toxic effects of NMDA and NO. The molecular basis of the resistance of nNOS neurons to toxic insults is unknown. To begin to understand the molecular mechanisms of the resistance of nNOS neurons, we developed a pheochromacytoma-derived cell line (PC12) that is resistant to the toxic effects of NO. We found through serial analysis of gene expression (SAGE) that manganese superoxide dismutase (MnSOD) is enriched in the NO-resistant PC12 cell-derived line (PC12-R). Antisense MnSOD renders PC12-R cells sensitive to NO toxicity and increases the sensitivity to NO in the parental, NO-sensitive PC12 line (PC12-S). Adenoviral transfer of MnSOD protects PC12-S cells against NO toxicity. We extended these studies to cortical cultures and showed that MnSOD is enriched in nNOS neurons and that antisense MnSOD renders nNOS neurons susceptible to NMDA neurotoxicity, although it has little effect on the overall susceptibility of cortical neurons to NMDA toxicity. Overexpression of MnSOD provides dramatic protection against NMDA and NO toxicity in cortical cultures, but not against kainate or AMPA neurotoxicity. Furthermore, nNOS neurons from MnSOD -/- mice are markedly sensitive to NMDA toxicity. Adenoviral transfer of MnSOD to MnSOD-/- cultures restores resistance of nNOS neurons to NMDA toxicity. Thus, MnSOD is a major protective protein that appears to be essential for the resistance of nNOS neurons in cortical cultures to NMDA mediated neurotoxicity.

Animals↗

PubMed1998

NMDAR1 glutamate receptor subunit isoforms in neostriatal, neocortical, and hippocampal nitric oxide synthase neurons.

Nitric oxide (NO), an unconventional and diffusible neurotransmitter, is synthesized by nitric oxide synthase (NOS). NMDA glutamate receptors are potent regulators of NO synthesis. We have used dual-label immunofluorescence and confocal microscopy to examine forebrain neurons in the rat that contain high levels of neuronal NOS (nNOS) for the presence of the NMDAR1 receptor subunit protein and regions of this protein encoded by three alternative spliced segments of the NMDAR1 mRNA: N1, C1, and C2. In the neostriatum, neocortex, and hippocampus, nNOS-labeled neurons exhibit strong NMDAR1 immunoreactivity (-ir). In all three of these regions, nNOS-positive neurons are characterized by the absence of immunoreactivity for the C1 segment of NMDAR1, whereas C1-ir is abundant in most nNOS-negative neurons. In addition, nNOS-ir neurons exhibit selective staining for the alternative C2' terminus of NMDAR1 that is produced when the C2 segment is absent. These results demonstrate directly that neurons with abundant nNOS-ir contain NMDAR1 receptor subunit proteins and that the NMDAR1 isoforms present in these cells differ from those of most other neurons in these regions. The distinct NMDA receptor phenotype of these nNOS-positive neurons is likely to contribute to both the physiological regulation of NO release by glutamate as well as to NO-mediated excitotoxic injury.

Animals↗

PubMed1998

Regulation of neuronal nitric oxide synthase and identification of novel nitric oxide signaling pathways.

Neuronal nitric oxide synthase (nNOS) participate in a variety of physiologic and pathologic processes in the nervous system. nNOS was originally felt to be a constitutively expressed enzyme, but recent observations suggest that its levels are dynamically controlled in response to neuronal development, plasticity and injury. nNOS expression is regulated through alternative promoter usage through alternative mRNA splicing and it is likely that this plays an important role in the inducibility of gene expression in response to extracellular stimuli. Emerging data also suggests that NO may be the key mediator linking activity to gene expression and long-lasting neuronal responses through NO activating p21Ras through redox-sensitive modulation.

Animals↗

PubMed1998

Nitric oxide in neurodegeneration.

Nitric oxide (NO) is a unique biological messenger molecule which mediates diverse physiologic roles. NO mediates blood vessel relaxation by endothelium, immune activity of macrophages and neurotransmission of central and peripheral neurons. NO is produced from three NO Synthase (NOS) isoforms: Neuronal NOS (nNOS), endothelial NOS, and inducible NOS (iNOS). In the central nervous system, NO may play important roles in neurotransmitter release, neurotransmitter reuptake, neurodevelopment, synaptic plasticity, and regulation of gene expression. However, excessive production of NO following a pathologic insult can lead to neurotoxicity. NO plays a role in mediating neurotoxicity associated with a variety of neurologic disorders, including stroke, Parkinson's Disease, and HIV dementia.

AIDS Dementia Complex↗

PubMed1998

Role of poly(ADP-ribose) synthetase in inflammation and ischaemia-reperfusion.

Oxidative and nitrosative stress can trigger DNA strand breakage, which then activates the nuclear enzyme poly(ADP-ribose) synthetase (PARS). This enzyme has also been termed poly(ADP-ribose) polymerase (PARP) or poly(ADP-ribose) transferase (pADPRT). Rapid activation of the enzyme depletes the intracellular concentration of its substrate, nicotinamide adenine dinucleotide, thus slowing the rate of glycolysis, electron transport and subsequently ATP formation. This process can result in cell dysfunction and cell death. In this article, Csaba Szabó and Valina Dawson overview the impact of pharmacological inhibition or genetic inactivation of PARS on the course of oxidant-induced cell death in vitro, and in inflammation and reperfusion injury in vivo. A major trigger for DNA damage in pathophysiological conditions is peroxynitrite, a cytotoxic oxidant formed by the reaction between the free radicals nitric oxide and superoxide. The pharmacological inhibition of poly(ADP-ribose) synthetase is a novel approach for the experimental therapy of various forms of inflammation and shock, stroke, myocardial and intestinal ischaemia-reperfusion, and diabetes mellitus.

Animals↗

PubMed1998

Free radicals as mediators of neuronal injury.

1. Free radicals may play an important role in several pathological conditions of the central nervous system (CNS) where they directly injure tissue and where their formation may also be a consequence of tissue injury. 2. Free radicals produce tissue damage through multiple mechanisms, including excito-toxicity, metabolic dysfunction, and disturbance of intracellular homeostasis of calcium. 3. Oxidative stress can significantly worsen acute insults, such as ischemia, as well as chronic neurodegenerative disorders including amyotrophic lateral sclerosis (ALS) and Parkinson's disease. 4. For instance, recent findings suggest a causal role for chronic oxidative stress in familial ALS, as this disease is linked to missence mutations of the copper/zinc superoxide dismutase (SOD). 5. Thus, therapeutic approaches which limit oxidative stress may be potentially beneficial in several neurological diseases.

Amyotrophic Lateral Sclerosis↗

PubMed1998

Truncated N-terminal fragments of huntingtin with expanded glutamine repeats form nuclear and cytoplasmic aggregates in cell culture.

Huntington's disease (HD) is a progressive neurodegenerative disorder caused by an expanding CAG repeat coding for polyglutamine in the huntingtin protein. Recent data have suggested the possibility that an N-terminal fragment of huntingtin may aggregate in neurons of patients with HD, both in the cytoplasm, forming dystrophic neurites, and in the nucleus, forming intranuclear neuronal inclusion bodies. An animal model of HD using the short N-terminal fragment of huntingtin has also been found to have intranuclear inclusions and this same fragment can aggregate in vitro . We have now developed a cell culture model demonstrating that N-terminal fragments of huntingtin with expanded glutamine repeats aggregate both in the cytoplasm and in the nucleus. Neuroblastoma cells transiently transfected with full-length huntingtin constructs with either a normal or expanded repeat had diffuse cytoplasmic localization of the protein. In contrast, cells transfected with truncated N-terminal fragments showed aggregation only if the glutamine repeat was expanded. The aggregates were often ubiquitinated. The shorter truncated product appeared to form more aggregates in the nucleus. Cells transfected with the expanded repeat construct but not the normal repeat construct showed enhanced toxicity to the apoptosis-inducing agent staurosporine. These data indicate that N-terminal truncated fragments of huntingtin with expanded glutamine repeats can aggregate in cells in culture and that this aggregation can be toxic to cells. This model will be useful for future experiments to test mechanisms of aggregation and toxicity and potentially for testing experimental therapeutic interventions.

Animals↗

PubMed1998

mdx muscle pathology is independent of nNOS perturbation.

In skeletal muscle, neuronal nitric oxide synthase (nNOS) is anchored to the sarcolemma via the dystrophin-glycoprotein complex. When dystrophin is absent, as in Duchenne muscular dystrophy patients and in mdx mice, nNOS is mislocalized to the interior of the muscle fiber where it continues to produce nitric oxide. This has led to the hypothesis that free radical toxicity from mislocalized nNOS may contribute to mdx muscle pathology. To test this hypothesis directly, we generated mice devoid of both nNOS and dystrophin. Overall, the nNOS-dystrophin null mice maintained the dystrophic characteristics of mdx mice. We evaluated the mice for several features of the dystrophic phenotype, including membrane damage and muscle morphology. Removal of nNOS did not alter the extent of sarcolemma damage, which is a hallmark of the dystrophic phenotype. Furthermore, muscle from nNOS-dystrophin null mice maintain the histological features of mdx pathology. Our results demonstrate that relocalization of nNOS to the cytosol does not contribute significantly to mdx pathogenesis.

Animals↗

PubMed1998

Impaired ovulation in mice with targeted deletion of the neuronal isoform of nitric oxide synthase.

BACKGROUND: Nitric oxide (NO) plays an important role in numerous reproductive processes. To date, most studies have assessed the role of NO by using nonspecific pharmacological inhibitors of the precursor to NO, nitric oxide synthase (NOS). These pharmacological NOS inhibitors suppress all isoforms of NOS; thus, the precise contribution of each isoform to female reproductive physiology is unknown. The purpose of this study was to determine the specific role of neuronal NOS (nNOS) in the regulation of ovulation in female mice lacking the gene that encodes for nNOS (nNOS-/-). MATERIALS AND METHODS: Ovulation was assessed in wild-type (WT) and nNOS-/- female mice by examining the number of ovarian rupture sites and number of oocytes recovered from the oviducts following mating or exposure to exogenous gonadotropins (i.e., 5 IU pregnant mares serum gonadotropin [PMSG] and 5 IU human chorionic gonadotropin [hCG]). Ovulatory efficiency was determined as the number of ovulated oocytes per number of ovarian rupture sites. To examine whether ovulatory deficits in nNOS-/- mice were due to alternations in central mechanisms, plasma luteinizing hormone (LH) concentrations were assessed in WT and nNOS-/- mice that were challenged with 25 ng of gonadotropin-releasing hormone (GnRH). To determine whether ovulatory deficits in nNOS-/- mice were due to local ovulation processes, nerves innervating the reproductive tract of WT and nNOS-/- females were examined for the presence of nNOS protein. RESULTS: There were substantial fertility deficits in nNOS-/- female mice; the nNOS-/- mice had fewer oocytes in their oviducts following spontaneous and gonadotropin-stimulated ovulation. Pituitary responsiveness to exogenous GnRH challenge was intact in nNOS-/- mice. Dense nNOS protein staining was observed in nerves innervating the reproductive tracts of WT mice. CONCLUSIONS: The reproductive deficits in nNOS-/- females are most likely due to alternations in the transfer of oocytes from the ovaries to the oviducts during ovulation. These results suggest that defects in neuronally derived NO production may contribute to female infertility.

Animals↗

PubMed1997

Aggressive behavior in male mice lacking the gene for neuronal nitric oxide synthase requires testosterone.

Nitric oxide acts as a neural messenger in both the central and peripheral nervous systems. Mice with targeted disruption of the neuronal isoform of nitric oxide synthase (nNOS - / -) are extremely aggressive relative to wild-type (WT) mice. Male nNOS - / - mice exhibit an increase in the number and duration of aggressive encounters compared to WT animals when tested in a variety of paradigms used to test rodent aggression. This inappropriate aggressive behavior has only been observed in male nNOS - /- mice; nNOS - /- females, like female WT mice, exhibit little or no aggression. The present study sought to test the dependence of increased aggressive behavior in nNOS - / - males on testosterone. Intact nNOS - / - males exhibited elevated levels of aggression relative to intact WT males. Castration reduced aggression in both WT and nNOS - /- males to equivalent low levels. Testosterone replacement restored aggression to precastration levels in both genotypes. These data provide evidence that increased aggressive behavior of nNOS - /- mice, like aggression in WT mice, is testosterone-dependent.

Aggression↗

PubMed1997

Differential susceptibility to neurotoxicity mediated by neurotrophins and neuronal nitric oxide synthase.

NMDA neurotoxicity, which is mediated, in part, by formation of nitric oxide (NO) via activation of neuronal NO synthase (nNOS), is modulated by neurotrophins. nNOS expression in rat and mouse primary neuronal cultures grown on a glial feeder layer is significantly less than that of neurons grown on a polyornithine (Poly-O) matrix. Neurotrophins markedly increase the number of nNOS neurons, nNOS protein, and NOS catalytic activity and enhance NMDA neurotoxicity via NO-dependent mechanisms when neurons are grown on glial feeder layers. In contrast, when rat or mouse primary cortical neurons are grown on a Poly-O matrix, neurotrophins have no influence on nNOS neuronal number or NOS catalytic activity and reduce NMDA neurotoxicity. Primary neuronal cultures from mice lacking nNOS grown on a glial feeder layer fail to respond to neurotrophin-mediated enhancement of neurotoxicity. Together, these results indicate that nNOS expression and NMDA NO-mediated neurotoxicity are dependent, in part, on the culture paradigm, and neurotrophins regulate the susceptibility to NMDA neurotoxicity via modulation of nNOS. Furthermore, these results support the idea that NMDA neurotoxicity in culture is critically dependent on the developmental state of the neurons being assessed and suggest that, when cortical neurons are cultured on a glial feeder layer, they do not reach nearly as mature a phenotype as when grown on a Poly-O matrix.

Animals↗

PubMed1997

Neuronal (type I) nitric oxide synthase regulates nuclear factor kappaB activity and immunologic (type II) nitric oxide synthase expression.

Nitric oxide subserves diverse physiologic roles in the nervous system. NO is produced from at least three different NO synthase (NOS) isoforms: neuronal NOS (nNOS), endothelial NOS, and immunologic NOS (iNOS). We show that nNOS is the predominant isoform constitutively expressed in glia. NO derived from nNOS in glia inhibits the transcription factor nuclear factor kappaB (NF kappaB) as NOS inhibitors enhance basal NF kappaB activation. Pyrrolidine dithiocarbamate (PDTC) is an inhibitor of NF kappaB in most cells; however, we show that PDTC is also a potent scavenger of NO through formation of mononitrosyl iron complexes with PDTC. In Jurkat cells, a human T-cell lymphoma cell line, tumor necrosis factor-alpha (TNF-alpha) induces NF kappaB activation that is inhibited by PDTC. Contrary to the results in Jurkat cells, PDTC did not inhibit tumor necrosis factor-alpha-induced NF kappaB activation in astrocytes; instead PDTC itself induces NF kappaB activation in astrocytes, and this may be related to scavenging of endogenously produced NO by the PDTC iron complex. In astrocytes PDTC also dramatically induces the NF kappaB-dependent enzyme, iNOS, supporting the physiologic relevance of endogenous NO regulation of NF kappaB. NF kappaB activation in glia from mice lacking nNOS responds more rapidly to PDTC compared with astrocytes from wild-type mice. Our data suggest that nNOS in astrocytes regulates NF kappaB activity and iNOS expression, and indicate a novel regulatory role for nNOS in tonically suppressing central nervous system, NF kappaB-regulated genes.

Animals↗

PubMed1997

Effects of nitric oxide on neuroendocrine function and behavior.

Nitric oxide (NO) is an unusual chemical messenger. NO mediates blood vessel relaxation when produced by endothelial cells. When produced by macrophages, NO contributes to the cytotoxic function of these immune cells. NO also functions as a neurotransmitter and neuromodulator in the central and peripheral nervous systems. The effects on blood vessel tone and neuronal function form the basis for an important role of NO on neuroendocrine function and behavior. NO mediates hypothalamic portal blood flow and, thus, affects oxytocin and vasopression secretion; furthermore, NO mediates neuroendocrine function in the hypothalamic-pituitary-gonadal and hypothalamic-pituitary-adrenal axes. NO influences several motivated behaviors including sexual, aggressive, and ingestive behaviors. Learning and memory are also influenced by NO. Taken together, NO is emerging as an important chemical mediator of neuroendocrine function and behavior.

Animals↗

PubMed1997

Urinary bladder-urethral sphincter dysfunction in mice with targeted disruption of neuronal nitric oxide synthase models idiopathic voiding disorders in humans.

Idiopathic voiding disorders affect up to 10-15% of men and women. We describe bladder abnormalities in mice with targeted deletion of the gene for neuronal nitric oxide synthase which model the clinical disorders. The mice possess hypertrophic dilated bladders and dysfunctional urinary outlets which do not relax in response to electrical field stimulation or L-arginine. The mice also display increased urinary frequency.

Animals↗

PubMed1997

Poly(ADP-ribose) polymerase gene disruption renders mice resistant to cerebral ischemia.

Nitric oxide (NO) and peroxynitrite, formed from NO and superoxide anion, have been implicated as mediators of neuronal damage following focal ischemia, but their molecular targets have not been defined. One candidate pathway is DNA damage leading to activation of the nuclear enzyme, poly(ADP-ribose) polymerase (PARP), which catalyzes attachment of ADP ribose units from NAD to nuclear proteins following DNA damage. Excessive activation of PARP can deplete NAD and ATP, which is consumed in regeneration of NAD, leading to cell death by energy depletion. We show that genetic disruption of PARP provides profound protection against glutamate-NO-mediated ischemic insults in vitro and major decreases in infarct volume after reversible middle cerebral artery occlusion. These results provide compelling evidence for a primary involvement of PARP activation in neuronal damage following focal ischemia and suggest that therapies designed towards inhibiting PARP may provide benefit in the treatment of cerebrovascular disease.

Adenosine Triphosphate↗