Biomedical subjects

T M Dawson

Publications and source records attributed to T M Dawson.

At least 73 records · Page 4Linked to original sources

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

NMDA-R1 subunit of the cerebral cortex co-localizes with neuronal nitric oxide synthase at pre- and postsynaptic sites and in spines.

The majority of nitric oxide's (NO) physiologic and pathologic actions in the brain has been linked to NMDA receptor activation. In order to determine how the NO-synthesizing enzyme within brain, neuronal NO synthase (nNOS), and NMDA receptors are functionally linked, previous studies have used in situ hybridization techniques in combination with light microscopic immunocytochemistry to show that the two are expressed within single neurons. However, this light microscopic finding does not guarantee that NMDA receptors are distributed sufficiently close to nNOS within single neurons to allow direct interaction of the two. Thus, in this study, dual immuno-electron microscopy was performed to determine whether nNOS and NMDA receptors co-exist within fine neuronal processes. We show that nNOS and the obligatory subunit of functional NMDA receptors, i.e. the NMDA-R1, co-exist within dendritic shafts, spines and terminals of the adult rat visual cortex. Axon terminals form asymmetric synaptic junctions with the dually labeled dendrites, suggesting that the presynaptic terminals release glutamate. Axons and dendrites expressing one without the other also are detected. These results indicate that it is possible for the generation of NO to be temporally coordinated with glutamatergic synaptic transmission at axo-dendritic and axo-axonic junctions and that NO may be generated independently of glutamatergic synaptic transmission. Together, our observations point to a greater complexity than previously recognized for glutamatergic neurotransmission, based on the joint versus independent actions of NO relative to NMDA receptors at pre- versus postsynaptic sites.

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

Neurotrophic actions of nonimmunosuppressive analogues of immunosuppressive drugs FK506, rapamycin and cyclosporin A.

We show that the nonimmunosuppressive analogues of the immunosuppressive drugs FK506, rapamycin and cyclosporin A promote neurite outgrowth both in PC12 cells and sensory neuronal cultures of dorsal root ganglia with potencies resembling their immunosuppressive homologues. Neurotrophic potencies of the immunophilin ligands resemble their potencies in binding to and inhibiting the rotamase activity of FKBP-12 of cyclophilin. Since nonimmunosuppressive immunophilin ligands, which are devoid of calcineurin inhibitory activity, are equally neurotrophic, inhibition of calcineurin activity is not the mediator of the neurotrophic effects. The immunophilin ligands are neurotrophic in intact animals. FK506 and L-685,818 (the C18-hydroxy, C21-ethyl derivative of FK506) treatment of rats with crushed sciatic nerves enhances both functional and morphologic recovery. The striking potency of these agents, their bioavailability and the dissociation of neurotrophic from immunosuppressant actions argue for their therapeutic relevance in the treatment of neurodegenerative diseases.

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↗

PubMed1997

Nitric oxide in health and disease of the nervous system.

Nitric oxide (NO) is a widespread and multifunctional biological messenger molecule. It mediates vasodilation of blood vessels, host defence against infectious agents and tumors, and neurotransmission of the central and peripheral nervous systems. In the nervous system, NO is generated by three nitric oxide synthase (NOS) isoforms (neuronal, endothelial and immunologic NOS). Endothelial NOS and neuronal NOS are constitutively expressed and activated by elevated intracellular calcium, whereas immunologic NOS is inducible with new RNA and protein synthesis upon immune stimulation. Neuronal NOS can be transcriptionally induced under conditions such as neuronal development and injury. NO may play a role not only in physiologic neuronal functions such as neurotransmitter release, neural development, regeneration, synaptic plasticity and regulation of gene expression but also in a variety of neurological disorders in which excessive production of NO leads to neural injury.

Animals↗

PubMed1997

Nitric oxide synthase in models of focal ischemia.

BACKGROUND AND PURPOSE: Cessation of blood flow to the brain, for even a few minutes, sets in motion a potential reversible cascade of events resulting in neuronal cell death. Oxygen free radicals and oxidants appear to play an important role in central nervous system injury after cerebral ischemia and reperfusion. Recently, divergent roles for the newly identified neuronal messenger molecule and oxygen radical, nitric oxide (NO), have been identified in various models of cerebral ischemia. Because of the chemical and physical properties of NO, the numerous physiological activities it mediates, and the lack of specific agents to modulate the activity of the different isoforms of NO synthase (NOS), reports regarding the role of NO in focal cerebral ischemia have been confounding and often conflicting. Recent advances in pharmacology and the development of transgenic knockout mice specific for the different isoforms of NOS have advanced our knowledge and clarified the role of NO in cerebral ischemia. METHODS: Animal models of focal ischemia employ occlusion of nutrient cerebral vessels, most commonly the middle cerebral artery. Primary cortical cultures are exposed to excitotoxic or ischemic conditions, and the activities of NOS isoforms or NO production are evaluated. Transgenic mice lacking expression of either the neuronal isoform of NOS (nNOS), the endothelial isoform of NOS (eNOS), or the immunologic isoform of NOS (iNOS) have been examined in models of excitotoxic injury and ischemia. RESULTS: Excitotoxic or ischemic conditions excessively activate nNOS, resulting in concentrations of NO that are toxic to surrounding neurons. Conversely, NO generated from eNOS is critical in maintaining cerebral blood flow and reducing infarct volume. iNOS, which is not normally present in healthy tissue, is induced shortly after ischemia and contributes to secondary late-phase damage. CONCLUSIONS: Pharmacological and genetic approaches have significantly advanced our knowledge regarding the role of NO and the different NOS isoforms in focal cerebral ischemia. nNOS and iNOS play key roles in neurodegeneration, while eNOS plays a prominent role in maintaining cerebral blood flow and preventing neuronal injury.

Animals↗

PubMed1997

Inhibition of neuronal nitric oxide synthase increases aggressive behavior in mice.

BACKGROUND: Mice with targeted disruption of the gene for the neuronal isoform of nitric oxide synthase (nNOS) display exaggerated aggression. Behavioral studies of mice with targeted gene deletions suffer from the criticism that the gene product is missing not only during the assessment period but also throughout development when critical processes, including activation of compensatory mechanisms, may be affected. To address this criticism, we have assessed aggressive behavior in mice treated with a specific pharmacological inhibitor of nNOS. MATERIALS AND METHODS: Aggressive behavior, as well as brain citrulline levels, were monitored in adult male mice after treatment with a specific nNOS inhibitor, 7-nitroindazole (7-NI) (50 mg/kg i.p.), which is known to reduce NOS activity in brain homogenates by > 90%. As controls, animals were treated with a related indazole, 3-indazolinone (3-I) (50 mg/kg i.p.) that does not affect nNOS or with on oil vehicle. RESULTS: Mice treated with 7-NI displayed substantially increased aggression as compared with oil- or 3-I-injected animals when tested in two different models of aggression. Drug treatment did not affect nonspecific locomotor activities or body temperature. Immunohistochemical staining for citrulline in the brain revealed a dramatic reduction in 7-NI-treated animals. CONCLUSIONS: 7-NI augmented aggression in WT mice to levels displayed by nNOS- mice, strongly implying that nNOS is a major mediator of aggression. NOS inhibitors may have therapeutic roles in inflammatory, cardiovascular, and neurologic diseases. The substantial aggressive behavior soon after administration of an nNOS inhibitor raises concerns about adverse behavioral sequelae of such pharmacological agents.

Aggression↗

PubMed1997

Colchicine induced rhabdomyolysis.

A 59-year-old man with chronic obstructive pulmonary disease (COPD), atrial fibrillation, and gout developed acute dyspnea, cough, and diffuse muscle aches and pains. He had commenced colchicine (0.6 mg b.i.d. p.o.), for the first time, one month earlier for recurrent gout attacks. Clinical examination revealed atrial fibrillation, an exacerbation of his pulmonary disease, tender muscles, especially calves, and diffuse muscle weakness. Laboratory results included creatinine phosphokinase 6961 U/l (1% MB), microscopic hematuria, myoglobinuria, elevated creatinine 1.6 mg/dl, and blood urea nitrogen 17 mg/dl. COPD and atrial fibrillation were treated and colchicine was discontinued. The patient made a full recovery. This 2nd reported case of colchicine induced rhabdomyolysis is the first reported in the treatment of gout.

Adrenal Cortex Hormones↗

PubMed1996

Immunologic NO synthase: elevation in severe AIDS dementia and induction by HIV-1 gp41.

Indirect mechanisms are implicated in the pathogenesis of the dementia associated with human immunodeficiency virus-type 1 (HIV-1) infection. Proinflammatory molecules such as tumor necrosis factor alpha and eicosanoids are elevated in the central nervous system of patients with HIV-1-related dementia. Nitric oxide (NO) is a potential mediator of neuronal injury, because cytokines may activate the immunologic (type II) isoform of NO synthase (iNOS). The levels of iNOS in severe HIV-1-associated dementia coincided with increased expression of the HIV-1 coat protein gp41. Furthermore, gp41 induced iNOS in primary cultures of mixed rat neuronal and glial cells and killed neurons through a NO-dependent mechanism. Thus, gp41-induced NO formation may contribute to the severe cognitive dysfunction associated with HIV-1 infection.

AIDS Dementia Complex↗

PubMed1996

Inhibition of nitric oxide synthase does not prevent ocular dominance plasticity in kitten visual cortex.

1. The neural messenger molecule nitric oxide (NO) has been shown to be involved in several forms of plasticity including hippocampal long-term potentiation. We examined the effects of chronic intracortical infusion of inhibitors of NO synthase (NOS) activity on the plasticity of visual cortical responses following monocular lid suture during the critical period. 2. Single unit recordings (618 cells) made in both the NOS inhibitor-treated (30 mM NG-methyl-L-arginine (L-NMMA), or 22 or 2 mM nitro-L-arginine (L-NOArg)) and saline-treated control hemispheres of barbiturate-anaesthetized, critical-period kittens (n = 8) revealed a profound shift in favour of the non-deprived eye. Shifts were of similar magnitude in hemispheres in which NOS was inhibited and in saline control hemispheres. 3. Subsequent analysis of NOS activity in the same cortical tissue in which recordings had been made showed a pronounced decrease in NOS activity in inhibitor-treated hemispheres. In the region in which all the single unit recordings were made (< 3 mm from the infusion cannula), 22 mM L-NOArg resulted in a reduction of NOS activity to 5.55 +/- 5.33% of control hemisphere NOS activity levels. L-NOArg (2 mM) and L-NMMA (30 mM) also produced clear, but smaller, inhibition of NOS activity. 4. These findings demonstrate that NOS activity is not essential for ocular dominance plasticity in visual cortex.

Animals↗

PubMed1996

Nitric oxide synthase generates superoxide and nitric oxide in arginine-depleted cells leading to peroxynitrite-mediated cellular injury.

Besides synthesizing nitric oxide (NO), purified neuronal NO synthase (nNOS) can produce superoxide (.O2-) at lower L-Arg concentrations. By using electron paramagnetic resonance spin-trapping techniques, we monitored NO and .O2- formation in nNOS-transfected human kidney 293 cells. In control transfected cells, the Ca2+ ionophore A23187 triggered NO generation but no .O2- was seen. With cells in L-Arg-free medium, we observed .O2- formation that increased as the cytosolic L-Arg levels decreased, while NO generation declined. .O2- formation was virtually abolished by the specific NOS blocker, N-nitro-L-arginine methyl ester (L-NAME). Nitrotyrosine, a specific nitration product of peroxynitrite, accumulated in L-Arg-depleted cells but not in control cells. Activation by A23187 was cytotoxic to L-Arg-depleted, but not to control cells, with marked lactate dehydrogenase release. The cytotoxicity was largely prevented by either superoxide dismutase or L-NAME. Thus, with reduced L-Arg availability NOS elicits cytotoxicity by generating .O2- and NO that interact to form the potent oxidant peroxynitrite. Regulating arginine levels may provide a therapeutic approach to disorders involving .O2-/NO-mediated cellular injury.

Arginine↗

PubMed1996

Induction of spinal cord neuronal nitric oxide synthase (NOS) after formalin injection in the rat hind paw.

The nitric oxide synthase (NOS) inhibitor L-nitroarginine methyl ester has been found to exhibit antinociceptive activity in a rat model of pain [Kitto, K.F. et al., Neurosci. Lett., 148 (1992) 1-5; Lee, J.H. et al., NeuroReport, 3 (1992) 841-844; Moore, P.K. et al., Br. J. Pharmacol., 102 (1991) 198-202]. We investigated the hypothesis that hind paw injection of formalin increases the number of dorsal horn neuronal nitric oxide synthase (nNOS) containing neurons. Results showed a bilateral increase in the number of nNOS-positive neurons at the L4-5 dorsal horn area following formalin injection. The increase was always greater on the ipsilateral side compared to the contralateral side. This upregulation of nNOS following formalin stimulation of the hind paw suggested that nitric oxide (NO) may play a role in the central mechanism of hyperalgesia that follows peripheral inflammation.

Animals↗

PubMed1996

Role of neuronal nitric oxide in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced dopaminergic neurotoxicity.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) causes nigrostriatal dopaminergic pathway damage similar to that observed in Parkinson disease (PD). To study the role of NO radical in MPTP-induced neurotoxicity, we injected MPTP into mice in which nitric oxide synthase (NOS) was inhibited by 7-nitroindazole (7-NI) in a time- and dose-dependent fashion. 7-NI dramatically protected MPTP-injected mice against indices of severe injury to the nigrostriatal dopaminergic pathway, including reduction in striatal dopamine contents, decreases in numbers of nigral tyrosine hydroxylase-positive neurons, and numerous silver-stained degenerating nigral neurons. The resistance of 7-NI-injected mice to MPTP is not due to alterations in striatal pharmacokinetics or content of 1-methyl-4-phenylpyridinium ion (MPP+), the active metabolite of MPTP. To study specifically the role of neuronal NOS (nNOS), MPTP was administered to mutant mice lacking the nNOS gene. Mutant mice are significantly more resistant to MPTP-induced neurotoxicity compared with wild-type littermates. These results indicate that neuronally derived NO mediates, in part, MPTP-induced neurotoxicity. The similarity between the MPTP model and PD raises the possibility that NO may play a significant role in the etiology of PD.

3,4-Dihydroxyphenylacetic Acid↗