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T M Dawson

Publications and source records attributed to T M Dawson.

At least 127 records · Page 7Linked to original sources
PubMed1994

Neuronal nitric oxide synthase is induced in spinal neurons by traumatic injury.

Nitric oxide appears to mediate the immune functions of macrophages, the influence of endothelial cells on blood vessel relaxation, and also to serve as a neurotransmitter in the central and peripheral nervous system. Macrophage nitric oxide synthase is inducible with massive increases in new nitric oxide synthase protein synthesis following immune stimulation of macrophages. By contrast, endothelial nitric oxide synthase and neuronal nitric oxide synthase are thought to be constitutive with activation induced by calcium entry into cells in the absence of new protein synthesis. Developmental studies showing the transient expression of neuronal nitric oxide synthase in embryonic and early postnatal life in rodent spinal motoneurons and cerebral cortical plate neurons (Bredt and Snyder, unpublished observations) implies inducibility of neuronal nitric oxide synthase. Moreover, neuronal nitric oxide synthase expression is greatly enhanced in sensory ganglia following peripheral axotomy. Staining for NADPH diaphorase in spinal motoneurons is greatly increased following ventral root avulsion. In many parts of the Central Nervous System NADPH diaphorase staining reflects nitric oxide synthase. In the present study, we have combined in situ hybridization for neuronal nitric oxide synthase, immunohistochemical staining of neuronal nitric oxide synthase, and NADPH diaphorase staining to establish that neuronal nitric oxide synthase expression is markedly augmented in spinal motoneurons following avulsion. The generality of this effect is evident from augmented staining in nucleus dorsalis following spinal cord transection.

Amino Acid Oxidoreductases↗
PubMed1994

Rat spinal cord neurons contain nitric oxide synthase.

We describe the distribution and characteristics of nitric oxide synthase-containing neurons in rat spinal cord using a polyclonal affinity-purified antibody against rat cerebellar nitric oxide synthase. Numerous neurons were stained throughout the entire rostrocaudal extent of the spinal cord. Cell bodies, dendrites and axons stained in a uniform manner. Nitric oxide synthase immunoreactivity was intense in neurons of laminae I-IV and X throughout the entire spinal cord. Neurons in the intermediolateral cell column of the thoracic and lumbar spinal cord were also intensely stained for nitric oxide synthase. The sacral cord demonstrated substantial nitric oxide synthase immunostaining within lamina VII. For the entire cord, scattered neurons in laminae V, VI, VII, and VIII were weakly positive. In addition, punctate nitric oxide synthase staining throughout laminae I, III and surrounding some large motor neurons in the ventral horn suggested the presence of nitric oxide synthase at synapses. Axons and dendritic terminals located in the gray and white matter were also stained. The majority of nitric oxide synthase positive neurons in the intermediolateral cell column were double-labelled by subcutaneously injected FluoroGold confirming that these cells were preganglionic autonomic neurons. Most NADPH-diaphorase-stained neurons were also nitric oxide synthase-positive. The distribution of nitric oxide synthase-containing neurons in spinal cord suggests that nitric oxide plays a role in spinal cord neurotransmission including: preganglionic sympathetic and parasympathetic, somatosensory, visceral sensory and possibly motor pathways. In particular, the autonomic nervous system appears enriched with nitric oxide synthase immunoreactivity. The precise role of each neuron type remains to be demonstrated in physiologic and pathophysiologic paradigms.

Amino Acid Oxidoreductases↗
PubMed1994

Nitric oxide mediates the formation of synaptic connections in developing and regenerating olfactory receptor neurons.

Nitric oxide (NO) is a diffusible free radical that functions as a second messenger and neurotransmitter. NO synthase (NOS) is highly and transiently expressed in neurons of the developing olfactory epithelium during migration and establishment of primary synapses in the olfactory bulb. NOS is first expressed at E11 in cells of the presumptive nervous layer of the olfactory placode. NOS immunoreactivity persists in the descendants of these cells that differentiate into embryonic olfactory receptor neurons (ORNs). Olfactory NOS expression in the ORN and in its afferents rapidly declines after birth and is undetectable by P7. Following bulbectomy, NOS expression is rapidly induced in the regenerating ORN and is particularly enriched in their outgrowing axons. Immunoblot and Northern blot analyses similarly demonstrate an induction of NOS protein and mRNA expression, respectively, the highest levels of which coincide with peaks of ORN regeneration. These data argue against a role for NO in odorant-sensitive signal transduction, but suggest a prominent function for NO in activity-dependent establishment of connections in both developing and regenerating olfactory neurons.

Amino Acid Oxidoreductases↗
PubMed1994

gp120 neurotoxicity in primary cortical cultures.

The human immunodeficiency virus type 1 coat protein, gp120, kills neurons in a nitric oxide dependent manner in primary cortical cultures at low picomolar concentrations. gp120 neurotoxicity also requires calcium and glutamate and is blocked by glutamate receptor antagonists. In addition, superoxide anions play a role in gp120 neurotoxicity since superoxide dismutase also attenuates neurotoxicity.

AIDS Dementia Complex↗
PubMed1994

Yttrium synovectomy in haemophilic arthropathy.

Between 1987 and 1991 we performed Yttrium-90 (Y-90) silicate radionuclide synovectomies on 40 joints of 20 haemophiliac patients with haemophilic arthropathy. All were male, their mean age was 31 yr and 15 of the 20 (75%) were HIV antibody positive. The number of joint bleeds and amount of factor (VIII and IX) replacement given in the 6 months pre- and 6 and 12 months post-radionuclide synovectomy was compared. Y-90 silicate synovectomy was shown significantly to reduce both the number of joint bleeds (P < 0.001) and factor usage (P < 0.001) in the 6 months after the procedure, a result maintained up to 12 months. Depot methyl prednisolone was co-administered with Y-90 but thought unlikely to contribute to joint response beyond 6 months. The reduction of joint bleeds and factor usage was even more dramatic in the 6- to 12-month period post-synovectomy although this was not reflected by the P value (P < 0.001). The reduction of joint bleeds and factor consumption post-synovectomy was most obvious in elbow joints, although the other joints as a group showed a significant reduction. Patients who were HIV antibody positive showed considerable improvement up to 12 months post-treatment, both in reduction of joint bleeds and as a consequence factor consumption. This improvement was seen to a lesser extent in the smaller HIV-negative group.

Adolescent↗
PubMed1994

Secondary mechanisms in neuronal trauma.

Secondary damage in central nervous system trauma results from toxic effects of a variety of modulators that magnify the initial traumatic damage. These modulators include the excitatory transmitter glutamate, the intracellular messenger calcium, and the intercellular messenger nitric oxide. Glutamate-induced toxicity, called excitotoxicity, occurs from excess glutamate release following trauma. Passage of calcium into the cell through a specific postsynaptic glutamate receptor ion channel, the N-methyl-D-aspartate (NMDA) receptor, is crucial in activating cellular pathways leading to excitotoxic damage. The NMDA receptor requires both glutamate and glycine for activation and is blocked by many drugs that act at either of these sites. It is also blocked by agents that selectively block the ion channel of this receptor. Blocking NMDA receptors at any of these sites decreases the cellular damage mediated by glutamate in neuronal trauma and improves physiological measures associated with traumatic damage. Other strategies to limit secondary damage include blockade of other calcium channels, of calcium-activated enzymes, and of processes that mediate the effects of calcium. Calcium-activated enzymes include nitric oxide synthase and phospholipases, which cause production of free radicals. In combination with NMDA receptor blockade, these sites represent promising areas for therapeutic intervention in secondary traumatic damage.

Animals↗
PubMed1994

Gases as biological messengers: nitric oxide and carbon monoxide in the brain.

In a remarkably brief period of time, NO and CO have been recognized as putative neurotransmitters. These two novel messenger molecules have greatly expanded the criteria for candidacy of a chemical for the status of neurotransmitter and our notions about how synaptic transmission takes place. The involvement of NO and CO in several important aspects of neuronal function suggests that agents affecting the synthesis, transactions, and disposition of these gases are bound to have clinical relevance.

Animals↗
PubMed1994

Cellular and subcellular localization of NMDA-R1 subunit immunoreactivity in the visual cortex of adult and neonatal rats.

NMDA receptor activation can alter synaptic strength, cause cell death, and may modulate the release of glutamate and other neurotransmitters. Using a specific and selective antiserum directed against the R1 subunit of the NMDA receptor, we examined (1) whether NMDA receptors in the adult rat visual cortex are exclusively postsynaptic or also presynaptic and (2) whether NMDA-R1 subunits are incorporated into the plasma membrane prior to, contemporaneously, or following the formation of synapses during postnatal development. By light microscopy, NMDA-R1 immunoreactivity in the adult visual cortex is easily detectable within perikarya and proximal dendrites in laminae 2-6. Many of them have the morphological features of pyramidal neurons. In addition, fine punctate labeling is evident throughout the neuropil. Electron microscopy reveals these puncta to reside at postsynaptic densities of axospinous junctions and at fine astrocytic processes and axon terminals. In the deeper laminae, the majority of labeled profiles are astrocytic. Visual cortices of animals in their first postnatal week show concentrated immunoreactivity in a few nonpyramidal neurons within laminae that have just differentiated from the cortical plate. Electron microscopy reveals diffuse labeling along the plasma membrane of dendritic shafts lacking morphologically identifiable synaptic junctions or appositions to axons. Immunoreactivity is detectable in dendritic processes by postnatal day (PND) 2, in axonal processes by PND 4, and in astrocytic profiles by PND 14. Immunoreactivity also is detectable along the postsynaptic membrane of presumably transient axosomatic junctions. At all ages, the prevalence of NMDA-R1-immunoreactive profiles is lamina 1 > 4/5 > 6/6B. These results provide the cellular basis for NMDA receptors' participation in (1) postsynaptic membrane excitability, (2) regulation of transmitter release, (3) and, in the deeper laminae, astrocyte responses. During development, NMDA-R1 subunits are associated with the plasma membrane prior to axons' arrival while clustering of receptors to junctions may be promoted by axonal contact. Finally, spatial segregation of axonal growth cones may be mediated by NMDA-R1 subunits on these axonal processes.

Aging↗
PubMed1993

Targeted disruption of the neuronal nitric oxide synthase gene.

By homologous recombination, we have generated mice that lack the neuronal nitric oxide synthase (NOS) gene. Neuronal NOS expression and NADPH-diaphorase (NDP) staining are absent in the mutant mice. Very low level residual catalytic activity suggests that other enzymes in the brain may generate nitric oxide. The neurons normally expressing NOS appear intact, and the mutant NOS mice are viable, fertile, and without evident histopathological abnormalities in the central nervous system. The most evident effect of disrupting the neuronal NOS gene is the development of grossly enlarged stomachs, with hypertrophy of the pyloric sphincter and the circular muscle layer. This phenotype resembles the human disorder infantile pyloric stenosis, in which gastric outlet obstruction is associated with the lack of NDP neurons in the pylorus.

Amino Acid Oxidoreductases↗
PubMed1993

Enhanced expression of nitric oxide synthase by rat retina following pterygopalatine parasympathetic denervation.

Removal of the pterygopalatine ganglion enhanced the expression of nitric oxide synthase (NOS) in the ipsilateral rat retina and optic nerve by immunohistochemical and biochemical criteria. The denervation procedure did not alter the apparent histochemical reactivity of retinal cells normally immunoreactive for NOS but did induce expression in retinal ganglion cells and their axons in the retinal nerve fiber layer and optic nerve. After denervation, the induced NOS immunohistochemical reactivity was consistently visualized by day 7, reached a maximum intensity during days 14 to 28, and thereafter gradually attenuated to become barely detectable by microscopy at 10 weeks. Biochemical assays performed two weeks after pterygopalatine denervation confirmed the immunohistochemical observations, especially with regard to the optic nerve. The induced enzyme activity in both retina and optic nerve showed calcium dependency. These results point towards interactions of the ocular parasympathetic innervation and the retina, between which no known neuronal connections exist.

Amino Acid Oxidoreductases↗
PubMed1993

Mitochondrial voltage-dependent anion channel. Immunochemical and immunohistochemical characterization in rat brain.

The purified mitochondrial benzodiazepine receptor (mBzR) is a complex comprising the voltage-dependent anion channel (VDAC), adenine nucleotide carrier, and an 18-kDa protein that binds isoquinoline carboxamide ligands (McEnery, M. W., Snowman, A. M., Trifiletti, R. R., and Snyder, S. H. (1992) Proc. Natl. Acad. Sci. U.S.A. 89, 3170-3174). An antiserum raised against the mBzR complex reacts selectively with VDAC and is used, along with purification, electrophysiological and immunohistochemical techniques, to characterize the properties and distribution of rat brain VDAC. Although purified VDAC displays biochemical and electrical conductance properties similar to VDAC from other sources, the immunohistochemical distribution of VDAC in rat brain is heterogeneous with pronounced regional variations; the pontine nuclei, the supraoptic nucleus, Purkinje cells of the cerebellum, and the caudate putamen evidence the highest density. The distribution of VDAC is inclusive of the more discretely localized 18-kDa mBzR protein, suggesting that only a portion of the total VDAC participates in the mBzR. The histochemical localizations of the mitochondrial marker enzymes glutamate dehydrogenase and cytochrome c oxidase also indicate marked regional variability in both mitochondrial content and composition. The discrete expression of VDAC reflects a striking heterogeneity of rat brain mitochondria and underlying differences in the utilization of mitochondrial outer membrane ion channels.

Animals↗
PubMed1993

Neurotransmitter release regulated by nitric oxide in PC-12 cells and brain synaptosomes.

BACKGROUND: Nitric oxide is a messenger molecule of the nervous system, which is produced by the enzyme nitric oxide synthase, which may regulate cyclic guanosine monophosphate levels and which has been implicated in the control of neurotransmitter release. PC-12 pheochromocytoma cells differentiate to form neuronal cells in culture when they are exposed to nerve growth factor. The levels of cyclic guanosine monophosphate in the cells and their ability to release acetylcholine in response to K(+)-depolarization are both maximal after eight days of treatment with nerve growth factor. We set out to assess a possible role for nitric oxide in the processes that occur in differentiating PC-12 cells. RESULTS: Nitric oxide synthase is first evident in differentiating PC-12 cells eight days after beginning treatment with nerve growth factor, coinciding with the marked increase in K(+)-depolarization-induced release of acetylcholine. The release of both acetylcholine and dopamine in response to K(+)-depolarization is blocked by inhibitors of nitric oxide synthase and by hemoglobin, which binds nitric oxide. Providing l-arginine, a precursor required for nitric oxide synthesis, reverses the effects of the inhibitors. In synaptosomal preparations from the corpus striatum, inhibitors of nitric oxide synthase prevent the release of glutamate in response to the glutamate derivative N-methyl-d-aspartate but not in response to K(+)-depolarization. CONCLUSION: Nitric oxide may mediate the release of acetylcholine and dopamine in response to K(+)-depolarization in PC-12 cells and the release of glutamate in response to N-methyl-d-aspartate in striatal synaptosomes. Nitric oxide synthase expression is induced after eight days of treating PC-12 cells with nerve growth factor, coinciding with a marked enhancement of the release of neurotransmitters in response to K(+)-depolarization.

Journal Article↗
PubMed1993

Immunosuppressant FK506 enhances phosphorylation of nitric oxide synthase and protects against glutamate neurotoxicity.

Immunosuppressants FK506 and cyclosporin A inhibit neurotoxicity of N-methyl-D-aspartate in primary cortical cultures, while having no effect on quisqualate- and kainate-mediated neurotoxicity. Rapamycin completely reverses the neuroprotective effect of FK506. Both FK506 and cyclosporin A inhibit NMDA-elicited/nitric oxide-mediated increases in cGMP levels in cortical cultures. FK506 has no effect on sodium nitroprusside-induced increases in cGMP. In a stably transfected human kidney 293 cell line overexpressing the gene encoding nitric oxide synthase [L-arginine, NADPH:oxygen oxidoreductase (nitric oxide-forming), EC 1.14.13.39], FK506 inhibits the calcium ionophore A23187, stimulated increases in nitrite (a breakdown product of nitric oxide), and potentiates phorbol ester-mediated inhibition of nitrite formation. FK506-mediated inhibition of nitric oxide formation is completely reversed by rapamycin. Calcineurin dephosphorylates protein kinase C-mediated phosphorylation of nitric oxide synthase. FK506 prevents the calcineurin-mediated dephosphorylation of nitric oxide synthase and thereby diminishes the enzyme's catalytic activity. These data establish nitric oxide synthase as a calcineurin substrate. Nitric oxide synthase catalytic activity is regulated by the phosphorylation state of the enzyme. Enhanced phosphorylation of nitric oxide synthase diminishes catalytic activity, and dephosphorylation (through activation of calcineurin) enhances catalytic activity. The neuroprotective effect of FK506 and cyclosporin A presumably involves the inhibition of calcineurin, preventing the dephosphorylation of nitric oxide synthase and its subsequent activation.

Amino Acid Oxidoreductases↗
PubMed1993

Human immunodeficiency virus type 1 coat protein neurotoxicity mediated by nitric oxide in primary cortical cultures.

The human immunodeficiency virus type 1 coat protein, gp120, kills neurons in primary cortical cultures at low picomolar concentrations. The toxicity requires external glutamate and calcium and is blocked by glutamate receptor antagonists. Nitric oxide (NO) contributes to gp120 toxicity, since nitroarginine, an inhibitor of NO synthase, prevents toxicity as does deletion of arginine from the incubation medium and hemoglobin, which binds NO. Superoxide dismutase also attenuates toxicity, implying a role for superoxide anions.

Animals↗
PubMed1993

Beta-adrenergic receptor kinase-2 and beta-arrestin-2 as mediators of odorant-induced desensitization.

beta-Adrenergic receptor kinase (beta ARK) and beta-arrestin function in the homologous or agonist-activated desensitization of G protein-coupled receptors. The isoforms beta ARK-2 and beta-arrestin-2 are highly enriched in and localized to the dendritic knobs and cilia of the olfactory receptor neurons where the initial events of olfactory signal transduction occur. Odorants induce a rapid and transient elevation of adenosine 3',5'-monophosphate (cAMP), which activates a nonspecific cation channel and produces membrane depolarization. Preincubation of rat olfactory cilia with antibodies raised against beta ARK-2 and beta-arrestin-2 increased the odorant-induced elevation of cAMP and attenuated desensitization. These results suggest that beta ARK-2 and beta-arrestin-2 mediate agonist-dependent desensitization in olfaction.

Animals↗
PubMed1993

Inositol 1,4,5-trisphosphate receptors: immunohistochemical localization to discrete areas of rat central nervous system.

The second messenger inositol 1,4,5-trisphosphate triggers the release of intracellular Ca2+ stores upon binding to the inositol 1,4,5-trisphosphate receptor protein, a calcium channel that has been purified and molecularly cloned. To clarify the roles of inositol 1,4,5-trisphosphate receptor in the central nervous system, we have examined in detail the distribution of inositol 1,4,5-trisphosphate receptors in the rat brain and spinal cord using immunohistochemical methods. Inositol 1,4,5-trisphosphate receptors are present in neuronal cells, fibers and terminals in a wide distribution of areas throughout the central nervous system. These include a number of areas not previously reported, such as the olfactory bulb, thalamic nuclei and dorsal horn of the spinal cord. In addition, we have noted a strikingly high density of inositol 1,4,5-trisphosphate receptors in circumventricular organs and neuroendocrine structures such as the area postrema, choroid plexus, subcommisural organ, pineal gland and pituitary. The distribution of inositol 1,4,5-trisphosphate receptors in discrete structures throughout the central nervous system, including interconnected neuronal systems and neuroendocrine and circumventricular organ structures, presumably reflects the importance of Ca2+ release mediated by the phosphoinositide second messenger system in control of diverse physiological processes.

Animals↗
PubMed1993

Possible origins and distribution of immunoreactive nitric oxide synthase-containing nerve fibers in cerebral arteries.

The distribution of perivascular nerve fibers expressing nitric oxide synthase (NOS)-immunoreactivity was examined in Sprague-Dawley and Long-Evans rats using affinity-purified rabbit antisera raised against NOS from rat cerebellum. NOS immunoreactivity was expressed within the endothelium and adventitial nerve fibers in both rat strains. Labeled axons were abundant and dense in the proximal anterior and middle cerebral arteries, but were less numerous in the caudal circle of Willis and in small pial arteries. The sphenopalatine ganglia were the major source of positive fibers in these vessels. Sectioning postganglionic parasympathetic fibers from both sphenopalatine ganglia reduced the density of NOS-immunoreactive (IR) nerve fibers by > 75% in the rostral circle of Willis. Moreover, NOS-IR was present in 70-80% of sphenopalatine ganglion cells. Twenty percent of these neurons also contained vasoactive intestinal polypeptide (VIP)-immunoreactivity. By contrast, the superior cervical ganglia did not contain NOS-IR cells. In the trigeminal ganglion, NO-IR neurons were found chiefly within the ophthalmic division; approximately 10-15% of neurons were positively labeled. Colocalization with calcitonin gene-related peptide (CGRP) was not observed. Sectioning the major trigeminal branch innervating the circle of Willis decreased positive fibers by < or = 25% in the ipsilateral vessels. In the nodose ganglion, 20-30% of neurons contained NOS-immunoreactivity, whereas less than 1% were in the C2 and C3 dorsal root ganglia. Three human circles of Willis obtained at autopsy showed sparse immunoreactive fibers, chiefly within vessels of the posterior circulation. Postmortem delay accounted for some of the reduced density. Our findings indicate that nerve fibers innervating cerebral arteries may serve as a nonendothelial source of the vasodilator nitric oxide (NO). The coexistence of NOS and VIP within sphenopalatine ganglion cells raises the possibility that two vasodilatory agents, one, a highly diffusable short-lived, low-molecular-weight molecule, and the other, a polar 28 amino acid-containing peptide, may serve as coneuromediators within the cerebral circulation.

Amino Acid Oxidoreductases↗