PubMed Health⌕ Search

Biomedical subjects

N Quan

Publications and source records attributed to N Quan.

36 records · Page 2Linked to original sources
PubMed1997

Induction of inhibitory factor kappaBalpha mRNA in the central nervous system after peripheral lipopolysaccharide administration: an in situ hybridization histochemistry study in the rat.

In this study we investigate the mRNA expression of inhibitory factor kappaBalpha (IkappaBalpha) in cells of the rat brain induced by an intraperitoneal (i.p.) injection of lipopolysaccharide (LPS). IkappaB controls the activity of nuclear factor kappaB, which regulates the transcription of many immune signal molecules. The detection of IkappaB induction, therefore, would reveal the extent and the cellular location of brain-derived immune molecules in response to peripheral immune challenges. Low levels of IkappaBalpha mRNA were found in the large blood vessels and in circumventricular organs (CVOs) of saline-injected control animals. After an i.p. LPS injection (2.5 mg/kg), dramatic induction of IkappaBalpha mRNA occurred in four spatio-temporal patterns. Induced signals were first detected at 0.5 hr in the lumen of large blood vessels and in blood vessels of the choroid plexus and CVOs. Second, at 1-2 hr, labeling dramatically increased in the CVOs and choroid plexus and spread to small vascular and glial cells throughout the entire brain; these responses peaked at 2 hr and declined thereafter. Third, cells of the meninges became activated at 2 hr and persisted until 12 hr after the LPS injection. Finally, only at 12 hr, induced signals were present in ventricular ependyma. Thus, IkappaBalpha mRNA is induced in brain after peripheral LPS injection, beginning in cells lining the blood side of the blood-brain barrier and progressing to cells inside brain. The spatiotemporal patterns suggest that cells of the blood-brain barrier synthesize immune signal molecules to activate cells inside the central nervous system in response to peripheral LPS. The cerebrospinal fluid appears to be a conduit for these signal molecules.

Animals↗
PubMed1997

Plasminogen activation by pro-urokinase in complex with its receptor--dependence on a tripeptide (Spectrozyme plasmin).

The intrinsic activity of single-chain pro-urinary-type plasminogen activator (pro-uPA) and whether its receptor (uPAR) potentiates this activity remains controversial. In this report, the pro-uPA/uPAR-(1-281)-peptide complex in solution is shown to have equivalent plasminogen-activator activity to that of active two-chain uPA (tc-uPA). However, the activity of the complex was dependent on a synthetic tripeptide, Spectrozyme plasmin (Spl, H-D-2-aminohexanoic acid(Ahx)-hexatyrosyl-lysine-p-nitroanilide), which can also be used as a chromogenic substrate for plasmin. Furthermore, this activity could be completely suppressed by commonly used carrier proteins and detergents. The pro-uPA/uPAR-(1-281)-peptide complex at 1 nM displayed similar activity to that of tc-uPA for either [Glu1]plasminogen or [Lys77]plasminogen in chromogenic assays with Spl present as the plasmin substrate. When assayed with another plasmin substrate, S2251, the pro-uPA/uPAR-(1-281)-peptide complex was unable to activate plasminogen. The pro-uPA/uPAR-(1-281)-peptide complex and tc-uPA also showed a similar extent of plasminogen activation as measured by SDS/PAGE, when incubated with plasminogen and Spl in the presence of 100 micro M aprotinin, and plasminogen activation by pro-uPA alone was also stimulated in the presence of Spl in this assay. Activation of plasminogen by the pro-uPA/uPAR-(1-281)-peptide strictly required the presence of Spl, and pro-uPA remained in single-chain form during these assays. This activity of the pro-uPA/uPAR-(1-281)-peptide complex but not that of tc-uPA was completely inhibited by human serum albumin, bovine serum albumin, Tween-80, Triton X-100, and Pluronic-F68. Taken together, the data indicates that uPAR-(1-281)-peptide itself is not sufficient to augment pro-uPA activity and the presence of an effector molecule (e.g. Spl) is required to elicit the full plasminogen-activator activity of the pro-uPA/uPAR-(1-281)-peptide complex. It remains to be seen whether there is a physiological counterpart to this phenomenon.

Enzyme Activation↗
PubMed1997

Soluble human urokinase receptor is composed of two active units.

The mechanism by which single-chain urokinase (scuPA) binds to its receptor (uPAR) is incompletely understood. We report that a fragment comprising the first domain of recombinant soluble uPAR (sDI) as well as a fragment comprising the remaining domains (sDII-DIII) competes with the binding of recombinant full-length soluble uPAR (suPAR) to scuPA with an IC50 = 253 nM and an IC50 = 1569, respectively. sDII-III binds directly to scuPA with Kd = 238 nM. Binding of scuPA to each fragment also induces the expression of plasminogen activator activity. sDI and sDII-DIII (200 nM each) induced activity equal to 66 and 36% of the maximum activity induced by full-length suPAR (5 nM), respectively. Each fragment also stimulates the binding of scuPA to cells lacking endogenous uPAR. Although scuPA binds to sDI and to sDII-DIII through its amino-terminal fragment, the fragments act synergistically to inhibit the binding of suPAR and to stimulate plasminogen activator activity. Furthermore, sDII-DIII retards the velocity and alters the pattern of cleavage of sDI by chymotrypsin. These results suggest that binding of scuPA to more than one epitope in suPAR is required for its optimal activation and association with cell membranes.

Humans↗
PubMed1994

Widespread activation and consequences of interleukin-1 in the brain.

The results described herein indicate that elevation of IL-1 in rat brain, either by infusion of IL-1 into the brain or by stimulation of release of endogenous IL-1 in the brain by LPS, rapidly suppresses a variety of immune responses measured in peripheral lymphocytes. This effect can be blocked by infusion of alpha-MSH into brain, an attribute that was used to indicate that the effects of LPS infusion occurred by stimulation of endogenous IL-1 and not some other influence of LPS. That suppression of cellular immune responses indeed describes the consequences of elevating IL-1 in brain was shown by determining the time course of effects and thereby demonstrating that rebound enhancement of cellular immune responses did not occur after either IL-1 or LPS. Studies that examined the mechanisms by which brain IL-1 affects immune responses indicated that IL-1 influences peripheral lymphocytes by stimulation of CRF in the central nervous system and that CRF in turn causes suppression of cellular immune responses through activation of both the pituitary-adrenal axis and the autonomic nervous system. These findings have also been observed in another laboratory. Moreover, Brown et al. have shown that IL-1 in brain suppresses macrophage function in addition to the suppression of lymphocyte functions described herein. The physiologic significance of IL-1 actions in the brain on immune responses remains to be determined, but the demonstration that this cytokine influences immune processes by acting in brain opens for study another means by which brain and immune system interact.

Animals↗
PubMed1994

Induction of interleukin-1 in various brain regions after peripheral and central injections of lipopolysaccharide.

The presence of bioactive interleukin-1 (IL-1) in various brain regions (cerebellum, cortex, brainstem, diencephalon or hippocampus) after either intraperitoneal (i.p.) or intraventricular (i.c.v.) injection of lipopolysaccharide (LPS) was studied in the rat. To detect IL-1, extracellular fluid and cell lysate were fractionated by gel exclusion chromatography and fractions tested for thymocyte stimulation; presence of IL-1 was confirmed by blockade of stimulation by addition to the assay of a monoclonal antibody (mAb) to IL-1 receptor. When LPS was infused i.c.v., IL-1 was detected in the brainstem and diencephalon 2 h after injection, and in all the brain regions except cerebellum 6 h after injection; IL-1 was not detected in the plasma of these animals. When LPS was injected i.p., IL-1 was detected in the plasma but not in the brain 2 h after the injection, and in all brain regions but not in the plasma 6 h after the injection. In all of these cases, IL-1 was found in extracellular fluid; in some cases (cortex, cerebellum) cell lysate of the region did not produce detectable bioactivity, thereby indicating that IL-1 in these brain regions is processed to active peptide during release, as has been reported in the periphery. In those cases where bioactivity was detected in cell lysate (brainstem, diencephalon), bioactivity was not blocked by IL-1 receptor mAb, indicating presence of a non-IL-1 stimulating factor. These results further support the idea that IL-1 is secreted by cells in the brain, and indicate that it is found in the extracellular fluid of many brain regions following an appropriate stimulus in the periphery as well as in the brain.

Animals↗
PubMed1994

Depression and anxiety: role of the locus coeruleus and corticotropin-releasing factor.

Based on studies of depression and anxiety using animal (rat) models, it is suggested that, contrary to a widely accepted theory, increased activity of locus coeruleus (LC) neurons does not appear to potentiate anxiety; instead, the influence of LC activity may be opposite to this. First, studies are described that indicate that behavioral changes resembling what is seen in human clinical depression occur in rats exposed to highly stressful conditions, and the research is then traced, which links this stress-induced depression to disturbance of normal noradrenergic regulation of LC activity. Second, the potential role of corticotrophin releasing factor (CRF) in stress-induced behavioral depression is explored. CRF infused into the LC did not produce behavioral depression in the swim test but did increase anxiety; by comparison, CRF infused into the parabrachial nucleus lateral to LC increased both depression and anxiety. Finally, to further explore the relationship between LC activity and anxiety, drugs were infused into LC region to attempt to specifically activate or depress firing of LC neurons. In contrast to expectations, infusion to decrease firing of LC cells increased anxious behavior, while infusion to increase firing decreased anxious behavior. Several other studies are discussed that point to a similar conclusion. It is suggested that, at least in rats, the capacity of stress-inducing or aversive stimuli to activate LC neurons does not potentiate anxiety under environmental conditions that elicit this response, but, rather, the increased activity of the LC/dorsal noradrenergic system under such conditions may exert a counterbalancing, antianxiety influence.

Animals↗
PubMed1993

Growth hormone expression in human Burkitt lymphoma serum-free Ramos cell line.

A human nonpituitary cell line grown under serum-free (sf) conditions (sfRamos Burkitt lymphoma cell line) has been reported to secrete a 29K PRL-like peptide which acts as an autocrine growth factor. Conditioned medium from these cells was examined for lactogenic activity using the Nb2 bioassay and RIAs specific for human GH (hGH) and hPRL. SfRamos conditioned medium stimulated the growth of Nb2 cells. Anti-hGH monoclonal antibodies but not anti-hPRL inhibited the mitogenic effect of sfRamos conditioned medium on Nb2 cells. Immunoreactive hGH but not hPRL was detected by RIA. Immunoprecipitation with anti-hGH polyclonal antibody followed by Western blot analysis with anti-hGH monoclonal antibody revealed a specific 22K band with the same mobility as pituitary hGH. Northern blot analysis with an hGH complementary DNA (cDNA) probe revealed a 1.0-kilobase transcript migrating coincident with pituitary hGH messenger RNA. A less abundant, 1.6-kilobase transcript was also observed. Reverse transcriptase-polymerase chain reaction using specific primers for the hGH cDNA generated the predicted 248-base pair band. Polymerase chain reaction sequencing of this fragment revealed sequence identity to the hGH-N cDNA, demonstrating conclusively the expression of the hGH-N gene in the sfRamos cell line.

Antibodies↗
PubMed1992

Validation of the hypothermic action of preoptic norepinephrine in guinea pigs.

Conscious guinea pigs were either microinjected intrapreoptically (iPO) with various doses of norepinephrine (NE) bilaterally or microdialyzed with pyrogen-free saline (PFS) or 10 micrograms/microliters NE unilaterally immediately and unilaterally or bilaterally 2 days after probe insertion. Core temperature (Tco), skin temperature (Tsk), and rate of oxygen consumption (VO2) were monitored continuously. The microinjection of low doses of NE induced Tco rises, whereas that of the highest dose (10 micrograms/microliters) caused an initial Tco fall followed by a rise. The microdialysis of PFS or NE immediately after probe insertion caused Tco rises; the former was abolished and the latter was converted into a fall by indomethacin (Indo, a prostaglandin synthase inhibitor) pretreatment. Two days later, PFS evoked no thermal response whereas NE induced a Tco fall; neither response was affected by Indo pretreatment. The falls in Tco produced by NE microdialyzed uni- or bilaterally were similar. The microdialysis of NE induced a 15% reduction in metabolic rate but no change in Tsk. These results indicate that the Tco rise induced by NE microinjected iPO is a methodological artifact mediated by PGE2, whereas the Tco fall observed in its microdialysis appears to represent the authentic physiological action of this transmitter effected by a reduction in metabolic rate.

Animals↗
PubMed1992

Preoptic norepinephrine-induced hypothermia is mediated by alpha 2-adrenoceptors.

We have shown previously that norepinephrine (NE) microdialyzed into the preoptic area of conscious guinea pigs evokes a fall in core temperature (Tco) that is mediated by a reduction in metabolic rate. To identify the adrenoceptor subtype(s) involved in this effect, we microdialyzed intrapreoptically various adrenergic agonists or antagonists singly or in combinations. Tco and ear skin temperatures of the animals were monitored throughout the experiments. alpha 1-, beta-, beta 1-, and beta 2-agonists and antagonists did not induce significant Tco changes. Although the alpha 2-antagonists yohimbine (Yoh) and rauwolscine (Rau) did not have thermal effects per se, the alpha 2-agonist clonidine evoked dose-dependent Tco falls that were abolished by codialyzed Yoh and Rau. The microdialysis of NE evoked, as before, a 0.7 +/- 0.2 degrees C Tco fall; it was abolished by the codialyzed alpha-antagonist phentolamine, Yoh, and Rau but not by the beta-antagonist propranolol. No adrenoceptor agonist induced changes in ear skin temperature. These results indicate that the hypothermizing effect of intrapreoptically microdialyzed NE is achieved by a reduction in metabolic heat production, mediated by alpha 2-adrenoceptors.

Animals↗
PubMed1991

Neuromodulation of fever: apparent involvement of opioids.

It was recently reported that the opiate antagonist, naloxone (Nal), blocks the changes induced by the endogenous pyrogen, interferon-alpha 2 (IFN), in the electrical activity of hypothalamic thermosensitive neurons in rat brain slice preparations. This study was undertaken to determine whether the pyrogenic response to this cytokine might, therefore, be modulated through Nal-reversible opiate receptors. To examine this possibility, conscious guinea pigs were injected IV with recombinant human (rh) IFN (10 MU/animal), or, for comparison, with S. enteritidis endotoxin (lipopolysaccharide, LPS; 2 micrograms/kg), rh tumor necrosis factor-alpha (TNF; 20 micrograms/kg), or rh interleukin-6 (IL6; 50 micrograms/kg); Nal (10 mg/kg, SC) was administered immediately before the pyrogens. And also for comparison, in separate experiments, indomethacin (Indo; 10 mg/kg, IM) was injected 20 min before the pyrogens. Both Nal and Indo abolished the febrile rises evoked by IFN, TNF, and IL6. Nal reduced the first and suppressed the second of the characteristically bimodal febrile response to LPS; Indo depressed both peaks. Neither blocker had any significant thermal effect by itself. These results suggest that two processes may mediate the pyrogenic effects of these substances, viz., an endogenous opioid- and a PGE-dependent mechanism.

Animals↗
PubMed1991

Microdialysis of norepinephrine into preoptic area of guinea pigs: characteristics of hypothermic effect.

This study was designed to characterize the previously described hypothermic action of norepinephrine (NE) microdialyzed into the medial preoptic area (MPO) of conscious guinea pigs. To this end, the effects on core temperature (Tco) of isotonic pyrogen-free saline (PFS), hypotonic PFS, inactive (oxidized) NE (hypertonic), 5-hydroxytryptamine (5-HT, 10 and 20 micrograms/microliter), PFS with or without 2.4 mM Ca2+, 10 micrograms/microliters NE with Ca2+, and various doses of NE (0.05-60 micrograms/microliters) were compared in a series of studies at an ambient temperature (Ta) of 24 degrees C. The Tco responses to 10 micrograms/microliters NE in a cold (15 +/- 2 degrees C) and a warm (31 +/- 1 degrees C) Ta and during the night in the dark in Ta 24 degrees C were also measured. Bromophenol blue (0.2%) was microdialyzed to assess the extent of diffusion of these dialysates. A stain was found in the MPO, which increased in density but did not spread beyond this region over 3 h of continuous microdialysis. Neither PFS nor the hypotonic and hypertonic solutions had any obvious effect on Tco. Similarly, neither dose of 5-HT evoked a thermal response. Ca2+ added to either PFS or NE did not alter the usual Tco responses to these two solutions. NE induced dose-dependent hypothermia in Ta 24 degrees C. NE microdialyzed in Ta 15 degrees C also produced Tco falls, but these responses were smaller than those in 24 degrees C. NE had no effect in the warm Ta. During the night, NE elicited similar Tco falls, but their recoveries after dialysis ended were slower than during the day.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Neuromodulation of acute-phase responses to interleukin-6 in guinea pigs.

It is now generally recognized that interleukin-6 (IL6) is one of the cytokines that mediate the various nonspecific host defense responses to infectious pathogens. Among its now well-demonstrated effects on systemic administration are fever and acute-phase proteinemia. These effects are also activated by the cytokine, IL1, and it has been shown that they are modulated in the preoptic-anterior hypothalamus (POA). This study was undertaken to determine whether this brain region similarly drives the febrile and proteinemic responses to IL6. We compared, therefore, these responses of conscious guinea pigs to human recombinant (hr)IL6 administered intravenously (IV) and into the POA. hrIL6 given IV was not pyrogenic at 1 microgram/kg, caused low-grade, dose-independent fevers (0.4 +/- 0.1 degree C) at 5-20 micrograms/kg, and dose-related fevers at 50 and 100 micrograms/kg (0.6 +/- 0.0 and 0.9 +/- 0.1 degree C, respectively). However, all doses of hrIL6 induced elevations in the plasma levels of ceruloplasmin (as an indicator of acute-phase proteins), albeit not in a dose-dependent manner. Indomethacin (10 mg/kg, injected intramuscularly 20 min before hrIL6) abolished the febrile response, but did not prevent the rise in plasma ceruloplasmin levels. Fever and ceruloplasminemia were also evoked by 50 and 100 ng of hrIL6 injected into the POA (1 microliter bilaterally), but not by 25 ng. These results indicate that the inductions of fever and plasma ceruloplasmin by IL6 are, like those of IL1, modulated in the POA, albeit the effective doses are much higher than those of IL1.

Acute-Phase Reaction↗
PubMed1989

Microdialysis: a system for localized drug delivery into the brain.

To determine why intrahypothalamic microinjections of pyrogen-free saline (PFS) often induce core temperature (Tco) rises, guide cannulas were implanted bilaterally into the preoptic-anterior hypothalamus (POA) of guinea pigs; 1 week later, injectors were inserted to 1 mm beyond the guides and either no injection or 1 microliter PFS was administered. Injector insertion without injection evoked a 0.5 degrees C Tco rise within 40 min, culminating in 3.7 hr. PFS microinjection elicited a 0.9 degrees C Tco rise within 10 min, culminating in 3.8 hr. PFS injected 4 hr later caused a further Tco rise. Indomethacin (10 mg/kg, IM), given 30 min before, prevented these effects. To determine whether microdialysis obviates them, a guide cannula was implanted unilaterally into the POA; 1 week later, a dialysis probe (nominal cutoff, 10kD) was inserted to 1 mm beyond the guide. PFS or prostaglandin E2 (PGE2, 1 microgram/microliter) was perfused 2 days later (2 microliter/min for 3 hr). Tco was unchanged during PFS perfusion but increased during PGE2 perfusion to 1.5 degrees C in 1.6 hr, and plateaued until 2 hr after dialysis. These results indicate the Tco rise induced by PFS microinjection is mediated by prostaglandins, probably released due to tissue puncture by the injectors and injury by the PFS droplet. Microdialysis prevents these effects. It should, therefore, be preferred over microinjection for intracerebral drug administration.

Animals↗
PubMed1989

Intrapreoptically microdialyzed and microinjected norepinephrine evokes different thermal responses.

Norepinephrine (NE) microdialyzed into the medial preoptic area (MPO) evokes a core temperature (Tco) fall in contrast to the rise when it is microinjected. Because prostaglandin E2 (PGE2) is a contaminant of the microinjection procedure per se, we determined whether it might account for these differential thermal responses. NE (1 microgram/microliter) was bilaterally microinjected into the MPO of conscious guinea pigs treated 20 min prior with a PG synthetase inhibitor, indomethacin (Indo, 10 mg/kg, im). Under these conditions, the latency of the NE-induced Tco rise was prolonged (138 +/- 18 min). When Indo was administered both 20 min before and 20 min after NE microinjection, NE was hypothermizing. NE (10 micrograms/microliter at 2 microliters/min for 3 h) microdialyzed into the MPO, lateral septum, or anterior hypothalamus caused Tco falls, whereas it induced no Tco change when dialyzed into the lateral preoptic area, indicating site specificity. PGE2 (1 microgram/microliter) caused a Tco rise when it was dialyzed intra-MPO. Microdialysis of PGE2 and NE together neutralized each other's effects. Indo given at the end of intra-MPO NE dialysis blocked the usual recovery of Tco from its lowered value. These results indicate that NE and PGE2 in the MPO may reciprocally influence the Tco of guinea pigs. The data further suggest that PGE may account for the different responses to microinjected and microdialyzed NE.

Animals↗
PubMedDate not supplied

Detection of interleukin-1 bioactivity in various brain regions of normal healthy rats.

Although interleukin-1 (IL-1) has been implicated in an array of brain functions, past studies usually have failed to detect IL-1 bioactivity in the brain of normal healthy animals. However, in view of the potency of IL-1 in brain, small amounts of this cytokine may normally act in brain, and such quantities can escape detection by assay methods usually employed. Although bioassays are highly sensitive for detecting IL-1, these can be compromised by molecules in brain tissue other than IL-1, and attempts to purify IL-1 from brain tissue can result in significant loss of IL-1 from samples. In this study, we have refined our method of assessing brain IL-1 bioactivity by first semi-isolating IL-1 with a Sephadex minicolumn and then measuring IL-1 activity with a sensitive D10 cell assay. To confirm that our assay was specific for IL-1, a monoclonal antibody against IL-1 receptor was used to block any observed IL-1 activity. We report here that IL-1 bioactivity can be reliably detected in both the cell-free supernatant and cell lysate of brainstem, cortex, diencephalon, and hippocampus of normal rat brain. These results lend support to some recent studies that found IL-1 may play important roles in the functions of normal brain.

Animals↗
PubMedDate not supplied

In vivo induction of interleukin-1 bioactivity in brain tissue after intracerebral infusion of native gp 120 and gp 160.

We have previously reported that intracerebral infusion of recombinant human immunodeficiency virus envelope protein gp 120 induced interleukin-1 (IL-1) bioactivity in rat brain. In this study, we tested the ability of native gp 120 and gp 160 to induce IL-1 activity in rat brain and also examined whether altering the secondary and tertiary structures of these proteins by carboxymethylation could influence the IL-1-inducing effect of these peptides. Results showed that both native gp 120 and gp 160 can induce IL-1 activity in rat brain in vivo, and that intact secondary and tertiary structures of these proteins appear critical for this effect.

Animals↗
PubMedDate not supplied

Imageability and word recognition in the left and right visual fields: a signal detection analysis.

Identifying the information processing constraints that determine whether or not imagery moderates visual field asymmetries is essential for constructing a dynamic model of hemispheric interaction during language processing. In this investigation, we manipulated the global experimental context in which imageable and nonimageable words were presented by contrasting mixed and blocked word lists using a lateralized lexical decision task. Signal detection analyses were employed to assess whether global stimulus context and imageability differentially affect word discriminability (d prime) and response bias (log beta) across visual fields. Both discriminability and response bias varied with imageability and stimulus context, but to a comparable extent across visual fields. This suggests that both hemispheres are sensitive to the global context in which words are presented, and can adjust processing based not only on semantic characteristics of the words themselves, but also on the variability of items in the stimulus environment.

Cognition↗