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Biomedical subjects

J Shelton

Publications and source records attributed to J Shelton.

At least 19 recordsLinked to original sources
PubMed2000

Interactions of the low density lipoprotein receptor gene family with cytosolic adaptor and scaffold proteins suggest diverse biological functions in cellular communication and signal transduction.

The members of the low density lipoprotein (LDL) receptor gene family bind a broad spectrum of extracellular ligands. Traditionally, they had been regarded as mere cargo receptors that promote the endocytosis and lysosomal delivery of these ligands. However, recent genetic experiments in mice have revealed critical functions for two LDL receptor family members, the very low density lipoprotein receptor and the apoE receptor-2, in the transmission of extracellular signals and the activation of intracellular tyrosine kinases. This process regulates neuronal migration and is crucial for brain development. Signaling through these receptors requires the interaction of their cytoplasmic tails with the intracellular adaptor protein Disabled-1 (DAB1). Here, we identify an extended set of cytoplasmic proteins that might also participate in signal transmission by the LDL receptor gene family. Most of these novel proteins are adaptor or scaffold proteins that contain PID or PDZ domains and function in the regulation of mitogen-activated protein kinases, cell adhesion, vesicle trafficking, or neurotransmission. We show that binding of DAB1 interferes with receptor internalization suggesting a mechanism by which signaling through this class of receptors might be regulated. Taken together, these findings imply much broader physiological functions for the LDL receptor family than had previously been appreciated. They form the basis for the elucidation of the molecular pathways by which cells respond to the diversity of ligands that bind to these multifunctional receptors on the cell surface.

Amino Acid Sequence↗
PubMed2000

Stimulation of slow skeletal muscle fiber gene expression by calcineurin in vivo.

Adult skeletal muscle fibers can be categorized into fast and slow twitch subtypes based on specialized contractile and metabolic properties and on distinctive patterns of muscle gene expression. Muscle fiber-type characteristics are dependent on the frequency of motor nerve stimulation and are thought to be controlled by calcium-dependent signaling. The calcium, calmodulin-dependent protein phosphatase, calcineurin, stimulates slow fiber-specific gene promoters in cultured skeletal muscle cells, and the calcineurin inhibitor, cyclosporin A, inhibits slow fiber gene expression in vivo, suggesting a key role of calcineurin in activation of the slow muscle fiber phenotype. Calcineurin has also been shown to induce hypertrophy of cardiac muscle and to mediate the hypertrophic effects of insulin-like growth factor-1 on skeletal myocytes in vitro. To determine whether activated calcineurin was sufficient to induce slow fiber gene expression and hypertrophy in adult skeletal muscle in vivo, we created transgenic mice that expressed activated calcineurin under control of the muscle creatine kinase enhancer. These mice exhibited an increase in slow muscle fibers, but no evidence for skeletal muscle hypertrophy. These results demonstrate that calcineurin activation is sufficient to induce the slow fiber gene regulatory program in vivo and suggest that additional signals are required for skeletal muscle hypertrophy.

Animals↗
PubMed2000

Elevated sympathetic activity contributes to hypertension and salt sensitivity in diabetic obese Zucker rats.

Zucker rats are a useful model in which to define the mechanisms that link obesity to diabetes and associated cardiovascular disease. The present study tests the hypothesis that diabetic obese (compared with nondiabetic lean) Zucker rats are hypertensive and display a further increase in arterial pressure when fed a high salt diet. Male, nondiabetic lean and diabetic obese Zucker rats were chronically instrumented with telemetry probes and fed a basal salt diet for 3 weeks followed by exposure to a high salt diet for 11 days. On the basal diet, obese (vs lean) rats had significantly higher arterial pressures ( approximately 13 mm Hg), and the high salt diet significantly elevated mean arterial pressure (MAP) in obese (but not lean) Zucker rats ( approximately 12 mm Hg). Blockade of the sympathetic nervous system with hexamethonium caused a significantly larger decrease in MAP in obese (vs lean) Zucker rats fed the basal diet (51 vs 33 mm Hg), but the high salt diet did not increase the hexamethonium-induced reduction in arterial pressure in obese rats. Acute blockade of angiotensin receptors with losartan resulted in similar decreases in MAP in both groups on either diet. Acetylcholine-induced vasodilatory capacity of the carotid artery was significantly less in the obese (vs lean) Zucker rats. Together these data indicate that increased sympathetic nervous system activity and decreased vascular reactivity may contribute to elevated arterial pressure in type 2 diabetic, obese Zucker rats, but the sympathetic nervous system does not appear to contribute to the dietary salt-sensitive hypertension in this model.

Angiotensin II↗
PubMed1999

Reeler/Disabled-like disruption of neuronal migration in knockout mice lacking the VLDL receptor and ApoE receptor 2.

Layering of neurons in the cerebral cortex and cerebellum requires Reelin, an extracellular matrix protein, and mammalian Disabled (mDab1), a cytosolic protein that activates tyrosine kinases. Here, we report the requirement for two other proteins, cell surface receptors termed very low density lipoprotein receptor (VLDLR) and apolipoprotein E receptor 2 (ApoER2). Both receptors can bind mDab1 on their cytoplasmic tails and are expressed in cortical and cerebellar layers adjacent to layers that express Reelin. mDab1 expression is upregulated in knockout mice that lack both VLDLR and ApoER2. Inversion of cortical layers and absence of cerebellar foliation in these animals precisely mimic the phenotype of mice lacking Reelin or mDab1. These findings suggest that VLDLR and ApoER2 participate in transmitting the extracellular Reelin signal to intracellular signaling processes initiated by mDab1.

Amino Acid Sequence↗
PubMed1998

Cardiac failure in transgenic mice with myocardial expression of tumor necrosis factor-alpha.

BACKGROUND: Tumor necrosis factor-alpha (TNF-alpha) is a multifunctional cytokine that has been detected in several human cardiac-related conditions, including congestive heart failure and septic cardiomyopathy. In these conditions, the origin of TNF-alpha secretion is, at least in part, cardiac myocytes. METHODS AND RESULTS: To determine the consequences of TNF-alpha production by cardiac myocytes in vivo, we developed transgenic mice in which expression of a murine TNF-alpha coding sequence was driven by the murine alpha-myosin heavy chain promoter. Four transgenic founders developed an identical illness consisting of tachypnea, decreased activity, and hunched posture. In vivo, ECG-gated MRI of symptomatic transgenic mice documented a severe impairment of cardiac function evidenced by biventricular dilatation and depressed ejection fractions. All transgenic mice died prematurely. Pathological examination of affected animals revealed a globular dilated heart, bilateral pleural effusions, myocyte apoptosis, and transmural myocarditis in both the right and left ventricular free walls, septum, and atrial chambers. In all terminally ill animals, there was significant biventricular fibrosis and atrial thrombosis. CONCLUSIONS: This is the first report detailing the effects of tissue-specific production of TNF-alpha by cardiac myocytes in vivo. These findings indicate that production of TNF-alpha by cardiac myocytes is sufficient to cause severe cardiac disease and support a causal role for this cytokine in the pathogenesis of human cardiac disease.

Animals↗
PubMed1997

Estrogen restores endothelial cell function in an experimental model of vascular injury.

BACKGROUND: It has been suggested that reendothelialization of damaged blood vessels protects against the vascular injury response. The goal of the present study was to determine whether estrogen restores endothelial cell function in balloon-injured rat carotid arteries. METHODS AND RESULTS: Ten-week-old male and female Sprague-Dawley rats with intact gonads underwent balloon injury to the right common carotid artery. Female rats were randomized to receive either daily subcutaneous injections of 17beta-estradiol (17betaE[2]; 20 microg x kg[-1] x d[-1]) or vehicle over the course of the study. Vessel morphology was assessed 2 weeks after injury. Significant neointima formation was observed in vehicle-treated males. This response was blunted in vehicle-treated and 17beta-E(2)-supplemented females. Intima-to-media ratios were 1.28+/-0.23 (males), 0.72+/-0.07 (vehicle-treated females), and 0.49+/-0.07 (17beta-E[2]supplemented females). To test whether reductions in neointimal lesion formation were related to the functional reendothelialization of the damaged vessel, endothelium-dependent relaxation was tested in isolated ring segments from the three experimental groups. Vessels were precontracted with phenylephrine followed by cumulative administration of acetylcholine, an endothelium-dependent vasodilator. Maximum relaxation to acetylcholine was 8.13+/-1.70% (males), 22.06+/-4.36% (vehicle-treated females), and 46.47+/-3.48% (17beta-E[2]-supplemented females). The enhanced endothelium-dependent relaxation of rings from 17betaE(2)-supplemented females correlated with reduced neointimal proliferation in this group. The concentration of nitric oxide metabolites in plasma correlated positively with plasma 17beta-E(2) concentration. CONCLUSIONS: These results suggest that estrogen protects against neointimal injury in the balloon-injured rat, at least in part, by facilitating the reendothelialization of the damaged vessel.

Acetylcholine↗
PubMed1997

Effects of thyrotropin-releasing hormone and its analogs on daytime sleepiness and cataplexy in canine narcolepsy.

The therapeutic potential of thyrotropin-releasing hormone (TRH) and TRH analogs in narcolepsy, a sleep disorder characterized by abnormal rapid eye movement (REM) sleep and daytime sleepiness, was examined using the canine model. The effects of TRH and the biologically stable TRH analogs CG3703, CG3509, and TA0910 on daytime sleep and cataplexy, a symptom of abnormal REM sleep, were assessed using polysomnographic recordings and the food elicited cataplexy test (FECT), respectively. CG3703 (100 and 400 microg/kg, i.v.) and TA0910 (100 and 400 microg/kg, i.v.) significantly increased wakefulness and decreased sleep in narcoleptic canines, whereas TRH (400 and 1600 microg/kg, i.v.) had no significant effect. TRH (25-1600 microg/kg, i.v.) and all three TRH analogs, CG3703 (6. 25-400 microg/kg, i.v., and 0.25-16 mg/kg, p.o.), CG3509 (25-1600 microg/kg, i.v.), and TA0910 (25-1600 microg/kg, i.v.), significantly reduced cataplexy in canine narcolepsy. These compounds did not produce any significant side effects during behavioral assays, nor did they alter free T3 and T4 levels in serum even when used at doses that completely suppressed cataplexy. Although more work is needed to establish the mode of action of TRH analogs on alertness and REM sleep-related symptoms, our results suggest a possible therapeutic application for TRH analogs in human sleep disorders.

Animals↗
PubMed1997

Molecular characterization of two mammalian bHLH-PAS domain proteins selectively expressed in the central nervous system.

Here we describe two mammalian transcription factors selectively expressed in the central nervous system. Both proteins, neuronal PAS domain protein (NPAS) 1 and NPAS2, are members of the basic helix-loop-helix-PAS family of transcription factors. cDNAs encoding mouse and human forms of NPAS1 and NPAS2 have been isolated and sequenced. RNA blotting assays demonstrated the selective presence of NPAS1 and NPAS2 mRNAs in brain and spinal cord tissues of adult mice. NPAS1 mRNA was first detected at embryonic day 15 of mouse development, shortly after early organogenesis of the brain. NPAS2 mRNA was first detected during early postnatal development of the mouse brain. In situ hybridization assays using brain tissue of postnatal mice revealed an exclusively neuronal pattern of expression for NPAS1 and NPAS2 mRNAs. The human NPAS1 gene was mapped to chromosome 19q13.2-q13.3, and the mouse Npas1 gene to chromosome 7 at 2 centimorgans. Similarly, the human NPAS2 gene was assigned to chromosome 2p11.2-2q13, and the mouse Npas2 gene to chromosome 1 at 21-22 centimorgans. The chromosomal regions to which human NPAS1 and NPAS2 map are syntenic with those containing the mouse Npas1 and Npas2 genes, indicating that the mouse and human genes are true homologs.

Amino Acid Sequence↗
PubMed1997

Temporospatial expression of the small HSP/alpha B-crystallin in cardiac and skeletal muscle during mouse development.

Although the small (22 Kd) heat shock protein/alpha B-crystallin functions as a major structural protein and molecular chaperone in the vertebrate lens, little is known about the protein's role in nonlenticular tissues such as the heart and skeletal muscle. Recent studies have demonstrated that alpha B-crystallin expression is uniquely regulated during myogenesis in vitro. We report here for the first time that the temporal and spatial expression of alpha B-crystallin is similarly regulated in vivo during mouse embryogenesis. Expression of alpha B-crystallin mRNA was detected by in situ hybridization in the primitive heart at 8.5 days postconception (p.c.) and in the myotome of the somites at 10.5 days p.c. This tissue-restricted pattern was corroborated by immunohistochemical studies. alpha B-crystallin mRNA and protein expression were uniform in the developing atria and ventricles without regional differences or gradients. alpha B-crystallin expression was absent in the endocardial cushion, pulmonary trunk, aorta, and endothelium. Examination of muscle precursors revealed expression throughout the dorsoventral aspect of the myotomes and in developing skeletal muscle. Our findings suggest that alpha B-crystallin may serve pivotal roles as a structural protein and a molecular chaperone in myofiber stabilization of metabolically active tissues during early embryogenesis. Thus, early alpha B-crystallin expression in myogenic lineages supports the hypothesis that the putative functions of alpha B-crystallin are coupled to the activation of genetic programs responsible for myogenic differentiation and cardiac morphogenesis.

Animals↗
PubMed1997

Modeled estimates of myocardial infarction and venous thromboembolic disease in users of second and third generation oral contraceptives.

Consistent reports from several recent studies suggest that users of third generation oral contraceptives (OCs) containing gestodene and desogestrel may be at increased risk of venous thromboembolic disease (VTE). Paradoxically, other reports indicate that these users may be at decreased risk of acute myocardial infarction (MI) compared with users of second generation OCs. To determine whether the potentially increased risk of VTE would outweigh the potentially reduced risk of MI in users of third generation OCs, we conducted an analysis to quantify the trade-offs providers and users may be faced to make between these formulations. The baseline rates of VTE and MI among non-users were calculated using US data on incidence and mortality of these conditions and estimates of the proportion of women exposed to these formulations in the US. These were multiplied by relative risks published in recent studies on third generation progestins to produce age- and formulation-specific risks. Results indicate that there would be small differences in disease burden between users of second and third generation OCs under the model assumptions at younger ages. However, among women 35-44 years of age, modeling results indicate that the potentially decreased incidence of MI among users of third generation OCs more than offsets the potentially increased risk of VTE at this age.

Adolescent↗
PubMed1997

Do behavior changes herald physical illness in adults with mental retardation?

A longitudinal study of 62 individuals with profound mental retardation was conducted to determine if direct care staff can identify behavior change prior to identifying symptoms of acute illness. Results indicate that staff were able to notice changes in sluggishness prior to the onset of illness. Self-care behavior was of borderline significance and there was no significant change in eight behavior dimensions (vocalizations, peer conflict, stereotypy, aggression, self injurious behavior, restlessness, distractibility, and depression). This finding should alert physicians and caregivers to the importance of prompt response to symptoms. Reliance on behavioral observation of direct care staff is not always sensitive enough to pick up changes in health status in less restrictive residential environments.

Activities of Daily Living↗
PubMed1996

Cutting thread at flexible endoscopy.

BACKGROUND: New thread-cutting techniques were developed for use at flexible endoscopy. A guillotine was designed to follow and cut thread at the endoscope tip. A new method was developed for guiding suture cutters. Efficacy of Nd: YAG laser cutting of threads was studied. Experimental and clinical experience with thread-cutting methods is presented. METHODS: A 2.4 mm diameter flexible thread-cutting guillotine was constructed featuring two lateral holes with sharp edges through which sutures to be cut are passed. Standard suture cutters were guided by backloading thread through the cutters extracorporeally. A snare cutter was constructed to retrieve objects sewn to tissue. Efficacy and speed of Nd: YAG laser in cutting twelve different threads were studied. RESULTS: The guillotine cut thread faster (p < 0.05) than standard suture cutters. Backloading thread shortened time taken to cut thread (p < 0.001) compared with free-hand cutting. Nd: YAG laser was ineffective in cutting uncolored threads and slower than mechanical cutters. Results of thread cutting in clinical studies using sewing machine (n = 77 cutting episodes in 21 patients), in-vivo experiments (n = 156), and postsurgical cases (n = 15 over 15 years) are presented. CONCLUSIONS: New thread-cutting methods are described and their efficacy demonstrated in experimental and clinical studies.

Animals↗
PubMed1995

Suppression of anti-thyrocyte autoreactivity by the lymphocytes of normal fetal lambs.

We have devised an experimental strategy to determine whether the developing immune system of normal fetal animals can spontaneously acquire the capacity to inhibit autoimmune responses by its cells as it matures. Whilst the existence of cells with the capacity to exert negative regulation and to curtail autoimmune responses has been demonstrated previously in response to the experimental induction of these responses, the relevance of such regulatory processes to the prevention of overt autoimmunity in normal animals has not been established. We have produced pairs of identical twin fetal lambs by splitting blastocysts and have subsequently deprived one of each pair of exposure to thyroid-specific antigens by surgical thyroidectomy before development of immunological self recognition. Thyroidectomized fetuses developed T lymphocytes autoreactive against self thyrocytes. However, their normal, identical co-twins were found to acquire a class of T lymphocytes with the capacity to block anti-thyrocyte autoreactive cells from the thyroidectomized fetal co-twin. Blocking of anti-thyroid autoreactivity required preliminary contact between these normal T lymphocytes and the target thyrocytes. Substitution of an allograft of fetal thyroid tissue for a fetal lamb's own thyroid gland failed to prevent the development of autoreactivity against autologous thyrocytes by the recipient's lymphocytes. However, the reactivity of those lymphocytes against thyrocytes from the specific allogeneic thyroid donor was markedly curtailed.

Animals↗
PubMed1995

Muscle atonia is triggered by cholinergic stimulation of the basal forebrain: implication for the pathophysiology of canine narcolepsy.

Narcolepsy is a sleep disorder characterized by excessive daytime sleepiness and rapid eye movement (REM) sleep-related symptoms, such as cataplexy. The exact pathophysiology underlying the disease is unknown but may involve central cholinergic systems. It is known that the brainstem cholinergic system is activated during REM sleep. Furthermore, REM sleep and REM sleep atonia similar to cataplexy can be triggered in normal and narcoleptic dogs by stimulating cholinergic receptors within the pontine brainstem. The pontine cholinergic system is, therefore, likely to play a role in triggering cataplexy and other REM-related abnormalities seen in narcolepsy. The other cholinergic system that could be involved in the pathophysiology of narcolepsy is located in the basal forebrain (BF). This system sends projections to the entire cerebral cortex. Since acetylcholine release in the cortex is increased both during REM and wake, the basocortical cholinergic system is believed to be involved in cortical desynchrony. In the current study, we analyzed the effect of cholinergic compounds injected into the forebrain structures of narcoleptic and control dogs. We found that carbachol (a cholinergic agonist) injected into the BF triggers cataplexy in narcoleptic dogs while it increases wakefulness in control dogs. Much higher doses of carbachol bilaterally injected in the BF were, however, shown to trigger muscle atonia even in control dogs. These results suggest that a cholinoceptive site in the BF is critically implicated in triggering muscle atonia and cataplexy. Together with similar results previously obtained in the pontine brainstem, it appears that a widespread hypersensitivity to cholinergic stimulation may be central to the pathophysiology of canine narcolepsy.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Effect of 5-HT1A receptor agonists and antagonists on canine cataplexy.

Pharmacological studies using a canine model of narcolepsy have demonstrated that adrenergic rather than serotonergic or dopaminergic uptake inhibition is the primary mode of action of antidepressants on cataplexy, a pathological manifestation of rapid eye movement (REM) sleep atonia that occurs in narcolepsy. This result is in line with the known involvement of adrenergic systems in the regulation of REM sleep. However, the lack of anticataplectic effects of selective serotonergic compounds was puzzling as serotonergic neurons of the dorsal raphe nuclei are known to decrease activity during the REM sleep in a manner similar to the adrenergic neurons of the locus coeruleus. To further explore the role of serotonergic systems, we tested the effect on canine cataplexy of six 5-HT1A agonists and five 5-HT1A antagonists. Results indicate that 5-HT1A agonists significantly suppress cataplexy in correlation with their in vitro affinities to the canine central 5-HT1A receptors. Anticataplectic effects were, however, accompanied by various behavioral changes, such as flattened body posture, increased panting and agitation. In contrast, the selective 5-HT1A antagonist did not aggravate cataplexy, although a 5-HT1A antagonist was able to block the anticataplectic effect of a 5-HT1A agonist. These results suggest that the anticataplectic effects of 5-HT1A agonists are truly mediated by 5-HT1A receptor stimulation. It is, however, likely that anticataplectic effects occur due to the behavioral side effects rather than the direct involvement of this receptor subtype in the regulation of cataplexy. Further studies are therefore necessary to address the question of whether these 5-HT1A agonists hold promise in the pharmacological treatment of human cataplexy.

Animals↗
PubMed1995

Comparative effects of modafinil and amphetamine on daytime sleepiness and cataplexy of narcoleptic dogs.

The effects of modafinil and amphetamine on daytime sleep (polysomnographic recordings) and cataplexy (the food-elicited cataplexy test) were compared using the narcoleptic canine model. Results indicate that both modafinil (5 and 10 mg/kg body weight i.v.) and amphetamine (100 and 200 micrograms/kg i.v.) increase wakefulness and reduce slow-wave sleep in control and narcoleptic dogs. In contrast, the results of cataplexy testing demonstrate that amphetamine (2.5-160 micrograms/kg i.v.), but not modafinil (0.125-8.0 mg/kg i.v.) significantly suppresses canine cataplexy. These results suggest that the pharmacological property of modafinil is distinct from amphetamine. Results of polysomnographic recordings also demonstrate that narcoleptic dogs slept significantly more during the daytime than control dogs and required very high doses (10 mg/kg i.v. modafinil; 200 micrograms/kg i.v. amphetamine) of stimulants to reduce their level of sleepiness to that of control dogs. This finding is consistent with the data collected in human narcolepsy and validates the use of this canine model for the screening of stimulant compounds.

Amphetamine↗
PubMed1993

Memory performance during the Amytal test in patients with non-temporal lobe epilepsy.

PROBLEM: The amobarbital (Amytal) sodium test has been considered an indispensable tool in the presurgical examination of patients for epilepsy surgery. However, the accuracy of the Amytal test for predicting memory deficits, especially the amnestic syndrome, has been questioned. METHOD: The Amytal test was administered bilaterally to three groups of patients with epilepsy: temporal lobe (n = 76), frontal lobe (n = 25), and primary generalized (n = 8). Each injected hemisphere for each patient was graded pass or fail for its ability to support memory. RESULTS: The percentages of hemispheres that failed the Amytal test were 31% for the temporal lobe group, 32% for the frontal lobe group, and 56% for the primary generalized group. CONCLUSIONS: The Amytal test may be a sensitive measure of memory dysfunction. However, the high percentage of failures remains at variance with the rare incidence of the amnestic syndrome, suggesting a low specificity for this test.

Adolescent↗