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J Walcott

Publications and source records attributed to J Walcott.

7 recordsLinked to original sources
PubMed2001

Expression of expanded repeat androgen receptor produces neurologic disease in transgenic mice.

Spinal and bulbar muscular atrophy (SBMA) is a motor neuron disease caused by the expansion of a polyglutamine tract within the androgen receptor. This disease is unusual among the polyglutamine diseases in that it involves lower motor and sensory neurons, with relative sparing of other brain structures. We describe the development of transgenic mice, created with a truncated, highly expanded androgen receptor driven by the neurofilament light chain promoter, which develop many of the motor symptoms of SBMA. In addition, transgenic mice created with the prion protein promoter develop widespread neurologic disease, reminiscent of juvenile forms of other polyglutamine diseases. Thus, in these experiments, the distribution of neurologic symptoms depends on the expression level and pattern of the promoter used, rather than on specific characteristics of androgen receptor metabolism or function. The transgenic mice described here develop neuronal intranuclear inclusions (NIIs), a hallmark of SBMA and the other polyglutamine diseases. We have shown these inclusions to be ubiquitinated and to sequester molecular chaperones, components of the 26S proteasome and the transcriptional activator CREB-binding protein. Apart from the presence of NIIs, evidence of neuropathology or neurogenic muscle atrophy was absent, suggesting that the neurologic phenotypes observed in these mice were the result of neuronal dysfunction rather than neuronal degeneration. These mice will provide a useful resource for characterizing specific aspects of motor neuron dysfunction, and for testing therapeutic strategies for this and other polyglutamine diseases.

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PubMed2000

CREB-binding protein sequestration by expanded polyglutamine.

Spinal and bulbar muscular atrophy (SBMA) is one of eight inherited neurodegenerative diseases known to be caused by CAG repeat expansion. The expansion results in an expanded polyglutamine tract, which likely confers a novel, toxic function to the affected protein. Cell culture and transgenic mouse studies have implicated the nucleus as a site for pathogenesis, suggesting that a critical nuclear factor or process is disrupted by the polyglutamine expansion. In this report we present evidence that CREB-binding protein (CBP), a transcriptional co-activator that orchestrates nuclear response to a variety of cell signaling cascades, is incorporated into nuclear inclusions formed by polyglutamine-containing proteins in cultured cells, transgenic mice and tissue from patients with SBMA. We also show CBP incorporation into nuclear inclusions formed in a cell culture model of another polyglutamine disease, spinocerebellar ataxia type 3. We present evidence that soluble levels of CBP are reduced in cells expressing expanded polyglutamine despite increased levels of CBP mRNA. Finally, we demonstrate that over-expression of CBP rescues cells from polyglutamine-mediated toxicity in neuronal cell culture. These data support a CBP-sequestration model of polyglutamine expansion disease.

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PubMed1996

A statistical survey of dioxin-like compounds in United States beef: a progress report.

The USEPA and the USDA have completed the first statistically designed survey of the occurrence and concentration of CDDs and CDFs in the fat of beef animals raised for human consumption in the United States. Back fat was sampled from 63 carcasses at federally inspected slaughter establishments nationwide. The sample design called for sampling beef animal classes in proportion to national annual slaughter statistics. All samples were analyzed using a modification of EPA method 1613, using isotope dilution, High Resolution GC/MS to determine the rate of occurrence of 2,3,7,8-substituted CDDs/CDFS. The whole weight method detection limits ranged from 0.05 ng kg-1 for TCDD to 3 ng kg-1 for OCDD. The results of this survey showed a mean concentration (reported as I-TEQ, lipid adjusted) in U.S. beef animals of 0.35 ng kg-1 and 0.89 ng kg-1 when either non-detects are treated as 0 value or assigned a value of 1/2 the detection limit, respectively.

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PubMed1993

Serotonergic modulation of L-glutamic acid-evoked release of endogenous norepinephrine from rat hypothalamus.

Hypothalamic slices (400 mu) from male Sprague-Dawley rats were perfused with a Mg+(+)-free medium containing nomifensine (10 microM) and tyrosine (50 microM). Spontaneous release of endogenous norepinephrine (NE), measured by high-performance liquid chromatography-electrochemical detection, averaged 102 +/- 13 (N = 76) fmol/mg of protein/3 min. L-Glutamic acid (L-GLU) (1 mM) more than doubled the rate of NE release. Preincubation with serotonin (5-HT) (0.1-10 microM) produced no change in spontaneous NE release but caused a concentration-dependent decrease of L-GLU-induced NE release with a maximal reduction of about 60 to 70%. 2-Methylserotonin, a 5-HT3 receptor agonist (0.07-10 microM), mimicked the 5-HT response. A highly selective 5-HT3 receptor antagonist, (3 alpha-tropanyl)1H-indole-3-carboxylic acid ester, 1 nM, inhibited the effect of both agonists. Neither ritanserin (1 microM) nor methylsergide (1 microM) modified either spontaneous or 1 mM L-GLU-evoked release of NE. However, if added to the superfusion medium simultaneously with 5-HT, they potentiated significantly the inhibition produced by 5-HT. Alpha-methylserotonin (1 microM) if added alone to the perfusion medium had no effect on 1 mM L-GLU-evoked release of NE but reversed the inhibition induced by 1 microM 2-methylserotonin. These observations provide direct evidence of a dual modulation by 5-HT of L-GLU-evoked release of endogenous NE from slices of rat hypothalamus: An inhibition mediated by 5-HT3 receptors and an opposing action mediated by receptors of the 5-HT1C/2 type.

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PubMed1992

Release of endogenous norepinephrine from rat hypothalamus by stimulation of N-methyl-D-aspartic acid receptors.

Release of endogenous dopamine and norepinephrine (NE) from rat hypothalamic slices superfused with Mg(++)-free medium in the presence of nomifensine and tyrosine was measured by high-performance liquid chromatography coupled to an electrochemical detector. Superfusion with L-glutamic acid or N-methyl-D-aspartic acid elicited a concentration-dependent release of NE but not of dopamine. The release of NE was transient, returning toward basal values despite the continued presence of the amino acid. Superfusion with 20 mM K+ caused a release of NE that declined at a slower rate. Mg++, DL-2-amino-5-phosphonopentanoic acid and MK-801 (D-5-methyl-10,11,dihydro-5H-dibenzo[a,d] cyclohepten-5-10-imine maleate), but not 6-cyano-7-nitroquinoxaline-2,3-dione, inhibited the L-glutamic acid-evoked release of NE. The release of NE by L-glutamic acid was virtually abolished by tetrodotoxin and by elimination of Ca++ from and inclusion of 2 mM ethylene glycol bis(beta-aminoethyl ether)-N,N'-tetraacetic acid in the superfusion medium. Repeated L-glutamic acid applications displayed a decreased response, whereas repeated exposure to 20 mM K+ did not. Exposure to L-glutamic acid in the absence of Ca++ (plus 2 mM ethylene glycol bis(beta-aminoethyl ether)-N,N'-tetraacetic acid) or in the presence of DL-2-amino-5-phosphonopentanoic acid did not reduce the effects seen on subsequent exposure to L-glutamic acid. Exposure to L-glutamic acid in the absence of Mg++ reduced the effect of a subsequent exposure to L-glutamic acid. These observations provide evidence for an indirect modulation of rat hypothalamic endogenous NE by the N-methyl-D-aspartate receptor.

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PubMed1991

Serotonergic modulation of the release of endogenous norepinephrine from rat hypothalamic slices.

Ca+(+)-dependent release of endogenous norepinephrine (NE) and dopamine from superfused rat hypothalamic slices was stimulated by 40 mM K+. 20 mM K+ released only NE. Two consecutive exposures to 20 mM K+ (S1 and S2, respectively) produced NE release of similar magnitude (S2/S1 = 1.03 +/- 0.08). Serotonin (5-HT), 3 to 10 microM, in the presence of methylsergide or ritanserin (antagonists at 5-HT1-like and 5-HT2 receptors), caused a concentration-dependent decrease of K(+)-evoked NE release. 5-HT alone did not alter K(+)-evoked NE release. 2-Methyl-serotonin, 2-methyl-5-hydroxytryptamine, 3 to 10 microM (a selective 5-HT3 agonist), mimicked the 5-HT response in the presence and in the absence of ritanserin. A highly selective 5-HT3 antagonist, (3 alpha-tropanyl)1H-indole-3-carboxylic acid ester (ICS 205-930), 1 nM, inhibited the effect of both agonists. The isomers of another highly selective 5-HT3 antagonist, zacopride, inhibited the effect of 2-methyl-serotonin, 2-methyl-5-hydroxytryptamine, at a concentration range, 0.03 to 20 nM, characteristic of their interaction with 5-HT3 receptors. alpha-Methyl-serotonin, alpha-methyl-5-hydroxytryptamine, a selective 5-HT1-like/5-HT2 agonist, failed to affect the K(+)-evoked NE release, but antagonized the effect of 2-methyl-serotonin, 2-methyl-5-hydroxytryptamine. These observations provide direct evidence that, in rat hypothalamus, 5-HT modulates release of endogenous NE through activation of 5-HT3 and, possibly, 5-HT1C receptors.

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