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H Baker

Publications and source records attributed to H Baker.

At least 73 records · Page 4Linked to original sources
PubMed1996

Inducible cAMP early repressor can modulate tyrosine hydroxylase gene expression after stimulation of cAMP synthesis.

Members of the CREB/CREM/ATF family of transcription factors either enhance or repress transcription after binding to the cAMP response elements (CREs) of numerous genes. The rat gene for tyrosine hydroxylase (TH) bears a canonical CRE, at base pairs -38 through -45 from the transcription initiation site, that is essential for basal and cAMP-stimulated transcription (Kim, K.-S., Lee, M. K., Carroll, J., and Joh, T. H. (1993) J. Biol. Chem. 268, 15689-15695; Lazaroff, M., Patankar, S., Yoon, S. O., and Chikaraishi, D. M. (1995) J. Biol. Chem. 270, 21579-21589). The current study identifies CRE-binding proteins induced in pharmacological paradigms characterized by TH activation. PC12- and rat adrenal gland-derived nuclear proteins retarded a TH-CRE oligonucleotide in gel mobility shift assays with virtually identical patterns. These differed substantially from patterns exhibited by extracts from locus ceruleus or from neuroblastoma (SK-N-BE()C) and locus ceruleus-derived (CATH.a) cell lines. Forskolin stimulation of PC12 cells and reserpine treatment of rats increased, in nuclear extracts derived from cells and adrenal glands, respectively, the amount of a fast moving CRE/protein complex that was supershifted by an anti-CREM antibody. Subsequent Western, Northern, and polymerase chain reaction analyses indicated that a specific member of the CREM family, the inducible cAMP early repressor (ICER), was strongly induced in both systems. Cotransfection of PC12 cells with TH2400CAT plasmid and the expression vector pCMV-ICER-Ib demonstrated that ICER efficiently represses the transcriptional activity of the TH gene promoter. In addition, PKA-stimulated transcriptional activity of the promoter was effectively suppressed by ICER. These results suggest that ICER can modulate cAMP-stimulated transcription of the TH gene and provide a model accounting for rapid reversal of increased TH transcription following elevations in cAMP.

Activating Transcription Factors↗
PubMed1996

Molecular cloning of ictacalcin: a novel calcium-binding protein from the channel catfish, Ictalurus punctatus.

Calcium is essential for a variety of functions in animals, including signal transduction, transmission of nerve impulses, and bone and scale growth. In freshwater adapted teleosts, blood calcium levels are maintained constant (2-4 mM) even at low external calcium concentration (< 0.01 mM). Epithelial cells in skin and gill have been implicated in calcium homeostasis. We have cloned a cDNA from Ictalurus punctatus, the channel catfish, that codes for ictacalcin, a novel member of the S100 family of calcium-binding protein. In-situ hybridization demonstrates ictacalcin mRNA is abundant in epithelial cells of olfactory rosette, barbel, skin and gill but not brain or muscle. The presence of ictacalcin protein in these tissues was confirmed by immuno-blot analysis. Tissue extracts and recombinant ictacalcin bind calcium with attendant changes in electrophoretic mobility indicative of changes in protein conformation. The calcium-binding activity and abundant localization of ictacalcin in epithelial cells of several tissues indicates that this protein plays an important role in catfish calcium homeostasis.

Amino Acid Sequence↗
PubMed1996

Olfactory marker protein (OMP) gene deletion causes altered physiological activity of olfactory sensory neurons.

Olfactory marker protein (OMP) is an abundant, phylogentically conserved, cytoplasmic protein of unknown function expressed almost exclusively in mature olfactory sensory neurons. To address its function, we generated OMP-deficient mice by gene targeting in embryonic stem cells. We report that these OMP-null mice are compromised in their ability to respond to odor stimull, providing insight to OMP function. The maximal electroolfactogram response of the olfactory neuroepithelium to several odorants was 20-40% smaller in the mutants compared with controls. In addition, the onset and recovery kinetics following isoamyl acetate stimulation are prolonged in the null mice. Furthermore, the ability of the mutants to respond to the second odor pulse of a pair is impaired, over a range of concentrations, compared with controls. These results imply that neural activity directed toward the olfactory bulb is also reduced. The bulbar phenotype observed in the OMP-null mouse is consistent with this hypothesis. Bulbar activity of tyrosine hydroxylase, the rate limiting enzyme of catecholamine biosynthesis, and content of the neuropeptide cholecystokinin are reduced by 65% and 50%, respectively. This similarity to postsynaptic changes in gene expression induced by peripheral olfactory deafferentation or naris blockade confirms that functional neural activity is reduced in both the olfactory neuroepithelium and the olfactory nerve projection to the bulb in the OMP-null mouse. These observations provide strong support for the conclusion that OMP is a novel modulatory component of the odor detection/signal transduction cascade.

Animals↗
PubMed1996

Antioxidant survey to assess antagonism to redox stress using a prokaryotic and an eukaryotic system.

Using a prokaryote (Escherichia coli) and a metazoa-resembling eukaryote (Ochromonas danica), we surveyed antioxidants which might overcome redox stress imposed by menadione sodium bisulphite (MD) and buthionine sulphoximine (BSO). BSO oxidant stress was evident only in O. danica; MD oxidant stress was evident in both organisms. Glutathione, its precursors, e.g. cysteine, homocysteine, and 2-oxo-4-thiazolidine carboxylic acid, and red blood cells, emerged as prime antioxidants for relieving BSO and MD oxidant stress. BSO and MD oxidant activity and antioxidant-annulling effect in O. danica were judged comparable to those found in animal cells whereas the results E. coli were not entirely equivalent. The O. danica system emerged as a practical, rapid, and useful system for pinpointing oxidant stressors and antioxidants, and shows promise for studies with mammalian systems.

Antioxidants↗
PubMed1996

Rapid down-regulation of tyrosine hydroxylase expression in the olfactory bulb of naris-occluded adult rats.

In most sensory systems, afferent innervation regulates morphological and biochemical characteristics of target cells for a limited time during development. Sensory deprivation experiments in adult rats also have suggested a critical period for afferent influences on olfactory bulb structure and function. Previous odorant deprivation studies that employed unilateral naris closure in neonatal rats demonstrated down-regulation of the catecholamine biosynthetic enzyme tyrosine hydroxylase (TH) in dopamine neurons intrinsic to the olfactory bulb. Accompanying the altered biochemical parameters was a decrease in bulb size. To distinguish between deprivation-induced alterations in TH expression secondary to developmental sequelae and those occurring in mature neurons, the consequences of unilateral naris closure were assessed in young adult rats. In agreement with previous studies significant postnatal increases occurred in TH expression and total protein, an indication of bulb size. At 30 days post-closure, total protein was unaltered in the ipsilateral olfactory bulb but showed a small (12.9%), significant decline at 60 days. In contrast to the limited morphological consequences of odor deprivation, profound reductions occurred in TH expression. TH activity ipsilateral to the closure decreased significantly by 14 days post-closure and remained depressed for up to 6 months. In parallel with enzyme activity, TH immunoreactivity did not decline in the first few days post-closure. In situ hybridization revealed that TH mRNA levels decreased rapidly, i.e., by 2 days post-closure, reached a nadir at 1 month, and remained depressed for at least 6 months. The capacity of odor deprivation in the adult rat olfactory system to down-regulate TH expression suggests that this phenotypic alteration occurs independently of a presumed critical period.

Animals↗
PubMed1996

Micronutrient profiles in HIV-1-infected heterosexual adults.

There is compelling evidence that micronutrients can profoundly affect immunity. We surveyed vitamin supplement use and circulating concentrations of 22 nutrients and glutathione in 64 HIV-1 seropositive men and women and 33 seronegative controls participating in a study of heterosexual HIV-1 transmission. We assayed antioxidants (vitamins A, C, and E; total carotenes), vitamins B6 and B12, folate, thiamin, niacin, biotin, riboflavin, pantothenic acid, free and total choline and carnitine, biopterin, inositol, copper, zinc, selenium, and magnesium. HIV-infected patients had lower mean circulating concentrations of magnesium (p < 0.0001), total carotenes (p = 0.009), total choline (p = 0.002), and glutathione (p = 0.045), and higher concentrations of niacin (p < 0.0001) than controls. Fifty-nine percent of HIV+ patients had low concentrations of magnesium, compared with 9% of controls (p < 0.0001). These abnormal concentrations were unrelated to stage of disease. Participants who took vitamin supplements had consistently fewer low concentrations of antioxidants, across HIV infection status and disease stage strata (p = 0.0006). Nevertheless, 29% of the HIV+ patients taking supplemental vitamins had subnormal levels of one or more antioxidants. The frequent occurrence of abnormal micronutrient nutriture, as found in these HIV+ subjects, may contribute to disease pathogenesis. The low magnesium concentrations may be particularly relevant to HIV-related symptoms of fatigue, lethargy, and impaired mentation.

Adult↗
PubMed1996

Holotranscobalamins in B12 and non B12 requiring prokaryotes and eukaryotes.

Transcobalamins, vitamin B12 binding proteins, deliver B12 to cell surface receptors which then permit B12 to cross cell membranes for metabolic use. There is little documentation concerning B12 binding proteins in bacteria and protists. We found that prokaryotes and eukaryotes requiring B12, as well as those protists synthesizing B12, also produce several transcobalamins for functionally transporting B12 similar to humans.

Animals↗
PubMed1996

Regulation of c-Fos mRNA and fos protein expression in olfactory bulbs from unilaterally odor-deprived adult mice.

Odorant deprivation, produced by unilateral naris closure, profoundly reduces tyrosine hydroxylase (TH) expression within intrinsic olfactory bulb dopamine neurons. The TH gene contains an AP-1 site, which interacts with the product of the immediate early gene, c-fos. c-Fos exhibits activity dependent regulation in the CNS. The hypothesis that odorant stimulation and deprivation might modify c-fos expression in TH neurons was tested in adult CD-1 mice, subjected to unilateral naris closure. After 2 months, naris closed and control mice were exposed to either clean air for 60 min or clean air for 60 min followed by 30 min of alternating exposure to 10% isoamyl acetate (1 min) and air (4 min). A parallel reduction occurred in TH and fos expression (both c-fos mRNA and fos-like immunoreactivity) in the glomerular layer of the odorant-deprived olfactory bulb. Odor stimulation induced a short-lived increase in c-fos mRNA and fos-like immunoreactivity in olfactory bulbs contralateral to naris closure. The increase in fos expression was region-specific in the glomerular layer but more diffuse in mitral and granule cell layers. In olfactory bulbs ipsilateral to naris closure, odor stimulation also induced c-fos mRNA expression in the mitral and granule cell layers and sparsely within limited periglomerular regions. Odor induced expression in mitral and granule cell layers may represent increased centrifugal activity acting on as yet unknown genes. These results suggest a correlation between c-fos mRNA expression and increased neuronal activity in the olfactory bulb which, in turn, acts to regulate TH expression in periglomerular neurons.

Animals↗
PubMed1996

A transgenic mouse model to study transsynaptic regulation of tyrosine hydroxylase gene expression.

Previous studies demonstrated that 9 kb of the rat tyrosine hydroxylase (TH) 5' flanking sequence directed appropriate spatiotemporal expression of a lacZ reporter gene to catecholaminergic cells in the CNS of transgenic mice. In the present study, specificity of transgene expression was further extended to demonstrate cell type-specific functional regulation of lacZ expression using manipulations known to alter endogenous TH expression. Alterations in lacZ reporter expression should parallel changes in endogenous TH levels if the DNA elements mediating these functional changes of TH expression in vivo reside within the 9 kb of the TH promoter region. Naris closure induced an activity-dependent decrease of TH expression in dopaminergic periglomerular cells in the olfactory bulb that was paralleled by down-regulation of lacZ expression in the transgenic mice. Densitometry and image analysis were used to quantify lacZ expression following acute reserpine administration (5 mg/kg s.c.), which up-regulates endogenous TH. At 48 h postinjection, analysis of OD values indicated a significant increase of X-gal staining in the locus coeruleus and ventral tegmental area but not in the substantia nigra or olfactory bulb of reserpine-treated transgenic animals. These data showed that the 9-kb sequence also mediates cell type-specific transsynaptic regulation of reporter gene expression. Analysis of this transgenic animal offers a useful model system to study in vivo regulation of TH gene expression.

Animals↗
PubMed1996

Regional reductions of transketolase in thiamine-deficient rat brain.

Thiamine deficiency impairs oxidative metabolism and causes metabolic encephalopathy. An early reduction in transketolase (TK) activity may be an important pathogenic event. To assess the role of TK, we have delineated the regional/cellular distribution of TK protein and mRNA in adult rat brain in pyrithiamine-induced thiamine deficiency. TK activity declined in both vulnerable and spared regions. Immunoblots showed a parallel reduction of TK protein. With a few exceptions, immunocytochemistry indicated an overall decline of TK immunoreactivity and the decrease was not specific to vulnerable areas. In contrast to the pronounced, general decline of TK protein, in situ hybridization revealed a regional decrease of 0-25% of TK mRNA in thiamine deficiency. Northern blots indicated a similar level of TK mRNA in whole brain in thiamine deficiency. These results show that the decline of TK activity results from a proportional decrease of TK protein, and the deficiency may be due to an instability of TK protein or an inhibition of TK mRNA translation. The lack of correlation of the distribution, and the absence of specific alteration, of TK in affected regions suggest that the reduced TK may not be linked directly to selective vulnerability in thiamine deficiency.

Animals↗
PubMed1996

Human plasma patterns during 14 days ingestion of vitamin E, beta-carotene, ascorbic acid, and their various combinations.

OBJECTIVE: We wanted to learn about plasma patterns of ascorbic acid (AA), beta carotene (BC), and vitamin E (vit E) when each or their various combinations were fed to humans. Conceivably, the combined absorption of these antioxidants could synergize maximum plasma redox potential. METHODS: Vit E (800 mg/day), BC (30 mg/day), and AA (1000 mg/day) were fed individually or in various combinations with each other to 91 volunteers divided into different feeding groups for 14 days. Plasma vit E, carotenes, and AA patterns were analyzed by standardized methods; values were compared with each group's baseline value. RESULTS: AA feeding did not significantly increase already saturated plasma AA concentrations above baseline. Intake of BC did not influence vitamin A (vit A) levels. Feeding of only vit E or only BC, with or without AA addition, or a combination of BC and vit E significantly increased plasma vit E and carotene levels after 2 days. A statistically (ANOVA) significant increase in plasma vit E above baseline was noted when vit E was ingested combined with AA or BC; this increase in plasma vit E was not significant when AA, BC and vit E were taken in combination. CONCLUSION: Our results show that BC or AA ingestion in combination with vit E significantly increases circulating vit E above that seen when vit E is individually ingested. Vit E in combination with BC or AA seems a practical means or increasing the circulating antioxidant potential afforded by vit E. Reasons why such synergism does not exist when an AA, BC, vit E combination is ingested is not yet obvious.

Adult↗
PubMed1996

Novel neuritic clusters with accumulations of amyloid precursor protein and amyloid precursor-like protein 2 immunoreactivity in brain regions damaged by thiamine deficiency.

Experimental thiamine deficiency (TD) is a classical model of a nutritional deficit associated with a generalized impairment of oxidative metabolism and selective cell loss in the brain. In rats, TD-induced cell degeneration is accompanied by an accumulation of amyloid precursor protein (APP)/amyloid precursor-like protein 2 (APLP2) immunoreactivity in abnormal neurites and perikarya along the periphery of, or scattered within, the lesion. Prompted by these data and our previous findings of a genetic variation in the development of TD symptoms, we extended our studies to mice. C57BL/6, ApoE knockout, and APP YAC transgenic mice received thiamine-deficient diet and pyrithiamine injections. Unlike rats, APP/APLP2-immunoreactive neurites in all strains of mice were sparsely scattered within damaged areas and did not delimit the thalamic lesion. In addition, abnormal clusters of intensely immunoreactive neurites occurred only in areas of damage including the thalamus, mammillary body, and inferior colliculus. The clusters appeared as either irregular clumps or round or oval rosettes that strikingly resembled the neuritic component of Alzheimer amyloid plaques. However, immunostaining using various antisera to synthetic amyloid beta-protein (A beta 1-40) and thioflavine S histochemistry failed to show evidence of a component of A beta Neither APP/APLP2-immunoreactive clusters nor amyloid plaques were observed in the brain from patients with Wernicke-Korsakoff syndrome, the clinical manifestation of TD in man. Our results demonstrate species (i.e., genetic) differences in the response to TD-induced damage and support a role for APP and APLP2 in the response to brain injury. This is the first report that chronic oxidative deficits can lead to this novel pathology.

Amyloid beta-Protein Precursor↗
PubMed1995

Innervation-independent changes in the mRNAs encoding tyrosine hydroxylase and the norepinephrine transporter in rat adrenal medulla after high-dose reserpine.

To determine whether a trans-synaptic mechanism triggered the effects of reserpine on adrenomedullary mRNAs encoding the norepinephrine transporter and tyrosine hydroxylase, we administered 10 mg/kg reserpine to rats after unilateral splanchnicotomy, and examined their adrenal medullas using quantitative in situ hybridization. Splanchnicotomy did not alter the decrease in norepinephrine transporter mRNA that follows reserpine administration, but diminished the reserpine-induced increase in tyrosine hydroxylase mRNA by almost 80%. Despite the latter effect, reserpine still induced a significant increase in tyrosine hydroxylase mRNA in denervated adrenal medullas, compared to vehicle-treated adrenal medullas. These results show that a trans-synaptic mechanism does not trigger the decrease in adrenomedullary norepinephrine transporter mRNA following reserpine. In addition, an innervation-independent mechanism mediates a portion of the reserpine-induced increase in adrenomedullary tyrosine hydroxylase mRNA.

Adrenal Medulla↗
PubMed1995

Accumulation of amyloid precursor protein-like immunoreactivity in rat brain in response to thiamine deficiency.

Thiamine deficiency (TD) is a classical model of impaired cerebral oxidation. As in Alzheimer's disease (AD), TD is characterized by selective neuronal loss, decreased activities of thiamine pyrophosphate-dependent enzymes, cholinergic deficits and memory loss. Amyloid beta-protein (A beta), a approximately 4 kDa fragment of the beta-amyloid precursor protein (APP), accumulates in the brains of patients with AD or Down's syndrome. In the current study, we examined APP and A beta immunoreactivity in the brains of thiamine-deficient rats. Animals received thiamine-deficient diet ad libitum and daily injections of the thiamine antagonist, pyrithiamine. Immunocytochemical staining and immunoblotting utilized a rabbit polyclonal antiserum against human APP645-694 (numbering according to APP695 isoform). Three, 6 and 9 days of TD did not appear to damage any brain region nor change APP-like immunoreactivity. However, 13 days of TD led to pathological lesions mainly in the thalamus, mammillary body, inferior colliculus and some periventricular areas. While immunocytochemistry and thioflavine S histochemistry failed to show fibrillar beta-amyloid, APP-like immunoreactivity accumulated in aggregates of swollen, abnormal neurites and perikarya along the periphery of the infarct-like lesion in the thalamus and medial geniculate nucleus. Immunoblotting of the thalamic region around the lesion revealed increased APP-like holoprotein immunoreactivity. APP-like immunoreactive neurites were scattered in the mammillary body and medial vestibular nuclei where the lesion did not resemble infarcts. In the inferior colliculus, increased perikaryal APP-like immunostaining occurred in neurons surrounding necrotic areas. Regions without apparent pathological lesions showed no alteration in APP-like immunoreactivity. Thus, the oxidative insult associated with cell loss, hemorrhage and infarct-like lesions during TD leads to altered APP metabolism. This is the first report to show a relationship between changes in APP expression, oxidative metabolism and selective cell damage caused by nutritional/cofactor deficiency. This model appears useful in defining the role of APP in the reponse to central nervous system injury, and may also be relevant to the pathophysiology of Wernicke-Korsakoff syndrome and AD.

Amyloid beta-Protein Precursor↗
PubMed1995

Blood-brain barrier abnormalities in vulnerable brain regions during thiamine deficiency.

Experimental thiamine deficiency (TD) is a classical model of metabolic encephalopathy and selective cell loss in the brain resulting from a generalized, low-grade oxidative deficit. Late stages of TD are characterized by hemorrhages in the brain indicating a disruption of the blood-brain barrier (BBB). However, the relation of the breakdown of the BBB to selective cell loss in TD is not understood. The current studies examined the BBB at different stages of TD using immunoglobulin G (IgG) as an indicator of BBB integrity. Adult rats received thiamine-deficient diet ad libitum and daily injections of the thiamine antagonist pyrithiamine. IgG immunoreactivity increased in the inferior colliculus and inferior olive as early as 10 days after the initiation of TD and prior to the onset of cell death and hemorrhage. After 11 or 12 days, IgG immunoreactivity increased in multiple vulnerable regions. On Day 13, intense IgG immunoreactivity was found in regions of tissue damage and hemorrhage such as the thalamus, inferior colliculus, mammillary body, medial geniculate nucleus, medial vestibular nucleus, and inferior olive. Nonvulnerable regions displayed little or no IgG immunoreactivity. Immunoblotting analysis confirmed the presence of IgG in vulnerable areas such as the thalamus and inferior colliculus but not in preserved regions such as the cortex. Preliminary electron microscopy of capillary endothelia in areas of IgG accumulation in the thalamus at Day 13 revealed perivascular edema and intact interendothelial tight junctions.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Heterogeneous expression of transketolase in rat brain.

Transketolase (TK; EC 2.2.1.1) is a key pentose phosphate shunt enzyme that plays an important role in the production of reducing equivalents and pentose sugars. TK activity declines in the brains of patients with Alzheimer's disease or Wernicke-Korsakoff syndrome, as well as in thiamine-deficient rats. Understanding the role of TK in the pathophysiology of these neurodegenerative conditions requires knowledge of its regional, cellular, and subcellular distribution within the brain. The current study employed in situ hybridization and immunocytochemistry to examine the distribution of TK mRNA and its encoded protein in adult rat brain. TK mRNA and protein were widely distributed throughout the brain. However, they were enriched in selective perikarya in the piriform cortex, nucleus of the diagonal band, red nucleus, dorsal raphe, pontine nucleus, locus coeruleus, trapezoid, inferior olive, and several cranial nerve nuclei. Lower expression of TK mRNA and protein occurred in layer V of cortex, olfactory tubercle, ventral pallidum, medial septal nucleus, hippocampus, thalamic and hypothalamic nuclei, mammillary body, central gray, and the substantia nigra. TK immunoreactivity also occurred in the nuclei of ubiquitously distributed glial cells, as well as ependymal cells. The heterogeneous distribution of TK may reflect a variety of metabolic activities among different brain regions but does not provide a simple molecular explanation for selective cell death in either thiamine deficiency or other conditions where TK is reduced.

Animals↗
PubMed1995

Differential in vivo regulation of mRNA encoding the norepinephrine transporter and tyrosine hydroxylase in rat adrenal medulla and locus ceruleus.

To investigate the regulation of norepinephrine transporter mRNA in vivo, we analyzed the effects of reserpine on its expression in the rat adrenal medulla and locus ceruleus. First, PCR was used to clone a 0.5-kb rat cDNA fragment that exhibits 87% nucleotide identity to the corresponding human norepinephrine transporter cDNA sequence. In situ, the cDNA hybridizes specifically within norepinephrine-secreting cells, but in neither dopamine nor serotonin neurons, suggesting strongly it is a partial rat norepinephrine transporter cDNA. Reserpine, 10 mg/kg administered 24 h premortem, decreased steady-state levels of norepinephrine transporter mRNA in the adrenal medulla by approximately 65% and in the locus ceruleus by approximately 25%, as determined by quantitative in situ hybridization. Northern analysis confirmed the results of the in situ hybridization analysis in the adrenal medulla but did not detect the smaller changes observed in the locus ceruleus. Both analyses showed that reserpine increased tyrosine hydroxylase expression in the adrenal medulla and locus ceruleus. These results suggest that noradrenergic neurons and adrenal chromaffin cells can coordinate opposing changes in systems mediating catecholamine uptake and synthesis, to compensate for catecholamine depletion.

Adrenal Medulla↗