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D Casper

Publications and source records attributed to D Casper.

At least 37 records · Page 2Linked to original sources
PubMed1997

Varying degradation rates of total nonstructural carbohydrates: effects on ruminal fermentation, blood metabolites, and milk production and composition in high producing Holstein cows.

Twelve multiparous Holstein cows (6 ruminally cannulated and 6 intact) at 56 to 77 d of lactation were used in an experiment with a 3 x 6 Latin square design. Cows were fed three total mixed rations that varied in degradation rates of total nonstructural carbohydrates (6.04, 6.98, and 7.94%/h). No interactions between treatment and square were detected. Higher ruminal degradation rates of dietary total nonstructural carbohydrates increased the nonammonia N (NAN) pool of the liquid fraction but did not alter the dry matter or volume of fractional pools, microbial NAN pools, or microbial composition. Treatment did not affect dry matter intake, total concentrations of volatile fatty acids, or fiber digestibility. As ruminal degradation rates of total nonstructural carbohydrates increased, the following effects were observed: 1) the turnover rates of solids increased linearly; 2) ruminal NH3 N concentrations and degradabilities of organic matter and N decreased, but propionate concentrations, bacterial efficiency, and total NAN flows tended to increase; 3) blood glucose and insulin concentrations were not affected, but blood urea N and nonesterified fatty acids were decreased; 4) intestinal and total tract digestibilities of organic matter and total nonstructural carbohydrates increased; and 5) milk production and milk true protein content and yield increased, but energetic efficiency of milk production did not change. The highest dietary ruminal degradation rate of total nonstructural carbohydrates increased the amount of nutrients digested in the intestine and increased milk production.

Animals↗
PubMed1996

Expression of vascular endothelial growth factor in pediatric and adult cerebral arteriovenous malformations: an immunocytochemical study.

Children and adults may differ with respect to their cerebral vasculature in both normal and pathological states. The authors have identified four pediatric patients in whom a cerebral arteriovenous malformation (AVM) recurred after surgery for removal of the AVM and in whom a normal postoperative angiogram had been obtained. This phenomenon has not been observed in adults. The propensity to regrow a cerebral AVM may reflect a less mature cerebral vasculature and a disregulated angiogenic process. Recently, attention has focused on vascular endothelial growth factor (VEGF) as a possible general mediator of angiogenesis in development and neoplasia. A retrospective immunocytochemical analysis of VEGF expression in AVM tissue was conducted to test the hypothesis that VEGF expression may be found in association with the regrowth of AVMs. The results demonstrate a high degree of astrocytic VEGF expression in four (100%) of four specimens from the initial operation in the children with recurrent AVMs as compared to one (14%) of seven nonrecurrent AVMs in the pediatric and two (25%) of eight adult specimens. All of the specimens from the first operation of the recurrent group demonstrate a clear association of cellular immunoreactivity to the abnormal blood vessels, a relationship that was not observed in the specimens from the nonrecurrent groups. These observations indicate that a humoral mechanism mediated by VEGF may play a role in AVM recurrence.

Adult↗
PubMed1995

Epidermal growth factor and basic fibroblast growth factor protect dopaminergic neurons from glutamate toxicity in culture.

In this report we characterize the toxicity of the excitatory amino acid L-glutamate with respect to dopaminergic neurons cultured from embryonic rat mesencephalon. We also demonstrate that two growth factors, epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF), can protect these neurons from damage. Micromolar concentrations of L-glutamate, as well as agonists that specifically activate N-methyl-D-aspartate (NMDA) and non-NMDA receptors, are all toxic to dopamine neurons in a concentration-dependent manner, as reflected by decreases in high-affinity dopamine uptake and confirmed by decreases in numbers of tyrosine hydroxylase-immunoreactive neurons. Although the non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione could attenuate the effects of quisqualate, treatment with this antagonist could not eliminate the effects of glutamate itself. Similarly, (+/-)-2-amino-5-phosphonopentanoic acid was effective against NMDA toxicity but could not protect cells from quisqualate toxicity. Thus, each type of receptor could mediate neurotoxicity independently of the other. The presence of EGF or bFGF in the culture medium conferred a relative resistance of dopaminergic neurons to glutamate and quisqualate neurotoxicity by increased glutamate transport. However, treatment of the cultures with L-trans-pyrrolidine-2,4-dicarboxylic acid, an inhibitor of glutamate transport, attenuated but did not eliminate the protective effects of both growth factors against glutamate toxicity. When cultures were incubated with conditioned medium from growth factor-treated cultures, neuroprotection was also achieved. These results suggest that both EGF and bFGF can protect neurons from neurotoxicity in culture by increasing the capacity of the culture for glutamate uptake as well as by the secretion of soluble factors into the medium.

Animals↗
PubMed1994

Epidermal growth factor and basic fibroblast growth factor have independent actions on mesencephalic dopamine neurons in culture.

Epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF) are both trophic for dopamine neurons in cultures of dissociated embryonic rat mesencephalon, but the significance of this apparent overlap in neurotrophic activity is not yet known. In this study, we investigated the mechanisms of action of these two growth factors and the potential relationship between them. Using a nuclease protection assay, we determined that bFGF mRNA was expressed in the cultures. Double-label immunocytochemistry revealed that bFGF immunoreactive material could be detected in tyrosine hydroxylase immunoreactive neurons and glial fibrillary acidic protein immunoreactive astrocytes. EGF treatment increased bFGF mRNA content per culture dish. As we have previously demonstrated that EGF exerts its dopaminergic neurotrophic activity via an intermediate cell type, studies were designed to address whether the pathway by which EGF acts on dopaminergic neurons is mediated by the release of bFGF. However, the trophic action of EGF on dopamine neurons, represented by high-affinity neuronal dopamine uptake, could not be blocked by immunoneutralization of bFGF, suggesting that the actions of EGF were not mediated by bFGF release. The time course of the effects of EGF and bFGF on dopamine uptake were similar, with significant increases detectable only after 5 days in culture. Both growth factors were active in the picomolar-to-nanomolar range with maximal trophic activity between 0.4 and 2.5 nM. EGF, however, was the more potent mitogen under these conditions. When cultures were simultaneously incubated with maximal concentrations of EGF and bFGF, the effect on dopamine uptake was significantly greater than with either growth factor alone and, in fact, approximated the sum of the individual effects. On the basis of these results we conclude that these growth factors have independent effects on dopamine neurons of the mesencephalon.

Animals↗
PubMed1993

Brain-specific tropomyosins TMBr-1 and TMBr-3 have distinct patterns of expression during development and in adult brain.

In this study we report on the developmental and regional expression of two brain-specific isoforms of tropomyosin, TMBr-1 and TMBr-3, that are generated from the rat alpha-tropomyosin gene via the use of alternative promoters and alternative RNA splicing. Western blot analysis using an exon-specific peptide polyclonal antibody revealed that the two isoforms are differentially expressed in development with TMBr-3 appearing in the embryonic brain at 16 days of gestation, followed by the expression of TMBr-1 at 20 days after birth. TMBr-3 was detected in all brain regions examined, whereas TMBr-1 was detected predominantly in brain areas that derived from the prosencephalon. Immunocytochemical studies on mixed primary cultures made from rat embryonic midbrain indicate that expression of the brain-specific epitope is restricted to neurons. The developmental pattern and neuronal localization of these forms of tropomyosin suggest that these isoforms have a specialized role in the development and plasticity of the nervous system.

Aging↗
PubMed1992

Clathrin light chain B: gene structure and neuron-specific splicing.

The clathrin light chains are components of clathrin coated vesicles, structural constituents involved in endocytosis and membrane recycling. The clathrin light chain B (LCB) gene encodes two isoforms, termed LCB2 and LCB3, via an alternative RNA splicing mechanism. We have determined the structure of the rat clathrin light chain B gene. The gene consists of six exons that extend over 11.9 kb. The first four exons and the last exon are common to the LCB2 and LCB3 isoforms. The fifth exon, termed EN, is included in the mRNA in brain, giving rise to the brain specific form LCB2 but is excluded in other tissues, generating the LCB3 isoform. Primary rat neuronal cell cultures express predominantly the brain specific LCB2 isoform, whereas primary rat cultures of glia express only the LCB3 isoform, suggesting that expression of the brain-specific LCB2 form is limited to neurons. Further evidence for neuronal localization of the LCB2 form is provided using a teratocarcinoma cell line, P19, which can be induced by retinoic acid to express a neuronal phenotype, concomitant with the induction of the LCB2 form. In order to determine the sequences involved in alternative splice site selection, we constructed a minigene containing the alternative spliced exon EN and its flanking intron and exon sequences. This minigene reflects the splicing pattern of the endogenous gene upon transfection in HeLa cell and primary neuronal cell cultures, indicating that this region of the LCB gene contains all the necessary information for neuron-specific splicing.

Alternative Splicing↗
PubMed1991

EGF enhances the survival of dopamine neurons in rat embryonic mesencephalon primary cell culture.

Epidermal growth factor (EGF) immunoreactive material has been demonstrated to be present in the basal ganglia. In this study, we investigated the effect of EGF on cells cultured from 16-day embryonic rat mesencephalon, which included dopamine neurons that project to the striatum in vivo. EGF receptors were detected in untreated cultures by [125I]-EGF binding. Treatment of the cultures with EGF resulted in up to 50-fold increases in neuronal high-affinity dopamine uptake. Scatchard analysis of uptake kinetics and counting of tyrosine hydroxylase-immunoreactive cells suggest that the effect of EGF on uptake is due to increased survival and maturation of dopaminergic neurons. By contrast, the high-affinity uptake for serotonin was increased only threefold over its controls. There was no significant effect on high-affinity gamma-aminobutyric acid (GABA) uptake. These results suggest that EGF is acting as a neurotrophic agent preferential for dopaminergic neurons in E16 mesencephalic cultures. Immunocytochemistry for glial fibrillary acidic protein demonstrated an increase in astroglia with EGF treatment. Fluorodeoxyuridine, an agent that is toxic to proliferating cells was able to eliminate the effect of EGF on dopamine uptake, suggesting that EGF may be increasing dopaminergic cell survival largely through a population of dividing cells.

Animals↗
PubMed1990

The Alzheimer's amyloid precursor protein is produced by type I astrocytes in primary cultures of rat neuroglia.

The production of beta-amyloid precursor protein (beta APP) by primary mixed glial cell cultures from cerebral cortex of 2-3 day postnatal rats was examined by Northern and Western blotting and by immunocytochemistry. A single 3.5 kb beta APP RNA transcript was detected using probes recognizing all forms of beta APP messenger RNA. No signal was detected with a probe specific for the alternately spliced Kunitz protease inhibitor (KPI) region. In Western blot analysis of protein extracts, antisera specific for either the cytoplasmic or extracellular parts of beta APP detected several proteins ranging from 105 to 140 kDa. None of these were recognized by an antiserum specific to the KPI insert of the beta APP. Multicolor immunofluorescence showed beta APP immunoreactivity in type I (GFAP+ A2B5-) astrocytes, distributed in a fibrillar pattern like that of glial fibrillary acidic protein (GFAP). No beta APP immunoreactivity was detected in oligodendrocytes (GC+) or in A2B5+ progenitor cells. Moreover, no cultured cells showed immunostaining with an antiserum specific for the KPI sequence of beta APP. We conclude that type I astrocytes in primary culture produce amyloid precursor protein, but that oligodendrocytes and their precursors do not. Moreover, type I astrocytes produce predominantly the beta APP subtypes which lacks the KPI sequence.

Amyloid↗
PubMed1989

Stimulation of choline acetyltransferase activity by retinoic acid and sodium butyrate in a cultured human neuroblastoma.

Choline acetyltransferase (Acetyl-CoA:choline O-acetyltransferase, EC 2.3.1.6, abbreviated ChAT), the biosynthetic enzyme for acetylcholine and acetylcholinesterase (EC 3.1.1.7, abbreviated AChE) are expressed in a human cholinergic neuroblastoma cell line, MC-IXC. We have shown that ChAT activity can be regulated in culture by retinoic acid, an active metabolite of vitamin A, and by sodium butyrate, an organic fatty acid. Optimal concentrations of these agents produce 4.3-fold and 1.6-fold increases in ChAT activity, respectively. The effects of retinoic acid are statistically significant after 24 h, whereas for sodium butyrate significant differences are seen only after 48 h. Since retinoic acid stimulation of ChAT activity was reversed only by trypsin treatment and not by removal of retinoic acid from the medium, this suggests that this agent may be acting at the level of the cell surface. Other differentiating conditions, such as culture in serum-free medium or addition of 1-2% dimethylsulfoxide did not increase ChAT activity. Acetylcholinesterase activity was shown to increase only in the presence of sodium butyrate, suggesting that retinoic acid and sodium butyrate may be acting via different pathways. Retinoic acid and sodium butyrate both seem to be permissive rather than instructive in regulating ChAT activity in that they are unable to induce ChAT expression de novo in cell lines which do not already express ChAT activity.

Butyrates↗
PubMed1989

Mechanism of activation of choline acetyltransferase in a human neuroblastoma cell line.

In our previous report we have shown that the enzyme choline acetyltransferase (ChAT), responsible for the synthesis of the neurotransmitter acetylcholine, can be regulated in response to treatment by either retinoic acid or sodium butyrate. These responses were dose and time dependent, but the mechanism by which these agents were acting was not understood. We now report the results of studies aimed at elucidating the level at which both sodium butyrate and retinoic acid are able to increase ChAT activity. The effects of these agents on macromolecular synthesis appeared to be limited to small but statistically significant increases in the rate of RNA synthesis. However, inhibition of DNA, RNA and protein synthesis in these cells had no effect on the stimulation of ChAT activity by either sodium butyrate or retinoic acid. Several experiments appeared to rule out a role for cyclic AMP or protein kinase C in the regulation of ChAT activity, even though retinoic acid treatment could increase endogenous levels of cyclic AMP 3- to 4-fold over the time course of ChAT activity stimulation. Experiments performed to determine kinetic parameters of this enzyme demonstrated changes only in the Vmax, but not the Km of ChAT, suggesting that the affinity of enzyme for either of its substrates was not responsible for the increase in specific activity. Taken together, this evidence suggests that the activation of choline acetyltransferase in this human neuroblastoma cell line occurs at the post-translational level.

Butyrates↗