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Biomedical subjects

G Kapatos

Publications and source records attributed to G Kapatos.

At least 55 records · Page 3Linked to original sources
PubMed1989

Tyrosine hydroxylase content of residual striatal dopamine nerve terminals following 6-hydroxydopamine administration: a flow cytometric study.

Fluorescence-activated cell sorting based on immunolabeling with a monoclonal antibody to tyrosine hydroxylase and a fluorescein-conjugated secondary antibody was used to identify striatal synaptosomes derived from nigrostriatal dopamine nerve terminals. The amount of tyrosine hydroxylase immunoreactivity in dopaminergic striatal synaptosomes prepared from control rats was compared to the amount in dopaminergic synaptosomes prepared from rats that had received intraventricular injections of 6-hydroxydopamine. Although the absolute number of dopaminergic synaptosomes was decreased in lesioned animals, those residual dopamine terminals present contained more tyrosine hydroxylase than did dopamine terminals from control rats. Both the decrease in the absolute number of dopamine terminals and the increase in tyrosine hydroxylase immunoreactivity in residual terminals were proportional to the extent of the lesion, as determined by measurement of striatal dopamine levels. These results suggest that an increase in the amount of tyrosine hydroxylase protein in residual terminals may represent one compensatory mechanism by which residual dopamine neurons maintain normal striatal function after partial destruction of the nigrostriatal dopamine projection.

Animals↗
PubMed1989

Flow cytometric analysis and isolation of permeabilized dopamine nerve terminals from rat striatum.

Fluorescence-activated cell sorting (FACS) was used to identify and isolate permeabilized dopaminergic nerve terminals from rat striatum based on immunofluorescent labeling of tyrosine hydroxylase (TH). Striatal synaptosomes were permeabilized by fixation with modified Zamboni fluid. A highly fluorescent subpopulation of particles was detected by FACS following sequential incubation with a monoclonal antibody to TH (LNC 1) and a fluorescein-conjugated secondary antibody. After correcting for nonsynaptosomal particles present in the synaptosomal fraction, analysis of these data suggested that approximately 12-15% of striatal synaptosomes were dopaminergic, consistent with previous estimates. Specific labelling by LNC 1 was decreased if synaptosomes were prepared from rats that had received intraventricular injections of 6-hydroxydopamine. The decrease in labeling was highly correlated with the extent of the lesion as determined by measurement of striatal dopamine levels, suggesting that LNC 1-labeled synaptosomes were derived from nigrostriatal dopamine terminals. In order to verify that LNC 1-labeled synaptosomes were enriched for TH, equal numbers of labeled and control synaptosomes were isolated by FACS and analyzed by SDS-PAGE. LNC 1-labeled synaptosomes were shown by Western blot techniques to be enriched 6-fold for TH compared with control synaptosomes, suggesting that the labeled population consisted almost entirely of dopaminergic synaptosomes.

Animals↗
PubMed1989

Flow cytometric analysis of rat striatal nerve terminals.

Methods were developed for the analysis and isolation of striatal nerve terminals (synaptosomes) using fluorescence-activated cell sorting (FACS). Comparison of the light-scattering properties of synaptosomal and mitochondrial fractions indicated that particles in the synaptosomal fraction were generally larger and more sensitive to hypotonic lysis, consistent with results obtained by other methods of analysis. FACS analysis using indirect immunofluorescence techniques indicated that approximately 84% of the synaptosomal fraction was labeled by monoclonal antibody (mAb) A2B5 and thus appeared to be of neuronal origin. After permeabilization, between 5 and 10% of the particles were labeled by a mAb to glial fibrillary acidic protein, suggesting that they were derived from astrocytes. A fluorescent voltage-sensitive dye (VSD) was used to distinguish intact synaptosomes from free mitochondria (only the former maintain a membrane potential under the present experimental conditions). Approximately 83% of the synaptosomal fraction exhibited increased fluorescence after incubation with the VSD; furthermore, the fluorescence signal decreased in response to depolarizing agents (elevated potassium and veratridine). A portion of the mitochondrial fraction responded similarly, consistent with the presence of contaminating synaptosomes. Analysis of synaptosomal labeling by 11 fluorescein-conjugated plant lectins indicated that striatal nerve terminals differ significantly in their cell surface glycoconjugates. Subpopulations of synaptosomes defined on the basis of lectin binding were collected by FACS onto filters and probed with a mAb to tyrosine hydroxylase (TH) using Western blot techniques. While subpopulations exhibited different amounts of TH immunoreactivity, none of the lectins appeared to recognize TH-positive (i.e., dopaminergic) synaptosomes exclusively. These findings demonstrate that synaptosomes can be characterized and isolated for further study based on FACS analysis of properties such as size, membrane potential, and the presence of intracellular or cell surface molecules.

Animals↗
PubMed1984

Biopterin synthesis defect. Treatment with L-dopa and 5-hydroxytryptophan compared with therapy with a tetrahydropterin.

We have identified a generalized deficiency of monoamine neurotransmitters in a patient with a defect in biopterin synthesis. Neurotransmitter precursors (L-3,4-dihydroxyphenylalanine [L-dopa]; 5-hydroxytryptophan [5-HTP] and a tetrahydropterin [6-methyltetrahydropterin (6MPH4)] were investigated for their ability to normalize monoamine neurotransmitter metabolism. Before treatment, the concentrations of dopamine (DA), norepinephrine, epinephrine, and six monoamine metabolites were very low or undetectable in plasma, cerebrospinal fluid, or urine. L-Dopa and 5-HTP replacement was begun at age 7 mo. This therapy generally corrected the deficiency of monoamines and their metabolites, and improved neurological development until the age of 25 mo. Despite these benefits, the intermittent administration of L-dopa could not produce a stable improvement of acute neurological function or DA metabolism. In the 3 h after L-dopa administration, plasma DA and the motor activity and alertness of the patient rose and fell in parallel. Doses of L-dopa that were clinically optimal produced normal plasma levels of norepinephrine and epinephrine, but excessive concentrations of DA and its metabolites. Furthermore, the clinical and biochemical effects of L-dopa were inhibited by phenylalanine and 5-HTP, respectively, demonstrating that these amino acids have antagonistic pharmacological effects. Physiological correction of the monoamine deficit and the hyperphenylalaninemia of this disorder was attempted at age 35 mo using high doses (8-38 mg/kg per d) of 6MPH4. 6MPH4, a synthetic analogue of tetrahydrobiopterin, controlled the hyperphenylalaninemia. Significant concentrations of 6MPH4 were obtained in the cerebrospinal fluid; no neurological improvement or stimulation of monoamine synthesis in the central nervous system was detected. These findings indicate the complexity in replacement therapy with L-dopa and 5-HTP, but suggest that this treatment may be partially effective in biopterin-deficient patients who are unresponsive to high doses of tetrahydropterins.

5-Hydroxytryptophan↗
PubMed1983

The development of tetrahydrobiopterin and guanosine-5'-triphosphate cyclohydrolase: differential patterns in rat brain and pineal gland.

The developmental patterns of appearance of 5,6,7,8-tetrahydrobiopterin (BH4) and the first enzyme in BH4 biosynthesis, guanosine-5'-triphosphate cyclohydrolase (GTPcyc), were examined in rat brain and pineal gland. A parallel relationship between BH4 content and GTPcyc activity was evident in both tissues during development. In brain, the maximal content of BH4 and activity of GTPcyc was observed 2 days prior to, and 10 days after, birth. In contrast, both pineal BH4 content and GTPcyc activity became maximal postnatally. The influence of neural input on the developmental appearance of pineal BH4 was examined in rats that had been superior cervical ganglionectomized shortly after birth. It was found that this procedure did not alter the developmental appearance of BH4.

Aging↗
PubMed1983

Tetrahydropterin therapy for hyperphenylalaninemia caused by defective synthesis of tetrahydrobiopterin.

A patient with hyperphenylalaninemia caused by a defect in the synthesis of tetrahydrobiopterin was treated with 6-methyltetrahydropterin. This synthetic analog of the naturally occurring hydroxylation cofactor tetrahydrobiopterin, when given orally at a daily dose of 20 mg per kilogram of body weight increased depressed plasma and cerebrospinal fluid levels of norepinephrine. At a daily dose of 8 mg/kg, this pterin increased depressed cerebrospinal fluid levels of the biogenic amine metabolites dihydroxyphenylacetic acid, homovanillic acid, and 5-hydroxyindoleacetic acid. At these doses of 6-methyltetrahydropterin, there was an improvement of the patient's neurological symptoms, including a pronounced decrease in eye rolling and drooling and a marked increase in muscle strength, coordination, and physical activity.

Biopterins↗
PubMed1982

Biosynthesis of biopterin by rat brain.

A method for the determination of [14C]biopterin biosynthesis from [14C]guanosine-5'-triphosphate by a desalted preparation from rat striatum, based on sequential reverse-phase and cation-exchange high performance liquid chromatography, is described. Synthesis of reduced forms of biopterin by this striatal extract was found to be dependent on enzymatic activity, guanosine-5'-triphosphate, magnesium ions, and a reduced pyridine nucleotide. As demonstrated by the technique of isotope dilution, isotope trapping, 6-lactyl-7,8-dihydropterin (sepiapterin) was found to be an intermediate in biopterin biosynthesis that is catalyzed by the striatal extract. Rat brain was also shown to synthesize biopterin in vivo from intraventricularly administered [14C]guanosine or sepiapterin. Intraventricular injection of sepiapterin increased dihydro- and 5,6,7,8-tetrahydrobiopterin levels in rat brain by more than eightfold. The temporal relationship between the appearance of dihydro- and 5,6,7,8-tetrahydrobiopterin following intraventricular injection of sepiapterin suggests that dihydrobiopterin is the immediate product of sepiapterin reduction which is then reduced further to the functional cofactor 5,6,7,8-tetrahydrobiopterin. Therefore, in contrast to previous reports, the biosynthesis of biopterin by rat brain does not appear to differ from that occurring in other, nonneural tissues.

Animals↗
PubMed1982

Use of tetrahydropterins in the treatment of hyperphenylalaninemia due to defective synthesis of tetrahydrobiopterin: evidence that peripherally administered tetrahydropterins enter the brain.

Substantial amounts of tetrahydrobiopterin and 6-methyltetrahydropterin can be detected in CSF when these pterins are given peripherally to patients with hyperphenylalaninemia due to defective biopterin synthesis. Results of this study suggest that administration of either of these pterins in proper doses may prove to be a treatment not only for the impaired peripheral phenylalanine metabolism, but also for the neurologic disorders that are characteristic of the variant forms of hyperphenylalaninemia due to defective tetrahydrobiopterin synthesis or metabolism.

Biopterins↗
PubMed1981

Biosynthesis of biopterin: adrenergic cyclic adenosine monophosphate-dependent inhibition in the pineal gland.

Pineal glands in organ culture synthesize and release biopterin and are able to maintain concentrations of biopterin occurring in vivo for up to 54 hours in vitro. The intracellular biopterin content is reduced 50 percent by treatment with l-norepinephrine or cyclic adenosine monophosphate derivatives, but not by d-norepinephrine. This is an indication that biopterin levels are regulated by an adrenergic cyclic adenosine monophosphate-dependent mechanism. The decline in tissue biopterin content, produced mainly by inhibited of biosynthesis, is maximal at 6 hours and is not associated with either an increase in biopterin release or a shift in the reduction state of the biopterin.

1-Methyl-3-isobutylxanthine↗
PubMed1981

Peripherally administered reduced pterins do enter the brain.

The content of tetrahydrobiopterin in rat brain was doubled by peripherally administered tetrahydrobiopterin, with the natural 1 diastereoisomer more effective than the unnatural d configuration. The model pteridine, 6-methyltetrahydropterin was ten times more efficient than tetrahydrobiopterin in crossing the blood-brain barrier, and striatal concentrations of 6-methyltetrahydropterin remained elevated for 2 hours, declining with a half-life of 3 hours. While no evidence for a specific uptake mechanism for concentrating 6-methyltetrahydropterin in cells containing tetrahydrobiopterin was detected, the pterin was found in ts presumed site of action, the nerve terminal. Replacement therapy with reduced pterins may therefore be effective in the treatment of the neurological disorders associated with the variant forms of hyperphenylalaninemia that result from defects in the biosynthesis or metabolism of tetrahydrobiopterin within the central nervous system.

Animals↗
PubMed1981

Effect of cyclic AMP-dependent protein phosphorylating conditions on the pH-dependent activity of tyrosine hydroxylase from beef and rat striata.

Tyrosine hydroxylase (TH, EC 1.14.16.2) from beef brain striata was purified 23-fold from an extract of an acetone powder. If this enzyme preparation is treated with a cyclic AMP[-dependent protein phosphorylation system, there is a change in the pH dependence of the enzyme activity. The pH optimum at saturating tetrahydrobiopterin (BH4) concentration is shifted from below pH 6 to about pH 6.7. At pH 7, activation is expressed mainly as an increase in Vmax, whereas at pH 6, activation is expressed mainly as a decrease in Km for the pterin cofactor. Further, even with the control enzyme the Km for pterin cofactor declines precipitously as the pH is increased from 6 toward neutrality. Similar data were obtained with G-25 Sephadex-treated rat striatal TH. Experiments in which rat striatal synaptosomes were used demonstrated that the in situ activation of TH by phosphorylating conditions is expressed primarily as an increase in the maximum rate of dopamine synthesis. These results indicate that changes in TH activity caused by cyclic AMP-dependent protein phosphorylation will depend to a large extent on the pH of the TH environment.

Animals↗
PubMed1979

Regulation of dopamine synthesis in striatal synaptosomes during depolarization.

Incubation of striatal synaptosomes under depolarizing conditions (veratridine or KCl) increased the release of dopamine (DA) and produced a small increase in DA synthesis. This was not accompanied by an activation of either soluble or membrane-bound tyrosine hydroxylase, but was associated with a large depletion of synaptosomal DA. Thus, depolarization may increase DA synthesis by reducing the inhibition of tyrosine hydroxylase by end-product.

Animals↗
PubMed1975

Hypothalamic hyperphagia despite imposed diurnal or nocturnal feeding and drinking rhythms.

Rats normally do most of their eating at night. When ad lib fed rats are made hyperphagic with lesions or parasagittal hypothalamic knife cuts the increases in eating occur primarily during the day. This suggests that a disruption of circadian rhythms may mediate the overeating. However, when knife cut rats were food and water deprived all day excessive eating occurred at night. Similarly, when they were deprived all night overeating occurred during the day. Under both conditions od deprivation the food intakes and rapid weight gains of the ad lib fed knife cut group were defended. It was concluded that: (1) in hypothalamic hyperphagia either the excessive food intake or the excessive weight gain is defended when food and water are available only half of each day, and (2) disruption of nocturnal feeding and drinking rhythms is not the cause of hypothalamic hyperhagia.

Animals↗