Biomedical subjects

A Lajtha

Publications and source records attributed to A Lajtha.

At least 127 records · Page 7Linked to original sources

PubMed1989

Chronic L-deprenyl does not alter the restoration of striatal dopamine in MPTP-lesioned mice.

The present study examined the effect of chronic L-deprenyl on dopaminergic terminal function after mouse striatal terminals were lesioned with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP; 2 x 30 mg/kg s.c.). In the MPTP-lesioned mice, the level of dopamine was decreased by 59% 1 week after MPTP administration and by 22% at 16 weeks. Chronic administration of L-deprenyl (0.1 mg/kg, once weekly for up to 16 weeks) did not alter striatal dopamine metabolism, although monoamine oxidase B activity was reduced by 50% during this 16-week period, and did not alter the rate of restoration of the level of striatal dopamine.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

PubMed1989

Increase in cathepsin D activity in rat brain in aging.

Cathepsin D-like activity in homogenates of five brain areas of 3-month-old and 24-month-old Fischer 344 rats was measured. With hemoglobin as substrate at pH 3.2, more than 90% of the activity was inhibited by pepstatin. In each area studied, activity was more than twice as high in the old rat brain: 140-160% higher in the cortex, cerebellum, pons-medulla, and striatum and 90-100% higher in the hippocampus and spinal cord. The greatly increased metabolic capacity in the absence of an increase in protein turnover may have a role in age-related pathological degeneration in the brain.

Aging↗

PubMed1989

Long-term blockade of the dopamine uptake complex by metaphit, an isothiocyanate derivative of phencyclidine.

[3H]Mazindol was used to label the dopamine uptake complex in mouse striatum in vitro in the presence and absence of metaphit, an isothiocyanate derivative of phencyclidine. In some experiments, metaphit was present in the incubation fluid throughout the procedure; in other experiments it was eliminated by several washings and centrifugations. It was found that after removal of the metaphit by washing and centrifugation, the mazindol binding was not restored. Membranes that were pretreated with metaphit and washed had a lower density of mazindol binding sites than control membranes; the remaining mazindol sites had the same afinity for [3H]mazindol. These findings are in agreement with the previous studies on [3H]cocaine and [3H]methylphenidate binding. The following observations support that metaphit is irreversibly acting and not slowly dissociating from the mazindol recognition sites of the dopamine uptake carrier complex: 1) Metaphit did not change the off-rate of [3H]mazindol binding, arguing against an allosteric action at a distinct site. 2) The presence of cocaine protected the mazindol binding sites from the action of metaphit, supporting binding of metaphit and mazindol to the same site. 3) Nine hours after metaphit pretreatment and removal, the degree of inhibition of mazindol binding was the same as immediately after pretreatment, consonant with an irreversible effect of metaphit. 4) The potency of metaphit in inhibiting mazindol binding was greater under slightly alkaline conditions, consistent with acylation of the mazindol sites. Furthermore, it was found that intracerebroventricular application of metaphit did not result in a decrease in the binding of [3H]mazindol 5 hr after the administration.

Animals↗

PubMed1989

Comparison of characteristics of dopamine uptake and mazindol binding in mouse striatum.

Biochemical and pharmacological studies suggest that the binding of [3H]mazindol is functionally related to the dopamine uptake carrier complex in rodent striatum. In order to study further the relationship between the substrate recognition site for dopamine uptake and the high-affinity binding site for mazindol the uptake of [3H]dopamine and the binding of [3H]mazindol was studied in BALB/cBy mouse striatum in various buffers (Tris, HEPES, bicarbonate-phosphate). Kinetic analysis showed that the Kd of the binding of [3H]mazindol and the Km of the uptake of [3H]dopamine was changed by different sodium concentrations and/or by the presence of Tris, while the Bmax and the Vmax remained essentially the same. However, the shape of the Na+ dependency curves was not the same for mazindol binding and dopamine uptake in the various buffers. The inhibitory effect of other cations such as K+ and Tris was also different on binding and uptake under similar experimental circumstances. Dopamine did not slow down the dissociation of mazindol from its site and this effect was not sodium-sensitive. These complexities can be accommodated by a model that involves overlapping sites for mazindol and dopamine on the dopamine uptake carrier complex, and translocation-reorientation steps.

Animals↗

PubMed1989

Uptake of acetyl-L-carnitine in the brain.

Analysis in mouse brain slices of the uptake of acetyl-L-[N-methyl-14C]carnitine with time showed it to be concentrative, and kinetic analysis gave a Km of 1.92 mM and a Vmax of 1.96 mumol/min per ml, indicating the presence of a low-affinity carrier system. The uptake was energy-requiring and sodium-dependent, being inhibited in the presence of nitrogen (absence of O2), sodium cyanide, low temperature (4 degrees C), and ouabain, and in the absence of Na+. The uptake of acetyl-L-carnitine was not strictly substrate-specific; gamma-butyrobetaine, L-carnitine, L-DABA, and GABA were potent inhibitors, hypotaurine and L-glutamate were moderate inhibitors, and glycine and beta-alanine were only weakly inhibitory. In vivo, acetyl-L-carnitine transport across the blood-brain barrier had a brain uptake index of 2.4 +/- 0.2, which was similar to that of GABA. These results indicate an affinity of acetyl-L-carnitine to the GABA transport system.

Acetylcarnitine↗

PubMed1989

Changes with aging in the levels of amino acids in rat CNS structural elements. I. Glutamate and related amino acids.

Glutamate and related amino acids were determined in 53 discrete brain areas of 3- and 29-month-old male Fischer 344 rats microdissected with the punch technique. The levels of amino acids showed high regional variation - the ratio of the highest to lowest level was 9 for aspartate, 5 for glutamate, 6 for glutamine, and 21 for GABA. Several areas were found to have all four amino acids at very high or at very low level, but also some areas had some amino acids at high, others at low level. With age, in more than half of the areas, significant changes could be observed; decrease occurred 5 times more frequently than increase. Changes occurred more often in levels of aspartate and GABA than in those of glutamate or glutamine. The regional levels of glutamate and its related amino acids show severalfold variations, with the levels tending to decrease in the aged brain.

Aging↗

PubMed1989

Changes with aging in the levels of amino acids in rat CNS structural elements. II. Taurine and small neutral amino acids.

Taurine (Tau) and the small neutral amino acids glycine (Gly), serine (Ser), threonine (Thr), and alanine (Ala) were measured in 53 brain areas of 3- and 29-month-old male Fisher 344 rats. The ratio of highest to lowest level was 34 for Tau, 9.1 for Thr, 7.6 for Gly and Ser, and 6.5 for Ala. The heterogeneity was found in numerous areas; for example, Tau levels were more than 90 nmol/mg protein in 6 areas, and less than 20 nmol/mg protein in 10 areas. Similar heterogeneity was found with the other amino acids. The relative distribution of the small neutral amino acids showed several similarities; Tau distribution was different. With age, four amino acids decreased in 10-18 areas, and increased in only 1-3, while Thr increased in more areas than it decreased. The five amino acids of this paper, and the four of the previous paper, are among the amino acids at highest level in the brain; the sequence in their levels shows considerable regional heterogeneity.

Aging↗

PubMed1989

In vivo rates of protein synthesis in brain, muscle, and liver of five vertebrate species.

To compare cerebral protein metabolism rates in vivo, protein synthesis rates of three organs of five vertebrate species were measured after a single i.p. injection of a flooding dose of [1-14C]valine. In muscle, brain, and liver, the respective average protein synthesis rates, expressed as percent of total protein-bound valine replaced per hour, that is, percent synthesis per hour, in goldfish at 22 degrees C body temperature, were 0.07, 0.23, and 0.57%; in the bullfrog at 20 degrees C, 0.06, 0.18, and 0.55%; in the white Leghorn chicken at 39 degrees C, 0.24, 0.70, and 2.17%; and in the mouse at 38 degrees C, 0.22, 0.65, and 2.0%. In the Tokay lizard at different body temperatures, the synthesis rates were 0.04, 0.13, and 0.43% at 26 degrees C; 0.05, 0.20, and 0.63% at 32 degrees C; and 0.07, 0.27, and 0.81% at 38 degrees C. The results demonstrate differences in protein synthesis rates in organs of the various species examined. The differences among the species seem to be due, to a major extent, to differences in body temperature; rates in lizard are below those in other species at temperatures tried. Protein synthesis rates in brain in all species are almost three times lower than those in liver and almost three times higher than those in muscle.

Animals↗

PubMed1989

The presence of ATP + ubiquitin-dependent proteinase and multicatalytic proteinase complex in bovine brain.

The presence of two distinct high-molecular-weight proteases with similar pH optima in the weakly alkaline region was shown in cytosol of the bovine brain cortex. They were separated by ammonium sulfate fractionation and each was further purified by DEAE-Sephacel, Sephacryl S-300, DEAE-Cibacron Blue 3GA-agarose, heparin-agarose, and Sepharose 6B chromatography. The larger enzyme (Mr 1,400 kDa), which precipitates at 0-38% ammonium sulfate saturation, seems to be active in ATP + ubiquitin (Ub)-dependent proteolysis; it has low basal caseinolytic activity that is stimulated 3-fold by ATP, and when Ub is present ATP causes a 4.5-fold stimulation. A second proteinase was also found to be present (Mr 700 kDa) that precipitates at 38-80% ammonium sulfate saturation, is composed of multiple subunits ranging in Mr from 18 to 30 kDa, and degrades both protein and peptide substrates, demonstrating trypsin-, chymotrypsin- and cucumisin-like activities. Catalytic, biochemical, and immunological characteristics of this proteinase indicate that it is a multicatalytic proteinase complex (MPC), whose enzyme activity, in contrast to that of MPC from bovine pituitaries (1-3), is stimulated 1.7-fold by addition of ATP in the absence of ubiquitin at the early steps of purification; this property is lost during the course of further purification. Both proteinases are present in the nerve cells, since the primary chicken embryonic telencephalon neuronal cell culture extracts contain both ATP + Ub-dependent proteinase and MPC activities.

Adenosine Triphosphate↗

PubMed1989

The effect of caffeine on some mouse brain free amino acid levels.

Changes in free amino acids were examined in the central nervous system of mice treated with caffeine for three weeks. Caffeine was administered in the drinking water, and at the end of three weeks the level of caffeine in the cerebral cortex was 113 +/- 19 micrograms/g. When amino acid levels in cerebral hemispheres, midbrain, pons and medulla, and cerebellum were measured a significant increase in glutamine levels was found in all four regions. Glycine, alanine, serine, threonine, and GABA were significantly reduced in some regions. Caffeine appears to alter some of the metabolic or transport processes regulating amino acid pools in the brain. The decrease of GABA found in pons and medulla may contribute to the observed increase in reflex excitability after caffeine.

Amino Acids↗

PubMed1989

Dopamine D1 receptor and dopamine D2 receptor binding activity changes during chronic administration of nicotine in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated mice.

The effect of nicotine on MPTP-induced changes in striatal dopamine receptors binding activity was investigated. Dopamine D1 and D2 receptors were labeled with [3H]SCH-23390 and [3H]spiperone respectively in BALB/cBy mice. With administration of only MPTP, which caused more than an 80% decrease in striatal dopamine level, binding of 0.15 nM [3H]spiperone was increased by 37%; whereas 0.3 nM [3H]SCH-23390 binding was unchanged. With chronic nicotine treatment (0.4 mg/kg twice daily for 7-9 days), [3H]SCH-23390 binding activity was increased by 27% and [3H]spiperone binding activity was unchanged. When nicotine was administered after MPTP, their separate effects could be seen in that both the D1 and D2 dopamine receptor ligand binding activities were increased and that nicotine elevated the ratio of D1/D2 receptor binding activities in MPTP-treated mice.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

PubMed1989

Phosphoinositide hydrolysis induced by depolarization and sodium channel activation in mouse cerebrocortical slices.

Carbachol, a muscarinic receptor agonist and the sodium channel-activating agents, scorpion venom, veratridine, batrachotoxin and aconitine, were shown to stimulate the formation of [3H]inositol phosphates in [3H]inositol-labelled miniprisms, obtained from the cerebral cortex of the mouse. The inositol response to the Na+ channel-activating agents was inhibited by the sodium channel blocker tetrodotoxin (TTX), while the response induced by carbachol was partially resistant to TTX. The response to scorpion venom and the TTX-insensitive portion of the response to carbachol was additive, indicating different mechanisms. The presence of high potassium (K+) induced hydrolysis of inositide in a TTX-insensitive manner and was not additive with that resulting from sodium channel activators, thus indicating a common mechanism. The addition of large concentrations of magnesium to block the release of acetylcholine, did not inhibit the inositol response to high K+ or to veratridine. Calcium channel blockers such as nickel or cobalt, or the dihydropyridine calcium (Ca2+) channel activator BAY K 8644 and the calcium channel blocker nifedipine, nimodipine or PN-200 110 had little effect. Monensin, a sodium ionophore, stimulated the turnover of phosphatidylinositol at non-depolarizing concentrations and the omission of Na+ ions inhibited the response to sodium channel agents and to high K+. Thus, membrane potential and gradients of K+, Na+ and Ca2+ are all important factors determining the final effect on the turnover of phosphatidylinositol. The data are consistent with a model in which all these factors impinge on the Na+/Ca2+ exchanger regulating internal Ca2+ that, in turn, activates phospholipase C.

Animals↗

PubMed1989

Motor effects of intracaudate injection of excitatory amino acids.

In a study of the role of excitatory amino acid receptors in movement disorders, the effect of the injection of glutamate (Glu), aspartate (Asp), N-methyl-D-aspartate (NMDA), quisqualate (Qu), or kainate (K) into the rat striatum was investigated. Rats were microinjected unilaterally through chronically implanted guide cannulas and their motor behavior was recorded. After 10-25 min L-Glu produced reversible periodic choreiform movements lasting 5-10 sec and contraversive rotation lasting 1-2 min. Both episodes were repeated every 2-3 min: the duration of motor effects was 60-80 min. L-Asp had an effect similar to that of L-Glu and in addition produced barrel rolling. The L-isomers of both Glu and Asp were active and the D-isomers were inactive. NMDA, Qu, and K were more potent than Glu or Asp. Each produced effects similar to that of Glu, and in addition NMDA and K produced wet-dog-shakes and masticatory movements. The motor behavior produced by Qu was identical to that of Glu, but it lasted longer. The motor effects of L-Glu were blocked by L-glutamic acid diethyl ester (GDEE) and by a larger sedative dose of 2-amino-5-phosphonopentanoic acid (AP5), but not by haloperidol, GABA, glycine (Gly), or a smaller nonsedative dose of AP5. The results suggest that the motor effects of L-Glu were produced by activation of the Qu-type (glutamatergic) receptors, not involving the dopamine and GABA systems. However, activation of the K-type receptors by L-Glu cannot be ruled out.

Amino Acids↗

PubMed1989

Rates of protein synthesis--a review.

The rates of protein synthesis can be measured by a variety of methods including pulse labeling, massive precursor administration, Scornik method, continuous feeding of labeled precursor, infusion, and pellet implantation. Each technique has some advantages and disadvantages. Massive precursor administration and infusion are the most widely used. The advantage of massive precursor administration is its simplicity, however, the amino acid concentration used is much higher than physiological levels. Infusion, however, is much more complicated as a technique and requires complicated calculations. The synthesis rates can also be calculated from degradation curves. Some of the above techniques can be used both in vivo and in vitro, and also for different organs (Shahbazian et al. (1987), Int. J. Dev. Neurosci., 5: 39-42). The brain has rapid rates of protein synthesis both in vivo and in vitro, the latter being much lower for adults.

Animals↗

PubMed1989

Ascorbic acid inhibits [3H]SCH-23390 binding to striatal dopamine D1 receptors.

The present study describes the inhibition of [3H]SCH-23390 binding to striatal dopamine D1 receptors in the presence of ascorbic acid. Specific [3H]SCH-23390 binding was maximally inhibited by 0.1 mM ascorbic acid. As determined by Scatchard analysis the binding in the presence of 0.01, 0.1, or 10 mM ascorbic acid was consonant with non-competitive inhibition with a 26%, 38%, or 19% decrease, respectively, in the maximal number of binding sites; the affinity of these binding sites was not affected. Inhibition of [3H]SCH-23390 binding by ascorbic acid was reversible; striatal homogenates incubated with 0.1 mM ascorbic acid and subsequently washed free of ascorbic acid had the same Scatchard parameters as untreated preparations.

Animals↗

PubMed1989

Oxidative metabolism of cocaine: comparison of brain and liver.

Norcocaine (NC) and N-hydroxynorcocaine (NHNC), products of the oxidative metabolism of cocaine, were examined in plasma, brain, and liver of mice injected intraperitoneally with cocaine. Plasma levels of NHNC were altered in vivo by inhibiting esterase activity with diazinon and chloral hydrate or activating esterase activity with phenobarbital, and activating the microsomal P-450 system with phenobarbital. Changes in plasma concentrations of NHNC resulted in similar changes in brain, which were often different from those in liver. After intracisternal administration of cocaine to mice, no appreciable amount of NC or NHNC could be detected in brain; the same results were obtained upon intracisternal and intraventricular administration to rats. Microsomal preparations from mouse brain were found to be considerably less active than those from liver in converting NC to NHNC. We conclude that the cerebral oxidative metabolism of cocaine is not appreciable and that most of the NC and NHNC found in the brain after systemic cocaine administration is derived from plasma rather than formed centrally by brain microsomal enzymes.

Animals↗

PubMed1989

Effect of N-ethylmaleimide treatment on naloxone binding in frog brain membranes.

Specific binding of (3H) naloxone to opioid receptors in frog (Rana esculenta) brain membranes was irreversibly inactivated by the sulfhydryl group alkylating agent N-ethylmaleimide (NEM). Saturation analysis of (3H) naloxone binding revealed a marked reduction in the number of ligand binding sites after N-ethylmaleimide treatment. Pretreatment of the membranes with unlabelled opioid ligands, i.e. naloxone, morphine, or the kappa selective dynorphin (1-13), and sodium ions resulted in considerable protection of (3H) naloxone binding against the N-ethylmaleimide blockade.

Animals↗

PubMed1988

Effect of chronic oral nicotine on dopaminergic function in the MPTP-treated mouse.

Although epidemiological studies have suggested a lower incidence of Parkinson's disease in cigarette smokers, repeated exposure to cigarette smoke or nicotine does not protect against neurotoxicity induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Since there is some evidence that nicotinic antagonists, nicotine, and neurotransmitters may have tropic effects on neurite outgrowth, the present study examined the effects of chronic nicotine administration for 16 weeks (in drinking water; 5 mg/kg consumed per day) on the rate of terminal recovery after striatal lesioning with MPTP (2 x 30 mg/kg, s.c.). Terminal recovery, as measured by the rate of recovery in the level of striatal dopamine, was not affected by nicotine. Monoamine oxidase-B activity was not reduced by MPTP, nor did nicotine affect its activity in striatal homogenates.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗