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A Lajtha

Publications and source records attributed to A Lajtha.

At least 217 records · Page 12Linked to original sources
PubMed1984

Effect of chronic ethanol administration on brain protein breakdown in mice in vivo.

Brain proteins of BALB/cBy mice were labeled for a period of 8 days by a single intraperitoneal injection of valine. Following this the mice received 10% ethanol and protein breakdown was estimated from the release of label from brain proteins. Ethanol intake resulted in a significant inhibition of cerebral protein breakdown in vivo as measured in whole brain and in subcellular brain fractions (myelin, synaptosomes, mitochondria, microsomes, and nuclei). The intake of 10% ethanol for 4.5 months resulted in minor alterations in amino acid levels; increase in some and decrease in others were observed in plasma and brain, but most of the changes were not significant (P greater than 0.05). The uptake of AIB in brain was decreased 17% by prolonged ethanol intake.

Alcoholism↗
PubMed1983

Met-enkephalin binding to opiate receptors is not functionally coupled to biodegradation.

Using synaptosomal rat brain membranes, the degradation of Met-enkephalin in both free and receptor-bound form was measured, together with the dissociation of Met-enkephalin from the receptors. The results show that the degradation rate of initially receptor-bound Met-enkephalin is significantly smaller than either the rate of dissociation from the receptors or that of the degradation of free Met-enkephalin. These data suggest that intact Met-enkephalin dissociates from the receptors and then it becomes a target for the same membrane-associated peptidases that split free Met-enkephalin. This view is supported by the good fitness of the measured degradation of initially receptor-bound Met-enkephalin to the predicted degradation curve calculated from the dissociation rate of receptor-bound Met-enkephalin and the degradation rate of free Met-enkephalin.

Animals↗
PubMed1983

Imipramine does not act as a false transmitter in the rat hypothalamus.

[3H]Imipramine was accumulated by rat hypothalamic slices mostly by a passive low-affinity process. Accumulated [3H]imipramine was released by 60 mM potassium, but the release was small and was not Ca2+-dependent. Imipramine induced some release of [3H]norepinephrine. None of these events were abolished by pretreatment of the rats with reserpine. These results do not favor the view that imipramine acts as a false transmitter in the rat hypothalamus. Rather, imipramine appears to be accumulated in an extragranular pool from which it releases extragranular norepinephrine.

Animals↗
PubMed1983

Purification and characterization of an enkephalin aminopeptidase from rat brain membranes.

A membrane-bound aminopeptidase was purified from rat brain, and its activity was assayed by high-pressure liquid chromatography with Met-enkephalin as the substrate. The enzyme was extracted with 1% Triton X-100 and purified by chromatography, successively on DEAE-Sepharose CL-6B, Bio-Gel HTP, and Sephadex G-200 columns. The overall purification was about 1200-fold, with 25% yield. The purified enzyme showed one band on disc gel electrophoresis and two bands on sodium dodecyl sulfate electrophoresis with molecular weights of 62 000 and 66 000. The aminopeptidase has a pH optimum of 7.0, a Km of 0.28 mM, and a Vmax of 45 mumol (mg of protein)-1 min-1 for Met-enkephalin. It releases tyrosine from Met-enkephalin, but it does not split the byproduct. It does not hydrolyze gamma- or beta-endorphin, or dynorphin, but it does hydrolyze neutral and basic aminoacyl beta-naphthylamides. The enzyme is inhibited by the aminopeptidase inhibitors amastatin, bestatin, and bestatin-Gly. Its properties, such as its subcellular localization, substrate specificity, pH optimum, and molecular weight, distinguish it from leucine aminopeptidase, aminopeptidase A, aminopeptidase B, aminopeptidase M, and the soluble aminopeptidase for enkephalin degradation.

Aminopeptidases↗
PubMed1983

Effects of cations and temperature on the binding of [3H]spiperone to sheep caudate nucleus.

The specific [3H]spiperone binding by sheep caudate nucleus homogenate is increased by divalent cations. The effect of Ca2+ or Mn2+ (5 mM) is temperature-dependent, and it is optimal at about 37 degrees, but is relatively low below 15 degrees and above 50 degrees. In the absence of added Ca2+ or Mn2+, the maximal specific [3H]spiperone binding is observed at about 25 degrees, and the cations shift the optimum to about 37 degrees. Under the experimental conditions used, the KD is about 0.6 nM and is not influenced by Ca2+ or Mn2+, or by temperature (25 and 37 degrees). In addition to Ca2+ and Mn2+, Mg2+ and Zn2+ also increase the specific [3H]spiperone binding, but to a smaller extent. At the concentrations of Ca2+, Mn2+, Mg2+ and Zn2+ which produce a maximal increase in the [3H]spiperone binding, the membranes are nearly saturated with the cations which bind about 100 nmoles of Ca2+ or Mg2+/mg of protein, 170 nmoles Zn2+/mg of protein and at least 300 nmoles Mn2+/mg of protein. It is suggested that the cations increase the [3H]spiperone binding by either exposing more binding sites, by preventing denaturation or by increasing the solubility of [3H]spiperone in the membrane phase, or by a combination of these processes.

Animals↗
PubMed1983

Developmental changes in the breakdown of brain tubulin by cerebral cathepsin D.

The activity of cathepsin D on hemoglobin and on cytoplasmic tubulin was measured in brain preparations at different ages--in newborn, 10- and 21-day-old, and young adult rats. Enzyme activity increased after birth, reaching a maximum at around 21 days, and then declined. This increase was not parallel with decreased turnover of proteins during development, but was parallel with decreasing level and increasing microheterogeneity and rate of assembly of tubulin during development. The breakdown of tubulin was heterogeneous, with initial fast breakdown of a large portion, followed by breakdown at a lower rate. This heterogeneity in breakdown persisted throughout development. The breakdown of tubulin, unlike that of hemoglobin, was at all ages greater at pH 5.8 than at pH 3.2. The possible role of cathepsin D in tubulin metabolism and the developmental changes under physiological conditions need further exploration.

Aging↗
PubMed1983

Anticonvulsant effects of some inhibitory neurotransmitter amino acids.

The anticonvulsive effects of GABA, taurine, and glycine were investigated on several chemically-induced and genetic seizure models. Intravenous injections of either GABA, taurine, or glycine provided protection against 3-mercaptopropionic acid (MPA)-induced convulsions in adult Swiss mice. GABA was partially effective against isonicotinic acid hydrazide and was without effect against bicuculline-induced convulsions. Prolonged administration of glycine prevented MPA-induced convulsions but not electrically induced seizures or seizures induced by strychnine or metrazol. Intragastric glycine protected young audiogenic seizure-susceptible DBA/2 mice against all three phases of sound-induced convulsions (wild running, clonic and tonic seizure), but GABA and taurine provided little or no protection. With increase of glycine, the cerebral levels of glutamine and serine also increased, but that of glutamic acid decreased. The endogenous glutamic and glycine levels were slightly higher in the brains of the audiogenic seizure-susceptible DBA/2 mice than in that of the resistant BALB/Cy strain.

Acoustic Stimulation↗
PubMed1983

Short-lived effect of (Des-Tyr)-gamma-endorphin in schizophrenia.

Des-tyrosine-gamma-endorphin (DT gamma E) has been reported to alleviate symptoms of schizophrenia. Attempting to replicate those reports, we administered 1 mg of DT gamma E, i.m., for 8 consecutive days to nine patients meeting the DSM-III criteria for schizophrenia. Patients in this double-blind, crossover, and placebo-controlled study showed a statistically significant, but clinically modest improvement. The improvement was detectable during the first several days of the DT gamma E treatment; the symptoms then returned to baseline level in spite of continued doses of DT gamma E. Testing the metabolism of DT gamma E in the patients' plasma, we found a high rate of formation and of degradation, but the metabolic rates were not related to clinical symptoms.

Adult↗
PubMed1983

High- and low-affinity binding of [3H]imipramine in mouse cerebral cortex.

Binding of [3H]imipramine in mouse cerebral cortex was found to be nonhomogeneous. Competition experiments, Scatchard analysis, and Hill plots are compatible with the existence of binding with high (nanomolar) and low (micromolar) affinity. Low-affinity binding could be eliminated by the use of low concentrations of imipramine as the competing ligand. In contrast to the high-affinity binding, the low-affinity binding was found to be unrelated to the neuronal uptake system for serotonin.

Animals↗
PubMed1983

Thyroid hormones and derivatives inhibit flunitrazepam binding.

Thyroid hormones and their derivatives were found to inhibit [3H]flunitrazepam binding stereospecifically and in a monophasic manner. Among the compounds tested, D-thyroxine was the most potent inhibitor (IC50 = 0.5 microM). The naturally occurring L-thyroxine was about 40-fold less potent (IC50 = 20 microM). The structure-activity relationships seem to imply that the thyronine base has the principal role in the inhibition of benzodiazepine receptor binding. The type of inhibition was examined with the most potent inhibitor, D-thyroxine, by Scatchard analysis. The apparent dissociation constant (KD) of the [3H]flunitrazepam binding increased and the receptor density (Bmax) decreased as a function of D-thyroxine concentration; this is characteristic of mixed-type inhibition.

Animals↗
PubMed1983

Effect of various compounds on enkephalin hydrolysis by an aminopeptidase from the thermophiles Thermomonospora fusca ATCC 27730 and Thermus thermophilus ATCC 27634.

The microbial peptides amastatin and bestatin as well as several dipeptide analogues of the latter exerted little or no inhibitory effect on enkephalin hydrolysis by an aminopeptidase purified from the thermophiles Thermomonospora fusca, ATCC 27730 (Tf) and Thermus thermophilus, ATCC 27634 (Tt). The enzyme catalyzes the cleavage of the tyrosyl-glycyl bond of leucine- and methionine-enkephalin. Intermediate compounds having the same amino acid sequence as the parent substrate disclosed that the residual tetrapeptide can be further degraded to its constituent parts. Each preparation also hydrolyzes to varying extents neutral dipeptides, tripeptides, tetrapeptides, can be further degraded to its constituent parts. Each preparation also hydrolyzes to varying extents neutral dipeptides, tripeptides, tetrapeptides, and larger molecules containing the Met-enkephalin sequence. The Tf enzyme has a pH optimum of 7.5, Km of 667 microM and Vmax of 92 nmol/min/mg of protein; the Tt enzyme, with a pH optimum of 7.2 has a Km of 400 microM and Vmax of 33 nmol/min/mg of protein. Activated by dithiothreitol (DTT) and inactivated by p-chloro- and p-hydroxymercuribenzoate, both are sulfhydryl enzymes. The activity lost by hydrolysis against EDTA can be restored, wholly or in part, by Co+2, Mg+2, and Mn+2; ions with an inhibitory effect were A1+3, Cd+2, Cu+2, Hg+2, and Zn+2. The enzymes are not glycoproteins since they pass unretained through a Con A-Sepharose column.

Actinomycetales↗
PubMed1983

Effect of bestatin analogues and other compounds on enkephalin hydrolysis by an aminopeptidase from the mesophiles pseudomonas sp ATCC 11299A and chromobacterium violaceum ATCC 12540.

In our studies on newly synthesized compounds for their potential analgesic effect, we decided for purposes of convenience and economy to investigate non-mammalian sources for the presence of enkephalin degrading enzymes. An aminopeptidase that catalyzes the hydrolysis of the tyrosylglycyl bond of leucine- and methionine enkephalin was purified from the mesophiles Pseudomonas sp ATCC 11299a (Ps) and Chromobacterium violaceum ATCC 12540 (Cv). Each preparation also hydrolyzed to varying extents neutral dipeptides, tripeptides, tetrapeptides and amino acid beta-naphthylamides. The Ps enzyme has a pH optimum of 6.8, Km of 80 microM and a Vmax of 6.7 nmoles/min/mg of protein. The Cv enzyme has a pH optimum of 6.8-7.2, Km of 111 microM and a Vmax of 42 nmoles/min/mg of protein. Both are sulfhydryl enzymes since they are activated by dithiothreitol (DTT) and inactivated by p-chloro- and p-hydroxymercuribenzoate. They are not glycoproteins since they pass unretained through a Con A-Sepharose column. The activity lost by dialysis against EDTA can be restored, wholly or in part, by Co+2, Mg+2, Mn+2 and Ni+2; ions exerting an inhibitory effect were A1+3, Cd+2, Cu+2, Hg+2 and Zn+2. From a range of organic compounds, the greatest inhibition was elicited by the microbial peptides amastatin and bestatin. Several dipeptide analogues of bestatin, synthesized from DL-threo-2-amino-3-hydroxy-3-phenylpropanoic acid (AHPP) as the N-terminal residue in order to define the stereospecific requirements of the alpha, beta-functional groups for maximal activity, were not as active as the parent compound.

Aminopeptidases↗
PubMed1983

A portion of [3H]cocaine binding in brain is associated with serotonergic neurons.

Three lines of evidence are brought forward in support of an association in the brain cortex of some, but not all, of the cocaine binding sites with serotonergic nerve terminals. The first is based upon the significant correlation observed between the inhibition of cocaine binding by various drugs and the inhibition of neuronal uptake of serotonin in the mouse cerebral cortex. The second is based upon the demonstration of cocaine binding in human blood platelets, a model system for central serotonergic neurons. The third comes from experiments in which rats were treated with p-chloroamphetamine and 5,7-dihydroxytryptamine (serotonin neurotoxins), 6-hydroxydopamine (catecholamine neurotoxin), or p-chlorophenylalanine (inhibitor of tryptophan hydroxylase). Only the serotonin neurotoxins decreased the binding of [3H]cocaine in the rat cerebral cortex, but to a lower extent than the binding of [3]imipramine, which is known to be associated with serotonergic terminals. In contrast to the cocaine binding in the mouse cerebral cortex, the binding in the rat cerebral cortex included a considerable portion of low-affinity binding that was relatively unaffected by lesions of serotonergic neurons.

Animals↗
PubMed1982

The rate of protein degradation in developing brain. Methodological considerations.

Recently we reported that the rate of protein breakdown decreases during development. Breakdown rates were calculated from the rates of protein synthesis and the changes in brain protein content with age. A different study, measuring breakdown by monitoring the loss of label from brain protein after an H14CO3- pulse, came to the opposite conclusion: that the rate of breakdown is low in immature brain and increases during development. We have now investigated some of the factors (the distribution of label in protein and the potential for recycling) that might introduce errors into these measurements. The specific radioactivities of both protein-bound and free amino acids were determined in the brains of young rats several days after an intraperitoneal pulse of H14CO3-. For a number of amino acids the specific radioactivity of the free amino acid is high compared with that of the protein-bound amino acid, and therefore recycling could result in an underestimate of the degradation rate. Because glutamic acid had a relatively low specific-radioactivity ratio, [1-14C]glutamic acid was used in a pulse-labelling experiment to measure degradation. The rate so obtained, 0.6% . h-1, is twice the rate found with H14CO3- labelling (based on total protein-bound radioactivity). Insofar as recycling is a possible complication, 0.6% . h-1 may be a minimum value. Although somewhat higher degradation rates are found after labelling with an intracranial pulse, which was considered as a possible route to limit recycling, there are difficulties in interpreting these data.

Amino Acids↗
PubMed1982

On the interaction between nicotine and cycloheximide.

This study examined whether the nicotine-induced reversal of the amnestic effect of cycloheximide is due to an interaction between nicotine and cycloheximide on brain protein synthesis, and whether it involves the sites in brain that saturably bind [3H]nicotine. Nicotine did not reverse the cycloheximide-induced inhibition of protein synthesis, both in in vivo (intact animal) and in vitro (brain slice), suggesting that on-going protein synthesis is not necessarily involved in memory consolidation. The nicotine binding sites were not affected by in vivo or in vitro treatment with cycloheximide in the presence or absence of nicotine.

Animals↗
PubMed1982

The inheritance and genetic correlation of tyrosine hydroxylase activities in the substantia nigra and corpus striatum in the C x B recombinant inbred mouse strains.

In mouse, strain differences in the activity of tyrosine hydroxylase (TH) in ventral midbrain dopamine systems of substantia nigra-A10 (SN) region of mouse brain and in a terminal field, the striatum (CS), can be entirely attributed to variations in the number of dopaminergic neurons2. To obtain further information about the complexity of the genetic systems influencing phenotypes for regional TH activity, we examined TH activity in the SN and CS of 7 recombinant inbred (RI) mouse strains, their progenitor strains (BALB/cBy and C57BL/6By), their reciprocal F1 hybrids and a CB6F2 segregating generation. Genetic analysis indicated that TH activity in both brain regions seems unlikely to be controlled by single gene effects. However, the mode of inheritance is presumably not very complex. Estimates of the degree of genetic determination for TH activity in SN and CS were relatively high with significant and positive correlations with respect to either the RI lines (r = 0.82) or the CB6F2 generation (r = 0.53). These positive correlations suggest that some of the genes of two gene sets influencing TH activities in the SN and CS are the same. However, additional non-shared genes may also be present. Assuming that our two measures reflect the number of dopaminergic neurons in SN-A10 area and density of their processes in corpus striatum, our results lead us to the hypothesis that the number of dopaminergic neurons and the axonal arborization of these neurons in the nigrostriatal system are in part under a common genetic control but that other genes may contribute to branching of SN neurons.

Animals↗