Regulation of the phosphorylation of the dopamine- and cAMP-regulated phosphoprotein of 32 kDa in vivo by dopamine D1, dopamine D2, and adenosine A2A receptors.
(17/276)
Dopamine D(1), dopamine D(2), and adenosine A(2A) receptors are highly expressed in striatal medium-sized spiny neurons. We have examined, in vivo, the influence of these receptors on the state of phosphorylation of the dopamine- and cAMP-regulated phosphoprotein of 32 kDa (DARPP-32). DARPP-32 is a potent endogenous inhibitor of protein phosphatase-1, which plays an obligatory role in dopaminergic transmission. A dose-dependent increase in the state of phosphorylation of DARPP-32 occurred in mouse striatum after systemic administration of the D(2) receptor antagonist eticlopride (0.1-2.0 mg/kg). This effect was abolished in mice in which the gene coding for the adenosine A(2A) receptor was disrupted by homologous recombination. A reduction was also observed in mice that had been pretreated with the selective A(2A) receptor antagonist SCH 58261 (10 mg/kg). The eticlopride-induced increase in DARPP-32 phosphorylation was also decreased by pretreatment with the D(1) receptor antagonist SCH 23390 (0.125 and 0.25 mg/kg) and completely reversed by combined pretreatment with SCH 23390 (0.25 mg/kg) plus SCH 58261 (10 mg/kg). SCH 23390, but not SCH 58261, abolished the increase in DARPP-32 caused by cocaine (15 mg/kg). The results indicate that, in vivo, the state of phosphorylation of DARPP-32 and, by implication, the activity of protein phosphatase-1 are regulated by tonic activation of D(1), D(2), and A(2A) receptors. The results also underscore the fact that the adenosine system plays a role in the generation of responses to dopamine D(2) antagonists in vivo. (+info)
Electron flow between photosystem II and oxygen in chloroplasts of photosystem I-deficient algae is mediated by a quinol oxidase involved in chlororespiration.
(18/276)
In Chlamydomonas reinhardtii mutants deficient in photosystem I because of inactivation of the chloroplast genes psaA or psaB, oxygen evolution from photosystem II occurs at significant rates and is coupled to a stimulation of oxygen uptake. Both activities can be simultaneously monitored by continuous mass spectrometry in the presence of (18)O(2). The light-driven O(2) exchange was shown to involve the plastoquinone pool as an electron carrier, but not cytochrome b(6)f. Photosystem II-dependent O(2) production and O(2) uptake were observed in isolated chloroplast fractions. Photosystem II-dependent oxygen exchange was insensitive to a variety of inhibitors (azide, carbon monoxide, cyanide, antimycin A, and salicylhydroxamic acid) and radical scavengers. It was, however, sensitive to propyl gallate. From inhibitors effects and electronic requirements of the O(2) uptake process, we conclude that an oxidase catalyzing oxidation of plastoquinol and reduction of oxygen to water is present in thylakoid membranes. From the sensitivity of flash-induced O(2) exchange to propyl gallate, we conclude that this oxidase is involved in chlororespiration. Clues to the identity of the protein implied in this process are given by pharmacological and immunological similarities with a protein (IMMUTANS) identified in Arabidopsis chloroplasts. (+info)
S-adenosylmethionine and Pneumocystis carinii.
(19/276)
We previously reported that S-adenosylmethionine (AdoMet), a key molecule in methylation reactions and polyamine biosynthesis, enhances axenic culture of the AIDS-associated opportunistic fungal pathogen Pneumocystis carinii. Here we report that AdoMet is absolutely required for continuous growth. Two transporters are present, one high affinity, K(m) = 4.5 microm, and one low affinity, K(m) = 333 microm. The physiologically relevant high affinity transporter has a pH optimum of 7.5 and no related natural compounds compete for uptake. Transport is 98% inhibited at 4 degrees C, 24% inhibited by 20 mm sodium azide, and 95% inhibited by the combination of 20 mm sodium azide and 1 mm salicylhydroxamic acid; thus transport is active and dependent on both a cytochrome chain and an alternative oxidase. In vitro, AdoMet is used at a rate of 1. 40 x 10(7) molecules cell(-1) min(-1). AdoMet synthetase activity was not detected by a sensitive radiolabel incorporation assay capable of detecting 0.1% of the activity in rat liver. In addition, the AdoMet plasma concentration of rats is inversely correlated with the number of P. carinii in the lungs. These findings demonstrate that P. carinii is an AdoMet auxotroph. The uptake and metabolism of this compound are rational chemotherapeutic targets. (+info)
Diseases causing end-stage renal failure in New South Wales.
(20/276)
The nature of the original renal disease was determined in 403 consecutive cases of end-stage renal failure, in 317 of which the clinical diagnosis was corroborated by histological examination of the kidney. Five diseases accounted for 20 or more cases--glomerulonephritis (31% of the total), analgesic nephropathy (29%), primary vesicoureteral reflux (8%), essential hypertension (6%), and polycystic kidneys (5%). In only four cases did renal failure result from chronic pyelonephritis without a demonstrable primary cause. Greater use of micturating cystography and cystoscopy and routine urine testing for salicylate are advocated for earlier diagnosis of the major causes of "pyelonephritis". The incidence of end-stage renal failure in people aged 15-55 in New South Wales was estimated to be at least 34 new cases per million of total population each year. (+info)
Amphetamine blocks long-term synaptic depression in the ventral tegmental area.
(21/276)
The mesolimbic dopamine system is essential for reward-seeking behavior, and drugs of abuse are thought to usurp the normal functioning of this pathway. A growing body of evidence suggests that glutamatergic synapses on dopamine neurons in the ventral tegmental area (VTA) are modified during exposure to addictive drugs, producing sensitization, a progressive augmentation in the rewarding properties of psychostimulant drugs with repeated exposure. We have tested the hypothesis that psychostimulant exposure interferes with the synaptic plasticity of glutamatergic inputs to the VTA. We find that excitatory synapses onto VTA dopamine neurons exhibit long-term depression (LTD) in response to low-frequency stimulation and modest depolarization. LTD in the VTA is NMDA receptor-independent but is dependent on intracellular Ca(2+) and can be induced by driving Ca(2+) into the dopamine neuron. Brief exposure to amphetamine entirely blocks LTD at glutamatergic synapses in the VTA, by releasing endogenous dopamine that acts at D2 dopamine receptors. The block of LTD is selective, because amphetamine has no effect on hippocampal LTD. The LTD we have discovered in the VTA is likely to be an important component of excitatory control of the reward pathway; amphetamine will inhibit LTD, removing this normal brake on the glutamatergic drive to dopamine neurons. This effect of amphetamine represents an important mechanism by which normal function of the brain reward system may be impaired during substance abuse. (+info)
Modulation of long-term depression by dopamine in the mesolimbic system.
(22/276)
Long-lasting adaptations in the mesolimbic dopamine (DA) system in response to drugs of abuse likely mediate many of the behavioral changes that underlie addiction. Recent work suggests that long-term changes in synaptic strength at excitatory synapses in the two major components of this system, the nucleus accumbens (NAc) and ventral tegmental area, may be particularly important for the development of drug-induced sensitization, a process that may contribute to addiction, as well as for normal response-reinforcement learning. Using whole-cell patch-clamp recording techniques from in vitro slice preparations, we have examined the existence and basic mechanisms of long-term depression (LTD) at excitatory synapses on both GABAergic medium spiny neurons in the NAc and dopaminergic neurons in the midbrain. We find that both sets of synapses express LTD but that their basic triggering mechanisms differ. Furthermore, DA blocks the induction of LTD in the midbrain via activation of D2-like receptors but has minimal effects on LTD in the NAc. The existence of LTD in mesolimbic structures and its modulation by DA represent mechanisms that may contribute to the modifications of neural circuitry that mediate reward-related learning as well as the development of addiction. (+info)
Early physiological and cytological events induced by wounding in potato tuber.
(23/276)
The response of potato tuber (Solanum tuberosum L. cv. Kennebec) to mechanical wounding was investigated at different times. Changes in the levels of indole-3-acetic acid (IAA), polyunsaturated fatty acids (PUFAs) and lipid hydroperoxides (LOOHs) were monitored up to 120 min after wounding and related to the cytological events occurring up to 24 h. Twenty minutes after injury, an increase in IAA and LOOH levels and a decrease in the levels of PUFAs was observed. Wounding induced mitoses in differentiated (parenchyma) cells starting at 120 min, and promoted an increase of mitotic activity in the meristematic cells (procambium and bud dome), after 360 min. The inhibition of the increase in LOOHs and IAA by lipoxygenase (LOX) inhibitors, as well as the ability of in vitro peroxidated linoleic acid to enhance IAA production, suggest a close relationship among lipoperoxidation, IAA and mitotic activity in the response of potato tuber cells to injury, resulting in a specific growth response, i.e. bud growth and periderm formation. (+info)
Comparison of HOCl traps with myeloperoxidase inhibitors in prevention of low density lipoprotein oxidation.
(24/276)
In this study, the production of the highly toxic oxidant hypochlorous acid (HOCl) by the phagocytic enzyme myeloperoxidase (MPO) was quantitated and the concomitant alterations of low density lipoprotein (LDL) were analyzed in view of the potential role of LDL in atherosclerosis. Using the monochlorodimedone assay, it was found that HOCl is produced in micromolar concentrations. The kinetics of the decrease of tryptophan fluorescence appeared to be a sensitive method to monitor LDL alterations under near in vivo conditions. Therefore, this method was used to subsequently compare the effectiveness of MPO inhibitors that block production of HOCl with compounds that act as HOCl traps. The efficiency of MPO inhibitors to prevent LDL damage increased in the series benzohydroxamic acid < salicylhydroxamic acid < 3-amino-1,2,4-triazole < sodium azide < potassium cyanide < p-hydroxy-benzoic acid hydrazide, while for the HOCl traps the protective efficiency increased in the series glycine < taurine < methionine. We conclude that HOCl traps may have high potential therapeutic impact in vivo due to their low toxicity, although high concentrations of them would have to reach sites of inflammation. In contrast, only low concentrations of a specific MPO inhibitor would be required to irreversibly inhibit the enzyme. (+info)