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R Alarcón

Publications and source records attributed to R Alarcón.

At least 19 recordsLinked to original sources
PubMed2002

Hemispheric differences in global and local processing with orientation classification tasks.

Hemispheric differences in global and local processing were examined in one experiment with hierarchical stimuli. The figures consisted of large squares with the right or left side missing made up of small squares with the right or left side missing. The subjects were asked to decide the opening (left/right) of the square either at the global level or at the local level. The findings showed that with the task and stimuli used here global judgements were as fast and accurate as local judgements, the interference was bidirectional and symmetrical and, finally, that the right hemisphere and the left hemisphere had the same ability to manage with global and local information. So, the experiment does not provide evidence for hemispheric specialisation in global and local processing.

Adult↗
PubMed2000

Porphyria cutanea tarda affecting lower lip.

In porphyria cutanea tarda, the most common type of porphyria, blisters of the skin occur because of high sensitivity to sunlight. This case report describes porphyria cutanea tarda of the lower lip mimicking an actinic cheilitis in a 62-year-old man with a history of Hodgkin's lymphoma.

Administration, Topical↗
PubMed2000

Absence of conspecific pollen advantage in the dynamics of an Ipomopsis (Polemoniaceae) hybrid zone.

The frequency of hybrid formation in angiosperms depends on how often heterospecific pollen is transferred to the stigma and on the success of that heterospecific pollen at fertilizing ovules. Even if heterospecific pollen is capable of effecting fertilization it may perform poorly when conspecific pollen is also available on the stigma. We applied pollen mixtures to stigmas to determine how pollen interactions affect siring success and the frequency of hybrid formation between two species of Ipomopsis (Polemoniaceae) in Colorado. Plants of both parental species and natural hybrids were pollinated with I. aggregata and I. tenuituba pollen in ratios of 100:0, 80:20, 50:50, 20:80, and 0:100 by mass. Plants were homozygous for different alleles at an isozyme marker, allowing us to distinguish the type of pollen parent for 2166 viable seeds from 273 fruits. In contrast to studies of many other hybridizing taxa, there was no evidence of an advantage to conspecific pollen, nor did composition of the stigmatic pollen load affect seed set. Instead, the frequency of seeds sired by a given species was proportional to its representation in the pollen load. In this hybrid zone, both the frequency of first-generation hybrid formation and the relative male fitness of the two parental species should be predictable from the rates of pollen transfer to stigmas.

Journal Article↗
PubMed1999

Hypoxia induces p53 accumulation through MDM2 down-regulation and inhibition of E6-mediated degradation.

Hypoxia, a result of DNA-damaging agents such as ionizing radiation, induces the nuclear accumulation of the p53 tumor suppressor protein. However, unlike the effect in ionizing radiation, hypoxia readily induces the nuclear accumulation of p53 in HPV E6-infected cells. In HPV-infected cells, a key regulator of p53 protein levels is the E6 oncoprotein. In association with the endogenous cellular protein E6-associated protein (E6AP), E6 can accelerate the degradation of p53 under aerobic conditions. To better define the mechanism of p53 induction in E6-infected cells by hypoxia, we studied the expression and association of E6 and E6AP with p53 in vivo. We found that hypoxia did not alter the protein levels of E6 or E6AP as compared with those found under aerobic growth conditions, indicating that protein inhibition of E6 or E6AP alone is not sufficient to explain the increased accumulation of p53 under hypoxic conditions. However, p53 did fail to coprecipitate with E6AP under hypoxia, indicating that hypoxia uncouples the interaction of p53 with E6 and E6AP. We also present evidence to indicate that hypoxia decreases the expression of the endogenous cellular regulator of p53 protein, the human MDM2 protein, resulting in an inhibition of p53 export from the nucleus to the cytoplasm for degradation. Taken together, these results suggest that the hypoxic induction of p53 is attributable to the down-regulation of MDM2 protein levels and uncoupling of p53 from its interaction with the E6/E6AP complex.

Cell Hypoxia↗
PubMed1998

Stable complexes involving acetylcholinesterase and amyloid-beta peptide change the biochemical properties of the enzyme and increase the neurotoxicity of Alzheimer's fibrils.

Brain acetylcholinesterase (AChE) forms stable complexes with amyloid-beta peptide (Abeta) during its assembly into filaments, in agreement with its colocalization with the Abeta deposits of Alzheimer's brain. The association of the enzyme with nascent Abeta aggregates occurs as early as after 30 min of incubation. Analysis of the catalytic activity of the AChE incorporated into these complexes shows an anomalous behavior reminiscent of the AChE associated with senile plaques, which includes a resistance to low pH, high substrate concentrations, and lower sensitivity to AChE inhibitors. Furthermore, the toxicity of the AChE-amyloid complexes is higher than that of the Abeta aggregates alone. Thus, in addition to its possible role as a heterogeneous nucleator during amyloid formation, AChE, by forming such stable complexes, may increase the neurotoxicity of Abeta fibrils and thus may determine the selective neuronal loss observed in Alzheimer's brain.

Acetylcholinesterase↗
PubMed1998

Erythro-1-(benzothiazol-2-yl)-1,2-dibromo-2-(2-chloro-5-nitrophenyl)ethane.

The title compound, C15H9Br2CIN2O2S, was synthesized by electrophilic addition of bromine to 2-(2-chloro-5-nitrostyryl)benzothiazole. The molecule consists of benzothiazole and 2-chloro-5-nitrophenyl rings linked by a 1,2-dibromoethane moiety. The dihedral angle between the benzothiazole and phenyl rings is 8.2(9) degrees. The benzothiazole ring is planar with a mean deviation of 0.168(7)A. The Br1--C8 and Br2--C9 bond distances are 1.972(5) and 2.007(6)A, respectively.

Antineoplastic Agents↗
PubMed1997

Acetylcholinesterase promotes the aggregation of amyloid-beta-peptide fragments by forming a complex with the growing fibrils.

Acetylcholinesterase (AChE), an enzyme involved in the hydrolysis of the neurotransmitter acetylcholine, consistently colocalizes with the amyloid deposits characteristic of Alzheimer's disease and may contribute to the generation of amyloid proteins and/or physically affect fibril assembly. In order to identify the structural domains of the amyloid-beta-peptide (Abeta) involved in the aggregation induced by AChE, we have studied the effect of this cholinergic enzyme on Abeta peptide fragments of different sizes. AChE enhanced the aggregation of the Abeta(12-28) and Abeta(25-35) peptides but not of the Abeta(1-16) fragment. The inductive effect of AChE on the aggregation of Abeta(12-28) was abolished by the presence of either Abeta(1-16) or Abeta(9-21). The effect of the enzyme was also analysed using two different mutant fragments, possessing a low and the other a high capacity for fibrillogenesis. The fragments used were Abeta(12-28)Val18-->Ala and Abeta(12-28)Glu22-->Gln, respectively. AChE was able to promote the aggregation of these fragments in a very specific way and both mutant peptides were able to form amyloid fibrils, as revealed by negative staining under the electron microscope. Binding assays indicated that AChE was bound to Abeta(12-28), as well as to the Abeta(1-16) peptide. AChE was seen to form strong complexes with the Abeta(12-28) fibrils as such complexes stained positively for both thioflavine-T and AChE activity, were resistant to high ionic strength treatment, and were partially sensitive to detergents, suggesting that hydrophobic interactions may play a role in the stabilization of the AChE-Abeta complex. Our results suggest that such amyloid-AChE complexes are formed when AChE interacts with the growing amyloid fibrils and accelerates the assembly of Abeta peptides. This is consistent with the fact that AChE is known to be present within Abeta deposits including the pre-amyloid diffuse and mature senile plaques found in Alzheimer's brain.

Acetylcholinesterase↗
PubMed1994

Blood markers in Alzheimer disease: subnormal acetylcholinesterase and butyrylcholinesterase in lymphocytes and erythrocytes.

In patients with the clinical diagnosis of Alzheimer disease (AD), we searched for systemic changes in components of the blood as a diagnostic tool. The acetylcholine-related enzymes acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) were measured in plasma, erythrocytes, platelets and lymphocytes. Results did not show a general effect; notwithstanding, specific cell types presented alterations either in AChE or BuChE but not in both enzymatic activities. In AD patients, AChE of lymphocytes was reduced by 60% compared with the age-matched controls. However, when patients were divided, the sporadic but not the familial subgroup exhibited a significant reduction. In erythrocytes the BuChE activity was reduced by 45% in sporadic AD. The molecular forms of the lymphocyte AChE were characterized by velocity sedimentation. Both globular forms were subnormal, more so the tetrameric G4 AChE form than the G2 form.

Acetylcholinesterase↗
PubMed1993

Platelet of Alzheimer patients: increased counts and subnormal uptake and accumulation of [14C]5-hydroxytryptamine.

Platelets are the main source of 5-hydroxytryptamine (5-HT) and amyloid precursor protein (APP) found in plasma. We studied a possible correlation between platelet markers and the clinical diagnosis of Alzheimer disease (AD). Our results indicate that in AD patients: (a) platelets are elevated, (b) their ability to accumulate 5-HT decreases and, (c) the kinetic parameters of 5-HT uptake are altered (decreased Km and Vmax), compared to non-demented healthy individuals. An aged Down syndrome patient presents even more deviant alterations. Our findings supports the idea that platelets may provide a systemic marker of AD, and eventually be useful for the clinical diagnosis of the disease.

Aged↗
PubMed1985

[The new biological revolution in psychiatry: a Latin American point of view (1st part)].

Several aspects of the new biological revolution in contemporary psychiatry are examined. The process originated around the mid-70's. The clinico-nosological bases, provided by advances such as DSM-III and the work on ICD-10 are described, as well as the most recent laboratory accomplishments: neuroendocrine tests and neuro-radiological techniques. These events are all analyzed from a Latin American perspective, which will be more extensively elaborated on in the second part of the paper.

Biological Psychiatry↗
PubMedDate not supplied

Molecular interactions of acetylcholinesterase with senile plaques.

Acetylcholinesterase (AChE) present in Alzheimer plaques is resistant to low pH, anti-ChE inhibitors and high substrate concentrations in comparison with the free enzyme. Kinetic and pharmacological studies of AChE-amyloid complexes indicate that steric hindrance by the amyloid over the gorge and the peripheral site of AChE is responsible for these effects.

Acetylcholinesterase↗