NMDA receptor antagonists such as Ketamine and PCP are potent psychoactive drugs used recreationally. This class of drug induces a number of phenomena in humans similar to those associated with schizophrenia including reduced selective attention, altered working memory, thought disorders and hallucinations. These psychotomimetic drugs have thus been used as a longstanding model to study this disease in animals. Importantly, such animal models allow for recording of brain activity using invasive techniques that are inappropriate in humans. Previous electrophysiological studies have shown that MK-801, a potent non-competitive NMDA receptor antagonist, increases gamma-frequency oscillations and produces a state of disinhibition in the prefrontal cortex of rats wherein the activity of putative excitatory pyramidal neurons increases while the activity of putative inhibitory interneurons decreases. These features are relevant to schizophrenia because molecular evidence suggests dysfunction of inhibitory cortical interneurons, while electroencephalographic recordings show altered gamma-frequency oscillations in this disease. It has been hypothesized that the disinhibited cortical state produces “noisy” information processing, but this has not been directly observed in the interaction of neuronal firing in either humans or animal models. We therefore tested this hypothesis by examining the synchronization of neural activity in the NMDA receptor antagonist model of schizophrenia. We used high-density electrophysiological recordings in the medial prefrontal cortex of freely moving rats before and after systemic injection of MK-801. Analysis of these recordings revealed that drug administration: (i) increases gamma power in field potentials in a manner dissociated from increased locomotion; (ii) does not change the gamma power in multi-unit activity; (iii) decreases spike synchronization among putative pyramidal neurons in the gamma range (30ms), and despite of this it (iv) does not change the synchronization between gamma-range field potentials or between sum-of-spikes and field potentials. These effects in synchronization may be revealing of potent cognitive effects associated with NMDA receptor antagonism, and may reflect impaired communication processing hypothesized to occur in schizophrenia. / xi, 42 leaves : ill. ; 29 cm

Alcohol affects many neurochemical processes, causing long-lasting changes in both the adult and developing brain. The Jak-Stat transcriptional activation pathway plays a role in the control of neuronal proliferation, survival and differentiation, but the effects of ethanol on the system have not been fully elucidated. The goal of this project was to define the effects of acute and subchronic ethanol exposure on the expression of proteins in the Jak-Stat pathway, using cultured NG108-15 cells, and in addition, to test the hypothesis that these effects are mediated through the NMDA receptor. I found that ethanol dose-dependently decreased Jak2 and Stat3 following subchronic exposure of NG108-15 in culture. Acute ethanol exposure caused a dose-dependent decrease in Stat3 protein levels. Incubation with MK-801 or ketamine, two noncompetitive NMDA receptor antagonists, or the receptor agonist NMDA, produced dose-dependent decreases in Stat3 protein as well.

No description available.

An aspartate transcarbamoylase (ATCase) gene from Bordetella pertussis was amplified by PCR and ligated into pT-ADV for expression in Escherichia coli. This particular ATCase (pyrB) was an inactive gene found adjacent to an inactive dihydroorotase (DHOase) gene (pyrC'). This experiment was undertaken to determine whether this pyrB gene was capable of expression alone or if it was capable of expression only when cotransformed with a functional pyrC'. When transformed into E. coli TB2 pyrB-, the gene did not produce any ATCase activity. The gene was then co-transformed into E. coli TB2 pyrB- along with a plasmid containing the pyrC' gene from Pseudomonas aeruginosa and assayed for ATCase activity. Negative results were again recorded.

Aspartate transcarbamoylase (ATCase) catalyzes the first committed step in pyrimidine biosynthesis. Bacterial ATCases are divided into three classes, A, B and C. Class A ATCases are largest at 450-500, are. dodecamers and represented by Pseudomonas ATCase. The overlapping pyrBC' genes encode the Pseudomonases ATCase, which is active only as a 480 kDa dodecamer and requires an inactive pyrC'-encoded DHOase for ATCase activity. ATCase has been studied in two non-pathogenic members of Mycobacterium, M. smegmatis and M. phlei. Their ATCases are dodecamers of molecular weight 480 kDa, composed of six PyrB and six PyrC polypeptides. Unlike the Pseudomonas ATCase, the PyrC polypeptide in these mycobacteria encodes an active DHOase. Moreover, the ATCase: DHOase complex in M. smegmatis is active both as the native 480 kDa and as a 390 kDa complex. The latter lacks two PyrC polypeptides yet retains ATCase activity. The ATCase from M. phlei is similar, except that it is active as the native 480 kDa form but also as 450,410 and 380 kDa forms. These complexes lack one, two, and three PyrC polypeptides, respectively. By contrast,.ATCases from pathogenic mycobacteria are active only at 480 kDa. Mycobacterial ATCases contain active DHOases and accordingly. are placed in class A1 . The class A1 ATCases contain active DHOases while class A2 ATCases contain inactive DHOases. ATCase has also been purified from Burkholderia cepacia and from an E. coli strain in which the cloned pyrB of B. cepacia was expressed. The B. cepacia ATCase has a molecular mass of 550 kDa, with two different polypeptides, PyrB (52 kDa) and PyrC of (39 kDa). The enzyme is active both as the native enzyme at 550 kDa and as smaller molecular forms including 240 kDa and 165 kDa. The ATCase synthesized by the cloned pyrB gene has a molecular weight of 165 kDa composed of three identical PyrB and no PyrC polypeptides. Nucleotide effectors ATP, CTP, and UTP inhibited all forms of enzymes. Because of its size and its activity as a trimer and smaller than native forms, the B. cepacia enzyme is placed in a new class.

Asparate transcarbamoylase catalyzes the first committed step in the de novo synthesis of pyrmidine nucleotides UMP, UDP, UTP, and CTP. The archetype enzyme found in Escherichia coli (310 kDa) exhibits sigmodial substrate binding kinetics with positive control by ATP and negative control with CTP and UTP. The ATCase characterized in this study is from the extreme thermophilic Archaebacterium, Methanococcus jannaschii. The enzyme was very stable at elevated temperatures and possessed activity from 20 degrees Celsius to 90 degrees Celsius. M. Jannaschii ATCase retained 75% of its activity after incubation at 100 degrees Celsius for a period of 90 minutes. No sigmodial allosteric response to substrate for the enzyme was observed. Velocity substrate plots gave Michaelis-Menten (hyperbolic) kinetics. The Km for aspartate was 7 mM at 30 degrees Celsius and the KM for carbamoylphosphate was .125 mM. The enzyme from M. jannaschii had a broad pH response with an optimum above pH 9. Kinetic measurements were significantly affected by changes in pH and temperature. The enzyme catalyzed reaction had an energy of activation of 10,300 calories per mole. ATCase from M. jannaschii was partially purified. The enzyme was shown to have a molecular weight of 110,000 Da., with a subunit molecular weight of 37,000 Da. The enzyme was thus a trimer composed of three identical subunits. The enzyme did not possess any regulatory response and no evidence for a regulatory polypeptide was found, DNA from M. jannaschii did hybridize to probes corresponding to genes for both the catalytic and regulatory subunits from E. coli. Analysis of DNA sequences for the M. jannaschii ATCase genes showed that the gene for the catalytic subunits shares significant homology with the pyrB genes from E. coli, and maximum homology amongst known ATCase genes to pyrB from Bacillus. An unlinked gene homologous to E. coli pyrl encoding the regulatory subunit was identified, though its expression and true function remain uncharacterized.

A importância na geração de oxaloacetato foi investigada através da determinação da atividade da piruvato carboxilase nos músculos estriados e da suplementação de seus precursores (aspartato e asparagina) na dieta de ratos. A atividade da piruvato carboxilase eleva-se durante o exercício físico e, portanto, deve fornecer mais oxaloacetato para a etapa inicial do ciclo de Krebs. A suplementação crônica (5 semanas) de aspartato e asparagina promove aumento da resistência ao esforço em ratos treinados em natação durante 1 hora diária por 5 semanas. Este efeito foi acompanhado de elevação no número e tamanho das mitocôndrias e alteração no metabolismo de glicose dos músculos esqueléticos (elevação do conteúdo de glicogênio e de sua síntese e diminuição da glicólise). Esses resultados sugerem que a geração de oxaloacetato desempenha papel fundamental na manutenção do esforço prolongado. A suplementação de aspartato e asparagina na dieta melhora a performance nessas condições, porém causa lesões na ultraestrutura muscular (mitocôndrias, linha \"Z\" e miofibrilas). / The importance of oxaloacetate formation was investigated by measuring pyruvate carboxylase activity in muscles and by given its precursors (aspartate, asparagine) in the diet of rats. The activity of pyruvate carboxylase markedly raised during physical effort and so might provide oxaloacetate for Krebs cycle functioning. The supplementation of aspartate and aspagine for a prolonged period of time (5 weeks) promotes increment in the resistance to exercise in rats trained to swimming during 1 hour daily for 5 weeks. This effect is accompanied by an increase in the size and number of mitochondria and also changes in glucose metabolism; elevation in glycogen synthesis and content and reduction in the rate of glycolysis. These results suggest that the production of oxaloacetate plays a role to maintain the moderate exercise during a prolonged period of time. Nevertheless, the aspartate and asparagine supplemented in the diet, despite improving the perfomance to moderate and prolonged exercise, provokes muscle ultraestructure lesions of mitochondria, \"Z\" line and miofibrils.

Não Consta Resumo na Publicação / Abstracts Not Available

No description available.

Abstract not available